CA1259660A - Method and apparatus for coordinating independent communications systems - Google Patents
Method and apparatus for coordinating independent communications systemsInfo
- Publication number
- CA1259660A CA1259660A CA000522440A CA522440A CA1259660A CA 1259660 A CA1259660 A CA 1259660A CA 000522440 A CA000522440 A CA 000522440A CA 522440 A CA522440 A CA 522440A CA 1259660 A CA1259660 A CA 1259660A
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- CA
- Canada
- Prior art keywords
- message
- signal strength
- fixed site
- representation
- fixed
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W36/00—Hand-off or reselection arrangements
- H04W36/24—Reselection being triggered by specific parameters
- H04W36/30—Reselection being triggered by specific parameters by measured or perceived connection quality data
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W36/00—Hand-off or reselection arrangements
- H04W36/14—Reselecting a network or an air interface
Abstract
METHOD AND APPARATUS FOR COORDINATING
INDEPENDENT COMMUNICATIONS SYSTEM
Abstract A method and apparatus for coordinating the transfer of communications control from one independent radio communications system to another is disclosed. A remote unit which communicates data messages is associated with a home system which has a plurality of fixed sites and overlapping radio coverage areas. As the remote unit travels away from its home system, communications may be maintained by providing radio coverage from an independent roam system. The last message received by the home and roam systems from the remote unit has the associated radio signal strength and time of reception stored at each system. When a current message is transmitted by the remote unit and both the home and the roam system receive the message, the roam system time stamps the message and calculates the signal strength associated with the current message. If the amount of time elapsed between the last and the current message exceeds a predetermined amount of time or if the signal strength exceeds a predetermined threshold, the roam system requests tranfer of control of the processing of the current message from the home system. When the home system receives this request, it calculates the difference in signal strength between the signal strength of the current message as received by the roam system and the signal strength of the current message as received by the home system. If the difference exceeds a predetermined amount, the request of the roam system to further process the message is granted.
INDEPENDENT COMMUNICATIONS SYSTEM
Abstract A method and apparatus for coordinating the transfer of communications control from one independent radio communications system to another is disclosed. A remote unit which communicates data messages is associated with a home system which has a plurality of fixed sites and overlapping radio coverage areas. As the remote unit travels away from its home system, communications may be maintained by providing radio coverage from an independent roam system. The last message received by the home and roam systems from the remote unit has the associated radio signal strength and time of reception stored at each system. When a current message is transmitted by the remote unit and both the home and the roam system receive the message, the roam system time stamps the message and calculates the signal strength associated with the current message. If the amount of time elapsed between the last and the current message exceeds a predetermined amount of time or if the signal strength exceeds a predetermined threshold, the roam system requests tranfer of control of the processing of the current message from the home system. When the home system receives this request, it calculates the difference in signal strength between the signal strength of the current message as received by the roam system and the signal strength of the current message as received by the home system. If the difference exceeds a predetermined amount, the request of the roam system to further process the message is granted.
Description
~s~`s~
L~ET~OD A~ID APPARTUS FO~ COORDINATING
INDEPENDENT CO~lUNICATIO~S SYSTEMS
Background of the In~lention The present invention generally relates to inter-system coordination or maintenance of communication and more specifically relates to the rnethod and apparatus useful for enabling a physically mobile re~ote unit to be able to automatically transmit and receive rnessa~es as it travels from the radio coverage area of one radio communications system to the ra~io coverage area of another, independent, radio communications syste[n.
Radio communication services often ~row in geographic extent such that a communication service radio covera~e area offered by one coordinatea systeln expands to reach if not partially cover areas which are alreaay covered by a second coordinated but independent system.
Typically, a mobile or portable radio transceiver (a remote unit) associated with one systern woul.d be denied service on the second system even thou~h the radio frequencies in use Toay be compatible. Proposals have been advanced to enable a remote unit to be able to obtain service in a "foreign" systern but generally such SysteMs require the remote unit operator or his fixed station cocommunicator (dis~atcher) to manually take solne action to preregister in the foreign system. (See "Advanced 8~0 M~z Trunked Radio Systems" published by Motorola, IncO as document RO 6-07 on November 1982, page 4).
~ Manual registration, besides being inconvenient for the user, forces the user to learn the radio boundaries of the systems so that the user must register in system A
while in certain locations and in system B while in other locations. This boundary learning detracts from the user's main purpose for having a remote unit: to communicate his message. Furthermore, registration in one system may result in messages directed to the user in the other system to be lost because the user is no longer present there.
Automatic handoff of radio communications has been well developed in cellular radiotelephone systems and the equipment and processes necessary to the handoff are well known~ Automatic handoff, however, occ~lrs`within a single coordinated system and not between separate systems. The body of knowledge regarding intrasystem handoff, therefore, is not of particular value when coordination between two independent systems is minimal.
Summary of the Invention Therefore, it is an object of the present invention to provide automatic transfer of communication capability as a remote unit travels from the ra~io coverage area of one system to the radio coverage of another system.
It is another object of the present invention to limit the required intersystem overhead communications.
It is a further object of tne present invention to consider the ~actor of time in the decision to transfer communication capability from one system to another.
Accordingly, these and other objects are achieved in the present invention of method and apparatus for coordinating intersystem transfer of communications -processing between two independent communicatiorls systems. Briefly, the present invention enables the transfer of a remote unit, which transmits discontinuous ., 25 91~6~
~ 3 ~ CM00168H
messa~es, from one of a plurality o~ fixed sites of a first communication system to one of a plurality of fixed sites of a second system. One of the fixed sites asqociated with the first system receives a ~irst message S transmitted by the remote unit, calculates the radio signal strength value repressntation, and stores the representation. When the remote unit transmits a second message, a different fixed site associated with the second system any also receive the second message. The radio signal strength representation for this second message is calculated by the second system fixed site and compared to a predetermined threshold representation. A
favorable comparison results in the second system fixed site requesting permission from the first system fixed site to process the remote unit's second message. The first system fixed site compares the second signal strength representation to the first system signal strength representation and may grant the permission request of the second system fixed site based on the comparison resul~s. This grant results in the automatic transferring of the remote unit from the first radio communications system to the second radio communications system.
Brief ~escriPkion of the Drawinqs Figure 1 is a representation of one fixed site of a conventional radio data communication system.
Figuxe 2 is a block diagram of the equipment which may conventionally be found at a fixed site such as that of Figure 1.
Figure 3 is a block diagram of a general communications controller which is found at a ~ixed site such as that of Figure 1 and which may be employed in the present invention.
~59~
~ 4 ~ CM00168H
Figure 4 is a block diagram o~ the paging executive of Fig. 2 and which may be employed in the present invention.
Figure 5 is a representation of the int~rsection of the radio coverage areas of two independent radio communications systems which may employ the present invention' Figure 6 is a repre~entation of the files which may be kept in the paging executive employed in the present invention.
Figures 7a and 7b, combined, are a flowchart of the method o~ trans~erring communications capability for a remote unit from a home communications system to a roam communications system and which may be empioyed in tha present in~ention.
Figures 8a and 8b, combined, are a flowchart of the method o~ transferring communication~ capability for a remote unit from a roam communications system to a home communication system and which may be employed in the present invention.
Figure 9 is a block diagram of a Network Control Processor such as that which may be employed in the present invention.
Detailed Description of the Preferred Embodiment A f ixed site of a conventional radio communication system is shown in Fig. 1. Here, a geographical area of radio coverage zones is illustrated as being served by three base sites 101, 103, and 105.
Located at each site are radio transmitters and radio receivers (transceivers) and transceiver control}ing devices (general communication controllers-GCC). These transceivers may be any suitable commercially available transceivers such as those described in Motorola Instruction Manual 63P81013E65 and GCC may be a suitable.
computer controlled devic~ such as a 5CC80 available ~rom Motorola, Inc. Located in or nearby the geographical zones of th~ fixed site is a netwoxk control processor ~ 6 ~
11~ which is coupled to the base sites 101, 103 and 105 in order that tranSItlissiOns and receptions of messages may be routed and controlled.
A radio communication system such as that which may advantageously employ the present invention generally consists of a plurality of network control processors under the control of a hi~her order controlling function such as a paging executive (not shown in Fig. 1). An organization such as this is especially useful to provide data communlcations over a lar~e ~eographic area segmented into conti~uous and overLapping coverage zones or~anized into fixed sites as previously described.
Although the system described herein is described in the context of a data on1y coMmunication system, both data signals and analog si~nals such as voice signals can be communicated over the radio channels.
A plurality of mobile and portable transceivers, ~enerically known as remote units (or porta~le terminals if a si~nificant portion of the message communicated is data), may travel throu~hout che covera~e area. The systen~ of the preferred embodiment utilizes portable radios oE compatible commercially av~.ilable types such as those shown and described in ~.S. Patent ~os. 3,90~,166, 3,962,553; or 4,4~h,624. Portable ter,ninals (~') employ such portable radlos and ~enerally include a receiver operable on a first radio carrier frequency an~ a transmitter operable on a second radio carrier frequency.
Referrin~ now to ~i~. 2, ic is shown that the fixed site includin~ the network control processor 11~ may be coupled to a pagin~ executive ~PE.Y) ~U1 whlch, in a data communication system, may be a host computer and may control a number of network control processors illustrated by network control processors ~3 and 110.
In the preferred embodiment, pa~in~ executive ~01 may ~ather data from, and dispatch data to, portable transceivers located throughout the geographic area. A
similar type of system is shown and describe~ in U.S.
Patent 4,525,861 assigned to assignee of the present invention.
In operation, the network control processor 110 transmits message signals to and receives message signals from portable terminals (PTs illustrated as PTs 205 and 207) via a base transceiver and a GCC. The message signals may include a binary preamble, a predetermined synchronization word, an information word containing a command, status or data, and one or more data words. The format of the data packets may be any of a number of existinq data formats and may be one of those shown and describPd in U.S. Patent Nos. 4,517,669 and 4,519,068 assigned to the assignee of the present nvention.
Message signals, which may be received from the public switched telephone network (PSTN), public data networks, or another PT, are routed by the paging executive (PEX) 201 to a selected network control processor (NCP) 110 for transmission by one of its corresponding base transceivers. Since the message signals are not transmitted on all transmitters simultaneously as in simulcast systems, it is necessary that the paging executive (PEX) 201 or network control processor (NCP) 110 have a reasonably accurate indication of the location of each portable transceiver with relation to the radio coverage zones of the base transceivers. Thus, the paging executive (PEX) 201 or network control processor (NCP) 110 may select the proper transmitter of a base transceiver which covers the zone in which a particular portable transceiver is located. The paging executive (PEX) 201 may also interface with the public switched telephone network (PSTN) to receive and transmit messages -` ~25'.36~iO
- 6a -therefrom and operate as described in U.S. Patent 4,644,351 filed in the name of Zabarsky et al and assigned to the assignee of the present invention.
6~
~ 7 - CM00168H
Referring again to Fig. l, it can be se~n that the geographic area covered by this ~ixed site may be divided into seven zones, Zl-Z7 which are radio coverage zones generated by the transmitters of the base sites 101, 103, and 105. Each time a portable terminal ~PT) transmits, signal strength readings are taken by the receivers of the base sites lOl, 103, and 105. These readings may be used by each GCC associated with the receiving receivers to compute an adju~ted signal strength representa~ion for e~ch of the zone~ Zl-æ7 by digitizing and adjusting the measured signal strength ~or each receiver by a corresponding predetermined factor associated with the particular zone and the particular receiving equipment. A similar technique is shown and described in U.S. Patent No. 4,481,670 assigned to the assignee of the present invention.
The predetermined factors used to compute the adjusted signal strength representations d~pend upon a number of ~actors such as the terrain, the height and gain o~ the antennas, and the sensitivity of the receivers. In other words, the predetermined factors associated with each zone are empirically determined and depend upon the characteristics, equipment, and terrain encountered at each fixed site. These predetermine~
factors can be arranged in a zone selection matrix which can then be used by ~he paging executive (PEX) 201 and the network control processor (NCP) llO to identify the zone which has the largest adjusted signal strenyth for a particular txansmission from a portable terminal. The selected zone for a particular portable terminal data message transmission may be stored with other data in a location of the memory of the paging executive 201 or the serving nctwork control processor associated with that portable terminal. Additionally/ the entire zone selection matrix may be stored thereby providing a composite history o~ all of the receivers which received the last PT transmission and the ad'Justed signal strength representation at each. In this way, a message to be transmitted to the particular PT can be dlrscted to the zone having the best signal strength.
Whenever transmitting a message to a particular portable terminal such a portabIQ terminal 205, the paging executive 201 or network control processor 110 will ~irst cause the message to be transmitted on the carrier frequency of the transmitter which covers the zone which had the largest adjusted signal strength for the last transmission from portable terminal 205.
In~ormation identifying both that zone and the transmitter covering it are stored in the memory of network control processor 110 or paging exècutive 201.
If ~he portable terminal (PT) 205 does not acknowledge the transmission o~ ths message, the paging executive (PEX) 201 or network control processor (NCP) 110 may attempt one or more retransmissions of the message via the selected transmitter. If the retransmissions likewise are not acknowledged by the PT 205, the paging executive (PEX) 201 or network control processor (NCP) 110 may then cause the transmission o~ the message via the base transceiver tra~smitter covering the zone which had the second largest adjusted signal strength during the last transmission from PT 205. Again, if PT 205 does not acknowledge the transmission, the message may again be transmitted one or more times~ via t:hat selected transmitter. If the PEX 201 or NCP 110 does not reach the selected PT by means of the,se twc base transceiver transmitters, PEX 201 or NCP 110 may either select another transmitter covering the last fixed sike receiving the PT 205 message, or it may initiate a polling sequence in which PT 205 is polled in every fixed site in the data communication system. If no acknowledgment is received from the PT, the messaye may be stored ~s will be described latsr.
A block diagram of a typical GCC (general communication controller) is shown in Fig. 3. Each GCC
includes a microcomputer 302 having a memory with stored program therein for communicating with a NCP (network control processor) and the portable terminals via an associated base transceiver. Microcomputer 302 can be any suitable commercially available microcomputer such a~
the Motorola types MCS800, MC6801, MC6805, or MC68000 microprocessor.
Microcomputer 302 i~ coupled to a conventional RS232 interface 304 which may, in turrl, be couplQd by a high speed modem (not shown) to a dedi.cated telephone line or other communication channel connected to an NCP
tsuch as NCP 110 shown in Fig. 2). Message eignals destined for a PT are received by microcomputer 302 from NCP 110 and are assembled into variable length messages.
These assembled messages are coupled to filter 306 and thereafter applied to its corresponding base transceiver transmitter.
Messagea received ~rom a portable terminal are coupled to a conventional filter 308 and therea~ter to conventional signal li~iter 310 for conversion of the analog signals into a nonreturn-to-zero binary signal.
The output of limiter 310 is applied to an input port of information and data therein.
Microcomputer 302 also accepts radio signal strength readings from the base transceiver receivers to which the NCP is coupled while it is receiving messages.
The signal strength indicator (SSI) signals from the receivers receiving a PT message are coup].ed to conventional A/D converter 312 which may continuously convert the analog SSI signal to a digitized SSI signal having 3 bits. Ths digitized SSI signal from A/D
converter 312 is applied to an input port o~
microcomputer 302. Several A/D conversions are performed while a PT message signal is being received. The digitized SSI siqnals for the several conversions are averaged by the microcomputer 302. The average SSI
- l o -signal is then appended to the received data message and sent by microco~puter 302 via RS232 interface 304 to NCP
110 and, if required by syste~ design to PEX 201. The information and SSI data frorn the received data message may be coded in any suitable conventional for~at for transmission to the ~C~ 110.
A network control processor such as that employed in the preferred embodiment is shown in Fi~ure 9. NCP 110 or 203 is controlled by a central processing unit (CPU) 900 which may be a hi~h end microprocessor similar to an MC68000, CIC68010, or ~IC6~020 manui-actured by ~lotorola, Inc. or similar type. Also contained within the CPU 900 is a limited amount of on-board memory and two serial ports. Primary a1emory may be provided by dynamic random access ~emory (RAM) 902 and may be backed-up by a disk storage 904. The disk storage enters the microprocessor via a universal disk controller (UDC) 90~, such as that available from Motorola, Inc. as an ~LN16~4A.
Interface with other elements of the communication system is accomplished via communication interface boards (CIB) 908, g10, ~12, and 914. A CI~ is a general purpose interface board, for example, an ~L~16~5A available from i-lotorola, Inc. which performs the interface between the ~rocessor bus and ~232-compatible external ~evices in a conventional fashion. ~onn~ction between an L~C~) and the ~X 201 is achieved via a CIB such as is shown employing CI~ 914.
The I~CP's functions are to coordinate the communications from the PEX 2~1 tv the proper transceiver through a GCC and vice versa. The t~CP 110 ~naintains lists of the active portable terlninals in the system with such infor1nation as the last call in, the received signal streny,th representations for eac!1 transceiver receivin~
the inbo~md transrl1ission, and a list of most probable transmitters for outbound transnlissivns. The CICP
maintains the Zone Selection C1atrix an~ uses this matrix ~ CM00168H
to calculate signal trength values as described in U.S.
Patent N0. 4,481,670. It is the NCP 110 that first detects that a transmis~ion from a particular portable terminal i9 not registered in the local system and makes the preliminary deci~ion concerning the dispo ition of the message based on files local to the NCP. A portable terminal message, that is not registered, is not automatically acknowledged, but the information is forwarded to ~he PEX for disposition, as described later~
lo A paging executive such as that employed in the preferred embodiment is shown in Fig. 4. PEX 201 is controlled by a central processing unit (CPU) 400 which may be a high end mlcroprocessor similar to an MC68000 manufactured by ~otorola, Inc. or similar type. Also contained wlthin the CPU 400 is a limited amount of on-board memory and two serial I/O ports. Primary memory may be provided by dynamic random access memory ~RAM) 402 and may be backed-up by a disk storage 404. The disk storage enters ~he microprocessor via a universal disk controller (UDC~ 406, ~uch as that a~ailable from Motorola, Inc. as an NLN 1684A.
Interface with other elements of the communication sy~tem is accomplished via communication interface boards (CIB) 408, 410, 412, and 414. A CIB is a general purpose interface board, for example, an NLN
1685A available from Motorola, Inc., which performs the interface betw~en the processor bus and RS232 compatible external devices in conventional fashion. Connection between an NCP and the PEX 201 is achieved via a CIB such as is shown employing CIB 408 and CIB 410.
Interface batween PEX 201 and PEXs of other communication ~ystQms may be realized via another CIB
412. Additionally, lnterface to the public switched telephone network (PSTN) or other communication networks ma~ be achieved via a CIB 414 and a network interface 416.
Messages directed to a PT are typically stored on disk storage 404 with the PT's unique address so that messages may be recalled and transmitted to the PT at an appropriate time, such as when a PT has not acknowledged a page but is now requesting the PEX 201 to deliver stored messages. Messages which have been recalled and all messa~es which are awaiting transrnission are placed in a transmission queue in RAM 4~2 before being transmitted. The messages stored in disk storage 404 are held for a predetermined period of time, for example 24 hours, and then deleted from storage. ~iessa~e statistics, such as time-of-message receipt in the PEX, time-of-message acknowledgment, number of characters in the message, and PT location when the message was acknowledged, are retained for user billing and audit trail purposes.
Relative PT location is an important element in the operation of a data com~unication system such as been described. PT location becomes increasingly important as additional independent communication systems come into existance. hhen two inde~endent systems are constructed adjacent to one another, as shown diagralnr~atically in Fi~. 5, unique problems in PT location and service continuation between systems beco~oe apparent. If a PT
were to travel into that part of zone Z1 which overlaps zone Z10 of the adjacent system, i.e. zone Z8, signal strength information which would be gathered by a receiver at base site 501 would not normally be made available to the pa~ing executive 201 and network control processor 110 because the syste~ns are wholly independent.
A full exchange of data could, of course, be arran~ed between the two systems but in a ~ractical situation, such as where the systems are under ownership of different parties, this exchange is likely to be limited.
In ~he present inven~ion, which seeks to enable continuation of communîcation services, a lirnited data exchange may be accomplished between respective P~X's (such as that between PEX 2Ul and PEX 505) or between S NCP's (such as between NCP 110 and NCP 507). If the two communication systems share the same set of radio frequencies the data line will, in the preferred ernbodiment, be established between the two NCP's via a CIB; if the systerns do not share the same frequencies the data line should be established between the two PEX's also via a CIB.
In order to accomplish the intersystem control, a PT
location file is maintained at each PEX which can share messages, Included in each PEX lo`cation file is a lis~
IS of PT addresses for those PT's which are registered in, and are billed from, that PEX (the "home" system). Also included in the file are the locations of those home PT's which have traveled ("roamed") to another ("roam") system, and the addresses of those PTs which have roamed to this system from another systern.
As diagramed in Fig. 6, the location file consists of three lists: a local file, a local roamer file, and foreign roamer list. The information included in the local or "home PT" rile 608 consists of the PT address, the base transceiver receiv~r's signal stren~th indicator values and priority established thereirom, a pointer to the memory location where messa~es for this PT may be follnd, a time stamp when the last messa~e producing si~nal strength inaication was received, and a roaming pointer to the roamer file if the home PT has roamed.
The roamer file essentially consists of two lists, a local roamer list and a forei~n roamer list. Since ~he local file contains the permanent record of each PT
registered in the home systern and is scanned whenever a message is directed to a PT, a roaming pointer field is included with the PT record ~0~ whenever a home PT roams 6~t to another system. This pointer directs the PEX to the local roamer list and to this specific local roamer record 610 associated with the roaming PT. The roamer record 610 contains a pointer back to the local file, the address of the PEX to which the PT has roamed, and the date and time the PT appeared in the foreign system.
The foreign roamer list contains a "foreign"
PT file 612 which cons.ists of a message location pointer and the address of those "foreign" PTs (PTs not registered or billed in this local system) which have roamed into the local system and which have been active, that is, initiated or received messages within a preceding period of time such as the past 24 hours.
This file is used primarily to allow the PEX to quickly deliver a response to a message directed to a roaming foreign PT by allowing the PEX to search the foreign roamer list and find an address of foreign active PT
rather than causing PEX to send an inquiry back to the foreign PT's home system and receiving a location message. This reduces the amount of traffic between system. D~scription of a similar filing system may be found in U.S. Patent 4,644,351 filed in the name of Zabarsky et al.
An important feature in the present invention, then, is the method for coordinating the message delivery and service grants to roaming PTs. The method employed by ~he preferred embodiment is diagrammed as a flowchart in Fig. 7a and Fig. 7b. It is expected that a PT will generate a series of discontinuous data messages as the PT user uses his PT. Since this equipment is, in the preferred embodiment, a portable unit, it is expected that the user will easily carry - 14a -the PT between radio zones and into an adjacent system.
As he travels across the interface zone, Z8, a decision must be made by the systems to transfer the PT service 5. at some po~nt from one system to the other if continuous service is to be realized. In zone Z8, of Fi~. 5, the PT data message may be received by both the base site 101 receiver and the base site 501 receiver. This reception at two base transceivers of two independent systems is shown as st~ps 701 and 703 in the flowchart of Fig. 7a. Considering first the steps taken by che roam system in the control of the PT communication, the PT message is given an indication of the time of reception (shown as time stamp step 705) and becomes a permanent part of the rnessage.
The zone si~nal stren~th value is then calculated (at step 707) from the SSI signal described previously. The message is stored (at step 708) in the RAM of the ~CP
until a decision is made whether the roam system is to process the message further. A determination of whether the roam system is already yroviding service to this PT
is made at decision block 7~9, where a positive response to this decision allows the PT communications to be processed normally at 711. A ne~ative response moves to step 713. If the PT is to be denied service in this system, such as for nonpa~1lent of bills, a determination is made at step 713 whether this PT is on the "black list" of undesirable units kept as part of the ~orei~n roamer list. A positive response to the decision results in the PT address being reMoved from the syst~m list at 715 and a negative response allows the process to move to step 717. If the PT address is not in the roamer file, as determined at 717, it is placed there at step 71~. A
comparison of the most recent tirne stamp to the last time stalnp and a comparison of current to last message signal stren~th values is made at the decision block 7~1.
A feature of particular advantage in the yre~sent invention is that of employin~ the time stalny recorJe~
Wittl the last received messa~e to determine whether the signal strength values last store~ are "rresh" enou~h to be used in determinin~ the relative position of the highly mobile PTs. Briefly, the tirne stamp may be ~2~
generated by a real time clook at the roam system NCP
receiving the message and coded and stored in numeric or ASCII ~orm with the received message and signal strength representations. Alternately, the real time clock and storage may be maintained at the PEX depending upon the requirement~ of the system. The stored clock values for a previous message may be compared to a newly received message time stamp at the NCP or PEX.
In order to decide whether the time and signal strength representations warrant a transfer of the PT to the roam system from the home system, a comparison is made of the current values at the home system to the values communicated by the roam system. Additionally, if the time stamp and the most recent message received by the roam system is more current than the values stored in the home PEX by a predetermined amount, which in the preferred embodiment is from one to five minutes, it is decided that a transfer is warranted. Alternately, if the two time stamps indicate messayes occurring within the predetermined amount, the largest thr~e adjusted valuPs o~ the stored home system signal strength representations are compared with the most recent received signal strength adjusted values. Current values of one or more adjusted signal strength readings in the roam ~ystem which exceed a predet~rmined threshold, creates a positive response to the decision of whether the values warrant a trans~er. This threshold is empirically determined for each site and is function o~
the terrain, the useable sensitivity of the receivers, and other site-specific parameters.
Given a positive decision at 721, a request is made o~ the home system to veri~y the status of the service-reguesting P~ at 723. A PT status check is made at the home system at 725 and a response is returned to the roam system. Re~erring now to Fig. 7b, if the veriftcation ls negative, the PT addres~ i~ added to the black list and all communication is purged from the receiving NCP at 727.
A nonnegative roamer verification causes the roam system to format a request message for the home syste[n at 729. This message includes the PT address, the received time stamped, and the three largest signal stren~th S values measured by the base transceiver receivers.
The home system receives the request message from the roam system (shown at 731~ via the intersystem data link and the home system decides whether a transfer of the PT is justified based on a site specific predetermined ratio of adjusted signal strength at the roam system to the adjusted signal stren~th at the ho~e system at 733. If the transfer is not justified, a message is returned to the roam system including the time stamp and signal strength representations of the last home system message received. The roam system, then, attempts no further communication with the PT re~arding this latest received message as shown as step 735. If the transfer is justified, a message so statin~ is transmitted to the roam system which responsively enters the YT address zone signal stren~th representations and time stamp into its active file and requests the PT to be recorded as a local roamer in its ho1ne system file throu~h the roam and home PEX at step 737. The horne system subsequently enters the PT address into its roaming file with the current PT location at step 73~.
While the roam system performs its calcula~ions, the home system time stamps the salne received inbound communication from step 7~3 at step 741 and calculates the zone si~nal stren~th representations at step 743. If the transfer is not justified as described previously for stép 733, the home system processes the PT communica~ion n a normal fashLon at step 745.
A similar method of PT transi-er occurs when the`~T
returns into its home systeM. A ~lowchart describin~ a preferred embodiment is shown in Fi~s. ~a and ~b. A
transmission from a PT which has previously left the ii9 Ei6~
coverage areas of its home system and has obtained service from a roam system may be received in both the roam and the home systems (as indicated at 801 and 803).
Since both systems can provide service, a decision must again be made whether to transfer the message providing service back to the home syste~. As in the transfer from the home system to the roam system described in the method of Figs. 7a and 7b, the system currently providing service rnakes the final determination whether a transfer of communication services should occur. The system not providing service but receiving the ~T transmission, however, may request transfer of communications.
Returning to Fig. 8a, upon receiving a transmission from ~T, both the service-providing roam system and the home systela time stamp the incoming cornmunication and calculate the zone signal strength values (shown at steps 805, ~7 and 809, 811 respectively). The home s~stem subsequently determines if the PT is being serviced from the home system (at step 813) and if the PT address is on the black list (at step ~15). Given that the address of the PT whose transmission has been received is currently in the local roamer file but is neither on the black list nor currently served from the home system, a determination is made at step 819 if the time stamp and signal strength representations warrant a transfer to the home system. If the representations warrant a transfer, a message is formatted and transmitted (at step ~21) to the roarn sys~em providing service (as recorded in the local roamer file). The home system need not obtain PT
address verification from any other system because the holne system itself maintains the service verification i-or its home PTs.
The roam system receive~s the home system transfer request (at 823) and determines whether a transfer is justifi~d (at 825 in Fig. 8b). If the transfer is granted, a message is sent to the home system (at ~27) ~ ;96~(~
and-the home system in response enters the zone signal stren~ths into the PT home file at ~9 and removes the PT
address from the local roamin~ file at ~31. The ro~n system deletes the PT address from its forei~n roamer file (at 833) following its grant of communication transfer. If the transfer is not granted the roam system notifies the home system (which does not respond to the PT's transmission at 835) and processes the PT's transmission in a normal fashion at ~7.
Thus, coordination between at least two independent communication systerns may be achieved with the present invention. A radio transmission by a physically ,nobile PT may be received by receivers in the plurality of systems thereby making a decision process necessary in order to select a system and provide optimum communications capability tor the PT user. Although it is possible for all decisions to be made by the PT's home system, an extensive aEnount o~ interface between the home system and a roam system would be required~ The present invention enables the decision as to which system can provide the best communication to be maae by the system last ~rovidin~ service to the PT. ~ request ~y another system to transfer communication service cannot be made unless the radio si~nal stren~th and timin~ of the PT
transmission meet certain unique requirements.
Therefore, while a particular embodiment of the invention has been described and shown, it shouLd be understood that the invention is not limited thereto since many modifications may be made those skilled in the art. It is therefore contemplated to cover by the present application any and all such modifications that tall within the true spirit and scope of the basic underlying principles disclosed and claimed herein.
I clai~:
L~ET~OD A~ID APPARTUS FO~ COORDINATING
INDEPENDENT CO~lUNICATIO~S SYSTEMS
Background of the In~lention The present invention generally relates to inter-system coordination or maintenance of communication and more specifically relates to the rnethod and apparatus useful for enabling a physically mobile re~ote unit to be able to automatically transmit and receive rnessa~es as it travels from the radio coverage area of one radio communications system to the ra~io coverage area of another, independent, radio communications syste[n.
Radio communication services often ~row in geographic extent such that a communication service radio covera~e area offered by one coordinatea systeln expands to reach if not partially cover areas which are alreaay covered by a second coordinated but independent system.
Typically, a mobile or portable radio transceiver (a remote unit) associated with one systern woul.d be denied service on the second system even thou~h the radio frequencies in use Toay be compatible. Proposals have been advanced to enable a remote unit to be able to obtain service in a "foreign" systern but generally such SysteMs require the remote unit operator or his fixed station cocommunicator (dis~atcher) to manually take solne action to preregister in the foreign system. (See "Advanced 8~0 M~z Trunked Radio Systems" published by Motorola, IncO as document RO 6-07 on November 1982, page 4).
~ Manual registration, besides being inconvenient for the user, forces the user to learn the radio boundaries of the systems so that the user must register in system A
while in certain locations and in system B while in other locations. This boundary learning detracts from the user's main purpose for having a remote unit: to communicate his message. Furthermore, registration in one system may result in messages directed to the user in the other system to be lost because the user is no longer present there.
Automatic handoff of radio communications has been well developed in cellular radiotelephone systems and the equipment and processes necessary to the handoff are well known~ Automatic handoff, however, occ~lrs`within a single coordinated system and not between separate systems. The body of knowledge regarding intrasystem handoff, therefore, is not of particular value when coordination between two independent systems is minimal.
Summary of the Invention Therefore, it is an object of the present invention to provide automatic transfer of communication capability as a remote unit travels from the ra~io coverage area of one system to the radio coverage of another system.
It is another object of the present invention to limit the required intersystem overhead communications.
It is a further object of tne present invention to consider the ~actor of time in the decision to transfer communication capability from one system to another.
Accordingly, these and other objects are achieved in the present invention of method and apparatus for coordinating intersystem transfer of communications -processing between two independent communicatiorls systems. Briefly, the present invention enables the transfer of a remote unit, which transmits discontinuous ., 25 91~6~
~ 3 ~ CM00168H
messa~es, from one of a plurality o~ fixed sites of a first communication system to one of a plurality of fixed sites of a second system. One of the fixed sites asqociated with the first system receives a ~irst message S transmitted by the remote unit, calculates the radio signal strength value repressntation, and stores the representation. When the remote unit transmits a second message, a different fixed site associated with the second system any also receive the second message. The radio signal strength representation for this second message is calculated by the second system fixed site and compared to a predetermined threshold representation. A
favorable comparison results in the second system fixed site requesting permission from the first system fixed site to process the remote unit's second message. The first system fixed site compares the second signal strength representation to the first system signal strength representation and may grant the permission request of the second system fixed site based on the comparison resul~s. This grant results in the automatic transferring of the remote unit from the first radio communications system to the second radio communications system.
Brief ~escriPkion of the Drawinqs Figure 1 is a representation of one fixed site of a conventional radio data communication system.
Figuxe 2 is a block diagram of the equipment which may conventionally be found at a fixed site such as that of Figure 1.
Figure 3 is a block diagram of a general communications controller which is found at a ~ixed site such as that of Figure 1 and which may be employed in the present invention.
~59~
~ 4 ~ CM00168H
Figure 4 is a block diagram o~ the paging executive of Fig. 2 and which may be employed in the present invention.
Figure 5 is a representation of the int~rsection of the radio coverage areas of two independent radio communications systems which may employ the present invention' Figure 6 is a repre~entation of the files which may be kept in the paging executive employed in the present invention.
Figures 7a and 7b, combined, are a flowchart of the method o~ trans~erring communications capability for a remote unit from a home communications system to a roam communications system and which may be empioyed in tha present in~ention.
Figures 8a and 8b, combined, are a flowchart of the method o~ transferring communication~ capability for a remote unit from a roam communications system to a home communication system and which may be employed in the present invention.
Figure 9 is a block diagram of a Network Control Processor such as that which may be employed in the present invention.
Detailed Description of the Preferred Embodiment A f ixed site of a conventional radio communication system is shown in Fig. 1. Here, a geographical area of radio coverage zones is illustrated as being served by three base sites 101, 103, and 105.
Located at each site are radio transmitters and radio receivers (transceivers) and transceiver control}ing devices (general communication controllers-GCC). These transceivers may be any suitable commercially available transceivers such as those described in Motorola Instruction Manual 63P81013E65 and GCC may be a suitable.
computer controlled devic~ such as a 5CC80 available ~rom Motorola, Inc. Located in or nearby the geographical zones of th~ fixed site is a netwoxk control processor ~ 6 ~
11~ which is coupled to the base sites 101, 103 and 105 in order that tranSItlissiOns and receptions of messages may be routed and controlled.
A radio communication system such as that which may advantageously employ the present invention generally consists of a plurality of network control processors under the control of a hi~her order controlling function such as a paging executive (not shown in Fig. 1). An organization such as this is especially useful to provide data communlcations over a lar~e ~eographic area segmented into conti~uous and overLapping coverage zones or~anized into fixed sites as previously described.
Although the system described herein is described in the context of a data on1y coMmunication system, both data signals and analog si~nals such as voice signals can be communicated over the radio channels.
A plurality of mobile and portable transceivers, ~enerically known as remote units (or porta~le terminals if a si~nificant portion of the message communicated is data), may travel throu~hout che covera~e area. The systen~ of the preferred embodiment utilizes portable radios oE compatible commercially av~.ilable types such as those shown and described in ~.S. Patent ~os. 3,90~,166, 3,962,553; or 4,4~h,624. Portable ter,ninals (~') employ such portable radlos and ~enerally include a receiver operable on a first radio carrier frequency an~ a transmitter operable on a second radio carrier frequency.
Referrin~ now to ~i~. 2, ic is shown that the fixed site includin~ the network control processor 11~ may be coupled to a pagin~ executive ~PE.Y) ~U1 whlch, in a data communication system, may be a host computer and may control a number of network control processors illustrated by network control processors ~3 and 110.
In the preferred embodiment, pa~in~ executive ~01 may ~ather data from, and dispatch data to, portable transceivers located throughout the geographic area. A
similar type of system is shown and describe~ in U.S.
Patent 4,525,861 assigned to assignee of the present invention.
In operation, the network control processor 110 transmits message signals to and receives message signals from portable terminals (PTs illustrated as PTs 205 and 207) via a base transceiver and a GCC. The message signals may include a binary preamble, a predetermined synchronization word, an information word containing a command, status or data, and one or more data words. The format of the data packets may be any of a number of existinq data formats and may be one of those shown and describPd in U.S. Patent Nos. 4,517,669 and 4,519,068 assigned to the assignee of the present nvention.
Message signals, which may be received from the public switched telephone network (PSTN), public data networks, or another PT, are routed by the paging executive (PEX) 201 to a selected network control processor (NCP) 110 for transmission by one of its corresponding base transceivers. Since the message signals are not transmitted on all transmitters simultaneously as in simulcast systems, it is necessary that the paging executive (PEX) 201 or network control processor (NCP) 110 have a reasonably accurate indication of the location of each portable transceiver with relation to the radio coverage zones of the base transceivers. Thus, the paging executive (PEX) 201 or network control processor (NCP) 110 may select the proper transmitter of a base transceiver which covers the zone in which a particular portable transceiver is located. The paging executive (PEX) 201 may also interface with the public switched telephone network (PSTN) to receive and transmit messages -` ~25'.36~iO
- 6a -therefrom and operate as described in U.S. Patent 4,644,351 filed in the name of Zabarsky et al and assigned to the assignee of the present invention.
6~
~ 7 - CM00168H
Referring again to Fig. l, it can be se~n that the geographic area covered by this ~ixed site may be divided into seven zones, Zl-Z7 which are radio coverage zones generated by the transmitters of the base sites 101, 103, and 105. Each time a portable terminal ~PT) transmits, signal strength readings are taken by the receivers of the base sites lOl, 103, and 105. These readings may be used by each GCC associated with the receiving receivers to compute an adju~ted signal strength representa~ion for e~ch of the zone~ Zl-æ7 by digitizing and adjusting the measured signal strength ~or each receiver by a corresponding predetermined factor associated with the particular zone and the particular receiving equipment. A similar technique is shown and described in U.S. Patent No. 4,481,670 assigned to the assignee of the present invention.
The predetermined factors used to compute the adjusted signal strength representations d~pend upon a number of ~actors such as the terrain, the height and gain o~ the antennas, and the sensitivity of the receivers. In other words, the predetermined factors associated with each zone are empirically determined and depend upon the characteristics, equipment, and terrain encountered at each fixed site. These predetermine~
factors can be arranged in a zone selection matrix which can then be used by ~he paging executive (PEX) 201 and the network control processor (NCP) llO to identify the zone which has the largest adjusted signal strenyth for a particular txansmission from a portable terminal. The selected zone for a particular portable terminal data message transmission may be stored with other data in a location of the memory of the paging executive 201 or the serving nctwork control processor associated with that portable terminal. Additionally/ the entire zone selection matrix may be stored thereby providing a composite history o~ all of the receivers which received the last PT transmission and the ad'Justed signal strength representation at each. In this way, a message to be transmitted to the particular PT can be dlrscted to the zone having the best signal strength.
Whenever transmitting a message to a particular portable terminal such a portabIQ terminal 205, the paging executive 201 or network control processor 110 will ~irst cause the message to be transmitted on the carrier frequency of the transmitter which covers the zone which had the largest adjusted signal strength for the last transmission from portable terminal 205.
In~ormation identifying both that zone and the transmitter covering it are stored in the memory of network control processor 110 or paging exècutive 201.
If ~he portable terminal (PT) 205 does not acknowledge the transmission o~ ths message, the paging executive (PEX) 201 or network control processor (NCP) 110 may attempt one or more retransmissions of the message via the selected transmitter. If the retransmissions likewise are not acknowledged by the PT 205, the paging executive (PEX) 201 or network control processor (NCP) 110 may then cause the transmission o~ the message via the base transceiver tra~smitter covering the zone which had the second largest adjusted signal strength during the last transmission from PT 205. Again, if PT 205 does not acknowledge the transmission, the message may again be transmitted one or more times~ via t:hat selected transmitter. If the PEX 201 or NCP 110 does not reach the selected PT by means of the,se twc base transceiver transmitters, PEX 201 or NCP 110 may either select another transmitter covering the last fixed sike receiving the PT 205 message, or it may initiate a polling sequence in which PT 205 is polled in every fixed site in the data communication system. If no acknowledgment is received from the PT, the messaye may be stored ~s will be described latsr.
A block diagram of a typical GCC (general communication controller) is shown in Fig. 3. Each GCC
includes a microcomputer 302 having a memory with stored program therein for communicating with a NCP (network control processor) and the portable terminals via an associated base transceiver. Microcomputer 302 can be any suitable commercially available microcomputer such a~
the Motorola types MCS800, MC6801, MC6805, or MC68000 microprocessor.
Microcomputer 302 i~ coupled to a conventional RS232 interface 304 which may, in turrl, be couplQd by a high speed modem (not shown) to a dedi.cated telephone line or other communication channel connected to an NCP
tsuch as NCP 110 shown in Fig. 2). Message eignals destined for a PT are received by microcomputer 302 from NCP 110 and are assembled into variable length messages.
These assembled messages are coupled to filter 306 and thereafter applied to its corresponding base transceiver transmitter.
Messagea received ~rom a portable terminal are coupled to a conventional filter 308 and therea~ter to conventional signal li~iter 310 for conversion of the analog signals into a nonreturn-to-zero binary signal.
The output of limiter 310 is applied to an input port of information and data therein.
Microcomputer 302 also accepts radio signal strength readings from the base transceiver receivers to which the NCP is coupled while it is receiving messages.
The signal strength indicator (SSI) signals from the receivers receiving a PT message are coup].ed to conventional A/D converter 312 which may continuously convert the analog SSI signal to a digitized SSI signal having 3 bits. Ths digitized SSI signal from A/D
converter 312 is applied to an input port o~
microcomputer 302. Several A/D conversions are performed while a PT message signal is being received. The digitized SSI siqnals for the several conversions are averaged by the microcomputer 302. The average SSI
- l o -signal is then appended to the received data message and sent by microco~puter 302 via RS232 interface 304 to NCP
110 and, if required by syste~ design to PEX 201. The information and SSI data frorn the received data message may be coded in any suitable conventional for~at for transmission to the ~C~ 110.
A network control processor such as that employed in the preferred embodiment is shown in Fi~ure 9. NCP 110 or 203 is controlled by a central processing unit (CPU) 900 which may be a hi~h end microprocessor similar to an MC68000, CIC68010, or ~IC6~020 manui-actured by ~lotorola, Inc. or similar type. Also contained within the CPU 900 is a limited amount of on-board memory and two serial ports. Primary a1emory may be provided by dynamic random access ~emory (RAM) 902 and may be backed-up by a disk storage 904. The disk storage enters the microprocessor via a universal disk controller (UDC) 90~, such as that available from Motorola, Inc. as an ~LN16~4A.
Interface with other elements of the communication system is accomplished via communication interface boards (CIB) 908, g10, ~12, and 914. A CI~ is a general purpose interface board, for example, an ~L~16~5A available from i-lotorola, Inc. which performs the interface between the ~rocessor bus and ~232-compatible external ~evices in a conventional fashion. ~onn~ction between an L~C~) and the ~X 201 is achieved via a CIB such as is shown employing CI~ 914.
The I~CP's functions are to coordinate the communications from the PEX 2~1 tv the proper transceiver through a GCC and vice versa. The t~CP 110 ~naintains lists of the active portable terlninals in the system with such infor1nation as the last call in, the received signal streny,th representations for eac!1 transceiver receivin~
the inbo~md transrl1ission, and a list of most probable transmitters for outbound transnlissivns. The CICP
maintains the Zone Selection C1atrix an~ uses this matrix ~ CM00168H
to calculate signal trength values as described in U.S.
Patent N0. 4,481,670. It is the NCP 110 that first detects that a transmis~ion from a particular portable terminal i9 not registered in the local system and makes the preliminary deci~ion concerning the dispo ition of the message based on files local to the NCP. A portable terminal message, that is not registered, is not automatically acknowledged, but the information is forwarded to ~he PEX for disposition, as described later~
lo A paging executive such as that employed in the preferred embodiment is shown in Fig. 4. PEX 201 is controlled by a central processing unit (CPU) 400 which may be a high end mlcroprocessor similar to an MC68000 manufactured by ~otorola, Inc. or similar type. Also contained wlthin the CPU 400 is a limited amount of on-board memory and two serial I/O ports. Primary memory may be provided by dynamic random access memory ~RAM) 402 and may be backed-up by a disk storage 404. The disk storage enters ~he microprocessor via a universal disk controller (UDC~ 406, ~uch as that a~ailable from Motorola, Inc. as an NLN 1684A.
Interface with other elements of the communication sy~tem is accomplished via communication interface boards (CIB) 408, 410, 412, and 414. A CIB is a general purpose interface board, for example, an NLN
1685A available from Motorola, Inc., which performs the interface betw~en the processor bus and RS232 compatible external devices in conventional fashion. Connection between an NCP and the PEX 201 is achieved via a CIB such as is shown employing CIB 408 and CIB 410.
Interface batween PEX 201 and PEXs of other communication ~ystQms may be realized via another CIB
412. Additionally, lnterface to the public switched telephone network (PSTN) or other communication networks ma~ be achieved via a CIB 414 and a network interface 416.
Messages directed to a PT are typically stored on disk storage 404 with the PT's unique address so that messages may be recalled and transmitted to the PT at an appropriate time, such as when a PT has not acknowledged a page but is now requesting the PEX 201 to deliver stored messages. Messages which have been recalled and all messa~es which are awaiting transrnission are placed in a transmission queue in RAM 4~2 before being transmitted. The messages stored in disk storage 404 are held for a predetermined period of time, for example 24 hours, and then deleted from storage. ~iessa~e statistics, such as time-of-message receipt in the PEX, time-of-message acknowledgment, number of characters in the message, and PT location when the message was acknowledged, are retained for user billing and audit trail purposes.
Relative PT location is an important element in the operation of a data com~unication system such as been described. PT location becomes increasingly important as additional independent communication systems come into existance. hhen two inde~endent systems are constructed adjacent to one another, as shown diagralnr~atically in Fi~. 5, unique problems in PT location and service continuation between systems beco~oe apparent. If a PT
were to travel into that part of zone Z1 which overlaps zone Z10 of the adjacent system, i.e. zone Z8, signal strength information which would be gathered by a receiver at base site 501 would not normally be made available to the pa~ing executive 201 and network control processor 110 because the syste~ns are wholly independent.
A full exchange of data could, of course, be arran~ed between the two systems but in a ~ractical situation, such as where the systems are under ownership of different parties, this exchange is likely to be limited.
In ~he present inven~ion, which seeks to enable continuation of communîcation services, a lirnited data exchange may be accomplished between respective P~X's (such as that between PEX 2Ul and PEX 505) or between S NCP's (such as between NCP 110 and NCP 507). If the two communication systems share the same set of radio frequencies the data line will, in the preferred ernbodiment, be established between the two NCP's via a CIB; if the systerns do not share the same frequencies the data line should be established between the two PEX's also via a CIB.
In order to accomplish the intersystem control, a PT
location file is maintained at each PEX which can share messages, Included in each PEX lo`cation file is a lis~
IS of PT addresses for those PT's which are registered in, and are billed from, that PEX (the "home" system). Also included in the file are the locations of those home PT's which have traveled ("roamed") to another ("roam") system, and the addresses of those PTs which have roamed to this system from another systern.
As diagramed in Fig. 6, the location file consists of three lists: a local file, a local roamer file, and foreign roamer list. The information included in the local or "home PT" rile 608 consists of the PT address, the base transceiver receiv~r's signal stren~th indicator values and priority established thereirom, a pointer to the memory location where messa~es for this PT may be follnd, a time stamp when the last messa~e producing si~nal strength inaication was received, and a roaming pointer to the roamer file if the home PT has roamed.
The roamer file essentially consists of two lists, a local roamer list and a forei~n roamer list. Since ~he local file contains the permanent record of each PT
registered in the home systern and is scanned whenever a message is directed to a PT, a roaming pointer field is included with the PT record ~0~ whenever a home PT roams 6~t to another system. This pointer directs the PEX to the local roamer list and to this specific local roamer record 610 associated with the roaming PT. The roamer record 610 contains a pointer back to the local file, the address of the PEX to which the PT has roamed, and the date and time the PT appeared in the foreign system.
The foreign roamer list contains a "foreign"
PT file 612 which cons.ists of a message location pointer and the address of those "foreign" PTs (PTs not registered or billed in this local system) which have roamed into the local system and which have been active, that is, initiated or received messages within a preceding period of time such as the past 24 hours.
This file is used primarily to allow the PEX to quickly deliver a response to a message directed to a roaming foreign PT by allowing the PEX to search the foreign roamer list and find an address of foreign active PT
rather than causing PEX to send an inquiry back to the foreign PT's home system and receiving a location message. This reduces the amount of traffic between system. D~scription of a similar filing system may be found in U.S. Patent 4,644,351 filed in the name of Zabarsky et al.
An important feature in the present invention, then, is the method for coordinating the message delivery and service grants to roaming PTs. The method employed by ~he preferred embodiment is diagrammed as a flowchart in Fig. 7a and Fig. 7b. It is expected that a PT will generate a series of discontinuous data messages as the PT user uses his PT. Since this equipment is, in the preferred embodiment, a portable unit, it is expected that the user will easily carry - 14a -the PT between radio zones and into an adjacent system.
As he travels across the interface zone, Z8, a decision must be made by the systems to transfer the PT service 5. at some po~nt from one system to the other if continuous service is to be realized. In zone Z8, of Fi~. 5, the PT data message may be received by both the base site 101 receiver and the base site 501 receiver. This reception at two base transceivers of two independent systems is shown as st~ps 701 and 703 in the flowchart of Fig. 7a. Considering first the steps taken by che roam system in the control of the PT communication, the PT message is given an indication of the time of reception (shown as time stamp step 705) and becomes a permanent part of the rnessage.
The zone si~nal stren~th value is then calculated (at step 707) from the SSI signal described previously. The message is stored (at step 708) in the RAM of the ~CP
until a decision is made whether the roam system is to process the message further. A determination of whether the roam system is already yroviding service to this PT
is made at decision block 7~9, where a positive response to this decision allows the PT communications to be processed normally at 711. A ne~ative response moves to step 713. If the PT is to be denied service in this system, such as for nonpa~1lent of bills, a determination is made at step 713 whether this PT is on the "black list" of undesirable units kept as part of the ~orei~n roamer list. A positive response to the decision results in the PT address being reMoved from the syst~m list at 715 and a negative response allows the process to move to step 717. If the PT address is not in the roamer file, as determined at 717, it is placed there at step 71~. A
comparison of the most recent tirne stamp to the last time stalnp and a comparison of current to last message signal stren~th values is made at the decision block 7~1.
A feature of particular advantage in the yre~sent invention is that of employin~ the time stalny recorJe~
Wittl the last received messa~e to determine whether the signal strength values last store~ are "rresh" enou~h to be used in determinin~ the relative position of the highly mobile PTs. Briefly, the tirne stamp may be ~2~
generated by a real time clook at the roam system NCP
receiving the message and coded and stored in numeric or ASCII ~orm with the received message and signal strength representations. Alternately, the real time clock and storage may be maintained at the PEX depending upon the requirement~ of the system. The stored clock values for a previous message may be compared to a newly received message time stamp at the NCP or PEX.
In order to decide whether the time and signal strength representations warrant a transfer of the PT to the roam system from the home system, a comparison is made of the current values at the home system to the values communicated by the roam system. Additionally, if the time stamp and the most recent message received by the roam system is more current than the values stored in the home PEX by a predetermined amount, which in the preferred embodiment is from one to five minutes, it is decided that a transfer is warranted. Alternately, if the two time stamps indicate messayes occurring within the predetermined amount, the largest thr~e adjusted valuPs o~ the stored home system signal strength representations are compared with the most recent received signal strength adjusted values. Current values of one or more adjusted signal strength readings in the roam ~ystem which exceed a predet~rmined threshold, creates a positive response to the decision of whether the values warrant a trans~er. This threshold is empirically determined for each site and is function o~
the terrain, the useable sensitivity of the receivers, and other site-specific parameters.
Given a positive decision at 721, a request is made o~ the home system to veri~y the status of the service-reguesting P~ at 723. A PT status check is made at the home system at 725 and a response is returned to the roam system. Re~erring now to Fig. 7b, if the veriftcation ls negative, the PT addres~ i~ added to the black list and all communication is purged from the receiving NCP at 727.
A nonnegative roamer verification causes the roam system to format a request message for the home syste[n at 729. This message includes the PT address, the received time stamped, and the three largest signal stren~th S values measured by the base transceiver receivers.
The home system receives the request message from the roam system (shown at 731~ via the intersystem data link and the home system decides whether a transfer of the PT is justified based on a site specific predetermined ratio of adjusted signal strength at the roam system to the adjusted signal stren~th at the ho~e system at 733. If the transfer is not justified, a message is returned to the roam system including the time stamp and signal strength representations of the last home system message received. The roam system, then, attempts no further communication with the PT re~arding this latest received message as shown as step 735. If the transfer is justified, a message so statin~ is transmitted to the roam system which responsively enters the YT address zone signal stren~th representations and time stamp into its active file and requests the PT to be recorded as a local roamer in its ho1ne system file throu~h the roam and home PEX at step 737. The horne system subsequently enters the PT address into its roaming file with the current PT location at step 73~.
While the roam system performs its calcula~ions, the home system time stamps the salne received inbound communication from step 7~3 at step 741 and calculates the zone si~nal stren~th representations at step 743. If the transfer is not justified as described previously for stép 733, the home system processes the PT communica~ion n a normal fashLon at step 745.
A similar method of PT transi-er occurs when the`~T
returns into its home systeM. A ~lowchart describin~ a preferred embodiment is shown in Fi~s. ~a and ~b. A
transmission from a PT which has previously left the ii9 Ei6~
coverage areas of its home system and has obtained service from a roam system may be received in both the roam and the home systems (as indicated at 801 and 803).
Since both systems can provide service, a decision must again be made whether to transfer the message providing service back to the home syste~. As in the transfer from the home system to the roam system described in the method of Figs. 7a and 7b, the system currently providing service rnakes the final determination whether a transfer of communication services should occur. The system not providing service but receiving the ~T transmission, however, may request transfer of communications.
Returning to Fig. 8a, upon receiving a transmission from ~T, both the service-providing roam system and the home systela time stamp the incoming cornmunication and calculate the zone signal strength values (shown at steps 805, ~7 and 809, 811 respectively). The home s~stem subsequently determines if the PT is being serviced from the home system (at step 813) and if the PT address is on the black list (at step ~15). Given that the address of the PT whose transmission has been received is currently in the local roamer file but is neither on the black list nor currently served from the home system, a determination is made at step 819 if the time stamp and signal strength representations warrant a transfer to the home system. If the representations warrant a transfer, a message is formatted and transmitted (at step ~21) to the roarn sys~em providing service (as recorded in the local roamer file). The home system need not obtain PT
address verification from any other system because the holne system itself maintains the service verification i-or its home PTs.
The roam system receive~s the home system transfer request (at 823) and determines whether a transfer is justifi~d (at 825 in Fig. 8b). If the transfer is granted, a message is sent to the home system (at ~27) ~ ;96~(~
and-the home system in response enters the zone signal stren~ths into the PT home file at ~9 and removes the PT
address from the local roamin~ file at ~31. The ro~n system deletes the PT address from its forei~n roamer file (at 833) following its grant of communication transfer. If the transfer is not granted the roam system notifies the home system (which does not respond to the PT's transmission at 835) and processes the PT's transmission in a normal fashion at ~7.
Thus, coordination between at least two independent communication systerns may be achieved with the present invention. A radio transmission by a physically ,nobile PT may be received by receivers in the plurality of systems thereby making a decision process necessary in order to select a system and provide optimum communications capability tor the PT user. Although it is possible for all decisions to be made by the PT's home system, an extensive aEnount o~ interface between the home system and a roam system would be required~ The present invention enables the decision as to which system can provide the best communication to be maae by the system last ~rovidin~ service to the PT. ~ request ~y another system to transfer communication service cannot be made unless the radio si~nal stren~th and timin~ of the PT
transmission meet certain unique requirements.
Therefore, while a particular embodiment of the invention has been described and shown, it shouLd be understood that the invention is not limited thereto since many modifications may be made those skilled in the art. It is therefore contemplated to cover by the present application any and all such modifications that tall within the true spirit and scope of the basic underlying principles disclosed and claimed herein.
I clai~:
Claims (15)
1. A coordinating apparatus for transfer of communications processing from a first independent communications system to a second independent communications system, each system having a plurality of fixed sites associated therewith and providing at least one radio channel at each fixed site which may be employed by a remote unit for communication of discontinuous messages, the coordinating apparatus comprising:
means at a first fixed site, associated with the first communications system, for receiving a first message from the remote unit and for calculating and storing a radio signal strength representation for said first message;
means at a second fixed site, associated with the second communications system, for receiving a second message and calculating a radio signal strength representation for said second message from the remote unit;
means at said second fixed site for comparing said second message signal strength representation to a threshold representation and, responsive to said comparison, for conveying said second message signal strength representation and for requesting permission from said first fixed site to process said second message; and means at said first fixed site, responsive to said permission request for comparing said second message signal strength representation to said stored first message signal strength representation and for granting said second fixed site request in response to said first and second signal strength representation comparison result, thereby transferring said remote unit communications processing from the first communications system to the second communication system.
means at a first fixed site, associated with the first communications system, for receiving a first message from the remote unit and for calculating and storing a radio signal strength representation for said first message;
means at a second fixed site, associated with the second communications system, for receiving a second message and calculating a radio signal strength representation for said second message from the remote unit;
means at said second fixed site for comparing said second message signal strength representation to a threshold representation and, responsive to said comparison, for conveying said second message signal strength representation and for requesting permission from said first fixed site to process said second message; and means at said first fixed site, responsive to said permission request for comparing said second message signal strength representation to said stored first message signal strength representation and for granting said second fixed site request in response to said first and second signal strength representation comparison result, thereby transferring said remote unit communications processing from the first communications system to the second communication system.
2. A coordinating apparatus in accordance with claim 1 further comprising means at said first and second fixed sites for inserting a time stamp in any message received, thereby indicating the time of message reception.
3. A coordinating apparatus in accordance with claim 2 further comprising means at said second fixed site for receiving said first message, calculating a signal strength representation at said second fixed site for said first message, inserting a time stamp in said first message, and storing said time stamp, said representation, and said first message.
4. A coordinating apparatus in accordance with claim 3 further comprising means for generating said thershold representation at said second fixed site from said first message signal strength representation stored at said second fixed site.
5. A coordinating apparatus in accordance with claim 3 further comprising means at said second fixed site for recalling said first message time stamp and comparing said first message time stamp to said second message time stamp.
6. A coordinating apparatus in accordance with claim 5 further comprising means at said second fixed site, responsive to said time stamp comparison indicating a difference in time greater than a predetermined amount, for requesting permission from said first fixed site to process said second message.
7. A coordinating apparatus in accordance with claim 1 wherein said first and said second messages are the same message received at said first and said second fixed sites, respectively.
8. A coordinating apparatus in accordance with claim 1 wherein said first and second fixed sites each further comprise at least two base transceivers with unique radio coverage zones.
9. A coordinating apparatus in accordance with claim 1 wherein said signal strength representation of said first and second messages further comprises signal strength values from each base transceiver of said first and second fixed sites.
10. A method of coordinating transfer of communications processing from a first independent communications system to a second independent system, each system having a plurality of fixed sites associated therewith and providing at least one radio channel at each fixed site which may be employed by a remote unit for communication of discontinuous messages, the method of coordinating transfer comprising the steps of:
receiving, at a first fixed site associated with the first communications system, a first message from the remote unit and calculating and storing a radio signal strength representation for said first message;
receiving a second message from the remote unit and calculating a radio signal strength representation for said second message at a second fixed site associated with the second communication system;
comparing, at said second fixed site, said second message signal strength representation to a threshold representation and, responsive to said comparison result, requesting permission from said first fixed site to process said second message; and comparing, in response to said request, said second message signal strength representation to said stored first mesage signal strength representation at said first fixed site and granting said second fixed site request in response to said first and second signal strength representation comparison result, thereby transferring said remote unit communications processing from the first communications system to the second communications system.
receiving, at a first fixed site associated with the first communications system, a first message from the remote unit and calculating and storing a radio signal strength representation for said first message;
receiving a second message from the remote unit and calculating a radio signal strength representation for said second message at a second fixed site associated with the second communication system;
comparing, at said second fixed site, said second message signal strength representation to a threshold representation and, responsive to said comparison result, requesting permission from said first fixed site to process said second message; and comparing, in response to said request, said second message signal strength representation to said stored first mesage signal strength representation at said first fixed site and granting said second fixed site request in response to said first and second signal strength representation comparison result, thereby transferring said remote unit communications processing from the first communications system to the second communications system.
11. A method in accordance with the method of claim 10 further comprising the step of inserting a time stamp in any message received at said first and second fixed sites, thereby indicating the time of message reception.
12. A method in accordance with the method of claim 11 further comprising the steps of receiving said first message at said second fixed site, calculating a signal strength representation at said second fixed site for said first message, inserting a time stamp in said first message, and storing said time stamp, said representation, and said first message at said first fixed site.
13. A method in accordance with the method of claim 12 further comprising the step of generating said threshold representation at said second fixed site from said first message signal strength representation stored at said second fixed site.
14. A method in accordance with the method of claim 12 further comprising the steps of recalling said first message time stamp and comparing said first message time stamp to said second message time stamp at said second fixed site.
15. A method in accordance with the method of claim 14 further comprising the step of requesting permission by said second fixed site from said first fixed site to process said second message in response to said time stamp comparison step indicating a difference greater than a predetermined amount.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US802,922 | 1985-11-29 | ||
| US06/802,922 US4670905A (en) | 1985-11-29 | 1985-11-29 | Method and apparatus for coordinating independent communications systems |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1259660A true CA1259660A (en) | 1989-09-19 |
Family
ID=25185096
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000522440A Expired CA1259660A (en) | 1985-11-29 | 1986-11-07 | Method and apparatus for coordinating independent communications systems |
Country Status (4)
| Country | Link |
|---|---|
| US (1) | US4670905A (en) |
| EP (1) | EP0247192A1 (en) |
| CA (1) | CA1259660A (en) |
| WO (1) | WO1987003438A1 (en) |
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-
1985
- 1985-11-29 US US06/802,922 patent/US4670905A/en not_active Expired - Lifetime
-
1986
- 1986-11-07 CA CA000522440A patent/CA1259660A/en not_active Expired
- 1986-11-26 WO PCT/US1986/002587 patent/WO1987003438A1/en unknown
- 1986-11-26 EP EP87900448A patent/EP0247192A1/en not_active Withdrawn
Also Published As
| Publication number | Publication date |
|---|---|
| EP0247192A1 (en) | 1987-12-02 |
| US4670905A (en) | 1987-06-02 |
| WO1987003438A1 (en) | 1987-06-04 |
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