WO2003069837A1

WO2003069837A1 - Method and arrangement for retransmission of packets in the base station sub-system

Info

Publication number: WO2003069837A1
Application number: PCT/SE2002/000274
Authority: WO
Inventors: Johan Erik Håkan ERIKSSON
Original assignee: Telefonaktiebolaget Lm Ericsson (Publ)
Priority date: 2002-02-15
Filing date: 2002-02-15
Publication date: 2003-08-21
Also published as: AU2002230367A1

Abstract

The present invention relates to a base station sub-system of GSM-based communication networks, e.g. applied for GPRS, and intends an efficient bandwidth usage for data transmission in acknowledged mode via the Abis-transport network. This is achieved by a data transmission that reduces the amount of retransmitted data, which is caused due to transmission errors, for parts of the network that have not been affected by said error while the overall flow control remains at the site of the sending unit, e.g. the Base Station Controller. Each transmitted data block is stored in an intermediate network unit, e.g. a Base Transceiver Station, together with a unique identification information. In case of a retransmission due to an error on the radio access network the Base Station Controller retransmits the unique identification information by help of which the Base Transceiver Station can retrieve and retransmit the missing data block.

Description

Method and arrangement for retransmission of packets in the base station sub-system

FIELD OF THE INVENTION

The present invention relates to a method and arrangement for efficient bandwidth usage in the base station sub-system of a GSM-based communication system, e.g. applied for GPRS.

BACKGROUND OF THE INVENTION

GSM-based communication systems are in principal designed to consist of two major sub-systems: One sub-system is the switching sub-system, which is mainly intended to manage the communication between GSM-users and other telecommunication users and provides various data base information that is needed for subscriber data or mobility management . The base station sub-system on the other hand includes the infrastructure that is specific to the radio cellular aspects of GSM. This sub-system is illustrated in figure la. A Base Transceiver Station (BTS) 13 is in contact with mobile stations 15 through a radio interface 14. It comprises the radio transmission and reception devices and also all signal processing devices specific to the radio interface. The Base Station Controller (BSC) 11 provides also the connection to the switches of the switching subsystem and is responsible for the management of channels on the radio interface and handovers. Typically, a Base Station Controller controls a plurality of Base Transceiver Stations . Message transfer between Base Station Controller and Base Transceiver Station occurs via a transport network 12 applying a so called Abis-interface for communication. Messages that are transmitted over the Abis-interface signalling links can be distinguished in a group of control messages between BSC and BTS and a group that embraces all the other types of messages that are exchanged between mobile stations and any infrastructure beyond the BSC.

Figure lb shows the protocol stack for the corresponding units in figure la. For data services in an acknowledged mode between Base Station Controller and Mobile Station the RLC-protocol 111 is, inter alia, responsible to retransmit erroneous data blocks while the MAC-protocol 112 is responsible for multiplexing said data blocks on the air interface. The RLC- and MAC-protocol are tightly coupled to each other and both implemented in the Packet Control Unit (PCU) of the Base Station Controller 11 and the Mobile Station 15. Physical layer transmissions 114 on the other hand are handled via the Channel Codec Unit (CCU) , which is implemented in the Base Transceiver Station 13. PCU and CCU communicate with each other over an appropriate signalling link protocol 113 in the Abis-network 12. The following description will by means of an example refer to the GPRS Signalling Link (GSL) protocol.

If an applied data service is in an acknowledged mode, erroneous data blocks must be retransmitted. Two measures to implement retransmissions of erroneous data blocks in the RLC-protocol are Link Adaptation (LA) and Incremental Redundancy (IR) , or Type II Hybrid ARQ.

For Incremental Redundancy (IR) the RLC-protocol selects a coding scheme and sends data blocks to the Mobile Station. If a data block cannot be successfully decoded, the Mobile Station will store it in its memory and respond with a negative acknowledgement for this data block when the PCU polls the Mobile Station for the reception status for transmitted data blocks. The RLC-protocol then retransmits the same block with the same coding scheme; however, the CCU will forward it with a different puncturing scheme on the air interface. The Mobile Station uses soft combining of the two blocks to decode the message. This is repeated until the whole block is decoded. Then, the Mobile Station responds with a positive acknowledgement for this data block to the PCU. MCS-9 has turned out to be an efficient coding scheme.

For Link Adaptation (LA) , which implies to adapt the coding scheme to a certain signal-to-interference level C/I, erroneous data blocks are not stored in the memory of the Mobile Station. Instead, the RLC-protocol can select a more robust coding scheme, i.e. a lower user data rate, when retransmitting the data block.

Today, the Abis interface is circuit-switched on a PCM- interface, whereby the Abis bandwidth is fixed per air timeslot. However, depending on the applied data service this can imply an inefficient use of the allocated Abis bandwidth. When applying, e.g., EGPRS (Enhanced General Packet Radio Service) , which is a new packet based data service in GSM-networks, each air timeslot used for EGPRS will allocate a fixed bandwidth of 64 kb/s on the Abis interface. This is due to the fact that it is required to transmit MCS-9 coded RLC/MAC-blocks . However, the actually used bandwidth for EGPRS will vary in time. For Link Adaptation, e.g., the bandwidth on the air interface will vary about 10 to 60 kb/s depending on the selected coding scheme. In addition, some Mobile Stations will only be capable of GMSK- odulation, which requires data rates from 10 to 23 kb/s.

On the other hand, when Incremental Redundancy is used on the downlink, all retransmissions are made over Abis, however, without the dynamic nature of Link Adaptation. For instance, MCS-9 as a coding scheme, theoretically provides a data rate of 160 byte per 20ms, i.e. 64 kb/s on Abis, which in practice however will not result in a higher average user data throughput than about 30 kb/s due to retransmissions via Abis. SUMMARY OF THE INVENTION

The present invention can be applied in the base station sub-system of GSM-based communication networks and addresses the problem that correction measures for transmission errors on the radio access network will cause unduly high amounts of traffic on the Abis-transport network due to retransmissions of data blocks or imply an inefficient use of the fixed allocated bandwidth for each communication channel on the radio access network, e.g. for Incremental Redundancy or Link Adaptation.

It is thus an object of the present invention to achieve an efficient bandwidth usage for data transmission in an acknowledged mode in a communication system, in particular in the Abis-transport network of a GSM-based communication system.

It is the principal idea of the present invention to achieve a data transmission that reduces the amount of retransmitted data, which is caused due to a transmission error, for those parts of the network that have not been affected by a transmission error while the flow control for the data transmission remains at the site of the sending unit, e.g. a Base Station Controller.

Briefly, these and other objects of the present invention are accomplished by the method according to the present invention. Each data block is transmitted from a Base Station Controller to a Mobile Station according to a first message format comprising at least said data block and a unique identification information. The data block is stored in an appropriate memory of the intermediate Base Transceiver Station together with the unique identification information for said block. In case of a necessary retransmission due to an error on the radio access network between Base Transceiver Station and Mobile Station it will be sufficient for the Base Station Controller to retransmit a message of a second message format, which comprises the unique identification information without the corresponding data block, such that the Base Transceiver Station can retrieve the missing data block from its memory and retransmit said data block to the Mobile Station. The Base Station Controller controls retransmissions on the radio access network by means of acknowledgement messages from the Mobile Station.

It is thus an advantage of the present invention that the bandwidth of the Abis-transport network can be used in a more efficient way.

Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings and claims.

For a better understanding, reference is made to the following drawings and preferred embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure la shows an overview of a part of communication system within which the method according to the present invention is performed and figure lb shows a corresponding protocol stack for the involved system units.

Figure 2 shows the message format that is applied for data transmission via the transport network.

Figures 3a-3c show signal flow charts that illustrate the method according to the present invention. Figures 4a-4c show the method steps according to the present invention that are performed in the Base Transceiver Station.

Figures 5a-5c show the method steps according to the present invention that are performed in the Base Station Controller.

Figure 6 shows an arrangement that is incorporated in or connected to the Base Station Controller in order to perform the method according to the present invention.

Figure 7 shows an arrangement that is incorporated in or connected to the Base Transceiver Station in order to perform the method according to the present invention.

Figure 8a shows a diagram of a possible distribution of the percentages p(n) of the number n of transmissions of data blocks and figure 8b shows the possible gain for the throughput when applying the method according to the present invention.

DETAILED DESCRIPTION

Figure 2 shows a general frame structure 20 for messages that are applied to transmit user data blocks in a radio communication system from a Base Station Controller to the Base Transceiver Station that shall forward said user data blocks to a receiving Mobile Station. User data is transmitted in data blocks 23 that each are encapsulated in a first header field 22, which is added by the RLC/MAC-layer of the Base Station Controller (BSC) for communication between BSC and the Mobile Station, and a GSL-header 21 that is added by the underlying GSL-layer for communication between Base Station Controller and Base Transceiver Station

(BTS) . These GSL-frames 20 are suitable for transmission via the GPRS Signalling Link in the transport network. The RLC- header contains, inter alia, the necessary information for forwarding said GSL- essages from the Base Station Controller to the Base Transceiver Station. In the following it is assumed that data transmission is performed via a so called Temporary Block Flow (TBF) , which denotes a specific transmission path between Base Station Controller and a Mobile Station that is intended to receive the data blocks via the Base Transceiver Station that provides communication services to said Mobile Station. Such Temporary Block Flows can be distinguished by means of Temporary Flow Identities

(TFI) 221 while each of the transmitted user data blocks can be distinguished by means of a Block Sequence Number (BSN)

222. Both identifiers are part of the RLC/MAC-header . Thus, a unique identification information for the transmitted user data blocks can be derived at least from at information on said Temporary Flow Identity (TFI) in order to specify the distinguished connection from a certain Base Station Controller to a certain Base Transceiver Station and the Block Sequence Number (BSN) in order to specifically point out a certain data block. The method according to the present invention applies two message formats between Base Station Controller and Base Transceiver Station: Messages of a first format comprise a GSL-header, a RLC/MAC-header, and a data block as shown in figure 2. This message format is applied to transmit user data information to the Base

Transceiver Station. Messages of a second format only consist of a GSL-header and a RLC/MAC-header without user data. According to the idea of the present invention this message format can be used for retransmissions of user data information that has already been successfully transmitted to the Base Transceiver Station but was affected by a failure in an other part of the transmission path to the receiving Mobile Station. In general, the message format must be suitable for data transmission between Base Station Controller and Base Transceiver Station and comprise a unique identification information, e.g., as described above. The following figures 3a-3c illustrate the method steps according to the present invention by help of signal flow charts for a Temporary Block Flow (TBF) between a Base Station Controller (BSC) and a Mobile Station (MS) . The corresponding method steps are presented in figures 4a-4c for the Base Transceiver Station (RBS) and in figures 5a-5c for the Base Station Controller (BSC) . Figures 3a, 4a, and 5a refer to the case that a transmission error has occurred in the radio access network while figures 3b and 3c, and the corresponding figures 4b-4c and 5b-5c, refer to two alternatives for correction of transmission errors that have occurred on the Abis-transport network.

The signal flow chart in figure 3a presumes that no transmission errors occurred on the Abis-transport network between Base Station Controller (BSC) and Base Transceiver Station (BTS) but focuses instead on the correction of a transmission error in the radio access network between Base Transceiver Station and the receiving Mobile Station (MS) . Data transmission shall be performed in an acknowledged mode, i.e. the sending unit can transmit sequences of messages before polling the receiving unit, i.e. the Mobile Station, for acknowledgement messages. The length WL of such a sequence, i.e. the number of data blocks that can be consecutively transmitted without having received and acknowledgement, can be defined by the network operator. A typical value could be

The Packet Control Unit (PCU) in the Base Station Controller (BSC) transmits user data blocks in sequences 311 of a first message format to the Base Transceiver Station that serves the Mobile Station that is intended to receive said data. Each of said messages of the first format includes at least a header portion for the GSL-header and the RLC/MAC-header, which contains a user data block and the unique identification information as explained above, i.e. the TFI and the specific BSN for this data block. The Base Transceiver Station will forward these data blocks to the receiving Mobile Station but keeps a copy of each passing data block together with the unique identification information in an appropriate memory unit, e.g., the Channel Codec Unit (CCU) . On receipt of said data blocks the Mobile Station will confirm successfully received data blocks by means of a positive acknowledgement messages

(ACK) 312 or respond with negative acknowledgement messages

(NACK) 312 for data blocks that have been affected by transmission errors or have not been received at all.

The advantage of the method according to the present invention becomes apparent in case of an erroneous transmission of a user data block via the access network. In the example of figure 3a a message sequence for three data blocks is transmitted before polling the Mobile Station to acknowledge their receipt. When assuming, for instance, that the Mobile Station has not received the second data block of this certain Temporary Block Flow due to a transmission error in the radio access network, the Mobile Station will after the polling from the Base Station Controller respond with a negative acknowledgement message (NACK) for this data block. However, as the Base Transceiver Station according to the idea of the present invention already has stored this data block in its memory it is not necessary to retransmit a message according to the first message format, i.e. including identification information and data block, but sufficient to retransmit a message 313 of a second format, which only includes the unique identification information that the Base Transceiver Station need to identify the missing data block. Hence, the amount of data that must be transmitted via the Abis-transport network is considerably reduced. The Base Transceiver Station that receives a message of said second message format can by help of the identification information retrieve the missing data block from its memory and retransmit it to the Mobile Station. Then, after having successfully received the missing data block, the Mobile Station will send a positive acknowledgement 314.

Figures 4a and 5a describe the method steps that are performed by the Base Transceiver Station and the Base Station Controller to achieve the above described signal flow. The Base Station Controller sends via a certain Temporary Block Flow user data information according to the first message format, block 51. If the Base Transceiver Station receives such a message, block 41 Yes, it stores the user data block together with the identification information, i.e. Temporary Flow Identity (TFI) and Block Sequence Numbers BSN, block 43, before forwarding the user data block to the Mobile Station, block 45. After having transmitted a message sequence the Base Station Controller polls the Mobile Station for acknowledgement messages for said transmitted user data blocks, block 53.

If the Mobile Station responds with a negative acknowledgement, it is the principal idea of the present invention that the Base Station Controller will retransmit a message of the second format that contains the unique identification information of the not acknowledged data block; however, without retransmitting the data blocks itself, block 54. In case of a transmission error in the radio access network the Base Station Controller only need to retransmit an indication of a user data block via the transport network because said user data block already has been successfully transmitted via said transport network. This implies that the amount of data that must be transmitted via the transport network can be considerably reduced because user data blocks need only to be retransmitted via those parts of the transmission path where the transmission failure has occurred. The Base Transceiver Station will on receipt of a message according to the second format, block 42 Yes, retrieve the not acknowledged user data block by help of the included unique identification information, block 44, and forward the user data block to the Mobile Station, block 45. The Base Station Controller will continue the retransmission procedure, block 56 No, until an acknowledgement has been received for each of the transmitted user data block, block 56 Yes.

However, the method according to the present invention as described above must not only consider transmission errors that occur on the radio access network but also errors in the transport network. This will now be described by help of the signal flow chart in figure 3b. According to a first embodiment of the inventive method it is the task of the Base Station Controller to initiate measures to verify that messages are successfully transmitted via the transport network. Therefore, the Base Station Controller polls the Base Transceiver Station for a reception status message 323 after having received a sequence of messages from the Base Station Controller. The reception status message reports whether or not the user data blocks that belong to a sequence of transmitted messages according to the first message format have been received. Thus, for the Temporary Block Flow as shown in the example of figure 3b, which is characterised by the Temporary Flow Identity TFI, the Base Transceiver Station will report in its reception status message 323 that the data blocks with Block Sequence Numbers BSN(l) and BSN(3) could be successfully stored but indicate that the data block with Block Sequence Number BS (2) has not been correctly received. In this case the Base Station Controller (BSC) must retransmit a message of the first message format for data block BSN (2) . If the retransmitted data block BSN (2) could be transmitted without error it is stored in the memory of the Base Transceiver Station and forwarded to the Mobile Station. Meanwhile, the Mobile Station will respond with positive or negative acknowledgement messages 322 for the transmitted data blocks. Figure 3b assumes for the purpose of simplicity that those data blocks that have been successfully transmitted through the transport network have also been correctly transmitted through the radio access network. For the data block BSN (2), which was not received at that time, the Mobile Station will respond with a negative acknowledgement message. The Base Station Controller must observe that this negative acknowledgement depends on a transmission error on the transport network that already has been indicated by the reception status message 323 and corrected by retransmitting a message 324 that contains the missing data block. On receipt of the positive acknowledgement messages the Base Station Controller can send a clear message 326 for BSN(l) and BSN (3) that informs the Base Transceiver Station to remove these data blocks from its memory. After that a positive acknowledgement message 325 also has been received for the retransmitted data block BSN (2) the Base Station Controller can also send a clear message 327 for this data block.

Another alternative to handle transmission errors on the transport network is shown in figure 3c. This alternative intends to reduce the amount of signalling traffic between Base Station Controller and Base Transceiver Station due to reports of stored data blocks in its memory or clear commands for a removal of stored data blocks from said memory. For this alternative, the Base Transceiver Station does not confirm a successful reception and storing of data blocks in its memory but only requests retransmissions of those data blocks that have not been correctly received from the Base Station Controller. For this it is necessary that the Base Transceiver Station reads each acknowledgement message for transmitted data blocks that is received from the Mobile Station. The Base Station Controller will not control the removal of stored data blocks in the memory of the Base Transceiver Station. After that the Base Station Controller has transmitted a sequence 331 of messages according to the first format the Base Transceiver Station will store a copy of each received data block together with the corresponding identification information; however, without sending a reception status message to the Base Station Controller or requesting a retransmission of not received data blocks at that stage. Instead, the Base Transceiver Station waits for acknowledgement messages 332 from the receiving Mobile Station and will interpret these messages. Data blocks that correspond to acknowledged Temporary Flow Identities TFI and Block Sequence Numbers BSN are removed from the memory of the Base Transceiver Station and the acknowledgement message is forwarded to the Base Station Controller. For not acknowledged data blocks the Base Transceiver Station must at first check whether this data block has previously been stored in its memory, i.e. the non-acknowledgement message depends on a transmission error that occurred in the access network. Otherwise, the non-acknowledgement message depends on a transmission error that occurred previously in the transport network and the Base Transceiver Station will forward a retransmission request 333 for this data block to the Base Station Controller. The negative acknowledgement is forwarded to the Base Station Controller. Thus, there are two possibilities for the Base Station Controller to respond on a received negative acknowledgement : Only in case of a received retransmission request for that data block the Base Station Controller must retransmit a message 334 of the first message format for this data block; otherwise it is sufficient to respond with a message of the second message format, i.e. indicating the missing data block that the Base Transceiver Station shall retransmit. Supposing a successful transmission, i.e. a positive acknowledgement 335 is returned to the Base Station Controller, this message will be treated by the Base Transceiver Station as described above for data blocks BSN(l) and BSN (3) . This alternative implies the advantage that the intermediate storing of data blocks in the Base Transceiver Station remains fairly transparent for the Base Station Controller. In this alternative the Base Transceiver Station itself takes care of the maintenance of its memory. However, this implies also that the Base Transceiver Station must read and interpret each acknowledgement that is received from the Mobile Station.

The method steps according to the first alternative that are performed in the Base Transceiver Station and Base Station Controller to verify that user data blocks have been successfully transmitted via the transport network will now be explained in more detail by help of the flow charts in figures 4b-4c and 5b-5c: According to the first alternative as presented in figures 4b and 5b the Base Station Controller initiates and controls such verification measures for the transport network, block 52, after that a sequence of messages according to the first message format has been sent, block 51, while the Base Transceiver Station provides the necessary verification measures, block 46. The Base Station Controller polls the Base Transceiver Station for a reception status message, block 521. On receipt of such a request, block 461, the Base Transceiver Station sends a reception status message, block 462, that indicates whether transmitted messages have been received. Upon that the Base Station Controller will retransmit messages of the first message format for data blocks that the Base Transceiver Station has not received according to the reception status message, block 522. Later, after the reception of acknowledgement messages from the Mobile Station, the Base Station Controller initiates verification measures, block 55, that request the Base Transceiver Station to remove those data blocks that have been successfully received and acknowledged by the Mobile Station, block 551. The Base Transceiver Station will on receipt of such a clear command, block 463 Yes, remove the indicated user data blocks from its memory, block 464.

Regarding the method steps according to the second alternative as presented in figures 4c and 5c, the Base Station Controller need not to initiate any verification measures after a transmission of data blocks according to the first message format, block 52. Instead, the Base Transceiver Station will check each of the positive or negative acknowledgements that have been received from the Mobile Station, block 471 and block 472. On receipt of a positive acknowledgement for a certain data block, block 471 Yes, the corresponding data block can be removed from the memory of the Base Transceiver Station, block 472, and the positive acknowledgement is forwarded to the Base Station Controller, block 476. In case of a negative acknowledgement, block 473 Yes, the Base Transceiver Station must at first check whether the user data block has not been delivered to the Mobile Station due to an error on the access network, i.e. the data block is available in the memory of the Base Transceiver Station, block 474 Yes, or due to an error on the transport network, i.e. the data block is not available in the memory of the Base Transceiver Station, block 474 No. If the data block is available, block 474 Yes, the negative acknowledgement is forwarded to the Base Station Controller, block 476, which in turn will retransmit a message according to the second format BSN for the missing user data block. As this data block has been successfully transmitted via the transport network the Base Transceiver Station can retrieve this data block and retransmit it to the Mobile Station as already described above. However, if said data block is not available, block 474 No, the Base Transceiver Station must request a retransmission of the missing user data block, block 475, i.e. the Base Station Controller retransmits a message according to the first format including the missing user data block, block 552. For this case the negative acknowledgement can optionally be forwarded to the Base Station Controller, block 476. However, the Base Station Controller must then keep in mind that it already has treated this negative acknowledgement by responding to the retransmission request of the Base Transceiver Station. From the point of view of the Base Station Controller, the verification measures, block 55, to retransmit, block 552, user data blocks that have been affected by a transmission failure on the transport network are initiated at a later stage compared to the first alternative.

Figure 6 shows an arrangement 60 that is incorporated in or connected to a Base Station Controller for performing the method steps according to the present invention. Said arrangement 60 comprises means 61 for composing user data information for an initial transmission according to a first message format and means 62 for composing user data information for a retransmission according to a second format of those already transmitted messages of user data information for which a negative acknowledgement has been received from the Mobile Station. When applying verification measures for the transmission of user data information between Base Station Controller and Base Transceiver Station the arrangement must also provide means 63 for polling reception status messages from the Base Transceiver Station and evaluating whether or not transmitted user data information according to the first format has been received by the Base Transceiver Station. For messages that have been indicated to be not received the arrangement 60 comprises means 64 for initiating a retransmission whereas further means 65 send clear messages for those messages that have been received by the Base Transceiver Station and acknowledged by the Mobile Station in order to indicate that these user data blocks can be removed from the storage of the Base Transceiver Station. Figure 7 shows a corresponding arrangement 70 that is incorporated in or connected to the Base Transceiver Station for performing the method steps according to the present invention. Copies of received user data information, i.e. user data block and unique identification information, from the Base Station Controller is stored, e.g., in the Channel Codec Unit 71. The arrangement 70 comprises further means 72 for retrieving the corresponding user data information that is indicated by the unique identification information in a received message of the second format. If it is the responsibility of the Base Station Controller to keep track on successful transmissions of user data information the Base Transceiver Station provides means 73 for sending reception status messages either at periodical times or on request of said Base Station Controller in order to indicate whether messages of a first format have been successfully stored. The arrangement 70 also provides means 74 for removing user data information as indicated by a clear message of the Base Station Controller.

In case of alternative verification measures to keep track on the transmission of user data information via the transport network the arrangement 70 provides means 75 for removing user data information for which the Mobile Station has sent a positive acknowledgement and means 76 for requesting a retransmission of data blocks for which the Mobile Station has sent a negative acknowledgement and that are not retrievable from the memory of the Base Transceiver Station.

The benefit of the method and arrangement according to the present invention will now be explained by help of figure

8a, which shows a possible distribution of the percentages p(n) for the expectable number n of transmissions of data blocks . Figure 8b shows the throughput in a network comprising channels of an allocated bandwidth Bmax and comprising a retransmission distribution characteristic 2__j P(n) - n , e.g. as presented in figure 8a. Due to n retransmissions the allocated bandwidth is reduced to a share c - B_mm that indicates the effectively used bandwidth.

Without using the method according to the present invention the throughput ₁ - B_max is calculated by help of the ratio between the amount of data that is intended to be transmitted and the amount of data that is actually necessary to transmit the intended amount, i.e.

1 , = ^■

∑P⁽"⁾'«

The advantage of the method according to the present invention is that the length I2 of retransmitted messages according to the second message format is considerably shorter than the length li of the originally transmitted messages according to the first message format. As for the example in figure 8b, the block lengths are assumed to be lι=160 and 12=10. The throughput α₂" _max when applying the method according to the present invention can be calculated by help of the ratio between the number of messages according to the first message format of length li and the sum of said number of messages according to the first message format of length li and the number of retransmitted messages according to the second message format of length I2, i.e.

Apparently, the throughput can be considerably increased when applying the method according to the present invention, which is expressed as a gain ( ₂ - _l )- B^^ . In addition, the throughput remains at a fairly high level even for an increasing number of retransmissions. This saving can be used to gain Abis-bandwidth. But since there are peaks of consecutive full MCS-9 blocks that must be handled, this gain is a maximum and will be lower in practice. The gain will be the closer to the maximum gain the higher delay one accept. However, as delay is a critical parameter it is better to rely on the statistical nature of traffic and, during peaks, e.g., hold up other non-delay critical traffic.

Claims

1. Method for providing packet data services in an acknowledged mode in a radio communication system (10) comprising a sending unit (11) and at least one receiving unit (15) connected to each other by means of an intermediate unit (13), which provides a connection to the sending unit (11) via a packet-based transport network (12) and a connection to the receiving unit (15) via an access network (14) ,

c h a r a c t e r i s e d b y

the sending unit (15) initially transmitting (51) user data information according to a first message format and transmitting (54) user data information according to a second message format for already transmitted messages of user data information for which a negative acknowledgement has been received from the receiver unit (15) ,

the intermediate unit (13) storing (43) a copy of received messages of the first message format (41 Yes) before forwarding (45) the user data information to the receiving unit (15) and retrieving (44) and forwarding (45) the corresponding user data information of a received message of the second format (42 Yes) .

2. The method according to claim 1, whereby user data information according to the first message format consists of a user data block and a unique identification information for said data block and user data information according to the second message format consists of a unique identification information that indicates a specific user data block.

3. The method according to claim 2 , whereby the unique identification information consists of a Temporary Flow Identity (TFI) and a Block Sequence Number (BSN) .

4. The method according to one of claims 1-3 whereby

the intermediate unit (13) sends (462) reception status messages to indicate whether it could successfully store the user data information of messages that have been transmitted according to a first message format,

the sending unit (11) retransmits (522) user data information, which the intermediate unit (13) indicates not to have received, according to the first message format,

the sending unit (11) sends clear messages (551) to indicate user data information that has been acknowledged by the receiver unit (15) ,

the intermediate unit (13) removes (464) user data information that has been indicated (463 Yes) by a clear message of the sending unit (11) .

5. The method according to claim 4, whereby the intermediate unit (13) sends reception status messages (462) on a polling request (461 Yes, 521) from the sending unit (11) .

6. The method according to one of claims 1-3 , whereby the intermediate unit (13) removes (472) data blocks for which the receiving unit (15) has sent a positive acknowledgement (471 Yes) and requests (475) a retransmission of data blocks for which the receiving unit (15) has sent a negative acknowledgement (473 Yes) and that are not retrievable (474 No) from the memory of the intermediate unit (13) .

7. The method according to one of the preceding claims, whereby the sending unit (11) consists of a Base Station Controller, the intermediate unit (13) of a Base Transceiver Station, and the receiving unit (15) of a Mobile Station.

8. Method in a Base Station Controller (11) for providing packet data services in an acknowledged mode in a radio communication system (10) comprising at least one Mobile Station (15) and a Base Transceiver Station (13), which provides a connection to the Base Station Controller (11) via a packet-based transport network (12) and a connection to the Mobile Station (15) via a radio access network (14) ,

c h a r a c t e r i s e d b y

initially transmitting (51) user data information according to a first message format,

transmitting (54) user data information according to a second format for already transmitted messages of user data information for which a negative acknowledgement has been received from the Mobile Station (15) .

9. The method according to claim 8, whereby user data information according to the first message format consists of a user data block and a unique identification information for said data block and user data information according to the second message format consists of a unique identification information that indicates a specific user data block.

10. The method according to claim 9, whereby the unique identification information consists of a Temporary Flow Identity (TFI) and a Block Sequence Number (BSN) .

11. The method according to one of claims 8-10, whereby the Base Station Controller (11) polls (521) the Base Transceiver Station (13) for reception status messages.

12. The method according to one of the claims 8-11, further comprising the steps of retransmitting (522) user data information, which the intermediate unit (13) indicates not to have received, according to the first message format,

sending (551) clear messages to indicate acknowledged user data blocks that can be removed from the storage of the Base Transceiver Station (13) .

13. The method according to one of claims 8-10, whereby user data information according to the first message format is retransmitted (552) on request of the Base Transceiver Station.

14. Method in a Base Transceiver Station (13) for providing packet data services in an acknowledged mode in a radio communication system (10) comprising a Base Station Controller (11) , which is connected to said Base Transceiver Station (13) via a packet-based transport network (12) and at least one Mobile Station (15), which is connected to said Base Transceiver Station (13) via a radio access network (14),

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storing (43) a copy of received messages of a first format (41 Yes) before forwarding (45) the included user data block to the Mobile Station (15),

retrieving (44) and forwarding (45) the corresponding user data information of a received message of the second format (42 Yes) .

15. The method according to claim 14, whereby user data information according to the first message format consists of a user data block and a unique identification information for said data block and user data information according to the second message format consists of a unique identification information that indicates a specific user data block.

16. The method according to claim 15, whereby the unique identification information consists of a Temporary Flow Identity (TFI) and a Block Sequence Number (BSN) .

17. The method according to one of claims 14-16, whereby the Base Transceiver Station (13) sends (462) reception status messages to indicate whether messages of a first format have been successfully stored and removes (464) user data information that has been indicated by a clear message (463 Yes) of the Base Station Controller (11) .

18. The method according to one of claims 14-16, whereby the reception status messages are sent (462) on a polling request (461 Yes, 521) of the Base Station Controller (11) .

19. The method according to one of claims 14-16, whereby the Base Transceiver Station (13) removes (472) user data information for which the Mobile Station (15) has sent a positive acknowledgement (471 Yes) and requests (475) a retransmission of data blocks for which the Mobile Station

(15) has sent a negative acknowledgement (473 Yes) and that are not retrievable (474 No) from the memory of the Base Transceiver Station (13).

20. An arrangement (60) related to a Base Station Controller (11) for providing packet data services in an acknowledged mode in a radio communication system (10) comprising at least one Mobile Station (15), which is connected to said Base Station Controller (11) by means of a Base Transceiver Station (13) providing a connection to the Base Station Controller (11) via a packet-based transport network (12) and a connection to the Mobile Station (15) via a radio access network (14) ,

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means (61) for composing user data information for an initial transmission according to a first message format, means (62) for composing user data information for a retransmission according to a second format of those already transmitted messages of user data information for which a negative acknowledgement has been received from the Mobile Station (15) .

21. The arrangement according to claim 20 further comprising

means (63) for polling and evaluating reception status messages from the Base Transceiver Station (13),

means (64) for initiating a retransmission of messages of the first format that have been indicated to be not received by said Base Transceiver Station (13),

means (65) for sending clear messages to indicate acknowledged user data blocks that can be removed from the storage of the Base Transceiver Station (13).

22. Arrangement related to a Base Transceiver Station (13) for providing packet data services in an acknowledged mode in a radio communication system (10) comprising a Base Station Controller (11) , which is connected to said Base Transceiver Station (13) via a packet-based transport network (12) and at least one Mobile Station (15) , which is connected to said Base Transceiver Station (13) via a radio access network (14),

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means (71) for storing a copy of received messages of a first format before forwarding the included user data information to the Mobile Station (15) and

means (72) for retrieving the corresponding user data information of a received message of the second format .

23. The arrangement according to claim 22 further comprising means (73) for sending reception status messages to indicate whether messages of a first format have been successfully stored,

means (74) for removing user data information as indicated by a clear message of the Base Station Controller (11) .

24. The arrangement according to claim 22 further comprising

means (75) for removing user data information for which the Mobile Station (15) has sent a positive acknowledgement,

means (76) for requesting a retransmission of data blocks for which the Mobile Station (15) has sent a negative acknowledgement and that are not retrievable from the memory of the Base Transceiver Station (13) .