Patent Publication Number: US-8538473-B2

Title: Method and system for controlling transmission power of a downlink signaling channel based on enhanced uplink transmission failure statistics

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. application Ser. No. 12/483,614, filed Jun. 12, 2009, which issued on Jul. 3, 2012 as U.S. Pat. No. 8,213,980, which is a continuation of U.S. application Ser. No. 11/116,017, filed Apr. 27, 2005, which issued on Oct. 6, 2009 as U.S. Pat. No. 7,599,707 which claims the benefit of U.S. Provisional Application No. 60/567,308, filed Apr. 30, 2004, all of which are 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 system for controlling transmission power of a downlink (DL) enhanced uplink (EU) signaling channel based on EU transmission and scheduling information reception failure statistics reported to the RNC by the WTRU and/or the Node-B such that enhanced dedicated channel (E-DCH) downlink signaling channels are more reliable. 
     BACKGROUND 
     Methods for improving uplink (UL) coverage, throughput, and transmission latency are currently being investigated in Release 6 of the Third Generation Partnership Project (3GPP). In order to achieve these goals, the Node-B will take over responsibility of scheduling and assigning uplink resources to WTRUs. The Node-B can make more efficient decisions and manage UL radio resources on a short-term basis better than the RNC, even if the RNC retains coarse overall control. 
     A new media access control (MAC) function/entity for enhanced uplink (EU) called MAC-e is created in a WTRU and the Node-B to handle the transmission and reception of the E-DCH transmissions. To properly support EU, information such as channel allocations, transmission feedback, (i.e., acknowledge (ACK) or non-acknowledge (NACK)), and other feedback information, (such as power control command or channel quality), must be transmitted to the WTRU via a DL EU signaling channel efficiently and reliably. 
     Power control on the shared DL EU signaling channel is essential to support proper operation of the DL EU signaling channel. Power control reduces overall interference and therefore results in more efficient use of radio resources. 
     SUMMARY 
     The present invention is a method and system for controlling transmission power of at least one DL EU signaling channel such that E-DCH DL signaling is delivered to the WTRU efficiently and reliably. For DL signaling dedicated to specific WTRUs, the transmit power of DL EU signaling channels is based on the current DL dedicated control channel power plus a power offset. For DL signaling common to multiple WTRUs, the transmit power of DL EU signaling channels is based on a power set by the RNC plus a power offset. The RNC monitors EU transmission failure statistics reported from the Node-B and the WTRU to estimate the NACK to ACK misinterpretation statistics. 
     The Node-B reports the statistics of EU transmission failures at the Node-B to the RNC and the WTRU reports the statistics of EU transmission failures at the WTRU to the RNC. The RNC then adjusts the NACK to ACK power ratio according to the estimated NACK to ACK misinterpretation statistics. The Node-B computes failed scheduling information, (i.e., channel allocation information), reception statistics by detecting when the WTRU does not initiate EU transmissions after the Node-B sends channel allocation information to the WTRU, or the data rate/frequency of E-DCH transmissions is not the same as specified in the channel allocation information. 
     The WTRU may also compute failed scheduling information reception statistics by detecting when there is no response to EU channel allocation requests within a specified time period following the request. The RNC monitors failed scheduling information reception statistics reported by the WTRU and the Node-B to estimate statistics of scheduling information reception error. The RNC adjusts the power offset of the scheduling information field based on the statistics of scheduling information reception failure. 
    
    
     
       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 signaling diagram between components of the system of  FIG. 1  for implementing transmission power control on a DL EU signaling channel in accordance with the present invention; 
         FIG. 3  is a flow diagram of a process for implementing transmission power control on a DL EU signaling channel in accordance with one embodiment of the present invention; and 
         FIG. 4  is a flow diagram of a process for implementing transmission power control on a DL EU signaling channel 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  comprises a WTRU  102 , at least one Node-B  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 initial transmission power level, maximum allowed EU transmission power or available channel resources per Node-B. Between the WTRU  102  and the Node-B  104 , a dedicated physical control channel (DPCCH)  114 , an E-DCH  108 , a UL EU signaling channel  112  and DL EU signaling channel  110  are established. 
     For E-DCH transmissions, the WTRU  102  sends an E-DCH allocation request to the Node-B  104  via either the E-DCH  108  or the UL EU signaling channel  112 . In response, the Node-B  104  sends channel allocation information to the WTRU  102  via a DL EU signaling channel  110 . After EU radio resources are allocated for the WTRU  102 , the WTRU  102  transmits data via the E-DCH  108 . In response to the E DCH transmissions, the Node-B  104  sends an ACK or NACK for hybrid-automatic repeat request (H-ARQ) operation via the DL EU signaling channel  110 . 
     When the WTRU  102  is configured to operate on the E-DCH  108  by the RNC  106 , the power offset of each information field, (e.g., ACK/NACK, scheduling information, etc.), transmitted via the DL EU signaling channel  110  is also configured by the RNC  106  and signaled to the Node-B  104  via Iub/Iur  118 . Those initial power offsets are determined by the RNC  106  based on the required error probability of information fields. During the operation of the E-DCH  108 , the power offsets of information fields in the DL EU signaling channel  110  need to be adjusted according to the actually experienced quality of service of the DL EU signaling channel  110 . 
     For DL signaling dedicated to specific WTRUs  102 , the transmit power of the DL EU signaling channel(s)  110  is based on the current DL dedicated control channel power plus a power offset. For DL signaling common to multiple WTRUs  102 , the transmit power of DL EU signaling channels  110  is based on a power level set by the RNC  106  plus a power offset. 
     For each WTRU  102 , the transmission power of the DL EU signaling channel  110  is controlled separately. The transmission power of the DL EU signaling channel  110  for a specific WTRU  102  is determined as the transmission power of the DL dedicated physical control channel (DPCCH)  114  of the WTRU  102  plus a power offset. In this sense, the power of DPCCH is used as reference. The transmission power of the DPCCH of the WTRU  102  is controlled as in Release 99/4/5 of the universal mobile telecommunication services (UMTS). 
     Different power offsets are used depending on the information, (i.e., ACK/NACK, channel quality feedback, scheduling information, etc.), to be sent by the Node-B  104 . For the ACK/NACK information field, a higher power offset is used to transmit NACK than to transmit ACK, because NACK to ACK misinterpretation causes a more serious problem than ACK to NACK misinterpretation. 
       FIG. 2  is a signaling diagram of a process  200  implemented by the system  100  for implementing transmission power control on a DL EU signaling channel  110  in accordance with the present invention. The RNC  106  sends an initial configuration of power offsets for the DL EU signaling channel  110  to the Node-B  104  (step  202 ). The RNC  106  monitors failed MAC-e transmissions and/or failed channel allocation information reception statistics reported by the WTRU  102  and/or the Node B  104  to estimate the error probability of the reception and transmission on the DL EU signaling channel  110  (steps  204 ,  206 ). In step  207 , the RNC  106  estimates the statistics of NACK to ACK misinterpretation based on the reported failed MAC-e transmissions statistics. If the estimate of statistics of NACK to ACK misinterpretation is higher than a threshold, the RNC  106  adjusts the NACK to ACK power ratio, (i.e., the ratio of power offsets), for the DL EU signaling channel  110  accordingly. Based on failed channel allocation information reception statistics received from the WTRU  102  and the Node-B  104 , the RNC  106  adjusts the power offset of the scheduling information field accordingly (step  208 ). In this way, proper operation of EU is maintained and radio resources are used efficiently. 
       FIG. 3  is a flow diagram of a process  300  for controlling the transmission power of a DL EU signaling channel in accordance with one embodiment of the present invention. The WTRU  102  is configured for EU operation (step  302 ). The WTRU  102  determines whether there is a data to be transmitted via the E-DCH  108  (step  304 ). If there is data to be transmitted, the WTRU  102  sends a channel allocation request to the Node-B  104  via either the E-DCH  108  or the UL EU signaling channel  112  (step  306 ). The Node-B  104  receives the request and sends channel allocation information to the WTRU  102  via the DL EU signaling channel  110  (step  308 ). 
     After sending the channel allocation request, the WTRU  102  monitors the DL EU signaling channel  110  for channel allocation information. The Node-B  104  also monitors E-DCH transmissions after sending the channel allocation information via the DL EU signaling channel  110  (step  310 ). 
     The channel allocation information sent to the WTRU  102  may not be delivered successfully. The consequence of failed transmission of the channel allocation information depends on the way that the allocation is performed. For deterministic allocation, the WTRU  102  will not transmit at all. For statistical allocation, the WTRU  102  either may not transmit at all, or may transmit the data at a rate and/or persistence level which is not the same as specified in the channel allocation information. 
     Deterministic allocation is the allocation in which the maximum allocated transmit power and/or data rate is specified and the WTRU  102  can transmit at any time as long as its transmit power and/or data rate does not exceed the maximum. Statistical allocation is the allocation in which in addition to the specified maximum allocated transmit power and/or data rate, persistence level (probability) is also specified. The WTRU  102  may transmit from time to time according to the persistence level or transmit at any time with transmit power and/or data rate determined by the persistence level. 
     The Node-B  104  computes and reports failed scheduling information reception statistics by detecting when the WTRU  102  does not initiate EU transmissions after the Node-B  104  sends the channel allocation information, or the data rate/frequency of E-DCH transmissions is not the same as specified in the channel allocation information (step  312 ). This may be based on a received power threshold. The WTRU  102  may also compute and report failed scheduling information reception statistics by detecting when there is no response to EU channel allocation requests within a specified time period following the transmission of the channel allocation request (step  312 ). 
     If failed transmission statistics of channel allocation information is higher than a predetermined threshold, the RNC  106  increases the transmission power offset of scheduling information field on the DL EU signaling channel  110  (step  314 ). The RNC  106  signals the adjusted power offset to the Node-B  104  via the Iub/Iur  118 . 
       FIG. 4  is a flow diagram of a process  400  for controlling transmission power of a DL EU signaling channel  110  in accordance with another embodiment of the present invention. After the WTRU  102  is configured for EU operation and receives channel allocation information at step  402 , the WTRU  102  transmits data via the E-DCH  108  (step  404 ). The Node-B  104  receives and decodes the data. The Node-B  104  then sends feedback information, (i.e., ACK or NACK), to the WTRU  102  in accordance with the decoded data (step  406 ). 
     The WTRU  102  and/or the Node-B  104  compute MAC-e failure statistics and report them to the RNC  106  to adjust NACK to ACK power ratio, (i.e., the ratio of power offsets), (step  408 ). In accordance with one embodiment, the WTRU  102  reports the number of MAC-e failures at the WTRU  102 , which is the number of data blocks that are not transmitted successfully. A MAC-e failure occurs when a data block fails in transmission at the MAC-e due to reasons such as a maximum number of retransmissions or maximum delay of a data block is reached. The Node-B  104  reports the number of MAC-e failures of the WTRU  102  at the Node-B  104 , which is the number of data blocks that are not received successfully at the MAC-e in the Node-B  104 . 
     Sometimes, a data block that the WTRU  102  interprets as being transmitted successfully may not actually be received successfully at the Node-B  104  because a NACK of the data block is misinterpreted as an ACK at the WTRU  102 . The RNC  106  determines the number of NACK to ACK misinterpretations of the WTRU  102  as the number of MAC-e failures of the WTRU  102  reported by the Node-B  104  minus the number of MAC-e failures of the WTRU  102  reported by the WTRU  102 . 
     Alternatively, the RNC  106  may determine the number of NACK to ACK misinterpretations utilizing the number of radio link control (RLC) recovery requests of E-DCH data for the WTRU  102  at the RNC  106 , which can be internally collected or computed by the RNC  106 . A data block that the WTRU  102  interprets as being transmitted successfully may later have an RLC recovery request for the data due to NACK to ACK misinterpretation. The RNC  106  determines the number of NACK to ACK misinterpretations of the WTRU  102  as the number of RLC recovery requests of E-DCH data for the WTRU  102  at the RNC  106  minus the number of MAC-e failures of the WTRU  102  reported by the WTRU  102 . 
     MAC-e failure statistics of the WTRU  102  at the WTRU  102  are reported to the RNC  106  via RRC procedures, and MAC-e failure statistics of the WTRU  102  at the Node-B  104  are reported to the RNC  106  via the Iub/Iur  118 . 
     If the NACK to ACK misinterpretation probability is higher than a predetermined threshold, the RNC  106  increases the power ratio of the NACK to ACK power offsets (step  410 ). With higher power offsets, NACK will be delivered to the WTRU more reliably. The RNC  106  signals adjusted power offsets for ACK and NACK, (or power ratio between ACK and NACK), to the Node-B  104  via Iub/Iur  118 , and the Node-B  104  uses the power offsets/ratio in setting the transmission power of EU DL signaling channel. 
     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.