WO2001052563A2

WO2001052563A2 - Radio communications system

Info

Publication number: WO2001052563A2
Application number: PCT/GB2001/000114
Authority: WO
Inventors: Peter William Stephens; Alister John Bailey
Original assignee: Simoco International Limited
Priority date: 2000-01-12
Filing date: 2001-01-12
Publication date: 2001-07-19
Also published as: GB2358562A; WO2001052563A3; GB0100887D0; GB0000634D0; AU2862201A

Abstract

A digital radio communications system in which data can be transmitted in two different pre-defined data structures each comprising a succession of timeslots. Each data structure has a defined process for generating digital data for transmission from an input signal and a defined process for channel coding the generated data prior to its transmission, which data generation and channel coding processes provide data for transmission in the form of discrete frames. When it is desired to transmit the data generated and coded using the defined processes for a first of the predefined data structures using the other predefined data structure, the coded data frames generated according to the data generation and channel coding processes for the first defined data structure are apportioned into timeslots of the second defined data structure in such a way that each timeslot of the second defined data structure contains only entire coded data frames.

Description

Radio Communications System

The present invention relates to radio communications systems and in particular to digital radio communications systems which transmit data in discrete timeslots, such as the TETRA (TErrestrial Trunked RAdio) system. In such digital radio systems, the structure and data capacity of the timeslots, which are usually of constant length, are usually predefined, typically in the radio communications air-interface Standard with which the radio system complies, and all data to be transmitted in the system must be arranged in accordance with the defined data transmission (timeslot) structure.

Where data, particularly data relating to a continuous data source (such as a speech or video signal) , is to be transmitted in such a digital radio system, the initial input signal (e.g. speech or video signal) is usually converted for transmission into a series of discrete frames or portions of digital bits, usually of constant length, so as to, for example, facilitate processing of the signal. The raw digital data frames generated from the input signal are usually then further processed or "coded" prior to transmission, as is known in the art, to, for example, add additional data bits to the raw digital data to provide protection against errors that may occur during transmission (which errors may be more likely given that a radio transmission is inherently more susceptible to transmission induced errors than some other forms of data transmission) . Such coding is generally referred to as "channel coding" , and the overall channel coding which is applied is usually made up of a number of different coding techniques. One such form of coding is "Forward Error Correction" (FEC) which codes the user data by adding "redundant" data in algorithmic fashion such that if errors occur in the coded data, then their presence can be detected and in some cases subsequently corrected for. Such coding schemes can be block or stream based and can additionally include techniques such as the interleaving of bits in the data stream. Examples of suitable coding schemes include Hamming codes, Reed-Solomon codes and Golay codes. A Cyclic Redundancy Check (CRC) is another form of coding which provides good error detection, but does not assist in error correction. Channel coding will usually include, but is not limited to, forward error correction.

Since it is the "coded" data which is actually transmitted and must therefore fit into the transmission timeslot structure, both the raw data frame generation process and the channel coding process used in a given radio system must be such that they provide coded data for transmission in a form compatible with the predefined data (timeslot) structure to be used for transmission. For this reason the raw data frame generation (e.g. speech coding) process and channel coding process used by a radio system will therefore, typically, also be predefined and fixed for the radio system, usually by the radio Standard with which the radio system complies. Thus, for example, the TETRA radio Standard has a defined data transmission timeslot structure, and channel coding and speech encoding processes . The channel coding and raw data generation processes intended for use with one data transmission timeslot structure will usually be optimised to that timeslot structure. They will therefore not normally be, and not be expected to be, readily suitable for use with a second, different air-interface data transmission timeslot structure, because they would generate data for transmission at a rate and in frames of a size which are not appropriate for the other transmission data structure .

This may not be a problem where radio systems are intended to be self-contained and not intended to interoperate with other systems. However, it is becoming increasingly desirable for radio units to be able to operate in more than one radio system, which systems may well use different air-interface data transmission structures. For example, it may be desired to introduce a newer radio system operating in accordance with a new radio standard into an area where there is a pre-existing radio system which uses a different radio standard. It could in such circumstances be useful if radio units could use both the new and the old systems, and if communication between the radio units provided for one system (e.g. the new one) and existing, unmodified radio units of the other (e.g. older) system could be achieved without the need to modify at least one of the systems, i.e. if the two radio systems could be interconnected.

One example of where this situation has arisen is in North America, where it is desired to introduce TETRA compliant radio systems into areas where radio systems that operate according to the APCO Project 25 Standard (the Project 25 Standard agreed by Associated Public Safety Communications Officers, Inc. (APCO), National Association of State Telecommunications Directors (NASTD) , and agencies of the US Federal Government (FED) and Telecommunications Industry Association (TIA) , (see, for example, the 102 Series of Documents by TIA, such as the Project 25 System and Standards Definition document (TIA/EIA TSB102-A)) - herein referred to as "APCO"), already exist, and to provide for dual-mode TETRA/APCO operation of radio units, and to allow new TETRA compliant radio units to communicate with existing, unmodified APCO radio units, i.e. to interconnect the TETRA and APCO systems. The most straightforward way to provide such dual-mode operation would be to equip radio units with the data generation (e.g. speech coders/decoders) and channel coding processes of the different radio systems (e.g. TETRA and APCO), which could then be used selectively as desired. However, the Applicants believe that in some circumstances it may be preferable, for example as regards data processing requirements, to reduce the number of raw data generation (e.g. speech coding) processes and/or channel coding processes provided in a given radio unit. However, there is then the problem of how to enable a radio unit which does not have all the defined data generation processes and/or all the defined channel coding processes (e.g. only has a single data generation process and/or only has a single channel coding process) , to use two different air-interface data transmission structures. It is an object of the present invention to provide solutions to this problem. According to a first aspect of the present invention, there is provided a method of operating a radio unit for use in a digital radio communications system, in which system data can be transmitted in two different pre-defined data structures each comprising a succession of timeslots, there being defined for each data structure a process for generating digital data for transmission from an input signal and a process for channel coding the generated data prior to its transmission, which data generation and channel coding processes provide data for transmission in the form of discrete frames, the method comprising: generating digital data for transmission from an input signal in accordance with the data generation process defined for a first one of said transmission data structures; coding the data generated from the input signal prior to its transmission using the channel coding process defined for said first one of said transmission data structures; when it is desired to transmit the coded data using the first of the two different predefined data structures, transmitting the data as defined for that transmission data structure; and when it is desired to transmit the coded data using the second of the two different predefined data structures, apportioning the coded data frames generated according to the data generation and channel coding processes for the first defined data structure into timeslots of the second defined data structure in such a way that each timeslot of the second defined data structure contains only entire coded data frames. According to a second aspect of the present invention, there is provided a radio unit for use in a digital radio communications system, in which system data can be transmitted in two different pre-defined data structures each comprising a succession of timeslots, there being defined for each predefined data transmission structure a process for generating digital data for transmission from an input signal and a process for channel coding the generated data prior to its transmission, which data generation and channel coding processes provide the data for transmission in the form of discrete frames, the radio unit comprising: means for generating digital data for transmission from an input signal in accordance with said data generation process defined for a first one of said transmission data structures; means for coding the data generated from the continuous input signal prior to its transmission using said channel coding process defined for said first one of said transmission data structures; and means for, when it is desired to transmit the coded data using the second of the two different predefined data structures, apportioning the coded data frames generated according to the data generation and channel coding processes for the first defined data structure into timeslots of the second defined data structure in such a way that each timeslot of the second defined data structure contains only entire coded data frames.

These aspects of the present invention relate to the situation where a radio system has two different predefined transmission data timeslot structures (which would typically each be in accordance with a different defined radio standard) , and each transmission data structure has predefined data generation and channel coding processes, such as might be the case in a joint TETRA/APCO system. However, instead of using the data generation and channel coding process intended for each transmission data structure as appropriate, in these aspects of the present invention the same data generation and channel coding processes are always used, and, furthermore, the processes used are those defined for the same data transmission structure. Thus, the raw data frames for transmission are generated according to the process defined for one of the defined transmission data structures, and raw data frames are then channel coded using the channel coding protocols defined for that same transmission data structure. Thus, for example, in an embodiment of an APCO/TETRA system which is in accordance with these aspects of the present invention, the APCO data generation and channel coding processes would always be used, regardless of whether an APCO or TETRA transmission was to be made. This arrangement has the advantage that the raw data generation and subsequent channel coding (e.g. forward error correction) processes used are both intended for use with the same, first defined transmission data structure (e.g. radio standard) , and will therefore, typically be optimised to each other and for transmission with the first data structure. It may also permit easier retrospective modification of existing equipment for use with both data structures, and permit easier interoperability between a new and an existing radio system, since, for example, no modifications to the data generation and channel coding processes in existing equipment configured for the first data structure (radio system) would be required. The data generated for transmission in this arrangement can, of course, be directly transmitted in the form of the defined transmission data structure for which the data generation and channel coding processes are defined. However, where it is desired to transmit the data in the other (i.e. second) defined data structure, the coded data frames (which are at that point entirely in accordance with the first defined data structure) must be fitted into that other, second defined data transmission structure.

In these aspects of the present invention, this is achieved by apportioning the coded data frames generated as for the first defined transmission data structure into the timeslots of the second defined data structure in such a way that each timeslot of the second structure contains only entire, complete coded frames (and thus no partial, or incomplete, coded frames) . This arrangement effectively means that there is no spreading of a coded data frame across timeslots of the second data structure. This is believed to be advantageous, since it helps to ensure that any successfully received timeslot can be fully processed by the receiver without the need to wait for another timeslot to be received, and helps to ensure that the improper reception or loss of a timeslot does not affect successful reception of data in other timeslots (as usually an entire coded data frame is needed for successful decoding) .

Preferably, the arrangement is such that the same integer number, which will typically be two or more, of complete coded data frames produced using the data generation and channel coding processes defined for the first transmission data structure are placed into ea timeslot of the second defined data transmission structure .

It is not essential to use all of the data capa in each timeslot of the second data structure, althc preferably as much of the timeslot data capacity is as possible. Equally, it would be possible to omit of the coded data frames from the transmission if nc all of those frames will fit into the second transmission data structure timeslots, although thiε less desirable as then some data would be lost . However, it could be possible in some cases to satisfactorily interpolate the missing data frames i the data frames that are transmitted. The arrangement of these aspects of the inventi is particularly applicable to a combined APCO and TΣ system, where one generates and channel codes the de for transmission according to the processes defined the APCO standard. In that case, a convenient way t apportion the APCO generated coded data frames into normal sized TETRA timeslot structure for transmiss- over a TETRA air-interface is to place three APCO cc frames into every TETRA timeslot (the Applicants ha^ found that three APCO coded data frames will fit in1 one TETRA timeslot) .

As will be appreciated from the above, the abo¹ aspects of the present invention are particularly suitable when the data generation and channel codin< processes defined for the one transmission data structure produce data frames of a size and at a ra that is less than or equal to the data frame capaci' the other, second transmission timeslot structure. However, it may be that some combinations of raw da frame generation and channel coding processes will result in more data in a given time interval than c carried in that time interval by one of the defined structures to be used for the data transmission. T could, for example, be the case where it is desired to use the channel coding process defined for one defined transmission data structure on raw data frames generated according to the process defined for another, different defined transmission data structure. For example, the Applicants have found that coding normal APCO generated raw speech frames using normal TETRA channel coding produces too much coded data (i.e. at too high a data rate) to fit into the TETRA transmission timeslot structure. In such a case the arrangement of the above aspects of the invention could be less useful.

It may be therefore that in some circumstances a different arrangement for allowing a radio unit to use two different air-interface data transmission structures would be desirable.

According to a third aspect of the present invention, there is provided a method of operating a radio unit for use in a digital radio system which can use two predetermined data transmission structures, each comprising timeslots of a defined size, and in which system data to be transmitted is generated from an input signal in the form of discrete frames, which raw data frames are then further processed by a channel coding process prior to transmission, each transmission data structure having its own defined data generation and channel coding processes, the method comprising: generating from an input signal frames of digital data using one of the defined data generating processes; processing the generated frames of digital data using one of the defined channel coding processes to produce a series of coded data frames for transmission; and modifying the data generating process and/or modifying the channel coding process when it is intended to transmit the data in accordance with at least one of the defined data structures, so as to alter the amount of data in each coded data frame to be transmitted as compared to the amount of data that would be present in each frame when using the unmodified as-defined processes .

Thus according to a fourth aspect of the present invention, there is provided an apparatus for use in a radio unit for use in a digital radio system which can use two predetermined data transmission structures, each comprising timeslots of a defined size, and in which system data to be transmitted is generated from an input signal in the form of discrete frames, which raw data frames are then further processed by a channel coding process prior to transmission, each transmission data structure having its own defined data generation and channel coding processes, the apparatus comprising: means for generating from an input signal frames of digital data using one of the defined data generating processes; means for processing the generated frames of digital data using one of the defined channel coding processes to produce a series of coded data frames for transmission; and means for modifying the data generating process and/or modifying the channel coding process when it is intended to transmit the data in accordance with at least one of the defined data structures, so as to alter the amount of data in each coded data frame to be transmitted as compared to the amount of data that would be present in each frame when using the unmodified as- defined processes. In these aspects of the invention the data generation and/or channel coding process used are modified so as to alter the size of the coded data frames to be transmitted. This provides a technique for altering, for example, reducing, the amount of overall data (i.e. the total of both the wanted user data and any added data such as "coding" or error correcting "redundancy" data) to be transmitted, but while avoiding - li the need to, for example, omit entire data frames from the transmission. It is believed that this technique may also be preferable to, for example, providing additional, alternative channel coding and/or data generation processes in the radio unit.

In these aspects of the invention, the processes could be modified so as to reduce the amount of overall data in each coded data frame (i.e. the size of each coded. data frame) to be transmitted as compared to the amount of data that would be present in . each frame when using the unmodified as-defined processes, for example where the unmodified processes produce too much data to fit into the timeslot structure to be used. The arrangement could also be so as to increase the amount of overall data in each coded data frame to be transmitted as compared to the amount of data that would be present in each frame when using the unmodified as- defined processes. This may be useful where the unmodified processes leave spare capacity in each timeslot.

The way that the processes are modified to alter the size of the coded data frames can be selected as desired. For example, the raw data frames could be generated at a different, e.g. lower, data rate. However, preferably the raw data frames are generated at the same rate as normal , so as to ensure that the amount of 'raw' or wanted user data is not altered, and instead the processes are modified such that a different amount, e.g. less, coded data is generated from that amount of 'raw¹ data. The Applicants believe that this is a preferable way to proceed, since it ensures that the amount of 'raw' data transmitted remains the same.

The way that this is achieved can be selected as desired. In many radio system data generation techniques, the raw data for transmission generated from an input signal includes data bits of different relative importance classifications. For example, many speech coding techniques (including those used by TETRA and APCO) generate digital data from the raw speech which includes bits of differing levels of relative importance, for example according to how important the bits are for accurate reproduction of the speech.

The channel coding techniques in such radio systems are then often also arranged to code the raw data in accordance with the relative importance levels of the raw data bits, and to, for example, apply greater error protection to the more important bits. This means that the number of additional "redundant" bits added by the channel coding per bit of the raw data typically varies depending on the relative importance levels of the raw data bits .

The Applicants have recognised that where the raw data is classified into bits of differing levels of relative importance and the subsequent channel coding introduces different numbers of additional bits into the coded data depending on the relative importance level of the given bits to be coded, then one way therefore to adjust the overall amount of coded data generated from a given amount of raw data is to modify the processes such that the channel coding process is effectively applied to a different classification of the importance levels of the generated raw data bits, such that the channel coding produces a different, e.g. reduced, number of coded bits from the raw data. In other words, the importance levels of bits in the raw data as effectively seen by the channel coding process are modified such that the coded data has a different, e.g. reduced, number of bits in it than it would have had had the modification not taken place. This technique of effectively changing the number of raw data bits at one or more relative importance levels thus allows the overall number of bits in the coded data to be altered but while still using (and without needing to modify) the predefined channel coding process .

The effective modification of the number of bits at each relative importance level could be carried out in the initial bit generation process, by modifying that process to generate different numbers of bits at each relative importance level to usual. Alternatively, or additionally, the processes could be modified such that the channel coding process interprets at least some of the raw data bits as having a different relative importance level to the level effectively allocated by the data generation process (e.g. to treat some or all high importance bits as having only medium importance for the purposes of the channel coding) . The relative importance levels of one or more of the bits in the raw data could also be changed prior to channel coding of the data, if desired. These latter techniques would allow the raw data to be generated using the defined data generation process (e.g. speech coding process) for the system. Thus, according to a fifth aspect of the present invention, there is provided a method of preparing data for transmission in a digital radio system, in which system data to be transmitted is generated from an input signal in the form of discrete frames which contain bits of different levels of relative importance, which raw data frames are then further processed prior to transmission by a channel coding process in which the number of bits in the coded data generated from a given bit in the raw data varies depending on the relative level of importance of the raw data bit, and which system has a pre-defined data generation process, the method comprising: causing the channel coding process to be effectively carried out on raw data in which the relative importance levels of one or more of the raw data bits differs to the relative importance level that the bits would have had under the defined data generation process, so as to alter the amount of data in each coded data frame to be transmitted as compared to the amount of data that would be present in each frame if the changing of the effective relative importance levels had not taken place.

According to a sixth aspect of the present invention, there is provided an apparatus for preparing data for transmission in a digital radio system, in which system data to be transmitted is generated from an input signal in the form of discrete frames which contain bits of different levels of relative importance, which raw data frames are then further processed prior to transmission by a channel coding process in which the number of bits in the coded data generated from a given bit in the raw data varies depending on the relative level of importance of the raw data bit, and which system has a pre-defined data generation process, the apparatus comprising: means for causing the channel coding process to be effectively carried out on raw data in which the relative importance levels of one or more of the raw data bits differs to the relative importance level that the bits would have had under the defined data generation process, so as to alter the amount of data in each coded data frame to be transmitted as compared to the amount of data that would be present in each frame if the changing of the effective relative importance levels had not taken place.

The effective change in the importance levels of the bits can be selected as desired. The changing and reclassification will primarily be governed by two factors.

The first is to ensure that the coded bits fit into the transmission data structure. One way to do this might be to reclassify the raw data bits such that the number of bits at each level of relative importance is similar to the number of bits at each level of relative importance which would be provided by a data generation process defined for the transmission data structure. A straightforward approach to reduce the amount of data might be simply to reduce the number of bits at the importance level which receives the most error protection, i.e. for which the largest number of additional bits are generated by the channel coding.

The second factor that should be borne in mind when reclassifying the importance levels of the data bits is to try to avoid too much degradation of the quality of the raw data (e.g. speech data) being transmitted. Thus, for example, the arrangement is preferably such that any quality critical parameters are less detrimentally affected by the importance level reclassification than other parameters in the raw data. For example, it could be arranged that highest importance level bits do not have their importance levels re-classified.

Where speech data is being transmitted, the fundamental frequency of the speech can be an important quality affecting parameter, as it may not only define the fundamental frequency but also the structure of the rest of the speech frame, and must in that case be error-free to allow the frame to be decoded correctly. Such a parameter should therefore preferably still be heavily error protected even after the importance level reclassification. On the other hand, some parameters in the raw data, such as certain synchronisation bits, may be redundant or unnecessary, and so can be reclassified to lower levels of importance (error protection) without any significant effect on data quality.

An alternative way of altering, e.g. reducing, the size of (number of bits in) the coded data frames that the Applicants have recognised, would be to modify the channel coding process so as to alter, e.g. reduce, the number of coded output bits produced as compared to when using the unmodified channel coding process. Channel coding processes typically generate additional "redundant" data bits which are included in the coded data. Therefore by adjusting the channel coding to alter, e.g. reduce, the number of additional data bits generated, i.e. the extent to which the channel coding process expands the raw data, one can alter, e.g. reduce, the size of the coded data frames generated from a given amount of raw, uncoded data.

According to a seventh aspect of the present invention, there is provided a method of preparing data for transmission in a digital radio system, in which system data to be transmitted is generated from an input signal in the form of discrete frames, which raw data frames are then further processed by a channel coding process prior to transmission, the method comprising: generating from an input signal frames of digital data; processing the generated frames of digital data using a channel coding process to produce a series of coded data frames for transmission; and selectively modifying the channel coding process so as to reduce the amount of data in each coded data frame to be transmitted as compared to the amount of data that would be present in each frame when using the unmodified process.

According to an eighth aspect of the present invention, there is provided an apparatus for preparing data for transmission in a digital radio system, in which system data to be transmitted is generated from an input signal in the form of discrete frames, which raw data frames are then further processed by a channel coding process prior to transmission, the radio unit comprising: means for generating from an input signal frames of digital data; means for processing the generated frames of digital data using a channel coding process to produce a series of coded data frames for transmission; and means for selectively modifying the channel coding process so as to reduce the amount of data in each coded data frame to be transmitted as compared to the amount of data that would be present in each frame when using the unmodified process.

Typically, a channel coding process will generate additional data bits at a given rate per 'raw' data bit (e.g. one additional data bit per two raw data bits: a channel coding rate of 0.5) . Thus one way to modify the channel coding process to alter, e.g. reduce, the number of coded bits would be to alter, e.g. reduce, the "coding" rate. Where the raw data has bits of different levels of relative importance, different coding rates are often used for each different level of importance. In such a case, the coding rates for one or more of the different levels of importance could be altered. One relatively straightforward way to achieve this might be to use the same coding rate for bits of two or more relative levels of importance (e.g. the same coding rate for both high and medium importance bits) . This could be a new, e.g. reduced, rate, or one could, for example, simply use one, e.g. the lower, of the already defined coding rates for both levels of relative importance. Preferably the coding process is modified such that the gross number of coded bits will fit into the defined transmission data structure, but whilst maximising the level, or retaining the same level, of error protection and/or detection (e.g. forward error correction code strength) for at least one, and preferably each, level of bit importance in the raw data.

It would, of course, be possible both to modify the channel coding process used and to re-classify importance levels of bits in the uncoded data to reduce, alter, e.g. the number of bits in the coded data for transmission, if desired. However, as this requires two levels of modification to existing processes, it may be preferable to use only one or other technique where that can acceptably be done .

Both of the above techniques, i.e. effectively re- classifying the relative importance levels of the generated data and modifying the channel coding, have been found by the Applicants to be particularly applicable to an arrangement where it is desired to channel code APCO generated speech frames using TETRA forward error correction protocols and to transmit the coded frames over a TETRA air-interface . For example, by using a 2/3 coding rate for the TETRA forward error correction coding protocols on both the high and medium importance bits produced by the APCO speech coding, it is possible to fit in such an arrangement three raw APCO speech frames into one TETRA timeslot.

The above examples have talked particularly about reducing the amount of coded data for transmission from a given amount of raw data. However, as discussed above, it may in some circumstances be desirable to increase the amount of coded data generated from the raw data. For example, where there is spare data capacity in the transmission data structure, additional data bits could be added to pad out the spare data capacity. Alternatively, the channel coding rate could be increased and/or data bits treated as having higher relative importance levels, so as to, for example, increase the error protection where there is the capacity to do so.

The above aspects of the present invention are concerned with the fitting of data into predefined transmission data (timeslot) structures. However, the Applicants have recognised that this may not be the only problem to be encountered when attempting to transmit over an air-interface using data generating and channel coding processes which are not specifically designed for that air-interface's transmission data structure.

In particular, many radio communications systems, particularly mobile radio communications systems, support, as is known in the art, the "stealing" of user data to allow other data such as control signalling to be transmitted in a stream of user data. In such an arrangement user data is replaced by the other data and the receiver usually attempts to interpolate the missing (stolen) user data from the data that it does receive. Such stealing techniques are usually arranged to ¹ steal ' an entire timeslot or part of a timeslot which matches exactly a number of complete coded data frames, as this avoids the stealing leaving partial coded data frames which would then typically result in the loss of all the data in the partial frames from the transmission as well (such that more user data than might strictly be necessary to provide space for the other, "stealing", data to be transmitted, is lost) .

This can be relatively easily achieved where the raw data frame generation process, channel coding process, transmission data (timeslot) structure, and stealing process are defined for use with each other, such as would be the case for a given radio Standard (such as TETRA) . However, where coded data frames generated using a raw data frame generation process and channel coding process are to be transmitted using a transmission data structure (i.e. air-interface protocol) for which the data generation and channel coding processes used are not optimised, it may be much more unlikely that the stealing process will steal an exact number of the coded data frames . For example, as discussed above three APCO speech frames will fit or can be fitted into a single TETRA transmission timeslot. Thus in such an arrangement, if an entire timeslot is to be stolen from the TETRA signal, the stealing process can proceed essentially as normal, as three entire APCO coded speech frames would be stolen and no partial coded speech frames would be left over. However, TETRA also supports the stealing of a half timeslot ('half-slot stealing'). Stealing half a TETRA timeslot in such an arrangement would require the space occupied by one and a half of the APCO coded speech frames. Thus the TETRA half-slot stealing arrangement would typically result in the loss of two of the three APCO coded speech frames to be carried in the timeslot which is being stolen from, even though the stealing only requires the timeslot space occupied by one and a half APCO frames. The Applicants have therefore developed a number of techniques for improving user data "stealing" operations in radio communications systems where the size of the stolen portion of the transmitted signal (e.g. timeslot or part timeslot) does not match exactly a whole number of complete coded data frames .

Thus, according to a ninth aspect of the present invention, there is provided a method of transmitting data in a radio communications system, which system supports stealing of data to allow the transmission of other data such as control signalling in a stream of data to be transmitted, and in which system data to be transmitted is arranged in a succession of discrete data frames, and is transmitted in a succession of discrete timeslots, each timeslot usually containing three or more of the data frames, and wherein stealing of a portion of a timeslot can take place, the method comprising: when stealing of a portion of a timeslot is to take place, selecting from the data frames which would have been transmitted in the timeslot, the data frame or frames still to transmit in the remainder of the timeslot in such a manner that immediately adjacent data frames in the data to be transmitted are not both stolen. According to a tenth aspect of the present invention, there is provided an apparatus for transmitting data in a radio communications system, which system supports stealing of data to allow the transmission of other data such as control signalling in a stream of data to be transmitted, and in which system data to be transmitted is arranged in a succession of discrete data frames, and is transmitted in a succession of discrete timeslots, each timeslot usually containing three or more of the data frames, and wherein stealing of a portion of a timeslot can take place, the apparatus comprising: means for, when stealing of a portion of a timeslot is to take place, selecting from the data frames which would have been transmitted in the timeslot, the data frame or frames still to transmit in the remainder of the timeslot in such a manner that immediately adjacent data frames in the data to be transmitted are not both stolen.

In these aspects of the present invention, where three or more data frames are included in a given transmission timeslot and a portion of the timeslot is to be stolen, the data frame or frames that are still transmitted in the remaining, 'unstolen' part of the timeslot are selected such that immediately consecutive data frames are not both stolen (i.e. immediately consecutive data frames are not both omitted from the transmission due to the stealing) . This produces relatively smaller gaps of missing data in the transmitted data, and although there may be more of these smaller gaps, the Applicants believe that such smaller gaps of missing data may result in, for example, less distortion of speech and thus allow more accurate interpolation of speech, than a single but much larger gap. Thus it is believed that these aspects of the invention should help to increase data recoverability when such stealing is occurring. This aspect of the present invention is applicable to the above example of a TETRA/APCO system where three APCO coded data frames are inserted in each TETRA timeslot and half-slot stealing is occurring over the TETRA air-interface. In such an arrangement, the centre frame (in time) of the three APCO frames that were to be transmitted in the TETRA timeslot would be selected as the data frame to transmit in its entirety in the remaining, unstolen TETRA half-slot.

According to an eleventh aspect of the present invention, there is provided a method of transmitting data in a radio communications system, which system supports stealing of data to allow the transmission of other data such as control signalling in a stream of data to be transmitted, and in which system data to be transmitted is arranged in a succession of discrete data frames, and is transmitted in a succession of discrete timeslots, each timeslot usually containing two or more of the data frames, and wherein stealing of a portion of a timeslot can take place, the method comprising: when stealing of a portion of a timeslot is to take place, selecting from the data frames which would have been transmitted in the timeslot, the data frame or frames still to transmit in the remainder of the timeslot on the basis of an assessment of the relative importance levels of the data frames that were to be transmitted. According to a twelfth aspect of the present invention, there is provided an apparatus for transmitting data in a radio communications system, which system supports stealing of data to allow the transmission of other data such as control signalling in a stream of data to be transmitted, and in which system data to be transmitted is arranged in a succession of discrete data frames, and is transmitted in a succession of discrete timeslots, each timeslot usually containing two or more of the data frames, and wherein stealing of a portion of a timeslot can take place, the apparatus comprising: means for, when stealing of a portion of a timeslot is to take place, selecting from the data frames which would have been transmitted in the timeslot, the data frame or frames still to transmit in the remainder of the timeslot on the basis of an assessment of the relative importance levels of the data frames that were to be transmitted.

In these aspects of the invention, when stealing of part of a timeslot takes place, a selection is again made as to which data frame to transmit in the remaining portion of the timeslot, but the selection is based on the relative importance to the data being transmitted of the data frames that were to be transmitted. The Applicants believe that such an "intelligent" selection of the data frame to still transmit would again offer advantages in terms of compensation for and interpolation of the missing data over a more arbitrary frame selecting process.

The frame or frames still transmitted should be that frame or those frames assessed to have the highest relative importance according to the assessment criteria used. The importance assessment could be carried out as desired. It could, for example, be based on an assessment of how useful each frame might be for the interpolation process or for preserving data intelligibility. Where the data is speech frames, the importance assessment could be based on any suitable speech importance assessment techniques, such as the speech energy of each frame, or a more sophisticated measure of speech importance. In these arrangements, an indication of which of the possible data frames has actually been transmitted is preferably also transmitted by the receiver. This could be useful where a selection based on frame importance is being made since in such an arrangement it will not necessarily always be the frame or frames in the same relative timing position which is still transmitted at each stealing event. In both of the above stealing arrangements, it is possible that there will be spare unused data capacity in the remaining unstolen part of the timeslot once the data frame or frames selected for transmission are inserted therein. This would be the case, for example, in the above discussed TETRA/APCO system where a single complete APCO frame is to be transmitted in the remaining TETRA half-slot. In such a case, the spare data capacity remaining in the timeslot is preferably used to transmit additional information that will help to interpolate and/or compensate for the missing (stolen) data. This additional information could, for example, be information which will aid interpolation across the data gaps and/or enhance intelligibility, such as information relating to or from the missing data (e.g. speech) frames. It could also or instead be information indicating which of the possible data frames has actually been transmitted.

The above stealing arrangements ensure that one or more entire data frames are still transmitted, but will typically mean that other data frames are omitted from the transmission in their entirety. The Applicants believe that in some circumstances it may be desirable to try to transmit at least some data from plural data frames, or data from as many data frames as is possible, even if the data frames are not all transmitted in their original, complete state.

Thus, according to a thirteenth aspect of the present invention, there is provided a method of transmitting data in radio communications system, in which system data to be transmitted is arranged in a succession of data frames, which frames are transmitted in timeslots, each timeslot usually containing two or more data frames, and in which system stealing of part of timeslot can occur to allow other data such as control signalling to be transmitted in a stream of data frames, the method comprising:

done by, for example, deleting the necessary number of bits from the data frame according to a systematic, predetermined process. In a preferred such arrangement, where bits in the data frame have differing levels of relative importance (e.g. where the raw data is generated having differing levels of relative importance) , then the bits of the lowest importance level are preferably preferentially deleted first, followed by bits of the next lowest importance level and so on. A further or alternative selection criteria such as the impact of the bits on the data quality could also be used to select those bits to omit in the reduced size data frame .

An additional or alternative way to reduce the size of the data frames in a system where raw data frames are channel coded to produce coded data frames for transmission, would be to modify the raw data frames or the data frame channel coding process to produce smaller coded data frames from a given amount of raw data. This could be done using, for example, any of the techniques for this discussed previously, such as changing the effective number of raw data bits at each level of relative importance as seen by the channel coding process, and/or by adjusting the coding process, e.g. the forward error correction coding rate, so as to produce less coded data from a given amount of raw data.

Only one data frame in the original data could be reduced in size when stealing is to take place. Alternatively, if desired, corresponding smaller, reduced data frames for transmission could be generated from two or more of the data frames originally to be transmitted in the timeslot.

The way that the data frames, including the reduced size data frame or frames, are arranged for transmission in the remaining part of the timeslot can be selected as desired. For example, one or more complete unmodified data frames could be transmitted and any remaining space in the remaining part of the timeslot filled with one or more reduced size data frames. Alternatively only a number of reduced size data frames could be transmitted in the unstolen part of the timeslot (i.e. such that no unreduced data frames are transmitted) .

Thus, for example, in the above discussed example of transmitting three APCO coded data frames in a TETRA timeslot, when half-slot stealing is to occur, the remaining TETRA half-slot could be used, for example, to transmit two reduced size data frames from the three intended for that timeslot, or to transmit one complete, unreduced data frame and one or two reduced size data frames .

Where, in the above arrangements, not all of the original data frames are to be transmitted and/or some are to be reduced and others still transmitted in their entirety, the frames to be omitted, reduced, etc, are preferably selected on the basis of an assessment of their relative importance to the data being transmitted. This selection can be done along the lines discussed above, for example where speech frames are being transmitted, on the basis of a speech importance assessment, e.g. a speech energy assessment.

As a further refinement to the stealing process, it would be possible to modify the stealing process such that a reduced size portion of the timeslot is stolen so as to allow more room for the user data frames to be transmitted. This would provide less capacity for the stealing data, e.g. control signalling, but may be acceptable in some circumstances as it allows more user data to be transmitted. This arrangement is preferably used in conjunction with transmitting one or more reduced size data frames in the remaining unstolen part of the timeslot, but could, if sufficient space can be left by using a reduced size stolen timeslot portion, be used with unmodified data frames being transmitted in the unstolen part of the timeslot. Thus according to a fifteenth aspect of the present invention, there is provided a method of transmitting data in a radio communications system, in which system data to be transmitted is generated as a succession of discrete data frames and the data frames are transmitted in a succession of discrete timeslots, and in which system there is a predefined data stealing process whereby a portion of a timeslot of a predetermined size is replaced with other data to allow transmission of other data such as control signalling in a stream of data frames, the method comprising: when it is determined that such stealing should occur selectively modifying the stealing process so as to steal a portion of the timeslot which is smaller than the size of said predetermined stealing portion so as to allow more space for the data frames that were to be transmitted to be fitted into the remaining unstolen part of the timeslot when such stealing occurs.

According to a sixteenth aspect of the present invention, there is provided an apparatus for transmitting data in a radio communications system, in which system data to be transmitted is generated as a succession of discrete data frames and the data frames are transmitted in a succession of discrete timeslots, and in which system there is a predefined data stealing process whereby a portion of a timeslot of a predetermined size is replaced with other data to allow transmission of other data such as control signalling in a stream of data frames, the apparatus comprising: means for, when it is determined that such stealing should occur, selectively modifying the stealing process so as to steal a portion of the timeslot which is smaller than the size of said predetermined stealing portion so as to allow more space for the data frames that were to be transmitted to be fitted into the remaining unstolen part of the timeslot when such stealing occurs. In these aspects of the present invention, the stealing process is modified so as to steal a smaller portion of the timeslot. This allows more space for the data frames that were to be transmitted to be fitted into the remaining unstolen part of the timeslot.

This technique would preferably be used where it is recognised that the data frames being transmitted are not of the normal size for the radio system (i.e. not of a size that is optimised to the stealing process (e.g. of the size that would match appropriately the predetermined portion of the timeslot to be stolen) ) , such that a modification to the stealing process may be desirable. This situation could be recognised by, for example, determining whether the data frames to be transmitted are of a predetermined size, and if it is determined that the data frames are not of said predetermined size, modifying the stealing process.

Thus, for example, in the above discussed example of transmitting three APCO-coded frames in a TETRA timeslot, the TETRA half-slot stealing process could be modified so as to steal less than half a slot (e.g. to steal one third of a slot so as to allow room for two of the three APCO frames in the remaining unstolen part of the TETRA timeslot) , preferably upon recognition that the data frames did not match the TETRA data frame size. In these arrangements an indication that a reduced size timeslot portion has been stolen is preferably transmitted to the receiver to allow the receiver to recognise that the stealing process is not in accordance with the usual, defined stealing process. This indication could comprise, for example, a stealing portion length indicating word, or a marker, e.g. escape sequence, at the end of the stolen portion of data. In an APCO/TETRA system operating in this way, each stolen timeslot portion could carry an indication as to whether the next timeslot portion is stolen, as is the case for normal TETRA stealing (in which the first half-slot indicates whether the second half-slot is also stolen, i.e. full-slot stealing is occurring).

In all of the above arrangements, where two or more data frames (whether both reduced in size or otherwise) are to be transmitted in the remaining portion of a partially stolen timeslot, then where a data interleaving technique is used for the data transmission, the data transmission preferably uses a modified interleaving structure across the entire remaining timeslot portion, rather than maintaining data frame boundaries as would be more usual , so as to increase the channel coding (e.g. forward error correction) immunity to burst errors.

Encryption is a further factor that the Applicants have recognised needs to be considered when combining data generation and channel coding processes defined for different data transmission structures, or when attempting to transmit data generated and channel coded according to processes defined for one form of transmission data structure using another different transmission data structure.

As is known in the art, many encryption processes, even if they do not generate additional data from the original unencrypted data, still require the transmission of encryption signalling, such as encryption algorithm and key identity data, encryption synchronisation information, etc, to the receiver to allow successful decrypting of the transmitted data. Where this data is normally sent in the stream of encrypted data, it becomes additional data which must be fitted into the timeslot structure being used. One way to achieve this would be to use the various data reduction and apportionment techniques already discussed to reduce the space occupied as a result of the user data (e.g. the size of the (coded) data frames) to be transmitted to allow the encryption signalling to fit into the timeslot structure. Thus, according to a seventeenth aspect of the present invention, there is provided a method of transmitting data in an encrypted form in a radio communications system, in which system data can be transmitted in one of two different predefined data structures, and in which system at least one of the data structures has defined for it a data generation process and a data encryption process, which encryption process requires for its use the transmission of encryption control information to the receiver, and in which system data to be transmitted is generated from an input signal in the form of discrete frames, which raw data frames are then further processed by a channel coding process prior to transmission, the method comprising: when it is desired to transmit encrypted data generated and encrypted according to the processes defined for said at least one data structure over the other data structure, including said encryption control information in the data transmission, and modifying the data generating process and/or modifying the channel coding process so as to alter the amount of data in each coded data frame to be transmitted as compared to the amount of data that would be present in each frame when using the unmodified as-defined processes. According to an eighteenth aspect of the present invention, there is provided an apparatus for transmitting data in an encrypted form in a radio communications system, in which system data can be transmitted in one of two different predefined data structures, and in which system at least one of the data structures has defined for it a data generation process and a data encryption process, which encryption process requires for its use the transmission of encryption control information to the receiver, and in which system data to be transmitted is generated from an input signal in the form of discrete frames, which raw data frames are then further processed by a channel coding process prior to transmission, the apparatus comprising: means for, when it is desired to transmit encrypted data generated and encrypted according to the processes defined for said at least one data structure over the other data structure, including said encryption control information in the data transmission, and for modifying the data generating process and/or modifying the channel coding process so as to alter the amount of data in each coded data frame to be transmitted as compared to the amount of data that would be present in each frame when using the unmodified as-defined processes.

In the application of this arrangement to a TETRA/APCO system, one could always define the use of the APCO codec as being in partnership with DES encryption and therefore embed 4 bits per speech frame of re-synchronisation information into the (start) of each speech frame. The bits could optionally be classified for forward error correction coding. In this arrangement the coded bit rate could be modified to reduce the coded frame size according to one of the techniques discussed above. The four bits could be set to an easily recognisable pattern, e.g. all one's or all zero's, when there is no encryption.

Thus according to a further aspect of the present invention, there is provided a method of transmitting encrypted data frames, comprising: allocating a predetermined number of bits of space for encryption synchronisation information in each data frame ; and setting the predetermined bits to a predetermined pattern when there is no encryption.

The Applicants believe that in some circumstances other techniques could be advantageous .

Thus, according to a nineteenth aspect of the present invention, there is provided a method of transmitting data in an encrypted form in a radio communications system, which system includes both a control channel for control signal transmission and one or more traffic radio channels for user data transmissions, and in which system data can be transmitted in one of two different predefined data structures and in which system at least one of the data structures has defined for it a data generation process and a data encryption process, which encryption process requires for its use the transmission of encryption control information to the receiver and which encryption control information is in the defined process effectively embedded in the user data to be transmitted, the method comprising: when it is desired to transmit encrypted data generated and encrypted according to the processes defined for said at least one data structure over the other data structure, removing said embedded encryption control information from the data to be transmitted over the traffic channel and transmitting it instead over a control channel . According to a twentieth aspect of the present invention, there is provided an apparatus for transmitting data in an encrypted form in a radio communications system, which system includes both a control channel for control signal transmission and one or more traffic radio channels for user data transmissions, and in which system data can be transmitted in one of two different predefined data structures and in which system at least one of the data structures has defined for it a data generation process and a data encryption process, which encryption process requires for its use the transmission of encryption control information to the receiver and which encryption control information is in the defined process effectively embedded in the user data to be transmitted, the apparatus comprising: means for, when it is desired to transmit encrypted data generated and encrypted according to the processes defined for said at least one data structure over the other data structure, removing said embedded encryption control information from the data to be transmitted over the traffic channel and transmitting it instead over a control channel .

In these aspects of the present invention, when a different timeslot structure is to be used for encrypted data transmission, the additional encryption control (synchronisation) information which is part of the data to be transmitted is removed from the data to be transmitted on the traffic channel and instead sent on a control channel of the radio system (as is known in the art many radio systems use a channel arrangement which includes both control channels for control signalling and traffic channels for the transmission of user data, e.g. speech data) . This means that capacity on the control channel, rather than traffic channel capacity, is used for the encryption control information transmission, thereby helping the fitting of the remaining user data onto the traffic channel. Also, by transmitting the encryption control information on the control channel, the receiver can more readily recognise it as being control signalling, whereas it may need specially marking to distinguish it from user data if it were transmitted on a traffic channel.

The encryption information can conveniently be sent on the control channel as part of the call set-up signalling, where appropriate.

This arrangement is applicable to an APCO/TETRA system where APCO coded data frames are to be end-to-end encrypted according to the APCO standard but then transmitted over a TETRA air-interface. APCO uses DES encryption (Data Encryption Standard from the National Institute of Standard and Technology (NIST) - see, for example, NIST, Data Encryption Standard, FIPS

Publication 46-2, and ANSI, Data Encryption Algorithm, ANSI X3.92 - 1981), which is applied as a stream cipher. The encryption cipher is initially synchronised with a key identity, algorithm identity and a message indicator, which initial encryption synchronisation information is included in the data stream to be transmitted to the receiver.

In accordance with the above aspects of the present invention, when it is desired to transmit such APCO encrypted data over a TETRA air-interface, the initial encryption synchronisation information would be stripped out of the data stream and transmitted as part of the call set-up signalling over a TETRA control channel, rather than as part of the data transmitted over the traffic channel. This avoids using traffic data capacity for the encryption synchronisation information transmission, and also allows TETRA to recognise that the data is control signalling without the need to mark it to distinguish it from e.g. speech data.

Many encryption arrangements also require the periodic transmission of encryption information during the encrypted data transmission, to permit, for example, so-called "late entry" to the transmission and to allow a receiver to remain synchronised to the encrypted signal. The APCO DES system, for example, requires the message indicator to be repeated every 18 data frames to facilitate late entry.

In the present invention, such late entry and periodic encryption signalling is also preferably transmitted on a control channel , preferably together with the encryption synchronisation information, at appropriate intervals, rather than including it in the traffic channel transmission.

An alternative way to send the late entry signalling in the present invention would be to send it by using a traffic channel data stealing process. This is believed to be preferable to allowing the late entry signalling to remain in the user data to be transmitted in the form that it is generated, since transmitting it by a stealing process can allow the encryption synchronisation data to be recognised as not being, e.g. speech data, without the need to transmit additional data or to modify existing processes. Where such traffic channel stealing techniques are used to transmit the late entry signalling, the frequency of the late entry signalling is preferably reduced, where this can acceptably be done (e.g. the Applicants have recognised that this would be possible in a TETRA/APCO system, as correct synchronisation at the receiver can be maintained over relatively longer time periods where the receive circuits are correctly clocked) .

A further factor that the Applicants have recognised needs to be considered where one is making encrypted transmissions in a system that can operate in accordance with the present invention, is that where a deliberately reduced or truncated data frame is to be sent, for example as in the case of the data stealing mechanisms discussed above, the missing data bits from the frame or frames will typically have to be allowed for in the encryption process so as to maintain correct encryption synchronisation.

In one preferred embodiment, this is achieved by removing the necessary number of data bits (to reduce the frame size) after encryption, with a corresponding number of bits being reinserted into the data in the receiver prior to decryption (or prior to passing the data into another part of the system, e.g. if the radio unit is acting as a gateway) , to maintain correct decryption synchronisation (i.e. to compensate for the "missing bits") . This provides a relatively straightforward way of maintaining encryption synchronisation while transmitting a reduced number of data bits. The bits added (reinserted) by the receiver are preferably added to the reduced size data frame according to a predetermined pattern, such as all being zero or other values selected so as to have a minimum impact upon the data, so as not to affect too adversely any subsequent data processing steps carried out on the decrypted data, such as speech decoding. The predetermined pattern of bits added to the partial data frame to replace the missing bits can be fixed, or vary in a predetermined manner (e.g. change frame by frame), if desired.

As will be appreciated by those skilled in the art, all of the above aspects and arrangements of the present invention can be used singly, and/or in appropriate combinations, in a radio unit and a radio system. The invention is particularly, although not exclusively, applicable to a combined TETRA/APCO system and in particular to permitting transmission (in particular of speech) over the TETRA air-interface by a radio unit which uses APCO speech coding with APCO or TETRA channel coding. Such a radio unit could include any one or more of the above aspects and arrangements of the present invention in appropriate combinations. Thus, according to a further aspect of the present invention, there is provided a method of transmitting speech frames generated in accordance with the APCO Project 25 radio Standard speech coding protocols over a TETRA radio Standard air-interface, comprising: generating from an input speech signal speech frames for transmission in accordance with the speech frame generation process defined for the APCO Project 25 radio Standard; channel coding the generated speech frames using the channel coding processes defined for the APCO

Project 25 radio Standard; and transmitting the coded speech frames over a TETRA air-interface by inserting three coded speech frames into each TETRA timeslot. According to a yet further aspect of the present invention, there is provided a method of transmitting speech frames generated from a speech signal in accordance with the APCO Project 25 radio Standard over a TETRA radio Standard air-interface, the method comprising: generating from a speech signal speech frames in- accordance with the speech frame generation process defined for the APCO Project 25 radio Standard; coding the generated speech data frames using the forward error correction process defined for the TETRA radio Standard, but causing the forward error correction processes to be effectively carried out on data frames in which the relative importance levels of at least some of the data bits differ from the relative importance levels that they would be given by an unmodified APCO Project 25 speech frame data generation process, so as to reduce the amount of data in each coded data frame to be transmitted as compared to the amount of data that would be present in each frame if the changing of the relative importance levels had not taken place; and transmitting the coded data frames over a TETRA air-interface.

According to a yet further aspect of the present invention, there is provided a method of transmitting speech frames generated in accordance with the APCO Project 25 radio Standard over a TETRA radio Standard air-interface, the method comprising: generating from a speech signal frames of speech data in accordance with the APCO Project 25 radio Standard; channel coding the generated speech frames using the channel coding processes defined for the TETRA radio Standard, but modified so as to reduce the coding rate for bits of at least one level of relative importance; and transmitting the so-coded frames over a radio channel structured in accordance with the TETRA radio Standard.

According to another aspect of the present invention, there is provided a method of transmitting speech data frames generated in accordance with the APCO Project 25 radio Standard over a TETRA radio Standard air-interface, the method comprising: transmitting data corresponding to three APCO generated speech frames in each TETRA timeslot; and when TETRA half-slot stealing is to occur, transmitting in the remaining half-slot of the timeslot which is to be ^'stolen from, data corresponding to the centre APCO speech frame of the three speech frames which were to be transmitted in the timeslot.

According to another aspect of the present invention, there is provided a method of transmitting speech data frames generated in accordance with the APCO Project 25 radio Standard over a TETRA radio Standard air-interface, the method comprising: transmitting data corresponding to three APCO generated speech frames in each TETRA timeslot; and when TETRA half-slot stealing is to occur, transmitting in the remaining half-slot of the timeslot which is to be stolen from, one of the three APCO speech frames which were to have been transmitted in the timeslot on the basis of an assessment of the relative speech importance levels of the speech frames that were to be transmitted in the timeslot.

According to another aspect of the present invention, there is provided a method of transmitting speech data frames generated in accordance with the APCO Project 25 radio Standard over a TETRA radio Standard air-interface, the method comprising: transmitting data corresponding to three APCO generated speech frames in each TETRA timeslot; and when TETRA half-slot stealing is to occur, generating from one or more of the APCO speech frames that were to have been transmitted in the timeslot a speech frame having a reduced size and transmitting that reduced size speech frame in the remaining unstolen part of the timeslot .

According to yet_. another aspect of the present invention, there is provided a method of transmitting speech frames generated according to the APCO Project 25 radio Standard over a TETRA radio Standard air- interface, the method comprising: when such frames are being transmitted over a TETRA air-interface and TETRA half-slot stealing is to take place, modifying the TETRA half-slot stealing process so as to steal a smaller portion of the timeslot than half of the timeslot, and, preferably, so as to steal one third of the timeslot.

According to a further aspect of the present invention, there is provided a method of transmitting encrypted speech frames generated and encrypted in accordance with the APCO Project 25 radio Standard over a TETRA radio Standard air-interface, the method comprising: allocating 4 bits of space for encryption synchronisation information in each speech frame; and setting the four bits to a predetermined pattern when there is no encryption.

According to another aspect of the present invention, there is provided a method of transmitting encrypted speech frames generated and encrypted in accordance with the APCO Project 25 radio Standard over a TETRA radio Standard air-interface, the method comprising: when it is desired to transmit such encrypted speech frames over the TETRA air-interface, transmitting the speech data over a TETRA traffic channel and transmitting the initial encryption synchronisation information over a TETRA control channel.

In this aspect of the invention, any periodic encryption information to be sent during the encrypted transmission is also preferably sent over a TETRA control channel or by means of TETRA stealing mechanisms .

The invention also extends to apparatus for carrying out, and radio units capable of carrying out, any or all of the above methods. Similarly, all of the above aspects of the invention can include any or all of the preferred features of the invention discussed.

Although the invention is applicable in many of its aspects, where appropriate, to transmission of data in radio systems in general, it is particularly applicable to the transmission of user traffic, such as in particular speech data and frames.

The methods in accordance with the present invention may be implemented at least partially using software e.g. computer programs. It will thus be seen that when viewed from further aspects the present invention provides computer software specifically adapted to carry out the methods hereinabove described when installed on data processing means, and a computer program element comprising computer software code portions for performing the methods hereinabove described when the program element is run on a data processing means. The invention also extends to a computer software carrier comprising such software which when used to operate a radio unit or system comprising a digital computer causes in conjunction with said computer said unit or system to carry out the steps of the method of the present invention. Such a computer software carrier could be a physical storage medium such as a ROM chip, CD ROM or disk, or could be a signal such as an electronic signal over wires, an optical signal or a radio signal such as to a satellite or the like.

It will further be appreciated that not all steps of the method of the invention need be carried out by computer software and thus from a further broad aspect the present invention provides computer software and such software installed on a computer software carrier for carrying out at least one of the steps of the methods set out hereinabove.

A number of preferred embodiments of the present invention will now be described by way of example only and with reference to the accompanying figure, Figure 1, which shows an arrangement for half-slot stealing over a TETRA air-interface in a combined APCO/TETRA system in accordance with one aspect of the present invention.

The present invention will be described with reference to the operation of a radio system which allows data transmission over an APCO Project 25 radio Standard air-interface ("APCO") and a TETRA radio Standard normal (i.e. not scaled in any way) air- interface. However, as will be appreciated, the present invention is not exclusively limited to such an arrangement and will be applicable to the combination of other radio Standards and systems .

The preferred embodiments of the invention will also be described with reference to the transmission of speech in such an APCO/TETRA system, since in most radio systems speech transmission will be of particular importance. However, as will be appreciated by those skilled in the art, the invention is applicable to transmissions other than of speech.

Both TETRA and APCO have defined transmission data structures which comprise plural discrete timeslots of a defined size. A given radio transmission will normally consist of periodic timeslots of a constant length and at a constant rate which can therefore carry a given, fixed, period of speech in a given time period. In both systems, digital data for transmission from an input speech signal is generated in the form of discrete speech frames by a speech coder/decoder (codec) . The speech frames are generated at a constant rate and have a constant size, such that a given number of speech frames will then carry a particular period of speech. The raw speech frames are then channel coded using, inter alia, forward error correction coding. In both systems the speech coding, and related channel coding are optimised to ensure that the best fit into the defined transmission data timeslot structure is achieved.

However, the two standards generate speech frames of differing sizes and have different channel coding processes. The various speech-related parameters of the two systems are summarised in the following table:

To illustrate the present invention, an arrangement where it is desired to transmit speech encoded using the APCO speech coding arrangement using the normal TETRA transmission data structure (i.e. over a standard TETRA air-interface) will be considered. It can be seen from the above table that a single TETRA timeslot is intended to transmit 60 milliseconds of speech, and that that period corresponds to the speech encoded in 3 APCO speech frames . Thus a common multiple unit of speech between the two standards is a speech period of 60 ms . This corresponds to two TETRA speech frames which is 274 bits of speech as output by the speech codec to be transmitted in each timeslot. Three APCO speech frames would contain 264 bits, so in principle, the three APCO speech frames could fit into a single TETRA timeslot.

However, there then arises the question of having to channel code the raw speech frames before they are transmitted. Applying the TETRA channel coding (forward error correction) to an APCO speech frame gives per coded speech frame :

(48 x 18/8) + (33 x 3/2) + 7 = 165 bits

when rounded up. This gives 495 (i.e. 3 x 165) bits per 60 ms of speech, i.e. per TETRA timeslot. However, each TETRA timeslot only has the capacity for 432 bits. Thus it is not directly possible to encode the raw APCO speech frames using unmodified TETRA channel coding, and then transmit them in the TETRA timeslot structure.

However, the Applicants have recognised that the APCO channel coding, which uses two basic types of coding for voice frames, Golay (23, 12) and Hamming (15, 11) , which block codes are applied to the most important and medium importance bits, in fact produce a total of 432 bits for the three APCO speech frames (bits per frame = (48 x 23/15) + (33 x 15/11) + 7 = 144). Therefore the APCO data generating and channel coding processes generate 432 bits of data for transmission per 60 ms of speech, which number of bits will fit into a single TETRA timeslot which is also intended to carry 60 ms of speech. Thus a first preferred embodiment of the present invention for transmitting APCO generated speech frames over a TETRA air-interface is to both generate the raw speech frames and code them in accordance with the APCO Standard, and to then place three APCO coded speech frames into each TETRA timeslot. (In TETRA the forward error correction coded speech is subsequently re-ordered, interleaved and scrambled, but as this results in no change to the number of bits it can be ignored for the purposes of fitting APCO coded speech frames into the TETRA timeslot structure . )

One potential disadvantage that the Applicants have recognised with the above arrangement which uses the APCO speech frame generation and channel coding systems is that new channel coding (forward error correction) encoding and decoding schemes would have to be employed within TETRA terminals designed to operate in this system, which could be disadvantageous. Such an arrangement may also no longer perform as required by the, e.g. TETRA radio Standard, and so may not be TETRA 'compliant' and/or require extensive testing to adapt it to meet the standard. It may therefore in some circumstances be preferable to use the APCO speech frame generation process, but to use TETRA channel coding processes on those speech frames. However, if TETRA forward error correction is applied directly to an APCO single speech frame, that yields:

(48 x 18/8) + (33 x 3/2) + 7 = 165 bits

when rounded up. Three such speech frames (i.e. 60 ms speech) would therefore result in 495 bits, which is greater than the capacity of single TETRA timeslot . It is not therefore possible to apply directly the TETRA forward error correction coding to APCO raw speech frames .

In alternative preferred embodiments of the present invention therefore, the Applicants propose to modify aspects of the speech coding process so as to produce coded frames using basic TETRA channel coding processes on APCO generated speech frames, but which contain less data bits and so will fit into the TETRA timeslot structure .

In a first preferred embodiment of this arrangement, the reduction in the amount of coded data generated from a given raw APCO speech frame is achieved by effectively reclassifying the importance levels of the output data bits from the APCO speech codec at least as regards their treatment by the TETRA forward error correction coding, while still using the TETRA forward error correction codes in an otherwise un-modified manner. In this embodiment the bits output in the APCO speech frames are effectively reassigned amongst the different relative importance classes so as to change the number of bits at each level of relative importance, so as to reduce the size of the frames after the channel coding is applied. The re-classification of the relative importance levels of the bits should be such that the number of coded bits generated per raw speech frame is reduced sufficiently that the output of three error coded APCO speech frames will fit, preferably exactly, into a single TETRA timeslot.

The way that the relative importance levels of the bits are reclassified can be selected as desired. One suitable reclassification would be a reclassification which results in an almost identical number of bits per relative importance class as for a standard TETRA speech encoding arrangement. The reclassification of the relative importance levels of the bits in the raw APCO speech frame should be done so as to try to minimise any impact on speech quality. Thus, for example, the fundamental frequency, which is a critical parameter, should still be heavily error protected, as it not only defines the frequency, but also the structure of the rest of the speech frame and must be error free in order to decode the frame correctly. On the other hand, the APCO sync bit is not needed in TETRA as TETRA time can be used instead for maintenance of synchronisation and so that bit can be reclassified to a lower importance level or be omitted, if desired.

It is believed that this arrangement may be a particularly convenient arrangement, since it allows standard TETRA forward error correction coding to be used and there is only some re-classification of the importance levels of the raw speech bits, which should involve relatively little change to existing equipment and processors.

An alternative technique for reducing the size of a coded data frame from a given APCO raw speech frame is to modify the TETRA forward error correction schemes to reduce the coding "rate", i.e. such that less coded data is generated for a given raw data bit. Again the rate should be appropriately adjusted such that three raw APCO speech frames will fit into a single TETRA timeslot .

Thus taking R2 as being the rate of the channel coding applied to the most important bits, and Rl as the rate applied to the medium importance bits (with no coding being required for the least important bits) , then for three APCO speech frames the total number of coded bits will be:

[1/R2 X ( (48 X 3 ) + 12 ) ] + [l/Rl X ( 33 x 3 ) ] + [7 X 3 ]

and this must be less than or, preferably, equal to, 432 bits to fit into a single TETRA timeslot when Rl and R2 are chosen. (The 12 bits added to the most important bits is for the 8 bit cyclic redundancy check and 4 tail bits needed for the TETRA forward error correction decoder. )

If the standard 2/3 TETRA forward error correction coding rate is applied to the medium importance bits in each APCO speech frame (i.e. Rl = 2/3), then the number of bits needed per TETRA timeslot for the coded medium importance bits is:

(3 x 33) x 3/2 = 149 bits

when rounded up. The least important APCO speech bits are not channel coded and so require (3 x 7) = 21 bits capacity per TETRA timeslot. This leaves

432 - 149 - 21 = 262

spare bits per TETRA timeslot for assignment to the most important bits in the three APCO frames to be contained in a timeslot . A suitable forward error correction coding rate, R2 , for the highest importance bits in this arrangement to use this available capacity is therefore:

( (48 x 3) + 12) /262 * 0.6.

Thus one possibility would be for Rl ~ 0.67 and R2 « 0.6. In that arrangement the protection applied to the most important bits would be lower than is normally used in APCO, but the medium importance bits would be better protected than they normally are in an APCO system.

A particularly preferred embodiment of this arrangement is to code both the high and the medium importance bits at the same rate of 2/3 using the TETRA forward error correction coding. This would result in:

((48 + 33) x 3/2) + 7 = 129 bits per APCO speech frame,

when rounded up, i.e. 387 bits per TETRA timeslot. This arrangement would use less capacity than is available in a TETRA timeslot, and the remaining capacity could be ignored or used for further error detection e.g. by use of a cyclic redundancy check. Alternatively, the coding rate for the high and medium importance bits could be increased from 2/3 to 81/137 to fill completely the available timeslot capacity, if desired.

The TETRA coding rate can be varied by modifying the "puncturing" scheme used. (As is known in the art, in TETRA the convolutional coding is produced from a mother code of rate 1/3 which is then "punctured" (i.e. bits are removed) to produce the lower rate code ("RCPC" code) actually used. In the receiver, the punctured bits are replaced by zeros into appropriate locations in the received data stream.) The above arrangements permit the combination of the speech codec defined for the APCO radio standard with TETRA forward error correction coding schemes such that data corresponding to three APCO speech frames will fit into a single TETRA speech traffic timeslot. This is achieved by effectively reducing the size of the coded data frames produced from the APCO raw speech frames, either by re-classification of the importance of the output data bits from the APCO speech codec such that even when using the TETRA forward error correction codes in an otherwise un-modified manner, the number of coded output bits generated is reduced, or by the modification of the TETRA forward error correction coding streams to reduce the "coding rate" so that the gross number of coded bits generated from the three raw APCO speech frames is reduced.

The above embodiments of the present invention transmit three APCO speech frames in each TETRA timeslot. This arrangement will operate satisfactorily during normal, continuous user data transmission. However, TETRA supports the "stealing" of user data, to, for example, permit the transmission of control signalling in a stream of user data. When such stealing occurs, the timeslot capacity is lost to signalling and the missing user data (e.g. speech) must be "recovered" at the receiver by some mechanism. Such user data stealing will also need to be taken account of in a combined APCO/TETRA system.

TETRA supports both full timeslot and half-timeslot stealing. When full-slot stealing occurs in the arrangements of the present invention where three APCO speech frames are transmitted in each TETRA timeslot, then the situation would be the same as for standard

TETRA, i.e. 60 ms of speech would be lost, and therefore no further mitigating action is required.

However, half-slot stealing is a different matter. As discussed above, in standard TETRA, half a time slot carries 216 bits which corresponds to 30 ms of speech, which is lost when stealing occurs. However, in the TETRA/APCO system of the present embodiment where three APCO speech frames are carried in one TETRA timeslot, the loss of half a TETRA timeslot to stealing would in an unmodified TETRA stealing arrangement cause the loss of two of the three APCO speech frames (i.e. 40 ms of speech) since it would not normally be expected for a partially complete speech frame to be of any use (as a complete frame is usually needed for decoding) . The two APCO speech frames lost would be the first two of the three APCO speech frames, i.e. only the third frame is transmitted, since it is the first half-slot which is stolen.

In a first preferred stealing arrangement of the present invention, where three APCO speech frames are transmitted in each TETRA timeslot, upon recognition of half-slot stealing over the TETRA air-interface, the second (centre) APCO speech frame (in time) rather than the third (last) frame of the three frames which were to be transmitted in the TETRA timeslot is transmitted. This provides two breaks of 20 ms in the transmitted speech data, which it is believed would be easier to interpolate compared to a single 40 ms break in the speech data. Figure 1 illustrates this arrangement. (In Figure 1, the speech frames from the slot previous to the slot to be stolen from are labelled, in increasing time order, A01, A02, A03, the speech frames in the slot to be stolen from are then All, A12, A13, and the speech frames in the next slot are in time order, A31, A32, A33.) As can be seen in Figure 1, when stealing occurs, the centre speech frame, A12, which was to be transmitted in the slot, is transmitted in the remaining unstolen TETRA half-slot.

In this arrangement there are some spare bits in the remaining TETRA half timeslot (since a single coded APCO speech frame will not fill the entire half-slot) . The spare bits are preferably used to transmit partial information about the missing speech frames to help the interpolation process and enhance intelligibility.

In an alternative arrangement, the one of the three speech frames to be transmitted could be selected based on an assessment of the relative speech "importance" of the respective speech frames, and/or how useful each frame might be for the interpolation process or for preserving intelligibility. The "speech importance" evaluation could be based on for example the speech energy in each frame, or a more sophisticated measure of speech importance. It is believed that this arrangement could offer a better quality of reconstructed speech, since the selection of the speech frame still to transmit is made in an intelligent way. In this arrangement, the spare capacity in the half-slot could be used to indicate to the receiver which of the three frames has been transmitted and also information regarding how to interpolate across the gaps.

In another preferred embodiment, when TETRA half- slot stealing is to occur two speech frames both with deliberately reduced speech data content (i.e. of a reduced size) are transmitted in the unstolen half-slot.

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should be transmitted to the receiver.

In each of the above arrangements, the speech frames to be transmitted (whether with reduced data or otherwise) are preferably selected on the basis of their relative "speech importance", as discussed above.

Each of the above stealing arrangements in which two speech frames are effectively transmitted in the remaining half-slot could additionally use a modified TETRA interleaving structure across the entire remaining half-slot, rather than maintaining speech frame boundaries, in order to provide the forward error correction coding with maximum immunity to burst errors . A further consideration with the above arrangements is where end-to-end encryption is required. APCO uses DES encryption which in APCO is applied as a stream cipher which is exclusive ORed with the data in the speech frames. This DES encryption should be applied before any channel (forward error correction) coding which relates to the air-interface in order to maintain compatibility with existing APCO systems.

APCO DES encryption does not modify the quantity of data, nor does it propagate errors. However, the encryption is initially synchronised with a key identity (KID = 16 bits) , an algorithm ID (ALGID = 8 bits) , and a message indicator (MI = 72 bits) . The message indicator is then repeated in APCO systems every 18 speech frames to provide "late entry". This initial encryption synchronisation data and the.subsequent late entry signalling must also be transmitted to a receiver to allow the receiver to decrypt the transmitted signal.

This encryption signalling could still be included in the user traffic (and fitted into the TETRA timeslot accordingly) . The TETRA D-INFO and U-INFO Packet Data Units (PDUs) could, for example, be used for carrying data embedded into the user traffic (e.g. synchronisation (Message Indicator) information) on the downlink (i.e. base station to mobile station) and uplink (i.e. mobile station to base station, respectively. Such transmission would ensure that the encryption synchronisation data maintains its relative synchronisation to the user data. Another way of sending the encryption synchronisation data would be to always define the use of the APCO codec as being in partnership with DES encryption and therefore embed 4 bits per speech frame of re-synchronisation information into the (start) of each speech frame. The bits could optionally be classified for forward error correction coding. In this arrangement the coded bit rate would need modification to reduce the coded frame size according to one of the techniques discussed above, and the encryption synchronisation should be put back together for forwarding to any existing APCO systems, so that they can use the Message Indicator in a block, to provide backwards compatibility. The four bits could be set to an easily recognisable pattern, e.g. all one's or all zero's, when an APCO codec is being used but there is no APCO DES encryption.

However, as will be appreciated from the above, when using the arrangement where three APCO generated and channel coded speech frames are being transmitted in each TETRA timeslot, there may be no remaining room in the TETRA timeslot for any of the encryption synchronisation information to be transmitted. Therefore, in another preferred embodiment of the present invention, the initial synchronisation information is sent as part of the call set-up signalling on a TETRA control channel, since that will not require capacity on the traffic channel . It is also preferred that late entry is effected by repeating the synchronisation information and the late entry signalling on the TETRA control channel. The TETRA

D-SETUP and U-SETUP Packet Data Units (PDUs) could be used to carry the initial downlink and uplink, respectively, call-set up information and late entry signalling on the control channel. (The inclusion of an encryption synchronisation message into a D-SETUP PDU for either call initiation or late-entry will require a reference to the TETRA time so that the call synchronises correctly.)

An alternative way to provide the late entry signalling would be to use TETRA half-slot stealing mechanisms. However, because, as will be discussed below, half-slot stealing in such an arrangement could imply the loss of a relatively larger amount of speech frames, it is preferred in such an arrangement that the late entry signalling is intercepted and reduced to a maximum of once per second in the TETRA system (the periodic repeat of the message indicator every 18 APCO speech frames represents a rate of 2.7 Hz) . The "missing" message indicators in such an arrangement would be compensated for by continued correct synchronisation at the receiver, which should be readily achievable if the received circuits are correctly clocked.

Thus, where encryption is being used, all the extra encryption signalling is preferably mapped to the call set-up control signalling and stealing channels available within TETRA, rather than embedded in the user data to be transmitted as normal on the TETRA traffic channels. This allows the TETRA system to, for example, more readily distinguish the encryption control signalling from the user data. It in effect uses the existing processes available for transmitting control signalling to transmit the encryption control information, rather than trying to modify traffic transmissions to do so.

It should be noted that the message indicator used in APCO contains 64 bits of data and an undefined 8 bit reserved field. The 8 bit reserved field could be used as a cyclic redundancy check or other error check in ω w - t μ> H in o in o in o in

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Ω φ LQ rt ϋ μ- td Hi 0 o Hi Ω Φ Si HJ Hi rt <! tr rt t a Hj r a

Ω φ TJ tr φ <! O rt a μ- a fi K tr m Φ D tr rt CD μ- Φ tr fi Hi μ- Ω ϋ μ- rt 0 o φ μ- TJ ^■<: rt φ 1 μ- SD tr μ- Hi Si TJ τ Φ O T a Φ 1 Hi a CQ o μ- a d o rt SD φ μ- Hj_ m 3 3 Hi Φ a 0 Φ φ rt Φ LQ rt SD LQ Hi o Q ^ ra d τ Hj SD ct M φ φ Hi CD Hi rt Φ μ- μ- Φ 3 0 3 Hi ED

CD ra rt SD a ^ HI a — ' SD TJ Φ Φ Ω 0 a Ω rt μ- 1 φ d rt

SD 3 TJ Φ φ a- rt ϋ w rt 3 Hi H Hi tr a ra tr tr D Φ TJ 0

CQ tr φ φ μ- > CD φ Φ rt 3 " φ μ- CQ a μ- rt Hi φ φ 0 0 SD Φ μ- Hi CD μ- fi ra

SD Hi Ω Hi a CD Ω Si a rt a φ tr SD φ μ- iQ μ- a fi ra rt

direct mode gateway.

The end-to-end encryption and use of the APCO speech codec are preferably defined as supplementary services for the TETRA air-interface. This would mean, for example, that the control data required could be sent using the "facility" field in TETRA. If they are not defined as supplementary services, they can be defined as proprietary services, with the "proprietary" field in TETRA then being used for control data transmission.

It can be seen from the above that the present invention provides techniques for in particular mapping a constant-rate data-stream generated in frames (e.g. from a voice or video coder) on to a telecommunications bearer which can carry data in a series of discrete timeslots at a normally constant data rate (except for occasional "stealing" of capacity for system control use) , and also provides a communications terminal which can be used in such a communications system which in effect contains a low-bit digital speech encoder/decoder function and an error encoding/decoding function and a mechanism for mapping the output data into "frames" for transmission/reception. It in particular applies to the situation where the data frame rate and size does not match the timeslots of the radio bearer transmission system exactly on a one-to-one basis, i.e. the basic coded data frame size and timeslot size are not equal. In the particular preferred embodiment described, such a communications system is provided which also maintains backwards compatibility to two already defined radio systems (TETRA and APCO Project 25) . In particular, techniques are provided for mapping speech generated by the APCO Digital Voice System Inc ' s Improved Multi-Band Excitation digital voice coder, which produces speech at a different frame-rate to the defined TETRA speech coding, onto TETRA's basic timeslot structure, by fitting three frames of coded APCO speech into each single TETRA timeslot (both of which correspond to 60 ms of speech) . In these arrangements, the APCO error correction scheme, or modified versions of the raw APCO speech data and/or of TETRA's forward error correction schemes, are used to allow mapping of the APCO speech frames into the TETRA timeslot structure .

The invention also provides techniques for allowing for TETRA' s timeslot and half-slot stealing protocols in the combined APCO/TETRA system. In particular, modifications are made to the error correction scheme and/or the timeslot (bursts) building protocol when half-slot stealing is to occur, to mitigate the problem of TETRA half-slot stealing resulting, because the APCO speech frames do not exactly fit into a TETRA half-slot, in more speech loss than with TETRA's normal speech encoding .

Finally, arrangements and modifications are proposed to allow the implementation of APCO DES encrypted frames into TETRA timeslots in a way which remains backwards compatible with APCO phase 1 and which can cope with TETRA half-slot stealing mechanisms.

All of these techniques are preferably used in appropriate combinations to provide a combined APCO/TETRA system.

Claims

1. A method of operating a radio unit for use in a digital radio system which can use two predetermined data transmission structures, each comprising timeslots of a defined size, and in which system data to be transmitted is generated from an input signal in the form of discrete frames, which raw data frames are then further processed by a channel coding process prior to transmission, each transmission data structure having its own defined data generation and channel coding processes, the method comprising: generating from an input signal frames of digital data using one of the defined data generating processes; processing the generated frames of digital data using one of the defined channel coding processes to produce a series of coded data frames for transmission; and modifying the data generating process and/or modifying the channel coding process when it is intended to transmit the data in accordance with at least one of the defined data structures, so as to alter the amount of data in each coded data frame to be transmitted as compared to the amount of data that would be present in each frame when using the unmodified as-defined processes.

2. The method of claim 1, wherein the data generating process and/or channel coding process is or are modified so as to reduce the amount of data in each coded data frame to be transmitted as compared to the amount of data that would be present in each frame when using the unmodified as-defined processes.

3. The method of claim 1 or 2 , wherein the data bits in the generated data frames are classified into differing levels of relative importance and the

D. Hj Φ Ω TJ μ- ϋ rt Ω rt Hi rt Si

P. μ- in rt μ- CD CO TJ > SD CQ tr TJ Ω 0 a ra

SD φ Hi o H{ SD tr tr tr Φ O Hi μ- . SD 3 • tr 3 0 d Hi • φ T d φ Hi 0 a d d rt Hi 3 φ TJ rt Φ SD Φ < Hi SD CQ rt TJ φ TJ 3 Ω 0 <! T Ω 0 fi tr

SD Φ TJ 1 0 ED a a Φ 3 a μ- ED 0 0 Φ a- Ω φ h-ⁱ tr 3 Ω Φ rt cy CQ rt Ω Hi fi Hi Ω a M CD Hj H3 ϋ Hi Φ μ- 0 Φ Di tr φ φ tr H- rt Ω H- φ rt <! 0 Φ Hi CQ 0 3 SD SD rt tr SD rt 0 rt CQ Hi CD Φ rt fi CD φ Hi Λ μ- μ- SD CQ Hi SD SD fi d Hi μ- Hj SD Φ rt SD Hi ^{^} ra tr α tr μ- CQ CD d rt Φ <! d μ- μ- a Hi φ Hi O rt 3 φ a SD a ED Φ 0 ED Hi Hi H{ φ

CD Φ CD a a Ω μ- Ci Ω rt Hi fi rt Hi Φ Ω 3 Ω rt rt ED Hi rt rt μ- SD d φ 0 a μ- H> μ- CQ φ Φ Φ 0 tr μ- Φ ED rt Ω φ Φ Q φ tr a 3 0 φ a Hi Hi rt

(i 3 ^ a Di ra i fi Φ Hi m ϋ fi tr tr rt Φ φ rt Si φ rt rt P. rt SD μ- J Q 0 SD μ- Hi Φ Ω μ- 0 SD tr a μ-¹ tr *"\ rt ^* SD a^* ** P" rt ED Ω

Hi 0 Ω D. Hi fi rt a Hi μ- 0 fi a φ o φ φ Hi φ 0 tr Φ φ 0 Φ μ- ϋ tr

Hi Hi SD rt SD Φ SD CQ TJ ED φ ra LQ < ϋ Hi <! SD Hi 0 Si 3 Hi Hi < ϋ SD

Φ rt Hj tr rt rt TJ Hi rt rt ra 0 φ φ SD φ s; Ω Si LQ μ- Ω 0 Φ μ- a

Hi SD Hi Φ SD - φ Q TJ 0 μ- Φ LQ x. Hi Si 0 rt tr Ω φ Hi tr Di ft Ω rt a ra a μ- φ a Φ Hj Ω <! φ ra ra Hi μ- D. SD tr 0 a Hi ED μ- tr 0 μ- μ- Φ

Ω Φ Ω CQ fi a 0 Φ Φ Hi a rt TJ TJ 0 rt SD a ED Hi Φ φ a Hi Φ 3 O rt Φ fi tr Φ Hi μ- Φ Ω CQ Hi Φ Φ Hj Hi 0 Ω a 0 rt a a Hi Hi a ^ TJ T a

0 SD a ED a Hi φ ra μ- ED Hi 3 φ μ- Hi SD Φ a Ω SD Φ Φ μ- Ω Hi 0 SD Ω

0 a φ sξ CQ SD CQ Φ 3 3 SD TJ 0 SD TJ rt H" Φ rt a r a tr μ- Hj 0 rt Φ d a Hi rt a fi TJ φ rt SD Hi 0 μ- Hj tr tr SD Φ rr CQ SD ra rt fi tr < rt Φ SD 0 Φ 0 CO Φ μ- Hj a 3 o Φ μ- Ω μ- ϋ Ω a μ- ED tr μ-

Φ Φ r-¹ rt ED a ϋ μ- TJ H fi a μ- rt Φ Ω rt 0 Ω 3 n 0 rt rt a a a μ- a

0 μ- rt a Hi ≤ a 0 ω Φ H" CQ Si 0 Hi Ei tr Φ LQ Ω rt LQ

Hj CD a Ω o SD rt Hi μ- ED tr Hi ^ LQ o CD φ μ- fi ) ED SD μ- ED φ ra

Φ 0 a tr Hi $, 0 a μ- Hj tr Ω Hj 0 ra <! ED a μ- •_" ≤ to a rt , TJ

H" 0 Hi fi tr Φ 0 tr Hi Ω Ω 0 μ- Si tr Hj • φ ra LQ a CQ CQ Ω tr μ- H e

SD Hi SD μ- TJ μ- g μ- Φ tr 3 Ω SD SD 3 LQ ≤ Si μ- TJ 0 Φ φ a 0 rt o

$ a Hi rt Hi Ω rt - tr rt P 0 > tr TJ tr ED Hi TJ H{ fi a < rt Ω μ- 0 LQ 0 - φ SD tr 0 Ω SD ED a Hi - Φ SD Hi TJ Φ rt μ- Hi 0 μ- φ 0 φ

<! a si Ω H-" 3 0 a ra Φ Φ Hi < o Hi Hi SD o 0 Ω a rt ra φ Φ SD TJ Φ SD SD LQ rt rt tr P * Hi s: μ- Ω 0 Φ SD Ω Φ LQ tr rt CQ ft Hi CQ a rt μ- tr Hi μ- rt μ- ra 0 0 tr Φ a Φ Ω μ- tr rt φ CD Φ 0 tr μ- 0 SD 0 m fi μ- < Φ ED Ω ED a rt Hi Ω Hi φ Ω LQ CO φ a μ- μ- CQ CD TJ Hi φ μ-

3 Hj Ω < φ a - μ- TJ Φ 0 Hj rt m ra rt 0 CQ Hi fi a

TJ μ- Φ s Φ a a ra P d 3 rt Si rt Φ μ- SD CO rt CQ a 0 0 ED rt Ω rt

0 3 a CD rt tr d 3 Hi rt Hj μ- tr μ- <! μ- tr • μ- Hj Ω rt a- 0 Hi

H O CQ tr μ- μ-¹ tr g μ- SD tr P. ED a Φ a Φ ϋ a μ- Φ 0 m Φ ED Φ fi o rt Hj z Φ Ω φ μ- ^* ra s: μ- CD SD a CQ μ- rt ra Hi rt CQ φ fi

SD φ tr rt tr <! rt φ CQ rt μ- rt CD tr rt x. Hi Φ ϋ φ tr CO LQ LQ Pi d a μ- 0 3 φ Hj μ- ϋ CD cQ SD 3 0 μ- - Hi Hi 0 SD rt Hi 0 Φ μ- Ω

Ω 0 Ω Φ CD H¹ μ- 0 SD a μ- Hi rt Φ ED φ T Hi rt tr Hi CD μ- a <! Pi Φ

Φ Hi P" tr rt *< a 0 a rt 0 ED rt CQ ra M Hj Hi SD Φ φ Φ ra Φ Φ SD ra

Φ a^{^} CQ O Hi Eu Hi μ 0 CD rt Hi Φ Φ ED Ω H a rt rt rt 0 rt Hi rt tr μ- tr μ- φ o μ- a rt Hi LQ μ- rt TJ 0 SD ED Pi

Φ tr tr fi Φ a¹ tr ^ Hi P. tr 0 Φ a μ-¹ Ω rt ra Φ Φ 3 μ- Hi Hj rt tr μ-

< Φ Φ 3 φ μ- Hi μ- a φ a SD SD a TJ <! 0 μ- μ- Ei Hi

Φ rt SD Sϋ Hi fi rt rt rt Hj SD 3 Φ 0 Φ Ω ED a rt Φ Hi

Hj tr Hj CQ 3 Hi rt μ- ED μ- Φ Φ rt 0 Hj Hj Φ Hi LQ CD TJ Φ

SD SD SD φ φ tr a rt Φ < ϋ h-¹ Si ED rt CD φ Φ H rt $, CQ ≤; μ- ra Hi φ ED φ SD μ- rt SD CD rt a Φ SD • rt a Φ tr Hj tr Φ Hi μ- a Φ rt O Si a

SD E SD a Ω CD 0 μ- rt rt a SD ^•<; μ- SD μ-

Hj rt s < CQ Φ LQ φ tr rt a Φ φ Si φ LQ

the bits would have had under the defined data generation process, so as to alter the amount of data in each coded data frame to be transmitted as compared to the amount of data that would be present in each frame if the changing of the effective relative importance levels had not taken place.

7. The method of any one of the preceding claims, comprising modifying the channel coding process so as to alter the number of coded output bits produced as compared to when using the unmodified channel coding process .

8. A method of preparing data for transmission in a digital radio system, in which system data to be transmitted is generated from an input signal in the form of discrete frames, which raw data frames are then further processed by a channel coding process prior to transmission, the method comprising: generating from an input signal frames of digital data; processing the generated frames of digital data using a channel coding process to produce a series of coded data frames for transmission; and selectively modifying the channel coding process so as to reduce the amount of data in each coded data frame to be transmitted as compared to the amount of data that would be present in each frame when using the unmodified process .

9. The method of claim 7 or 8, wherein the channel coding process generates additional data bits at a given rate per original data bit, comprising modifying the channel coding process so as to alter the coding rate .

10. The method of claim 9, comprising, where the original data has bits of different levels of relative importance, altering the coding rates for one or more but not all of the different levels of importance.

11. An apparatus for use in a radio unit for use in a digital radio system which can use two predetermined data transmission structures, each comprising timeslots of a defined size, and in which system data to be transmitted is generated from an input signal in the form of discrete frames, which raw data frames are then further processed by a channel coding process prior to transmission, each transmission data structure having its own defined data generation and channel coding processes, the apparatus comprising: means for generating from an input signal frames of digital data using one of the defined data generating processes; means for processing the generated frames of digital data using one of the defined channel coding processes to produce a series of coded data frames for transmission; and means for modifying the data generating process and/or modifying the channel coding ^"process when it is intended to transmit the data in accordance with at least one of the defined data structures, so as to alter the amount of data in each coded data frame to be transmitted as compared to the amount of data that would be present in each frame when using the unmodified as- defined processes.

12. The apparatus of claim 11, wherein the data bits in the generated data frames are classified into differing levels of relative importance and the subsequent channel coding process introduces different numbers of additional bits into the coded data depending on the relative importance level of the given bits to be coded, further comprising means for, when the data generating process and/or the channel coding process is or are to u> CJ to to μ> M in o en o in o in

φ LQ rt α hj φ Ω TJ μ- ϋ rt Ω rt hti rt SD μ> 0 3 Hi H rt μ- ra CD Ω 3 μ» SD CQ tr

SD Φ tr SD φ Hi 0 Hi 3 ED tr tr tr φ 0 Hi on Hi 0 0 > tr a 3 0 d 0 0 ω Φ T d Φ

Ω Φ rt Hi Φ TJ rt Φ ED Φ <i Hi SD ϋ • Hi H{ . Φ TJ 3 Ω Si Si . < TJ Ω tr Φ SD SD Φ TJ 1 o SD a a φ 3 a μ- rt Φ 0 φ tr μ- μ- Φ h-¹ tr 3

Hi tr rt Ω Hj . Hi Ω t a h-¹ CQ LQ tr Ω ϋ HJ μ- δ

Ω SD H- tr μ- r rt <! 0 Φ Hi CQ a Hi

3 μ- Φ 0 3 μ-

H- rt S Φ 0 tr H SD rt 0 rt LQ a φ rt fi rt r Hi m r

0 t μ- <! μ- φ D Hi SD SD D. H d Hi SD tr rt ED Hi a μ- tr fi tr μ-

Ei μ- O rt Φ < SD μ- μ- a Hi Φ Hi 0 rt SD fi a Φ SD a SD T a Φ 0 SD Hi φ 0 CQ φ a a a Ω μ- Di Ω rt Hi ϋ rt SD fD rt LQ Ω rt rt Hi LQ Hi rt rt μ-

Di a € μ- CQ LQ φ φ φ 0 tr μ- Φ TJ rt tr μ- S LQ φ tr 0 SD 0 Φ

0 fi 3 ^> ; •• Di CO Di fi Φ hi CQ fi H{ TJ SD φ a T Φ φ rt Ω rt TJ rt rt Di

D- TJ d μ- TJ Hi 0 SD μ- hi Φ Ω ED SD • CQ TJ a tr φ tr TJ tr SD tr

SD Hj μ-¹ Hi 0 Ω o P- Hi Pi rt a Hi μ- Ei Hi tr SD φ φ Hi Φ CQ φ SD Φ φ rt 0 fi Hi Hj SD Hj SD φ SD CQ TJ SD φ m μ- SD μ- rt Hj Hj <! SD CQ Hi ϋ 3

ED Ω Φ rt rt rt TJ Hi rt rt 0 rt rt tr SD ED Φ Ω fi SD CQ μ- Ω 0

Φ tr hi ED Hj Ω ED tr φ LQ TJ 0 μ- φ ω d CQ Φ rt rt p- 3 ED rt Φ Hi tr D-

Hi ra °J CD a μ- SD Φ a φ h{ Ω <! Φ CQ CD d μ- ϋ SD 0 rt d a Hi ED μ-

Hj ra <! Ω Φ d LQ D. a o φ Φ Hi a μ- Hi CQ O rt SD a fi SD ra Φ φ a Hi

SD φ rt φ ϋ CQ Φ H μ- φ Ω CQ hi Φ CQ Hi a Φ a 0 rt a μ- Hj Hj a x;

3 0 μ- a ED a Hj φ CD μ- SD Hi rt 0 0 SD Φ Hi CQ 0 SD φ Φ μ- φ CQ tr H" 0 a φ ^ LQ SD CD Φ 3 3 ED Φ Hi rt SD Hi TJ rt H-¹ μ- Φ hti rt a ->

0 SD rt Φ d LQ Hj rt CQ a

D. TJ φ rt 3 tr rt Hj tr tr φ P φ rt LQ rt fi tr < rt ED Si 0 Φ 0 CQ Φ TJ Φ μ- Ω 0 Φ μ- Ω m Φ Ω Si Ω

0 ED Φ Φ rt rt SD a ϋ μ- TJ Hi ϋ hi < Ω r 0 Hi I-¹ Ω 0 rt

CD d - 0 tr μ- rt hi rt i a 3 μ- Φ Hi φ SD Φ μ m fi rt ED ED Hi fi tr tr P hi ra a Φ 0 SD rt H μ- SD tr Hi P TJ SD μ- CQ φ μ- tr rt μ- ED ED μ- SD ,

Φ rt p. φ a tr Hj 3 0 a μ- hi SD ≤ μ- 3 CO <! SD a SD μ- 3 ra a r '

0 Φ H¹ 0 Hi Ω tr Φ 0 a- Hi Ω Ω 0 Hi 3 • Φ ra LQ rt CQ LQ rt hi SD Hi SD μ- a a^* TJ μ- 3 μ- Φ tr 3 tr fi T μ> h-¹ CQ μ> ϋ μ- J U ϋ SD rt 3 SD hj rt Hi Ω rt - μ- a SD O to tr T TJ to SD Hi TJ Hi

SD rt μ- 0 a 0 Φ ED tr 0 Ω SD Ω CQ rt Hi φ SD Hj H TJ _^ rt μ- Hj a rt a 0 i tr < a Si Ω H" 2 0 a tr ED rt 0 Hi <! 0 0 Hi SD Ω 0 Ω '

CD Φ Φ φ Φ SD Φ Φ SD ED CQ rt rt tr a fi SD Hi Hi μ- Ω Ω 0 $ SD Ω φ

3 Hj rt CD a rt μ- tr Hi μ- rt μ- CD SD TJ a Φ a Φ Φ Ω tr tr rt Φ CQ μ- fi μ- 0 SD CD ϋ μ- <! Φ SD Ω SD a ^>< rt hj Ω μ> Ω CQ m CQ Φ Φ μ- μ- CQ CQ rt rt Φ 3 H Ω » < φ a tr μ- TJ CD ED μ- Φ ω rt ra CQ m H rt 0 ra rt tr Hi TJ μ- 0 $, Φ a a CD a d rt 0 ~. μ- SD CD Φ CD a 0

Φ Φ μ- 0 3 a fi rt tr d 3 Hi rt φ Hi hi μ-¹ <J μ- 0 μ- . μ- Hj

P. a Hi 0 μ- tr μ- H tr μ- SD tr 3 0 Φ Ω φ fi t Hi a Hi ED a 0 Q

SD φ r $, a Φ Ω φ μ- cr ra 3 μ- CQ Hi rt <! 0 μ- rt a Hi rt

Sϋ 3 D. SD Φ tr LQ tr <! rt Φ ra rt μ- fi 0 Φ 3 ^ Hi Φ rt ϋ rt φ tr

CD 0 a μ- ED φ Hj μ- fi CQ cQ ED rt r-> TJ Hi Hi tr tr rt Hi 0 d ft Ω 0 Ω TJ TJ CD μ- 0 SD a rt li Ω CQ Hi ED φ TJ 0 o Φ tr Hi ra

Ω a SD φ Hi tr Hi TJ • ; a 0 a rt 0 SD ED SD tr μ- Hi Hi CQ Hi φ Φ Φ

0 rt rt 0 ED CQ 0 Hi ED Hi h-¹

SD rt rt Hi rt tr rt w a fD 0 ra Φ Φ Φ 3 Ω rt Ω Hj r a Hi μ- 0 a rt Ω Φ μ- rt TJ

TJ 0 φ tr tr φ SD Φ t tr x. Hi ϋ μ- 0 3 a

3 φ μ- Hi μ- a μ- a Ω rt m T tr SD 3 μ- hj

ED Hi <! φ φ ra rt Φ 0 LQ SD Hi ED J <! o hj Φ CQ a T d rt ED SD Hi tr CQ μ^j a rt Hi ED 0 a D 0 Φ Ω

Φ P. M H CD tr Hi ra 3 Hi rt Φ CQ Φ 3 Φ φ rt Ω a Hj Φ

P. ED SD rt SD ED φ Φ tr μ- Ω Φ Si φ Φ Hi rt x. ra rt rt £ 0 CD =^> μ- ra hi φ 0 0 0 SD SD ra 0 ED CQ rt fu tr a Φ a ϋ Hi D tr SD SD μ- a tr rt Φ CQ Hi a φ

0 S CQ ^ μ- SD φ Ω CQ μ- rt Φ hj a rt μ- a <! CD CQ φ P Φ a LQ Φ rt

the amount of data that would be present in each frame if the changing of the effective relative importance levels had not taken place.

16. An apparatus for preparing data for transmission in a digital radio system, in which system data to be transmitted is generated from an input signal in the form of discrete frames, which raw data frames are then further processed by a channel coding process prior to transmission, the radio unit comprising: means for generating from an input signal frames of digital data; means for processing the generated frames of digital data using a channel coding process to produce a series of coded data frames for transmission; and means for selectively modifying the channel coding process so as to reduce the amount of data in each coded data frame to be transmitted as compared to the amount of data that would be present in each frame when using the unmodified process.

17. The apparatus of claim 16, wherein the channel coding process generates additional data bits at a given rate per original data bit, comprising means for modifying the channel coding process so as to alter the coding rate .

18. A method of transmitting data in a radio communications system, which system supports stealing of data to allow the transmission of other data such as control signalling in a stream of data to be transmitted, and in which system data to be transmitted is arranged in a succession of discrete data frames, and is transmitted in a succession of discrete timeslots, each timeslot usually containing three or more of the data frames, and wherein stealing of a portion of a timeslot can take place, the method comprising: > ω to to H μ> in o in o in o in

to CD £ Hi Ω to rt rt to rt μ- rt Hi tr TJ Ω Hi Φ μ- μ- rt Ω fi Ω H> rt Hi rt Hi tr T to rt μ- φ 0 μ> tr Hi O Hi 3 μ- hi Φ ED Hi SD m ra Hi 0 fD 0 LO μ- Hj μ- hi Φ

• 0 3 3 • Φ ED • fϋ TJ 3 ED Φ SD a SD Ω SD a rt 3 • 3 SD 3 SD Φ SD

SD T a a 0 Φ 3 a Ω 3 tr rt SD a rt fu 3 φ 3 Φ 3 a Ω

Φ H- Hi TJ ra CQ Hi D φ φ rt φ Hi hj CD Hi d ra Φ m Φ Φ a tr a μ- Hi 0 3 Hi 3 rt M CQ rt - 5^» fu CD rt ED Hj 3 0 rt a CQ CQ rt £ φ μ- CD tr CD μ- tr μ- ED 0 Hj tr W - μ- a SD μ- O μ- 0 0 Hi tr g fi a μ- Φ m rt Φ rt a rt CO ED CQ Φ Φ 3 CD a rt Ω 3 rt μ- rt CD ED CD Φ

Φ SD TJ LQ a μ- rt rt Ω rt a Φ a ED Φ 3 CQ rt CQ SD ED Φ a rt a Φ a rt rt LQ 3 tr μ- 3 Φ Φ 0 μ- ra h-¹ TJ a CD μ- φ Φ μ- μ-¹ rt rt ED μ- μ- CD tr ED rt μ- Φ a Φ fi a H" 3 Φ CQ Si rt Di Si LQ μ- tr Hi rt a 3 φ CD

0 0 a rt rt φ LQ rt μ^j μ- Ω rt SD o rt -- a 0 0 0 Φ tr μ- Ω rt ϋ Hi tr a^* φ rt rt rt Φ Ω s: rt Φ μ- SD =s a fi Φ CD rt rt Φ μ- rt ED 0 Si rt 0 < a⁴ rt rt μ- fϋ Φ tr Si a fϋ CD a d rt rt μ- SD

0 a tr a ϋ ED 0 fi Φ Φ 0 Φ a r-¹ - Φ d a et 0 0 ϋ Ω 0 Φ a

Hi rt Φ CO rt ϋ LQ μ- Hi ra μ- ED ϋ μ- tr ra Hi rt SD tr fi CQ μ- φ 3 0 SD rt 0 ra tr rt a rt Φ d a a Φ ^•^ rt rt a rt Hi rt μ- Hi tr Hi SD hj μ- Hi LQ tr μ- SD CQ μ- CQ CD rt tr SD fu HJ μ- Hi iQ

Hi TJ μ- rt Hi Φ 0 CQ SD a Hi Φ a h-¹ ED d a rt rt hi 0 ED a Hi

ED o 3 rt Ω hi Ω Hi μ- a 0 0 Ω μ- Hi Φ fϋ rt rt 3 a 0 0 a μ φ μ- Sϋ hi CD CQ rt 3 Hi 3 CD x; CD Ω ^ a ED 3 a tr 0 SD CD rt 3 Hi

CD ED D a ED 3 Φ fu rt 3 tr φ rt d φ a- a CQ a 3 tr

3 rt CQ μ- φ Ω μ- a- 0 μ- φ rt SD rt Φ Ω Ω CQ μ- SD ra 3 ra tr a μ- φ rt SD μ- Φ 0 3 CD φ 3 φ Hi rt tr a" SD 0 Ω CQ Ω 3 S μ- ^' rt SD Φ rt tr rt rt μ- μ- rt Φ TJ 0 h-¹ a φ μ- a^* CD μ- tr rt 0 <. ϋ rt φ TJ rt ED a μ> tr <! μ> Ei SD μ- μ- 0 Si μ- rt CQ 0 rt CQ μ- rt Φ μ- μ- 0 | μ- a Eϋ α. SD φ oo SD a a 3 fi Hi a SD CD a CQ Hi O Ω μ- Φ rt a 3 Si Hi a ϋ ϋ ED - CD H{ rt Φ fϋ rt Ω LQ μ- μ- ^><: φ μ- a- a a tr tr Φ ED ^ CD Q fi a 0 SD SD rt CQ rt μ- 0 a 0 0 ra SD 0 LQ • Φ £D rt CD rt - 1

0 μ- x. μ> SD SD Hi CD tr ED 0 3 0 μ- a Hi rt 3 a CQ Φ rt tr H SD 0 fi hi rt D Ω a Hi CQ φ 0 a T Hi a Φ " fi a φ 0 3 i

ED μ- CD rt μ> Hi Φ rt Hi Hj LQ 0 fi 3 0 o CQ ED μ- rt Hi rt Ω 0 TJ 0 d μ- D SD CQ Hi » hi 0 μ- SD Hi μ- Hi Hi rt rt rt 3 Hi - Hj 0

ED 0 a SD Hj SD a - 3 CQ φ SD Hi ra rt ra fi Φ SD Hi 3 φ ED Hi

3 fD Hi h-¹ p. φ 3 3 rt 3 μ- TJ £ fi Ω fu ϋ 0 3 SD φ 3 rt 3 μ- TJ Φ to H" μ- Hi ra Φ SD tr φ SD a 0 0 μ- Hi rt SD rt μ- a fi SD a- φ ED a Φ o X. Ω d a μ- Φ CQ LQ Hi CD φ ED rt tr CQ a m μ- μ- Φ ra a μ- ϋ - ED Hi rt rt P rt rt 0 Ω rt SD Φ d 3 Sϋ a rt

Hi ra a ED tr rt rt tr Si Di ≤ μ- μ- hj Hj Φ rt Hj T ED μ- rt ϋ fi μ-

ED SD Hi rt Hi α μ- a- SD 0 Φ SD tr 3 0 φ 0 rt T rt Φ φ ED tr 3 fi rt 0 ED d Φ 0 Φ rt Hi Hi rt μ- Φ a 3 rt fi 0 fi 0 Hi rt h-¹ Hj rt μ- φ μ- Φ Hi Hj P a hi SD Ω CQ 0 Φ SD tr SD Hi ED Φ * SD Ω CD

0 3 Ω rt Ξ rt 0 tr H" 0 H{ rt Φ tr rt rt fi fi 0 tr μ¹

Hi ED ED tr rt 0 Ω Φ tr Hi Hi 0 Hi Φ rt ED φ fu CD μ- SD Hi Hi 0

0 rt TJ Φ H Hi 0 Hi Φ Hj ≤ rt μ- rt 0 μ- ϋ Hj £, rt

Hi μ- SD Hj Sϋ 3 Φ rt SD o Sϋ o 3 Hi H CQ CQ a ι_J- rt SD o

O Ω a s: TJ Hi tr 3 d μ- Hi φ Hi fu d rt SD tr 3 d μ- rt a μ- CQ tr hi rt φ Φ φ ra rt CD SD a Ω Φ rt Ω Φ Φ ar tr rt 3 μ- μ- 0 P μ- rt h-¹ 3 CQ tr SD tr Φ fi φ rt ^•<! μ- Ω m SD 0 rt 3 a¹ 0 φ 3 φ a 0 rt tr rt a^* μ- tr rt Hj tr 0 Φ φ rt ra μ- fD μ- rt H tr 0

SD rt a Φ μ- SD m ra ^ rt CQ a SD rt Φ 0 iQ <! <! rt μ-" Si - rt LQ Di <1 rt fi Hi Φ φ Sϋ 0 SD SD Φ SD Φ Sϋ .V rt rt a ϋ 0 rt Φ ED Hi SD Φ

10 > to to μ> H in o in o in O in

hj TJ rt ra Di rt Ω to rt SD Hj Ω to Pi CQ 0 CD Hi Hi to rt ED Hi rt Hi rt μ- 0 CD d £ rt Ω

Φ 0 a' d fϋ hi 0 in hi μ φ 0 μ> ED 3 Hi μ- Hj ED ω μ- a Hi tr hi μ- a rt * CO tr Hi 0

TJ Hi Φ Ω rt SD 3 • SD fi 3 • rt fu N ED £ • 3 Si 0 ED Sϋ 3 tr CQ d μ- SD 3 rt H Ω SD a 3 a 0 d TJ SD rt Φ 3 φ 3 rt 3 Φ SD Φ rt ED Ω a 3

SD μ- Φ φ ra d CO . Ω hj r-¹ a' Φ ϋ ra tr φ CQ Hj Φ ^* CD d

Ω 0 ar Hi 3 a 3 φ μ- h_ Φ Φ O CQ Sϋ m Φ s: S CD 3 r-> 3 a φ a μ- CQ Hi μ- μ- μ- 3 fi m tr Hi Hi rt tr 0 CD SD tr O tr rt fi ^ Hi μ- μ- fi CQ μ- fD rt Ω 3 rt 0 μ- Φ fi Hi SD Φ rt rt 0 CD SD rt φ Hi fu CQ Hi rt Ω

0 0 3 rt Sϋ Φ rt hi CD a Ω fu rt 0 Hj < a φ ft ft Ω SD rt ED t Hi fu a Φ Φ rt rt Φ Φ μ- LQ 3 0 rt tr Hi Hi 3 ED SD rt μ- μ- Sϋ EU φ 0 3 Φ rt μ- CD fi μ- tr ϋ N Φ Si SD Φ hi Φ a m 0 P ra μ- 3 SD a Φ fi μ- rt ED TJ 0 0 0 hi Φ 3 rt φ rt Sϋ rt CQ LQ rt CO rt CD 0 tr Hi Hi SD μ- a fi 0 0 tr P. Hi D. Hj 3 tr 3 rt tr rt 0 d μ- SD μ- rt a

Φ a CQ CQ 0 T P. o Hi SD SD φ 0 μ- 0 Φ SD 0 μ- Hi Ω a μ- Eϋ CD CQ

0 μ- fi fi fi 0 3 0 μ- ϋ Pi ED rt a CO rt ra tr LQ a Hj rt 3 Φ μ- LQ CQ Hi hj Hi ED 3 SD CQ rt ED rt H{ rt Si μ- Φ fϋ CQ tr Φ Hi CQ rt Φ >< Hi rt •<: 0 rt φ 3 SD 0 Φ Hi Φ ED P. SD ED 0 a Hi *<

Φ ra μ- Ω tr a ra rt 0 μ- μ- Hi ED Hi μ- Hi Hi fi h-¹ ED Si Φ rt CQ Hi LQ rt Hi O

Hj a Hi Φ φ rt Hi H 0 a Ω Hi ra Φ 0 a d Φ rt Eϋ Hi fϋ rt

0 φ φ Hj Φ SD a LQ SD Hi a' SD CQ Ω μ- ^ m Ω Φ Ω TJ rt (D a Φ fi rt Di rt Di fϋ 3 a rt a Hi ED 3 μ- Ω a 3 Φ TJ Hi Hi 0 SD ^ a LQ 3

SD Φ ED rt CQ tr 0 rt ^ ED a φ 0 tr fu ϋ μ- Pi 3 hj a hj 0 ra Φ rt 0 D. rt Φ 3 Φ Hi tr 3 a CO a SD μ- rt SD rt ED μ- SD rt rt 3 fi

ED Hi SD rt ED D. μ- μ- φ 0 Φ Φ - a 3 ' rt rt CQ Ω a 3 hj 0 μ- μ- rt μ- a rt d rt a CQ tr a Φ ED Φ μ- Φ φ φ 0 0 Hi rt μ- rt a

SD ED 3 Hi ED rt ra tr CD Φ " Hi Φ to fi N fi CQ Hi rt a

0 Φ Hi CD s- μ- φ Φ rt Hi Ω d μ-¹ to Hi Hi Φ - 3 Φ

TJ CO D SD ^* a hj φ 0 Hi 0 3 Hj - Φ Hj μ- LQ rt CD rt 0 Si SD tr O

SD Hj rt 3 SD μ- LQ rt fϋ Hi 0 fi 0 rt Ω 3 0 a Hi φ - rt μ- μ- Hi μ- σi φ Φ 0 φ Ω Si μ- 3 μ- ϋ a^* 0 £ SD 3 Hj a Sϋ a' LQ 3 Φ μ- CD Ω

M fi ED rt CQ CD tr fi ED 3 μ- Ω a μ- Φ P. tr μ- rt 0 Φ rt Φ a φ a d tr

0 Φ r-¹ CD d fu rt Φ a h-¹ SD LQ Hi Hj Φ Φ a rt tr 3 hj SD CQ Si Ω

S rt μ- _^ ED Ω CQ rt ED CD LQ SD x; Du Hi μ- tr Φ SD CD 3 μ-¹ h-¹ SD rt Ω ra

Φ a Hi Ω ^ SD μ- LQ TJ μ- Ω Φ a ED 0 rt rt φ 0 rt μ- Φ •<; rt hj LQ Sϋ Φ Φ CQ Hi 0 T 3 μ- Hi a 0 rt μ- LQ rt rt P μ- Φ rt μ- rt SD 3 CQ CQ

Hj 3 a CQ rt μ- Hi rt Hj ra <! 0 LQ 3 0 a μ- φ a ED tr a Φ CQ rt

SD μ- TJ ϋ rt CD Φ a EU 0 Φ Ω TJ d Hi 3 IQ h-¹ 0 LQ Ω Hi ra μ- φ a a Hi hj μ- 3 3 μ- Ω μ> a φ rt Hi TJ μ- a Hi φ 0 μ- fi Eu Hi 0 3

CQ φ 0 μ- SD 0 SD Φ CQ Φ ∞ ra a' μ- Hi a CO SD CD Hi ED a rt

Ω a a a D CD ra Eϋ CQ Φ co 0 ¹ rt a ED 0 a

3 Di rt 3 μ- LQ Ω 0 3 rt fi μ- φ CQ SD Hi CQ ra rt 3 μ- D. rt 0 Φ 0 rt 0 0 φ ra 0 SD

CQ ω ra s 3 0 rt ED rt rt 0 0 rt Hj a d tr rt tr μ-¹ 0 3 tr Ω CO - Hi rt

CQ μ- CQ tr μ- Hi SD ϋ 0 0 CQ d 0 SD LQ Ω Φ φ rt φ Φ Hi TJ Φ Ω ED μ- N μ- rt μ- μ-¹ d to a $ φ a 0 rt SD Hi d φ fi

0 φ Ω rt Si rt O tr φ Ω ω rt TJ Hj H 0 fi CD TJ μ- rt Hj SD SD SD rt a tr tr Φ μ- 0 φ a tr - Hi ϋ φ Ω Sϋ T Hi ED rt Sϋ m H a Ω rt 0 μ- φ fi CQ 0 0 SD Si 0 ϋ SD μ- tr rt Hi μ- EU rt ϋ tr SD

0 ra Hi CQ Ω tr CQ rt Hi Hi P. rt d Di μ- Hj rt Φ SD 0 rt a a 0 tr

Hi φ • ! μ- Hj φ 0 P^* d d ED Ω Φ 0 rt a LQ CD μ- rt Hi Φ tr CQ P φ SD Hj Hi Ω μ- Pi μ- CD Hi Φ 0 •• 3 EU a μ- Hi

0 K. rt rt SD rt rt ED φ Hi a CQ 0 a rt Hi Hi μ- μ-¹ 3 fD rt Φ ED Φ CD tr £ Hi LQ Pi ^ Hi rt 0 SD fi rt r-¹ 5^> Φ 3 ' SD 3 SD Φ fϋ fϋ ra O 3 SD SD rt 0 tr CD φ

Φ rt Hi 3 rt rt rt rt Φ φ rt Φ s- μ- μ-¹ ra

Hi 0 a ED φ tr a CQ SD fi Ω 0 Φ^* 3 Φ tr rt

data such as control signalling in a stream of data frames, the method comprising: when it is determined that such stealing should occur selectively modifying the stealing process so as to steal a portion of the timeslot which is smaller than the size of said predetermined stealing portion so as to allow more space for the data frames that were to be transmitted to be fitted into the remaining unstolen part of the timeslot when such stealing occurs.

26. The method of claim 24 or 25, further comprising transmitting to the receiver an indication that a reduced size timeslot portion has been stolen.

27. The method of any one of claims 18 to 26, further comprising determining whether the data frames to be transmitted are of a predetermined size, and if it is determined that the data frames are not of said predetermined size, modifying the stealing process, but if it is determined that the data frames are of said predetermined size, not modifying the stealing process.

28. The method of any one of claims 18 to 27, wherein when two or more data frames are to be transmitted in the remaining portion of a partially stolen timeslot, and a data interleaving technique is used for the data transmission, further comprising using a modified interleaving structure across the entire remaining timeslot portion, rather than maintaining data frame boundaries .

29. A method of transmitting data in an encrypted form in a radio communications system, in which system data can be transmitted in one of two different predefined data structures, and in which system at least one of the data structures has defined for it a data generation process and a data encryption process, which encryption process requires for its use. the transmission of encryption control information to the receiver, and in which system data to be transmitted is generated from an input signal in the form of discrete frames, which raw data frames are then further processed by a channel coding process prior to transmission, the method comprising: when it is desired to transmit encrypted data generated and encrypted according to the processes defined for said at least one data structure over the other data structure, including said encryption control information in the data transmission, and modifying the data generating process and/or modifying the channel coding process so as to alter the amount of data in each coded data frame to be transmitted as compared to the amount of data that would be present in each frame when using the unmodified as-defined processes.

30. A method of transmitting encrypted data frames, comprising: allocating a predetermined number of bits of space for encryption synchronisation information in each data frame; and setting the predetermined bits to a predetermined pattern when there is no encryption.

31. A method of transmitting data in an encrypted form in a radio communications system, which system includes both a control channel for control signal transmission and one or more traffic radio channels for user data transmissions, and in which system data can be transmitted in one of two different predefined data structures and in which system at least one of the data structures has defined for it a data generation process and a data encryption process, which encryption process requires for its use the transmission of encryption control information to the receiver and which encryption control information is in the defined process effectively embedded in the user data to be transmitted, the method comprising: when it is desired to transmit encrypted data generated and encrypted according to the processes defined for said at least one data structure over the other data structure, removing said embedded encryption control information from the data to be transmitted over the traffic channel and transmitting it instead over a control channel .

32. The method of claim 31, further comprising transmitting late entry and periodic encryption signalling on a control channel, rather than including it in the traffic channel transmission.

33. The method of claim 31, further comprising transmitting late entry and periodic encryption signalling by using a traffic channel data stealing process .

34. The method of any of any one of claims 18 to 33 further comprising, when data is to be encrypted and reduced size data frames are to be transmitted, removing the necessary number of data bits to reduce the frame size after encryption, and the receiver reinserting a corresponding number of bits into the data prior to decryption or prior to passing the data into another part of the system, to maintain correct decryption synchronisation.

35. The method of claim 34, wherein the bits reinserted by the receiver are added to the reduced size data frame according to a predetermined pattern.

36. A method of operating a radio unit for use in a w ω to to μ¹ H in o in o in o in

SD μ- rt rt ω CO s- rt TJ SD CQ rt rt O rt fi TJ TJ fi TJ μ- Ω rt LQ rt Hi TJ rt ϋ fi Pi a TJ ' hj -j rt ED μ- Hj Ω rt tr ii rt a¹ ED Hi H SD Hj a 0 Hi φ tr Hj Hi μ- SD fD μ- m rt O Φ fD • Hi ^ 3 0 Ω Hi φ SD Hi Φ rt 0 μ- rt 0 TJ 3 ED a Φ o 0 3 rt rt LQ td 0 O a d Φ Ω 0 d a d SD Ω 0 SD Ω d TJ a Φ 3 Ω φ SD SD μ-

Hi T ra Ω rt ra Φ Hj Ω ra CQ Ω Hi Φ Hi Φ rt Hi CO Hi LQ Φ ra rt g rt LQ Hi 3 _ rt tr h-¹ CD fi rt Φ :^> 3 rt μ- 3 CD CQ Ω CQ ra LQ μ- 3 SD φ ED ra CD Ω fD tr Φ 0 μ- tr d SD 0 ra μ- d Ω tr μ- d H tr rt ra rt 0 rt CQ CQ Φ CQ μ- rt a a CQ 0 rt SD h-¹

Φ a Ω CD Φ HJ rt rt Φ a Hi 0 Φ CQ Hi CD φ Hi 0 fi Hj μ- a μ- CQ μ- Φ rt Hi a

SD Φ Φ ra Φ D D LQ Φ a a CD φ rt a d (i μ- d fi CQ Φ a ra 0 hi μ- Hi CD d hi

H- μ_ Hj CQ μ- 3 Φ CQ fi μ- C^Q Ω φ μ- a Ω φ a Hi iQ μ- a SD 5 0 Ω tr fϋ

Hj t SD CQ 0 Φ Ω SD 0 Hi rt μ- 0 •« 0 μ- rt Hi rt LQ rt Hi ED ED 0 rt TJ Hj rt Φ fi

1 m rt Φ a rt 0 Ω Hi 0 0 0 rt a Hi rt d μ- CQ d μ- rt a SD Φ d rt d μ- μ- s Φ CQ a' a a' Hj SD Hi rt Hi a rt hj a μ- a ϋ rt LQ tr hj rt 0 a fi μ- 0 rt rt rt TJ μ- fi hj rt μ- φ φ rt tr φ φ μ- a μ- P. Φ Φ φ Hi rt Si ra Di ED rt tr rt tr T rt w fϋ SD ^{^} ra CQ Si Hi Φ ra Pi a CQ a Pi CQ a Hi CD ED Ω

Φ rt fϋ Φ μ- μ- Φ tr Φ 0 tr rt a Φ » ED -.. Ω ED μ- Φ φ a 0

Hj μ- a Hi LQ 0 a 3 Φ Hi φ fi SD CO fi Hi a Di Hi SD ϋ rt tr rt LQ Hi Φ CQ 3

Hi 3 P. μ- Φ Hi CD Φ CD Di rt φ 3 rt φ 0 ra Eu 0 Ω μ- tr fD Sϋ a fD tr EU 3 3

Sϋ Φ a a CD φ Hi ED μ- rt CO CQ μ- $. CQ Hi 3 rt H Ω cQ Φ a Sϋ rt Φ Ω μ- d

Ω CQ Ω φ Φ Ω 0 r-> Ω μ- rt 0 S μ- rt rt 0 μ- μ- ED 0 μ- a TJ H¹ μ- μ- tr rt a φ 0 Di hj a 0 0 Hj Eϋ a 0 Hj H{ rt Hi CO CQ fu Hi rt Hi Φ Hj a a rt μ-

0 Pi fu ED H¹ rt a CQ μ- Φ d μ- fi Φ SD Q LQ fi SD 0 h-> μ- SD CQ LQ Ω Φ Ω tr rt φ Hi rt μ- K. Si rt LQ a fi Pi Ω a μ- fi μ- μ- Φ Hi SD Hj O a 0 fi Sϋ

" Di 0 φ 3 O Φ LQ μ- rt LQ Hi fi o a μ- a 3 Ω hj ϋ fi fi j-. rt

CQ Hi fi Φ Hi D- ϋ a Hi rt d Hi rt a Φ Hi Ω ϋ 0 μ- φ T μ- μ-

TJ rt Di > a Φ Φ φ rt Hi 0 Hj rt φ 0 Hi Hj ra Φ ED 0 fi rt SD LQ Hi Hj a 0 , r-> Hj fϋ rt fu σi rt rt Hi Hi hi tr Φ Φ tr Hi μ- d SD rt rt Hi μ- 0 μ- μ- μ- a

£D d rt tr a μ- tr μ- μ- Eu Φ H{ rt -. φ Φ rt Hi CQ rt 3 ED a TJ rt a ra rt CD |

Ω Ω fu Φ ϋ H{ Φ a a rt Φ hi a Hi CD μ- Φ 0 μ- Si LQ μ- Hj ED Φ μ- ^ o μ- rt s: Φ Φ Φ μ- Ω a fD SD fi rt fu rt a ϋ a rt Hi μ- rt 0 H¹ fi a 0 CD a d Hi > Ω tr D D. ϋ 0 0 rt a a fu a CQ Φ a- 0 ra TJ CO Ω Q ^ I

CQ Hi Hj TJ ' Φ Ω Φ a fi ra P. rt T ra 0 Hi Hi Ω H φ fi Hi P. ra

Φ Sϋ π ED Hi 0 Ω D. D. Φ TJ 3 fu Hi 3 a rt Hi 0 rt H 0 rt ra fϋ 0 Eu μ- rt rt 3 o a Φ Si 0 Sϋ SD fϋ D- hi μ- Φ μ- Φ a' 0 Hi tr rt φ Ω Hi CQ rt Hi Hi φ tr Hi Φ a μ- Φ a rt rt a Φ rt SD fi rt φ 3 φ hj rt φ ED fϋ ra Hi 3

Hj 0 CQ ra Φ a & fi ED Eϋ ϋ D. D. CO Φ 0 CD SD φ O a Hi Φ d φ

Φ Hi rt H fu φ rt Hi rt Hi Ω rt fu Si a CD CO 0 Hi fϋ Ω Hi

Φ SD SU rt Di D- D CQ Ω rt Hi tr P. μ- tr tr tr μ- Eϋ CQ Hi Φ 3 Hi 0 Ω Ω Φ μ- rt H a Ω tr SD φ . rt rt tr SD μ- Φ Φ a Φ CD EU φ ϋ rt 3 Hi CQ μ- hi tr φ a a ii φ fi 0 Φ rt Hi Hi hi SD a Hi φ fu a ED μ- ED CQ Ω CQ rt

TJ SD Sϋ fi ED μ- d d a Hi φ Ω μ- D. Ω μ- a μ- rt CD 3 T CQ tr rt Si m ≤

Q a SD hj Φ α a Ω Ω a Hi P. 0 a 0 Di Φ 5 Hi LQ CD Φ Hi μ- ED li SD μ- TJ tr

O CD TJ fi Di SD Hi φ rt rt Φ SD P. Φ D. fi TJ ED Φ μ- CQ 0 0 a SD rt 0 H{ μ-

3 TJ rt Hi D. d d H 3 P. φ D. SD Φ rt d a a 0 - <! a a a SD a φ Ω

Ω μ- 0 ED SD SD hi Hi φ ED Pi rt Di Hi Ω rt ra Φ a μ- Φ CQ 1 tr

0 co hi ED Ω 3 Di Φ φ Ω CQ rt Hi ED fϋ 0 3 Hi rt α 3 CD 0 fi fi CQ rt a Ω Hi φ fD 0 SD D. 0 Di a fi CQ μ- SD Hi tr Φ Z μ- rt Hi Φ CD

Φ μ- μ- fi o 0 CD rt μ- μ- Si LQ Sϋ hj fϋ CQ μ- μ- D rt Hj Φ tr Ω CQ M Hi ^> ; i 0 0 Hi H • Eu a a μ- φ rt rt 3 a cQ CQ μ- O D. μ- 0 CD d μ- CD a a rt fi rt a a SD rt SD μ- LQ a μ- 0 3 3 SD Ω fi μ- Ω a rt

Hi Φ ET μ- ra 0 LQ φ ^* ra SD 0 a Φ rt a^* μ- 0 rt φ Φ

Hj 0 ϋ φ a d Hj d SD d ra H" a Eu rt SD a a d Pi 3

ED <! LQ Ω SD CD rt CQ μ- a a¹ Si LQ Hi

3 Φ tr rt μ- μ- 0 0 Hi Sϋ φ

Φ Hj rt φ a a a fi 0 rt ra 0 EU ϋ LQ CQ Hi SD SD

ω 10 to to μ> μ> in o in O in o in

rt Hi rt Hi ≤ μ- Ω Hi Φ μ- μ- rt Ω fi Ω 10 rt fi rt Hi s^> μ- rt fi Φ μ- μ- rt Ω fi Ω LO μ-

0 Φ tr Hj 0 to ED hi SD CQ CQ Hi 0 SD 0 10 μ- SD tr Hi O m μ- SD Eu ra CQ Hi 0 SD 0 00 μ-¹ Φ fu a d a SD Ω SD a rt 3 • 3 rt Φ SD d 3 rt Ω Eu a rt 3 • rt tr SD 3 r-> rt 3 tr rt ED a rt ED 3 Φ SD 3 rt Φ SU tr rt fu a rt SD 3 0

Φ rt rt φ Si 0 rt Φ Hi Hi CD Hj d ra rt Φ fi 0 CD Hi Hi CD Hi d μ- μ- 3 fϋ CQ rt ED Hj 3 0 rt a h-¹

5 Hi μ- 3 Hi rt SU hi 3 0 rt a φ rt < 3 0 tr rt φ - μ- a SD μ- μ-¹ 0 μ- 0 Hi 3 0 tr rt Φ 0 Hi μ- a SD μ- μ-¹ 0 μ- a <

Hi Φ Φ Hj SD (D SD Φ 3 ra a rt Ω rt fu Φ Hi fu fu SD rt SD 3 CO a rt Ω φ

SD CD < ?f a SD φ 3 LQ rt ra SD Eu Eu 3 ra <! ?? a 3 Φ 3 LQ rt CQ Sϋ SD fu Hi a μ- Hi φ Φ CD TJ a CQ μ- Φ Φ μ- rt TJ SD Φ μ^j Hi Φ Φ CQ Ω Φ CD μ- Φ Φ μ- rt TJ * ra 3 0 Hj H D- M rt Si Di LQ H μ- T Hj CD 0 Hj Eu CQ H¹ rt Pi LQ μ^j μ- TJ

3 J rt SD tr TJ Hi SD 0 rt a 0 0 SD φ rt SD tr TJ Hi a - 0 rt a 0 0 SD μ] μ- 0 3 Φ μ^j 0 Ω s- rt Φ μ- SD £. a Hi μ- 3 Φ h-¹ 0 rt Φ μ- SD $ a Hi td rt H 0 Φ Φ SD Hj φ tr Si a Eu -¹ CQ Eu a a μ- φ Φ SD K rt EU ϋ a Eu CD SD rt rt m a CQ a Ω - - φ d a H¹ rt rt 0 O P Ω rt a - SD a d a H¹ rt rt

Φ SD Φ H ra μ- SD fi μ- tr CQ d rt Φ W fi CD μ- SD fi μ- tr CD d a rt $ fi ω rr 3 rt φ d a a Φ K. ra tr CQ CD rt -

• 3 Φ d a

Ω tr rt Hj a Φ *< CQ tr tr μ- SD CQ μ- LQ CQ tr Φ d rt H tr 3 EU CD μ- CQ CQ rt

Φ φ μ- ED CQ Φ Φ a ED d a rt rt Hi 0 Ω μ- SD CD Φ TJ a- μ SD d a rt rt Hi μ- a Φ a μ^j Ω μ- Hi Φ 0 rt ϋ tr a Φ a Φ μ^j Ω μ- Hi Φ o 3 h-¹ tr CD Eϋ CQ x; CD Ω , a SD 3 Hi tr SD μ^j CD μ^j SD Hi ^ O Ω % a T rt d φ tr a rt Eu 3 φ ar a ED 3 Hi Φ

Φ Sϋ 3 Φ r Ω Φ d Φ tr a ra

<! ra rt μ- Ω rt TJ Φ Ω Ω CO μ- ED CD rt CQ Eu rt μ- Ω rt φ μ- Ω Ω ra μ- SD ra rt ^j

Φ μ- 0 rt rt Φ Eu ED 0 Ω CQ Ω 3 $ Hi rt 3 0 rt rt Φ a 0 Ω ra Ω 3 Hi 0

H" CQ rt μ- SD Hi a Φ μ- tr CD μ- tr EU 0 rt EU rt μ- Eu rt a Φ μ- tr CQ μ- tr SD rt

CQ rt Φ P h-¹ SD μ- rt CD 0 rt ra μ- a o a Φ a H¹ rt CD rt CD o rt m μ- a " [

0 H{ fi LQ μ- rt a ED CD a CQ Hi CO Ω CO φ a Hj fi LQ μ- a- rt Eu CD CQ Hj CD

0 μ- μ- a CD Ω

Hi SD a d LQ μ- μ- "< φ μ- tr 3 a tr Φ fD a Φ Φ ^ φ μ- - 3 -_^J

Hi a μ- Hi LQ CQ a 0 0 CQ fu 0 μ- • SD Hi a μ- Hi LQ fu a 0 0 CQ (D 0 μ- (—1

SD CQ a hi 0 μ- a Hi rt 3 a ra rt <. ra a H Eu r~> μ- a Hi rt 3 a CO rt rt a 3 0 0 Ω Hi a Φ ^• ; rt Φ rt 3 0 0 TJ μ- a Φ ^■ ! rt I tr μ- rt 3 Hi 0 IQ 0 fi 3 0 0 CQ μ- a^* μ- rt 3 Hi TJ a LQ 0 fi 3 0 o CO μ- φ SD rt tr 3 SD Hi μ- Hi Hi rt a tr fu rt tr Eu LQ Hi μ- Hi Hi rt a ra Φ rt £ϋ TJ rt CQ fi Φ LQ Φ rt Φ rt Eu Hi rt CQ fi Φ LQ fi CQ μ- a- hj TJ £ fi Ω fu fi 0 3 Φ μ- tr EU 0 a- i Ω fu ϋ 0 3 fϋ φ a rt Φ TJ μ- 0 0 μ- H rt Eu rt fi a μ- a rt Φ TJ rt Hi Hi μ- Hi rt SD rt ϋ rt CQ μ- 0 o Hj ra Φ SD rt " ra SD 3 μ- 0 d Φ CQ φ fu rt a" CD (D

Eu CD rt 3 fi Hj μ- rt 0 Ω rt fD d rt rt 3 rt 3 fi Hi CD ED Φ Ω rt Eu Φ d rt

3 a- Φ ED rt a μ- Hi Hi Φ rt Hi TJ SD Hi Φ tr φ SD rt Hi Φ rt Hi TJ Eu

Hi Φ φ CD rt μ- LQ 0 Φ 0 rt TJ SD ϋ Φ CD rt μ- Ω TJ 0 φ 0 rt TJ

Hi a M SD 0 a 3 rt Di 0 si 0 μ- a μ- H¹ Eu 0 0 0 Hi rt fi 0 ϋ 0 μ-

EU rt Hi 0 a 0 Φ fϋ tr SD hi a CD Eu Hi 0 a 3 Hi Φ Sϋ tr fu Hi a

3 φ rt Hi 0 Hi rt Φ tr rt rt 3 rt Φ rt Hi TJ rt 3 rt Φ tr rt rt φ 0 3 - hj 0 Hi Φ rt fu φ SD D Eu μ- Φ 3 - Hj 0 Hi μ- 0 rt SD Φ fD m SD

CD Hi SD SD Hi μ- rt rt μ^j fu SD Hi μ- 0 Hi μ- rt μ- rt 3 SD o 3 Hi Hi CQ CQ Hj rt K . μ- rt 3 ra a Φ 3 Hi Hi ra CD H; rt rt a tr Φ SD Hi φ Hj ED d rt SD φ

Ω Φ a tr φ SD μ- φ Hj fu d rt SD a^{^} tr fi φ ra rt CQ ED a ϋ Ei Sϋ P. φ CD a 0 o ra EU a Ω Φ Ei fu Φ φ rt μ- rt μ^j 3 CD tr SD μ- ϋ φ rt IQ Hi Hi 3 ra tr ED μ- rt Hj Di 3 μ- 3 ^* 0 φ 3 H" o μ- t_l. Hi fi $. μ- .. 0 φ 3 0 fu tr 3 Φ Φ rt CQ μ- Eu μ- a SD fu tr 3 ED rt rt ra μ- fu μ-

Z o rt μ- φ CQ CO -* rt CD a Ω 0 rt μ- Φ tr CD • rt m μ^j a w Hi SD Ω ra fi - rt LQ rt Φ Hi fϋ Ω ra φ - rt LQ

Hj tr H¹ 0 ED SD Φ rt rt a- a tr Eu Φ

Φ 0 a Si o Φ rt 0 fi 0 rt Sϋ Si Hi rt a ϋ Hi

10 ιo to to μ> μ> in o n o in o in

Ω φ> rt SD rt Ω . ED Ω 3 3 Ω ra .F* TJ rt rt fi 0 TJ μ- 0 ra d C rt Ω > rt ≤ 3 >

0 κ Hj CD tr 0 lO 0 o φ 0 ^•<; to Sϋ o o fu a fu a rt "< CD a- Hi 0 Hi tr Φ O

3 • £ϋ su 3 . LQ fi ϋ Eu D. CQ • hi rt Φ Hi a^j CQ d μ- SD 3 > SU μ- ED

3 a rt rt T μ- μ- μ- a Φ rt rt Hi tr SD rt SD Φ rt SD Ω a 3 a Ω a d CD 0 Hi < a Hi CD D. φ μ- Φ fi Hi Φ a- m d ra tr ra a 3 SD μ- Hi φ LQ ^• ! 3 ^ 0 rt Hi fu 0 3 CD 3 3

& t Hi a 3 Hi μ- μ- ED CQ tr a μ- Hi Di tr Hi ra HJ r Φ rt fi ^> Hi μ- μ- & μ- 0 Hi tr

Ω rt Hj μ- φ TJ a 0 SD ii φ μ- rt SU SD Eu Hi SU CO Hi rt Ω rt Hi 0 Φ

SD SD rt H Φ a SD Hj CQ Hi rt Sϋ rt a 0 3 fu a Φ rt rt Ω SD rt EU SD rt Hi rt TJ Φ 0 fi LQ 3 3 0 SD 3 fu tr rt Φ Hi ra SD SD Φ 0 3 Φ rt TJ Φ rt su μ- TJ fi 3 d φ 0 Ω rt Hi TJ Φ 0 φ CD Hj rt 3 SD a φ fi μ- T tr rt TJ

0 SD Ω 3 rt d φ tr Φ Hi ϋ TJ a SD μ- Hi CO H¹ rt CQ 0 SD Φ H TJ a Hi 3 φ φ ET a IT- Φ fi H SD fu rt ED rt 3 3 0 0 d μ- EU μ- a Hi SU fu

CQ ED 0 fi fu 0 rt CD d ED rt Hi μ- a Hi ' Φ φ H{ Hi Ω a μ- ED CQ CD fϋ TJ a hj rt Hj a fi ϋ Ω 3 Eu fu 3 fi Hj SD ra - tr LQ a Hi rt 0 CD SU

CQ d φ m ra o rt SD μ- φ rt Φ 0 rt tr fi μ- Φ Eu ra d CD 3 rt

^> CQ μ- o Hi 0 ≤ a CQ Hi d CD tr 3 SD 0 3 SD su 0 a Hi * ra m μ- d

CQ Hj N Hi Hi LQ H CD φ 3 <! rt tr rr CQ Hi LQ rt hj CD μ- rt CD rt Hi 0 Φ 0 Hi TJ fi Hi ED 0 EU μ- Φ Sϋ Hj SU rt Hi tr rt

Φ 0 0 Hi fD SD hj SD rt 0 3 0 rt rt ra CQ a μ- a Ω TJ rt EU a Φ 0 μ- 0

3 hi 3 TJ a € 0 rt tr Hi Φ Hi • Hi 0 CQ m Hi 0 SD Z. a CQ 3 hi φ a Hi

0 3 x. fi ED Φ ra fu rt μ- Hi a Hi 0 CQ φ ^ LQ rt Hi Hj 0 ϋ d rt Ω a SD 0 SD rt rt ED rt rt 3 ϋ rt fi Ω μ- h{ 0 rt fi 0 SD Ω Hi CO hj fD CD CD 0 3 hj 0 μ- μ- Hi Eu rt H a SD Hj μ- μ- a rt Φ Hi μ- EU Hi SD 3 tr Hi μ- Φ O 0 Hi rt μ- a SD rt 0 SD a 0 Hi Φ Eu SD N a Φ μ- μ- rt φ φ rt CQ CD r-¹ Hi rt t a a SD H- |

3 CD r a *< < CD 3 Φ CQ 3 rt 0 Sϋ - 3 Φ ^ ra rt 3 tr 3 tr μ- 0 3 Φ 3 Ω rt rt ?r fi CQ rt 0 fi SD a- 3 Hi P" μ- μ- Φ 0 a Hi fu CD 0 μ- tr tϋ. Φ SD Hj Ω φ φ r μ- μ- Hj μ- μ- H Φ w t

Ω rt Hi LQ μ-¹ Hi ra fu μ> fi Su Φ rt tr LQ 3 Φ μ- CQ Ω rt SD 00 tr rt d Ω H¹ 0 ra a - a ϋ TJ Φ Φ a Φ a d a' rt 3 hi μ- CD rt rt r-¹ φ Hi rt μ- a μ- 0 CD Hi ED CD fi Ω μ- φ Φ 0

CQ a Φ tr tr fu Hi tr 0 φ 3 a ϊ^> 3 ra su 3 ED μ-¹ μ-¹ Eu rt Ω CD a ra Ω Hi

^■ : LQ Hi Φ Φ μ- rt Φ a tr μ- μ- Ω μ- TJ 0 rt μ- φ * LQ Φ

CQ 3 Ω ^* φ rt fi rt txi φ a TJ μ- rt SD 3 ra CQ tr μ- ω rt fi ϋ rt CQ CQ 0 Φ D. Ω Hj a- fu rt φ - φ ED a Φ CD rt fi SD <J o φ SD SD μ- rt fi fu Hi 0 Φ φ rt Φ Di Hj CQ Ω Hi CD μ- Φ fu CD Φ

3 rt rt 3 Φ LO Φ ϋ rt d fi μ- fu fi Hi LQ Eu SU Hi 0 3 rt ii

Eu SD Φ fu ω P. SD SD Hi φ a Hi Hi Φ rt rt rt a SD 0 a Eu su Hi fi ra rt rt fi φ Hi μ- 0 a tr d 0 3 rt fi Ω Eu d

SD μ- Hi H μ- rt Pi EU Hi μ- 3 Hi a 3 Φ fu CQ 0 Φ CO 0 fu μ- rt a Hi rt a H{ 0 a 0 fϋ Hi Φ rt a SD 0 Hi rt tr Ω CQ - Hi rt a d rt

SD EU rt CQ rt Hi SD Hj 0 μ- 3 rt 0 SD Ω Φ Ω - SD su μ- tr

ED 3 fu Hi 3 rt a tr a rt CQ 0 d Φ Si Hi H¹ a Φ rt φ μ- TJ to SD Φ Ω TJ tr μ- rt Φ Φ μ- rt 3 rt ii Eϋ SD SD rt Su fi Hj

0 Hi m CQ hj - Hi 3 CQ 0 Hi Φ a tr a Φ TJ Hi a Ω rt 0 ϋ *< μ-

SD 0 Hi φ 3 0 LQ fϋ rt 0 LQ Eu Hi ED rt ϋ a- SD μ- Ω Ω tr fi rt CD Ω Hi SD tr TJ fi Hi rt μ- Hi h-¹ μ- a 0 tr 0 tr fu 0

Φ μ- 0 rt φ d 3 Ω *<; hj d SD d 3 SD μ- CQ CQ μ- rt Hi Φ Φ rt

0 0 CQ hj Φ ar μ- Ω Di a Hi Φ rt rt a μ- 3 ED a μ- Hi Φ μ- 3 TJ tr H" CQ rt CQ SD m Φ μ- CD ii CD tr LQ a μ- 3 SD a 0 Hi φ Φ tr a μ- 0 rt SD φ H¹ LQ rt * Φ 3 a μ- a CQ Φ Hi a a 0 3 0 Φ 0 •• rt 0 tr ra Φ Q d Hi hi Φ iQ Φ rt Eu Hi Φ £ μ- CD 0 μ-

CD Ω 0 Φ CQ ϋ Ω 0 _^ Hi a

0 tr 3 a rt tr rt LQ

) ω to to H μ> in o in O in o in

0 Φ LQ 0 TJ ϋ Hi

T Eu ra Hi rt Ω > rt 3 ra Hi rt TJ CQ CD CQ Hi fi Hi TJ rt ra ϋ rt

Hi a Φ a Hi SD 0 •J Hi a ED 0 0 O σ. tr φ in rt Φ tr 0 3 O tr Hi fϋ Φ 0 tr d ϋ Hj

Ω a Φ Φ rt Hj • Φ fi μ- Hj 3 • ED SD • Φ 3 ED hi SD 0 $u rt T Hi φ Ω rt SD

Φ Hi Φ fi fu 3 fi - tr TJ rt a ED SD rt rt H ED d 3 Su h- rt Hi Ω ED hj μ- - a a 0 Φ Φ Φ hj CQ μ μ- μ-¹ CQ φ SD μ- φ φ CD

Ω τ SD Hi Hi Ω μ- rt Hl TJ μ- μ- HI ED H μ- a 0 φ fi 3 ra CD Ω 0 CQ Hi

S 3

Hi rt rt μ- SD a Φ Hj Hi rt ra tr Hi V a μ- Φ a Hj rt φ - d Φ a μ- ra hi μ-

S μ- μ- rt a a Hi μ- φ Hi μ- Φ Hi 0 Φ LQ Hi

ED SD a 0 0 SD Ω D. CD μ- fu rt

TJ 0 0 tr Φ 3 rt Pi μ- ED a φ Hi LQ Φ CD rt Ω a rt tr 0 0 3 rt rt a a φ D. tr TJ μ- φ rt a IQ 3 fi Sϋ 0 0 tr ra Ω CQ tr S Hi su a Φ Φ μ- Φ Hj TJ a μ- rt CD φ d rt TJ Ω d rt SD rt d Φ su μ- CO Si

0 TJ TJ fi fi ED SD φ m Φ μ- 3 3 rt Ω Hj TJ Ω a 0 fu

Hj Hi fϋ Eu rt a Φ Hi Hi D rt ED TJ 0 a Ei Hj ϋ Hi CD μ- Φ ' Φ SD SD d CD CQ Eu - 0 su a- H Hi fu μ-

0 0 rt rt Hi μ- ED fi 3 rt Eϋ 0 fi a Hj Hi rt tr rt Hj TJ Ω rt φ a Q

Ω Ω Ω SD Eu SD 0 rt CD φ μ- P. rt a P. CQ SD ra 0 Φ rt tr CD TJ 0 0 μ- ϋ Si fi

0 Φ Φ a m a d μ- rt a φ Φ CD CQ 3 rt • 0 Φ ED Φ SD a rt 3 Φ μ- LQ a r ra ra m Ω ra N Φ φ rt ϋ 0 μ- μ- d Φ rt ≤ ϋ rt tr φ Hi CD rt Φ rt CD ra rt rt 3 0 ^■ Φ Hi p. Φ Hi Hi N rt CQ a Hi fu ra TJ Φ tr EU Hj Φ CD μ- Ω tr a

H Hi hi μ- 3 Hi - 3 hi 0 Φ rt ED H¹ μ- 0 Ω Φ rt 0 Hi μ-¹ a Hi Φ φ

0 Hj su d d rt 3 0 μ- CQ 3 hi hi SD μ- 0 TJ a N Hi rt

Φ rt μ- a d 0 φ Φ Hj μ-¹ Φ a Ω Ω rt d Hj a a μ- μ- Φ a rt a Hi SD CD 0 ra fi rt Di rt Di fu fi rt rt Φ a 0 Φ t i a ϋ > μ- LQ Hi 3 £ μ- <! μ- CD fu Φ fu rt μ- % d d fi μ- rt rt P. Φ φ 0 Φ 3 Ω rt μ- o 0 Φ rt Ω μ- rt 0 rt Φ a μ- fu hj hi Ω Hi •• i Hi rt 0 Φ rt μ-¹ rt 3 Hi a 0 iQ Eu Hi SD rt SD fi

Hi Hi φ φ μ- SD SD 3 rt Φ a CO 0 (D O rt 0 > μ- 3 a rt μ-

0 Φ ϋ D ra a rt a 0 tr 3 rt SD Hi Φ μ- Hi Φ Hi CD 0 m TJ SD rt ED SU 3 Hi Eu ,

Hi CD SD - μ- CQ P. fu 0 tr 3 0 rt 3 Si Φ SD Hi 3 Hi 0 Φ Hi CQ

3 rt tr 0 0 3 μ- rt fi SD TJ μ- 0 rt tr rt μ- 0 ϋ μ- μ-¹ TJ CQ ra SD fu Hi SD SD SD a a μ- Hi μ- rt Hi a Hi Φ φ. tr rt CQ Di rt Di Φ CD μ- SD Hi rt r-> 3 D ω rt 0 CD a Φ CQ rt *< rt Hi Φ μ- TJ ι Φ 0 TJ tr μ- rt μ- a H" Φ Φ 0 φ μ- Hj φ α rt μ- tr *< rt ϋ a Ω 0 Hj fu TJ Φ Hi Φ a LQ ϋ Eu rr CD O ,

0 a D. 0 CQ H- a Φ μ- tr Φ LQ H Hi Φ 0 rt tr Ω Hj ^ Hj LQ 0 Φ H¹ CD d a μ- Ω φ μ- Hi a CQ a φ rt fu rt Ω H μ- Φ Φ φ rt μ- 3 .. μ- ^ rt μ- - Eu Ω rt Hi Hi a ra CQ ϋ CQ Φ Z μ- μ- Φ 3 fi μ- a μ- a Φ a hi Ω rt CQ 3 μ- rt rt rt fu ϋ Hj tr 3 0 μ- tP=. Φ Hi Hi φ 3 LQ a rt Hi LQ SD φ Φ

0 a ≤ 3 Φ fi tr rt rt SD 3 φ CD a <! W μ- 0 rt Φ φ SD Hi 3 a CQ d rt φ tr 0 3 fϋ φ ED tr rt μ- rt φ -> rt Hj Φ CO rt Si Eu μ- TJ α rt CQ rt CQ μ- D. μ- rt φ fu a tr 10 tr Hj 0 rt Hj T CD a a Hi Hi μ- tr Φ 0 Ω fi Eu CQ Hi φ Φ ∞ ED Hi rt Φ rt 3 0 φ rt rt CO φ 0 μ- ø t o

Φ a Hi tr μ- μ- rt Hi ra Hi ϋ Hi CQ SD d fi tr μ- r ¹ Hi 3 ϋ Ω rt a a a

0 Hi a μ- Φ SD rt hi rt a hi % Φ a CD SD φ μ- φ CD hi tr TJ hi CD Hi a fu 3 φ fu CD rt 0 tr rt tr μ- Φ % rt rt SD ra CQ CQ ^ 3 0

Φ Φ Hj *< φ s φ SD 3 μ- tr Φ μ- a' Φ a fi Di tr Φ 3 CD μ- CD tr μ- Hi

Ω 0 μ- CD hj tr fu μ- CQ Φ N Φ Φ> Φ a φ a rt ED μ- ED ra μ- N μ- rt φ rt Ω rt rt Φ μ- a a μ- CD φ in a fi Hi 0 rt CD Ω d 0 0 φ £ Ω rt μ- Hi Φ Φ α a Ω LQ SD a fi _^ μ- CD Sϋ rt tr μ- Ω Hi a tr tr Φ μ-

< SD CQ S 3 rt tr φ Hi CQ Sϋ SD m Ω Ω d rt Φ a tr μ- φ P. Q

Φ a ra a TJ Φ Hi SD rt Hi rt fu 0 Ω tr Hi fu μ- LQ ϋ 0 co Hi ra Ω

Hj CQ - Si fu ra Ω Hj TJ φ a ED d 0 rt tr Φ Hi μ-¹ ra ra Sϋ Hi φ •<; μ- Hj

•« 3 ED rt ^ Hi 0 0 Hj ϋ Hi μ- TJ fu μ- TJ rt rt tr ra a φ μ- $ rt CO Ω Hi 0 a Hi rt Φ 0 hi 3 a Hj Φ Eu 0 τ3 ^ rt rt

ED CQ tr fu rt Φ Ω 0 3 Hi tr a a μ- Φ LQ 0 ED rt Φ Sϋ Φ a CQ μ- Φ Φ rt CD CO Φ rt φ SD Φ • ra CQ Ω tr SU 3 fi μ- Ω SD 3 Φ CD SD CQ Eϋ 3 Hi μ- Φ μ- Φ 0 tr CQ D. μ- CQ 0 a Φ a CD Hi a rt fi Hi CD CD LQ CQ a

LQ

in which system data to be transmitted is generated from an input signal in the form of discrete frames, which raw data frames are then further processed by a channel coding process prior to transmission, the apparatus comprising: means for, when it is desired to transmit encrypted data generated and encrypted according to the processes defined for said at least one data structure over the other data structure, including said encryption control information in the data transmission, and for modifying the data generating process and/or modifying the channel coding process so as to alter the amount of data in each coded data frame to be transmitted as compared to the amount of data that would be present in each frame when using the unmodified as-defined processes.

48. An apparatus for transmitting data in an encrypted form in a radio communications system, which system includes both a control channel for control signal transmission and one or more traffic radio channels for user data transmissions, and in which system data can be transmitted in- one of two different predefined data structures and in which system at least one of the data structures has defined for it a data generation process and a data encryption process, which encryption process requires for its use the transmission of encryption control information to the receiver and which encryption control information is in the defined process effectively embedded in the user data to be transmitted, the apparatus comprising: means for, when it is desired to transmit encrypted data generated and encrypted according to the processes defined for said at least one data structure over the other data structure, removing said embedded encryption control information from the data to be transmitted over the traffic channel and transmitting it instead over a control channel . lO lO to to H μ> in o in o in o in

in > rt Ω Ω rt rt in CQ ra μ- Ω LQ α fi 0 CQ Ω rt LQ Hi hj Hi LQ rt Hi EU ϋ Φ rt Ω μf=. μ> TJ H{ 0 0 tr hi o rt d a 0 φ SD ED Hi S 0 Hi φ Hi SD 0 Φ tr Hi Φ EU Hi 0 o

. O EU Si 3 Φ SD • hi Ω rt fi a rt rt μ- a SD a 0 Si hj a Φ 0 TJ Hi Ω SD 3 .

O TJ a d tr 0 μ- ra a Φ φ SD fϋ CD D. rt a Φ 3 μ- Φ 3 Hi μ- tr

D. ϋ TJ CO Ω a Hj SD μ- a 3 ra Hj 0 rt Hj LQ 0 a CQ d

> Ω 3 μ- Hi 3 μ_ rt su rt LQ SD CD d 3 μ- Ω a 3 3 ED 3 Hj Sϋ Φ ED Ω φ Ω 3 a >

0 μ- D- ra 0 μ- tr d μ- rt rt CD Φ Di tr d φ μ- rt a Φ d (D rt a a φ fi 0 μ- μ-

Ω fi ra SD μ- Ω m φ Hi S 3 TJ φ hi μ- fu fϋ 0 Su o μ- fu a a μ- Φ CQ 3 rt Ω Hj

0 Φ ra rt a Φ CQ Φ EU Φ Hj P. d a a rt a a Q 0 μ- a μ- CD 0 Hi μ- CQ Hi TJ rt SD SD

3 D. μ- fu LQ CQ μ- Hi CQ 0 Ω LQ m Hi a CQ CQ μ- a 3 CQ rt 3 a ED a 0 hi Φ rt ϋ

TJ 0 CQ 0 fu Ω Ω SD rt fu Φ 0 TJ μ- rt TJ Hi Hj μ- fi μ- μ- d Hi a Hi 3 φ a Ω. 0 rt o φ Ω d rt Hi a h-¹ μ- Hi a TJ d Hi Ω CQ SD Φ d 0 ra 0 0 rt hi Hi Φ CQ μ- a tr rt CQ Ω ϋ tr 0 ra _S 0 hj rt 0 0 ra a fi rt Hi Φ μ- μ- a

Φ Sϋ 0 SD Su μ- 0 rt SD D D 0 Φ φ Hi 3 Ω TJ Hj ϋ 0 Hi 3 μ- Si fϋ a a CQ d

Hj 3 < 3 a D. ra ED rt Φ Hi CD - μ- 0 d SD Ω ra TJ 0 P. CD LQ Ω LQ a φ Φ φ CD φ d μ- 0 ra ϋ • CD co fi rt Ω rt Φ μ- IQ Hj a Ω fD μ- φ tr rt CQ μ-

TJ ra Hi CD Hi LQ a a Φ Hi μ- Φ $. CQ μ- O ED CD CQ φ μ- a^* rt LQ a SD ^ ^> rt ϋ Hi μ- φ μ- O SD Hi a SD Ω tr μ- a m fi CD a a ra μ- SD fu a φ TJ 0 CD

O μ- SD μ- 0 a a rt Ω rt 0 LQ TJ 0 Φ 0 LQ μ- μ- m ED Φ μ- a a Eu Hi Hi CO rt Hi

IQ a a Hi φ Φ 0 tr tr Hj TJ a a a LQ a rt fi Hi a a TJ H¹ SD Φ d Pi Φ 0 hi rt Hi rt fi Hi 0 a φ rt 0 fi TJ a LQ Hi Φ SD LQ rt Φ Hj rt fi Ω μ- 3 Hj

SD 0 td 0 Sϋ Eu Hi r-> rt rt 0 hi μ- fi Hi $D d Hi μ- rt .* tr -¹ μ- fu μ- Φ Ω Hi

3 Hi TJ Hi rt ^ μ- CD a- rt 0 rt fu 0 h-¹ rt Ω μ- a μ- Φ o a a Hi φ Hi d φ rt TJ g 0 Φ Ω 3 φ Φ rt μ- Hi rt Ω a rt a a Ω Hj ϋ CQ μ- CD φ μ- CD

Φ tr 0 Hj P. Φ Φ Ω tr" 0 μ- EU φ TJ Φ d φ SD LQ Hi o a ra Hi a Φ h-¹ φ Φ Hi fu a CD 0 Hi Φ - rt a rt m CQ H Hj ϋ Ω 0 P. rt Q⁾ fi Φ μ- φ

Φ Hj SD rt rt fD μ a μ- μ- tr ra ra μ- fi φ Ω ϋ Hj μ- 0 μ- Pi 0 a ^ μ-

3 ^ μ- H μ- tr a 3 μ- 0 Si Hi Pi a Φ P. rt 0 fu ra Hi 0 μ- 3 a TJ LQ a rt tr ^ -j φ hi td 0 Φ fi hi rt CD SD LQ Φ hi D. Hj rt -• 0 Hi CQ LQ μ- ϋ μ- P. μ- a in

Hi 1 HI a > φ fi rt rt rt ra d φ Eϋ Hi Ei μ- 0 rt 0 rt SD 0 TJ Ω fu rt td μ- μ- Ω vo 0 Φ SD rt $. μ- Ω Hi rt SD rt Hi TJ CQ Ω EU rt Hi Hi ^{^} m a a TJ tr •» Ω Hi Hi i a^{^} 0 Hi rt μ- 0 LQ SD a fu Hj φ fu φ fi

Ω rt

S LQ o fϋ 0 μ- Φ LQ Φ φ d a Φ Ω Si 0 rt ra rt 1 CD μ-

0 Φ rt o a 3 D_ rt a Hi Φ fi Di Hj Φ μ- a Hi φ μ- Ω Hi CO ϋ rt μ- fi ^• ; LQ

3 Hi μ- rt a tr Φ V Φ μ- a Ω μ- φ P. rt Φ μ- Di CQ φ fD SD Hi 3 Φ CD μ-

TJ rt Hi 3 tr ra Φ Φ Si Φ Di a Φ 0 Hi rt ra CQ Hi ϋ $, SD Ω ra a Hi rt SD Φ Hi rt rt hi μ- Eu φ Φ rt H" hj φ H Si Hi 0 Hi Eu CQ μ- rt Hj CD CQ 0 Eu a CQ μ- Φ fϋ μ- 3 Ω ra SD Φ Di CQ Di Pi £D φ Φ 0 rt rt rt rt Eu φ φ 3 Hi m a 3 -¹ ra Φ Φ r-> a Ω μ- Eϋ φ Su rt Si Hi rt Eu Hi Hi Φ a- rt ra μ- Hi 3 0 φ μ- CD 0 TJ Di 0 a rt Ω rt P. μ- Φ Hj a SD fi 0 Hi Φ ra Ω 0 μ- rt Pi P. hj a tr rr o ED fi SD 0 SU Eu 0 Ei a SD fi CD a a ra 0 TJ ra tr Hi ra CQ fu fu

CQ 0 "< o hi Φ rt rt a rt a ED rt a fϋ ra Hi Φ fu ii Hi Hi μ- SD CO •> fi rt ϋ

CD fi fi tr Hi fi CQ SD rt CO μ- 3 H μ- Hi 0 0 a rt μ- SD EU μ-

Ω . TJ rt LQ Φ Hj rt SD Eu T 3 Pi μ- 0 0 rt SD < a a Hi 0 rt rt 0

0 h-¹ Hi φ fu SD Di Hj CD a Hi μ- ra 3 Hi Hi 3 μ- Φ Sϋ a tr EU Ω

3 SD d a Hi Ω fi 3 Φ d rt ϋ Hi Φ rt Hi co Di SU φ Pi D a Φ SD

TJ Ω Ω Φ d Ω fu Φ Hi Ω Hi Hj fi μ- μ- rt CQ S a CQ φ $. CD O H CD a d μ- rt hj Hj 0 rt CD μ- rt d Ω SD φ rt hi 0 tr SD rt CD •» tr Ω 3 rt Φ rt rt a d SU rt Hi EU • a d Ω tr 3 Hi tr CQ a Φ μ- SD 3 rt μ- 0 μ- Hi Hi tr

Φ LQ Hi rt tr fi φ hj rt su Φ μ- Φ rt Pi μ- r tr Ω fi CD d tr d φ

Hj Φ Φ φ μ- Hi Di Φ d ra ra tr φ tr μ- CQ Ω Φ Ω rt a a d ϋ H a 0 Hj a φ Ω 0 CQ CQ φ a μ- rt μ- rt a' Hi LQ Hi Di μ- φ Φ Di 0 a μ- μ- Pi fi LQ 0 d a d

Hi o fϋ SD t rt a Si Φ a 0 SD fϋ a Hi LQ Hi

Φ Hi a r Φ LQ a rt rt Φ φ

Φ fi 0 Su D. ED SD CD

software code portions for performing the methods of any one of claims 1 to 10 or of any one of claims 18 to 37 when the program element is run on a data processing means .

52. A method of operating a radio unit substantially as hereinbefore described.

53. A method of preparing data for transmission substantially as hereinbefore described.

54. A method of transmitting data substantially as hereinbefore described.

55. An apparatus for use in a radio unit substantially as hereinbefore described.

56. An apparatus for preparing data for transmission substantially as hereinbefore described.

57. An apparatus for transmitting data substantially as hereinbefore described.

58. A radio unit substantially as hereinbefore described.