Abstract:
A method of reducing loading on backhaul communications links in a wireless communications system suppresses a portion of the upward flow of frame information for idle and/or erased frames in certain situations, such as when multiple ones of such frames are successively encountered. A radio base station abstains from sending a frame header to a BSC/ANC for second and following frames of the Idle type and/or the radio base station abstains from sending a frame header to a BSC/ANC for second and following frames of the Erased type. The header may also or alternatively be suppressed for an Idle frame immediately following a Good frame. The BSC/ANC in effect fills in the suppressed frame information in such situations, forwards appropriate indications of frame type to the frame selection algorithm.

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 frames and/or information about reverse link frames 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 link 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. The high speed packet data channel is a time shared channel, with downlink transmissions, e.g., from a base station to the mobile stations, typically time-multiplexed and transmitted at full power.  
         [0003]     In addition to receiving downlink transmissions, mobile stations transmit packet data to the base stations on what is called the reverse link. While the mobile station may be served at a given time on the downlink by a single serving radio base station, the reverse link frames transmitted by that mobile station may be received by a plurality of radio base stations, such as during soft handoff. The multiple receiving radio base stations typically forward the received frames to a call anchor node in the system for further processing, such as for outer loop power control. Thus, some measure of diversity gain may be realized on the reverse link. However, in order to achieve this diversity gain, some additional traffic is placed on the backhaul communications links internal to the system. These backhaul communications links carry information conceptually “upward” in the communications system, such as from a radio base station to its controlling base station controller, or from a non-anchor base station to a call anchor base station. For example, an A bis  link between base stations may be used as a backhaul communication link, as can an I ub  link between a Radio Network Controller (RNC) and a Base Transceiver Station (BTS) in a Universal Mobile Telecommunications System (UMTS) system. The additional traffic placed on the backhaul communication link(s) in forwarding the relevant frame information from multiple radio base stations to the call anchor in order to achieve the diversity gain places a burden on those backhaul link(s), which, in some instances, may negatively impact overall system performance.  
       SUMMARY OF THE INVENTION  
       [0004]     The present invention provides a method of reducing loading on backhaul communications links by suppressing a portion of the upward flow of frame information for idle and/or erased frames when multiple ones of such frames are successively encountered. In some embodiments, the radio base station abstains from sending a frame header to the BSC/ANC (suppresses the header) for second and following frames of the same type, if the type is either Idle or Erased. Alternatively, or in addition thereto, the radio base station may suppress the header when an Idle frame immediately follows a good frame. The BSC/ANC in effect fills in the suppressed frame information in such situations, and forwards appropriate indications of frame type to the frame selection algorithm.  
         [0005]     In one embodiment, the present invention provides a method of controlling frame forwarding operations of a first radio base station in a wireless communications system comprising: receiving first and second successive frames from a mobile station at the first radio base station, the second frame received after the first frame; classifying the first and second frames at the first radio base station; in response to both the first and second frames being classified differently, the first radio base station sending at least a header associated with the second frame to a call anchor associated with the mobile station; the header indicating the classification of the second frame; in response to both the first and second frames being classified as erased frames, the first radio base station abstaining from sending the header to the call anchor. The available frame classifications may be good, idle, or erased. If the second frame is classified as a good frame, the first radio station may send the header and a payload associated with the second frame to the call anchor. A frame may be classified as idle if a corresponding frame boundary is encountered without receipt of corresponding frame transmissions from the mobile station. If both the first and second frames are classified as idle frames, the first radio base station advantageously abstains from sending the header to the call anchor. A corresponding apparatus is also described.  
         [0006]     In another embodiment, the present invention provides a method of controlling frame forwarding operations of a first radio base station in a wireless communications system comprising: receiving first and second successive frames from a mobile station at the first radio base station, the second frame received after the first frame; classifying the first and second frames at the first radio base station; in response to both the first and second frames being classified differently, the first radio base station sending at least a header associated with the second frame to a call anchor associated with the mobile station; the header indicating the classification of the second frame; in response to both the first and second frames being classified as idle frames, the first radio base station abstaining from sending the header to the call anchor. The available frame classifications may be good, idle, or erased. If the second frame is classified as a good frame, the first radio station may send the header and a payload associated with the second frame to the call anchor. A frame may be classified as idle if a corresponding frame boundary is encountered without receipt of corresponding frame transmissions from the mobile station. A corresponding apparatus is also described.  
         [0007]     In another embodiment, the present invention provides a method of controlling frame forwarding operations of a first radio base station in a wireless communications system comprising: receiving first and second successive frames from a mobile station at the first radio base station, the second frame received after the first frame; classifying the first and second frames at the first radio base station; in response to both the first and second frames being classified differently, the first radio base station: a) if the second frame is other than an idle frame, sending at least a header associated with the second frame to a call anchor associated with the mobile station; the header indicating the classification of the second frame; b) if the second frame is an idle frame and the first frame is an erased frame, sending the header to the call anchor; the header indicating the classification of the second frame; c) if the second frame is an idle frame and the first frame is a good frame, abstaining from sending the header to the call anchor; in response to both the first and second frames being classified as idle frames, the first radio base station abstaining from sending the header to the call anchor. A corresponding apparatus is also described.  
         [0008]     In another embodiment, the present invention provides a method of supplying frame classification information to a frame selection algorithm by an anchor base station, the anchor base station having at least an idle frame receipt state; a good frame receipt state, and an erased frame receipt state; the method comprising: in response to being in the idle frame receipt state and receiving neither a frame nor a header from the first radio base station at a frame boundary, supplying an indication, corresponding to the first base station, to the frame selection algorithm indicating an idle frame and remaining in the idle frame receipt state; and, in response to being in the erased frame receipt state and receiving neither a frame nor a header from a first radio base station at a frame boundary, supplying an indication, corresponding to the first base station, to the frame selection algorithm indicating an erased frame and remaining in the erased frame receipt state. A corresponding apparatus is also described.  
         [0009]     In another embodiment, the present invention provides a method of supplying frame classification information by an anchor base station to a frame selection algorithm, the anchor base station having at least an idle frame receipt state; a good frame receipt state, and an erased frame receipt state; the method comprising: in response to being in the good frame receipt state and receiving neither a frame nor a header from the first radio base station at a frame boundary, the anchor base station supplying an indication, corresponding to the first base station, to the frame selection algorithm indicating an idle frame and transitioning to the idle frame receipt state; in response to being in the idle frame receipt state and receiving neither a frame nor a header from the first radio base station at a frame boundary, the anchor base station supplying an indication, corresponding to the first base station, to the frame selection algorithm indicating an idle frame and remaining in the idle frame receipt state. A corresponding apparatus is also described. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]      FIG. 1  shows an exemplary wireless communication system.  
         [0011]      FIG. 2  shows an exemplary base station configuration.  
         [0012]      FIG. 3  shows another exemplary base station configuration.  
         [0013]      FIG. 4  shows a mobile station communicating with multiple RBSs, such as during soft handoff.  
         [0014]      FIG. 5  shows a state diagram for a radio base station according to one embodiment of the present invention.  
         [0015]      FIG. 6  shows a state diagram for a BSC/ANC according to one embodiment of the present invention.  
         [0016]      FIG. 7  shows a process flowchart for a frame selection algorithm useful with various embodiments of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0017]     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 communication systems may aid in understanding the present invention.  
         [0018]      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, Worldwide Interoperability for Microwave Access (also known as WiMAX, see IEEE 802.16), or other standard. Advantageously, the wireless communication network  10  is a packet-switched network that employs a forward packet data channel (F-PDCH) to transmit traffic data to the mobile stations  90  and a reverse packet data channel (R-PDCH) 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 .  
         [0019]     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 .  
         [0020]     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  48  to schedule packet data transmissions on the Forward Packet Data Channel (F-PDCH). The scheduler  48  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 .  
         [0021]     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 .  
         [0022]     Some exemplary wireless communications systems  10  are less centralized than the wireless communications system  10  of  FIGS. 1-2 . For these systems, it is not uncommon for the functionality of the BSC  34  and the PCF  32  to be dedicated to a specific RBS  36  and pushed downward to be co-located with that RBS. For example,  FIG. 3  shows a base station  40 ′ in such an architecture. The base station  40 ′ has an access network controller (ANC)  60  and a packet control function (PCF)  32 ′. ANC  60  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  may travel over an A 10  communication link, while signaling data may travel between the base station  40 ′ and PDSN  22  over an A 11  link. Communications between ANCs  60  of different base stations  40 ′ travel over an A 13  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.  
         [0023]     A mobile station  90  may receive downlink (DL) transmissions, indicated in dashed lines in  FIG. 4 , from an RBS  36  operating under the control of an BSC/ANC  70 . The designation “BSC/ANC” is used in  FIG. 4  because either a BSC  34  or an ANC  60  may be responsible for controlling the RBS  36 , depending on the system architecture. While a single RBS  36  may be serving the mobile station  90  on the downlink, a plurality of RBS  36  may be receiving reverse link transmissions from a given mobile station  90  in a given situation, such as during soft handoff. For simplicity, two RBS—labeled X and Y—are shown, but it should be understood that there may be three or more RBSs  36 . These two RBS  36  both communicate with BSC/ANC  70 , which in turn communicates with a frame selection algorithm  80 . The frame selection algorithm  80  is typically located in the call anchor, and is involved with supplying information for outer loop power control and the like. The call anchor is typically the BSC/ANC  70  through which the mobile station  90  initially set up the communications session, as is well known in the art.  
         [0024]     Conceptually reverse link frames are received at RBS X-Y from mobile station  90 , and forwarded to BSC/ANC  70 . The BSC/ANC  70  examines the classification (e.g., good, idle, erased) of the frames from each RBS  36 , and forwards an appropriate indication to the frame selection algorithm  80  for further processing. To do so in conventional systems, each RBS  36  forwards its classification of the frame to the BSC/ANC  70 , thereby imposing a load on the backhaul communications link between the BSC/ANC  70  and the various RBS X-Y. The present invention provides a means for lessening this loading in some circumstances.  
         [0025]     In the present invention, each RBS  36  may be thought of as operating in three different states depending on the classification of the last frame from mobile station  90 . For simplicity, the three states are referred to as the Good Frame State  102 , Erased Frame State  104 , and the Idle Frame State  106 . See  FIG. 5 . For each frame received, or at the corresponding frame boundary if no frame is received, the RBS  36  controls its operational state and the information sent (or not sent) to the BSC/ANC  70  based on the classification of the “new” frame. For purposes of this illustrative example, it will be assumed that each new frame may be classified as either Good, Idle, or Bad. Good frames are frames that are properly received and decoded, and typically contain a data payload. Bad frames are frames that are improperly received and/or are not decoded correctly. Idle frames are frames where the frame boundary is encountered without receiving reverse link transmissions from the mobile station  90 . Depending on the new frame&#39;s classification and the RBS&#39;s current operational state, the RBS  36  responds as shown in  FIG. 5  and described below.  
         [0026]     If the RBS  36  is in the Good Frame State  102  the RBS  36  responds as follows: 1) if the new frame is a Good frame, the RBS  36  sends the frame payload to the BSC/ANC  70  along with a corresponding header, and remains in the Good Frame State  102 ; 2) if the new frame is a Bad frame, the RBS  36  sends a header with an erasure indication to the BSC/ANC  70 , but not the frame&#39;s payload, and transitions to the Erased Frame State  104 ; 3) if the new frame is an Idle frame, the RBS  36  sends a header with an idle indication to the BSC/ANC  70 , but not the frame&#39;s payload, and transitions to the Idle Frame State  106 .  
         [0027]     If the RBS  36  is in the Erased Frame State  104  the RBS  36  responds as follows: 1) if the new frame is a Good frame, the RBS  36  sends the frame payload to the BSC/ANC  70  along with a corresponding header, and transitions to the Good Frame State  102 ; 2) if the new frame is a Bad frame, the RBS  36  refrains from sending a header or the frame&#39;s payload to the BSC/ANC  70  (i.e., sends neither) and remains in the Erased Frame State  104 ; 3) if the new frame is an Idle frame, the RBS  36  sends a header with an idle indication to the BSC/ANC  70 , but not the frame&#39;s payload, and transitions to the Idle Frame State  106 .  
         [0028]     If the RBS  36  is in the Idle Frame State  106  the RBS  36  responds as follows: 1) if the new frame is a Good frame, the RBS  36  sends the frame payload to the BSC/ANC  70  along with a corresponding header, and transitions to the Good Frame State  102 ; 2) if the new frame is a Bad frame, the RBS  36  sends a header with a erasure indication, but not the frame&#39;s payload, to the BSC/ANC  70  and transitions to the Erased Frame State  104 ; 3) if the new frame is an Idle frame, the RBS  36  refrains from sending a header or the frame&#39;s payload to the BSC/ANC  70  (i.e., sends neither) and remains in the Idle Frame State  106 .  
         [0029]     Thus, as can be seen, the illustrative embodiment of the RBS  36  logic refrains from sending Idle frame headers and Erased frame headers to the BSC/ANC  70  if the RBS  36  is already in corresponding state. As such, the load on the backhaul communication link to the BSC/ANC  70  is reduced when multiple Idle frames are encountered in succession and when multiple Erased frames are encountered in succession.  
         [0030]     Some complementary changes in logic at the BSC/ANC  70  allow the presence of the present invention to be transparent to the frame selection algorithm. At the BSC/ANC  70 , the Good/Idle/Erased frame inputs for the new frame from the various RBSs  36  are examined, and a corresponding frame indication (and sometimes payload) are sent to the frame selection algorithm  80 . In essence, the BSC/ANC  70  maintains a state machine S for each RBS  36  in the active set (e.g., S X , S Y ) that reports to that BSC/ANC  70 , and the inputs to the frame selection algorithm  80  for each RBS  36  are determined based on the current state of the corresponding state machine and the classification of the “new” frame from that RBS  36 . Each state machine S X ,S Y  in the BSC/ANC  70  may be thought of as having three operational states: Good State  112 , Erased State  114 , and Idle State  116 . Depending on the frame classification data from the corresponding RBS  36  and the state machine&#39;s current operational state, the state machine S X ,S Y  responds as shown in  FIG. 6  and described below.  
         [0031]     If the state machine (S X  or S Y ) is in the Good State  112 , the state machine responds as follows: 1) for a Good frame indication from the RBS  36 , the state machine indicates a Good frame to the frame selection algorithm  80 , forwards the corresponding frame payload to the appropriate entities for further processing, and remains in the Good State  112 ; 2) for a Erased frame indication from the RBS  36 , the state machine indicates an Erased frame to the frame selection algorithm  80  and transitions to the Erased State  114 ; 3) for an Idle frame indication from the RBS  36 , the state machine sends an idle indication to the frame selection algorithm  80  and transitions to the Idle State  116 .  
         [0032]     If the state machine (S X  or S Y ) is in the Erased State  114  the state machine responds as follows: 1) for a Good frame indication from the RBS  36 , the state machine indicates a Good frame to the frame selection algorithm  80 , forwards the corresponding frame payload to the appropriate entities for further processing, and transitions to the Good State  112 ; 2) if the state machine does not receive any frame classification indication from the RBS  36  at the frame boundary, thereby indicating an Erased frame, the state machine indicates an Erased frame to the frame selection algorithm  80  and remains in the Erased State  114 ; 3) for an Idle frame indication from the RBS  36 , the state machine sends an Idle frame indication to the frame selection algorithm  80  and transitions to the Idle State  116 .  
         [0033]     If the state machine (S X  or S Y ) is in the Idle State  116 , the state machine responds as follows: 1) for a Good frame indication from the RBS  36 , the state machine indicates a Good frame to the frame selection algorithm  80 , forwards the corresponding frame payload to the appropriate entities for further processing, and transitions to the Good State  112 ; 2) for a Erased frame indication from the RBS  36 , the state machine indicates an Erased frame to the frame selection algorithm  80  and transitions to the Erased State  114 ; 3) if the state machine does not receive any frame classification indication from the RBS  36  at the frame boundary, thereby indicating an Idle frame, the state machine sends an indication of an Idle frame to the frame selection algorithm  80  and remains in the Idle State  116 .  
         [0034]     As can be seen, the logic of the state machine (S X  or S Y ) in effect supplies the “missing” indications of frame classification to the frame selection algorithm  80  for those classification reports that were abstained from due to the logic of  FIG. 5 . Thus, the frame selection algorithm  80  is not adversely affected by the reduction in backhaul communication link loading made available by the present invention.  
         [0035]     The frame selection algorithm  80  may function to select the good frame when any of the state machines S X ,S Y  indicate a Good frame; select an idle frame when at all the state machines S X ,S Y  indicate an Idle frame; and select an erased frame when any of the state machines S X ,S Y  indicate an Erased frame with no state machines S X ,S Y  indicating a Good frame. An exemplary process flowchart for this process is shown in  FIG. 7 . At step  210 , the inputs from the various state machines S X ,S Y  for all of the RBSs  36  in the active set are collected. If any of the state machines S X ,S Y  indicate a Good frame (step  220 ), a Good frame is selected (step  230 ). If not, the process proceeds to check whether all of the state machines S X ,S Y  indicate an Idle frame (step  240 ). If so, an Idle frame is selected (step  250 ). If not, then, in this example, all state machines S X ,S Y  must be indicating an Erased frame, and an Erase frame is selected (step  260 ).  
         [0036]     In some embodiments, an alternative approach may be taken that implicitly indicates an Idle frame after a Good frame. For this embodiment, the RBS  36  may operate generally as described above, but when an Idle frame is detected while in the Good Frame State  102 , the RBS  36  may not send the header to the BSC/ANC  70 . That is, if the RBS  36  is in the Good Frame State  102 , the RBS  36  responds to an Idle frame by refraining from sending a header to the BSC/ANC  70  (i.e., sends nothing) and transitions to the Idle Frame State  106 . To handle this modification, the logic of the BSC/ANC  70  is modified for the Good State  112 . In this embodiment, if the state machine (S X  or S Y ) is in the Good State  112 , and no frame classification indication is received from the RBS  36  at the frame boundary, this is treated as an Idle frame indication, and the state machine sends an indication of an Idle frame to the frame selection algorithm  80  and transitions to the Idle State  116 . As before, this modification is essentially transparent to the frame selection algorithm  80 .  
         [0037]     As can be appreciated, loading on the backhaul communication link from the RBSs  36  to the BSC/ANC  70  may be reduced via the present invention. While it is believed the most load reduction is achieved if both the Idle frames and Erased frames are handled as described above, some embodiments of the present invention handle only Idle frames or only Erased frames as described above, and resort to conventional handling of the other frame classifications.  
         [0038]     As pointed out above, the present invention may be practiced in a wide variety of system architectures. Further, it should be noted that the BSC/ANC  70  providing the state machine functionality used to generate the indications input to the frame selection algorithm may be the call anchor or may be some other BSC/ANC  70  in the system  10 .  
         [0039]     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.  
         [0040]     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.