Patent Publication Number: US-2003235180-A1

Title: Method and apparatus for efficient channel assignment

Description:
REFERENCE(S) TO RELATED APPLICATION(S)  
     [0001] The present application claims priority from U.S. provisional application, Serial No. 60/375681, entitled “METHOD AND APPARATUS FOR EFFICIENT CHANNEL ASSIGNMENT,” filed Apr. 26, 2002, which is commonly owned and incorporated herein by reference in its entirety. 
    
    
     
       [0002] This application is related to a co-pending application entitled “METHOD AND APPARATUS FOR REDUCING CALL SETUP TIME,” filed on even date herewith, assigned to the assignee of the instant application, and hereby incorporated by reference.  
       [0003] This application is related to a co-pending application, Ser. No. 10/303255, entitled “METHOD FOR EXPEDITING TRANSITIONS BETWEEN STATES OF OPERATION IN COMMUNICATIONS EQUIPMENT,” filed on Nov. 25, 2002, and assigned to the assignee of the instant application.  
       [0004] This application is related to a co-pending application, Ser. No. 09/887172, entitled “DISPATCH CALL ORIGINATION AND SET UP IN A CDMA MOBILE COMMUNICATION SYSTEM,” filed on Jun. 22, 2001, and assigned to the assignee of the instant application.  
       [0005] This application is related to a co-pending application, Ser. No. 10/108405, entitled “METHOD AND APPARATUS FOR WIRELESS DATA TRANSFER WITH REDUCED DELAY,” filed on Mar. 28, 2002, and assigned to the assignee of the instant application.  
       [0006] This application is related to a co-pending application, Ser. No. 10/108783, entitled “METHOD AND APPARATUS TO REDUCE WIRELESS DATA TRANSFER DELAY,” filed on Mar. 28, 2002, and assigned to the assignee of the instant application.  
       FIELD OF THE INVENTION  
       [0007] The present invention relates generally to communication systems and, in particular, to efficient channel assignment in communication systems.  
       BACKGROUND OF THE INVENTION  
       [0008] Dispatch communication services are not yet provided on CDMA-based communication systems. Unlike the interconnect services provided by today&#39;s cellular systems, dispatch services have been traditionally provided by two-way radio systems. Such services allow a user to communicate in ways that are difficult or costly using today&#39;s cellular systems. The dispatch group call service, for example, enables a user to communicate with a group of people simultaneously and instantaneously, usually just by depressing a push-to-talk (PTT) button. Using a cellular system, such a call could not occur instantaneously since either telephone numbers would need to be dialed for a three-way call or arrangements would need to be made to setup a conference call.  
       [0009] Likewise, the dispatch individual (typically called a private call) call service enables a user to communicate with another user quickly and spontaneously. This feature is ideal for two people who are working together but are unable to speak with one another directly such as two people working in concert but in different parts of a building. Where a wireless telephone call is more appropriate for a conversation, short messages between two people as they work are better facilitated by the dispatch individual call service.  
       [0010] Because of the instantaneous nature of dispatch communication, low delay is a critical factor for dispatch calls. For example, delay that is acceptable for a typical interconnect voice call, can be unacceptable for dispatch services which rely on a very fast connection being made to the called party. Therefore, the time it takes to setup a dispatch call is critical. Low delay (or latency) is also critical when establishing and re-establishing data sessions.  
       [0011] One proposal to shorten this call setup procedure is to page with a channel assignment message. Thus, upon receiving such a channel assignment message, the target mobile jumps to the assigned traffic channel. This approach has the benefit of reducing the time from when a page/channel assignment is sent to the mobile until the mobile is on the traffic channel. However, channel assignment messages are significantly longer than paging messages. Many inactive mobiles awake from their power saving mode to listen to their common paging slot. If channel assignment messages are transmitted in place of paging messages, mobiles will need to awaken for a longer period of time and thus use more power. This will substantially reduce their battery life.  
       [0012] Therefore, a need exists for a method and apparatus to efficiently perform channel assignment in a manner that reduces call setup time. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
     [0013]FIG. 1 is a block diagram depiction of a communication system in accordance with an embodiment of the present invention.  
     [0014]FIG. 2 is a block diagram depiction of a broadcast message in accordance with an embodiment of the present invention.  
     [0015]FIG. 3 is a block diagram depiction of an abbreviated channel assignment message in accordance with an embodiment of the present invention.  
     [0016]FIG. 4 is a logic flow diagram of steps executed by a radio access network (RAN) in accordance with an embodiment of the present invention.  
     [0017]FIG. 5 is a logic flow diagram of steps executed by a remote unit in accordance with an embodiment of the present invention.  
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS  
     [0018] To address the need for efficiently performing channel assignment in a manner that reduces call setup time, the present embodiments provide an abbreviated channel assignment message that references information stored by a remote unit. The information that is referenced can be removed from the message. By shrinking the channel assignment message in this manner, the present embodiment allows it to be transmitted in a paging slot without negatively impacting the battery life of listening units. Thus, the reduced-call-setup-time benefit of transmitting a channel assignment message in a paging slot can be realized without trading off battery life. The present embodiment can be more fully understood with reference to FIGS.  1 - 5 . FIG. 1 is a block diagram depiction of a communication system  100  in accordance with an embodiment of the present invention. Communication system  100  is a well-known Code Division Multiple Access (CDMA) system, specifically a CDMA  2000  system, which is based on the Telecommunications Industry Association Electronic Industries Association (TIA/EIA) standard IS-2000, suitably modified to implement the present invention. Alternative embodiments of the present invention may be implemented in communication systems that employ other technologies such as WCDMA, UMTS, GSM, GPRS, and EDGE.  
     [0019] The first embodiment of the present invention includes radio access network (RAN)  103  and remote units, such as mobile stations (MSs)  113  and  120 . However, the present invention is not limited to remote units that are mobile. For example, a remote unit may comprise a desktop computer wirelessly connected to the radio access network. In general, throughout this document the terms “base station” (BS) and Radio Access Network (“RAN”) can be seen as synonymous. Similarly, the terms “mobile station,” “user equipment,” “mobile terminal,” “mobile unit” and “remote unit” can be seen, in general, as synonymous.  
     [0020] Those skilled in the art will recognize that FIG. 1 does not depict all of the network equipment necessary for system  100  to operate but only those system blocks particularly relevant to the description of embodiments of the present invention. For example, RAN  103  comprises well-known entities such as a transmitter  106 , receiver  105 , and controller  107 . Those skilled in the art are aware of the many ways each of these entities can be implemented and/or purchased from wireless communications companies such as “MOTOROLA.” Controllers, for example, typically comprise components such as processors, memory, and/or logic circuitry designed to implement algorithms that have been expressed as computer instructions and/or in circuitry. Given an algorithm or a logic flow, those skilled in the art are aware of the many design and development techniques available to implement a controller to perform the logic.  
     [0021] Typically, RAN transmitters and receivers are components of RAN base transceiver stations (BTSs), which interface with devices such as base site controllers, mobile switching centers/visitor location registers (MSC/VLR), home location registers (HLR), etc. In a first embodiment of the present invention, a known CDMA  2000  RAN is adapted using known telecommunications design and development techniques to implement the RAN aspect of the present invention. The result is RAN  103 , which performs the method described with respect to FIG. 4. Those skilled in the art will recognize that the RAN aspect of the present invention may be implemented in and across various physical components of RAN  103 .  
     [0022] MS  113  comprises receiver  115 , transmitter  116 , and processor  117  (comprising e.g., memory and processing devices). Transmitters, receivers, and processors as used in CDMA MSs are all well known in the art. This common set of MS components is adapted using known telecommunications design and development techniques to implement the remote unit aspect of the present invention. Thus modified, MS  113  performs the method described with respect to FIG. 5.  
     [0023] RAN  103  and MSs  113  and  120  communicate via CDMA  2000  air interface resources  124 - 125  and  130 - 133 . Resource  130  comprises a paging channel, resource  124  comprises an access channel, resource  131  comprises a broadcast channel, and resources  125 ,  132 , and  133  comprise traffic channels (TCHs).  
     [0024] Operation of communication system  100  in accordance with an embodiment of the present invention occurs substantially as follows. RAN  103  transmits overhead broadcast messaging containing information identifying a fast call setup (FCS) channel, specifically TCH  132 . Although only FCS channel  132  is depicted, the overhead messaging will typically identify a set of TCHs as FCS channels.  
     [0025]FIG. 2 is a block diagram depiction of an exemplary broadcast message  200  in accordance with an embodiment of the present invention. Broadcast message  200  first contains a field indicating how many FCS channels will be identified. The FCS channels are identified by their Walsh codes and, possibly, by Medium Access Control Id (MAC_ID) for some CDMA channels or by their pre-assigned time slot identifiers for TDMA channels. The FCS channels may alternatively be identified by their pre-assigned band class and carrier frequency.  
     [0026] Broadcast message  200  further contains information that identifies subsets of pilots that can be assigned in soft handoff. First, it contains a field indicating the number pilots to be identified. The pilots are then identified by their pseudo-noise (PN) offsets.  
     [0027] MS  113  monitors broadcast channel  131  and receives the broadcast message. MS  113  then stores the information identifying the FCS channels and pilots and their associated indexes or numbers according to the broadcast message. Thus, the FCS channels and the pilots can now be referenced by their index or number rather than their Walsh code or PN offset.  
     [0028] In addition to storing information received in the broadcast messaging, MS  113  and RAN  103  also store wireless configuration information from service sessions or connections involving MS  113 . This configuration history, indexed from the most recent session to the oldest, generally contains basic information like the service type, Walsh codes of the channels used, PN offsets of the pilots used (a.k.a., the active set), and other relevant configuration information most needed to get a communication service started on a TCH. This would include the physical and radio channel characteristics such as the initial power level and whether the transmission is continuous or discontinuous. It would also include parameters associated with the provision of the service such as vocoder options and quality of service parameters.  
     [0029] In addition to storing information received in the broadcast messaging and storing configuration information from previous service sessions, MS  113  and RAN  103  also store information from MS  113 &#39;s dormant state reporting. This includes channels using a set of pilots that have been reported by MS  113  to be suitable for communication. Thus, both RAN  103  and MS  113  maintain all of this channel assignment related information for later reference.  
     [0030] A calling unit, MS  120 , transmits a service request to RAN  103  via access channel  124 . As depicted in FIG. 1, RAN  103  is shown to have a single transmitter and receiver. However, as is well known, a RAN may encompass many base sites covering a wide geographic area. Thus, MSs  113  and  120  may be anywhere within RAN  103  and are certainly not limited to the same base site or location area. In fact, the calling unit may instead be a public switched telephone network (PSTN) user rather than a mobile user.  
     [0031] Upon receiving the service request (e.g., a dispatch service request or a packet data (re)connection request) from calling unit  120 , RAN  103  begins TCH setup with MS  120  using available TCH  125 . RAN  103  also needs to locate and determine the availability of target MS  113 . This would normally be done by paging MS  113 . However, to reduce call setup time RAN  103  assembles a channel assignment message rather than page message and pages the MS  113  by transmitting the channel assignment message rather than a page message. In effect, RAN  103  pages MS  113  with this channel assignment message by transmitting it from base sites in MS  113 &#39;s location area, in paging slots that MS  113  would regularly monitor for pages.  
     [0032] The channel assignment message sent via paging channel  130  is an abbreviated channel assignment message. FIG. 3 is a block diagram depiction of exemplary channel assignment message  300  in accordance with an embodiment of the present invention. Channel assignment message  300  provides RAN  103  a great deal of flexibility in communicating, very succinctly, a channel and service assignment to MS  113 .  
     [0033] Channel assignment message  300  has a first field to address MS  113  and then a number of fields RAN  103  can use to reference information both MS  113  and RAN  103  have stored. The stored information may be wireless configuration information used in a previous service session between RAN  103  and MS  113 , information previously broadcast by RAN  103 , or information from MS  113 &#39;s dormant state reporting. Channel assignment message  300  has a second field allowing RAN  103  to indicate which of the last “n” stored configurations to use. Channel assignment message  300  has third and fourth fields allowing RAN  103  to indicate which of the last “n” stored service types to use for the primary and secondary services, respectively. The fifth field allows RAN  103  to indicate that the previous Walsh codes should be used, thereby indicating which channels MS  113  is to use. The sixth field allows RAN  103  to indicate which of the FCS channels to use, and the seventh field allows RAN  103  to indicate that the previous active set of pilots should be used. Finally, the eighth field allows RAN  103  to indicate which FCS pilots (previously identified in the overhead broadcast messaging) should be used for soft handoff.  
     [0034] Thus, by referring to previously stored information, the channel assignment message can be made much shorter in length. Exemplary channel assignment message  300  is less than 60 bits long. Additional information could be added, up to a total of 96 bits, without overrunning a half-frame limit on a paging channel. By shrinking the channel assignment message to such as size, the present embodiment allows it to be transmitted in a paging slot without negatively impacting the battery life of listening units. Thus, the reduced-call-setup-time benefit of transmitting a channel assignment message in a paging slot can be realized without the battery life trade-off.  
     [0035]FIG. 4 is a logic flow diagram of steps executed by a RAN in accordance with an embodiment of the present invention. Logic flow  400  begins ( 402 ) with the RAN transmitting ( 404 ) overhead broadcast messaging containing information that identifies a FCS channel. The RAN is also storing ( 406 ) information that describes a wireless configuration used for service sessions with a remote unit. When the RAN receives ( 408 ) a request from a calling unit to establish a service with the remote unit, the RAN transmits ( 410 ) a channel assignment message to the remote unit via a paging channel. The channel assignment message references the information previously broadcast and the wireless configuration information stored.  
     [0036] For the case where the remote unit is assigned to a FCS channel by the channel assignment message, the RAN transmits ( 412 ) a handoff message to the remote unit via the FCS channel instructing the remote unit to handoff to another traffic channel. This frees the FCS channel for use as a temporary TCH in a subsequent channel assignment message. Since FCS channels are identified in the broadcast messaging, they are limited in number and thus should be used only as temporary TCHs.  
     [0037]FIG. 5 is a logic flow diagram of steps executed by a remote unit in accordance with an embodiment of the present invention. Logic flow  500  begins ( 502 ) with the remote unit storing ( 504 ) information received from the RAN overhead broadcast messaging. This messaging contains information that identifies FCS channels. The remote unit is also storing ( 506 ) information that describes wireless configurations used for service sessions with the RAN. At some point in time, the remote unit receives ( 508 ) a channel assignment message from the RAN via a paging channel. The message assigns a channel and a service to the remote unit by referencing the stored information. For the case where the remote unit is assigned to a FCS channel, the remote unit will receive a handoff message via the FCS channel that instructs it to handoff to another traffic channel. Logic flow  500  thus ends ( 512 ).  
     [0038] The table below is a very detailed depiction of the information contained in FIG. 2, of a broadcast message in accordance with an embodiment of the present invention.  
                                                          Length           Field Name   (bits)                       ASSIGN_PAGE_INFO_INCL   1           FOR_CODE_CHAN_INCL   0 or 1           NUM_FOR_CODE_CHAN   0 or 2                 NUM_FOR_CHAN + 1 occurrences of the following one-field       record:                             FOR_CODE_CHAN   8           FOR_CPCSCH_INCL   0 or 1           NUM_FOR_CPCSCH   0 or 2                 NUM_FOR_CPCSCH + 1 occurrences of the following one-field       record:                             FOR_CPCSCH   5           MAC_ID_INCL   0 or 1           NUM_MAC_ID   0 or 2                 NUM_MAC_ID + 1 occurrences of the following one-field record:                             MAC_ID   8                             Field Description       ASSIGN_PAGE-                             _INFO_INCL   Page with abbreviated channel assignment           additional information included indicator.           The base station shall set this field to ‘1’ if           additional information related to mobile           station-addressed page with abbreviated           channel assignment is included in this           message; otherwise, the base station shall           set this field to ‘0’.       FOR_CODE_CHAN_INCL   Forward code channel index information           included indicator.           If ASSIGN_PAGE_INFO_INCL is set           to ‘0’, the base station shall omit this field;           otherwise, the base station shall include           this field and set it as follows:           The base station shall set this field to ‘1’ if           at least one occurrence of the           FOR_CODE_CHAN field is included           in this message; otherwise, the base station           shall set this field to ‘0’.       NUM_FOR_CODE_CHAN   Number of code channel indexes.           If FOR_CODE_CHAN_INCL is set           to ‘0’, the base station shall omit this field;           otherwise, the base station shall include           this field and set it to the number of           occurrences of the FOR_CODE_CHAN           field included in this message minus one.                 If NUM_FOR_CODE_CHAN is included in this message, then the       base station shall include NUM_FOR_CODE_CHAN + 1       occurrences of the following one-field record:                     FOR_CODE_CHAN   Forward code channel index.           The base station shall set this field to the           code channel index (see [2]) that can be           assigned using a mobile-addressed page           with abbreviated channel assignment.           If Radio Configuration 1, 2, 3, or 5 (see           [2]) is used, the base station shall set this           field in the range 1 to 63 inclusive. If           Radio Configuration 4, 6 or 8 is used, the           base station shall set this field in the           range 1 to 127 inclusive. If Radio Con-           figuration 7 or 9 is used, the base station           shall set this field in the range 1 to 255           inclusive.       FOR_CPCSCH_INCL   Forward Common Power Control Channel           Subchannel information included           indicator.           If ASSIGN_PAGE_INFO_INCL is set           to ‘0’, the base station shall omit this field;           otherwise, the base station shall include           this field and set it as follows:           The base station shall set this field to ‘1’ if           at least one occurrence of the           FOR_CPCSCH field is included in this           message; otherwise, the base station shall           set this field to ‘0’.       NUM_FOR_CPCSCH   Number of Forward Common Power           Control Channel Subchannels.           If FOR_CPCSCH_INCL is set to ‘0’, the           base station shall omit this field;           otherwise, the base station shall include           this field and set it to the number of           occurrences of the FOR_CPCSCH field           included in this message minus one.                 If NUM_FOR_CPCSCH is included in this message, then the base       station shall include NUM_FOR_CPCSCH + 1 occurrences of the       following one-field record:                     FOR_CPCSCH   Forward Common Power Control Channel           Subchannel.           The base station shall set this field to the           Forward Common Power Control Channel           Subchannel that can be assigned using           a mobile-addressed page with abbreviated           channel assignment.       MAC_ID_INCL   MAC index information included           indicator.           If ASSIGN_PAGE_INFO_INCL is set           to ‘0’, the base station shall omit this field;           otherwise, the base station shall include           this field and set it as follows:           The base station shall set this field to ‘1’ if           at least one occurrence of the MAC_ID           field is included in this message;           otherwise, the base station shall set           this field to ‘0’.       NUM_MAC_ID   Number of Medium Access Control           indexes.           If MAC_ID_INCL is set to ‘0’, the base           station shall omit this field; otherwise,           the base station shall include this field           and set it to the number of occurrences of           the MAC_ID field included in this           message minus one.                 If NUM_MAC_ID is included in this message, then the base station       shall include NUM_MAC_ID + 1 occurrences of the following       one-field record:                     MAC_ID   Medium Access Control index.           The base station shall set this field to the           Medium Access Control index that can be           assigned using a mobile-addressed page           with abbreviated channel assignment.                  
 
     [0039] The tables below provide a very detailed depiction of the information contained in FIG. 3, of an abbreviated channel assignment message in accordance with an embodiment of the present invention.  
     [0040] PDU Format for a mobile station-addressed page with abbreviated channel assignment:  
                                                       Length           Field   (bits)                          RESPONSE_IND   2           SR_ID_RESTORE   3           USE_PREV_ACTIVE_SET   1           FOR_CHAN_ID   2           MAC_ID_ID   2           Additional record fields   4                 If USE_PREV_ACTIVE_SET = ‘0’, the additional record fields       shall be:                             NEW_ACTIVE_SET   2                 If USE_PREV_ACTIVE_SET = ‘1’, the additional record fields       shall be:                             USE_PREV_FOR_CHAN   1           USE_PREV MAC_ID   1                                 CONFIG_MSG_SEQ   Configuration message sequence number.           The base station shall set this field to           CONFIG_SEQ (see 3.6.2.2).       [. . .]       ADD_BCAST_RECORD   Additional broadcast information record.           The base station shall omit this field if           EXT_BCAST_SDU_LENGTH_IND (see           [4]) is set to ‘00’ or ‘01’; otherwise, the base           station shall include           EXT_BCAST_SDU_LENGTH (see [4])           octets in this field.       RESPONSE_IND   Response requested indicator.           The base station shall set this field according           to Table 3.7.2.3.2.17-1.                  
 
     [0041]               TABLE 3.7.2.3.2.17-1                          RESPONSE_IND values                         RESPONSE_IND       Response       (binary)   Response (accept)   (reject)               00   The mobile station is not to   The mobile           respond on the r-csch.   station is to       01   The mobile station is to respond   respond with           with a Page Response Message in   a Mobile           unassured mode on the r-csch.   Station Reject       10   The mobile station is to respond   Order with           with a Page Response Message in   ORDQ equal           assured mode on the r-csch.   to ‘00000111’       11   Reserved.                             SR_ID_RESTORE   Service reference identifier to be restored.           The base station shall set this field to           ‘111’ if the mobile station is to restore all           the service option connections from the           stored service configuration; otherwise,           the base station shall set this field to the           service reference identifier corresponding           to the service option connection to be           restored.       USE_PREV_ACTIVE_SET   Use previous Active Set indicator.           The base station shall set this field to ‘1’           to indicate that the mobile station&#39;s Active           Set on the Traffic Channel is to be the           same as that stored by the mobile station           when it left the Mobile Station Control on           the Traffic Channel State; otherwise, the           base station shall set this field to ‘0’.           FOR_CHAN_ID - Forward code channel           or F-CPCSCH identifier.           If USE_PREV_ACTIVE_SET is equal           to ‘0’, or USE_PREV_ACTIVE_SET           is equal to ‘1’ and           USE_PREV_FOR_CHAN is equal to           ‘0’, then the base station shall set this           field as follows:           If a Forward Fundicated Channel is           assigned, the base station shall set this           field to the identifier corresponding to the           walsh code of the Forward Traffic           Channel associated with           FPC_PRI_CHAN assigned to the mobile           station on all pilots.           If a Forward Fundicated Channel is not           assigned, the base station shall set this           field to the identifier corresponding to the           Forward Common Power Control Channel           Subchannel assigned to the mobile station           on all pilots.           Otherwise, the base station shall set this           field to ‘00’.       MAC_ID_ID   Medium access control index identifier.           If a Forward Packet Data Channel is not           assigned, or USE_PREV_ACTIVE_SET           is equal to ‘1’ and           USE_PREV_MAC_ID is equal to ‘1’,           then the base station shall set this field           to ‘00’.           Otherwise, the base station shall set this           field to the identifier corresponding to the           MAC index assigned to the mobile station           on all pilots.                 If USE_PREV_ACTIVE_SET is equal to ‘0’, then the base station       shall include the following four-field record:                     NEW_ACTIVE_SET   New Active Set.           The base station shall set this field           according to Table 3.7.2.3.2.17-2.                    
     [0042]               TABLE 3.7.2.3.2.17-2                          NEW_ACTIVE_SET values                     NEW_ACTIVE_SET           (binary)   Active Set               00   The mobile station is to use the first (i.e.           strongest) pilot reported in the last Radio           Environment Report Message as the Active           Set on the Traffic Channel.       01   The mobile station is to use the second pilot           reported in the last Radio Environment           Report Message as the Active Set on the           Traffic Channel.       10   The mobile station is to use the first two           pilots reported in the last Radio           Environment Report Message as the Active           Set on the Traffic Channel. The Forward           Traffic Channel associated with each pilot           do not carry the same closed-loop power           control subchannel bits.       11   The mobile station is to use the first two           pilots reported in the last Radio           Environment Report Message as the Active           Set on the Traffic Channel. The Forward           Traffic Channel associated with each pilot           carry the same closed-loop power control           subchannel bits.                         If USE_PREV_ACTIVE_SET is equal to ‘1’, then the base station       shall include the following three-field record:                             USE_PREV_FOR_CHAN   Use previous forward code channel or           F-CPCSCH indicator.           The base station shall set this field to ‘1’           to indicate that the mobile station&#39;s           Forward Fundicated Channel walsh code           or Forward Common Power Control           Channel Subchannel is to be the same as           that stored by the mobile station when it           left the Mobile Station Control on the           Traffic Channel State; otherwise, the base           station shall set this field to ‘0’.       USE_PREV_MAC_ID   Use previous MAC index indicator.           The base station shall set this field to ‘1’           to indicate that the mobile station&#39;s MAC           index is to be the same as that stored by           the mobile station when it left the Mobile           Station Control on the Traffic Channel           State; otherwise, the base station shall set           this field to ‘0’. If the Forward Packet           Data Channel is not assigned, then the           base station shall set this field to ‘0’.                    
     [0043] While the present invention has been particularly shown and described with reference to particular embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention.