Patent Publication Number: US-2012033580-A1

Title: Radio network controller peer-to-peer exchange of user equipment measurement information

Description:
CROSS REFERENCE TO RELATED APPLICATION(S) 
     This application is a continuation of U.S. Non-Provisional Application No. 10/606,716 filed Jun. 26, 2003 which claims priority from U.S. provisional application No. 60/392,122, filed Jun. 27, 2002, which are incorporated by reference as if fully set forth. 
    
    
     FIELD OF INVENTION 
     This invention relates to wireless communication systems. In particular, the invention relates to the transfer of information between radio network controllers in such systems. 
     BACKGROUND 
       FIG. 1  is an illustration of a wireless communication system where all the users are handled by a radio network controller (RNC)  20 . Each user, wireless transmit/receive unit (WTRU)  24 , wirelessly communicates with a Node-B  22   1 . A group of Node-Bs  22   1 - 22   2  are controlled by the radio network controller (RNC)  20 . 
     As the WTRU  24  moves, the WTRU  24   1 ,  24   2  is handed off between base stations/Node-Bs  32 ,  34 .  FIG. 2  is an illustration of a WTRU  24   1 ,  24   2  moving from an area handled by a first RNC  28  to an area handled by a second RNC  26 . The WTRU  24   2  is considered to have “drifted” into the new RNC&#39;s region and that RNC (the second RNC) is considered the drift RNC (D-RNC)  26 . The D-RNC  26  has Node-Bs  32 , which it controls. The first RNC is referred to as the servicing RNC (S-RNC)  28 . Typically, the RNCs (S-RNC  28  and D-RNC  26 ) can communicate some information to each other over a RNC interface (Iur). After the WTRU  24   2  “drifts” to the D-RNC  26 , the D-RNC  26  performs functions, such as dynamic channel allocation (DCA), admission control, scheduling and RRM functions for the “drifting” WTRU  24   2 . The S-RNC  28  still performs other functions for the “drifting” WTRU  24   2 , such as handoff decisions and collecting of WTRU downlink measurements. When the WTRU  24  has not “drifted”, such as in  FIG. 1 , the RNC  20  handling the WTRU  24  performs the functions of both the S-RNC  28  and D-RNC  26 . 
     Under the R99, R4 and R5 Iur specifications as proposed for the third generation partnership project (3GPP), when the WTRU  24   1 ,  24   2  is handed over from the S-RNC  28  to the D-RNC  26 , cell loading and many Node-B measurements are sent from the S-RNC  28  to the D-RNC  26 . However, there is no mechanism to transfer certain information from the S-RNC  28  to the D-RNC  26 , such as the WTRU measurements. 
     Accordingly, it is desirable to have better peer-to-peer communications between RNCs. 
     SUMMARY 
     A drifting wireless transmit/receive unit (WTRU) has an associated drift radio network controller (D-RNC) and an associated servicing radio network controller (S-RNC). The D-RNC sends a request message to the S-RNC requesting measurements of the drifting WTRU. The S-RNC receives the request message and sends an information message with the requested measurements to the D-RNC. The D-RNC receives the information message. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING(S) 
         FIG. 1  is an illustration of a RNC handling a WTRU. 
         FIG. 2  is an illustration of a WTRU drifting between RNCs. 
         FIG. 3  is a block diagram of a preferred embodiment for peer-to-peer information exchange. 
         FIG. 4  is a flow chart of a preferred embodiment for peer-to-peer information exchange. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S) 
     Although the preferred embodiments are described in conjunction with a third generation partnership program (3GPP) wideband code division multiple access (W-CDMA) system, the embodiments are applicable to other wireless communication systems. 
     Hereafter, a wireless transmit/receive unit (WTRU) includes but is not limited to a user equipment, mobile station, fixed or mobile subscriber unit, pager, or any other type of device capable of operating in a wireless environment. 
       FIG. 3  is a simplified block diagram of a S-RNC  40 , a D-RNC  38  and an IUR  36  for a “drifting” WTRU  24   2  using peer-to-peer information exchange.  FIG. 4  is a flow chart of peer-to-peer information exchange. The S-RNC  40  typically performs functions such as handoff decisions and collecting of WTRU downlink measurements for the “drifting” WTRU  24   2 . The D-RNC  38  typically performs functions such as DCA, admission control, scheduling and RRM functions for the “drifting” WTRU  24   2 . 
     The D-RNC  38  has a RRM  42 . The RRM  42  controls the resources for the WTRUs of cells associated with the D-RNC  38 . The D-RNC  38  collects uplink measurements for the cell of the “drifting” WTRU  24   2  as well as other cells using an uplink measurement collection device  44 . These measurements are available to the RRM  42  for use in resource allocation and management. The RRM  42  also has information for WTRUs that it is performing S-RNC functions. 
     The D-RNC  38  has logic associated with the RRM  42 . When the RRM  42  requires downlink measurements of the “drifting” WTRU  24   2  or a group or WTRUs, the logic  46  initiates a WTRU measurement request device  48  to send a message through the Iur  36  for such information, step  60 . 
     Examples of the information that may be requested by the D-RNC  38 , include downlink common control physical channel (CCPCH) received signal code power (RSCP), interference signal code power (ISCP) measurements and/or traffic volume measurements. Preferably, the D-RNC information request messages can not request the WTRU  24   2  to make and send measurements, but the D-RNC  38  requests such measurement information currently available at the S-RNC  40 . 
     The signaling messages on the Iur  36  allows any D-RNC  38  to initiate information exchange with S-RNCs on an individual WTRU, groups of WTRUs or WTRUs present in one or more cells for which it does not assume itself the role of an S-RNC. This procedure is preferably not a simple “forwarding” of WTRU-specific information, such as WTRU measurements. Preferably, the D-RNC logic  46  generally makes the decision of the type of information to request, although the logic function  46  may be performed by the controlling RNC (C-RNC). A logic function  46  in the D-RNC  38  decides if and when it will request measurements to be forwarded from the S-RNC  40 . For example, if the D-RNC  38  detects that more than a threshold number or percentage, such as 10%, of its WTRUs are in “drift” mode, it would typically start requesting measurements to be forwarded. In the preferred implementation, existing information elements and standardized WTRU measurements/reporting mechanisms defined by the 3GPP standard for Node-B interface (Iub)/Iur are utilized. 
     One preferred message allows the D-RNC  38  to request measurements for a particular “drift” WTRU  24   2  for a given time frame or for all the “drift” WTRUs in a given cell or group of cells associated with the S-RNC  40  for a given time frame. One scenario that requesting a group of WTRUs information is desirable is when many WTRUs having a particular S-RNC are in “drift” mode. For example, a first train station is supported by a first RNC and a second train station by a second RNC. All of the WTRUs boarding a train starting at the first station and departing at the second station may have the first RNC as the S-RNC  40  and the second RNC as the D-RNC  38 . In this scenario, requesting WTRU information for the group of “drifting” WTRUs reduces the messaging overhead. However, a scenario where the procedure allows only a single WTRU per message may be used, with increased messaging overhead. 
     The message is received by the “drifting” WTRU&#39;s S-RNC  40 , step  62 . That S-RNC  40  has a WTRU measurement collection device  52 . The WTRU measurement collection device  52  stores the particular WTRU&#39;s downlink measurements. A WTRU measurement response device  50  sends a measurement/information message to the D-RNC  38  through the Iur  36 , step  64 . The D-RNC RRM  42  uses these measurements in its resource allocations and management, step  66 . One benefit of transferring such data through the IUR  36  is such data transfer is typically quite fast. 
     One preferred approach for requesting and transferring the WTRU measurements uses the radio network sublayer application part (RNSAP) procedures. RNSAP has four basic modules. One of these modules is the “Global Procedures” module. That module contains procedures that involve signaling for exchange of cell level information between RNCs. For example, received total wide band power, load and global positioning system (GPS) timing information is exchanged using the Common Measurement messages. 
     The list of information exchanged using RNSAP Global Procedures is expanded to allow for better RRM. In particular, this information aids primarily handover decisions. For example, information associated with cell biasing of handovers to neighboring RNCs would aid in such decisions. In the proposed 3GPP system, the information exchanged using the Global Procedures module is not related to a particular WTRU or group of WTRUs. As a result, it does not support the transfer of WTRU data transfer across the Iur  36 . Preferably, information should transferred across the Iur  36  using RNSAP procedures, if the analogous cell information is available in the S-RNC  40  for relevant RRM decisions by the D-RNC  38 . 
     Such information exchange over the Iur  36  allows a D-RNC  38  to request WTRU measurement information from the S-RNC  40  and allows more cell information to be exchanged between peer RNCs using the RNSAP Global Procedures module. Typically, this exchange of information enhances the performance of RRM algorithms (DCA, Admission Control, Scheduling and others) in the D-RNC  38 , due to the availability of WTRU measurements. Enhanced RRM, especially DCA, facilitates performance, efficiency and robustness in wireless systems, such as the time division duplex (TDD) mode of 3GPP.