Abstract:
An approach to controlling packet forwarding in a wireless communications system that helps limit the burden placed on internal communication links while maintaining some or all of the advantages of diversity gain on the reverse link. A primary base station sends its peers a forwarding control message if a packet is successfully received. If the forwarding control message is received at the peer base stations before a timer elapses, the peer base stations refrain from forwarding their versions of the packet to the call anchor. The timer&#39;s duration may be varied as appropriate, and the forwarding control message process may be bypassed for small packets and/or certain application types.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention relates to wireless communications systems; and, more particularly, to methods of controlling the forwarding of reverse link packets in the wireless communications system.  
         [0002]     The demand for wireless data services, such as mobile Internet, video streaming, and voice over IP (VoIP), have led to the development of high speed packet data channels to provide high data rates needed for such services. High speed packet data channels are employed on the forward and reverse links in a variety of mobile communication systems, including TIA-2000 (also known as 1xEV-DV), TIA-856 (also known as 1xEV-DO), and Wideband Code Division Multiple Access (WCDMA) systems. For the forward link, the high speed packet data channel is a time shared channel, with downlink transmissions, e.g., from a base station to the mobile stations, time-multiplexed and typically transmitted at full power. For the reverse link, the high speed packet data traffic channel carries uplink transmissions, e.g., from a mobile station to a base station, that are code-multiplexed and transmitted at a closely controlled power level.  
         [0003]     In most systems, a mobile station is typically served at any given time on the downlink by a single serving base station. However, it is common for the reverse link packets from the mobile station to be received by a plurality of base stations. The multiple receiving base stations then forward the received packets to a call anchor node in the system for combining. Thus, some measure of diversity gain is realized on the reverse link. However, in order to achieve this diversity gain, some additional burden is placed on the communication links internal to the system, such as A13 links between base stations, in forwarding the packets from multiple base stations.  
       SUMMARY OF THE INVENTION  
       [0004]     The present invention provides an approach that helps limit the burden placed on the communication links internal to the wireless communications system while maintaining some or all of the advantages of diversity gain on the reverse link. To achieve this, one of the base stations, denoted the primary base station, sends its peers a forwarding control message if a packet is successfully received. In response to receiving the forwarding control message in a timely fashion, the peer base stations, denoted as secondary base stations, refrain from forwarding their versions of the packet to the call anchor. Thus, a form of selection combining is imposed where a packet successfully received by a “first among equals” base station is used by the call anchor if possible, with packets from the other base stations becoming relevant if the packet is not successfully received by the “first among equals” base station.  
         [0005]     In one embodiment, the present invention provides a method of controlling packet forwarding operations of base stations in a wireless communications system, comprising a first base station: receiving a reverse link packet from a mobile station; determining if the packet was successfully received by the first base station; and selectively sending a forwarding control message to at least one other peer base station based on the determining, the forwarding control message instructing the other base station to refrain from forwarding the packet to a call anchor associated with the mobile station. The first base station advantageously also forwards the packet to the call anchor in response to the packet being successfully received. The first base station may also condition the sending of the forwarding control message on the size of the reverse link packet and/or an application type associated with the reverse link packet. The first base station advantageously also functions as the downlink serving base station for the mobile station substantially contemporaneously with the receiving. A corresponding apparatus is also described.  
         [0006]     In another embodiment, the present invention provides a method of controlling packet forwarding operations of a base station in a wireless communications system, comprising: successfully receiving a reverse link packet from a mobile station at a secondary base station; buffering the packet; receiving a corresponding forwarding control message from a primary base station instructing the secondary base station to refrain from forwarding the packet to a call anchor associated with the mobile station; and the secondary base station selectively refraining from forwarding the packet to the call anchor based on the forwarding control message. The secondary base station may forward the packet to the call anchor if a predetermined time period elapses before the receipt of the corresponding forwarding control message. The predetermined time period may vary based on an application type associated with the reverse link packet. A corresponding apparatus is also described.  
         [0007]     In another embodiment, the present invention provides a method of controlling packet forwarding operations of base stations in a wireless communications system, comprising: successfully receiving a reverse link packet from a mobile station at a secondary base station; determining whether to forward or refrain from forwarding the packet from the secondary base station to a call anchor associated with the mobile station based upon whether a corresponding forwarding control message is received from a primary base station prior to an expiration of a predetermined time period after the successful receipt of the packet; and wherein the secondary base station refrains from forwarding the packet to the call anchor if the forwarding control message is received prior to the expiration. A corresponding apparatus is also described.  
         [0008]     In another embodiment, the present invention provides a method of controlling packet forwarding operations of base stations in a wireless communications system, comprising: successfully receiving a reverse link packet from a mobile station at a plurality of base stations, including a primary base station and at least one secondary base station; the base stations normally programmed to forward the packet to an anchor processor responsible for the mobile station for selection combining at the anchor processor; in response to the successful receipt of the packet, the primary base station sending a forwarding control message to at least one secondary base station; each of the secondary base stations respectively selectively refraining from forwarding the packet to the anchor processor in response to receiving the forwarding control message prior to an expiration of a predetermined time period after the successful receipt of the packet by the secondary base station. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]      FIG. 1  shows an exemplary wireless communication system.  
         [0010]      FIG. 2  shows an exemplary base station from  FIG. 1 .  
         [0011]      FIG. 3  shows another exemplary wireless communications system.  
         [0012]      FIG. 4  shows an exemplary base station from  FIG. 3 .  
         [0013]      FIG. 5  shows reverse link communications from a mobile station to several base stations.  
         [0014]      FIG. 6  shows a flowchart for a process according to one embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0015]     The present invention relates to controlling packet forwarding operations in a wireless communications system having a plurality of mobile stations operating therein. As such, a brief overview of exemplary wireless communications systems may aid in understanding the present invention.  
         [0016]      FIG. 1  illustrates the logical entities of an exemplary wireless communication network  10  that provides packet data services to mobile stations  90 . In general, the wireless communication network  10  may be configured according to the TIA-2000 standard, W-CDMA standard, 1xEV-DO, or other standard. Advantageously, the wireless communication network  10  is a packet-switched network that employs a Forward Traffic Channel (FTC) to transmit traffic data to the mobile stations  90  and a Reverse Traffic Channel (RTC) to receive traffic data from the mobile stations  90 . Wireless communication network  10  includes a packet-switched core network  20  and a radio access network (RAN)  30 . The core network  20  includes a Packet Data Serving Node (PDSN)  22  that connects to an external packet data network (PDN)  16 , such as the Internet, and supports PPP connections to and from the mobile stations  90 . Core network  20  adds and removes IP streams to and from the RAN  30  and routes packets between the external packet data network  16  and the RAN  30 .  
         [0017]     RAN  30  connects to the core network  20  and gives mobile stations  90  access to the core network  20 . RAN includes a Packet Control Function (PCF)  32 , one or more base station controllers (BSCs)  34  and one or more radio base stations (RBSs)  36 . The primary function of the PCF  32  is to establish, maintain, and terminate connections to the PDSN  22 . The BSCs  34  manage radio resources within their respective coverage areas. The RBSs  36  include the radio equipment for communicating over the air interface with mobile stations  90 . A BSC  34  can manage more than one RBS  36 . In this illustrative embodiment, a BSC  34  and an RBS  36  comprise a base station  40 , while the BSC  34  is the control part of the base station  40 . The RBS  36  is the part of the base station  40  that includes the radio equipment and is normally associated with a cell site. As shown, a single BSC  34  may function as the control part of multiple base stations  40 . In other network architectures, the network components comprising the base station  40  may be different, but the overall functionality will be the same or similar. For example, see the discussion below regarding  FIGS. 3-4 .  
         [0018]     Referring to  FIG. 2 , the components in the exemplary base station embodiment are distributed between a RBS  36  and a BSC  34 . The RBS  36  includes RF circuits  42 , baseband processing and control circuits  44 , and interface circuits  46  for communicating with the BSC  34 . The RF circuits  42  include one or more transmitters  42 T and receivers  42 R, which transmit signals to, and receive signals from, the mobile stations  40 . For example, the receiver  42 T receives reverse link data packets transmitted by the mobile stations  90  and passes the same on to the baseband processing and control circuits  44  for processing. The baseband processing and control circuits  44  perform baseband processing of transmitted and received signals. In the embodiment shown in  FIG. 2 , the baseband processing and control circuit  44  includes a scheduler  60  to schedule packet data transmissions on the Forward Traffic Channel (FTC). The scheduler  60  makes scheduling decisions and selects the appropriate modulation and coding schemes for downlink transmissions based on, inter alia, channel feedback from the mobile stations  90 . The baseband processing and control circuit  44  may be implemented as one or more processing circuits, comprising hardware, software, or any combination thereof, that are configured as appropriate to implement one or more of the processes described herein. For example, the baseband processing and control circuit  44  may be implemented as stored program instructions executed by one or more microprocessors or other logic circuits included in RBS  36 .  
         [0019]     The BSC  34  includes interface circuits  50  for communicating with the RBS  36 , communication control circuits  52 , and interface circuits  54  for communicating with PCF. The communication control circuits  52  manage the radio and communication resources used by the base station  40 . The communication control circuits  52  are responsible for setting up, maintaining and tearing down communication channels between the RBS  36  and mobile station  90 . The communication control circuits  52  may also allocate Walsh codes and perform power control functions. The communication control circuits  52  may be implemented in software, hardware, or some combination of both. For example, the communication control circuits  52  may be implemented as stored program instructions executed by one or more microprocessors or other logic circuits included in BSC  34 .  
         [0020]      FIG. 3  illustrates an alternative exemplary architecture for a wireless communications system  10 ′ that is less centralized than the wireless communications system  10  of  FIGS. 1-2 . Like the wireless communications system  10  of  FIG. 1 , the system  10 ′ of  FIG. 3  includes a core network  20  having a PDSN  22 , and a RAN  30  having a plurality of base stations  40 ′, which are advantageously identical to each other. In addition, the system  10 ′ of  FIG. 3  includes an IP-based transport network  60 , comprising one or more routers  62 , that connect the core network  20  with RAN  30 . In this exemplary architecture, the base stations  40 ′ are conceptually somewhat similar to the base stations  40  of  FIG. 1 , but with much of the “intelligence” of the BSC  34  distributed downward to be co-located with the RBS  36 .  FIG. 4  illustrates the logical elements of an exemplary base station  40 ′ for this system architecture. As shown in  FIG. 4 , each base station  40 ′ has an access network controller (ANC)  70  and a packet control function (PCF)  32 ′. ANC  70  functions similar to the communication control circuit  52  of  FIG. 2 &#39;s BSC  34  in that it manages radio resources for the associated RBS  36 . PCF  32 ′ functions similar to PCF  32  of  FIG. 1  in that it functions to establish, maintain, and terminate connections to the PDSN  22 . With reference to  FIG. 4 , packet data between the base station  40 ′ and the PDSN  22  travels over an A10 communication link, while signaling data travels between the base station  40 ′ and PDSN  22  over an A11 link. Communications between ANCs  70  of different base stations  40 ′ travel over an A13 communication link; which is sometimes referred to as a sidehaul connection. The base stations  40 ′ may operate, for example, according to TIA-856-A, which defines an air interface between the base station  40 ′ and mobile station  90 . Those skilled in the art will appreciate that the present invention may also use other air interface standards, as indicated above. Thus, the architecture of  FIG. 3  is conceptually similar to that shown in  FIG. 1 , but with each RBS  36  in effect having its own co-located dedicated communications controller  52  (ANC  70 ) and PCF  32  (PCF  32 ′).  
         [0021]     Turning to  FIG. 5 , one embodiment of the present invention will be explained in the context of the distributed architecture of  FIG. 3 . As shown in  FIG. 5 , several base stations  40 ′ may be receiving reverse link transmissions from a given mobile station  90 . For simplicity, three base stations—labeled X, Y, and Z, are shown, but it should be understood that there may be more or less. The base stations  40 ′ communicate with each other using an A13 link, as discussed above. The set of base stations  40 ′ that should be receiving the reverse link transmissions are called the “active set” for that mobile station  90 . Thus, base stations X, Y, and Z are considered, for purposes of this example, to be in the active set of the mobile station  90 . Further, this example will assume that base station X is functioning as the call anchor, and that base station Y is the downlink serving base station. The call anchor forms the primary connection to the PDSN  22  using an A10 connection, and is typically the base station  40 ′ through which the mobile station  90  initially set up the communications session. The downlink serving base station is the base station  40 ′ that actually transmits the downlink data traffic to the mobile station  90  over the air interface. Note that these downlink, or forward link (FL) communications are shown in dashed lines in  FIG. 5 .  
         [0022]     As illustrated in  FIG. 5 , the mobile station  90  transmits a reverse link (RL) packet (step  100 ). The base stations X, Y and Z all receive the reverse link transmissions from the mobile station  90 . Looking first at primary base station Y, primary base station Y receives the reverse link packet (step  210 ) and determines if it has successfully received the packet (step  220 ). Thus, base station Y attempts to decode the reverse link packet, with a successful decoding indicating a successful reception of the packet. For example, base station Y may perform a CRC check on the packet to determine if decoding was successful. If the packet is not successfully received (e.g., CRC failure), base station Y simply awaits the next packet. If the packet is successfully received (e.g., CRC passes), then primary base station Y sends a forwarding control message to the other base stations  40 ′ in the active set (base stations X and Z in this example) on the sidehaul A13 link (step  240 ) and forwards the packet to the call anchor (step  290 ). The forwarding control message helps control whether or not the other base stations  40 ′ also send the packet to the call anchor, as explained further below. The relevant packet is identified in the forwarding control message, such as by suitable time stamp, flow identifier, and/or service reference identifier (SRID), etc. Turning now to the peer base station Z, sometimes referred to herein as a secondary base station, this base station  40 ′ also receives the reverse link packet (step  310 ) transmitted by the mobile station  90 . Base station Z checks to see if the packet is received successfully (step  320 ), typically using a CRC check. Assuming base station Z successfully receives the packet, base station Z would, under the prior art, automatically forward the packet to the call anchor. However, in the present invention, base station Z instead starts a timer  72  (step  340 ) that governs a waiting period of predetermined duration before base station Z forwards the packet to the call anchor. If, during this waiting period, the forwarding control message is received (step  350 ), then the packet is not forwarded to the call anchor, and may be discarded (step  370 ). If the call forwarding control message is not received (step  350 ) before the timer expires (step  360 ), then base station Z forwards the packet to the call anchor (step  390 ). Base station X reacts in the same fashion as base station Z, but would in effect forward the packet to itself, as it is functioning as the call anchor. The call anchor then selection combines the received packets and processes the information in a conventional fashion.  
         [0023]     The processes described above may be augmented by selectively bypassing the forwarding control message sending/checking steps for small size packets, if desired. For example, the primary base station may look at the size of the packet (step  230 ), and bypass sending the forwarding control message (step  240 ) for small size packets. One rationale underlying this optional operation is that the use of the forwarding control message adds traffic to the A13 links, and using the forwarding control messages may not result in a net decrease in traffic for small packets. Likewise, the secondary base stations  40 ′ may examine the size of the successfully received packet (step  330 ), and bypass steps  340 - 370  for small size packets. Note that both step  230  and step  330  are shown in dashed lines in  FIG. 6  due to their optional nature. Alternatively, or in addition, a similar bypass logic can be applied based on the packet belonging to certain application types, such as those that are known to be very delay intolerant and/or of typically small packet size. For example, VoIP applications may be relatively delay intolerant, due to quality of service restrictions, and typically use small packet sizes, and therefore steps  230 ,  330 - 370  may be bypassed for packets having VoIP application type data.  
         [0024]     On a related note, the length of the predetermined waiting period at the secondary base stations  40 ′ may be constant for all packets. Or, alternatively, the length of the waiting period (i.e., setting of timer  72 ) may vary based on the packet&#39;s application type. For example, VoIP application packets may have very short waiting periods, while other application types may have longer waiting periods.  
         [0025]     The discussion above assumed that the downlink serving base station Y was the “first among equals” base station  40 ′ from which the forwarding control messages originated. Thus, base station Y functioned as the primary base station; with the base stations  40 ′ targeted by the forwarding control messages, base stations X and Z, being the secondary base stations. However, while it is believed to be more efficient if the downlink serving base station  40 ′ functions as the primary base station, this is not required. In some embodiments, another base station  40 ′ in the active set, such as base station Z, may function as the primary base station if desired. Further, in some embodiments, a given base station  40 ′ may function as both the primary base station and the call anchor.  
         [0026]     While the discussion above has been in terms of the wireless communication system  10  being configured according to the TIA-2000 standard, W-CDMA standard, or the 1xEV-DO standard, it should be realized that other packet data standards may alternatively be used, including without limitation systems using Worldwide Interoperability for Microwave Access (also known as WiMAX, see IEEE 802.16).  
         [0027]     As used herein, the term “mobile station”  90  may include a cellular radiotelephone, a Personal Communications System (PCS) terminal that may combine a cellular radiotelephone with data processing, facsimile, and data communications capabilities; a Personal Data Assistant (PDA) that may include a pager, Web browser, radiotelephone, Internet/intranet access, organizer, calendar, and a conventional laptop and/or palmtop receiver or other appliances that include a radiotelephone transceiver.  
         [0028]     The present invention may, of course, be carried out in other specific ways than those herein set forth without departing from the scope and essential characteristics of the invention. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive, and all changes coming within the meaning and equivalency range of the appended claims are intended to be embraced therein.