Abstract:
In the processing of a data transmission received on wireless data channel HS-DSCH during HS-SCCH-less (HSL) operation according to 3GPP TS 25.214 V7.7.0, a situation is identified wherein redundancy version information corresponding to the received data transmission cannot be obtained from wireless control channel HS-SCCH. The redundancy version information is normally indicative of an HSL redundancy version that specifies derate matching for the received data transmission. In response to identification of the situation, derate matching is applied to the received data transmission according to an HSL redundancy version other than the HSL redundancy version that is specified by HSL for derate matching in the situation.

Description:
FIELD 
       [0001]    The present work relates generally to wireless communication and, more particularly, to downlink wireless communication. 
       BACKGROUND 
       [0002]    The following Technical Specifications are incorporated herein by reference: 
         [0003]    “3GPP TS 25.214 V7.7.0 (2007-11)”, also known as “3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Physical layer procedures (FDD) (Release 7)” (referred to herein as “TrS 25.214”); and 
         [0004]    “3GPP TS 25.212 V7.7.0 (2007-11)”, also known as “3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Multiplexing and channel coding (FDD) (Release 7)”. 
         [0005]    The document TS 25.214 specifies “HS-SCCH-less” (also referred to as “HSL”) operation that targets low throughput applications that utilize HSDPA (High Speed Downlink Packet Access). Examples of applications include Voice over IP (VoIP) communication, and interactive gaming. The HS-SCCH-less feature aims to increase cell capacity in HSDPA operation by reducing signalling overhead normally associated with the control channel known as HS-SCCH (High Speed Shared Control Channel). As its name implies, the HS-SCCH-less feature supports HSDPA operation without the control signalling overhead associated with the use of HS-SCCH. 
         [0006]    Normally in HSDPA operation, each downlink data transmission on HS-DSCH is preceded by a corresponding downlink transmission of control information on HS-SCCH. This control information specifies how the UE (user equipment, for example, a cell phone) is to decode the corresponding data transmission. It normally identifies an HS-DSCH transport format. An HS-DSCH transport format (TF) specifies the following parameters: transport block size (physical layer packet size); set of OVSF (Orthogonal Variable Spreading Factor) codes associated with HS-PDSCH (High Speed Physical Downlink Shared Channel); and modulation (e.g., QPSK). 
         [0007]    The HSL mode of operation provides for up to three attempts at the physical layer to transmit a given data transport block on the downlink data channel known as HS-DSCH (High Speed Downlink Shared Channel). If a first transmission attempt is unsuccessful, as evidenced by the absence of an expected acknowledgement (ACK) on the uplink from the UE, then a second transmission attempt (i.e., a first retransmission) occurs. If the second transmission attempt is unsuccessful, as evidenced by the absence of an ACK or the presence of a NACK (negative acknowledgment) on the uplink from the UE, then a third transmission attempt (i.e., a second retransmission) occurs. In HSL mode, a given data transmission on HS-DSCH is characterized by any one of (up to) four possible transport formats (TFs). 
         [0008]    According to HSL operation, HS-SCCH is not used to transmit control information associated with the first downlink data transmission attempt for a given data transport block. The UE is thus required to decode the data transmission without any control information that specifies how the decoding should be done. This decoding of a data transmission without benefit of associated control information is referred to as blind decoding. For blind decoding of the first downlink data transmission attempt, the UE assumes a given transport format, and performs derate matching (i.e., de-puncturing or de-repeating of bits in the received transport block) according to a redundancy version (RV) that TS 25.214 specifies for the first downlink data transmission attempt. The UE attempts to blind decode the first downlink data transmission using the RV that TS 25.214 specifies for the first downlink data transmission attempt, and up to four (if necessary) transport formats. The document TS 25.214 indicates that the UE will apply this same blind decoding procedure with respect to any downlink data transmission attempt for which no corresponding HS-SCCH control information can be decoded. 
         [0009]    It is desirable to provide for improving the success rate of blind decoding at the user equipment. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  illustrates operations that may be performed according to exemplary embodiments of the present work. 
           [0011]      FIG. 2  diagrammatically illustrates a wireless communication system according to exemplary embodiments of the present work. 
           [0012]      FIG. 3  illustrates operations that may be performed according to exemplary embodiments of the present work. 
       
    
    
     DETAILED DESCRIPTION 
       [0013]    All embodiments described herein that receive and process control and data and transmissions produced according to TS 25.214 and TS 25.212 are to be understood to encompass products that receive and process control and data transmissions that are produced compatibly with TS 25.214 and TS 25.212, including control and data transmissions produced according to future versions of TS 25.214 and TS 25.212. 
         [0014]    The present work exploits the fact that the document TS 25.214 specifies the redundancy versions that are to be used for second and third downlink data transmission attempts (first and second retransmissions) in HSL operation. As mentioned above, if the control information transmitted on HS-SCCH in conjunction with either a first or a second downlink data retransmission is not successfully decoded, TS 25.214 indicates that the user equipment will attempt blind decoding of the retransmission. The present work recognizes that, inasmuch as the redundancy versions assigned to the respective first and second data retransmissions are specified by TS 25.214, the user equipment may advantageously utilize these known redundancy versions when it is necessary to blind decode what is actually a first or second data retransmission (i.e., when the associated control information transmitted on HS-SCCH is not successfully decoded). 
         [0015]    A redundancy version fully specifies the rate matching procedure (for a given Transport Format), that is, specifies the position of the bits that are punctured or (less typically) repeated at the transmitter between the coded bits stream and the physical channel bits stream. At the UE, derate matching according to the RV allows depuncturing (i.e. introduction of bits erasures at the correct positions) or, less typically, accumulation of the repeated bits. Typically, each retransmission uses an RV that differs from the one used for the earlier transmission(s) of the same transport block. For HSL operation, the RV sequence for the first transmission and the subsequent two retransmissions is uniquely defined in TS 25.214. Since retransmissions are normally combined with the previous transmissions of the same transport block for decoding, this leads to efficient incremental redundancy gains. A redundancy version that is specified by TS 25.214 for use in HSL operation is also referred to herein as an HSL redundancy version. 
         [0016]    For blind decoding of what is actually a first data retransmission, the present work permits the user equipment to use the known redundancy version of that retransmission, in combination with each of the four possible transport formats. Similarly, for blind decoding of what is actually a second data retransmission, the user equipment may use the known redundancy version of that retransmission, in combination with each of the four possible transport formats. The flexibility to use the redundancy version of a given data retransmission enhances the likelihood that the user equipment will be able to blind decode that retransmission successfully, whereas using only the improper redundancy version of the first transmission results (as is done in conventional HSL operation) almost surely in decode failures. 
         [0017]      FIG. 1  illustrates operations that may be performed by user equipment receiving downlink communications according to exemplary embodiments of the present work. It is determined at  11  whether the applicable transport format and redundancy version are known from the control information received on HS-SCCH. Any given combination of transport format (TF) and redundancy version (RV) is also referred to herein as TF/RV. If the applicable TF/RV is known at  11 , which may be the case for the first and second retransmission attempts when HS-SCCH is successfully decoded, then blind decoding is not required. The known TF/RV is selected at  12 , after which derate matching based on the known TF/RV is performed according to conventional techniques at  13 . The processing of the downlink data transmission then proceeds according to conventional techniques at  14 , ultimately producing a CRC check value. If the CRC check passes at  15 , then the decoding of the data transmission is successful. Otherwise, the decoding has failed. 
         [0018]    If the TF/RV is not known from HS-SCCH at  11 , then blind decoding is required. The TF/RV is never known for the first transmission attempt, and is not known for the first and second retransmission attempts if HS-SCCH decoding fails. If the TF/RV is not known at  11 , a first possible TF/RV for the data transmission is selected at  16 . Derate matching based on the selected TF/RV is performed according to conventional techniques at  17 . The processing of the downlink data transmission then proceeds according to conventional techniques at  18 , ultimately producing a CRC check value. If the CRC check passes at  19 , then the blind decoding of the data transmission is successful. Otherwise, it is determined at  20  whether there is another possible TF/RV for the data transmission. If so, the next possible TF/RV is selected at  16 . The operations at  16 - 20  are repeated until a CRC check value passes at  19  (indicating that the blind decoding is successful), or until no possible TF/RVs remain at  20 . If it is determined at  20  that no possible TF/RVs remain, then the blind decoding of the data transmission has failed. 
         [0019]      FIG. 2  diagrammatically illustrates a wireless communication system according to exemplary embodiments of the present work. In some embodiments, the system of  FIG. 2  is capable of performing the operations illustrated in  FIG. 1 . In some embodiments, the user equipment UE of  FIG. 2  is capable of receiving and processing downlink communications specified for HSL operation in TS 25.214. In the system of  FIG. 2 , a base transceiver station  20 , referred to as Node B in TS 25.214, uses conventional techniques to transmit downlink communications on HS-SCCH (control information) and HS-DSCH (data) to the user equipment UE via a wireless communication link  21 . A first processing portion  24 , operating according to conventional techniques, attempts to decode the HS-SCCH transmission and thereby obtain the applicable TF/RV. If the processing portion  24  successfully obtains a TF/RV from HS-SCCH, it provides a signal  27  to indicate that success, and further provides the successfully obtained TF/RV at  30 . The processing portion  24 , further operating according to conventional techniques, processes the data transmission received on HS-DSCH up to the stage, indicated generally at  29 , where rate matching is to be applied. 
         [0020]    A control portion  22  is coupled to the processing portion  24  to receive the success indication signal  27 . Of course, there will be no success indication at  27  when processing a first downlink transmission during HSL operation, because no TF/RV is transmitted on HS-SCCH. However, TF/RV may be successfully obtained from HS-SCCH when processing a first or second retransmission during HSL operation. If the TF/RV is successfully obtained at  24 , blind decoding is not required. In that case, the signal  27  indicates success, and the control portion  22  responds by controlling a selector  23  appropriately to pass the known TF/RV from  30  to a derate matching portion  25  coupled to the output  33  of the selector  23 . The derate matching portion  25  is also coupled to the output  29  of the processing portion  24 , and uses conventional techniques to perform derate matching according to the TF/RV received from the selector  23 . 
         [0021]    A post-derate matching portion  26  is coupled to the derate matching portion  25 , and processes the output result  31  of the derate matching portion  25  according to conventional techniques, ultimately producing a CRC check value, and evaluating that CRC check value to determine whether the decoding of the data transmission is successful. The post-derate matching portion  26  provides an output signal  28  indicative of whether the decoding of the data transmission on HS-DSCH is successful. The post-derate matching portion  26  also receives the selected TF/RV information from the output  33  of selector  23 , and uses the TF information in conventional fashion in its data processing operations. 
         [0022]    Referring again to the control portion  22 , if the signal  27  indicates no success in obtaining a TF/RV from HS-SCCH, then blind decoding is required. During blind decoding operation, that is, when the signal  27  indicates no success in obtaining a TF/RV from HS-SCCH, the control portion  22  controls the selector  23  appropriately to pass a selected one of a plurality of possible TF/RVs (designated at  32 ) to the derate matching portion  25 . The derate matching portion  25  then performs derate matching according to the selected TF/RV, and passes the result  31  to the post-derate matching portion  26 . During blind decoding operation (i.e., with the signal  27  indicating no success in obtaining a TF/RV from HS-SCCH), if the signal  28  indicates no success in decoding the data transmission using the currently selected TF/RV, the control portion  22  controls the selector  23  to pass another selected one of the possible TF/RVs to the derate matching portion  25 . The control portion  22  continues controlling the selector  23  appropriately to sequence through the possible TF/RVs at  32  until a selected TF/RV results in a success indication at  28 , or until all of the possible TF/RVs have been tried unsuccessfully. 
         [0023]    An application execution portion  34  receives from the post-derate matching portion  26  application information contained in successfully decoded data transmissions. The application execution portion  34  uses the application information in the execution of a user application, for example, a VoIP application, an interactive gaming application, etc. 
         [0024]    Various embodiments use various sets of possible TF/RVs (see, e.g.,  16  and  20  in  FIG. 1 , and  32  in  FIG. 2 ) for blind decoding. For example, when blind decoding what could be any given one of the three transmissions, some embodiments use all three possible RVs, namely, the RVs that TS 25.214 specifies for the first, second and third transmissions. In such embodiments, a total of twelve TF/RVs are considered as possibilities for use in conjunction with each transmission. Other embodiments use various other sets of possible TF/RVs for the various transmissions. 
         [0025]    Some embodiments limit the number of possible TF/RVs, that is, limit the size of the set of possible TF/RVs (see, e.g.,  16  and  20  in  FIG. 1 , and  32  in  FIG. 2 ) based on various considerations. For example, in some typical situations, some of the twelve possible TF/RVs are inapplicable. In TS 25.214, the RV specified for the first retransmission is not self-decodable. With this particular RV, the rate matching procedure at Node B punctures systematic bits first in priority before puncturing parity bits, if needed. Systematic bits are those information data bits passed as is from the channel encoder to its output. Parity bits represent the redundant bits generated for protection by the coder. If systematic bits are punctured at Node B, the UE cannot successfully decode the transport block by itself Rather, it must rely on combining with a previous version of that data transmission for which systematic bits were not punctured. This is normally achieved when receiving a first retransmission for which the control information is received successfully, because the control information contains information relating to the previous (first) transmission whose RV is self-decodable. However, when the UE cannot obtain control information on a first retransmission attempt, that retransmission can only be decoded on its own. When systematic bits are punctured at Node B, this is not possible. In a first retransmission, unless the transport block size of the TF is relatively small, systematic bit puncturing will typically occur at Node B. In some embodiments, all of the four TF/RVs possible for a first retransmission are unconditionally excluded from the set of possible TF/RVs employed by the UE. 
         [0026]    Some embodiments exclude a TF/RV that is possible for a first retransmission only if the transport block size of the TF exceeds a threshold. Such embodiments recognize that systematic bit puncturing will typically occur at Node B if the transport block size of the TF exceeds the threshold, but will typically not occur if the transport block size does not exceed the threshold.  FIG. 3  illustrates exemplary operations that may be used according to such embodiments to define the set of possible TF/RVs (see, e.g.,  16  and  20  in  FIG. 1 , and  32  in  FIG. 2 ) that will be used for blind decoding. As shown at  100 , all possible TF/RVs are initially included in the set. One of the four possible transport formats (all of which are known from conventional network provisioning) is selected at  101 , and its corresponding transport block (TB) size is compared to a threshold TH at  102 . In some embodiments, TH=292 bits. If the transport block size exceeds the threshold TH, it is assumed that systematic bit puncturing will occur during first retransmission rate matching at Node B. Accordingly, the TF/RV that corresponds to first retransmissions and the currently selected transport block size is removed from the set at  103 . As seen from  101  and  104 , the operations at  102  and  103  are performed for each of the four possible transport formats and their corresponding transport block sizes. The resultant set of possible TF/RVs produced at  105  will be the same as the initial set produced at  100  if none of the four transport block sizes exceeds the threshold at  102 . Otherwise, various resultant sets are produced by reducing the initial set by one, two, three, or all four of the TF/RVs associated with first retransmissions, depending on how many of the transport block sizes exceed the threshold at  102 . 
         [0027]    As will be evident to workers in the art, embodiments such as those described above may be readily implemented in software, hardware, or a combination of software and hardware, for example, by suitably modifying software, hardware or a combination of software and hardware in conventional instances of TS 25.214-compliant user equipment. 
         [0028]    Although exemplary embodiments of the invention have been described above in detail, this does not limit the scope of the invention, which can be practiced in a variety of embodiments.