Abstract:
A wireless communication method and apparatus for detecting and decoding enhanced dedicated channel (E-DCH) hybrid automatic repeat request (H-ARQ) indicator channel (E-HICH) transmissions are disclosed. A wireless transmit/receive unit (WTRU) receives E-HICH transmissions and detects an H-ARQ indicator transmitted via the E-HICH by performing a binary hypothesis test. The WTRU then generates an acknowledgement (ACK) message or a non-acknowledgement (NACK) message based on the detected H-ARQ indicator. A reliability test may be further performed to improve performance, whereby the binary hypothesis test may be performed only if the reliability test is passed.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. patent application Ser. No. 11/477,278, filed Jun. 29, 2006, which issued on Aug. 11, 2009 as U.S. Pat. No. 7,574,645, which claims the benefit of U.S. Provisional Application Ser. No. 60/709,952, filed Aug. 18, 2005, which are incorporated by reference as if fully set forth. 
    
    
     FIELD OF INVENTION 
     The present invention is related to a wireless communication system. More particularly, the present invention is related to a wireless communication method and apparatus for detecting and decoding enhanced dedicated channel (E-DCH) hybrid automatic repeat request (H-ARQ) indicator channel (E-HICH) transmissions. 
     BACKGROUND 
     Enhanced Uplink (EU) is one of the major features in third generation partnership project (3GPP) frequency division duplex (FDD) systems. EU offers a peak data rate of 5.76 Mbps. In order to support EU operation, several downlink physical channels are provided to transmit control information. One of the downlink physical channels is the E-HICH. 
       FIG. 1  is a block diagram of a conventional wireless communication system  100  which supports EU. The system  100  comprises a wireless transmit/receive unit (WTRU)  102 , a Node-B  104  and a radio network controller (RNC)  106 . The RNC  106  controls overall E-DCH operation by configuring E-DCH parameters for the Node-B  104  and the WTRU  102 , such as initial transmit power level, maximum allowed transmit power or available channel resources per Node-B. Between the WTRU  102  and the Node-B  104 , an E-DCH  108 , an E-DCH dedicated physical control channel (E-DPCCH), an E-DCH absolute grant channel (E-AGCH)  112 , an E-DCH relative grant channel (E-RGCH)  114  and an E-HICH  116  are established for supporting E-DCH operations. 
     For E-DCH transmissions, the WTRU  102  sends triggered scheduling information, (also known as a rate request), for the logical channels which a radio resource control (RRC) determines that reporting is needed to be made to the Node-B  104  via the E-DCH  108 . The Node-B  104  sends a scheduling grant to the WTRU  102  via the E-AGCH  112  or the E-RGCH  114 . After E-DCH radio resources are allocated for the WTRU  102 , the WTRU  102  transmits uplink (UL) data via the E-DCH  108 . In response to E-DCH or E-DPCCH transmissions, the Node-B  104  sends an acknowledgement (ACK) or a non-acknowledgement (NACK) message for H-ARQ operation via the E-HICH  116 . 
     The E-HICH  116  is a very important channel for fast transmission and retransmission of E-DCH data. A reliable detection of the E-HICH transmission is therefore critical for EU operation. A successful detection and decoding of the E-HICH transmission significantly affects the performance of data transmissions for the E-DCH, and affects the performance of the entire EU systems. Therefore, it is desirable to have a method and apparatus for efficiently detecting and decoding E-HICH transmissions. 
     SUMMARY 
     The present invention is related to a wireless communication method and apparatus for detecting and decoding E-HICH transmissions. A WTRU receives E-HICH transmissions and detects an H-ARQ indicator transmitted via the E-HICH by performing a binary hypothesis test. The WTRU then generates an ACK message or a NACK message based on the detected H-ARQ indicator. A reliability test may be further performed to improve performance, whereby the binary hypothesis test may be performed only if the reliability test is passed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       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: 
         FIG. 1  is a block diagram of a conventional wireless communication system; 
         FIG. 2  is a flow diagram of a process for detecting and decoding E-HICH transmissions in accordance with the present invention; 
         FIG. 3  is a flow diagram of a process for detecting an H-ARQ indicator in accordance with the present invention; 
         FIG. 4  is a flow diagram of a process for generating an ACK message or a NACK message from the detected H-ARQ indicator in accordance with the present invention; and 
         FIG. 5  is a block diagram of an exemplary WTRU configured in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     When referred to 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. 2  is a flow diagram of a process  200  for detecting and decoding E-HICH transmissions in accordance with the present invention. In step  202 , a WTRU receives E-HICH transmissions from a serving radio link set (RLS) and possibly from at least one non-serving radio link (RL) as well. A serving RLS is a set of cells which contains at least a serving E-DCH cell and from which the WTRU shall receive an absolute grant. A WTRU may receive relative grant(s) from the serving RLS. In the case when the WTRU receives multiple relative grants from the serving RLS, the received relative grants may be soft combined for enhanced received signal-to-noise ratio (SNR) and improved signal quality. The WTRU has only one serving RLS. A non-serving RL is a cell which belongs to the E-DCH active set but does not belong to the serving RLS and from which the WTRU may receive a relative grant. The WTRU may have zero, one or several non-serving RL(s). In step  204 , the WTRU detects and decodes an H-ARQ indicator from each E-HICH transmission by performing a binary hypothesis test, which will be explained in detail hereinafter. In step  206 , the WTRU generates an ACK message or a NACK message based on the detected H-ARQ indicators. 
     The detection of the H-ARQ indicator is performed by the binary hypothesis test for both a serving RLS and a non-serving RL. Optionally, a reliability tests may also be performed in combination with the binary hypothesis tests for additional performance improvement, which will be explained in detail hereinafter. 
     The H-ARQ indicator transmitted by the serving RLS or the non-serving RL may be either an ACK indicator or a NACK indicator. The H-ARQ indicator from the serving RLS may be detected with a detection threshold of zero, while the H-ARQ indicator from the non-serving RL may be detected with a non-zero detection threshold. Alternatively, if the performance requirement is different between detecting an ACK indicator and a NACK indicator, the detection of the H-ARQ indicator from the serving RLS may be detected with a non-zero detection threshold. In this case, non-symmetric detection thresholds are required for the detection of the H-ARQ indicator from a non-serving RL. 
     Assume that the E-HICH has an average energy E l  for the l-th RLS after correlation and soft combining. Without loss of generality it is assumed that the first RLS, (i.e., l=1), is the serving RLS and the remaining RLSs, (i.e., l=2, . . . , L), are the non-serving RLs. For a serving RLS, an ACK indicator and a NACK indicator are sent with an amplitude √{square root over (E l )} and −√{square root over (E l )}, respectively. For a non-serving RL, an ACK indicator and a NACK indicator are sent with an amplitude √{square root over (E l )} and 0, respectively. 
     y (l)  denotes the soft indicator, (i.e., a soft sample), after correlation for the l-th RLS. A log likelihood ratio (LLR) for the binary hypothesis tests for detection of an ACK indicator and a NACK indicator is expressed as follows: 
                       LLR     (   l   )       =     ln   ⁢         P   r     ⁡     (       y     (   l   )       ❘     H   1       )           P   r     ⁡     (       y     (   l   )       ❘     H   0       )             ;           Equation   ⁢           ⁢     (   1   )                 
where H 0  and H 1  denote the hypothesis tests NACK and ACK, respectively.
 
     Assuming white Gaussian noise with variance σ n   2  after correlation, the H-ARQ indicator for the serving RLS is detected as an ACK indicator or a NACK indicator as follows; 
     an ACK indicator, if 
               LLR     (   l   )       =         2     σ   n       ⁢     y     (   l   )       ⁢       γ   l         ≥   0           
(or simply if LLR (l) =y (l) ≧0); and
 
     a NACK indicator, otherwise; 
     where 
               γ   l     ,     (       γ   l     =       E   l       σ   n   2         )     ,         
denotes the average SNR of an E-HICH for the serving RLS, (i.e., l=1), after correlation and soft combining.
 
     The LLR for the binary hypothesis tests for a non-serving RL is expressed as follows: 
     
       
         
           
             
               
                 
                   
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     An H-ARQ indicator for the non-serving RL is detected as an ACK indicator or a NACK indicator as follows: 
     an ACK indicator, if 
                 LLR     (   l   )       =           1     σ   n       ⁢     y     (   l   )       ⁢       γ   l         -       1   2     ⁢     γ   l         ≥     T     (   l   )           ;         
and
 
     a NACK indicator, otherwise. 
     where γ l  denotes the average SNR of an E-HICH for the non-serving RL, (the l-th RLS, i.e., l=2, 3, . . . , L), after correlation. T (l)  is a detection threshold for the l-th RLS. T (l)  may be the same for all the non-serving RLs or may be different between non-serving RLs based on the designs and performance requirements for detection. 
     When multiple measurements are available, the detection of an H-ARQ indicator using multiple measurement hypothesis tests may be performed. Assume that there are M measurements. y m   l  denotes the soft indicator, (i.e., soft sample), after correlation for the l-th RLS and the m-th correlation output or decoding measurement for the E-HICH. Similarly without loss of generality, it is assumed that the first RLS, (i.e., l=1), is the serving RLS and the remaining RLSs, (i.e., l=2, . . . , L), are non-serving RLs. The LLR for multiple measurement hypothesis tests for detection of an ACK indicator and a NACK indicator for the serving RLS is expressed as follows: 
     
       
         
           
             
               
                 
                   
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     The H-ARQ indicator for the serving RLS is detected as an ACK indicator or a NACK indicator using multiple measurement hypothesis tests as follows: 
     an ACK indicator, if 
               LLR     (   l   )       =       ∑     m   =   1     M     ⁢     (           2     σ   n       ⁢     y   m     (   l   )       ⁢         γ   l     )         ≥   0     ;               
and
 
     a NACK indicator, otherwise. 
     The H-ARQ indicator for the non-serving RL is detected as an ACK indicator or a NACK indicator as follows: 
     an ACK indicator, if 
                 LLR     (   l   )       =         ∑     m   =   1     M     ⁢     (         1     σ   n       ⁢     y   m     (   l   )       ⁢       γ   l         -       1   2     ⁢     γ   l         )       ≥     T     (   l   )           ;         
and
 
     a NACK indicator, otherwise. 
     T (l)  is a detection threshold for the l-th RLS. T (l)  may be the same for all the non-serving RLs or may be different between non-serving RLs based on the designs and performance requirements for detection. 
       FIG. 3  is a flow diagram of a process  300  for detecting an H-ARQ indicator in accordance with the present invention. A WTRU receives E-HICH transmissions from a serving RLS and at least one non-serving RL (step  302 ). An E-HICH transmission from the first RLS is selected (step  304 ). An optional reliability test may be then performed. The reliability test may not be performed in some cases when performance requirement has satisfied. For the reliability test, SNR, (measured or calculated), of the selected E-HICH transmission is compared to an SNR threshold (step  306 ). If the SNR is not higher than the SNR threshold, the reliability test fails and the process  300  proceeds to step  308  to select an E-HICH transmission from the next RLS. If the SNR is equal to or greater than the SNR threshold, the reception of the E-HICH transmission is said to be reliable in terms of signal quality, and a binary hypothesis test is performed. 
     For the binary hypothesis test, it is first determined whether the selected E-HICH transmission is from the serving RLS or from the non-serving RL(s) (step  310 ). If the selected E-HICH transmission is determined in step  310  to be from the serving RLS, an LLR is compared to a zero detection threshold. If the LLR is higher than the zero detection threshold, an ACK indicator is detected for the serving RLS (step  316 ) and if the LLR is not higher than the zero detection threshold, a NACK indicator is detected for the serving RLS (step  318 ). If the selected E-HICH transmission is determined in step  310  to be from the non-serving RL, the LLR is compared to a non-zero detection threshold (step  314 ). If the LLR is higher than the detection threshold, an ACK indicator is detected for the non-serving RL (step  316 ) and if the LLR is not higher than the detection threshold, a NACK indicator is detected for the non-serving RL (step  318 ). Alternatively, a non-zero detection threshold may be used for the serving RLS and non-symmetric detection thresholds between ACK and NACK may be used for both the serving RLS and non-serving RLs. 
       FIG. 4  is a flow diagram of a process  400  for generating an ACK message or a NACK message in accordance with the present invention. When macro diversity combining is implemented, the WTRU may receive multiple H-ARQ indicators from the serving RLS and the non-serving RL(s). The H-ARQ indicators from different RLs are independent from each other. Generally, the WTRU generates an ACK message if the WTRU detects at least one ACK indicator from any RLs and generates a NACK message if the WTRU does not detect any ACK indicator. An H-ARQ indicator associated with triggered scheduling information which is sent by the WTRU for requesting a scheduling grant from a serving E-DCH cell is an exception, which will be explained in detail hereinafter. 
     The WTRU continuously monitors H-ARQ indicators from the serving RLS and at least one non-serving RL (step  402 ). If it is determined at step  404  that any H-ARQ indicator is detected, the WTRU determines whether the detected H-ARQ indicator is associated with triggered scheduling information (step  406 ). 
     If the detected H-ARQ indicator is not associated with triggered scheduling information, the WTRU further determines whether at least one ACK indicator has been received from either the serving RLS or the non-serving RL(s) (step  412 ). If at least one ACK indicator has been received, the WTRU generates an ACK message (step  422 ). If an ACK indicator has not been received, the WTRU generates a NACK message (step  420 ). 
     If, in step  406 , it is determined that the detected H-ARQ indicator is associated with triggered scheduling information, it is further determined whether at least one ACK indicator has been received from the serving RLS (step  408 ). In the case of triggered scheduling information, an ACK indicator or a NACK indicator should be sent to the WTRU from the serving RLS to indicate success or failure of reception of the scheduling information at the serving RLS. Since only the serving cell can send the scheduling grants in response to the triggered scheduling information, the ACK/NACK indicators are distinguished between the serving RLS and the non-serving RL(s). If, in step  408 , it is determined that at least one ACK indicator was received from the serving RLS, an ACK message is generated for the serving RLS by the WTRU (step  418 ). If, in step  408 , it is determined that there is no ACK indicator received from the serving RLS, it is then determined whether at least one ACK indicator has been received from the non-serving RL(s) (step  410 ). If an ACK indicator is received from the non-serving RL, an ACK message for the non-serving RL(s) is generated (step  414 ). If there is no ACK indicator received from the non-serving RL(s), a NACK message is generated (step  416 ). 
     Non-serving E-DCH RLs do not transfer the received triggered scheduling information to the serving E-DCH cell from which the absolute grant is sent to the WTRU to respond to the triggered scheduling information. If an ACK is received by the WTRU for the serving E-DCH cell in response to the transmission of the triggered scheduling information, it indicates that the transmission of the triggered scheduling information is successfully received by the serving cell scheduler in the serving E-DCH cell. For data other than triggered scheduling information, if there is at least one ACK from ether the serving RLS or non-serving RL(s), it is sufficient for the data since the data is processed in a core network higher than the serving RLS. If, in response to the transmission of the triggered scheduling information, a NACK is received by the WTRU for the serving E-DCH RLS but an ACK is received for the non-serving RL(s), the triggered scheduling information should be re-transmitted. After generation of an ACK or a NACK message, the process  400  waits for a next transmission time interval (TTI) (step  424 ). 
       FIG. 5  is a block diagram of an exemplary WTRU  500  configured in accordance with the present invention. The WTRU  500  includes a receiver  502 , an H-ARQ indicator detection unit  504 , a plurality of H-ARQ processes  506 , an H-ARQ process controller  508 , a measurement unit  510  and a comparator  512 . The receiver  502  receives E-HICH transmissions from the serving RLS and the non-serving RL. The H-ARQ indicator detection unit  504  detects H-ARQ indicators transmitted via the E-HICH by performing a binary hypothesis test as described hereinabove. The H-ARQ process controller  508  controls the H-ARQ processes  506  and generates an ACK or a NACK message based on the detected H-ARQ indicator. 
     The H-ARQ indicator detection unit  504  includes an LLR calculation unit  514  and a comparator  516 . The LLR calculation unit  514  calculates an LLR of conditional probability of an ACK and a NACK on the E-HICH transmission. The comparator  516  compares the LLR with a detection threshold. The H-ARQ process controller  508  generates a NACK message if the LLR is below the detection threshold, and generates an ACK message if the LLR is not below the detection threshold. The measurement unit  510  measures the SNR of the E-HICH, and the comparator  512  compares the SNR with an SNR threshold for performing the reliability test. 
     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.