Patent Publication Number: US-10333597-B2

Title: Method and system for enabling block bundling in LTE-A systems

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) AND CLAIM OF PRIORITY 
     This application is a continuation of U.S. Non-Provisional patent application Ser. No. 14/571,171 filed Dec. 15, 2014 and entitled METHOD AND SYSTEM FOR ENABLING RESOURCE BLOCK BUNDLING IN LTE-A SYSTEMS, now U.S. Pat. No. 9,516,655, which is a continuation of U.S. Non-Provisional patent application Ser. No. 12/970,717 filed Dec. 16, 2010 and entitled METHOD AND SYSTEM FOR ENABLING RESOURCE BLOCK BUNDLING IN LTE-A SYSTEMS, now U.S. Pat. No. 9,253,784, which claims priority to U.S. Provisional Patent Application No. 61/294,010 filed Jan. 11, 2010 and entitled “RESOURCE BLOCK BUNDLING FOR LTE-A SYSTEMS.” The content of the above-identified patent documents is hereby incorporated by reference. 
    
    
     TECHNICAL FIELD 
     The present application relates generally to wireless communications and, more specifically, to a method and system for enabling resource block bundling. 
     BACKGROUND 
     In 3 rd  Generation Partnership Project Long Term Evolution (3GPP LTE) systems, Orthogonal Frequency Division Multiplexing (OFDM) is adopted as a downlink (DL) transmission scheme. 
     SUMMARY 
     A base station is provided. The base station includes a transmit path circuitry configured to transmit an indication of whether a subscriber station is configured with precoding matrix indicator/rank indicator (PMI/RI) reporting. The transmit path circuitry is configured to set a pre-coding granularity to multiple physical resource blocks in the frequency domain to perform a same pre-coding over a bundled resource block if the subscriber station is configured with PMI/RI reporting. The bundled resource block comprises multiple consecutive physical resource blocks in the frequency domain. The base station also includes a receive path circuitry configured to receive feedback from the subscriber station. 
     A method of operating a base station is provided. The method includes transmitting an indication of whether a subscriber station is configured with precoding matrix indicator/rank indicator (PMI/RI) reporting, and setting a pre-coding granularity to multiple physical resource blocks in the frequency domain to perform a same pre-coding over a bundled resource block if the subscriber station is configured with PMI/RI reporting. The bundled resource block comprises multiple consecutive physical resource blocks in the frequency domain. The method also includes receiving feedback from the subscriber station. 
     A subscriber station is provided. The subscriber station includes a receive path circuitry configured to receive from a base station an indication of whether the subscriber station is configured with precoding matrix indicator/rank indicator (PMI/RI) reporting, and perform a channel estimation over a bundled resource block if the subscriber station is configured with PMI/RI reporting. The bundled resource block comprises multiple consecutive physical resource blocks in the frequency domain. The subscriber station also includes a transmit path circuitry configured to transmit the channel estimation as feedback to the base station. 
     A method of operating a subscriber station is provided. The method includes receiving from a base station an indication of whether the subscriber station is configured with precoding matrix indicator/rank indicator (PMI/RI) reporting, and performing a channel estimation over a bundled resource block if the subscriber station is configured with PMI/RI reporting. The bundled resource block comprises multiple consecutive physical resource blocks in the frequency domain. The method also includes transmitting the channel estimation as feedback to the base station. 
     A base station is provided. The base station includes a transmit path circuitry configured to transmit an indication of either a first feedback mode or a second feedback mode to a subscriber station. The transmit path circuitry is also configured to set a pre-coding granularity to multiple physical resource blocks in the frequency domain to perform a same pre-coding over a bundled resource block if the first feedback mode is indicated by the indicator. The bundled resource block comprises multiple consecutive physical resource blocks in the frequency domain. The base station also includes a receive path circuitry configured to receive feedback from the subscriber station. 
     A method of operating a base station is provided. The method includes transmitting an indication of either a first feedback mode or a second feedback mode to a subscriber station and receiving feedback from the subscriber station, and setting a pre-coding granularity to multiple physical resource blocks in the frequency domain to perform a same pre-coding over a bundled resource block if the first feedback mode is indicated by the indicator. The bundled resource block comprises multiple consecutive physical resource blocks in the frequency domain. The method also includes receiving feedback from the subscriber station. 
     A subscriber station is provided. The subscriber station includes a receive path circuitry configured to receive an indication of either a first feedback mode or a second feedback mode from a base station, and perform a channel estimation over a bundled resource block if the first feedback mode is indicated by the indicator. The bundled resource block comprises multiple consecutive physical resource blocks in the frequency domain. The subscriber station also includes a transmit path circuitry configured to transmit the channel estimation as feedback to the base station. 
     Before undertaking the DETAILED DESCRIPTION below, it may be advantageous to set forth definitions of certain words and phrases used throughout this patent document: the terms “include” and “comprise,” as well as derivatives thereof, mean inclusion without limitation; the term “or,” is inclusive, meaning and/or; the phrases “associated with” and “associated therewith,” as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, or the like; and the term “controller” means any device, system or part thereof that controls at least one operation, such a device may be implemented in hardware, firmware or software, or some combination of at least two of the same. It should be noted that the functionality associated with any particular controller may be centralized or distributed, whether locally or remotely. Definitions for certain words and phrases are provided throughout this patent document, those of ordinary skill in the art should understand that in many, if not most instances, such definitions apply to prior, as well as future uses of such defined words and phrases. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the present disclosure and its advantages, reference is now made to the following description taken in conjunction with the accompanying drawings, in which like reference numerals represent like parts: 
         FIG. 1  illustrates an exemplary wireless network that transmits messages in the uplink according to the principles of this disclosure; 
         FIG. 2  is a high-level diagram of an orthogonal frequency division multiple access (OFDMA) transmitter according to one embodiment of this disclosure; 
         FIG. 3  is a high-level diagram of an OFDMA receiver according to one embodiment of this disclosure; 
         FIG. 4  illustrates a diagram of a base station in communication with a plurality of mobile stations according to an embodiment of this disclosure; 
         FIG. 5  illustrates a spatial division multiple access (SDMA) scheme according to an embodiment of this disclosure; 
         FIGS. 6 and 6A through 6C  collectively illustrate dedicated reference signal (DRS) patterns that support two and four layer transmissions according to an embodiment of this disclosure; 
         FIG. 7  illustrates DRS patterns that support eight layer transmissions according to an embodiment of this disclosure; 
         FIG. 8  illustrates a table depicting the use of a one bit signaling to turn on or turn off resource block (RB) bundling according to an embodiment of this disclosure; 
         FIG. 9  illustrates a table depicting the use of available downlink control information (DCI) code-points to turn on or turn off resource block RB bundling according to an embodiment of this disclosure; 
         FIG. 10  illustrates subbands bundled together according to an embodiment of this disclosure; 
         FIG. 11  illustrates a DCI format 2C according to an embodiment of this disclosure; 
         FIG. 12  illustrates a table depicting restricted subsets according to an embodiment of this disclosure; 
         FIG. 13  illustrates a table depicting a mapping of states in a restricted subset to codepoints in DCI format 2C according to an embodiment of this disclosure; 
         FIG. 14  illustrates a table depicting restricted subsets according to another embodiment of this disclosure; 
         FIG. 15  illustrates a table depicting a mapping of states in a restricted subset to codepoints in DCI format 2C according to another embodiment of this disclosure; 
         FIG. 16  illustrates a method of operating a base station according to an embodiment of this disclosure; 
         FIG. 17  illustrates a method of operating a subscriber station according to an embodiment of this disclosure; 
         FIG. 18  illustrates a method of operating a base station according to another embodiment of this disclosure; and 
         FIG. 19  illustrates a method of operating a subscriber station according to another embodiment of this disclosure. 
     
    
    
     DETAILED DESCRIPTION 
       FIGS. 1 through 19 , discussed below, and the various embodiments used to describe the principles of the present disclosure in this patent document are by way of illustration only and should not be construed in any way to limit the scope of the disclosure. Those skilled in the art will understand that the principles of the present disclosure may be implemented in any suitably arranged wireless communication system. 
     With regard to the following description, it is noted that the Long Term Evolution (LTE) term “node B” is another term for “base station” used below. Also, the LTE term “user equipment” or “UE” is another term for “subscriber station” used below. 
       FIG. 1  illustrates exemplary wireless network  100 , which transmits messages according to the principles of the present disclosure. In the illustrated embodiment, wireless network  100  includes base station (BS)  101 , base station (BS)  102 , base station (BS)  103 , and other similar base stations (not shown). Base station  101  is in communication with Internet  130  or a similar IP-based network (not shown). Base station  102  provides wireless broadband access to Internet  130  to a first plurality of subscriber stations within coverage area  120  of base station  102 . The first plurality of subscriber stations includes subscriber station  111 , which may be located in a small business (SB), subscriber station  112 , which may be located in an enterprise (E), subscriber station  113 , which may be located in a WiFi hotspot (HS), subscriber station  114 , which may be located in a first residence (R), subscriber station  115 , which may be located in a second residence (R), and subscriber station  116 , which may be a mobile device (M), such as a cell phone, a wireless laptop, a wireless PDA, or the like. 
     Base station  103  provides wireless broadband access to Internet  130  to a second plurality of subscriber stations within coverage area  125  of base station  103 . The second plurality of subscriber stations includes subscriber station  115  and subscriber station  116 . In an exemplary embodiment, base stations  101 - 103  may communicate with each other and with subscriber stations  111 - 116  using OFDM or OFDMA techniques. 
     While only six subscriber stations are depicted in  FIG. 1 , it is understood that wireless network  100  may provide wireless broadband access to additional subscriber stations. It is noted that subscriber station  115  and subscriber station  116  are located on the edges of both coverage area  120  and coverage area  125 . Subscriber station  115  and subscriber station  116  each communicate with both base station  102  and base station  103  and may be said to be operating in handoff mode, as known to those of skill in the art. 
     Subscriber stations  111 - 116  may access voice, data, video, video conferencing, and/or other broadband services via Internet  130 . In an exemplary embodiment, one or more of subscriber stations  111 - 116  may be associated with an access point (AP) of a WiFi WLAN. Subscriber station  116  may be any of a number of mobile devices, including a wireless-enabled laptop computer, personal data assistant, notebook, handheld device, or other wireless-enabled device. Subscriber stations  114  and  115  may be, for example, a wireless-enabled personal computer (PC), a laptop computer, a gateway, or another device. 
       FIG. 2  is a high-level diagram of an orthogonal frequency division multiple access (OFDMA) transmit path  200 .  FIG. 3  is a high-level diagram of an orthogonal frequency division multiple access (OFDMA) receive path  300 . In  FIGS. 2 and 3 , the OFDMA transmit path  200  is implemented in base station (BS)  102  and the OFDMA receive path  300  is implemented in subscriber station (SS)  116  for the purposes of illustration and explanation only. However, it will be understood by those skilled in the art that the OFDMA receive path  300  may also be implemented in BS  102  and the OFDMA transmit path  200  may be implemented in SS  116 . 
     The transmit path  200  in BS  102  comprises a channel coding and modulation block  205 , a serial-to-parallel (S-to-P) block  210 , a size N Inverse Fast Fourier Transform (IFFT) block  215 , a parallel-to-serial (P-to-S) block  220 , an add cyclic prefix block  225 , an up-converter (UC)  230 , a reference signal multiplexer  290 , and a reference signal allocator  295 . 
     The receive path  300  in SS  116  comprises a down-converter (DC)  255 , a remove cyclic prefix block  260 , a serial-to-parallel (S-to-P) block  265 , a size N Fast Fourier Transform (FFT) block  270 , a parallel-to-serial (P-to-S) block  275 , and a channel decoding and demodulation block  280 . 
     At least some of the components in  FIGS. 2 and 3  may be implemented in software while other components may be implemented by configurable hardware or a mixture of software and configurable hardware. In particular, it is noted that the FFT blocks and the IFFT blocks described in the present disclosure document may be implemented as configurable software algorithms, where the value of Size N may be modified according to the implementation. 
     Furthermore, although the present disclosure is directed to an embodiment that implements the Fast Fourier Transform and the Inverse Fast Fourier Transform, this is by way of illustration only and should not be construed to limit the scope of the disclosure. It will be appreciated that in an alternate embodiment of the disclosure, the Fast Fourier Transform functions and the Inverse Fast Fourier Transform functions may easily be replaced by Discrete Fourier Transform (DFT) functions and Inverse Discrete Fourier Transform (IDFT) functions, respectively. It will be appreciated that, for DFT and IDFT functions, the value of the N variable may be any integer number (i.e., 1, 2, 3, 4, etc.), while for FFT and IFFT functions, the value of the N variable may be any integer number that is a power of two (i.e., 1, 2, 4, 8, 16, etc.). 
     In BS  102 , channel coding and modulation block  205  receives a set of information bits, applies coding (e.g., Turbo coding) and modulates (e.g., QPSK, QAM) the input bits to produce a sequence of frequency-domain modulation symbols. Serial-to-parallel block  210  converts (i.e., de-multiplexes) the serial modulated symbols to parallel data to produce N parallel symbol streams where N is the IFFT/FFT size used in BS  102  and SS  116 . Size N IFFT block  215  then performs an IFFT operation on the N parallel symbol streams to produce time-domain output signals. Parallel-to-serial block  220  converts (i.e., multiplexes) the parallel time-domain output symbols from Size N IFFT block  215  to produce a serial time-domain signal. Add cyclic prefix block  225  then inserts a cyclic prefix to the time-domain signal. Finally, up-converter  230  modulates (i.e., up-converts) the output of add cyclic prefix block  225  to RF frequency for transmission via a wireless channel. The signal may also be filtered at baseband before conversion to RF frequency. In some embodiments, reference signal multiplexer  290  is operable to multiplex the reference signals using code division multiplexing (CDM) or time/frequency division multiplexing (TFDM). Reference signal allocator  295  is operable to dynamically allocate reference signals in an OFDM signal in accordance with the methods and system disclosed in the present disclosure. 
     The transmitted RF signal arrives at SS  116  after passing through the wireless channel and reverse operations performed at BS  102 . Down-converter  255  down-converts the received signal to baseband frequency and remove cyclic prefix block  260  removes the cyclic prefix to produce the serial time-domain baseband signal. Serial-to-parallel block  265  converts the time-domain baseband signal to parallel time domain signals. Size N FFT block  270  then performs an FFT algorithm to produce N parallel frequency-domain signals. Parallel-to-serial block  275  converts the parallel frequency-domain signals to a sequence of modulated data symbols. Channel decoding and demodulation block  280  demodulates and then decodes the modulated symbols to recover the original input data stream. 
     Each of base stations  101 - 103  may implement a transmit path that is analogous to transmitting in the downlink to subscriber stations  111 - 116  and may implement a receive path that is analogous to receiving in the uplink from subscriber stations  111 - 116 . Similarly, each one of subscriber stations  111 - 116  may implement a transmit path corresponding to the architecture for transmitting in the uplink to base stations  101 - 103  and may implement a receive path corresponding to the architecture for receiving in the downlink from base stations  101 - 103 . 
     The total bandwidth in an OFDM system is divided into narrowband frequency units called subcarriers. The number of subcarriers is equal to the FFT/IFFT size N used in the system. In general, the number of subcarriers used for data is less than N because some subcarriers at the edge of the frequency spectrum are reserved as guard subcarriers. In general, no information is transmitted on guard subcarriers. 
     The transmitted signal in each downlink (DL) slot of a resource block is described by a resource grid of N RB   DL N sc   RB  subcarriers and N symb   DL  OFDM symbols. The quantity N RB   DL  depends on the downlink transmission bandwidth configured in the cell and fulfills N RB   min,DL ≤N RB   DL ≤N RB   max,DL , where N RB   min,DL  and N RB   max,DL  are respectively the smallest and largest downlink bandwidths supported. In some embodiments, subcarriers are considered the smallest elements that are capable of being modulated. 
     In case of multi-antenna transmission, there is one resource grid defined per antenna port. Each element in the resource grid for antenna port p is called a resource element (RE) and is uniquely identified by the index pair (k,l) in a slot where k=0, . . . , N RB   DL N sc   RB −1 and l=0, . . . , N symb   DL −1 are the indices in the frequency and time domains, respectively. Resource element (k,l) on antenna port p corresponds to the complex value a k,l   (p) . If there is no risk for confusion or no particular antenna port is specified, the index p may be dropped. 
     In LTE, DL reference signals (RSs) are used for two purposes. First, UEs measure channel quality information (CQI), rank information (RI) and precoder matrix information (PMI) using DL RSs. Second, each UE demodulates the DL transmission signal intended for itself using the DL RSs. In addition, DL RSs are divided into three categories: cell-specific RSs, multi-media broadcast over a single frequency network (MBSFN) RSs, and UE-specific RSs or dedicated RSs (DRSs). 
     Cell-specific reference signals (or common reference signals: CRSs) are transmitted in all downlink subframes in a cell supporting non-MBSFN transmission. If a subframe is used for transmission with MBSFN, only the first a few (0, 1 or 2) OFDM symbols in a subframe can be used for transmission of cell-specific reference symbols. The notation R p  is used to denote a resource element used for reference signal transmission on antenna port p. 
     UE-specific reference signals (or dedicated RSs: DRSs) are supported for single-antenna-port transmission on the Physical Downlink Shared Channel (PDSCH) and are transmitted on antenna port 5. The UE is informed by higher layers whether the UE-specific reference signal is present and is a valid phase reference for PDSCH demodulation or not. UE-specific reference signals are transmitted only on the resource blocks upon which the corresponding PDSCH is mapped. 
     The time resources of an LTE system are partitioned into 10 msec frames, and each frame is further partitioned into 10 subframes of one msec duration each. A subframe is divided into two time slots, each of which spans 0.5 msec. A subframe is partitioned in the frequency domain into multiple resource blocks (RBs), where an RB is composed of 12 subcarriers. 
       FIG. 4  illustrates a diagram  400  of a base station  420  in communication with a plurality of mobile stations  402 ,  404 ,  406 , and  408  according to an embodiment of this disclosure. As shown in  FIG. 4 , base station  420  simultaneously communicates with multiple of mobile stations through the use of multiple antenna beams, each antenna beam is formed toward its intended mobile station at the same time and same frequency. Base station  420  and mobile stations  402 ,  404 ,  406 , and  408  are employing multiple antennas for transmission and reception of radio wave signals. The radio wave signals can be Orthogonal Frequency Division Multiplexing (OFDM) signals. 
     In this embodiment, base station  420  performs simultaneous beamforming through a plurality of transmitters to each mobile station. For instance, base station  420  transmits data to mobile station  402  through a beamformed signal  410 , data to mobile station  404  through a beamformed signal  412 , data to mobile station  406  through a beamformed signal  414 , and data to mobile station  408  through a beamformed signal  416 . In some embodiments of this disclosure, base station  420  is capable of simultaneously beamforming to the mobile stations  402 ,  404 ,  406 , and  408 . In some embodiments, each beamformed signal is formed toward its intended mobile station at the same time and the same frequency. For the purpose of clarity, the communication from a base station to a mobile station may also be referred to as downlink communication, and the communication from a mobile station to a base station may be referred to as uplink communication. 
     Base station  420  and mobile stations  402 ,  404 ,  406 , and  408  employ multiple antennas for transmitting and receiving wireless signals. It is understood that the wireless signals may be radio wave signals, and the wireless signals may use any transmission scheme known to one skilled in the art, including an Orthogonal Frequency Division Multiplexing (OFDM) transmission scheme. 
     Mobile stations  402 ,  404 ,  406 , and  408  may be any device that is capable receiving wireless signals. Examples of mobile stations  402 ,  404 ,  406 , and  408  include, but are not limited to, a personal data assistant (PDA), laptop, mobile telephone, handheld device, or any other device that is capable of receiving the beamformed transmissions. 
     The use of multiple transmit antennas and multiple receive antennas at both a base station and a single mobile station to improve the capacity and reliability of a wireless communication channel is known as a Single User Multiple Input Multiple Output (SU-MIMO) system. A MIMO system promises linear increase in capacity with K where K is the minimum of number of transmit (M) and receive antennas (N) (i.e., K=min(M,N)). A MIMO system can be implemented with the schemes of spatial multiplexing, a transmit/receive beamforming, or transmit/receive diversity. 
     As an extension of SU-MIMO, multi-user MIMO (MU-MIMO) is a communication scenario where a base station with multiple transmit antennas can simultaneously communicate with multiple mobile stations through the use of multi-user beamforming schemes such as Spatial Division Multiple Access (SDMA) to improve the capacity and reliability of a wireless communication channel. 
       FIG. 5  illustrates an SDMA scheme according to an embodiment of this disclosure. As shown in  FIG. 5 , base station  420  is equipped with 8 transmit antennas while mobile stations  402 ,  404 ,  406 , and  408  are each equipped two antennas. In this example, base station  420  has eight transmit antennas. Each of the transmit antennas transmits one of beamformed signals  410 ,  502 ,  504 ,  412 ,  414 ,  506 ,  416 , and  508 . In this example, mobile station  402  receives beamformed transmissions  410  and  502 , mobile station  404  receives beamformed transmissions  504  and  412 , mobile station  406  receives beamformed transmissions  506  and  414 , and mobile station  408  receives beamformed transmissions  508  and  416 . 
     Since base station  420  has eight transmit antenna beams (each antenna beams one stream of data streams), eight streams of beamformed data can be formed at base station  420 . Each mobile station can potentially receive up to 2 streams (beams) of data in this example. If each of the mobile stations  402 ,  404 ,  406 , and  408  was limited to receive only a single stream (beam) of data, instead of multiple streams simultaneously, this would be multi-user beamforming (i.e., MU-BF). 
     In Release 8 LTE systems, a UE is required to perform channel estimation based on common reference signals (CRSs) over the entire bandwidth. Once channel estimation is performed, the UE performs demodulation based on different transmission modes indicated by the different formats of the downlink control information. For example, when downlink spatial multiplexing is performed, downlink control information (DCI) format 2 is used, and the UE performs demodulation based on the resource assignment and TPMI (transmission PMI) contained in the DCI format. For example, in 3GPP TS 36.212 v 8.8.0, “E-UTRA, Multiplexing and Channel Coding,” December 2009, the definition of TPMI is defined in Table 5.3.3.1.5-4 (2 antenna ports) and in Table 5.3.3.1.5-5 (4 antenna ports) of Section 5.3.3.1.5, which is hereby incorporated by reference into the present application as if fully set forth herein. 
     The eNodeB indicates whether it is wideband precoding or subband precoding to UE based on the UE&#39;s feedback, and the UE performs downlink demodulation accordingly. 
     In LTE-Advanced (LTE-A) systems, the downlink demodulation is based on dedicated reference signals (DRS), a.k.a. UE-specific reference signals (UE-RS). 
     In LTE-Advanced systems, demodulation of the data channel is based precoded UE-specific reference signal, that is, the reference signals are precoded using the same precoder as the data channel as described in R1-090529 “Way forward on CoMP and MIMO DL RS,” Outcome of ad hoc discussions, January 2009, and R1-091066 “Way forward on downlink reference signals for LTE-A,” CATT, CMCC, Ericsson, Huawei, LGE, Motorola, Nokia, Nokia Siemens Networks, Nortel, Panasonic, Philips, Qualcomm Europe, Samsung, Texas Instruments, March 2009, both of which are hereby incorporated by reference into the present application as if fully set forth herein. 
     RSs targeting PDSCH demodulation (for LTE-A operation) are UE specific and are transmitted only in scheduled RBs and the corresponding layers. Different layers can target the same or different UEs. The design principle is an extension of the concept of Rel-8 UE-specific RS (used for beamforming) to multiple layers. RSs on different layers are mutually orthogonal. RSs and data are subject to the same precoding operation, and complementary use of Rel-8 CRS by the UE is not precluded. 
     In R1-094413, “Way forward on the details of DCI format 2B for enhanced DL transmission,” 3GPP RAN1#58bis, Miyazaki, October 2009, which is hereby incorporated by reference into the present application as if fully set forth herein, an agreement has been made for DCI format 2B as follows: 
     The DCI Format 2B is based on DCI Format 2A; 
     1 bit is added for the source channel identifier (SC-ID); 
     The Swap Flag is removed; 
     For rank 1 transmission, the new data indicator (NDI) bit of the disabled transport block is re-used to indicate port information. A value of 0 is used to indicate an enabled transport block (TB) associated with port 7. A value of 1 is used to indicate an enabled transport block associated with port 8; and 
     For rank 2 transmission, TB1 is associated with port 7, and TB2 associated with port 8. 
     DCI format 2C can be constructed based on DCI format 2B for Rel. 10 transmission modes for facilitating dynamic SU- and MU-MIMO switching. 
     Since an eNodeB could potentially perform resource block (RB)-based precoding, the baseline granularity for channel estimation and demodulation is one RB. However, as disclosed in R1-093105, “UE-RS Patterns for LTE-A,” Qualcomm Europe, August 2009, which is hereby incorporated by reference into the present application as if fully set forth herein, “RB-bundling” (bundle contiguous RBs together to perform channel estimation and demodulation) will help higher rank (i.e., rank 5 to 8) transmissions achieve adequate channel estimation accuracy along with a low overhead. It is also disclosed in R1-094575, “Discussion on DM-RS for LTE-Advanced,” Samsung, November 2009; R1-094438, “On Rel-10 DM RS design for rank 5-8,” Ericsson, ST-Ericsson, November 2009; and R1-094548, “Further investigation on DMRS design for LTE-A,” CATT, November 2009, which are hereby incorporated by reference into the present application as if fully set forth herein, that “RB bundling” could be used to balance the transmission power imbalance across OFDM symbols for some high rank DM-RS patterns. 
       FIGS. 6 and 6A through 6C  collectively illustrate dedicated reference signal (DRS) patterns that support two and four layer transmissions according to an embodiment of this disclosure. The patterns in  FIGS. 6A through 6C  are related as indicated diagrammatically in  FIG. 6 . DRS patterns  601  and  603  illustrate pilot patterns that can support up to 2 layer transmissions. DRS REs labeled with 0,1 in DRS pattern  601  carry DRS for layer 0 and 1 with the RSs of the two layers code-division multiplexed (CDMed). Similarly, for DRS REs labeled with 2,3 in DRS pattern  603  carry DRS for layer 2 and 3 with the RSs of the two layers code-division multiplexed (CDMed). 
     In the two adjacent DRS REs labeled with 0,1, DRS symbols [r0 r1] for layer 0 are mapped to the two REs spread by a Walsh code [1 1], which results in [r0 r1], while DRS symbols r2 and r3 for layer 1 are mapped to the two REs spread by a Walsh code [1 −1], which results in [r2 −r3]. 
     DRS pattern  605  illustrates a pilot pattern that can support up to four layer transmissions, where the DRS REs are again partitioned into two, those labeled with 0,1 and those with 2,3. In this pattern, the DRS REs labeled with 0,1 carry DRSs for layer 0 and 1 with the RSs of the two layers code-division multiplexed (CDMed), and the DRS REs labeled with 2,3 carry DRSs for layer 2 and 3 with the RSs of the two layers code-division multiplexed (CDMed). 
       FIG. 7  illustrates DRS patterns that support eight layer transmissions according to an embodiment of this disclosure. With regard to  FIG. 7 , REs labeled with alphabet X, where X is one of G, H, I, J, L, K, are used for carrying a number of DRS among the 8 DRS, where the number of DRS are CDM&#39;ed. DRS pattern  701  is based on spreading factor 2 CDM across two time-adjacent REs with the same alphabet label. DRS pattern  703  is based on spreading factor 4 CDM across two groups of two time-adjacent REs with the same alphabet label. In this embodiment, the 8 antenna ports in a Rank-8 pattern are referred to as antenna ports 4, 5, 6, 7, 8, 9, 10, 11 in the sequel to distinguish them from the antenna ports in Rank-2 and Rank-4 patterns. 
     It is noted that in Rel-8 LTE, antenna ports 0, 1, 2, 3, 4, 5 are used for CRS, MBSFN RS and Rel-8 DRS. Hence, if the numbering convention extending Rel-8 LTE is followed, the new antenna port numbers will start from 6. Rank-2 pattern will have antenna ports 6, 7. Rank-4 pattern will have antenna ports 7, 8, 9, 10. Rank-8 pattern will have antenna ports 11, 12, 13, 14, 15, 16, 17, 18. 
     In one embodiment of DRS pattern  701 , G carries DRS 4,5. H carries DRS 6,7. I carries DRS 8,9. J carries DRS 10,11. In one embodiment of DRS pattern  703 , K carries DRS 4, 5, 6, 7; and L carries DRS 8, 9, 10, 11. 
     Each of the DM-RS patterns in  FIGS. 6 and 7  is RB based. Accordingly, a UE could perform channel estimation and demodulation per RB. Alternatively, if RB bundling is supported, the UE could perform channel estimation and demodulation jointly across bundled RBs. In this way, the performance of channel estimation and demodulation can be improved. 
     RB-bundling gain is achieved only when an eNodeB performs the same downlink precoding vectors across the bundled RBs. Accordingly, a UE will have to perform channel estimation and demodulation over the bundled RBs jointly. 
     In other words, RB bundling will reduce the precoding flexibility since the precoding vectors within the bundled RBs have to be the same. This clearly suggests a trade-off between gains from increasing channel interpolation span in frequency versus losses from increasing frequency selective precoding granularity. 
     The advantage of RB bundling is that channel estimation performance is improved. However, the eNodeB cannot perform per RB encoding if the eNode B does not receive per RB feedback from the UE due to large overhead. 
     The advantage of not enabling RB bundling is that the eNodeB does not need the UE to feedback the PMI in order to perform channel estimation and demodulation. Instead, the eNodeB could rely upon uplink channel sounding in TDD systems. Furthermore, the eNodeB would have the flexibility to perform per RB pre-coding, which results in a higher pre-coding gain. However, the UE would then have to perform per RB channel estimation if the channel is very selective. 
     Therefore, it would be advantageous to be able to turn on or off the feature of RB-bundling depending on the channel conditions. 
     This disclosure provides systems and methods for enabling RB-bundling. 
     In some embodiments of this disclosure, an eNodeB transmits an indication to turn on or off the feature of RB-bundling to a UE. 
     When RB-bundling is turned on or enabled, the eNodeB performs the same downlink precoding vectors across a number of continuous RBs (the RB-bundling size), and the UE performs channel estimation and demodulation jointly on the bundled RBs. When RB-bundling is turning off or not enabled, the eNodeB performs downlink precoding on a per-RB basis, and the UE performs channel estimation and demodulation on a per RB basis as well. 
     The indication from the eNodeB to the UE to indicate whether RB bundling is enabled can be achieved several ways. 
     In some embodiments of this disclosure, a signaling from the eNodeB to UE indicating whether RB-bundling is enabled can be either semi-statically signaled through higher-layer signaling or dynamically signaled utilizing the available code-points in a DCI format. Furthermore, this signaling can be either explicit or implicit. 
       FIG. 8  illustrates a table  800  depicting the use of a one bit signaling to turn on or turn off resource block (RB) bundling according to an embodiment of this disclosure. In some embodiments of this disclosure, explicit signaling is used to turn on or off RB-bundling. For example, higher layer signaling is used to semi-statistically turn on or off RB bundling. For example, as shown in table  800 , a one bit signaling can be used to semi-statistically turn on or turn off RB bundling. In this particular example, a first value of “0” indicates a first state in which RB bundling is turned off or disabled. A second value of “1” indicates a second state in which RB bundling is turned on or enabled. In another example, a sequence of bits is used to indicate states related to RB-bundling. One particular state indicated by this sequence of bits could be interpreted at the UE as turning off RB-bundling. 
       FIG. 9  illustrates a table  900  depicting the use of available downlink control information (DCI) code-points to turn on or turn off resource block RB bundling according to an embodiment of this disclosure. As shown in  FIG. 9 , available DCI code-points are also used to dynamically turn on or off RB bundling. For example, in DCI format 2X, a state is defined to turn on RB bundling by adding an additional field to DCI format 2C. In this particular example, a first state indicated by the additional field is a state in which RB bundling is turned on or enabled. A second state indicated by the additional field is a state in which RB bundling is turned off or disabled. 
     In some embodiments of this disclosure, implicit signaling is used to turn on or off RB-bundling. For example, whether RB bundling is enabled is based on a specific transmission mode, the DCI format used for a DL grant, the transmission scheme, and the radio network temporary identifier (RNTI) configuration. 
     For example, RB bundling is turned on or enabled if a UE is configured in Rel. 9 transmission mode (mode 8 in 3GPP 36.213), and if the UE received a physical downlink shared channel (PDSCH) packet scheduled with DCI format 2B. 
     In addition, if the UE receives a PDSCH packet scheduled with DCI format 1A and the associated transmission scheme is T×D (scheduled by semi-persistent scheduling (SPS) RNTI, and for the case when the physical broadcast channel (PBCH) signals multiple antenna ports), then RB bundling is turned off or disabled. If the UE receives a PDSCH packet scheduled with DCI format 1A, and the associated transmission scheme is single antenna port transmission (1. scheduled by SPS-RNTI, and for the case when the PBCH signals one antenna port; or 2. scheduled by cell radio network temporary identifier (C-RNTI)), then RB bundling is turned on or enabled. 
     For example, RB bundling is turned on or enabled if a UE is configured in Rel. 10 transmission mode for both SU and MU MIMO transmission, and if the UE received a PDSCH packet scheduled with DCI format 2C (DCI format in Rel-10 used to support 2 codeword MIMO transmission). 
     In addition, if the UE receives a PDSCH packet scheduled with DCI format 1A, and the associated transmission scheme is TxD (scheduled by SPS RNTI, and for the case when the PBCH signals multiple antenna ports), then RB bundling is turned off or disabled. If the UE receives a PDSCH packet scheduled with DCI format 1A, and the associated transmission scheme is single antenna port transmission (1. scheduled by SPS-RNTI, and for the case when the PBCH signals one antenna port; or 2. scheduled by C-RNTI), then RB bundling is turned on or enabled. 
     In other embodiments of this disclosure, RB bundling is turned on or off based on a specific feedback mode. 
     For example, if a UE is configured in Rel-9 and Rel-10 transmission modes and precoding matrix indicator/rank indicator (PMI/RI) feedback is configured, RB bundling is turned on or enabled. Otherwise, if the UE is configured in Rel-10 and beyond Rel-10 transmission modes and PMI/RI feedback is not configured, RB bundling is turned off or disabled. This is because the application scenario for configuring PMI/RI feedback is for frequency-division duplexing (FDD) systems while the application scenario for configuring PMI/RI feedback is not for time-division duplexing TDD systems. As discussed early in TDD systems, an eNodeB may obtain the channel state information using uplink sounding to perform frequency selective precoding. In this case, PRB bundling should be turned off accordingly. Furthermore, even in FDD systems, when the eNodeB decides to perform open-loop operations, the eNodeB will not configure the UE to feedback PMI/RI. Therefore, PRB bundling is also turned off in this case to allow for flexible operation at the eNodeB. 
     In another example, when wideband channel quality indicator (CQI)/PMI/RI (wideband CQI) feedback mode is configured, RB bundling is turned on or enabled. When subband CQI/PMI/RI (subband CQI) feedback mode is configured, RB bundling is turned off or disabled. 
     In other embodiments of this disclosure, an RB bundling on/off indication can also be realized through other system indications from the eNodeB to the UE. For example, RB bundling is enabled once the rank indicator (RI) is greater than a predetermined value. 
     In yet other embodiments of this disclosure, RB bundling is always on for demodulation using Rel. 9 or Rel. 10 UE-RS. 
     In order to perform different types of feedback reports, the UE is configured by the eNodeB in different feedback modes. 
     In some embodiments of this disclosure, RB-bundling is turned on or off based on the specific feedback mode configured by the eNodeB. 
     In one embodiment, RB-bundling is turned on or off based on the specific physical uplink control channel (PUCCH) feedback mode. 
     For example, RB bundling is turned on or enabled when when the UE is configured with PMI/RI reporting, and RB bundling is turned off or disabled when the UE is not configured with PMI/RI reporting. 
     Accordingly, when the UE is configured with PMI/RI reporting, the pre-coding granularity at the eNodeB is multiple physical resource blocks. That is the eNodeB performs the same pre-coding over a bundled resource block where a bundled resource block comprises multiple consecutive physical resource blocks. 
     Accordingly, when the UE is configured with PMI/RI reporting, the feedback granularity at the UE is set to multiple physical resource blocks such that the UE performs a channel estimation over a bundled resource block where a bundled resource block comprises multiple consecutive physical resource blocks. 
     Furthermore, when the UE is not configured with PMI/RI reporting, the pre-coding granularity at the eNodeB is a single physical resource block. That is the eNodeB performs pre-coding on a per physical resource block basis. 
     Accordingly, when the UE is not configured with PMI/RI reporting, the feedback granularity at the UE is set to a single physical resource block such that the UE performs a channel estimation on a per physical resource block basis. 
     In 3GPP TS 36.213 v 8.8.0, “E-UTRA, Physical Layer Procedures,” December 2009, which is hereby incorporated by reference into the present application as if fully set forth herein, depending on the mode of periodic PUCCH feedback, RB bundling is turned on or enabled when the UE is configured in mode 1-1 and mode 2-1 of Table 7.2.2-1, and RB bundling is turned off or disabled when the UE is configured in mode 1-0 and mode 2-0. 
     In other embodiments of this disclosure, RB-bundling is turned on or off based on the based on the specific physical uplink shared channel (PUSCH) feedback mode. 
     In some embodiments of this disclosure, RB bundling is turned on or enabled when the UE is configured for “single PMI” and/or “multiple PMI” feedback, and RB bundling is turned off or disabled otherwise. 
     For example, RB bundling is turned on or enabled when the UE is configured for “single PMI” feedback, and RB bundling is turned off or disabled when the UE is configured for “No PMI” or “Multiple PMI” feedback. 
     In another example, RB bundling is turned on or enabled when the UE is configured for “single PMI” and “Multiple PMI” feedback, and RB bundling is turned off or disabled when the UE is configured for “No PMI” feedback. 
     In yet another example, RB bundling is turned on or enabled when the UE is configured for “Multiple PMI” feedback, and RB-bundling is turned off or disabled when the UE is configured for “No PMI” or “Single PMI” feedback. 
     For example, in 3GPP TS 36.213 v 8.8.0, “E-UTRA, Physical Layer Procedures,” December 2009, depending on the mode of aperiodic PUSCH feedback, RB bundling is turned on or enabled when the UE is configured in mode 3-1, and RB bundling is turned off or disabled in other feedback modes. 
     Once RB bundling is on or enabled, the granularity of the RB bundling has to be decided. As described earlier, the granularity of the RB bundling refers to the number of continuous PRBs used for channel estimation and demodulation. 
     In some embodiments of this disclosure, the RB-bundling granularity is set to be the unit of downlink resource allocation. 
     For example, in 3GPP TS 36.211 v 8.8.0, “E-UTRA, Physical channels and modulation,” December 2009, which is hereby incorporated by reference into the present application as if fully set forth herein, the unit of downlink resource allocation is a resource block group (RBG), the size of RBG is dependent on the total system bandwidth. Therefore, the granularity of RB bundling can be the RBG size. 
     In other embodiments of this disclosure, the RB-bundling granularity is set to be the feedback granularity. The feedback granularity refers to the number of continuous RBs used by the UE to perform PMI/CQI/RI feedback. 
     For example, in 3GPP TS 36.211 v 8.8.0, “E-UTRA, Physical channels and modulation,” December 2009, feedback granularity for PUSCH feedback is the subband size defined in Section 7.2.1 for higher layer-configured subband feedback or UE-selected subband feedback. The feedback granularity for PUCCH feedback is defined in Section 7.2.2. 
     Therefore, in some embodiments, the RB-bundling granularity is set to be the subband size of the PUCCH feedback as a function of the total system bandwidth. 
     Alternatively, the RB-bundling granularity is related to the subband size of the PUSCH feedback. 
     For example, if RB bundling is turned on or enabled by the eNodeB configuring specific feedback mode, then the granularity of RB is the subband size of the corresponding feedback mode. 
       FIG. 10  illustrates subbands bundled together according to an embodiment of this disclosure. In yet other embodiments of this disclosure, the RB-bundling granularity is set to be jointly decided by the feedback granularity as well as the downlink resource allocation unit. Feedback granularity refers to the number of continuous RBs used by the UE to perform PMI/CQI/RI feedback. 
     For example when a UE is configured to have PUSCH “Multiple PMI” feedback, the eNodeB would perform downlink precoding based on the UE feedback subband size, and the UE would assume the RBs in the downlink resource allocation from the same subband bundled together as shown in  FIG. 10 . 
     In  FIG. 10 , a first subband  1010  includes a first RB bundle  1001 , and a second subband  1020  includes a second RB bundle  1011 . The first RB bundle  1001  and the second RB bundle  1011  are bundled together to form an RBG  1030 . 
     In further embodiments of this disclosure, the RB-bundling granularity is set according to the subband size associated with the configured feedback modes. 
     In one such embodiment, the RB-bundling granularity depends on the configured PUSCH feedback modes. 
     For example, when wideband feedback is configured (mode 3-1), all the allocated RBs are bundled to perform channel estimation and demodulation. 
     In another example, when subband feedback is configured (mode 1-2, mode 2-2), RB bundling follows the subband size from the UE PUSCH feedback and/or the resource block group (RBG) size. 
     In a further example, when no PMI feedback is configured (mode 2-0, mode 3-0), RB bundling is turned off or disabled. 
     In some embodiments of this disclosure, the RB-bundling granularity depends on the configured PUCCH feedback modes. 
     For example, when wideband feedback is configured (mode 1-1, mode 2-1), RB bundling follows the subband size from the PUCCH feedback (higher layer configured feedback subband size) and/or the RBG size. 
     For example, when no PMI feedback is configured (mode 1-0, mode 2-0), RB bundling is turned off or disabled. 
     In some embodiments of this disclosure, the size of RB bundling is fixed. 
     For example, the size of RB bundling can be an even number to facilitate pattern rotation of UE-RS patterns for higher ranks as suggested in R1-094575, “Discussion on DM-RS for LTE-Advanced,” Samsung, November 2009, which is hereby incorporated by reference into the present application as if fully set forth herein. 
       FIG. 11  illustrates a DCI format 2C  1100  according to an embodiment of this disclosure. As shown in  FIG. 11 , in some embodiments of this disclosure, DCI format 2C  1100  is constructed by adding a new N3-bit for the indication of a combination of a selected DM RS pattern and a DM RS index set to DCI format 2B to support dynamic switching of SU- and MU-MIMO. A new data indicator (NDI) bit of a disabled transport block (TB) in DCI format 2B is used for indicating a DM RS index in the case of rank-1 indication in Rel-9 LTE. Hence, this embodiment uses codepoints constructed by a combination of an NDI bit of a disabled TB, such as the NDI bit in NDI field  1101  or NDI field  1103 , and the new N3-bit in the N3-bit field  1105  for indicating rank-1 states in the restricted subset. 
       FIG. 12  illustrates a table  1200  depicting restricted subsets according to an embodiment of this disclosure. In some embodiments, a state in a restricted subset A is signalled by DCI format 2C, where the restricted subset A is shown in table  1200  as an example. In particular embodiments, the restricted subset A is constructed such that all possible states from Rank-2 patterns A and B are included, no Rank-2 states from Rank-4 are included, and only higher rank states are included from Rank-8. 
     The motivations of this subset restriction are that: 
     rank 1 and rank 2 transmissions are supported with minimal UE-RS overhead; 
     MU-MIMO is explicitly supported only for rank-1 with orthogonal UE-RS in Rank-2 and Rank-4 patterns; and 
     higher RS overhead is allowed only for ranks 3 or above. 
       FIG. 13  illustrates a table  1300  depicting a mapping of states in a restricted subset to codepoints in DCI format 2C according to an embodiment of this disclosure.  FIG. 13  illustrates one example mapping of states in restricted subset A to codepoints in DCI format 2C. 
       FIG. 14  illustrates a table  1400  depicting restricted subsets according to another embodiment of this disclosure. In this embodiment, a state in restricted subset B is signalled by DCI format 2C. In this embodiment, the restricted subset B is constructed such that all possible states from Rank-2 patterns A and B are included, no Rank-2 states from Rank-4 are included, and only higher rank states are included from Rank-8. The motivations of this subset restriction are that: 
     MU-MIMO is explicitly supported for rank-1 with orthogonal UE-RS in Rank-2 and Rank-4 patterns; 
     MU-MIMO is explicitly supported for rank-2 with orthogonal UE-RS in Rank-4 pattern; and 
     higher RS overhead is allowed for ranks 2 or above. 
       FIG. 15  illustrates a table  1500  depicting a mapping of states in a restricted subset to codepoints in DCI format 2C according to another embodiment of this disclosure.  FIG. 15  illustrates one example mapping of states in restricted subset B to codepoints in DCI format 2C. 
       FIG. 16  illustrates a method  1600  of operating a base station according to an embodiment of this disclosure. The method  1600  includes transmitting an indication of either a first feedback mode or a second feedback mode to a subscriber station (block  1601 ) and determining whether the first feedback mode is indicated by the indicator (block  1603 ). The method  1600  also includes setting the pre-coding granularity at the base station to multiple physical resource blocks in the frequency domain such that the base station performs the same pre-coding over a bundled resource block where a bundled resource block comprises multiple consecutive physical resource blocks in the frequency domain if the first feedback mode is indicated by the indicator (block  1605 ) and setting the pre-coding granularity at the base station to one physical resource block if the second feedback mode is indicated by the indicator (block  1607 ). The method  1600  further includes receiving feedback from the subscriber station (block  1609 ). 
       FIG. 17  illustrates a method  1700  of operating a subscriber station according to an embodiment of this disclosure. The method  1700  includes receiving an indication of a first feedback mode or a second feedback mode from a base station (block  1701 ), and determining whether the first feedback mode is indicated by the indicator (block  1703 ). The method  1700  also includes performing a channel estimation over a bundled resource block where a bundled resource block comprises multiple consecutive physical resource blocks in the frequency domain if the first feedback mode is indicated by the indicator (block  1705 ), and performing channel estimation only on a per physical resource block basis if the second feedback mode is indicated by the indicator (block  1707 ). The method  1700  further includes transmitting the channel estimation as feedback to the base station (block  1709 ). 
       FIG. 18  illustrates a method  1800  of operating a base station according to another embodiment of this disclosure. The method  1800  includes transmitting an indication of whether a subscriber station is configured with precoding matrix indicator/rank indicator (PMI/RI) reporting (block  1801 ), and determining whether the subscriber station is configured with PMI/RI reporting (block  1803 ). The method  1800  also includes setting the pre-coding granularity at the base station to multiple physical resource blocks in the frequency domain such that the base station performs the same pre-coding over a bundled resource block where a bundled resource block comprises multiple consecutive physical resource blocks in the frequency domain if the subscriber station is configured with PMI/RI reporting (block  1805 ) and setting the pre-coding granularity at the base station to one physical resource block if the subscriber station is not configured with PMI/RI reporting (block  1807 ). The method  1800  further includes receiving feedback from the subscriber station (block  1809 ). 
       FIG. 19  illustrates a method  1900  of operating a subscriber station according to another embodiment of this disclosure. The method  1900  includes receiving from a base station an indication of whether the subscriber station is configured with precoding matrix indicator/rank indicator (PMI/RI) reporting (block  1901 ), and determining whether the subscriber station is configured with PMI/RI reporting (block  1903 ). The method  1900  also includes performing a channel estimation over a bundled resource block where a bundled resource block comprises multiple consecutive physical resource blocks in the frequency domain if the subscriber station is configured with PMI/RI reporting (block  1905 ), and performing channel estimation only on a per physical resource block basis if the subscriber station is not configured with PMI/RI reporting (block  1907 ). The method  1900  further includes transmitting the channel estimation as feedback to the base station (block  1909 ). 
     Although the present disclosure has been described with an exemplary embodiment, various changes and modifications may be suggested to one skilled in the art. It is intended that the present disclosure encompass such changes and modifications as fall within the scope of the appended claims.