Abstract:
A wireless communication method and system for supporting an enhanced uplink dedicated channel (EU-DCH) inter-Node-B serving cell change. The system includes at least one wireless transmit/receive unit (WTRU) for transmitting data blocks, a target Node-B, a source Node-B and a serving radio network controller (S-RNC). The S-RNC includes a re-ordering buffer which stores data blocks correctly received from the WTRU. The S-RNC informs the target Node-B of a need for an EU-DCH inter-Node-B serving cell change from the source Node-B to the target Node-B. A medium access control (MAC) entity that handles EU-DCH functionalities is set up in the target Node-B. Hybrid automatic repeat request (HARQ) processes and transmission sequence numbers (TSNs) are not reset at the WTRU. Using a new data indicator, the WTRU transmits a data block to the target Node-B that was previously transmitted to the source Node-B, but was not correctly received by the source Node-B.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a continuation of U.S. patent application Ser. No. 10/945,355, filed Sep. 20, 2004, which claims the benefit of U.S. Provisional Patent Application Ser. No. 60/517,694, filed Nov. 5, 2003, which are incorporated by reference as if fully set forth herein. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to the field of wireless communications. More specifically, the present invention relates to efficiently implementing an enhanced uplink dedicated channel (EU-DCH) inter-Node-B serving cell change in a multi-cell wireless communication system, such as a frequency division duplex (FDD) or time division duplex (TDD) system. 
       BACKGROUND 
       [0003]    Methods for improving uplink coverage, throughput and transmission latency are currently being investigated in third generation partnership project (3GPP) in the context of the Release 6 (R6) universal mobile telecommunications system (UMTS) study item “FDD uplink enhancements”. 
         [0004]    It is widely anticipated that in order to achieve these goals, Node-B (base station) will take over the responsibility of scheduling and assigning uplink resources (physical channels) to users. The principle is that Node-B can make more efficient decisions and manage uplink radio resources on a short-term basis better than the Radio Network Controller (RNC), even if the RNC retains coarse overall control. A similar approach has already been adopted in the downlink for Release 5 (R5) high speed downlink packet access (HSDPA) in both UMTS FDD and TDD modes. 
         [0005]    It is also envisioned there could be several independent uplink transmissions processed between a wireless transmit/receive unit (WTRU) and a universal terrestrial radio access network (UTRAN) within a common time interval. One example of this would be medium access control (MAC) layer hybrid automatic repeat request (HARQ) or simply MAC layer automatic repeat request (ARQ) operation where each individual transmission may require a different number of retransmissions to be successfully received by UTRAN. To limit the impact on system architecture, it is expected that protocol layers above the MAC should not be affected by introduction of the EU-DCH. One requirement that is introduced by this is the in-sequence data delivery to the radio link control (RLC) protocol layer. Therefore, similar to HSDPA operation in the downlink, a UTRAN re-ordering function is needed to organize the received data blocks according to the sequence generated by the WTRU RLC entity. 
         [0006]    In a conventional wireless communication system based on downlink HSDPA operation, new MAC entities for the EU-DCH in the WTRU and Node B are required. The Node B MAC entity would be responsible for scheduling and assignment of physical resources, and the re-ordering function would be incorporated in the system for in-sequence delivery to the RNC. 
         [0007]      FIG. 1  is a signal flow diagram depicting the operation of a conventional wireless communication system  100  in which out-of-sequence delivery to an RLC entity in the serving-RNC (S-RNC) and RLC recovery occur on the WTRU side during an EU-DCH inter-Node-B serving cell change. The wireless communication system  100  includes a WTRU  105 , a target Node-B  110 , a source Node-B  115  and an S-RNC  120 . 
         [0008]    Still referring to  FIG. 1 , when the S-RNC  120  realizes a need for an EU-DCH inter-Node-B serving cell change (step  125 ), the S-RNC sends an Iub request message  130  to the target Node-B  110 . The target Node-B  110  is informed of the EU-DCH inter-Node-B serving cell change and a MAC entity is set up (step  135 ). The target Node-B sends an Iub response message  140  to the S-RNC  120  which, in turn, sends a radio resource control (RRC) request message  145  to the WTRU  105 . The EU-DCH inter-Node-B serving cell change is realized in the WTRU  105 , whereby HARQ processes and transmission sequence numbers (TSNs) are reset (step  150 ). The WTRU  105  then sends an RRC complete message  155  to the S-RNC  120  which, in turn, sends an Iub request message  160  to the source Node-B  115 . The source Node-B  115  is informed of the EU-DCH inter-Node-B serving cell change and the re-ordering buffer is flushed (step  165 ). The source Node-B then sends an Iub response message  170  to the S-RNC and an out-of-sequence delivery message  175  to the RLC in the S-RNC  120 . An RLC status report message  180  is then sent from the S-RNC  120  to the WTRU  105  to initiate an RLC recovery process  185 . 
         [0009]    Since the EU-DCH inter-Node-B serving cell change results in switching from one Node-B to another, and the re-ordering queue status is only known to the source Node-B, it is necessary to reset the HARQ processes and TSNs in the WTRU  105 , and flush the re-ordering queues in the source Node-B  115 . This results in out-of-sequence delivery to higher layers and significant delay in recovering data lost in the WTRU  105 . 
         [0010]    An example of out-of-sequence delivery to RLC and RLC recoveries caused EU-DCH inter-Node-B serving cell change in the conventional wireless communication system  200  is shown in  FIG. 2 . The wireless communication system  200  includes a WTRU  205 , a target Node-B  210 , a source Node-B  215  and an S-RNC  220 . 
         [0011]    Before the EU serving cell is changed, protocol data units (PDUs) with sequence numbers (SNs)  1 - 5  are sent from a data buffer  225 , located in the WTRU  205 , to the source Node-B  215 . However, in the example shown in  FIG. 2 , only the PDU with SNs  1 ,  3  and  4  are received correctly by the source Node-B  215  and stored in a re-ordering buffer  230  in the source Node-B  215 . Thus, in this example, the PDUs with SNs  2  and  5  are missing. 
         [0012]    Still referring to  FIG. 2 , after the EU serving cell is changed, the HARQ processes and SNs in the WTRU  205  are reset (step  235 ), and the re-ordering buffer  230  in the source Node-B  215  is flushed (step  240 ). In step  245 , an out-of-sequence delivery, (i.e., PDUs  1 ,  3 ,  4 ), to the RLC in the S-RNC  220  occurs. The RLC in the S-RNC  220  then generates a first RLC status report message  250  requesting PDUs associated with the old SN  2 . The terminology “old” refers to the fact that the PDU with SN  2  is missing in the source Node-B  215  before handover. In response to receiving the message  250 , the WTRU  205  transmits the PDUs, associated with the old SN  2 , with a new SN  1  to a re-ordering buffer  285  in the target Node-B  210  (step  285 ). Additionally, the WTRU  205  transmits the PDUs, associated with the old SN  6 , with a new SN  2  to the re-ordering buffer  285  in the target Node-B  210  (step  258 ). The new SN  1  and SN  2  are then forwarded to the RLC in the S-RNC  220  (respective steps  285  and  285 ). In step  285 , an out-of-sequence delivery to the RLC in the S-RNC  220  occurs again. The RLC in the S-RNC  220  then generates a second RLC status report message  285  requesting PDUs associated with the old SN  5 . In response to receiving the message  285 , the WTRU  205  transmits the PDUs, associated with the old SN  5 , with a new SN  3  to a re-ordering buffer  285  in the target Node-B  210  (step  290 ). The new SN  3  is then forwarded to the RLC in the S-RNC  220  (step  295 ). 
         [0013]    The conventional systems  100 ,  200 , shown in  FIGS. 1 and 2 , respectively, experience significant delays due to flushing a re-ordering buffer and recovering PDUs from the WTRUs  105 ,  205 . It is desired to reduce such delays. 
       SUMMARY 
       [0014]    A wireless communication method and system for supporting an EU-DCH inter-Node-B serving cell change. The system includes at least one wireless transmit/receive unit (WTRU) for transmitting data blocks, a target Node-B, a source Node-B and a serving radio network controller (S-RNC). The S-RNC includes a re-ordering buffer used for storing data blocks correctly received by the source Node-B and the target Node-B from the WTRU. The S-RNC sends an Iub request message to the target Node-B informing the target Node-B of a need for an EU-DCH inter-Node-B serving cell change from the source Node-B to the target Node-B. A MAC entity that handles EU-DCH functionalities is set up in the target Node-B, and the target Node-B sends an Iub response message back to the S-RNC. The S-RNC then sends a radio resource control (RRC) request message to the WTRU. The WTRU then sends an RRC complete message to the S-RNC. 
         [0015]    Before the EU-DCH serving cell change takes place, a MAC entity that handles EU-DCH functionalities may be set up in the target Node-B. The WTRU then sends an RRC message to the S-RNC indicating that the EU-DCH serving cell change has been completed. The S-RNC may send an Iub request message to the source Node-B indicating that the EU-DCH serving cell change has been completed. The MAC entity that handles EU-DCH functionalities in the source Node-B may be released and the source Node-B may send an Iub response message to the S-RNC in response to the Iub Request message. After the EU-DCH inter-Node-B serving cell change is completed, if there is any data block that was previously transmitted by the WTRU to the source Node-B that was not successfully acknowledged, the WTRU transmits it using a new data indicator to the target Node-B. The target Node-B may forward the data block to the re-ordering buffer in the S-RNC. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    A more detailed understanding of the invention may be had from the following description, given by way of example and to be understood in conjunction with the accompanying drawings wherein: 
           [0017]      FIGS. 1 and 2  are signal flow diagrams depicting the operation of conventional wireless communication systems in which out-of-sequence delivery to the RLC and RLC recovery occur during an EU serving cell change; 
           [0018]      FIG. 3  shows a wireless communication system in which a Node-B communicates with an RNC having a re-ordering buffer located therein in accordance with the present invention; 
           [0019]      FIG. 4  is a signal flow diagram depicting an example of the operation of a wireless communication system during EU serving cell change in accordance with the present invention; 
           [0020]      FIG. 5  is a signal flow diagram depicting the operation of a wireless communication system before, during and after an EU-DCH inter-Node-B serving cell change in accordance with the present invention; and 
           [0021]      FIG. 6  is a flow chart of a process including method steps for supporting an EU-DCH inter-Node-B serving cell change in accordance with the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0022]    The preferred embodiments will be described with reference to the drawing figures where like numerals represent like elements throughout. 
         [0023]    Hereafter, the terminology “WTRU” includes but is not limited to a user equipment, a mobile station, a fixed or mobile subscriber unit, a pager, or any other type of device capable of operating in a wireless environment. When referred to hereafter, the terminology “Node-B” includes but is not limited to a base station, a site controller, an access point or any other type of interfacing device in a wireless environment. 
         [0024]    The present invention is applicable to any type of wireless communication systems such as UMTS-TDD and FDD, time division synchronous code division multiple access (TD-SCDMA), code division multiple access 2000 (CDMA 2000), and CDMA in general or any other type of wireless communication system. With respect to CDMA 2000, the present invention may be implemented in EV-DO (i.e. data only) and EV-DV (i.e. data and voice). 
         [0025]    The present invention implements a re-ordering function for EU at the RNC. With the proper implementation of re-ordering function, HARQ processes and TSNs do not need to be reset in the WTRU, and the re-ordering buffer does not need to be flushed during an EU-DCH inter-Node-B serving cell change. This helps to avoid the loss of MAC data and RLC recoveries during an EU-DCH inter-Node-B serving cell change and reduces transmission delay. 
         [0026]    In its transmission to the new target Node-B, the WTRU sets a “new data indicator” for data blocks that are not acknowledged (ACK) by the source Node-B by the time of EU-DCH inter-Node-B serving cell change, and the WTRU should resume the same sequence numbers for data blocks from where it stopped in the source Node-B. By moving the re-ordering buffers to the RNC, transmission sequence can be maintained across Node-B&#39;s. Transmission sequence and re-ordering are not affected by the change of Node-B&#39;s. 
         [0027]      FIG. 3  shows the architecture of a wireless communication system  300  including a Node-B  305  and an RNC  310  operating in accordance with the present invention. At least one re-ordering buffer  315  exists within the RNC  310 . An HARQ/ARQ entity  320  for EU-DCH is located at the Node-B  305  within a MAC entity  325  that handles EU-DCH functionalities. If a data block is decoded successfully at the Node-B  305 , it is forwarded to the re-ordering buffer  315  in the RNC  310 . The re-ordering buffer  315  performs a re-ordering function for data blocks correctly received from the Node-B  305  so as to support in-sequence delivery to higher protocol layers  330  of the RNC  310 . 
         [0028]    The WTRU will maintain TSNs used in the source cell. Transmissions that are already transmitted in the source cell, but not successfully acknowledged, will be retransmitted in the target cell. No data is lost in the WTRU. For proper combining in the target cell, it necessary to set the new data indicator for all new transmissions in the target cell, including transmissions that were already attempted without success in the source cell. 
         [0029]    The re-ordering buffer  315  located at the RNC  310  is not affected by an EU-DCH inter-Node-B serving cell change (hard handover). A re-ordering buffer does not need to be flushed in the source Node-B and reinitialized in the target Node-B. In-sequence delivery can therefore be maintained. Transmissions attempted in a source cell but not yet successfully acknowledged are reinitiated in a new cell without loss of data. 
         [0030]    The WTRU performs several actions after an EU-DCH inter-Node-B serving cell change. Since TSNs are maintained, the MAC entity that handles EU-DCH functionalities in the WTRU does not need to reset the HARQ processes. All it needs to do is to set “new data indicator” for data blocks that are not ACKed by the source Node-B by the time of an EU-DCH inter-Node-B serving cell change. The sequence numbers of those data blocks are kept the same. For transmission of other new data in the target cell, the WTRU starts the sequence number after the sequence number where it stopped in the source Node-B by the time of an EU-DCH inter-Node-B serving cell change. TSNs are not affected by the cell change. 
         [0031]      FIG. 4  is a signal flow diagram depicting an example of the operation of a wireless communication system  400  during an EU-DCH inter-Node-B serving cell change. The wireless communication system  400  includes a WTRU  405 , a target Node-B  410 , a source Node-B  415  and an S-RNC  420 . 
         [0032]    Before the EU inter-Node-B serving cell is changed, PDUs with SNs  1 - 5  are transmitted from a data buffer  425 , located in the WTRU  405 , to the source Node-B  415 . However, in the example shown in  FIG. 4 , only SNs  1 ,  3  and  4  are received correctly by the source Node-B  415  and forwarded to a re-ordering buffer  430  in the S-RNC  420 . The PDUs with SNs  2  and  5  are missing. After the EU-DCH inter-Node-B serving cell change, the same SNs are maintained (step  435 ) and the WTRU  405  retransmits PDUs with SNs  2  and  5  to the target Node-B  410  (i.e., target cell) with a new data indicator set. Based on the SN where transmission stopped in the source cell (i.e., SN  5 ), the WTRU  405  increments the SN (starting from SN  6 ) for other new data in the target cell. The gap of missing SN is filled at the S-RNC  420  (step  440 ). 
         [0033]    The present invention dramatically reduces delay as compared to the delay experienced by the conventional wireless systems  100  and  200 , shown in  FIGS. 1 and 2 , respectively. 
         [0034]      FIG. 5  is a signal flow diagram depicting signaling for a wireless communication system  500  before, during and after an EU-DCH inter-Node-B serving cell change (hard-handover) in accordance with the present invention. The wireless communication system  500  includes a WTRU  505 , a target Node-B  510 , a source Node-B  515  and an S-RNC  520 . A re-ordering buffer  315  is located at the S-RNC  520 . 
         [0035]    Still referring to  FIG. 5 , when the S-RNC  520  realizes a need for an EU-DCH inter-Node-B serving cell change (step  525 ), the S-RNC sends an Iub request message  530  to the target Node-B  510 . The target Node-B  510  is informed of the cell change and a MAC entity that handles EU-DCH functionalities is set up in the target Node-B  510  (step  535 ). The target Node-B sends an Iub response message  540  to the S-RNC  520  which, in turn, sends an RRC request message to the WTRU  505 . In step  550 , the EU-DCH inter-Node-B serving cell change is realized in the WTRU  505  and a “new data indicator” is set for data blocks that are not ACKed by the source Node-B  515  yet for transmission in the target cell. 
         [0036]    In system  500 , the HARQ processes and SNs are maintained at the WTRU during hard handover, unlike in the conventional systems  100  and  200  shown in  FIGS. 1 and 2 , respectively, in which the HARQ processes and SNs are reset at the WTRU during hard handover. The WTRU  505  then sends an RRC complete message  555  to the S-RNC  520  which, in turn, sends an Iub request message  560  to the source Node-B  515 . The source Node-B is informed of the cell change and the MAC entity that handles the EU-DCH functionalities in the source Node-B  515  is released (step  565 ). 
         [0037]    The wireless communication system  500  is advantageous over the conventional systems  100  and  200  depicted in  FIGS. 1 and 2  because the re-ordering buffer  315  in the S-RNC  520  is not flushed during the EU-DCH inter-Node-B serving cell change. Additionally, as previously mentioned, in the target cell the SNs and H-ARQ processes within the WTRU  505  are not reset and only the new data indicator is set for data blocks that are not ACKed by the source Node-B by the time of an EU-DCH inter-Node-B serving cell change. No out-of-sequence delivery to the RLC and no RLC recovery (on the WTRU side) are caused by the EU-DCH inter-Node-B serving cell change. 
         [0038]      FIG. 6  is a flow chart of a process  600  including method steps for supporting an EU-DCH inter-Node-B serving cell change in accordance with the present invention. In step  605 , the S-RNC  520  sends a first (Iub request) message  530  to the target Node-B  510  informing the target Node-B  510  of a need for an EU-DCH inter-Node-B serving cell change. In step  610 , a MAC entity that handles EU-DCH functionalities is set up in the target Node-B  510 . In step  615 , the target Node-B responds to the first message by sending a second (Iub response) message to the S-RNC  520 . In response to receiving the second message, the S-RNC  520  sends a third (RRC request) message to the WTRU  505  informing the WTRU  505  of the need for an EU-DCH inter-Node-B serving cell change (step  620 ). By using a new data indicator, the WTRU  505  transmits a data block to the target Node-B  510  that was previously transmitted by the WTRU  505  to the source Node-B  515 , but was not correctly received by the source Node-B  515  (step  625 ). 
         [0039]    Still referring to  FIG. 6 , the WTRU  505  sends a fourth (RRC complete) message to the S-RNC indicating that the EU-DCH inter-Node-B serving cell change has been completed (step  630 ). In step  635 , the S-RNC  520  sends a fifth (Iub request) message to the source Node-B  515  indicating that the EU-DCH inter-Node-B serving cell change has been completed. In step  640 , the MAC entity in the source Node-B is released. Finally, in step  645 , the source Node-B  515  sends a sixth (Iub response) message to the S-RNC  520  in response to the fifth message. 
         [0040]    While the present invention has been described in terms of the preferred embodiment, other variations which are within the scope of the invention as outlined in the claims below will be apparent to those skilled in the art.