Abstract:
Disclosed is multiplexing transmissions of Uplink Control Information (UCI) signals having variable payloads from User Equipments (UEs). The UCI transmission uses a first format type if its size is less than or equal to a predetermined values and it uses a second format type if its size is greater than a predetermined value. When the first format type is used the UE multiplexing is through a first method while when the second format type is used the UE multiplexing is through a second method which is different than the first method. The structure of the second format type is the same as the structure used for the transmission of data information by UEs. The UEs can also be grouped and UCI transmission can be triggered through the reception of control signaling addressing a group of UEs and indicating UCI transmission by a sub-group of UEs in the group of UEs.

Description:
PRIORITY 
       [0001]    This application claims priority under 35 U.S.C. §119(e) to U.S. Provisional Application No. 61/172,432, entitled “Multiplexing Transmissions of Channel State Information”, which was filed on Apr. 24, 2009, the contents of which are incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention is directed to wireless communication systems and, more particularly, to multiplexing transmissions conveying large payloads of control information from user equipments. 
         [0004]    2. Description of the Related Art 
         [0005]    A communication system consists of a DownLink (DL), supporting transmissions of signals from a base station (Node B) to User Equipments (UEs), and of an UpLink (UL), supporting transmissions of signals from UEs to the Node B. A UE, also commonly referred to as a terminal or a mobile station, may be fixed or mobile and may be a wireless device, a cellular phone, a personal computer device, etc. A Node B is generally a fixed station and may also be referred to as a Base Transceiver System (BTS), an access point, or some other terminology. 
         [0006]    The DL signals consist of data signals, carrying the information content, control signals providing Downlink Control Information (DCI), and Reference Signals (RS) which are also known as pilots. The Node B transmits DCI through a Physical Downlink Control CHannel (PDCCH) and data information through a Physical Downlink Shared CHannel (PDSCH). 
         [0007]    The UL signals consist of data signals, carrying the information content, control signals providing Uplink Control Information (UCI), and Reference Signals (RS). The UEs convey UL data signals through a Physical Uplink Shared CHannel (PUSCH). UCI signals include acknowledgement signals associated with the application of a Hybrid Automatic Repeat reQuest (HARQ) process, Service Request (SR) signals, Channel Quality Indicator (CQI) signals, Precoding Matrix Indicator (PMI) signals, and Rank Indicator (RI) signals. The combination of CQI, PMI, and RI will be referred to as Channel State Information (CSI). UCI can be transmitted in a Physical Uplink Control CHannel (PUCCH) or, together with data, in the PUSCH. 
         [0008]    The CSI is used to inform the Node B of the channel conditions the UE experiences in the DL in order for the Node B to select the appropriate parameters, such as the Modulation and Coding Scheme (MCS), for the PDCCH or PDSCH transmission to the UE and ensure a desired BLock Error Rate (BLER) for the respective information. The CQI provides a measure of the Signal to Interference and Noise Ratio (SINR) over sub-bands or over the whole operating DL BandWidth (BW), typically in the form of the highest MCS for which a predetermined BLER target can be achieved for a signal transmission by the Node B in the respective BW. The PMI and RI are used to inform the Node B how to combine a signal transmission to the UE from multiple Node B antennas in accordance with the Multiple-Input Multiple-Output (MIMO) principle. Full channel state information in the form of channel coefficients allows the selection of the precoding weights with MIMO to closely match the channel experienced by the UE and offer improved DL performance at the expense of increased UL overhead required to feedback the channel coefficients relative to other CSI signal types. 
         [0009]    An exemplary structure for the PUSCH transmission in the UL Transmission Time Interval (TTI), which for simplicity is assumed to consist of one sub-frame, is shown in  FIG. 1 . The sub-frame  110  includes two slots. Each slot  120  includes N symb   UL  symbols used for the transmission of data signals, control signals, or RS. Each symbol  130  further includes a Cyclic Prefix (CP) to mitigate interference due to channel propagation effects. The PUSCH transmission in one slot may be located at the same or at a different part of the operating BW than the PUSCH transmission in the other slot. Some symbols in each slot can be used for RS transmission  140  to provide channel estimation and enable coherent demodulation of the received signal. The transmission BW is assumed to consist of frequency resource units which will be referred to as Physical Resource Blocks (PRBs). Each PRB is further assumed to consist of N sc   RB  sub-carriers, or Resource Elements (REs), and a UE is allocated M PUSCH  PRBs  150  for PUSCH transmission for a total of M sc   PUSCH =M PUSCH ·N sc   RB  REs for the PUSCH transmission BW. 
         [0010]    An exemplary UE transmitter block diagram for UCI and data transmission in the same PUSCH sub-frame is illustrated in  FIG. 2 . Coded CQI bits  205  and coded data bits  210  are multiplexed  220 . If HARQ-ACK bits also need to be multiplexed, data bits are punctured to accommodate HARQ-ACK bits. Discrete Fourier Transform (DFT) of the combined data bits is performed in DFT unit  230 . UCI bits are then obtained by performing sub-carrier mapping in sub-carrier mapping unit  240 , wherein the REs corresponding to the assigned transmission BW are selected in control unit  250 . Inverse Fast Fourier Transform (IFFT) is performed in the IFFT unit  260 . Finally the CP is inserted in CP Insertion unit  270  and filtering is performed in Time Windowing unit  280 , which outputs the transmitted signal  290 . For brevity, additional transmitter circuitry such as digital-to-analog converter, analog filters, amplifiers, and transmitter antennas are not illustrated. Also, the encoding process for the data bits and the CSI bits, as well as the modulation process for all transmitted bits, are omitted for brevity. The PUSCH signal transmission is assumed to be over clusters of contiguous REs in accordance to the DFT Spread Orthogonal Frequency Multiple Access (DFT-S-OFDM) method allowing signal transmission over one cluster  295 A (also known as Single-Carrier Frequency Division Multiple Access (SC-FDMA)), or over multiple non-contiguous clusters of contiguous BW  295 B. 
         [0011]    The Node B receiver performs the reverse (complementary) operations of the UE transmitter. This is conceptually illustrated in  FIG. 3  where the reverse operations of those illustrated in  FIG. 2  are performed. After an antenna receives the Radio-Frequency (RF) analog signal and after further processing units (such as filters, amplifiers, frequency down-converters, and analog-to-digital converters) which are not shown for brevity, the received signal  310  is filtered in Time Windowing unit  320  and the CP is removed in CP Removal unit  330 . Subsequently, the Node B receiver applies a Fast Fourier Transform (FFT) in FFT unit  340 , selects the REs used by the UE transmitter in Sub-Carrier Demapping unit  350 , applies an Inverse DFT (IDFT) in IDFT unit  360 , extracts the HARQ-ACK bits and places respective erasures for the data bits in Extraction unit  370 , and de-multiplexes in Demultiplexer unit  380  the data bits  390  and CSI bits  395 . As for the UE transmitter, well known Node B receiver functionalities such as channel estimation, demodulation, and decoding are not shown for brevity. 
         [0012]    An exemplary structure for the CSI transmission in one slot of the PUCCH is illustrated in  FIG. 4 . A similar structure may also be used for the HARQ-ACK transmission in the PUCCH. The transmission in the other slot, which may be at a different part of the operating BW for frequency diversity, is assumed to effectively have the same structure. The CSI signal transmission in the PUCCH is assumed to be in one PRB. The CSI transmission structure  410  comprises the transmission of CSI signals and RS for enabling coherent demodulation of the CSI signals. The CQI bits  420  are modulated in modulators  430  with a “Constant Amplitude Zero Auto-Correlation (CAZAC)” sequence  440 , for example with QPSK modulation, which is then transmitted after performing the IFFT operation as it is subsequently described. Each RS  450  is transmitted through the unmodulated CAZAC sequence. 
         [0013]    An example of CAZAC sequences is given by Equation (1) 
         [0000]    
       
         
           
             
               
                 
                   
                     
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         [0000]    where L is the length of the CAZAC sequence, n is the index of an element of the sequence n={0,1, . . . , L-1}, and k is the index of the sequence. If L is a prime integer, there are L- 1  distinct sequences which are defined as k ranges in {0,1, . . . , L-1}. If the PRBs comprise of an even number of REs, such as for example N sc   RB =12, CAZAC sequences with even length can be directly generated through computer search for sequences satisfying the CAZAC properties. 
         [0014]      FIG. 5  shows an exemplary transmitter structure for a CAZAC sequence that can be used without modulation as RS or with modulation as CSI signal. The frequency-domain version of a computer generated CAZAC sequence, generated in CAZAC Sequence generator  510 , is used. The REs corresponding to the assigned PUCCH BW are selected in Control unit  520  for mapping in Sub-Carrier Mapping unit  530  the CAZAC sequence. An IFFT is performed in IFFT unit  540 , and a Cyclic Shift (CS), as it is subsequently described, is applied to the output in Cyclic Shift unit  550 . Finally, the CP is inserted in CP Insertion unit  560  and filtering is performed in Time Windowing unit  570 , which outputs transmitted signal  580 . A UE is assumed to apply zero padding in REs used for signal transmission by other UEs and in guard REs (not shown). Moreover, for brevity, additional transmitter circuitry such as digital-to-analog converter, analog filters, amplifiers, and transmitter antennas as they are known in the art, are not shown. 
         [0015]    The reverse (complementary) transmitter functions are performed for the reception of the CAZAC sequence. This is conceptually illustrated in  FIG. 6  where the reverse operations of those in  FIG. 5  apply. An antenna receives RF analog signal and after further processing units (such as filters, amplifiers, frequency down-converters, and analog-to-digital converters) the digital received signal  610  is filtered in Time Windowing unit  620  and the CP is removed in CP Removal unit  630 . Subsequently, the CS is restored in the CS Restore unit  640 , and a Fast Fourier Transform (FFT) is performed in FFT unit  650 . The transmitted REs are selected in Sub-Carrier Demapping unit  660  under control of Control unit  665 .  FIG. 6  also shows the subsequent correlation in Multiplier  670  with the replica of the CAZAC sequence produced in CAZAC Based Sequence unit  680 . Finally, the output  690  is obtained which can then be passed to a channel estimation unit, such as a time-frequency interpolator, in case of a RS, or can to detect the transmitted information, in case the CAZAC sequence is modulated by CSI information bits. 
         [0016]    Different CSs of the same CAZAC sequence provide orthogonal CAZAC sequences. Therefore, different CSs of the same CAZAC sequence can be allocated to different UEs in the same PRB for their RS or CSI transmission and achieve orthogonal UE multiplexing. This principle is illustrated in  FIG. 7 . In order for the multiple CAZAC sequences  710 ,  730 ,  750 ,  770  generated respectively from multiple CSs  720 ,  740 ,  760 ,  780  of the same root CAZAC sequence to be orthogonal, the CS value  790  should exceed the channel propagation delay spread DELTA (including a time uncertainty error and filter spillover effects). If T S  is the DFT-S-OFDM symbol duration, the number of such CSs is equal to the mathematical floor of the ratio T S /D. 
         [0017]    For the CSI transmission structure in the PUCCH sub-frame, as illustrated in  FIG. 4 , for one of the two sub-frame slots, 5 symbols carry CSI and 2 symbols carry RS. As the CSI transmission needs to be relatively reliable and cannot utilize HARQ retransmissions, it needs to be protected through reliable channel coding. As a result, the CSI payload supported in the PUCCH is small. For example, puncturing a (32, 10) Reed-Mueller (RM) code to (20, 10), 10 CSI bits can be transmitted using QPSK modulation and coding rate of ½ (20 coded bits). 
         [0018]    In order to support higher data rates than possible in legacy communication systems, aggregation of multiple Component Carriers (CCs) can be used in both the DL and the UL to provide higher operating BWs. For example, to support communication over 100 MHz, aggregation of five 20 MHz CCs can be used. UEs capable of operating only over a single DL/UL CC pair will be referred to as “Legacy-UEs (L-UEs)” while UEs capable of operating over multiple DL/UL CCs will be referred to as “Advanced-UEs (A-UEs)”. The invention assumes that if an A-UE receives PDSCH in multiple DL CCs or transmits PUSCH in multiple UL CCs, a different data packet having its own HARQ process is conveyed by each such PDSCH or PUSCH transmission. 
         [0019]      FIG. 8  further illustrates the principle of CC aggregation. An operating DL BW of 100 MHz  810  is constructed by the aggregation of 5 (contiguous, for simplicity) DL CCs,  821 ,  822 ,  823 ,  824 ,  825 , each having a BW of 20 MHz. Similarly, an operating UL BW of 100 MHz  820  is constructed by the aggregation of 5 UL CCs,  831 ,  832 ,  833 ,  834 ,  835 , each having a BW of 20 MHz. Each DL CC is assumed to be uniquely mapped to a UL CC (symmetric CC aggregation) but it is also possible for more than 1 DL CC to be mapped to a single UL CC or for more than 1 UL CC to be mapped to a single DL CC (asymmetric CC aggregation, not shown for brevity). The link between DL CCs and UL CCs can be UE-specific. 
         [0020]    To improve cell coverage and increase cell-edge data rates in the DL, Coordinated Multiple Point (CoMP) transmission/reception through Joint Processing (JP) can be used where multiple Node Bs transmit the same data signal to a UE. The DL CoMP principle is illustrated in  FIG. 9  wherein two Node Bs, Node B 1   910  and Node B 2   920 , transmit a first data signal to UE 1   930  and a second data signal to UE 2   940 . The Node Bs share the information content for a UE operating in DL CoMP mode through backhaul which is typically referred to as X 2  interface  950 . The backhaul, for example, may be a fiber optic link or a microwave link. 
         [0021]    To support PDSCH reception by an A-UE over multiple DL CCs, the A-UE should be able to transmit substantially larger CSI or HARQ-ACK information payloads to the Node B than an L-UE having PDSCH reception only in a single DL CC. While for symmetric DL/UL CC aggregations UCI transmission may fundamentally appear just as a parallelization of the one for single DL/UL CC pair to multiple DL/UL CC pairs, it is instead preferable for a UE to transmit all UCI in only one UL CC. This allows addressing all possible UE-specific symmetric or asymmetric DL/UL CC aggregations with a single design. It also avoids Transmission Power Control (TPC) problems that may occur if the UE simultaneously transmits UCI signals with substantially different powers in different UL CCs. Therefore, it is advantageous to consider UCI signaling structures where the transmission is in a single UL CC. This further necessitates the transmission of larger UCI payloads, than legacy ones, in a single channel. 
         [0022]    DL CoMP also represents a challenging scenario with respect to required payloads of CSI feedback signaling. Even for the benign case of CQI-only feedback, the respective payload increases proportionally with the number of Node Bs in the CoMP CSI reporting set. For example, for 3 Node Bs in the CoMP CSI reporting set, the total CSI payload is 30 bits and cannot be supported by the PUCCH structure in  FIG. 4 . Since a CoMP UE is often likely to also experience low UL SINR, supporting higher CSI payloads becomes even more challenging. The combination of CoMP and multiple DL CCs further increases the required CSI payloads. 
         [0023]    The PUSCH can support substantially larger payloads than the PUCCH and can accommodate the increased UCI payloads. However, as the minimum PUSCH granularity is 1 PRB, the UL overhead from using conventional PUSCH to support only UCI transmissions can become substantial even when this is done for a few UEs per sub-frame. 
         [0024]    Therefore, there is a need to design PUCCH structures supporting large payloads for UCI signaling in a communication system supporting DL CC aggregation or DL CoMP. 
         [0025]    There is another need to minimize the UL overhead corresponding to the transmission of large UCI payloads. 
         [0026]    Finally, there is a need to efficiently manage the PUCCH and PUSCH resources while supporting the transmission of large UCI payloads. 
       SUMMARY OF THE INVENTION 
       [0027]    Accordingly, the present invention has been designed to solve at least the aforementioned limitations and problems in the prior art and the present invention provides methods and apparatus for using different channel structures for the transmission of Uplink Control Information (UCI) according to the UCI payload, for multiplexing UCI transmissions from User Equipments (UEs) in the selected channel structure, and for managing the resources associated with UCI transmissions from different UEs. 
         [0028]    In accordance with a first embodiment of the present invention, periodic UCI transmission in a Physical Uplink Control CHannel (PUCCH) uses a first PUCCH format if the UCI payload is less than or equal to a predetermined value and uses a second PUCCH format if the UCI payload is greater than the predetermined value. The second PUCCH format has the same structure as the one used for the transmission of data information by UEs. 
         [0029]    In accordance with a second embodiment of the present invention, UCI transmissions from multiple UEs are multiplexed in the second PUCCH format using either Time Division Multiplexing (TDM) or Frequency Division Multiplexing (FDM). The UEs also transmit Reference Signals (RS) which are multiplexed in the same time-frequency resources using different cyclic shifts of a Constant Amplitude Zero Auto-Correlation (CAZAC) sequence. 
         [0030]    In accordance with a third embodiment of the present invention, a Node B assigns UEs into UCI groups with each UCI group having an identity. UCI transmission by UEs in a UCI group is activated through the reception of a Downlink Control Information (DCI) format containing the UCI group identity. The DCI format also contains a bit-map wherein at least one location in the bit-map is associated with one UE in the UCI group. If the value of the bit-map in a reference location equals to one, the respective UE transmits the corresponding UCI type; otherwise no transmission occurs. The resources for the UCI transmission are predetermined for each UE and can be linked to the location in the bit-map associated with the UE. A UE may belong to multiple UCI groups. The DCI format with the UCI group identity can be designed to have the same size as another DCI format the UEs decode. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0031]    The above and other aspects, features, and advantages of the present invention will be more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which: 
           [0032]      FIG. 1  is a diagram illustrating a sub-frame structure for PUSCH transmission; 
           [0033]      FIG. 2  is a block diagram illustrating a transmitter structure for the transmission of data information and control information in the PUSCH; 
           [0034]      FIG. 3  is a block diagram illustrating a receiver structure for the reception of data information and control information in the PUSCH; 
           [0035]      FIG. 4  is a block diagram illustrating a sub-frame structure for CQI transmission in the PUCCH; 
           [0036]      FIG. 5  is a block diagram illustrating a transmitter structure for a CAZAC sequence; 
           [0037]      FIG. 6  is a block diagram illustrating a receiver structure for a CAZAC sequence; 
           [0038]      FIG. 7  is a diagram illustrating multiplexing of CAZAC sequences through the application of different cyclic shifts; 
           [0039]      FIG. 8  is a diagram illustrating the principle of Carrier Aggregation (CA); 
           [0040]      FIG. 9  is a diagram illustrating the application of the Downlink CoMP principle; 
           [0041]      FIG. 10  is a diagram illustrating exemplary CSI contents for 3 Downlink Component Carriers; 
           [0042]      FIG. 11  is a diagram illustrating the concept of using multiple PUCCH formats to transmit UCI according to its payload; 
           [0043]      FIG. 12  is a diagram illustrating Time Division Multiplexing (TDM) of 2 UEs in a PUCCH format having the PUSCH sub-frame structure; 
           [0044]      FIG. 13  is a diagram illustrating Time Division Multiplexing (TDM) of 3 UEs in a PUCCH format having the PUSCH sub-frame structure; 
           [0045]      FIG. 14  is a diagram illustrating Time Division Multiplexing (TDM) of 4 UEs in a PUCCH format having the PUSCH sub-frame structure; 
           [0046]      FIG. 15  is a diagram illustrating Frequency Division Multiplexing (FDM) of 2 UEs in a PUCCH format having the PUSCH sub-frame structure; 
           [0047]      FIG. 16  is a diagram illustrating Time Division Multiplexing (TDM) and Frequency Division Multiplexing (FDM) of 4 UEs in a PUCCH format having the PUSCH sub-frame structure; 
           [0048]      FIG. 17  is a block diagram illustrating a transmitter for UCI transmission using a PUCCH format having the PUSCH sub-frame structure; 
           [0049]      FIG. 18  is a block diagram illustrating a receiver for UCI transmission using a PUCCH format having the PUSCH sub-frame structure; 
           [0050]      FIG. 19  is a block diagram illustrating a transmission process for the PDCCH CSI format from the Node B; 
           [0051]      FIG. 20  is a block diagram illustrating a reception process for the PDCCH CSI format from a UE; 
           [0052]      FIG. 21  is a diagram illustrating the 1-to-1 mapping between the UEs in a CSI group and the bits in the PDCCH CSI format bit-map; and 
           [0053]      FIG. 22  is a diagram illustrating the processing of the bit-map information by a UE in the CSI group addressed by a respective PDCCH CSI format. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0054]    The present invention will now be described more fully hereinafter with reference to the accompanying drawings. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete and will fully convey the scope of the invention to those skilled in the art. 
         [0055]    Additionally, although the present invention is described in relation to an Orthogonal Frequency Division Multiple Access (OFDMA) communication system, it also applies to all Frequency Division Multiplexing (FDM) systems in general and to Single-Carrier Frequency Division Multiple Access (SC-FDMA), OFDM, FDMA, Discrete Fourier Transform (DFT)-spread OFDM, DFT-spread OFDMA, SC-OFDMA, and SC-OFDM in particular. 
         [0056]    In order to support larger UCI payloads than in a legacy system operating with single DL/UL CCs and without DL CoMP, the supportable UCI payload sizes need to be expanded. The first object of the present invention considers the definition of a PUCCH format using the PUSCH transmission structure. The embodiment considers the CSI transmission. 
         [0057]      FIG. 10  illustrates CSI content for 3 DL CCs  1010  consisting of {CQI  1 , PMI  1 , RI  1 }  1020 , {CQI  2 , PMI  2 , RI  2 }  1030 , and {CQI  3 , PMI  3 , RI  3 }  1040 , and of the CSI for 2 DL CoMP cells  1060  consisting of {CQI  1 , PMI  1 , RI  1 }  1070 , {CQI  2 , PMI  2 , RI  2 }  1080 . For the purposes of  FIG. 10 , a DL CC can be viewed as a DL CoMP cell and the reverse. Not all of the {CQI, PMI, RI} need to be included in the CSI. For example, the CSI for the first DL CC  1020  may consist of only CQI while the CSI for the second DL CC  1030  may consist of only RI. 
         [0058]      FIG. 11  illustrates the concept of using multiple PUCCH formats  1110  (format  2   1110 A and format  3   1110 B) for CSI transmission. The structure of the PUCCH format for small CSI payloads and high UE multiplexing capacity can be as described in  FIG. 4  and will be referred to as PUCCH format  2   1120 . The structure of the PUCCH format for large CSI payloads and lower UE multiplexing capacity can be as described in  FIG. 1  for the PUSCH and will be referred to as PUCCH format  3   1130 . Unlike PUCCH format  2  for which CSI transmission is always confined to one PRB, the CSI transmission for PUCCH format  3  may be in one or more PRBs. The total BW allocated in each sub-frame to the PUCCH formats for CSI transmission, in number of PRBs, can be signaled by the Node B through a broadcast channel. In the embodiment, after the BW for PUCCH formats  2  and  3  is allocated, the adjacent PRBs towards the interior of the operating BW can be used for other PUCCH transmissions  1140 , such as SR or HARQ-ACK transmissions which for L-UEs are assumed to be through the use of a PUCCH formats which will be referred to as PUCCH format  1 . Subsequently, the remaining PRBs in the interior of the operating BW can be allocated to PUSCH transmissions  1150 . 
         [0059]    Unlike PUCCH format  2  where multiple UEs, for example six UEs, can have CSI transmission in the same PRB using different cyclic shifts of a CAZAC sequence ( FIG. 4 ), only one UE can have CSI transmission using PUCCH format  3  having the PUSCH sub-frame structure ( FIG. 1 ). As a consequence, the UL overhead resulting from the use of PUCCH format  3  is substantially increased, for example by a factor of six. 
         [0060]    The second object of the invention considers the multiplexing of CSI transmissions from multiple UEs in the PUCCH format  3  and establishes a trade-off between the payload size and the multiplexing capacity in order to control the respective UL overhead. For example, a goal can be to allow flexible multiplexing of CSI transmissions from up to four UEs in PUCCH format  3  and use PUCCH format  2  for multiplexing CSI transmissions from six UEs. The supportable CSI payloads in PUCCH format  3  can progressively decrease as the UE multiplexing capacity increases and the smallest CSI payload and largest UE multiplexing capacity can be provided by PUCCH format  2 . For example, PUCCH format  3  can be used for CSI transmission of payloads above 20 bits from 1-4 UEs while PUCCH format  2  can be used for CSI transmission of payloads of about 10 bits from 6 UEs. 
         [0061]      FIG. 12  illustrates the multiplexing of 2 UEs in PUCCH format  3  using the PUSCH sub-frame structure in accordance with the second object of the invention. The CSI feedback from 2 UEs is multiplexed in one PRB. The first UE, UE 1   1210 , has CSI transmission in the first part of each slot and the second UE, UE 2   1220 , has CSI transmission in the second part of each slot. The RS from the first or the second UE  1230  is transmitted using a respective first cyclic shift or a second cyclic shift of the CAZAC sequence used in the cell. Each UE can have its own pre-assigned MCS for the CSI feedback transmission (all transmission parameters for CSI signaling in the PUCCH are allocated by higher layers). Since each PRB is assumed to consist of 12 REs, each UE can transmit 144 coded CSI bits with QPSK modulation, or 72 CSI information bits with code rate of ½, or 64 CSI information bits and 8 Cyclic Redundancy Check (CRC) bits. Such CSI payloads are substantially larger than 10 bits CSI payload which can be supported using PUCCH format  2  with code rate of ½, such as the punctured (20, 10) RM code. 
         [0062]    In the case of UEs with moderate or high SINRs or with enhanced transmission or reception based on respective antenna diversity, the received signal is reliable enough to support CSI transmission with a modulation order greater than QPSK, such as 8 PSK or QAM16, or with a higher code rate, such as ⅔. For such UEs, CSI transmission can be in only one slot to increase the UE multiplexing capacity in PUCCH format  3  and reduce the respective UL overhead. 
         [0063]      FIG. 13  illustrates the multiplexing of 3 UEs in PUCCH format  3  using the PUSCH sub-frame structure. CSI from a first UE, UE 1   1310 , is transmitted only in the first part of the first slot of the sub-frame, CSI from the second UE, UE 2   1320 , is transmitted only in the second part of the second slot of the sub-frame, while CSI from a third UE, UE 3   1330 , is transmitted in both slots of the sub-frame. The position in each slot of the CSI transmission from each UE is exemplary. The RS  1340  from UE 1  and UE 2  and the RS  1350  for UE 2  and UE 3  are multiplexed in the respective slots using different cyclic shifts of the same CAZAC sequence. 
         [0064]    Following the same principles,  FIG. 14  illustrates the multiplexing of 4 UEs in PUCCH format  3  using the PUSCH sub-frame structure. CSI from a first UE, UE 1   1410 , is transmitted only in the first part of the first slot of the sub-frame, CSI from the second UE, UE 2   1420 , is transmitted only in the second part of the first slot of the sub-frame, CSI from a third UE, UE 3   1430 , is transmitted only in the first part of the second slot of the sub-frame, and CSI from the fourth UE, UE 4   1440 , is transmitted only in the second part of the second slot of the sub-frame. The RS  1450  from UE 1  and UE 2  and the RS  1460  for UE 3  and UE 4  are multiplexed in the respective slots using different cyclic shifts of the same CAZAC sequence. 
         [0065]    In addition to the Time Division Multiplexing (TDM) structure described in  FIG. 12  through  FIG. 14 , Frequency Division Multiplexing (FDM) can also be applied as shown in  FIG. 15  for the case of 2 UEs. The N sc   RB =12 REs of one PRB  1510  are divided in a top sub-set of 6 contiguous REs allocated to a first UE, UE  1   1520 , and bottom sub-set of 6 contiguous REs allocated to a second UE, UE  2   1530 . Unlike the CSI transmission from each UE which is over half the BW of a PRB, the RS transmission  1540  from each UE occupies the entire PRB and the multiplexing is through the use of two different CSs, one CS for each UE, of the same CAZAC sequence as it was previously described. The reason for the RS transmission being over the entire PRB is to avoid a reduction in the number of available CAZAC sequences that would result from reducing their length to less than 12. Each UE transmits in both the first slot  1550  and the second slot  1560  of the sub-frame. FDM can be generalized to more than 2 RE clusters per PRB, the relative position of the clusters may change on a sub-frame symbol basis or on a slot basis (not shown for brevity). Additionally, FDM can be generalized so that the REs allocated to each UE are not contiguous. For example, the first UE may be allocated REs  1 ,  3 ,  5 ,  7 ,  9 , and  11  while UE 2  may be allocated REs  2 ,  4 ,  6 ,  8 ,  10 , and  12 . 
         [0066]    FDM can be combined with TDM as shown, for example, in  FIG. 16 . The N sc   RB =12 REs of one PRB  1610  are again divided in a top sub-set of 6 contiguous REs allocated to a first UE, UE  1   1620 , and bottom sub-set of 6 contiguous REs allocated to a second UE, UE  2   1630  in the first part of each slot and to a third UE, UE  3   1640 , and to a fourth UE, UE  4   1650 , respectively, in the second part of each slot. The RS transmission  1650  from each UE occupies the entire PRB and the multiplexing is through the use of four different CS, one CS for each UE, of the same CAZAC sequence as it was previously described. Each UE transmits in both the first slot  1660  and second slot  1670  of the sub-frame. 
         [0067]      FIG. 17  illustrates a transmitter block diagram for the CSI transmission using the PUSCH sub-frame structure. The CSI information bits  1710  are coded, rate matched to the allocated resources, and modulated in Coding, Rate Matching and Modulation unit  1720 . A controller  1730  selects the PUSCH sub-frame symbols over which the CSI is transmitted. The DFT of the combined data bits, if any, and CSI bits is then obtained in DFT unit  1740 , the REs are produced in Sub-Carrier Mapping unit  1750  corresponding to the assigned transmission BW are selected by control unit  175 , the IFFT is performed by IFFT unit  1760  and finally the CP is inserted in CP Insertion unit  1770  and filtering is performed in Time Windowing unit  1780 , which outputs the transmitted signal  1790 . For brevity, additional transmitter circuitry such as digital-to-analog converter, analog filters, amplifiers, and transmitter antennas are not illustrated. The placement of the controller  1730  for the selected PUSCH sub-frame symbols with CSI transmission in the transmitter chain is exemplary and another location may instead be used (for example, the controller  1730  may be placed immediately after the CP insertion  1770 ). 
         [0068]      FIG. 18  illustrates a receiver block diagram for the CSI transmitted using the PUSCH sub-frame structure. The reverse (complementary) operations of  FIG. 17  are performed. After an antenna receives the Radio-Frequency (RF) analog signal and after further processing units (such as filters, amplifiers, frequency down-converters, and analog-to-digital converters) which are not shown for brevity, the digital signal  1810  is filtered in Time Windowing Unit  1820  and the CP is removed in CP Removal unit  1830 . Subsequently, the receiver unit applies a FFT in FFT unit  1840 , selects by Control unit  1850  the REs used by the transmitter in Sub-Carrier Demapping unit  1855 , applies an IDFT in IDFT unit  1860 , and selects the PUSCH sub-frame symbols over which the CSI is transmitted from a reference UE in control unit  1870 . Then, after demodulation, rate matching, and decoding in De-Modulation, Rate-Matching and Decoding unit  1880 , the CSI bits are obtained  1890 . As for the transmitter, well known receiver functionalities such as channel estimation, demodulation, and decoding are not shown for brevity. The placement of the controller  1870  for the selected PUSCH sub-frame symbols with CSI transmission is exemplary and another location may instead be used (for example, the controller  1870  may be placed immediately before the CP removal unit  1820 ). Note that for both the RS transmission and the RS reception, the conventional transmitter and receiver structures for CAZAC sequences respectively apply with the only consideration being that more than one UE transmit RS in the same PRB using different cyclic shifts of the same CAZAC sequence. 
         [0069]    Therefore, the second object of the present invention provides method and means for multiplexing the CSI transmission from up to 4 UEs in a PUCCH format having the PUSCH sub-frame structure. The tradeoff is the increased multiplexing capacity at the expense of reduced CSI symbol space for each UE. The multiplexing of transmissions can be generalized to support transmissions of both CSI and data. For example, in  FIG. 12 , the first UE may transmit CSI while the second UE may transmit data such as a Voice over Internet Protocol (VoIP) packet. 
         [0070]    Although CSI transmissions with PUCCH format  3  can be either periodic or dynamic, the objective to minimize the PDCCH overhead requires that these CSI transmissions are periodically configured with parameters provided to each respective UE through higher layer signaling. However, this reduces the flexibility in managing the CSI transmissions depending on their usefulness. The third object of the present invention provides a tradeoff between having full flexibility of a CSI transmission that is dynamically scheduled per sub-frame through a respective PDCCH transmission to a UE and having limited flexibility of a CSI transmission that is semi-statically scheduled to occur periodically in predetermined sub-frames. A trade-off between these two extreme setups can be achieved by grouping multiple UEs in a “CSI group”, such as for example a group of DL CoMP UEs, and dynamically scheduling the CSI transmission of selected UEs in a CSI group, using preconfigured transmission parameters, through the transmission of a PDCCH format which will be referred to as PDCCH CSI format.  FIG. 19  describes the PDCCH CSI format transmission from the Node B. A group of UEs is assigned a CSI group IDentity (ID) in  1910 . The PDCCH CSI format uses the CSI group ID for identification. For example, the CRC computed in  1920  from the bit-map information from  1930  conveyed by the PDCCH CSI format is masked by the CSI group ID though an exclusive OR (XOR) operation in  1940 . The masked CRC is then appended to the bit-map information in  1950 , channel coding is applied in  1960 , rate matching to the allocated transmission resources is performed in  1970 , and finally the PDCCH CSI format is transmitted in  1980 . 
         [0071]    At the UE receiver the reverse operations are performed as described in  FIG. 20 . A received candidate PDCCH CSI format  2010  is rate de-matched in  2020 , decoded in  2030 , and the masked CRC  2040  and the bit-map information are extracted in  2045 . The masked CRC is then unmasked by performing the exclusive OR (XOR) operation in  2050  with the CSI group ID  2060 . Then, the CRC checking is performed in  2070  and it is determined in  2080  whether the CRC passes  2082  or not  2084 . If the CRC passes, the candidate PDCCH CSI format is considered valid and the bit-map information is further processed by the UE in  2090 . If the CRC does not pass, the candidate PDCCH CSI format is considered invalid and its contents are discarded from further processing in  2095 . 
         [0072]    A CSI group c consists of N CSI  UEs and all CSI groups are assumed to have the same size. A UE may belong to multiple CSI groups where each of those CSI groups corresponds to the transmission of different CSI payloads. A total of M c  resources are allocated to the CSI transmission from UEs in CSI group c. This information is known to all UEs and can be communicated by the Node B to each UE either through broadcast signaling or through dedicated higher layer signaling. The bit-map information consists of at least N CSI  bits and its size can be selected to be equal to the size of another PDCCH format the UE always attempts to decode, such as for example the PDCCH format scheduling data transmissions from the UE in the PUSCH, so that there are no additional blind decoding operations (only an additional CRC unmasking and checking). Otherwise, the CSI PDCCH format can be padded so that it achieves a size equal to the size of another PDCCH format the UEs always decode. The CSI PDCCH format may also contain Transmission Power Control (TPC) commands with each TPC command associated with a UCI transmission by the respective UE. Alternatively, a separate PDCCH format may be used to provide these TPC commands and, for the simplicity of the description, this will be assumed in the following. 
         [0073]    Each UE is also informed through higher layer signaling of its position in the CSI group relative to other UEs in the group and there is a 1-to-1 mapping between a bit in the bit-map and a UE in the CSI group.  FIG. 21  illustrates the 1-to-1 mapping between the UEs in the CSI group  2110  and the bits in the PDCCH CSI format bit-map  2120 . Each UE may also be informed of the MCS it should use for the CSI transmission for a respective CSI payload; otherwise, the MCS is assumed to be predetermined either for each CSI group (common to all UEs in the same CSI group) or for all CSI groups (common to all UEs in all CSI groups). The resources used for the CSI transmission are assumed to be the same for all UEs in the same CSI group, such as for example multiplexing 1 UE in 1 PRB over 1 sub-frame for UEs in a first CSI group or multiplexing 2 UEs in 1 PRB over 1 sub-frame for UEs in a second CSI group. The first PRB used by the first CSI group, if more than 1 CSI groups exist in a given sub-frame, may either be predetermined to be the first PRB in the operating BW or it may be communicated to the UEs through broadcast signaling by the Node B, or it may be informed by some predetermined bits in the PDCCH CSI format. As previously mentioned, the size of the PDCCH CSI format  2130 , which consists of N CSI  bit-map bits  2132   and N   CRC     —     CSI  CRC bits masked with the CSI group ID  2134 , may be the same as the size of a PDCCH format  2140  conveying a UL Scheduling Assignment (SA) to a UE for PUSCH transmission with data and consists of N UL     —     SA  bits  2142  providing the scheduling information and N CRC     —     UE  CRC bits masked with the reference UE ID  2144 . That is, N CSI +N CRC     —     CSI =N UL     —     SA +N CRC     —     UE . The length of the CRC for the PDCCH CSI format may be less than the length of the UL SA PDCCH format since a smaller number of UEs will typically attempt to decode the PDCCH CSI format. 
         [0074]    The UE processing of the bit-map information in  FIG. 19  is described in  FIG. 22 . It is assumed that a bit value of 0 in the bit-map indicates that the corresponding UE in the CSI group should not transmit CSI while a bit value of 1 indicates CSI transmission. After successfully decoding the candidate PDCCH CSI format and obtaining the bit-map information  2210 , the n th  UE in the CSI group determines in  2220  whether the value of the n th  bit is equal to 1. If it is not equal to 1 (i.e.  2230 ), the UE does not transmit CSI in  2240 . If it is equal to 1 (i.e.  2250 ), the UE determines the sum m of the previous n−1 bits, if any, in  2260  and transmits CSI using resource m+1 in  2270 . The processing steps need not necessarily be in the previously described order (for example, the UE may first obtain the sum of the first n−1 bits or it may simply compute the number of bits, in the first n−1 bits, having value 1). Nevertheless, the functionalities for determining the resource for CSI transmission at the referenced n th  UE are fully described by  FIG. 22 . 
         [0075]    The PDCCH CSI format can be generalized to request transmission of different CSI types. For example, a first CSI type can be CQI and a second CSI type can be the coefficients of the channel medium. For this generalized PDCCH CSI format, the same principles apply as previously described, with the only exception that the bit-map now includes more than 1 bit for each UE such as, for example, 2 bits. A UE determines the resources for the assigned type of CSI transmission, if any, by considering the UEs with CSI transmission of the same type having an earlier bit-map location as it was previously described for the case of 1 bit per UE in the bitmap. 
         [0076]    While the present invention has been shown and described with reference to certain preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the appended claims.