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.

Description:
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  101   a - b  for illustrative purpose. Similarly, the receiver module  102  may have one or multiple antennas, e.g., antennas  102   a - b  for illustrative purpose. The transmitter antennas  101   a - b  may transmit data symbols via a wireless channel  105  to the receiver antennas  102   a - b , and the channel parameters can be represented as h 11 , h 12 , h 21  and h 22 . 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  201   a  (L-STF), the legacy long-training field  201   b  (L-LTF) and legacy signal  201   c  (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:
 
 T   HEW =3.6 us/ r   TS +GI
 
wherein r Ts  is the tone spacing ratio with respect to current transmission frequency of 312.5 kHz. Different options can be used, for example, a ¼ tone spacing and GI option [0.4 us 0.8 us 1.6 us, 3.2 us], with a corresponding new symbol time: T HEW =[14.8 us 15.2 us 16 us 17.6 us]. Alternatively, a ½ tone spacing and GI options [0.4 us 0.8 us 1.6 us] with a corresponding new symbol time T HEW =[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 T HEW =[3.6 us 4.0 us 4.8 us].
 
     The padding bit number N PAD  can be computed in 802.11ac. For example, for binary convolutional coding (BCC), the bit number per data symbol N SYM  and the padding bit number N PAD  can be calculated according to the following: 
               N   SYM     =       m   STBC     ⁢     ⌈         8   ·   L     +     N   Service     +       N   Tail     ⁢     N   Es             m   STBC     ⁢     N   DBPS         ⌉               N   PAD   =N   SYM   N   DBPS −8· L−N   Service   −N   Tail   N   Es  
 
     wherein L is the number of information bytes to be transmitted in a current packet; m STBC  equals 2 when STBC is used, or  1  otherwise; N Service  is the number of service bits; N Tail  is the number of tail bits; N DBPS  is the number of BCC encoders for the DATA field; and N DBPS  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 N SYM  and the padding bit number N PAD  can be calculated according to the following: 
               N   SYM     =       m   STBC     ⁢     ⌈         8   ·   L     +     N   Service           m   STBC     ⁢     N   DBPS         ⌉               N   PAD   =N   SYM   N   DBPS −8· L−N   Service  
 
       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 x 1 , x 2 , x 3  and x 4  can be transmitted in a matrix form, e.g., at  301  conjugate versions of data symbols x 1  and x 2  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 ¼ 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       ⌉             N   PAD   =N   SYM   N   DBPS −8· L−N   Service   −N   Tail   N   Es  
 
     wherein the parameters are defined in a similar way as discussed above. For LDPC, 
               N   SYM     =     ⌈         8   ·   L     +     N   Service         N   DBPS       ⌉             N   PAD   =N   SYM   N   DBPS −8· L−N   Service  
 
     Thus, in this case, the average number of padding is half symbol. 
     Thus, when N SYM  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 N SYM  is odd, the STBC transmission scheme  405  can be used with pre-coding parameters V 1    406   a  and V 2    406   b , 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 h 1  and h 2  ( 407   a - 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.,  201   c  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 N SYM  after the data padding at  603 , and determine whether N SYM  is even or odd at  604 . If N SYM  is even at  605 , the transmitter may use STBC transmission as illustrated at  401  in  FIG. 4 ; otherwise, if N SYM  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.