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 . fig1 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 . fig2 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 : 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 fig3 provides an exemplary block diagram illustrating an example stbc transmission scheme in a mimo system . the example mimo system in fig3 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 . fig4 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 fig1 ). 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 fig3 can be used , at 401 ( e . g ., similar to 310 in fig3 ). 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 . fig5 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 : the padding symbol transmit antenna can be indicated in the hew - sig field ( e . g ., 201 c in fig2 ), 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 : fig6 provides an exemplary flow diagram illustrating transmitting data symbols with an stbc pre - coded with available channel information ( e . g ., see 405 in fig4 ). at 601 , a mimo transmitter module ( e . g ., see 101 in fig1 ) 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 fig4 . 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 fig4 ; 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 fig4 . 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 .