SOFT HANDOFF METHOD AND APPARATUS

Abstract: Disclosed is a method and apparatus for establishing an inter-system soft handoff using a direct base station to base station standardized protocol connection over a network which bypasses the time consuming prior art MSC to MSC communication link using the IS-41 protocol. This new protocol has recently received industry agreement for use between different type architecture CDMA systems and uses A7 and A3 protocols as defined in IS-634 rev A.

Description: SOFT HANDOFF METHOD AND APPARATUS This Application is a continuation in part of and claims the benefit of U.S. Provisional Application Number 60/053,939, filed 29 July 1997. TECHNICAL FIELD The present invention relates in general to soft handoffs and in particular to methods and systems for establishing soft handoffs between two CDMA base stations (BSs) using a direct base station (BS) to BS link even where the SDUs associated to the BS comprise part of different configuration systems. BACKGROUND When a mobile station (MS) , in a cellular communication system, crosses from one cell to another adjacent cell a process designated as handoff is initiated. Handoff is the process by which a new air interface channel between a mobile station and a base station is established. There are several types of handoff in the wireless communication industry. A "hard handoff" is a handoff which requires a mobile station to tune its radio equipment or to reestablish synchronization. A "soft handoff" is a handoff that does not require the mobile station to tune its radio equipment or to reestablish synchronization and that uses the same frame selection function for (and voice trans-coding function, if this is a voice call) in the network for both the old and new air interface channels. Other types of handoffs, such as a semi soft handoff, are not pertinent to an understanding of the present invention. At the present time, only code division multiple access (CDMA) wireless communication systems are capable of accomplishing soft handoffs. In a CDMA wireless communication system, using cellular transmission technology, the process of establishing a soft handoff from the time an MS sees a new pilot signal, received from a nearby base transceiver station (BTS) defining another cell, to the time an MS sends a handoff completion message can be segregated into at least three phases . Phase 1 may be defined as occurring from the time the MS sees a new pilot to the time that the pilot strength exceeds a predetermined threshold and may be referred to as the detection phase. Phase 2 may be defined as occurring between the time an MS sends a pilot strength measurement (PSM) message until it receives a handoff direction message and may be referred to as the establishing phase (when successful) . Phase 3 may be defined as the time from when an MS receives a handoff direction message to the time the MS sends a handoff completion message and may be referred to as the completion phase. As is well-known in the art, many standards are used by the communication industry to define functional standards by which communication equipment will operate so that equipment from various manufacturers may compatibly inter-operate. One such standard is IS-95 Revision A entitled "Mobile Station - Base Station Compatibility Standard for Dual-Mode Wideband Spread Spectrum Cellular Systems; May, 1995". Another standard is IS-634 Rev A ballot version dated April 20, 1997 entitled "MSC BS Interface for Public Wireless Communication" that among other items defines radio access to switch or intr-system interfaces. A further standard mentioned in this document is IS-41-C entitled "Cellular Radiotelecommunications Intersystem Operations; 1996". Each of these standards are incorporated herein by reference. The IS-634 standard has defined and standardized communications between a mobile switching center (MSC) and a BS by industry agreement such that different manufacturers equipment could be combined into a composite cellular system by a user. However this standard has not previously attempted to standardize any signaling messages between base stations. Thus, signaling messages bound from a source base station to a target base station, must be first relayed to an MSC in a standardized manner and protocol before being received by the target base station. To support soft handoff of an MS moving from one cell to another, adjacent cells must operate at the same frequency. Once an MS detects a new pilot, the MS may experience same frequency interference from adjacent cells. In accordance with the standards of IS-95, 12 consecutive bad frames detected by an MS may cause the MS to drop a call. The total network processing time that may cause a call to be dropped is primarily a function of the phase 2 time period. At this time the received signal has already degraded enough that a handoff has been requested. This typically means that the MS is still moving away from its signal source. Thus the degradation of received signal quality, before handoff completion, may result in the occurrence of 12 consecutive bad frames as detected by the MS. One prior art system used 12 steps and including the transmission of 12 messages for an intra-system inter-BS handoff during phase 2. The series of setup and request messages went from the MS, to the serving BTS, to the selection/distribution unit (SDU) , the serving base station controller (BSC) , the mobile switching center (MSC) , the target BSC, and the target BTS. The response messages came from the target BTS to the target BSC, the MSC, the serving BSC, the SDU and finally the serving BTS. For an inter-system handoff, at least 14 steps were completed because of the extra MSC and even the STP involved in both directions. It takes time to successfully transmit a message and to process the message after receipt. It will be apparent that the time required to complete the referenced 14 steps must occur prior to the length of time it takes the MS to move to a position where the quality of the signal received by the MS has degraded to a point whereby the MS detects 12 consecutive bad frames. This time problem is especially severe when the MSC is involved in many administrative tasks other than call processing. Thus a system whereby the number of steps involved and the number of messages transmitted could be reduced for the establishment process of phase 2 would lessen the chances of a call being dropped due to extensive time required to complete this phase. The elimination of the MSC from the message path, even where there was no reduction in number of steps involved, due to a required addition of dedicated processing entities, would also reduce the time required to complete phase 2 in some circumstances. It would further be desirable, if base stations, whether identical or made by different manufacturers, could communicate directly with one another to establish a soft handoff of an MS across cellular boundaries of communication cells managed by different base stations. One attempt to solve the above problem was presented in a patent application assigned to the assignee of the present invention, filed April 7, 1998, entitled "METHODS AND SYSTEMS FOR STANDARDIZING INTER BASE STATION COMMUNICATIONS" and having a filing number designation of 09/056,370. There are two architectures supported in the referenced IS- 634 standard. An Architecture A network infrastructure is distinguished by the fact that the voice coding and frame selection function of the SDU is always located at the source base station. An Architecture B network infrastructure is distinguished by the fact that the voice coding and frame selection function of the SDU is located remote from the source base station and thus requires the use of an A4 communication interface as defined in the standard. A typical location for the SDU in an architecture B network is in the MSC although it may, if so desired, be physically isolated from the rest of the system. The above referenced patent application does not address a solution to the quicker establishment of soft handoffs between base stations comprising part of different architecture systems . SUMMARY OF THE INVENTION The present invention comprises providing a soft handoff signaling channel or communication link directly between source and target systems. This communication link in combination with an enhanced signaling link from the source SDU to the target BS, operate to permit the transmission of both signaling and voice information from the SDU, and removes the involvement of the MSC from the soft handoff establishing phase process. BRIEF DESCRIPTION OF THE DRAWINGS For a more complete understanding of the present invention, and its advantages, reference will now be made in the following Detailed Description to the accompanying drawings, in which: FIGURE 1 is a basic block diagram illustrating the mechanism whereby a soft handoff occurred in the prior art regardless of network architecture; FIGURE 2 is a basic block diagram illustrating the mechanism whereby a soft handoff occurred in the prior art between architecture A networks as described in the above referenced patent application; FIGURE 3 is a basic block diagram illustrating the mechanism for providing a direct link for soft handoff between architecture B networks instead of involving IS-41 in the soft handoff establishing phase; FIGURE 4 is a basic block diagram illustrating the mechanism for providing a soft handoff between architecture A and architecture B networks; FIGURE 5 is a block diagram illustrating the mechanism for providing a soft handoff where the source, of an inter- architecture soft handoff, is an architecture B type network; FIGURE 6 is a block diagram illustrating the mechanism for providing a soft handoff where the source, of an inter- architecture soft handoff, is an architecture A type network; FIGURE 7 illustrates, in a message time sequence diagram form, a methodology of the establishment phase of a soft handoff between two type A architecture systems; FIGURE 8 illustrates, in a message time sequence diagram form, a methodology of the establishment phase of a soft handoff between two type B architecture systems; FIGURE 9 illustrates, in a message time sequence diagram form, a methodology of the establishment phase of a soft handoff between two systems where the source is a type A architecture and the target is type B architecture; and FIGURE 10 illustrates, in a message time sequence diagram form, a methodology of the establishment phase of a soft handoff between two systems where the source is a type B architecture and the target is type A architecture. DETAILED DESCRIPTION The referenced copending application is directed to the idea of adding a communication link between base stations to bypass or eliminate the requirement of signals passing through the MSC. The concept as presented therein is not readily implementable as applied to CDMA architecture B type systems or to a SHO. between systems having different architecture types. In this application, separate signaling and traffic links are utilized to allow inter-system soft handoff operations to bypass the MSC whether the systems are both architecture type B, or both type A or between different architecture types . This is accomplished by using 3 links, as will be explained in greater detail later, A7 signaling, A3 signaling and A3 traffic. Each link may terminate logically at different entities in different architecture type systems. This flexibility of link termination provides the inter-operability necessary in establishing direct links between certain entities in different architecture type systems and as required to remove the involvement of the MSC from the soft handoff establishing phase of the operation. In FIGURE 1 a block designated as MSC is also labeled 10. MSC 10 is connected via a communication link 12 to a cloud designated as 14 and also labeled STP . STP refers to a signal transfer point, gateway or other signal switching network such as the public switched telephone network (PSTN) . The link 12 transfers data according to an IS-41 protocol as referenced in the previously mentioned industry standard. Cloud 14 is further connected via a link 16 to a further MSC block 18. Link 16 also conforms to the IS-41 protocol. A base station block 20 is connected via a communication link 22 to MSC 18. The communication link 22 conforms to IS-634 standards. A further base station 24 is connected via a communication link 26 to MSC 10. Link 26 also conforms to the IS-634 protocol. A circle 28 represents a mobile station (MS) that is moving from the base station 24 towards base station 20. An airwave communication link 30 represents communications between MS 28 and base station 24. A dash line 32 represents airwave communications between MS 28 and base station 20. The cellular system represented by blocks 10 and 24 may be either an architecture A or architecture B type system as defined in IS-634. As shown in the drawing, the same applies to a second cellular system represented by blocks 18 and 20. Figure 2 provides the basic components involved in a soft handoff between two systems conforming to architecture A. This is the model used in the referenced patent application. An MSC block 40 communicates over a link 42, through a cloud 44 and a further link 46 with a second MSC 48 in the same manner as shown in FIGURE 1. MSC 40 also communicates with a BS 50 over a link 52 conforming to IS- 634 standards. A further BS 54 communicates with MSC 48 over a communication link 56 where 56 is IS-634 compliant. Both BSs 50 and 54 actually comprise at least one BSC and normally a plurality of BTSs . A communication link is shown providing a direct connection between a voice and signaling (V/S) portion of BS 50 and a similar portion of BS 54. The V/S portion in most CDMA systems comprise an SDU and associated soft handoff controller (SHC) . A interconnection function (ICF) block (not shown) may be required in older system designs to transmit data over the link 58 in a protocol that complies with an accepted industry standard. As shown in FIGURE 1, the mobile station 28 has been communicating with base station 24. As MS 28 moves towards the base station 20, the mobile station 28 receives pilot signals from BS 20 of increasing amplitude. When the signals exceeded a predefined value, the mobile station 28 informs base station 24 that it wants to be transferred to the system represented by base station 20. The base station 24 informs MSC 10 which transfers messages over communication link 12 through STP 14 and eventually to BS 20. BS 20 allocates resources so that it may communicate with mobile station 28. Messages are then sent back through STP 14 to base station 24 to acknowledge that BS 20 is prepared to complete a connection with mobile station 28. The process of transferring these messages and the many steps involved, when using only MSC to MSC communication, is set forth in detail in the referenced patent application. The referenced patent application is directed to the idea of providing direct BS to BS signaling to establish the soft handoff connection. As presented, the invention suggested that one method of accomplishing this soft handoff signaling link is to enhance an existing voice and signaling communication channel designated in the standards as A3. Such a system is illustrated in FIGURE 2. FIGURE 3 shows the same concept applied to a handoff between architecture B type systems. As shown, one system comprises an MSC 70 and a BS 72. A second system comprises an MSC 74 and a BS 76. IS-41 links connect the two MSCs together via an STP cloud 78. A direct link labeled as 80 provides signaling and voice communication between the appropriate components of the two systems necessary to establish a soft handoff. Non designated communication links interconnect the MSC and its associated BS and these links are IS-634 compliant. While the number of message steps saved may be slightly less than occurs between two architecture A systems, the time saved may still be significant . A further significant advantage will be apparent from an examination of FIGURE 4 where a soft handoff is shown occurring between two different architecture type systems. An architecture B system is shown having the basic components of an MSC 90 and a BS 92. An architecture A system is shown having the basic components of an MSC 94 and a BS 96. IS-41 links connect the two MSCs together via an STP cloud 98. A V/S to V/S direct link labeled as 100 provides signaling and voice communication between the appropriate components of the two systems necessary to establish a soft handoff. Non designated communication links interconnect the MSC and its associated BS and these links are IS-634 compliant. By setting up a standardized protocol whereby each of the links 58, 80 and 100 in the appropriate FIGURES 2, 3 and 4 conform to the same communication standard, any architecture type system may establish a soft handoff with another system without having to pass the establishing messages to the STP cloud. The inter-operability approach set forth in FIGURE 4 is expanded upon in FIGURES 5 and 6 and the manner in which messages are exchanged between systems for four different source and target combination possibilities is presented in FIGURES 7 through 10. In FIGURE 5, a network or switch mechanism labeled as STP and given a designation of 110 is connected to each of a plurality of MSC blocks 112, 114, 116 and 118 over IS-41 compliant communication links. MSCs 112 and 114 provide the main switch function for two architecture A type cellular systems. MSCs 116 and 118 provide the main switch function for two architecture B type cellular systems. Each of the MSCs is connected to base station equipment over IS-634 compliant communication links. MSC 112 controls a BSC 120 which in turn controls a first plurality of BTSs 122 and a second plurality of BTSs 124. Internal to BSC block 120 there is shown an SDU block 126. MSC 114 controls a BSC 128 which in turn controls a plurality of BTSs 130. Internal to BSC block 128 there is shown an SDU block 132. MSC 116 controls a BSC 134 which in turn controls a plurality of BTSs 136. Internal to MSC block 116 there is shown an SDU block 138. MSC 118 controls a BSC 140 which in turn controls a plurality of BTSs 142. Internal to MSC block 118 there is shown an SDU block 144. Three asynchronous transfer mode (ATM) clouds 146, 148 and 150 provide direct V/S to V/S interconnection between the four cellular systems. The connections are shown as solid, dashed and dotted lines for different types of communications. The bold solid lines designated A3T represents A3 protocol voice or data (traffic) packets, the dotted line designated as A3S represents A3 protocol signaling data packets and the dash line designated as A7 represents a data packet protocol for passing resource allocation signaling type messages. Three different MS blocks are designated as 152, 154 and 156. MS 152 is shown as being handed off from a source system using one of the BTSs 124 to a target system using one of the BTSs 130. Similarly, MS 154 is shown as being handed off from one of a set of source BTS 136 to one of the set of target BTSs 130. Finally, MS 156 is illustrated as being handed off from one of the source BTSs 136 to one of the target BTSs 142. The cellular systems using BSCs 120 and 134 are further labeled SOURCE while the systems using BSCs 128 and 140 are further labeled TARGET in accordance with the above paragraph. The A3 and A7 communication links as shown are used to help illustrate the paths messages travel in performing a soft handoff between a source system and a target system in the practice of this invention. When the source and target systems are both architecture A type systems all communications take place between the BSCs as shown in connection with ATM 146. The A3 protocol signaling and voice messages are transferred between the BSs in each of the two systems . The A7 resource allocation messages are transferred between the soft handoff controllers internal the respective BSCs to transfer a handoff request and the response acknowledgement to that request between the appropriate BTS entities. In FIGURE 6, a network or switch mechanism labeled as STP and given a designation of 200 is connected to each of a plurality of MSC blocks 202, 204, 206 and 208 over IS-41 compliant communication links. MSCs 202 and 204 provide the main switch function for two architecture A type cellular systems. MSCs 206 and 208 provide the main switch function for two architecture B type cellular systems. Each of the MSCs is connected to base station equipment over IS-634 compliant communication links. MSC 202 controls a BSC 210 which in turn controls a first plurality of BTSs 212 and a second plurality of BTSs 214. Internal to BSC block 210 there is shown an SDU block 216. MSC 204 controls a BSC 218 which in turn controls a plurality of BTSs 220. Internal to BSC block 218 there is shown an SDU block 222. MSC 206 controls a BSC 224 which in turn controls a plurality of BTSs 226. Internal to MSC block 206 there is shown an SDU block 228. MSC 208 controls a BSC 230 which in turn controls a plurality of BTSs 232. Internal to MSC block 208 there is shown an SDU block 234. Three asynchronous transfer mode (ATM) clouds 236, 238 and 240 provide direct V/S to V/S interconnection between the four cellular systems. The connections are shown as solid, dashed and dotted lines for different types of communications. The bold solid lines designated A3T represents A3 protocol voice (traffic) data packets, the dotted line designated as A3S represents A3 protocol signaling data packets and the dash line designated as A7 represents a data packet protocol for passing resource allocation signaling type messages. Three different MS blocks are designated as 242, 244 and 246. MS 242 is shown as being handed off from a source system using a BTS such as 220 to a target system using one of the BTSs such as 214. Similarly, MS 244 is shown as being handed off from one of a set of source BTSs 220 to one of the set of target BTSs 226. Finally, MS 246 is illustrated as being handed off from one of the source BTSs 232 to one of the target BTSs 226. The cellular systems using BSCs 218 and 230 are further labeled SOURCE while the systems using BSCs 210 and 224 are further labeled TARGET in accordance with the above paragraph. The A3 and A7 communication links as shown are used to help illustrate the paths messages travel in performing a soft handoff between a source system and a target system in the practice of this invention. When the source and target systems are both architecture A type systems, all communications take place between the BSCs as shown in connection with ATM 236 in the same manner as discussed in connection with FIGURE 5. The same holds true when the source and target systems are both architecture B type systems. The differences occur when the source and target systems are of different types. This will be further explained in connection with the following figures. In FIGURE 7 an MS is labeled 300 and is shown sending a pilot strength measurement signal to a BS block 302 which represents a combination of BTS/SDU/SHC/ICF entities since the communication link interconnections of these entities are proprietary to each manufacturer. The block 302 and an MSC1 block 304 represent a source system. An MSC2 block 306 in combination with a BS block 308 represents a target system. As above the block 308 represents a combination of BTS/SDU/SHC/ICF entities. As mentioned previously, the messages passed illustrate the time sequence of messages, labeled from "a" to "1", when a soft handoff is being established between two type A systems. This would be representative of a soft handoff between the two left hand systems of either FIGURES 5 or 6. When the source BS determines that one or more cells at a target BS are needed to support an already established call, it sends an A7 Handoff Request to the target BS as shown in line "b" . The target BS initiates an A3S connection by sending a Connect message in return. (Although only one connect message is shown, multiple connect messages may occur if the request includes multiple cells.) Acknowledgments soon follow both the HO request and connect messages . Forward frames are commenced from the source to the target BS as shown in line "f" as soon as synchronization is established. A message is then sent to the target BS to begin forwarding traffic frames to the MS as set forth in lines "g" and "h" . An acknowledgement message is sent in line "j". After the extended HO direction message is sent, the source MSC is informed that the HO has been performed. As set forth above, the MSC is bypassed from the establishment phase and is merely informed that the HO is complete after the fact . The messages used in the establishment phase of a soft handoff between B architecture type systems in accordance with this invention are presented in FIGURE 8. As mentioned previously, the SDU in B architecture type systems is not located in the base station. It may be isolated by itself but is often found in proximity to an MSC as shown in both FIGURES 5 and 6. A MS labeled as 350 may represent either MS 156 in FIGURE 5 or MS 246 in FIGURE 6. A BSC block 352, an SDU block 354 and an MSC1 block 356 represent a source system through which the MS 350 has been communicating. In FIGURE 5 this would be the system having MSC 116 while in FIGURE 6 it would be the system having MSC 208. A MSC2 block 358, a BSC block 360 and a BTS block 362 represent a target system such as shown and labeled in FIGURES 5 and 6. As shown, the pilot strength measurement signal is sent to the SDU 354 via an A3 communication link. As will be apparent to those skilled in the art, the A3 communication link is distinct from the previously 'discussed A3S and A3T communication links although the protocol used is the same. A HO Request, as shown on line "c", is sent on an A4 communication link to the BSC represented by 352. This request is then forwarded, as shown on line "d", over the A7 communication link to BSC 360 and is forwarded over a proprietary link to the BTS 362 representing an appropriate target BTS. A connect signal is returned to the source SDU 354 over an A3S communication link as shown on line "e" . The remaining signals utilized in establishing SHO in a type B architecture system are shown and a comparison with either FIGURE 5 or 6 will disclose the signal paths used to provide the communication link. As before, the MSC is not involved until the handoff is completed and a HO performed message is sent from the BSC to the MSC as shown in line "o" over communication link A7. The signaling messages are substantially identical in both FIGURES 7 and 8 although some need to be forwarded in accordance with established protocols over standardized communication links, such as A4 and A3. In FIGURE 9, a signal transfer methodology is shown for establishing a SHO between a source type B architecture system and a target type B architecture system. A block 400 represents an MS such as 154 in FIGURE 5. A BSC block 402, an SDU block 404 and an MSC1 block 406 represents components of the source system in FIGURE 5 having MSC 116. A target MSC2 block 408 and a BSC block 410 are representative of the system shown having MSC 114. As in FIGURE 7, the block 410 includes at least the functional entities ICF, SHC and BTS used to respond to the intersystem messages used in this invention. In a manner identical to FIGURE 8, the BSC 402 forwards a HO request message subsequent to the occurrence of an appropriate pilot strength measurement message of line "a" and a resulting HO request message of line "b" . This HO request message is received over communication link A7 from a BSC such as 134 in FIGURE 5. A connect message, as shown on line "d" , is returned over an A3S communication link to the SDU such as 138. As shown, acknowledgment message of lines "e" and "f" are sent over communication links A3S and A7 respectively to the entities shown. The remaining messages and communication links used are self evident in view of the material already discussed. The messages provided in FIGURE 10 illustrate the entities involved in establishing a SHO between a source architecture A type system and a target architecture B type system such as may occur in connection with MS 244 in FIGURE 6. A block 450 represents an MS while a BS block 452 and a MSCl block 454 represent a source system through which the MS has been communicating. The BS block 452 includes, as before, at least entities such as a BTS, a SDU, a SHC and an ICF. A target system is represented by MSC2 block 456, a BSC block 458 and a BTS block 460. The HO request message is sent over the A7 communication link to BSC 458 which is inherently programed to forward same over a communication link, proprietary to type B architecture systems, to a BTS as represented by block 460 and such as one of those designated as 226 in FIGURE 6. A connect signal is returned over the A3S communication link and then acknowledgments follow as described previously, The remaining messages are transmitted and, when the SHO operation is completed, a message is sent to the MSC 454 and designated as 204 in FIGURE 6 that the HO has been performed. Thus the MSC again is not involved in the establishment phase until it is completed and thus does not act to impede the time required to complete the SHO operation. The present invention thus establishes a methodology that not only bypasses the MSC when attempting a SHO operation between type A architecture systems as shown in the referenced patent application, but allows the MSC bypassing when attempting a SHO between different type systems. A standardized set of signals is set forth herein whereby all CDMA systems can communicate for the purpose of establishing a SHO without involving the MSC. For the messages involved in the establishing phase as well as in the release phase, Appendix A provides an example set of message-layout and information elements. Although the invention has been described with reference to specific embodiments, these descriptions are not meant to be construed in a limiting sense. Various modifications of the disclosed embodiments, as well as alternative embodiments of the invention, will become apparent to persons skilled in the art upon reference to the description of the invention. It is therefore, contemplated that the claims will cover any such modifications or embodiments that fall within the true scope and spirit of the invention. I Appendix: Message Layout and Information Elements 2 : : ~ 3 4 Nol?: The secϋon numbers are refeπed (o IS-6J tev Λ ballυi version, daled April 20, 5 1997. 9 B.1.X.X PMC_A3 HO ngquont 10 T his tiiessage is sent from ilie source US io the laigct i)S lo ϊTϊϋicate dial for a given MS I I which already lias a dedicated radio resource assigned, a handoff is requited. 12 13 Allowable cause values arc: Soft linn-doff; Uplink quality; Uplink 14 strength; Downlink quality; Do nlink strcngUt; Distance; Interference; 15 belter cell (I.e., Power butlgct); ιcstx.ιιsc to MSC Invocaϋon; OΛMAP 16 Intervention; IS-41 Invocation; pi i vale options. 17 This element contains the im-lcπαl list of tatget cells In order of 18 predJcted best performance. 19 c. Tills element Indicates llic signaling modes the mobile Is capable of 20 opctatlng In. 21 Used for 15-95 soil hnndoll i-nκ cdmcs, when the source BS needs to 22 convey sub-tale circuit Inlutmntion to die tatget BS. Λ maximum of 5 23 Instances of ϋtls element can be included In this message. APPENDIX Λ - Page I . ol 19. 1 e. Conveys ctnieiil Voice Privacy mode, as well as eitiier Voice Privacy or 2 Signaling Message Iinciypiioii Keys, if sipplicable. 3 r. T his clciiiciit provides the signaling type thai the mobile is cuiienlly 4 using, Only one is pcimitiπl. 5 g. Specifics the current I V5 ( 'lιaιιιιcl(s). 6 It. T his clement Is tcψriu d loi IS-V5 liandolf and musl contain llic 7 mobile's I3SN, so lliat (li tai ei US can calculate die Public Long 8 Code Mask. Λ maximum ol iwυ instances of Uiis element may be 9 included, In which case the fust instance will contain Uic MI /IMSI. I U I. T ills element provides infoi malhm (υi each cell in die Cell Identifier 1 1 List clement. 12 J. Only icqulicd for niulli -cell IKS's. Disc minator types I, 2 or 5 must 13 be used. 14 k. ' I Ids clement Indicates llic cuncnl lιπ|ucιιcy band dial die MS is 15 operaUng on. 16 I. T is element Indicates the in -nested set vice conllgtirndon. 17 m. Hiese elements ate icqtiiicd when a packet mode channel Is being used 18 to suppott lite call. 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 APPENDIX Λ - I'πgc 2. of 19. 47 48 49 50 6.1.X.X PMC.A3 HO noqU9»( Λck T his message Is sent from t e tarp.el US tυ the stance DS. in iesjxH.se lo die l'Mθ HO Request, to indicate llial a target channel lias been allocated for handoff as requested. Tids message is also used lo Initiate a layer 3 connection to siψpυit die lansfer of user ύiforniadon for a newly added radio link in suit liandυlf . Information Element Ittf. Direction Type I'MC Message Type Section 6.2.2... laιgct_ϋS->Source_BS M Call Connection Refetence Section 6.2.2.9R lnrgct_BS->Sot_rce_BS M IS-95 Clianncl ldendty Section 6.2.2.10 i aιget_BS • > Sourcc_BS M Cell Identity Section 6.2.2.20 I at eLBS -> Source_BS M CEID Section 0.2.2.x • >. iι.tget_BS->Source_BS M CE_Node ID Section 6.2.2.xx i__ge(_BS->Sot-rce_BS M Λ3_TraIDc Circuit ID Section 6.2.2.96 lπrgel„BS->Sot-rce_BS M ΛJ ltaiαcCoanecdonlD Section 6.2.2.9/ latgelj3S->Sotιrce_BS M Tag Section 6.2.2..ι2 lnrget_BS->Source_BS O SDU ID Section 6.2.2.91 lnjgct_BS->Sot_rce_BS O SDU Node ID Section 6.2.2.90 l gcl_BS->Source_BS 0 l'MC_Λ3 CεU lnlotniadon Record Section 6.2.2. R9 laiget_BS->Source_BS 0 Bxteodcd lL_ndo_I Dliecϋoa Parainetcts Section 6.2.2 /3 laιgct_BS->Sot-tce_BS 0 a. Included If the olr .mαlncc .linnncl nllocaled by the target Is ΛNSl/EIMIΛ-553, 15-91. IS- . b. Included If the air Inicifncc channel allocaietl by Hie target Is 1S-95. It lists IS-95 channels that have 1-ccιι allocated by tl>e target BS. c. Λ maxlimim of 5 Channel Hiimiicr elements may be included In this message. APPENDIX Λ - P.tgc 3. <>! ' 19. • 1 d. Needed by source US lot soil hniidoll (SHU) Drop Target message raid 2 for llaiidofr I'cifotmcd message. 3 e. Included If nil 15-95 sort liandoll pi o cduic is being pc-fυπιιed for a call 4 dial requires a leπcsliial citαiit. Λ mn.xiti_uin or 5 instances of dils 5 - element may be Included, l lic order ol die ciict t Identities must match 6 die otdcr of die Cliaiinel Ninuhci elements and die order of die IS-95 7 channels listed In die 15-95 Channel Ii. element, so that die source DS 8 can determine which ciicnii is connected lo which laigel lS-95 channel. 9 f. Por 15-54 only. I U g. Por 1S-95 sofl liandoll di p somce pioccduie. Tlic target US may 1 1 ptυpose an nltcti.advc ' l iansiD.lei l landolf T ime lo lite source DS. 12 Ii. Vw 15-136 only. 13 1. This element Indicates llic granted service c ufigurαtloii. 14 J. Included If au IS-95 soil liandoll pirxcdtne Is being perfotmed. Λ 15 tiinxbnuin ot 5 Instances ol (Ids clement may be included. The order or 16 the Neighbor List elements shall match die order of die Channel 17 Number elements and Hie order of ihc lS-95 channels listed in die 15-95 18 Channel IU element, so (hat the source DS can determine which 19 neighbor list Is associated with which targel lS-95 channel. 20 21 22 23 24 25 2(3 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 47 APPENDIX Λ - itg 4. υr 19. 48 49 50 i 2 3 4 5 6 7 8 9 10 I I 12 8.1 .5.1 2 liandolf P g rtormod 13 Tltis JL-S-vtΛP message Is seal Uom the US lυ liϊcTMS in older lo indicate llial llie DS as 14 peifoMiied a handoff. In case of soil liandolf, this message is senl from source BS lo llie 15 source MSC only when llie leleience cell has been changed upon completion of llie new 16 handoff. The handoff may have been Inlctual ot in conjunction wilh another BS. The 17 purpose of lids message is lo updale die call α.tiligui.iiuin for the MSC. The Cell Identifier 18 List and channel identities rue optionally Included lot billing, trace, court ordered 19 surveillance, etc. 20 a. Allowable cause values arc: Uplink quality, Uplink slrengdi, Downlink 21 quality, Downlink strength, Distance, Interference, Detler cell (I.e., 22 Power budgel), Response lo MSC invocation, OΛM&P intervention, 23 or Private opdotts. Por 15-95 sou liaudυfT procedures: Inter-DS soft 24 liandofT drop target; lnlci-US soft handolT add target; hilra-BS soft 25 handoff drop target; Inlin US soli handoir add target; Equipment Pailure. 26 b Λ maxhnu of 6 Channel Nuiubci clciiienls may be Included in lids 27 message. 28 c. Por lS-95, all cells cuncnlly supporting the call appear in dds list. Tlie 29 first cell on die list Is the iclcicucc cell. Tlie algotid i of determining 30 of a rcfetence cell is on discretion or DS manufacturers. Por 31 ΛNS1/E1M1Λ-553 and 15-91. only one cell can be specified. 32 d. This element Is lequhtd when a packet mode channel Is being used lo 33 support die call. 34 APPENDIX Λ - nμc 5. of 19. 35 36 37 1 2 3 4 5 6 7 8 9 10 I I 12 13 14 15 6. 1 .9. PMC_Λ3 Begin PWD Trnfllc 16 This packet mode channel message is sen. hum th sυuiee US to the target BS lυ 17 acknowledge successful completion of llie Packet Mode Ciiaiuiel co iecl operation. This 18 message also triggeis llie Iransudssion of lot waul ii allic Irauies al lhe targel DS. If an error 19 has occurred in tlie υj>eraliun, tlie PMC Cause clement indicales the reason for tlie failure. 0 21 Tlie PMC Cause element must be present if a failure has occurred. Its 22 absence Implies success. 23 24 APPENDIX Λ - Page 6. of 19. 25 26 6.1 .9.x PMC_A3 Boglπ FWD Traffic Ack T his packet mode channel message is seut from die target fiS lo die source BS to acknowledge P_viC_A3 Begin FWD Traffic Λck. APPENDIX Λ - Page 7. of 19. Tlie PMC Cause element must be present If a failure has occurred. Its absence Implies success. 6.1 .9.X PMC_A3 Channol Count (rw _ 1 his packet mode channel message is sent fioin die source __-_. to die target BS lo indicate die number of IS-95 channels involved in a call. APPENDIX A - Page 8. of 19. 6.1.9.x PMC_A3 Rac»ylng_I.»vorB« Framα This packet mode channel message is sent from die target BS to die source BS to indicate receviifg of reverse frames at the target BS. APPENDIX A - Page 9. of 19. I 6.1 .9.x PMC_Λ3 Drop Targat Tills packet mode channel message Is sent iTtTiTTtiic sout c US io llie largel BS lo request a soil liandolf leg lo be dioped. This may oi may not icsuli in the disconnection of Λ3 connection depending on whellier a consolidalion/soli combining is applied al llie target BS. APPENDIX A - age 10. υl ' 19. 1 Tlie MC Cause element must be picsent if a failure as occurred. Its 2 absence Implies success. 3 4 5 6 7 8 9 10 U 12 13 14 15 1G 17 18 19 20 21 22 23 24 APPENDIX A - Page 11. of 19. 25 26 27 6.1.9.x PMC_A3 Drop Tnrgal Ack ' 1 his packel mode ciiaiuiel message is senl horn ii.e target DS lo tlie source BS to acknowledge successful complellon of a soil handoff drop largel. If an error lias occurred in the o|>eratiυn, Uie I'MC Cause elemcnl indicates llic icason for llie failure. The MC Cause clement must be present if a failure has occurred. Its absence Implies success. APPENDIX A - ane 12. υf 19. I 6.1 .9.6 P C_A3 Propagation Dølny Mσnsuron.Qt.t Report 2 Plus message is sent lioni llie DS(Ci-.)io tlie « I) 0 immcdialely following die acquisition of 3 the mobile and subsequently whenever llie delay changes by two or more PN cldps. 4 5 6 7 8 9 10 I I 12 13 14 15 16 17 18 19 20 21 22 23 APPENDIX A - a e I T of 19. 24 25 26 27 6.1.9.11 P C_A3 CDMA Long Codo ' IrnnsUion Directive Tins message Is sent irom llie souice BS lo ihe laigei US over the A3 interface.11 conveys llie long code masks tyoe (public or private) as well as llic code itsellf lo be used by the Uie lar el DS.11 also rovides llie ex ected li e ul iiansitiun lυ ϋie new lon code mask. APPENDIX A - μe 14. of 19. G.1.9.12 PMC_A9 CDMA Long Codo hniisilion Dliocllvβ Λck tills messa e is sent Itom Uie tøS(Ct- tυ lite SDΪ fυvei llie A3 si nalin inlet lace lo Allowable MC Cause vnlucs ate: I'livate long code not available or not supported. APPENDIX A - Pag 15. of 19. I 2 3 4 5 6 7 8 9 10 II 12 13 14 15 APPENDIX Λ- Page 16. ol 19. I The WaJsh Code Chanuel Index sι>eciπes one of 64 |>o.s.sible Walsh Codes used lo 2 channelize die downlink IIP bit stream in an 1S-95 call. 3 Octets 4tι4 1 and 4n+2 contain die Pilot PN Code. T he Pilot PN Code Is one of 51 1 unique 4 values for die Pilot Channel olfset. The offsets ate in increments or 4 PN chips. 5 6 The Po " wer Combined Held Is a flag dial, when sel to " I ", indicates dial die power control 7 sub-channel or this 1S-95 code channel should be diversity combined with t e previous IS- 8 95 code channel listed in U s element, hi υdier woids, if this is the second replication of 9 octets 4n through 4ιι 1 , then Uie power control sub-channel r this lS-95 code channel 10 should be diversity combined with power control sub channel ol the previous repllcaUon or I I octets 4ιι through 4n+3. The first occurrence or diis lield in die 1S-95 Channel friendly 12 element Is set to zero. 13 14 Prequency Included Is a llag Indicating whedier die lietpieney assignment is included. A 15 "0 " indicales no freαuency assignment Is present, a " I " indicales a frequency assigimienl is 16 present and Is specified hi Uie ΛRPCN lield ol this element. Pot code channel assignments 17 Uiat a e on the same 1S-95 channel frequency, this lield shall be sel lo "0". 18 The Kate Sel Held Is coded as Tollows: 19 0 0: Pale Set 1 1 1: Rale Set 2 2 3 Tlie Band Class field Is coded as follows: 5 0: A band 6 I: D band 7 8 The ΛRPCN (Absolute IIP Chatmel Ntjtnbei) in ocieis -In ι-2 and 4n 13 idenUfles die 1S-95 9 frequency being used lit die current mobile connection. T his ΛRPCN has a range or - 0 1023 lo accommodate die frequency bands ol each signaling syslem. The frequency bands 1 are shown below for clarllicaUoil. 32 33 The Iretiuency bands reserved Tor 1S-95 signaling systems ate coveted wldi ie following 34 channel nuinbeiliig scheme: 35 36 37 38 39 B.2.2.XX Public Long Codt 40 1 Ids element Is a fixed length element, It cυtiialns Pu lc Long Code. 4 Octet Element Identifier I Length LSB . Public Long Code Public Long Code MSB 41 The LeiigUi Indlcaior (octet ϊ) Is a btnaiy iiulil erind i eating die absolute leng u 1 Tό 42 contents after die length Indlcaior octet The Λlgotithπi-lnlo Held is coded as foUows: APPENDIX A - Page 17. of 19. 2 Public Longcotle! Tlie length is 42 bits, citctnlcd in 6 octets, such that the 6 unused 3 bils aie sel equal lυ U', and occupy the high -υidci positions or Hie most significant octet. 4 5 6 7 8 6.2.2. x CE Node ID . 9 Tills liiloriiialion element Identifies llie iieiwυik node thai cυnlains die instance υl Uie 10 Ciiaiuiel ,leιneιιt (CE) hi use for Uie call octet Element Idetiiiliu Lengdi ly e (MSB) i CE Node Idcnliticr (LSD) variable I I J__£_JL&IIΪΓ Tills lieid indicales ihe number ol ocieis llial follow, 12 including ihc number of octets in boUi Uie Type and 13 CE Node Idenlilicr fields, 14 Type: ' l ids lield indicales Uie lype and format of Hie CE 15 Node idenlilicr llial follows.. 16 17 CR Node Identlllεr: This field lias a vatiable length Hiat is dependent on 18 Ihe Ty|κ. field. The internal formal or lliis field may 19 be sj.ecil.ed via llie Type field. APPENDIX A - Page 18. of 19. I 8.2.2.X) c CE ID 2 iliis iiiloi illation eleinenl iϋeiilllies a patϋculai L ' E insiance wiUiin an C 5 Node. 7 6 . 5 4 3 2 1 0 octet Plcinctil Idcntilici I Lengdi 2 (MSD) 3 CE IdeniUlct • •• ! (LSD) variable 3 eUI Ufa: l ids field indicales the number of octets in Uie CE 4 Ideiiliϋci lield. 5 Ωttsteimsi' This lield liar, a vaiiable lengUi. The actual length is 6 indicated in llie len Ui field and is dependent u|K)n 7 Uie pailictilai i plcmcnlaUoii. 8 9 10 11 12 6.2.2. xx Power Control Subchannel ount 13 liis iniormalion element indicates Hie iiumbei ol subchannel involved in a soil liandolf for 14 power control purposes. 7 6 5 4 J 2 1 0 octet Hlcuicnl ldcnliliπ 1 Length 2 Subchannel Count 3 15 16 17 18 19 20 21. 22 23 24 25 26 27 28 APPENDIX A - Page 19. of 19.

Claims: WHAT IS CLAIMED IS: 1. A method of establishing a soft handoff comprising the steps of : sending a resource allocation message from a source base station (BS) directly to a target BS on a signaling first link; establishing and completing a traffic connection between the target BS and a source selection/distribution unit (SDU) via a direct signaling connection between a source system and a target BS using a signaling second link; and transferring voice signals between said source (SDU) and said target BS over a traffic link. 2. The method of claim 1 wherein: the soft handoff is of a mobile station (MS) between a source BS and a target BS in a code division multiple access (CDMA) mobile communication system. 3. The method of claim 1 wherein: said signaling first link conforms to an industry standardized protocol known in the art as A7 ; and said signaling second link conforms to an industry standardized protocol known in the art as A3S. 4. Apparatus for establishing a soft handoff comprising: means for sending a resource allocation message from a source (BS) directly to a target BS on a signaling first link; means for establishing and completing a traffic connection between the target BS and a source selection/distribution unit (SDU) via a direct signaling connection between a source system and a target BS using a signaling second link; and means for transferring voice signals between said source (SDU) and said target BS over a traffic link. 5. Apparatus as claimed in claim 4 wherein the soft handoff is of a mobile station (MS) between a source BS and a target BS in a code division multiple access (CDMA) mobile communication system. 6. The apparatus of claim 4 wherein: said signaling first link conforms to an industry standardized protocol known in the art as A7; and said signaling second link conforms to an industry standardized protocol known in the art as A3S. 7. A method of initiating the establishment of a soft handoff between source and target base stations (BS) each comprising a part of different type architecture systems comprising the single step of : sending a resource allocation message from a source base station (BS) directly to a target BS . 8. The method of claim 7 wherein: the resource allocation message is sent from one of an Architecture A type system and an Architecture B type system to the other of said Architecture A and Architecture B type systems . 9. The method of claim 7 wherein: said resource allocation message is sent over a communication link conforming to an industry standardized protocol known in the art as A7. 10. Apparatus for initiating the establishment of a soft handoff between source and target base stations (BS) comprising: a target BS comprising a part of a first architecture type system; a source BS comprising a part of a architecture type system differing from said first architecture type system; and means for sending a resource allocation message from said source BS directly to said target BS . 11. The apparatus of claim 10 wherein: the resource allocation message is sent from one of an Architecture A type system and an Architecture B type system to the other of said Architecture A and Architecture B type systems . 12. The apparatus of claim 10 wherein: said means for sending a resource allocation message from said source BS directly to said target BS conforms to an industry standardized protocol known in the art as A7.

Inventors: AHMAD AZEEM, EDUPUGANTY BAJI, ILLIDGE WILLIAM EDWARD, JIANG JIANPING, TURNER-HARRIS JERRI L, AHMAD, AZEEM, EDUPUGANTY, BAJI, ILLIDGE, WILLIAM, EDWARD, JIANG, JIANPING, TURNER-HARRIS, JERRI, L.
Applicants: AHMAD AZEEM, EDUPUGANTY BAJI, ILLIDGE WILLIAM EDWARD, JIANG JIANPING, NORTHERN TELECOM LTD, TURNER HARRIS JERRI L, AHMAD, AZEEM, EDUPUGANTY, BAJI, ILLIDGE, WILLIAM, EDWARD, JIANG, JIANPING, NORTHERN TELECOM LIMITED, TURNER-HARRIS, JERRI, L.
Application year: 1998
Main classification: H04Q7
IPC codes: H04W36