Abstract:
A method and apparatus for feedback in a wireless transmit receive unit (WTRU) includes transmitting feedback over an aggregate of predefined control channel elements (CCEs) wherein the feedback is one of a channel quality indicator (CQI), a precoding matrix index (PMI) or a rank index.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. provisional application No. 60/942,013, filed Jun. 5, 2007, which is incorporated by reference as if fully set forth. 
     
    
     FIELD OF INVENTION 
       [0002]    This application is related to wireless communications. 
       BACKGROUND 
       [0003]    A goal of the Third Generation Partnership Project (3GPP) Long Term Evolution (LTE) program is to develop new technology, new architecture and new methods for settings and configurations in wireless communication systems in order to improve spectral efficiency, reduce latency and better utilize the radio resource to bring faster user experiences and richer applications and services to users with lower costs. 
         [0004]    Wireless communication systems usually require feedback signaling to enable uplink and downlink communications. For example, hybrid automatic retransmission request (HARQ) enablement requires acknowledge/negative-acknowledge (ACK/NACK) feedback. Adaptive modulation and coding (AMC) requires channel quality index (CQI) feedback from a receiver. Multiple Input/Multiple Output (MIMO) systems or preceding requires rank and/or precoding matrix index (PMI) feedback from a receiver. Efficient signaling is essential to an evolved universal mobile telephone system (UMTS) terrestrial radio access network (E-UTRAN). 
         [0005]    A wireless transmit receive unit (WTRU) may feedback a channel quality index (CQI) or a preceding matrix index (PMI) or antenna weight to a base station (BS) or an e Node B (eNB). 
         [0006]    CQI and PMI feedback may be reported on the physical uplink control channel (PUCCH) or the physical uplink shared channel (PUSCH) in specific reporting modes. Each mode specifies the subbands for which feedback is reported and the mechanism for reporting. For example, if wideband CQI and no PMI is reported, mode 1-0 may be used. Mode 1-0 includes, for example, instruction for the WTRU to report a rank index by reporting a type 3 report that includes one rank index, and instructions for the WTRU to report CQI in a type 4 report including one wideband CQI. For other combinations of CQI and PMI, other modes may be used that include other specific instructions. 
         [0007]    Generally, feedback reporting on the PUSCH allows for a greater variety of feedback modes, and allows a greater number of bits to be transmitted in a single transmission time interval (TTI). Feedback reporting on the PUCCH may require splitting the feedback across multiple TTIs. 
         [0008]    Each PMI may be represented by L bits. The value of L depends upon the multiple input/multiple output (MIMO) antenna configuration and codebook sizes. A WTRU may report one PMI per subband that is selected by the WTRU or configured by an eNB. The WTRU may also report one CQI per codeword. 
         [0009]    As the number of the feedback bits becomes larger, it may be desirable to have more efficient feedback mechanisms. 
       SUMMARY 
       [0010]    Disclosed is a method and apparatus for feedback signaling in a wireless communication system. The feedback may include channel quality index (CQI), precoding matrix index (PMI), rank and/or acknowledge/negative-acknowledge (ACK/NACK). A WTRU may perform a method that includes several different report modes providing a PMI, CQI, rank index and/or ACK/NACK and transmitting the PMI, CQI rank index and/or ACK/NACK over an aggregation of predefined channel control elements (CCEs). 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    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: 
           [0012]      FIG. 1  shows a wireless communication system including a plurality of WTRUs and an eNB; 
           [0013]      FIG. 2  is a functional block diagram of the WTRU and the eNB of the wireless communication system of  FIG. 1 ; 
           [0014]      FIG. 3  shows the use of CCEs to transmit CQI and PMI; and 
           [0015]      FIG. 4  shows the use of CCEs to transmit CQI and PMI with ACK/NACK bits. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    When referred to hereafter, the terminology “wireless transmit/receive unit (WTRU)” includes but is not limited to a user equipment (UE), a mobile station, a fixed or mobile subscriber unit, a pager, a cellular telephone, a personal digital assistant (PDA), a computer, or any other type of user device capable of operating in a wireless environment. When referred to hereafter, the terminology “base station” includes but is not limited to a Node-B, a site controller, an access point (AP), or any other type of interfacing device capable of operating in a wireless environment. 
         [0017]      FIG. 1  shows a wireless communication system  100  including a plurality of WTRUs  110  and an eNB  120 . As shown in  FIG. 1 , the WTRUs  110  are in communication with the eNB  120 . Although three WTRUs  110  and one eNB  120  are shown in  FIG. 1 , it should be noted that any combination of wireless and wired devices may be included in the wireless communication system  100 . Each WTRU  110  may report feedback bits on a periodic or aperiodic basis to the eNB  120 . The eNB  120  may configure the type of feedback reported and the timing of the feedback. 
         [0018]      FIG. 2  is a functional block diagram  200  of the WTRU  110  and the eNB  120  of the wireless communication system  100  of  FIG. 1 . As shown in  FIG. 2 , the WTRU  110  is in communication with the eNB  120 . The WTRU  110  is configured to transmit feedback signals and control signals to the eNB  120 . The WTRU  110  is also configured to determine CQI and PMI as configured by the eNB  120  and to transmit the feedback and control signals to the eNB  120  on a periodic or aperiodic basis. Both the eNB  120  and the WTRU  110  are configured to process signals that are modulated and coded. 
         [0019]    In addition to the components that may be found in a typical WTRU, the WTRU  110  includes a processor  215 , a receiver  216 , a transmitter  217 , and an antenna  218 . The receiver  216  and the transmitter  217  are in communication with the processor  215 . The antenna  218  is in communication with both the receiver  216  and the transmitter  217  to facilitate the transmission and reception of wireless data. 
         [0020]    In addition to the components that may be found in a typical eNB, the eNB  120  includes a processor  225 , a receiver  226 , a transmitter  227 , and an antenna  228 . The receiver  226  and the transmitter  227  are in communication with the processor  225 . The antenna  228  is in communication with both the receiver  226  and the transmitter  227  to facilitate the transmission and reception of wireless data. 
         [0021]    A WTRU may transmit CQI feedback, PMI feedback and/or rank index feedback to an eNB. While this disclosure makes reference to PMI, CQI, and rank index, one skilled in the art should recognize that other feedback signals may also be used. 
         [0022]    A channel control element (CCE) may be defined as J resource elements, where J is an integer value and a resource element is defined as a specific sub-carrier during a specific orthogonal frequency division multiplex (OFDM) symbol interval. A fixed size uplink channel control element may be defined and used to carry uplink CQI, PMI and rank information. The size of the CCE may depend on many factors, including, but not limited to, the minimum size of a WTRU feedback report, system load, quality of service (QoS), and bandwidth. For each reporting period, or feedback instance, a different number of CCEs may be used, based on the aforementioned factors. 
         [0023]    The number of CCEs used to transmit the feedback may be determined for each feedback instance, and may change from one feedback instance to the next. The number of CCEs may depend on the number of feedback bits that are going to be transmitted in any feedback instance. The WTRU may determine the number of CCEs required for any particular feedback instance. 
         [0024]    PMI may be reported in different types of formats. PMI may be based on the feedback mode, which may be based on the uplink channel and the type of feedback that is being reported. In a first PMI format, a non-differential PMI may be used. Non-differential PMI may be used, for example, when a WTRU resets the PMI. The number of resource blocks represented by a PMI may be configured by a higher layer, such as a MAC or RLC, for example. 
         [0025]    In a second PMI format, the PMI may be reported differentially. The difference between the PMI of a sub-frame and the last reported full PMI is reported. The measurement of the sub-frame PMI may be based on the feedback mode, similar to the full PMI. 
         [0026]    CQI may be reported in at least one of three formats. In a first CQI format, a wideband average CQI, may be used. Wideband CQI is an average of all CQIs across all the subbands of a particular bandwidth. 
         [0027]    In a second CQI format, a best M, or preferred M, average CQI may be reported. Hereinafter, the terms “best M” and “preferred M” may be considered synonymous and interchangeable. The best M average CQI may be a frequency-selective CQI. The best M average CQI is the average of the best M subband CQIs chosen from all the subbands, where M is an integer. The best M average CQI is chosen by the WTRU and may be reported on the physical uplink shared channel (PUSCH) or on the physical uplink control channel (PUCCH). 
         [0028]    In a third CQI format, CQI may be reported as a best M individual CQI from amongst all the subbands. The best M individual CQI may also be a frequency-selective CQI. This is subband CQI and may be configured by a higher layer, such as a medium access control (MAC) or radio link control (RLC), for example. Best M individual CQI may also be reported on the PUSCH or on the PUCCH. 
         [0029]      FIG. 3  shows the use of a first set of CCEs  300  to transmit CQI and PMI formats. A rank index, a PMI and a CQI can be reported in 1, 2 or 3 CCEs  300 , depending on the format of the PMI and the format of the CQI. In a first feedback signal  302 , two (2) CCEs  300  may be used to transmit a best M average CQI  304 , a differential PMI  306  and a rank index  308 . In a second feedback signal  310 , a wideband CQI  312 , a full PMI  314  and a rank index  316  are also transmitted in two (2) CCEs  300 . In a third feedback signal  318 , a wideband CQI  320 , a differential PMI  322  and a rank index  324  may be transmitted in one (1) CCE. In a fourth feedback signal  326 , an individual best M CQI  328 , a differential PMI  330  and a rank index  332  may be transmitted in three (3) CCEs. 
         [0030]    ACK/NACK signaling occurs regularly in a wireless network and is on-demand. It is generally driven by downlink data traffic. An ACK/NACK transmission from a WTRU to an eNB may coincide with CQI, PMI, and/or rank feedback reporting. In that case, the ACK/NACK bits may be transmitted with the feedback bits in the defined aggregate CCEs. 
         [0031]      FIG. 4  shows the use of a second set of CCEs  400  to transmit CQI and PMI with ACK/NACK bits. A rank index, a PMI, a CQI and an ACK/NACK can be reported in 1, 2 or 3 CCEs  400 , depending on the format of the PMI and the format of the CQI. For example, in a first feedback signal  402 , two (2) CCEs  400  may be used to transmit a best M average CQI  406 , a differential PMI  408 , a rank index  410  and an ACK/NACK  404 . In a second feedback signal  412 , a wideband CQI  416 , a full PMI  418 , a rank index  420  and an ACK/NACK  414  are also transmitted in two (2) CCEs  400 . In a third feedback signal  422 , a wideband CQI  426 , a differential PMI  428 , a rank index  440  and an ACK/NACK  424  may be transmitted in one (1) CCE  400 . In a fourth feedback signal  430 , an individual best M CQI  434 , a differential PMI  436 , a rank index  438  and an ACK/NACK  432  may be transmitted in three (3) CCEs  400 . 
         [0032]    Time and frequency resources used by a WTRU to report PMI and/or CQI may be controlled by an eNB. If the WTRU has a PUSCH allocation, the WTRU may transmit feedback bits on a scheduled PUSCH transmission with or without an associated scheduling grant or without an uplink shared channel (UL-SCH). The WTRU may transmit feedback on a PUCCH if it does not have PUSCH allocation. 
         [0033]    Reporting may be periodic or aperiodic. When reporting in aperiodic mode, the WTRU may use the PUSCH. However, when reporting in periodic mode, the WTRU may use the PUSCH or the PUCCH. If both periodic and aperiodic reporting occurs in the same subframe, the WTRU may only transmit the aperiodic report in that particular sub-frame. 
         [0034]    The set of resource block groups (RBGs) that a WTRU may evaluate for CQI reporting may be semi-statically configured by a higher layers, such as a medium access layer (MAC) or a radio link control (RLC). The term RBG and subband are interchangeable in the content of this disclosure. A number of resource blocks (k) in each resource block group may also be semi-statically configured by a higher layer. 
         [0035]    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. The methods or flow charts provided in the present invention may be implemented in a computer program, software, or firmware tangibly embodied in a computer-readable storage medium for execution by a general purpose computer or a processor. Examples of computer-readable storage mediums include a read only memory (ROM), a random access memory (RAM), a register, cache memory, semiconductor memory devices, magnetic media such as internal hard disks and removable disks, magneto-optical media, and optical media such as CD-ROM disks, and digital versatile disks (DVDs). 
         [0036]    Suitable processors include, by way of example, a general purpose processor, a special purpose processor, a conventional processor, a digital signal processor (DSP), a plurality of microprocessors, one or more microprocessors in association with a DSP core, a controller, a microcontroller, Application Specific Integrated Circuits (ASICs), Field Programmable Gate Arrays (FPGAs) circuits, any other type of integrated circuit (IC), and/or a state machine. 
         [0037]    A processor in association with software may be used to implement a radio frequency transceiver for use in a wireless transmit receive unit (WTRU), user equipment (UE), terminal, base station, radio network controller (RNC), or any host computer. The WTRU may be used in conjunction with modules, implemented in hardware and/or software, such as a camera, a video camera module, a videophone, a speakerphone, a vibration device, a speaker, a microphone, a television transceiver, a hands free headset, a keyboard, a Bluetooth® module, a frequency modulated (FM) radio unit, a liquid crystal display (LCD) display unit, an organic light-emitting diode (OLED) display unit, a digital music player, a media player, a video game player module, an Internet browser, and/or any wireless local area network (WLAN) module.