PATENT DOCUMENT

Publication Number: US-10340990-B2
Application Number: US-201816049080-A
Country: US
Kind Code: B2

Title: Wireless feedback system and method

Abstract:
A codebook C is provided in a MIMO transmitter as well as a MIMO receiver. The codebook C will include M codewords c i , where i is a unique codeword index for each codeword c i . Each codeword defines weighting factors to apply to the MIMO signals, and may correspond to channel matrices or vectors to apply to the MIMO signals prior to transmission from the respective antennas of the MIMO transmitter. The present invention creates codeword subsets S i  for each codeword c i  of the codebook C. Each codeword subset S i  defines L codewords c j , which are selected from all the codewords c i  in the codebook C. The codewords c j  in a codeword subset S i  are the L codewords in the entire codebook that best correlate with the corresponding codeword c i .

Claims:
What is claimed is: 
     
       1. A method of providing feedback from a wireless receiver to a multiple-input multiple-output (MIMO) transmitter, the method comprising, at the wireless receiver:
 obtaining a channel estimate from a transmission from the MIMO transmitter, the channel estimate providing channel information; 
 selecting a first codeword from a plurality of codewords in a codebook based on first channel information at a first time; 
 determining second channel information for a MIMO channel at a subsequent time; 
 selecting a subset codeword from a subset of codebook codewords, which corresponds to the first codeword, based on the second channel information; and 
 transmitting a subset index for the subset codeword. 
 
     
     
       2. The method of  claim 1 , wherein obtaining the channel estimate includes employing automatic gain control. 
     
     
       3. The method of  claim 1 , wherein obtaining the channel estimate includes employing down conversion circuitry. 
     
     
       4. The method of  claim 1 , wherein obtaining the channel estimate includes employing synchronization circuitry. 
     
     
       5. The method of  claim 1 , wherein the transmission from the MIMO transmitter employs redundancy to facilitate error correction. 
     
     
       6. The method of  claim 1 , wherein the transmission from the MIMO transmitter employs bit interleaving. 
     
     
       7. The method of  claim 1 , wherein the transmission from the MIMO transmitter employs an inverse discrete Fourier Transform. 
     
     
       8. The method of  claim 1 , wherein the subset of codewords is determined based on the first codeword. 
     
     
       9. The method of  claim 1 , further comprising, at the wireless receiver:
 determining the first channel information at the first time; and 
 transmitting a first codeword index for the first codeword prior to the first time. 
 
     
     
       10. The method of  claim 9 , further comprising, at the wireless receiver:
 iteratively feeding back new first codeword indices, wherein for each new first codeword index there is a plurality of subset indices for the subset of codebook codewords associated with the new first codeword that is fed back. 
 
     
     
       11. A wireless receiver configured for providing feedback to a multiple-input multiple-output (MIMO) transmitter, the wireless receiver comprising:
 logic configured to obtain a channel estimate from a transmission from the MIMO transmitter, the channel estimate providing channel information; 
 logic configured to select a first codeword from a plurality of codewords in a codebook based on first channel information at a first time; 
 logic configured to determine second channel information for a MIMO channel at a subsequent time; 
 logic configured to determine a subset of codewords; 
 logic configured to select, based on the second channel information, a subset codeword from the subset of codewords; and 
 logic configured to transmit a subset index for the subset codeword. 
 
     
     
       12. The wireless receiver of  claim 11 , wherein the logic configured to obtain the channel estimate includes logic configured to employ automatic gain control. 
     
     
       13. The wireless receiver of  claim 11 , wherein the logic configured to obtain the channel estimate includes down conversion circuitry. 
     
     
       14. The wireless receiver of  claim 11 , wherein the logic configured to obtain the channel estimate includes synchronization circuitry. 
     
     
       15. The wireless receiver of  claim 11 , wherein the transmission from the MIMO transmitter employs redundancy to facilitate error correction. 
     
     
       16. The wireless receiver of  claim 11 , wherein the transmission from the MIMO transmitter employs bit interleaving. 
     
     
       17. The wireless receiver of  claim 11 , wherein the transmission from the MIMO transmitter employs an inverse discrete Fourier Transform. 
     
     
       18. The wireless receiver of  claim 11 , wherein the subset of codewords is determined based on the first codeword. 
     
     
       19. The wireless receiver of  claim 11 , further comprising:
 logic configured to determine the first channel information at the first time; and 
 logic configured to transmit a first codeword index for the first codeword prior to the first time. 
 
     
     
       20. The wireless receiver of  claim 19 , further comprising:
 logic configured to iteratively feed back new first codeword indices, wherein for each new first codeword index there is a plurality of subset indices for the subset of codebook codewords associated with the new first codeword that is fed back.

Description:
PRIORITY CLAIM 
     This application is a continuation of and claims the benefit of priority from U.S. patent application Ser. No. 15/852,585, entitled “Wireless Feedback System and Method” and filed on Dec. 22, 2017, which is a continuation of and claims the benefit of priority from U.S. patent application Ser. No. 15/665,711, entitled “Wireless Feedback System and Method” and filed on Aug. 1, 2017 (now U.S. Pat. No. 9,900,069, issued on Feb. 20, 2018), which is a continuation of and claims the benefit of priority from U.S. patent application Ser. No. 15/175,246, entitled “Wireless Feedback System and Method” and filed on Jun. 7, 2016 (now U.S. Pat. No. 9,742,478, issued on Aug. 22, 2017), which is a continuation of and claims the benefit of priority from U.S. patent application Ser. No. 14/853,539, of the same title and filed on Sep. 14, 2015 (now U.S. Pat. No. 9,369,190, issued on Jun. 14, 2016), which is a continuation of and claims the benefit of priority from U.S. patent application Ser. No. 14/551,053, of the same title and filed on Nov. 23, 2014 (now U.S. Pat. No. 9,136,923, issued on Sep. 15, 2015), which is a continuation of and claims the benefit of priority from U.S. patent application Ser. No. 14/072,779, of the same title and filed on Nov. 5, 2013 (now U.S. Pat. No. 8,897,384, issued on Nov. 25, 2014), which is a continuation of and claims the benefit of priority from U.S. patent application Ser. No. 13/464,640, of the same title and filed on May 4, 2012 (now U.S. Pat. No. 8,605,812, issued on Dec. 10, 2013), which is a continuation of and claims the benefit of priority from U.S. patent application Ser. No. 12/066,322, of the same title and filed on Nov. 5, 2008 (now U.S. Pat. No. 8,189,714, issued on May 29, 2012), which is a 35 U.S.C. § 371 National Application of and claims the benefit of priority from International Patent Application Serial No. PCT/IB2006/001157, of the same title and filed on May 4, 2006, which claims the benefit of priority from U.S. Provisional Patent Application Ser. No. 60/677,493, of the same title and filed on May 4, 2005, all of which are fully incorporated herein by reference for all purposes and to the extent not inconsistent with this application. 
     The claims in the instant application are different than those of the parent application or other related applications. The Applicant therefore rescinds any disclaimer of claim scope made in the parent application or any predecessor application in relation to the instant application. The Examiner is therefore advised that any such previous disclaimer and the cited references that it was made to avoid, may need to be revisited. Further, any disclaimer made in the instant application should not be read into or against the parent application or other related applications. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to communications, and in particular to providing feedback information in a multiple-input multiple-output communication environment. 
     BACKGROUND OF THE INVENTION 
     Providing feedback in a multiple-input multiple-output (MIMO) communication environment has proven to significantly benefit performance. In early systems that employed feedback, weighting factors were created at the MIMO receiver based on channel conditions. A codeword was fed back from the MIMO receiver to the transmitter, which would apply the weighting factors to the respective signals to be transmitted from the different MIMO transmitter antennas. The weighting factors effectively pre-distorted the signals to be transmitted to reverse the effects of the communication channel. Accordingly, the signals received at the MIMO receiver&#39;s antennas approximated those that would have been received without weighting through a clear channel. Unfortunately, channel conditions frequently if not continuously change, and the weighting factors to represent channel conditions are data-intensive. In light of the limited bandwidth available for feedback, providing weighting factors for changing channel conditions became unfeasible. 
     In an effort to reduce the bandwidth required to provide feedback for a MIMO channel, designers developed codebooks, which are maintained at the MIMO transmitter and MIMO receiver. The codebooks include codewords, which are predefined weighting factors. These predefined weighting factors are configured to cover the range of possible channel conditions through a fixed number of discrete weighting factors. Each of the codewords in a codebook is associated with a codeword index. In operation, the MIMO receiver will systematically determine the channel conditions and select the most appropriate codeword in light of the channel conditions. Instead of sending the codeword, which includes the weighting factors, the MIMO receiver will send the codeword index to the MIMO transmitter over an appropriate feedback channel. The MIMO transmitter will receive the codeword index, obtain the weighting factors of the corresponding codeword, and apply those weighting factors to the signals to be transmitted from the different transmit antennas. 
     The number of codewords in the codebook impacts the bandwidth required for feedback and the performance enhancement associated with using feedback. Unfortunately, as the number of codewords increases, the bandwidth required to feed back the codeword index to the MIMO transmitter from the MIMO receiver increases. Although incorporating the use of codebooks and providing the codeword index instead of the entire codeword as feedback has provided performance enhancement over systems providing the entire codeword as feedback, there is still a need to increase the number of available codewords while minimizing the bandwidth required to provide feedback from the MIMO receiver to the MIMO transmitter. 
     SUMMARY OF THE INVENTION 
     A codebook C is provided in a MIMO transmitter as well as a MIMO receiver. The codebook C will include M codewords c i , where i is a unique codeword index for each codeword c i . Each codeword defines weighting factors to apply to MIMO signals, and may correspond to channel matrices or vectors to apply to the MIMO signals prior to transmission from the respective antennas of the MIMO transmitter. The present invention creates codeword subsets S i  for each codeword c i  of the codebook C. Each codeword subset S i  defines L codewords c j , which are selected from all the codewords c i  in the codebook C. The codewords c j  in a codeword subset S i  are the L codewords in the entire codebook that best correlate with the corresponding codeword c i . 
     In operation, the MIMO receiver will initially identify the channel conditions of the MIMO channel and search the entire codebook C for the most appropriate codeword c i  based on the channel conditions of the MIMO channel. The MIMO receiver will then transmit the codeword index i corresponding to the selected codeword c i  back to the MIMO transmitter as feedback. The MIMO transmitter will use the codeword index i to identify the codeword c i  to employ when weighting the MIMO signals to be transmitted to the MIMO receiver. For a subsequent period of time or a given number of feedback instances, the MIMO receiver will again identify channel conditions for the MIMO channel. Instead of searching the entire codebook C for the best codeword c i  in light of the channel conditions, the MIMO receiver will limit its search to the codeword subset S i , which corresponds to the codeword c i  that was selected from a search of the entire codebook C. 
     As such, a limited number of L codewords c j  of the codeword subset S i  are searched, instead of the M codewords c i  of the entire codebook C. From the L codewords c j  of the codeword subset S i , the MIMO receiver will select the most appropriate codeword c j  and then provide the subset index k corresponding to the selected codeword c j  back to the MIMO transmitter as feedback. The MIMO transmitter will use the subset index k to identify the codeword c j  from the codeword subset S i  that corresponds to the codeword c j , which was provided by the MIMO receiver in response to the most recent full codebook search. Once the appropriate codeword c j  is obtained, the corresponding weighting factors are provided to the MIMO signals being transmitted to the MIMO receiver from the MIMO transmitter. 
     Those skilled in the art will appreciate the scope of the present invention and realize additional aspects thereof after reading the following detailed description of the preferred embodiments in association with the accompanying drawing figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING FIGURES 
       The accompanying drawing figures incorporated in and forming a part of this specification illustrate several aspects of the invention, and together with the description serve to explain the principles of the invention. 
         FIG. 1  is a block representation of a MIMO communication environment according to one embodiment of the present invention. 
         FIG. 2  illustrates a traditional codebook construction. 
         FIG. 3  illustrates a codebook constructed according to one embodiment of the present invention. 
         FIG. 4  illustrates a codeword subset according to one embodiment of the present invention. 
         FIG. 5  is a flow diagram illustrating operation of a MIMO receiver according to one embodiment of the present invention. 
         FIG. 6  is a flow diagram illustrating operation of a MIMO transmitter according to one embodiment of the present invention. 
         FIG. 7  is a block representation of a wireless communication system according to one embodiment of the present invention. 
         FIG. 8  is a block representation of a base station according to one embodiment of the present invention. 
         FIG. 9  is a block representation of a user element according to one embodiment of the present invention. 
         FIG. 10  is a logical breakdown of a MIMO transmitter architecture according to one embodiment of the present invention. 
         FIG. 11  is a logical breakdown of a MIMO receiver architecture according to one embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The embodiments set forth below represent the necessary information to enable those skilled in the art to practice the invention and illustrate the best mode of practicing the invention. Upon reading the following description in light of the accompanying drawing figures, those skilled in the art will understand the concepts of the invention and will recognize applications of these concepts not particularly addressed herein. It should be understood that these concepts and applications fall within the scope of the disclosure and the accompanying claims. 
     The present invention improves performance of multiple-input multiple-output (MIMO) communication systems. As shown in  FIG. 1 , a MIMO transmitter  2  has multiple transmit antennas  4  from which MIMO signals are transmitted over a MIMO communication channel to a MIMO receiver  6 . The MIMO signals may be space-time coded (STC) signals, which are defined to be any spatially diverse signals or spatially multiplexed signals. As such, the signals transmitted from different transmit antennas  4  may be the same or different signals. The MIMO signals are received at the MIMO receiver by multiple receive antennas  8 . 
     In operation, a codebook C, such as that illustrated in  FIG. 2 , is provided in the MIMO transmitter  2  as well as the MIMO receiver  6 . The codebook C will include M codewords c i , where i is a unique codeword index for each codeword c i . In this example, there are 64 codewords c i  (M=64), and as such, the codeword index i will range from zero to M−1, Each codeword defines weighting factors to apply to the MIMO signals, and may correspond to channel matrices or vectors to apply to the MIMO signals prior to transmission from the respective antennas  4  of the MIMO transmitter  2 . 
     As noted above, current systems employing codebooks operate as follows. Initially, the MIMO receiver  6  will obtain channel conditions for the MIMO channel, and identify the codeword c i  that would provide the best compensation of the MIMO signals in light of the channel conditions of the MIMO channel. The MIMO receiver  6  will search all of the codewords c i  of the codebook C to determine the most appropriate codeword c i . Once the codeword c i  is determined, the MIMO receiver  6  will provide feedback to the MIMO transmitter  2  to identify the corresponding codeword index i. The MIMO transmitter  2  will use the received codeword index i to identify the corresponding codeword c i  and apply the weighting factors defined by the codeword c i  to the MIMO signals transmitted from the antennas  4 . The process will continue, wherein the MIMO receiver  6  will systematically monitor the channel conditions of the MIMO channel and identify the most appropriate codeword c i  by providing a search of all of the codewords c i  in the codebook C. 
     The present invention improves upon the current state of the art by creating codeword subsets S i  for each codeword c i  of the codebook C, as illustrated in  FIG. 3 . Each codeword subset S i  defines L codewords c j , which are selected from all the codewords c i  in the codebook C. The codewords c j  in a codeword subset S i  are the L codewords in the entire codebook that best correlate with the corresponding codeword c i . 
     As illustrated in  FIG. 4 , a codeword subset S 7 , which corresponds to the codeword c 7 , is defined to include k codewords c j , where k=0, 1, 2, . . . , L−1, where L=8. As such, the codeword subset S 7  has eight codewords c j . The codewords c j  in the codeword subset S 7  are the eight codewords that best correlate with codeword c 7 . In this example, the codeword subset S 7  associated with codeword c 7  is defined to include codewords c 3 , c 13 , c 16 , c 25 , c 37 , c 41 , c 49 , and c 60 . Notably, each codeword c i  in the codebook C will have a corresponding codeword subset S i , where the codewords c j  in the codeword subset S i  will differ from one codeword subset S i  to another. Notably, the codeword c j  of the codeword subset S i  may or may not include the corresponding codeword c i  with which the codeword subset S i  is associated. 
     The codeword subsets S i  are created by identifying the L codewords c j  that have the highest correlations with c i . Those skilled in the art will recognize various techniques for determining codewords c i , c j , that have the highest correlations. For example, identifying the codewords c i , c j  having the highest correlations may be determined using the normalized interproduct criterion defined as: 
     
       
         
           
             
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     In one embodiment, the subset index k, which is used to identify each of the codewords c j  of the codeword subset S i , will require log 2 (L) bits, whereas the codebook index i requires log 2 (M) bits. Thus, L is preferably significantly smaller than M. In the examples of  FIGS. 2-4 , the number of codewords c j  (L) is eight times less than the number of codewords c i  in the entire codebook C (M). Again, the codebook C, including the codeword subset extensions, is provided in the MIMO transmitter  2  as well as in the MIMO receiver  6 . The codebook C will remain substantially fixed, and if there is a change to a codebook C in the MIMO transmitter  2 , there must be corresponding changes in the MIMO receiver  6  to ensure that the codebooks C remain the same. 
     In operation, the MIMO receiver  6  will initially identify the channel conditions of the MIMO channel and search the entire codebook C for the most appropriate codeword c i  based on the channel conditions of the MIMO channel. The MIMO receiver  6  will then transmit the codeword index i corresponding to the selected codeword c i  back to the MIMO transmitter  2  as feedback. The MIMO transmitter  2  will use the codeword index i to identify the codeword c i  to employ when weighting the MIMO signals to be transmitted to the MIMO receiver  6 . For a subsequent period of time or a given number of feedback instances, the MIMO receiver  6  will again identify channel conditions for the MIMO channel. Instead of searching the entire codebook C for the best codeword c i  in light of the channel conditions, the MIMO receiver  6  will limit its search to the codeword subset S i , which corresponds to the codeword c i  that was selected from a search of the entire codebook C. 
     As such, a limited number of L codewords c j  of the codeword subset S i  are searched, instead of the M codewords c i  of the entire codebook C. From the L codewords c j  of the codeword subset S i , the MIMO receiver  6  will select the most appropriate codeword c j  and then provide the subset index k corresponding to the selected codeword c j  back to the MIMO transmitter  2  as feedback. The MIMO transmitter  2  will use the subset index k to identify the codeword c j  from the codeword subset S i  that corresponds to the codeword c i , which was provided by the MIMO receiver  6  in response to the most recent full codebook search. Once the appropriate codeword c j  is obtained, the corresponding weighting factors are provided to the MIMO signals being transmitted to the MIMO receiver  6  from the MIMO transmitter  2 . 
     With reference to  FIG. 5 , a flow diagram illustrating operation of the MIMO receiver  6  is provided. Operation begins (step  100 ) where the MIMO receiver  6  selects a codeword c i  from a full codebook search based on channel estimates (step  102 ). The MIMO receiver  6  will transmit the codeword index i of the selected codeword c i  to the MIMO transmitter  2  (step  104 ). After a full codebook search, the MIMO receiver  6  may set a time instance counter (N−1) (step  106 ) and then proceed by selecting a codeword c j  from codeword subset S i  for the codeword c i  based on new channel estimates (step  108 ). The MIMO receiver  6  will transmit the subset index k of the selected codeword c j  to the MIMO transmitter  2  (step  110 ) and adjust the time instance counter accordingly (step  112 ). Based on the time instance counter, the MIMO receiver  6  will determine whether or not a full codebook search is required (step  114 ). If a full codebook search is not required, the MIMO receiver  6  will once again select a codeword c j  from the codeword subset S i  for the codeword c i  based on new channel estimates (step  108 ). Notably, the new channel estimates may result in a different codeword c j  being selected from the same codeword subset S i  for consecutive feedback instances. Further, the codeword subset S i  will not change until a full codebook search is provided. As such, until the time instance counter is incremented to N−1 or decremented to zero, the iterative process of selecting a codeword c j  from the codeword subset S i  and transmitting the corresponding subset index k back to the MIMO transmitter  2  repeats. 
     When it is time to provide a full codebook search (step  114 ), the overall process will begin anew, wherein a codeword c i  is selected from a full codebook search based on new channel estimates (step  102 ). Codeword index i is transmitted to the MIMO transmitter  2  (step  104 ), and the time instance counter is set (step  106 ). At this point, a new codeword subset S i  is selected, assuming channel estimates have changed from the last full codebook search, and subsequent feedback instances will result in searches of only the appropriate codeword subset S i  until a full codebook search is needed. 
     With reference to  FIG. 6 , a flow diagram is provided to illustrate operation of a MIMO transmitter  2  according to one embodiment of the present invention. Operation begins (step  200 ) where the MIMO transmitter  2  will receive a codeword index i for the full codebook C (step  202 ). The MIMO transmitter  2  will identify the codeword c i  from the full codebook C based on the codeword index i (step  204 ). The MIMO transmitter  2  will then apply the codeword c i  to the MIMO signals to be transmitted to the MIMO receiver  6  (step  206 ). The MIMO transmitter  2  will then set a time instance counter (step  208 ) and receive a subset index k for the codeword subset S i  (step  210 ). The MIMO transmitter  2  will be able to identify the codeword subset S i  based on the previous codeword c i  as recovered from the codeword index i from the prior feedback of the MIMO receiver  6 . The MIMO transmitter  2  will use the subset index k to identify the codeword c j  from the codeword subset S i  (step  212 ) and apply the codeword c j  to the MIMO signals to be transmitted (step  214 ). The MIMO transmitter  2  may then adjust the time instance counter (step  216 ) and determine whether or not a full codebook C should be used on the next feedback from the MIMO receiver  6  (step  218 ). 
     If the codeword subset S i  should be used, the next feedback from the MIMO receiver  6  will identify subset index k for a codeword subset S i  (step  210 ). The codeword c j  is identified based on the subset index k and applied to the MIMO signals to be transmitted (step  210 ). This process will continue until the full codebook C is to be used to identify a codeword c i  based on a codebook index i being fed back from the MIMO receiver  6 . When it is time to use the full codebook C (step  218 ), the MIMO receiver  6  will provide a codeword index i (step  202 ), which will be used by the MIMO transmitter  2  to identify a codeword c i  from the full codebook C (step  204 ). Codeword c i  will be applied to the MIMO signals to be transmitted (step  206 ), and the MIMO transmitter  2  will begin receiving subset indices k from the MIMO receiver  6  and identify codeword c j  of the codeword subset S i  based on the subset index k until the full codebook C needs to be accessed again. 
     Those skilled in the art will recognize that codewords may have various configurations, but in any case will effectively define weighting factors in the form of matrices, vectors, and the like to apply to MIMO signals to be transmitted from the various antennas  4  of the MIMO transmitter  2 . Further, cycling between using the full codebook C and a significantly smaller codeword subset S i  may be based on feedback instances, transmission instances, and time periods, as well as the extent to which channel conditions are actually changing. Further, the MIMO transmitter  2  and the MIMO receiver  6  may coordinate with one another to selectively invoke the use of the codeword subsets such that they may operate according to the prior art for a certain period of time or under certain conditions at certain times, while at other times they may operate according to the concepts of the present invention. 
     Further, for OFDM systems, the codeword subsets may be arranged by time and frequency. As such, the subset indices may relate to and be selected from codebook codewords having the best correlations in the time or frequency direction in the OFDM spectrum. 
     With reference to  FIG. 7 , a basic MIMO wireless communication environment is illustrated. In general, a base station controller (B S C)  10  controls wireless communications within one or more cells  12 , which are served by corresponding base stations (BS)  14 . Each base station  14  facilitates communications with user elements  16 , which are within the cell  12  associated with the corresponding base station  14 . For the present invention, the base stations  14  and user elements  16  include multiple antennas to provide spatial diversity for communications. Notably, the base station  14  may be any type of wireless access point for cellular, wireless local area network, or like wireless network. For the present invention, the base station  14  and the user elements  16  may act as the MIMO transmitter  2  as well as the MIMO receiver  6 . For clarity and conciseness, the following embodiments employ the MIMO transmitter  2  in the base station  14  and MIMO receiver  6  in the user elements  16 . 
     With reference to  FIG. 8 , a base station  14  configured according to one embodiment of the present invention is illustrated. The base station  14  generally includes a control system  20 , a baseband processor  22 , transmit circuitry  24 , receive circuitry  26 , multiple antennas  28 , and a network interface  30 . The receive circuitry  26  receives radio frequency signals through antennas  28  bearing information from one or more remote transmitters provided by user elements  16 . Preferably, a low noise amplifier and a filter (not shown) cooperate to amplify and remove broadband interference from the signal for processing. Downconversion and digitization circuitry (not shown) will then downconvert the filtered, received signal to an intermediate or baseband frequency signal, which is then digitized into one or more digital streams. 
     The baseband processor  22  processes the digitized received signal to extract the information or data bits conveyed in the received signal. This processing typically comprises demodulation, decoding, and error correction operations. As such, the baseband processor  22  is generally implemented in one or more digital signal processors (DSPs). The received information is then sent across a wireless network via the network interface  30  or transmitted to another user element  16  serviced by the base station  14 . The network interface  30  will typically interact with the base station controller  10  and a circuit-switched network forming a part of a wireless network, which may be coupled to the public switched telephone network (PSTN). 
     On the transmit side, the baseband processor  22  receives digitized data, which may represent voice, data, or control information, from the network interface  30  under the control of the control system  20 , and encodes the data for transmission. The encoded data is output to the transmit circuitry  24 , where it is modulated by a carrier signal having a desired transmit frequency or frequencies. A power amplifier (not shown) will amplify the modulated carrier signal to a level appropriate for transmission, and deliver the modulated carrier signal to the antennas  28  through a matching network (not shown). The multiple antennas  28  and the replicated transmit and receive circuitries  24 ,  26  provide spatial diversity. 
     With reference to  FIG. 9 , a user element  16  configured according to one embodiment of the present invention is illustrated. Similarly to the base station  14 , the user element  16  will include a control system  32 , a baseband processor  34 , transmit circuitry  36 , receive circuitry  38 , multiple antennas  40 , and user interface circuitry  42 . The receive circuitry  38  receives radio frequency signals through antennas  40  bearing information from one or more base stations  14 . Preferably, a low noise amplifier and a filter (not shown) cooperate to amplify and remove broadband interference from the signal for processing. Downconversion and digitization circuitry (not shown) will then downconvert the filtered, received signal to an intermediate or baseband frequency signal, which is then digitized into one or more digital streams. 
     The baseband processor  34  processes the digitized received signal to extract the information or data bits conveyed in the received signal. This processing typically comprises demodulation, decoding, and error correction operations, as will be discussed in greater detail below. The baseband processor  34  is generally implemented in one or more digital signal processors (DSPs) and application-specific integrated circuits (ASICs). 
     For transmission, the baseband processor  34  receives digitized data, which may represent voice, data, or control information, from the control system  32 , which it encodes for transmission. The encoded data is output to the transmit circuitry  36 , where it is used by a modulator to modulate a carrier signal that is at a desired transmit frequency or frequencies. A power amplifier (not shown) will amplify the modulated carrier signal to a level appropriate for transmission, and deliver the modulated carrier signal to the antennas  40  through a matching network (not shown). The multiple antennas  40  and the replicated transmit and receive circuitries  36 ,  38  provide spatial diversity. 
     With reference to  FIG. 10 , a transmission architecture is provided according to one embodiment. The transmission architecture is described as being that of the base station  14 , but those skilled in the art will recognize the applicability of the illustrated architecture for both uplink and downlink communications. Further, the transmission architecture is intended to represent a variety of multiple access architectures, including, but not limited to code division multiple access (CDMA), frequency division multiple access (FDMA), time division multiple access (TDMA), and orthogonal frequency division multiplexing (OFDM). 
     Initially, the base station controller  10  sends data  44  intended for a user element  16  to the base station  14  for scheduling. The scheduled data  44 , which is a stream of bits, is scrambled in a manner reducing the peak-to-average power ratio associated with the data using data scrambling logic  46 . A cyclic redundancy check (CRC) for the scrambled data is determined and appended to the scrambled data using CRC adding logic  48 . Next, channel encoding is performed using channel encoder logic  50  to effectively add redundancy to the data to facilitate recovery and error correction at the user element  16 . The channel encoder logic  50  uses known Turbo encoding techniques in one embodiment. The encoded data is then processed by rate matching logic  52  to compensate for the data expansion associated with encoding. 
     Bit interleaver logic  54  systematically reorders the bits in the encoded data to minimize the loss of consecutive data bits. The resultant data bits are systematically mapped into corresponding symbols depending on the chosen baseband modulation by mapping logic  56 . Preferably, a form of Quadrature Amplitude Modulation (QAM) or Quadrature Phase Shift Key (QPSK) modulation is used. The symbols may be systematically reordered to further bolster the immunity of the transmitted signal to periodic data loss caused by frequency selective fading using symbol interleaver logic  58 . 
     At this point, groups of bits have been mapped into symbols representing locations in an amplitude and phase constellation. Blocks of symbols are then processed by space-time code (STC) encoder logic  60 . The STC encoder logic  60  will process the incoming symbols according to a selected STC encoding mode and provide n outputs corresponding to the number of transmit antennas  28  for the base station  14 . The codeword feedback from the user element  16  (MIMO receiver  6 ) is recovered from the corresponding receive circuitry  26  and used to identify the codeword to apply to the symbols. Further detail regarding the SIC encoding is provided later in the description. Assume the symbols for the n outputs are representative of the weighted data to be transmitted and capable of being recovered by the user element  16 . Further detail is provided in A. F. Naguib, N. Seshadri, and A. R. Calderbank, “Applications of space-time codes and interference suppression for high capacity and high data rate wireless systems,” Thirty-Second Asilomar Conference on Signals, Systems &amp; Computers, Volume 2, pp. 1803-1810, 1998; R. van Nee, A. van Zelst and G. A. Atwater, “Maximum Likelihood Decoding in a Space Division Multiplex System”, IEEE VTC. 2000, pp. 6-10, Tokyo, Japan, May 2000; and P. W. Wolniansky et al., “V-BLAST: An Architecture for Realizing Very High Data Rates over the Rich-Scattering Wireless Channel,” Proc. IEEE ISSSE-98, Pisa, Italy, Sep. 30, 1998 which are incorporated herein by reference in their entireties. 
     For illustration, assume the base station  14  has selected two of a number of antennas  28  (n=2) and the STC encoder logic  60  provides two output streams of symbols. Accordingly, each of the symbol streams output by the STC encoder logic  60  is sent to a corresponding multiple access modulation function  62 , illustrated separately for ease of understanding. Those skilled in the art will recognize that one or more processors may be used to provide such analog or digital signal processing alone or in combination with other processing described herein. For example, the multiple access modulation function  62  in a CDMA function would provide the requisite PN code multiplication, wherein an OFDM function would operate on the respective symbols using inverse discrete Fourier transform (IDFT) or like processing to effect an Inverse Fourier Transform. 
     Each of the resultant signals is up-converted in the digital domain to an intermediate frequency and converted to an analog signal via the corresponding digital up-conversion (DUC) circuitry  64  and digital-to-analog (D/A) conversion circuitry  66 . The resultant analog signals are then simultaneously modulated at the desired RF frequency, amplified, and transmitted via the RF circuitry  68  and antennas  28 . Notably, the transmitted data may be preceded by pilot signals, which are known by the intended user element  16 . The user element  16 , which is discussed in detail below, may use the pilot signals for channel estimation and interference suppression and the header for identification of the base station  14 . 
     Reference is now made to  FIG. 11  to illustrate reception of the transmitted signals by a user element  16  and provision of codeword feedback to the base station  14 . Upon arrival of the transmitted signals at each of the antennas  40  of the user element  16 , the respective signals are demodulated and amplified by corresponding RF circuitry  74 . For the sake of conciseness and clarity, only one of the multiple receive paths in the user element  16  is described and illustrated in detail. Analog-to-digital (A/D) conversion and downconversion circuitry (DCC)  76  digitizes and downconverts the analog signal for digital processing. The resultant digitized signal may be used by automatic gain control circuitry (AGC)  78  to control the gain of the amplifiers in the RE circuitry  74  based on the received signal level. 
     The digitized signal is also fed to synchronization circuitry  80  and a multiple access demodulation function  82 , which will recover the incoming signal received at a corresponding antenna  40  in each receiver path. The synchronization circuitry  80  facilitates alignment or correlation of the incoming signal with the multiple access demodulation function  82  to aid in the recovery of the incoming signal, which is provided to a signaling processing function  84  and channel estimation function  86 . The signaling processing function  84  processes basic signaling and header information to provide information sufficient to generate a channel quality measurement, which may bear on an overall signal-to-noise ratio for the link, which takes into account channel conditions and/or signal-to-noise ratios for each receive path. The channel estimation function  86  for each receive path provides channel responses corresponding to channel conditions of the MIMO channel. 
     The symbols from the incoming signal and perhaps channel estimates for each receive path are provided to an STC decoder  88 , which provides STC decoding on each receive path to recover the transmitted symbols. The channel estimates may provide channel response information to allow the STC decoder  88  to better decode the symbols according to the STC encoding used by the base station  14 . 
     The recovered symbols are placed back in order using symbol de-interleaver logic  90 , which corresponds to the symbol interleaver logic  58  of the base station  14 . The de-interleaved symbols are then demodulated or de-mapped to a corresponding bitstream using de-mapping logic  92 . The bits are then de-interleaved using bit de-interleaver logic  94 , which corresponds to the bit interleaver logic  54  of the transmitter architecture. The de-interleaved bits are then processed by rate de-matching logic  96  and presented to channel decoder logic  98  to recover the initially scrambled data and the CRC checksum. Accordingly, CRC logic  100  removes the CRC checksum, checks the scrambled data in traditional fashion, and provides it to the de-scrambling logic  102  for de-scrambling using the known base station de-scrambling code to recover the originally transmitted data  104 . 
     For the present invention, the channel conditions of the MIMO channel are provided to feedback processing circuitry  106 , which will function to determine codewords for the codebook C or codeword subset S i  and provide the corresponding indices as codeword feedback to the base station  14  via the transmit circuitry  36 . The feedback processing circuitry  106  may be considered part of the control system  32 , but is separated for clarity. 
     Those skilled in the art will recognize improvements and modifications to the preferred embodiments of the present invention. All such improvements and modifications are considered within the scope of the concepts disclosed herein and the claims that follow.

Metadata:
Filing Date: 20180730
Publication Date: 20190702
Grant Date: 20190702
Priority Date: 20050504
Inventors: TONG, WEN
NIKOPOUR, HOSEIN
KHANDANI, AMIR
XU, HUA
JIA, MING
ZHU, PEIYING
YU, DONG-SHENG
Assignee: APPLE INC
CPC Classifications: [{"code": "H04L69/14", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04B7/0478", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04B7/0639", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04B7/0417", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04B7/0456", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L69/04", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04B7/0634", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04B7/0417", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04B7/0634", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04L69/14", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L69/04", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04B7/0639", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04B7/0634", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04B7/0478", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04B7/0417", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04B7/0456", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L69/14", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L69/04", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04B7/0639", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 37307628