# Patent

## Title
Systems and methods for a multiple-input-multiple-output (MIMO) data transmission scheme using a space time block code (STBC)

## Abstract

Systems and methods described herein provide a system for transmitting data on an MIMO channel using a STBC. The system comprises a wireless transmitter. The wireless transmitter obtains plurality of data symbols to transmit, and performs data padding for the plurality of data symbols based on a non-STBC manner. The wireless transmitter further calculates a number of bits per data symbol after the data padding and pre-codes a data symbol from the plurality of data symbols based on available channel information when the number of data symbols is an odd number. The wireless transmitter generates an STBC based on the pre-coded data symbols, and transmits the generated STBC to the MIMO channel.

## Background
CROSS-REFERENCE TO RELATED APPLICATION
This disclosure claims the benefit of U.S. Provisional Patent Application No. 62/119,933, filed Feb. 24, 2015, which is hereby incorporated by reference herein in its entirety.


FIELD OF USE
This disclosure relates to a channel coding scheme in a multiple-input-multiple-output (MIMO) wireless data transmission system, for example, a wireless local area network (WLAN) implementing the Institute of Electrical and Electronics Engineers (IEEE) 802.11 standard, which can be used to provide wireless transfer of data in outdoor deployments, outdoor-to-indoor communications, and device-to-device (P2P) networks.
BACKGROUND OF THE DISCLOSURE
The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the inventors hereof, to the extent the work is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted to be prior art against the present disclosure.
Multiple-input and multiple-output (MIMO) transmission can be adopted in a wireless local area network. By using multiple transmit and receive antennas to transmit data symbols, MIMO multiplies the capacity of a radio link to exploit multipath propagation. MIMO has become an essential element of wireless communication standards including IEEE 802.11n (Wi-Fi), IEEE 802.11ac (Wi-Fi), HSPA+(3G), WiMAX (4G), and Long Term Evolution (4G).
In a MIMO system, an encoding scheme such as the space-time block code (STBC) can be used to transmit multiple copies of a data stream across the multiple antennas at the transmitter. For example, an STBC can take a form similar to a matrix having data entries of data symbols. A same data symbol can occupy multiple data entries in an STBC matrix such that the same data symbol can be received in various versions to improve the reliability of data transfer.
SUMMARY
Systems and methods described herein provide a method for transmitting data on a multiple-input-multiple-output (MIMO) channel using a space time block code (STBC). The method comprises obtaining, at a wireless transmitter, a plurality of data symbols to transmit. The method further comprises performing data padding for the plurality of data symbols based on a non-STBC manner. The method further comprises calculating a number of bits per data symbol after the data padding. The method further comprises pre-coding a data symbol from the plurality of data symbols when the number of data symbols is an odd number. The method further comprises generating an STBC based on the pre-coded data symbols. The method further comprises transmitting the generated STBC to the MIMO channel.
In some implementations, the plurality of data symbols have an orthogonal frequency-divisional multiplexing (OFDM) data format.
In some implementations, the STBC takes a form of a matrix that have data entries of one or more data symbols and the conjugates of the one or more data symbols.
In some implementations, an average number of the data padding is half symbol.
In some implementations, a last padding data symbol from the data padding is transmitted using one symbol time.
In some implementations, the pre-coding includes applying a pre-coding matrix to the plurality of data symbols depending on availability of channel information.
In some implementations, the pre-coding matrix indicates that a last padding data symbol is transmitted using one antenna at the wireless transmitter.
In some implementations, the transmission power is normalized based on a number of utilized antennas at the wireless transmitter.
In some implementations, the pre-coding matrix is predetermined and known by both the wireless transmitter and a respective wireless receiver.
In some implementations, the pre-coding matrix indicates that a last padding data symbol is transmitted through multiple antennas at the wireless transmitter.
Systems and methods described herein provide a system for transmitting data on an MIMO channel using a STBC. The system comprises a wireless transmitter. The wireless transmitter obtains plurality of data symbols to transmit, and performs data padding for the plurality of data symbols based on a non-STBC manner. The wireless transmitter further calculates a number of bits per data symbol after the data padding and pre-codes a data symbol from the plurality of data symbols based on available channel information when the number of data symbols is an odd number. The wireless transmitter generates an STBC based on the pre-coded data symbols, and transmits the generated STBC to the MIMO channel.



BRIEF DESCRIPTION OF THE DRAWINGS
Further features of the disclosure, its nature and various advantages will become apparent upon consideration of the following detailed description, taken in conjunction with the accompanying drawings, in which like reference characters refer to like parts throughout, and in which:
FIG. 1 provides an exemplary block diagram illustrating an example MIMO system.
FIG. 2 provides an exemplary block diagram illustrating an example orthogonal frequency-division multiplexing (OFDM) format in the IEEE 802.11ax standards.
FIG. 3 provides an exemplary block diagram illustrating an example STBC transmission scheme in a MIMO system.
FIG. 4 provides an exemplary block diagram illustrating an example STBC transmission scheme pre-coded with available channel information (e.g., from the MIMO channel 105 in FIG. 1).
FIG. 5 provides an exemplary block diagram illustrating transmission pre-coding.
FIG. 6 provides an exemplary flow diagram illustrating transmitting data symbols with a STBC pre-coded with available channel information (e.g., see 405 in FIG. 4).



DETAILED DESCRIPTION
This disclosure describes methods and systems for a MIMO data transmission scheme using an STBC. According to this disclosure, a new STBC padding and transmission procedure is adopted if the number of data symbols is odd, in which the first even number of data symbols are encoded with an STBC scheme and the last data symbol is specially encoded with and without available channel information. In this way, transmission efficiency of the data symbols can be improved.
FIG. 1 provides an exemplary block diagram illustrating an example MIMO system. The wireless transmission system 100 includes a transmitter module 101 and receiver module 102. The transmitter module 101 may have one or multiple antennas, e.g., antennas 101a-b for illustrative purpose. Similarly, the receiver module 102 may have one or multiple antennas, e.g., antennas 102a-b for illustrative purpose. The transmitter antennas 101a-b may transmit data symbols via a wireless channel 105 to the receiver antennas 102a-b, and the channel parameters can be represented as h11, h12, h21 and h22. Therefore, the MIMO system 100 can be represented as:




  y
  =
  
    
      [
      
        
          
            
              y
              1
            
          
        
        
          
            
              y
              2
            
          
        
      
      ]
    
    =
    
      
        
          
            [
            
              
                
                  
                    h
                    11
                  
                
                
                  
                    h
                    21
                  
                
              
              
                
                  
                    h
                    12
                  
                
                
                  
                    h
                    22
                  
                
              
            
            ]
          
          ⁡
          
            [
            
              
                
                  
                    x
                    1
                  
                
              
              
                
                  
                    x
                    2
                  
                
              
            
            ]
          
        
        +
        
          [
          
            
              
                
                  n
                  1
                
              
            
            
              
                
                  n
                  2
                
              
            
          
          ]
        
      
      =
      
        
          H
          ⁢
          
            
          
          ⁢
          x
        
        +
        n
      
    
  




where y denotes the received data vector, and x denotes the sent data vector; H denotes the channel matrix, and n denotes the channel noise vector.

FIG. 2 provides an exemplary block diagram illustrating an example orthogonal frequency-division multiplexing (OFDM) format in the IEEE 802.11ax standards. To improve the transmission efficiency, tone spacing (TS) is adopted in 802.11ax high efficiency WLAN (HEW). In HEW, a variety of options of OFDM formats can be adopted, and padding symbol(s) may be added. For example, as shown at the data packet format 200, the example OFDM packet may have a backward compatible portion preamble 201, including the legacy short-training field 201a (L-STF), the legacy long-training field 201b (L-LTF) and legacy signal 201c (L-SIG). The data packet 200 may further include an HEW portion preamble 202, an HEW data field 203, and data symbol padding 204.
HEW data symbol may adopt various tone spacing (TS) and/or guard intervals (GI), and each HEW symbol time can be computed as:

THEW=3.6 us/rTS+GI

wherein rTs is the tone spacing ratio with respect to current transmission frequency of 312.5 kHz. Different options can be used, for example, a 1⁄4 tone spacing and GI option [0.4 us 0.8 us 1.6 us, 3.2 us], with a corresponding new symbol time: THEW=[14.8 us 15.2 us 16 us 17.6 us]. Alternatively, a 1⁄2 tone spacing and GI options [0.4 us 0.8 us 1.6 us] with a corresponding new symbol time THEW=[7.6 us 8.0 us 8.8 us]. Or a normal tone spacing and GI option [0.4 us 0.8 us 1.6 us] with a corresponding new symbol time THEW=[3.6 us 4.0 us 4.8 us].

The padding bit number NPAD can be computed in 802.11ac. For example, for binary convolutional coding (BCC), the bit number per data symbol NSYM and the padding bit number NPAD can be calculated according to the following:




  
    N
    SYM
  
  =
  
    
      m
      STBC
    
    ⁢
    
      ⌈
      
        
          
            8
            ·
            L
          
          +
          
            N
            Service
          
          +
          
            
              N
              Tail
            
            ⁢
            
              N
              Es
            
          
        
        
          
            m
            STBC
          
          ⁢
          
            N
            DBPS
          
        
      
      ⌉
    
  




NPAD=NSYMNDBPS−8·L−NService−NTailNEs 

wherein L is the number of information bytes to be transmitted in a current packet; mSTBC equals 2 when STBC is used, or 1 otherwise; NService is the number of service bits; NTail is the number of tail bits; NDBPS is the number of BCC encoders for the DATA field; and NDBPS is the number of data bits per OFDM symbol.
For another example, for low-density parity-check (LDPC) coding, the bit number per data symbol NSYM and the padding bit number NPAD can be calculated according to the following:




  
    N
    SYM
  
  =
  
    
      m
      STBC
    
    ⁢
    
      ⌈
      
        
          
            8
            ·
            L
          
          +
          
            N
            Service
          
        
        
          
            m
            STBC
          
          ⁢
          
            N
            DBPS
          
        
      
      ⌉
    
  




NPAD=NSYMNDBPS−8·L−NService 

FIG. 3 provides an exemplary block diagram illustrating an example STBC transmission scheme in a MIMO system. The example MIMO system in FIG. 3 has two transmitter antennas and one receiver antenna. Data symbols x1, x2, x3 and x4 can be transmitted in a matrix form, e.g., at 301 conjugate versions of data symbols x1 and x2 can be re-transmitted.
When STBC is used, each data stream may have an even number of data symbols. Thus, if




  
    N
    SYM
  
  =
  
    ⌈
    
      
        
          8
          ·
          L
        
        +
        
          N
          Service
        
        +
        
          
            N
            Tail
          
          ⁢
          
            N
            Es
          
        
      
      
        N
        DBPS
      
    
    ⌉
  




is even (as shown at 310), the average padding length is half-symbol (e.g., see 315); or, if





  
    N
    SYM
  
  =
  
    ⌈
    
      
        
          8
          ·
          L
        
        +
        
          N
          Service
        
        +
        
          
            N
            Tail
          
          ⁢
          
            N
            Es
          
        
      
      
        N
        DBPS
      
    
    ⌉
  




is odd (as shown at 320), then average padding length is 1.5 symbols (e.g., see 325). In the latter case, more than one symbol time may be needed for padding bits transmission.

In HEW, smaller tone spacing may be adopted. Smaller tone spacing can infer longer OFDM symbol length, and the traditional data padding method may encounter lower efficiency. For example, for HEW with 1⁄4 tone spacing, the padding transmission time can be greater than 22 μs, which results in a significant efficiency reduction. In particular, in MIMO transmission with STBC, the average number of padding symbols is doubled to guarantee, an even number of OFDM symbols; thus, the physical layer efficiency can be significantly impaired in 802.11ax.
FIG. 4 provides an exemplary block diagram illustrating an example STBC transmission scheme pre-coded with available channel information (e.g., from the MIMO channel 105 in FIG. 1). The padding scheme can be the same as that in a non-STBC transmission case. For example, for BCC,




  
    N
    SYM
  
  =
  
    ⌈
    
      
        
          8
          ·
          L
        
        +
        
          N
          Service
        
        +
        
          
            N
            Tail
          
          ⁢
          
            N
            Es
          
        
      
      
        N
        DBPS
      
    
    ⌉
  




NPAD=NSYMNDBPS−8·L−NService−NTailNEs 

wherein the parameters are defined in a similar way as discussed above. For LDPC,




  
    N
    SYM
  
  =
  
    ⌈
    
      
        
          8
          ·
          L
        
        +
        
          N
          Service
        
      
      
        N
        DBPS
      
    
    ⌉
  




NPAD=NSYMNDBPS−8·L−NService 

Thus, in this case, the average number of padding is half symbol.
Thus, when NSYM is even, the same STBC transmission scheme as that discussed in FIG. 3 can be used, at 401 (e.g., similar to 310 in FIG. 3). When NSYM is odd, the STBC transmission scheme 405 can be used with pre-coding parameters V1 406a and V2 406b, which are obtained based on the availability of channel information, and thus the received data vector y can be represented as:




  y
  =
  
    
      
        
          [
          
            
              
                
                  h
                  1
                
              
              
                
                  h
                  2
                
              
            
          
          ]
        
        ⁡
        
          [
          
            
              
                
                  V
                  1
                
              
            
            
              
                
                  V
                  2
                
              
            
          
          ]
        
      
      ⁢
      x
    
    +
    n
  




wherein h1 and h2 (407a-b) are the channel coefficients in the 2-transmitter-1-receiver MIMO system. The last padded symbol may be transmitted using one symbol time.

FIG. 5 provides an exemplary block diagram illustrating transmission pre-coding. At 501, the last padding symbol can be transmitted using only one transmit antenna, e.g., by setting the pre-coding matrix V as:




  V
  =
  
    
      [
      
        
          
            1
          
        
        
          
            0
          
        
      
      ]
    
    ⁢
    
      or
      ⁢
      
        
      
      [
      
        
          
            0
          
        
        
          
            1
          
        
      
      ]
    
  




The padding symbol transmit antenna can be indicated in the HEW-SIG field (e.g., 201c in FIG. 2), and the transmit power is normalized based on the number of utilized antennas.
Alternatively, in a different implementation at 502, the last padding symbol can be transmitted with some predetermined pre-coder known by both the transmitter and the receiver, for example, by setting the pre-coding matrix V as:




  V
  =
  
    [
    
      
        
          1
        
      
      
        
          1
        
      
    
    ]
  




FIG. 6 provides an exemplary flow diagram illustrating transmitting data symbols with an STBC pre-coded with available channel information (e.g., see 405 in FIG. 4). At 601, a MIMO transmitter module (e.g., see 101 in FIG. 1) may prepare data symbols to transmit. The transmitter may then perform data padding as in a non-STBC case at 602, e.g., as illustrated at 401 in FIG. 4. The transmitter may calculate the number of data symbols NSYM after the data padding at 603, and determine whether NSYM is even or odd at 604. If NSYM is even at 605, the transmitter may use STBC transmission as illustrated at 401 in FIG. 4; otherwise, if NSYM is odd at 606, the transmitter may use STBC pre-coded by a pre-coding matrix, as illustrated at 405 in FIG. 4. The transmitter may then transmit the padded STBC to a wireless channel to reach the receiver at 607.
While various embodiments of the present disclosure have been shown and described herein, it will be obvious to those skilled in the art that such embodiments are provided by way of example only. Numerous variations, changes, and substitutions will now occur to those skilled in the art without departing from the disclosure. It should be understood that various alternatives to the embodiments of the disclosure described herein may be employed in practicing the disclosure. It is intended that the following claims define the scope of the disclosure and that methods and structures within the scope of these claims and their equivalents be covered thereby.
The foregoing is merely illustrative of the principles of this disclosure, and various modifications can be made without departing from the scope of the present disclosure. The above-described embodiments of the present disclosure are presented for purposes of illustration and not of limitation, and the present disclosure is limited only by the claims that follow.

## Claims

1. A method for transmitting data on a multiple-input-multiple-output (MIMO) channel using a space time block code (STBC), the method comprising:
obtaining, at a wireless transmitter, a plurality of data symbols to transmit;
performing data padding for the plurality of data symbols based on a non-STBC manner;
calculating a number of data symbols in the plurality of data symbols after the data padding;
determining whether the calculated number of data symbols in the plurality of data symbols is an even number or an odd number;
pre-coding a data symbol from the plurality of data symbols and generating an STBC based on the pre-coded data symbol when the number of data symbols in the plurality of data symbols is an odd number;
generating an STBC based on the plurality of data symbols when the number of data symbols in the plurality of data symbols is an even number; and
transmitting the generated STBC to the MIMO channel.

2. The method of claim 1, wherein the plurality of data symbols have an orthogonal frequency-divisional multiplexing (OFDM) data format.

3. The method of claim 1, wherein the STBC takes a form of a matrix that has data entries of one or more of the data symbols and conjugates of the one or more data symbols.

4. The method of claim 1, wherein an average number of the data padding is half symbol.

5. The method of claim 1, wherein a last padding data symbol from the data padding is transmitted using one symbol time.

6. The method of claim 1, wherein the pre-coding includes applying a pre-coding matrix to the plurality of data symbols depending on availability of channel information.

7. The method of claim 6, wherein the pre-coding matrix indicates that a last padding data symbol is transmitted using one antenna at the wireless transmitter.

8. The method of claim 7, wherein the transmission power is normalized based on a number of utilized antennas at the wireless transmitter.

9. The method of claim 6, wherein the pre-coding matrix is predetermined and known by both the wireless transmitter and a respective wireless receiver.

10. The method of claim 9, wherein the pre-coding matrix indicates that a last padding data symbol is transmitted through multiple antennas at the wireless transmitter.

11. A system for transmitting data on a multiple-input-multiple-output (MIMO) channel using a space time block code (STBC), the system comprising:
a wireless transmitter to:
obtain a plurality of data symbols to transmit;
perform data padding for the plurality of data symbols based on a non-STBC manner;
calculate a number of data symbols in the plurality of data symbols after the data padding;
determine whether the calculated number of data symbols in the plurality of data symbols is an even number or an odd number;
pre-code a data symbol from the plurality of data symbols based on available channel information and generate an STBC based on the pre-coded data symbols when the number of data symbols is an odd number; and
generate an STBC based on the plurality of data symbols when the number of data symbols in the plurality of data symbols is an even number; and
transmit the generated STBC to the MIMO channel.

12. The system of claim 11, wherein the plurality of data symbols have an orthogonal frequency-divisional multiplexing (OFDM) data format.

13. The system of claim 11, wherein the STBC takes a form of a matrix that have data entries of one or more of the data symbols and the conjugates of the one or more data symbols.

14. The system of claim 11, wherein an average number of the data padding is half symbol.

15. The system of claim 11, wherein a last padding data symbol from the data padding is transmitted using one symbol time.

16. The system of claim 11, wherein the pre-coding includes applying a pre-coding matrix to the plurality of data symbols depending on availability of channel information.

17. The system of claim 16, wherein the pre-coding matrix indicates that a last padding data symbol is transmitted using one antenna at the wireless transmitter.

18. The system of claim 17, wherein the transmission power is normalized based on a number of utilized antennas at the wireless transmitter.

19. The system of claim 16, wherein the pre-coding matrix is predetermined and known by both the wireless transmitter and a respective wireless receiver.

20. The system of claim 19, wherein the pre-coding matrix indicates that a last padding data symbol is transmitted through multiple antennas at the wireless transmitter.