Abstract:
A method and apparatus for minimizing redundant enhanced uplink (EU) allocation requests and fault-isolating EU transmission failures that occur between a wireless transmit/receive unit (WTRU) and a Node-B. The WTRU transmits an enhanced dedicated channel (E-DCH) allocation request to the Node-B over an uplink (UL) EU channel. In one embodiment, if E-DCH allocation cannot be provided within a predetermined time period, the Node-B sends an acknowledgement message to the WTRU via a downlink (DL) EU signaling channel without sending E-DCH allocation information. The request is queued in the Node-B and the WTRU refrains from transmitting the same request until after the time period expires or resources become available. In another embodiment, appropriate actions are taken to correct EU transmission failures by determining whether an E-DCH allocation request was unsuccessfully delivered via the UL EU channel or whether channel allocation information was unsuccessfully delivered via the DL EU signaling channel.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Application No. 60/567,144 filed Apr. 30, 2004, which is incorporated by reference as if fully set forth. 
    
    
     FIELD OF INVENTION 
     The present invention is related to a wireless communication system including a wireless transmit/receive unit (WTRU), at least one Node-B and a radio network controller (RNC). More particularly, the present invention is a method and apparatus for minimizing redundant enhanced uplink (EU) allocation requests and fault-isolating EU transmission failures. 
     BACKGROUND 
     Methods for improving uplink (UL) coverage, throughput and transmission latency are being investigated in Release 6 (R6) of the 3rd Generation Partnership Project (3GPP). In order to successfully implement these methods, the scheduling and assigning of UL radio resources have been moved from a radio network controller (RNC) to a Node-B such that the Node-B can make decisions and manage UL radio resources on a short-term basis more efficiently than the RNC, even if the RNC retains overall control over the Node-B. 
     In order for the WTRU to transmit on enhanced dedicated channel (E-DCH), the WTRU must identify the need for E-DCH transmissions by transmitting E-DCH channel allocation requests to the Node-B. Then, the Node-B provides allocation of E-DCH physical resources to the WTRU that have requested the E-DCH channel. 
     When there are not enough UL resources for the E-DCH channel allocation requests, the Node-B cannot immediately allocate resources of E-DCH transmission for all WTRUs that have requested the E-DCH. If the WTRU does not receive an E-DCH allocation within a predetermined time period, the WTRU may retransmit the request until the WTRU receives E-DCH channel allocation information. 
     Since the transmission of an E-DCH channel allocation request interferes with other WTRUs, when each WTRU transmits and retransmits the same channel allocation request multiple times, the UL EU channel will increase UL interference. Thus, the overall efficiency of the system will be degraded. 
     Therefore, there is a need to minimize utilization of the UL signaling channel while maintaining proper EU scheduling operation. Furthermore, a procedure for fault-isolating EU transmission failures is desired. 
     SUMMARY 
     The present invention is a method and apparatus for minimizing redundant EU allocation requests and fault-isolating EU transmission failures that occur between a WTRU and a Node-B. The WTRU transmits an enhanced dedicated channel (E-DCH) allocation request to the Node-B over a UL EU channel when the WTRU has scheduled E-DCH data to transmit. 
     In one embodiment, the Node-B receives the channel allocation request and determines whether channel allocation can be provided for the WTRU within a predetermined channel request response time period. If channel allocation for the WTRU can be provided within the predetermined channel request response time period, the Node-B sends scheduling information, (i.e., E-DCH channel allocation information), to the WTRU. Otherwise, the Node-B only sends an acknowledgment message to the WTRU indicating that the channel allocation request has been received without sending a channel allocation. In response to the acknowledgement message, the WTRU refrains from transmitting the same channel allocation request for a predetermined maximum time to allocate period and the request is queued in the Node-B. If the maximum time to allocate period expires without receiving a channel allocation, the WTRU retransmits the channel allocation request. 
     In another embodiment, appropriate actions are taken to correct EU transmission failures by determining whether an E-DCH allocation request was unsuccessfully delivered via the UL EU channel or whether channel allocation information was unsuccessfully delivered via the DL EU signaling channel. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more detailed understanding of the invention may be had from the following description of a preferred embodiment, given by way of example and to be understood in conjunction with the accompanying drawing wherein: 
         FIG. 1  is a block diagram of a wireless communication system in accordance with the present invention; 
         FIG. 2  is a flow diagram of a process for reducing congestion in a UL EU channel established in the system of  FIG. 1  in accordance with one embodiment of the present invention; and 
         FIG. 3  is a flow diagram of a process for determining signaling channel failure during channel allocation and taking corrective actions in accordance with another embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereafter, the terminology “WTRU” includes but is not limited to a user equipment (UE), 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. 
     The features of the present invention may be incorporated into an integrated circuit (IC) or be configured in a circuit comprising a multitude of interconnecting components. 
       FIG. 1  is a block diagram of a wireless communication system  100  in accordance with the present invention. The system  100  includes a WTRU  102 , one or more Node-Bs  104  and an RNC  106 . The RNC  106  controls overall EU operation by configuring EU parameters for the Node-B  104  and the WTRU  102 , such as maximum allowed EU transmit power or available channel resources per Node-B. The WTRU  102  sends a channel allocation request to the Node-B  104  via a UL EU channel  110  and the Node-B  104  sends channel allocation information via one or more downlink (DL) EU signaling channels  112 . After EU radio resources are allocated for the WTRU  102 , the WTRU  102  transmits data via the UL EU channel  110 . The Node-B  104  includes a request priority queue  114  for queuing E-DCH allocation requests and a maximum time to allocate timer  116  for establishing an E-DCH allocation request response time period. The WTRU includes a channel allocation response timer  118  for generating periodic channel allocation requests when a channel allocation has not been received from the Node-B  104 . 
       FIG. 2  is a flow diagram of a process  200  for reducing congestion in the UL EU channel  110  in accordance with one embodiment of the present invention. When the WTRU  102  has E-DCH data to transmit, the WTRU  102  sends an E-DCH allocation request to the Node-B  104  via the UL EU channel  110  (step  202 ). The signaling of the E-DCH allocation request may be either physical or medium access control (MAC) layer signaling. 
     Upon receiving the E-DCH allocation request from the WTRU  102 , the Node-B  104  determines whether there are resources available for allocation of the E-DCH to the WTRU within a predetermined channel request response time period (step  204 ). The channel request response time period is a maximum time period within which the Node-B  104  should respond to the channel allocation request. The channel request response time period established by the maximum time to allocate timer  116  of the Node-B  104  is activated when the E-DCH allocation request is received by the Node-B  104 . The channel request response time period may be a fixed value in the system or configured by the RNC  106  for each EU radio access bearer (RAB) and signaled to both the Node-B  104  and the WTRU  102 . 
     If E-DCH resources are available, the Node-B  104  sends an acknowledgement message to the WTRU  102  indicating that the E-DCH allocation request has been received (step  206 ), and also sends scheduling information, (i.e., E-DCH allocation information), within the channel request response time period via the DL EU signaling channel  112  (step  207 ). The WTRU  102  then transmits data through the UL EU channel  110  in accordance with the scheduling information (step  208 ). 
     If the E-DCH resources cannot be allocated before the channel request response time period expires, the Node-B  104  sends an acknowledgement message to the WTRU  102  indicating that the E-DCH allocation request has been received, but does not send scheduling information to the WTRU  102  before the channel request response time period expires (step  210 ). The acknowledgement message does not include scheduling information, but merely confirms that the Node-B  104  has received the channel allocation request and will process the request when resources become available. 
     In accordance with one embodiment of the present invention, the E-DCH allocation request indicates a priority. After sending the acknowledgement message to the WTRU  102  confirming reception of the E-DCH allocation request, the E-DCH allocation request is stored in a request priority queue  114  in the Node-B  104  based on the indicated priority of the request (step  212 ). When the request is placed in the request priority queue  114 , the maximum time to allocate timer  116  is activated or, equivalently, the time of reception of the E-DCH allocation request is recorded. The maximum time to allocate is a maximum time period within which the E-DCH allocation request should be served before the E-DCH allocation request is finally determined to have failed. The maximum time to allocate may be unique to each transmission that maps to a particular data flow or data priority class. 
     The requests within the request priority queue  114  in the Node-B  104  may be serviced on a first-in first-out (FIFO) basis. If there are not enough resources, the allocation is further delayed until it becomes available. If there are available resources, the Node-B  104  services at least one request in the request priority queue  114 . 
     Upon receiving the acknowledgement message from the Node-B  104  in response to receiving the E-DCH allocation request, the WTRU  102  checks whether scheduling information was also received, or whether only the reception of the channel allocation request was acknowledged. If the scheduling information was received, the WTRU  102  transmits data through the UL EU channel  110  according to the scheduling information specified by the Node-B  104  (step  208 ). If only an acknowledgement of reception of the E-DCH allocation request was received, the WTRU  102  knows that the Node-B  104  has received the E-DCH allocation request and refrains from retransmitting the same request (step  214 ). 
     After the channel allocation request has been received and confirmed without scheduling information, the Node-B  104  may provide EU channel allocations later on for the WTRU  102  whose requests have been queued in the request priority queue  114  of the Node-B  104 . Periodically, potentially each transmit time interval (TTI) at step  216 , the Node-B  104  determines whether resources are available for allocation for the requests in the request priority queue  114  (step  218 ). If there are resources available, the process  200  proceeds to steps  207  and  208 . 
     If there are no resources available, the Node-B  104  determines whether the maximum time to allocate timer  116  expired (step  220 ). 
     If the maximum time to allocate timer  116  did not expire, as determined at step  220 , the process  200  waits for the next TTI at step  216 . The Node-B  104  may prioritize allocations that are close to expiration of the maximum time to allocate. 
     After the maximum time to allocate timer  116  has expired or, equivalently, a predetermined time period elapses after the recorded request reception time, the WTRU  102  relies on its channel allocation response timer  118  for tracking the maximum allocate time period for each E-DCH allocation request. The WTRU  102  sets the channel allocation response timer  118  each time the WTRU  102  sends an E-DCH allocation request to the Node-B  104 , and recognizes the allocation failure upon expiration of the channel allocation response timer  118 . Alternatively, if the WTRU  102  does not maintain its own equivalent channel allocation response timer  118 , the Node-B  104  notifies the WTRU  102  of the failure of allocation. If the WTRU  102  maintains its own channel allocation response timer  118 , there is no need for the Node-B  104  to notify the WTRU  102  of the failure. 
     When the E-DCH allocation failure occurs, the WTRU  102  has several options. The WTRU  102  may retransmit the E-DCH allocation request or an updated request to the Node-B  104  (step  224 ). Step  224  may be performed on a periodic basis, each time the channel allocation response timer  118  expires. Alternatively, the WTRU  102  may discard the data for which it requested an allocation and send an updated E-DCH allocation request if the WTRU  102  has more E-DCH data to transmit (step  226 ). 
       FIG. 3  is a flow diagram of a process  300  for determining signaling channel failure during channel allocation in accordance with another embodiment of the present invention. When the WTRU  102  has EU data to be transmitted, the WTRU  102  sends an E-DCH allocation request to the Node-B  104  and activates the channel allocation response timer  118  (step  302 ). After sending the E-DCH allocation request, the WTRU  102  waits to receive scheduling information, (i.e., E-DCH allocation information), from the Node-B  104  until the channel allocation response timer  118  expires. If the WTRU  102  fails to receive scheduling information from the Node-B  104  before the channel allocation response timer  118  expires (step  304 ), the WTRU  102  retransmits the same E-DCH allocation request with a retransmission indicator or an updated E-DCH allocation request (step  306 ). 
     In this case, the WTRU  102  does not know if either the UL EU signaling, (i.e., E-DCH allocation request), or the DL EU signaling, (i.e., channel allocation), is lost. If the Node-B  104  receives a retransmitted E-DCH allocation request (step  308 ), the Node-B  104  determines where the failure occurs, (i.e., either the E-DCH allocation request in the UL EU channel  110  or the channel allocation through the DL EU signaling channel  112 ). If the Node-B  104  receives a retransmitted E-DCH allocation request which was not served, the Node-B  104  determines that the E-DCH allocation request was not delivered successfully on the UL EU channel  110  (step  312 ). If the Node-B  104  receives a retransmitted E-DCH allocation request which was served, the Node-B  104  determines that the channel allocation information was not delivered successfully on the DL EU signaling channel  112  (step  314 ). For either of steps  312  and  314 , the Node-B  104  then takes appropriate corrective actions in accordance with the determined failure. The Node-B  104  then processes the received request (step  316 ). 
     The present invention assures that E-DCH allocation requests have been received by the Node-B  104  and the EU UL signaling load is minimized when the E-DCH channel allocation is not immediately provided by the Node-B  104 . Using the method of the present invention results in a more efficient use of UL physical resources. 
     Although the features and elements of the present invention are described in the preferred embodiments in particular combinations, each feature or element can be used alone without the other features and elements of the preferred embodiments or in various combinations with or without other features and elements of the present invention. 
     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.