Patent Publication Number: US-2007104286-A1

Title: Equipment and method for MIMO SC-FED communication system

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to an equipment and method for a multi-input/multi-output (MIMO) single carrier frequency encoding/decoding (SC-FED) communication system. More particularly, the present invention relates to a MIMO SC-FED communication system suitable for a selective frequency attenuation channel.  
      2. Description of the Related Art  
      Among the variety of communication methods currently in use, single carrier and multiple carrier modulation is quite a reliable technique. In these two techniques, a channel distortion resulting from multi-path transmission can easily be equalized through a fast Fourier transform and its inverse transformation in the frequency domain.  
      Looking from another perspective, the development of the space time block coding (STBC) and the multi-input/multi-output (MIMO) system can effective resist signal attenuation under a variety of different transmission and/or reception schemes. For a frequency bandwidth with frequency selected attenuation channel, a different MIMO orthogonal frequency division multiplexing (OFDM) system is usually selected. However, this technique requires the receiving end to have a near perfect computational estimation of the channel so that the system can synchronize with decoding and other management decisions.  
      When the conditions of the channel change slowly, the transmission end facilitates the receiving end to obtain an accurate estimation of the channel conditions by providing a series of pilot sequences. Yet, in an environment where the channel conditions change rapidly, the job of obtaining an accurate estimation of the channel conditions is very difficult.  
     SUMMARY OF THE INVENTION  
      Accordingly, at least one objective of the present invention is to provide a multi-input/multi-output (MIMO) differential single carrier frequency encoding/decoding (SC-FED) communication system and a method suitable for working under a communication environment whose channel attenuation conditions change very rapidly.  
      To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention provides a MIMO differential SC-FED communication system having a transmitter and a receiver. The transmitter has a differential block encoder module for receiving a plurality of data block pairs and performing a circular convolution operation on the data blocks to obtain a plurality of coded data blocks in a space-time block coding (STBC) unit. The STBC unit will perform a space-time block encoding process on the output from the differential block encoder module to produce a plurality of transmitting data blocks. A plurality of frame generators receives the respective transmitting data blocks and adds a cyclic prefix to the corresponding transmitting data blocks to generate a plurality of block frames. Then, the frame generators send the block frames to the receiver of the present invention via a corresponding transmitting antenna.  
      In the embodiment of the present invention, the receiver includes a receiving antenna unit for receiving the block frames produced by the transmitter. Furthermore, the receiving antenna unit will also transmit the received block frames to a computational module. The computational module performs a divergent Fourier transform (DFT) and a conjugation of the block frames and then outputs the block frames to a decoding module. Thus, the decoding module can perform a complex conjugate transformation or a matrix inversion operation of the previous output from the computational module and then multiply with the current output from the computational module. Thereafter, a fast Fourier transform inversion operation is performed. In addition, the receiver further includes a decision unit coupled to the decoding unit for converting the output from the decoding unit back to the original data block.  
      From another perspective, the present invention also provides a MIMO differential SC-FED communicating method suitable for a frequency selected attenuation channel. The communicating method includes the following steps. First, a plurality of data block pairs is received. Then, a convolution operation is performed on these data blocks to obtain a plurality of encoded data blocks. Thereafter, a space-time block encoding process is performed on these encoded data blocks to obtain a plurality of transmitting data blocks. After that, a cyclic prefix is added to each transmitting data block. Lastly, a block frame is produced and transmitted.  
      In the embodiment of the present invention, a convolution operation on the coded data blocks in a previous production and the newly received data block is carried out to obtain the newest coded data block.  
      In addition, the present invention further include receiving the aforesaid block frames to generate a plurality of received sample blocks. Then, a divergent Fourier transform computation of these received sample blocks is carried out to obtain a plurality of Fourier transformation matrices. Thereafter, a diagonalization of each Fourier transform matrix is performed to obtain a receiving signal matrix. After that, a complex conjugate transformation or a matrix inversion operation on the previously received signal matrix is carried out and then multiplied by the currently received signal matrix to obtain a data block matrix. Finally, an inverse Fourier transform of the data block matrix is performed to obtain the original data blocks.  
      Because there is no need to perform a channel estimation at the transmitting end and the receiving end in the present invention, the present invention is suitable for a communication environment whose channel attenuation conditions change rapidly.  
      It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.  
       FIG. 1  is a block diagram showing the circuit structure of a transmitter according to one preferred embodiment of the present invention.  
       FIG. 2  is a block diagram showing the circuit structure of a receiver according to one preferred embodiment of the present invention.  
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      Reference will now be made in detail to the present preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts.  
       FIG. 1  is a block diagram showing the circuit structure of a transmitter according to one preferred embodiment of the present invention. The transmitter is suitable for a MIMO differential SC-FED communication system. As shown in  FIG. 1 , the transmitter  100  includes a differential block encoder module  102 . The output of the transmitter  100  is coupled to a space-time block coding (STBC) unit  104 . The outputs of the STBC unit  104  are coupled to a pair of transmitting antenna units  110  and  112  through block frame generator modules  106  and  108  respectively.  
      The differential block encoding module  102  can include a differential transmission unit  114  and a block delay unit  116 . The differential transmission unit  114  is used for receiving N pairs of data blocks, where N is a positive integer. For example, in the d 1   (k) (0) to d 1   (k) (N−1) and d 2   (k) (0) to d 2   (k) (N−1), the upper label k represents the k th  block space with k equal to 0, 2, 4. . . and so on. The lower label represents the index value, for example, the data block with the lower label  1  is transmitted through the transmitting antenna unit  110 . On the contrary, the data block with the lower label  2  is transmitted through the transmitting antenna unit  112 .  
      When the differential transmission unit  114  receives the data blocks, the data blocks will be encoded to produce a plurality of coded data blocks x i   (k) . Similarly, the upper label k in the coded data block x i   (k)  represents the data space value and the lower label i is the index value of the antenna. When the differential transmission unit  114  generates a plurality of coded data blocks x i   (k) , the encoded data blocks will be transmitted to the STBC unit  104  and the data block delay unit  116 . The data block delay unit  116  will be fed back to the differential transmission unit  114  after the coded data block x i   (k)  from the differential transmission unit  114  has undergone a delay so that a newer coded data block x i   (k)  is produced.  
      In the present invention, the differential transmission unit  114  performs a circular convolution operation on the previously obtained coded data block x i   (k)  and the currently acquired data block to produce the newest coded data block x i   (k) . Thus, the method of generating the coded data block x i   (k)  can be represented by the following matrix formula:  
         [           x   1     (   k   )                 x   2     (   k   )             ]     =     [             (       x   1     (     k   -   2     )       *     d   1     (   k   )         )     +     (       x   1     (     k   -   1     )       *     d   2     (   k   )         )                   (       x   2     (     k   -   2     )       *     d   1     (   k   )         )     +     (       x   2     (     k   -   1     )       *     d   2     (   k   )         )             ]         
          where 
 
 X   1   (k−2)   =[X   1   (k−2) (0) X   1   (k−2) (1) . . .  X   1   (k−2) (N−1)] T  
 
 X   2   (k−2)   =[X   2   (k−2) (0) X   2   (k−2) (1) . . .  X   2   (k−2) (N−1) ] T  
 
 X   1   (k−1)   =[−X   2   (k−2)* (0)− X   2   (k−2)* (N−1) . . .  X   2   (k−2)* (1)] T  
 
 X   2   (k−1)   =[X   1   (k−2)* (0) X   1   (k−2)* (N−1) . . .  X   1   (k−2)* (1)] T  
    and the symbol * represents a circular convolution operation.        

      Thereafter, the differential transmission unit  114  will transmit the output to the STBC unit  104  to perform a space-time block encoding process. After the STBC unit  104  has encoded the output from the differential transmission unit  114 , a plurality of transmitting data blocks is produced. These transmission data blocks will be delivered to a corresponding frame generator module ( 106  or  108 ). The frame generator module  106  and  108  will add a cyclic prefix to the output from the STBC unit  104  to produce frame blocks and then transmit the frame blocks to the receiver of the communication system in the present invention through the corresponding transmitting antenna unit ( 110  or  112 ).  
       FIG. 2  is a block diagram showing the circuit structure of a receiver according to one preferred embodiment of the present invention. Similarly, the receiver is suitable for the MIMO differential SC-FED communication system of the present invention. As shown in  FIG. 2 , the receiver  200  includes a receiving antenna unit  202  that couples to a computational module  210 . The output from the computational module  210  is transmitted to a decoding module  220  and the output of the decoding module  220  is coupled to a decision unit  230 .  
      Although the channel used for transmitting the frame blocks operates as a linear convolution operation, the operation will perform as a circular convolution operation due to the action of the cyclic prefix. After the receiving antenna unit  202  has received the frame blocks transmitted from the transmitter shown in  FIG. 1 , a plurality of data sample blocks is generated. Because the number of transmitting antenna unit is  2  while the number of receiving antenna unit is just  1 , the data sample blocks can be represented by the following formula: 
 
 y   (j)   =H   1   (j)   x   1   (j)   +H   2   (j)   x   2   (j)   +n   (j)  
 
 where the upper label j represents the j th  received frame block and is a positive integer. H 1   (j)  and H 2   (j) , due to the cyclic prefix, is an N×N circular matrix. In addition, the term n (j)  is a noise-generated vector. 
 
      Because H (disregarding the superscript and the underscript) is a circular matrix, an Eigen-decomposition of the matrix can be represented by the following formula: 
 
H=Q H ΛQ 
 
 where (.) H  represents a complex conjugate transform matrix and Q is a standardized divergent Fourier transform matrix, and Λ is a diagonalized Eigen-value matrix. 
 
      As shown in  FIG. 2 , the computational module  210  further includes fast Fourier transform (FFT) units  212  and  214  and a conjugation computation unit  216 . After the receiving antenna unit  202  has generated the data sample blocks, the fast Fourier transform units  212  and  214  will perform a divergent Fourier transform of the output from the receiving antenna unit  202 , which can be represented by the following formula: 
 
 {tilde over (y)}   (j)   =Qy   (j) =Λ 1   (j)   {tilde over (x)}   1   (j) +Λ 2   (j)   {tilde over (x)}   2   (j)   +ñ   (j)   (1) 
 
 where {tilde over (x)} i   (j) =Qx i   (j)  and ñ (j)l =Qn   (j) . 
 
      After the fast Fourier transform (FFT) unit  212  has performed a divergent Fourier transform on the output from the receiving antenna unit  202 , the conjugation computation unit  216  will perform a conjugation operation on the output from the fast Fourier transform (FFT) unit  212 . Through this operation, the output from the computation module  210  can be represented by the following formulae: 
 
 {tilde over (Y)}   (k) =Λ 1   (k)   {tilde over (x)}   1   (k) +Λ 2   (k)   {tilde over (x)}   2   (k)   +{tilde over (n )}(k)  
 
 {tilde over (Y)}   (k)* =Λ 1   (k)H   {tilde over (x)}   1   (k)* +Λ 2   (k)H   {tilde over (x)}   2   (k)*   +ñ   (k)*  
 
 {tilde over (Y)}   (k+1)* =−Λ 1   (k+1)     H     {tilde over (x)}   2   (k) +Λ 2   (k+1)H   {tilde over (x)}   1   (k)   +ñ   (k+1)*  
 
 {tilde over (Y)}   (k+1) =−Λ 1   (k+1)   {tilde over (x)}   2   (k)* +Λ 2   (k+1)   {tilde over (x)}   1   (k)*   +ñ   (k+1)   (2) 
 
 In addition, assume the two consecutive blocks in the channel are fixed, that is, 
 
H i   (k+1) =H 1   (k) =H i  
 
Λ i   (k+1)=Λ   i   (k) =Λ i   (3) 
 
 By combining the formula (2) and the formula (3), the following received signal matrix is obtained:  
                           ⁢         Y             ⁢   _         (   k   )       =       ⁢     [           diag   ⁡     (       Y   ~       (   k   )       )             diag   ⁡     (       Y   ~       (     k   +   1     )       )                 diag   ⁡     (       Y   ~         (     k   +   1     )     *       )             -     diag   ⁡     (       Y   ~     1       (   k   )     *       )               ]                   =       ⁢         [           Λ   1           Λ   2                 Λ   2   H     -           Λ   1   H           ]     ⁡     [           diag   ⁡     (       x   ~     1     (   k   )       )             -     diag   ⁡     (       x   ~     2       (   k   )     *       )                   diag   ⁡     (       x   ~     2     (   k   )       )             diag   ⁡     (       x   ~     1       (   k   )     *       )             ]       +       N   _       (   k   )                       (   4   )             
 
 Similarly, according to formula (1), the next batch of received signal matrix can be represented by the following formula:  
                   Y   _       (     k   +   2     )       =       [             Y   ~       (     k   +   2     )                   Y   ~         (     k   +   3     )     *             ]     =       [           Λ   1           Λ   2               Λ   2   H           -     Λ   1   H             ]     ⁡     [             x   ~     1     (     k   +   2     )                   x   ~     2     (     k   +   2     )             ]           ⁢     
     ⁢   where   ⁢     
     ⁢             [             x   ~     1     (     k   ⁢           +           ⁢   2     )                   x   ~     2     (     k   ⁢           +           ⁢   2     )             ]     =       [         Q       0           0       Q         ]     ⁡     [           x             ⁢   1       (     k   ⁢           +           ⁢   2     )                 x             ⁢   2       (     k   ⁢           +           ⁢   2     )             ]                   =     [               diag   ⁢           ⁢     {     Q   ⁢     (           ⁢       x             ⁢   1       (   k   )       *           ⁢     d             ⁢   1       (     k   ⁢           +   2     )         )       }       ⁢           +     diag   ⁢           ⁢     {     Q   ⁢           ⁢     (           ⁢       x             ⁢   1       (     k   +   1     )       *           ⁢     d             ⁢   2       (     k   +   2     )         )       }         ⁢                         diag   ⁢           ⁢     {     Q   ⁢     (           ⁢       x             ⁢   2       (   k   )       *           ⁢     d             ⁢   1       (     k   ⁢           +   2     )         )       }       ⁢           +           ⁢     diag   ⁢           ⁢     {     Q   ⁢           ⁢     (           ⁢       x             ⁢   2       (     k   +   1     )       *           ⁢     d             ⁢   2       (     k   +   2     )         )       }               ]                 =       [             diag   ⁢     (           ⁢               ⁢     x   ~       1     (   k   )       )       ⁢                   -     diag   (           ⁢               ⁢     x   ~       2             ⁢       (   k   )     *         )                 diag   ⁢     (           ⁢               ⁢     x   ~       2     (   k   )       )             diag   ⁢     (           ⁢               ⁢     x   ~       1             ⁢       (   k   )     *         )             ]     ⁡     [                   ⁢               ⁢     d   ~       1     (     k   +   2     )                           ⁢               ⁢     d   ~       2     (     k   +   2     )               ]                       (   5   )             
 
 Because of the circular convolution characteristics of the divergent Fourier transform, {tilde over (d)} i   (k+2) =Qd i   (k+2)  and formula (5) can be re-written as:  
                 Y             ⁢   _         (     k   ⁢           +           ⁢   2     )       =       ⁢     [             Y   ~       (     k   ⁢           +           ⁢   2     )                   Y   ~               ⁢       (     k   ⁢           +           ⁢   3     )     *               ]                 =       ⁢       [           Λ             ⁢   1             Λ             ⁢   2                         ⁢     Λ             ⁢   2               ⁢   H       ⁢                   -     Λ             ⁢   1               ⁢   H               ]     ⁡     [             diag   ⁢     (           ⁢               ⁢     x   ~       1     (   k   )       )       ⁢                   -     diag   (           ⁢               ⁢     x   ~       2             ⁢       (   k   )     *         )                 diag   ⁢     (           ⁢               ⁢     x   ~       2     (   k   )                 diag   ⁢     (           ⁢               ⁢     x   ~       1             ⁢       (   k   )     *         )             ]                       ⁢       [             d   ~     1     (     k   +   2     )                   d   ~     2     (     k   +   2     )             ]     +       N             ⁢   _         (     k   ⁢           +           ⁢   2     )                   
 
      When the computational module  210  transmits the output to the decoding module  220 , the frequency-band block equalizer unit  222  and the block delay unit  224  will simultaneously receive the output from the computational module  210 . The block delay unit  224  will transmit the output from the computational module  210  to the frequency-band block equalizer unit  222  after a delay period. The frequency-band block equalizer unit  222  will perform a complex conjugate transform on the previous batch of received signal matrix and then multiply with the current received signal matrix. The process may be represented using the following formula:  
         [             d   _     1     (     k   +   2     )                   d   _     2     (     k   +   2     )             ]     =           Y   _         (   k   )     H       ⁢       Y   _       (     k   +   2     )         =           [           Λ   ~         0           0         Λ   ~           ]     ⁡     [           X   ~         0           0         X   ~           ]       ⁡     [             d   ~     1     (     k   +   2     )                   d   ~     2     (     k   +   2     )             ]       +       n   _       (     k   +   2     )               
 
 Here, {tilde over (Λ)}=|Λ 1 | 2 +|Λ 2   2  and {tilde over (X)}=diag(|{tilde over (x)} 1   (k) | 2  +|{tilde over (x)} 2   (k) | 2  ). 
 
      In some other embodiment, the frequency-band block equalizer unit  222  performs an inverse matrix transform operation on the previous batch of received signal matrix and then multiplies with the current received signal matrix, that is,  
         [             d   _     1     (     k   +   2     )                   d   _     2     (     k   +   2     )             ]     =           Y   _         (   k   )       -   1         ⁢       Y   _       (     k   +   2     )         =         [         I       0           0       I         ]     ⁡     [             d   ~     1     (     k   +   2     )                   d   ~     2     (     k   +   2     )             ]       +       n   _       (     k   +   2     )               
 
      Lastly, the output from the frequency-band block equalizer unit  222  is transmitted to an inverse fast Fourier transform (IFFT) unit  226  to perform a Fourier transform inversion operation. Then, the result is output to the decision unit  230 . Thus, the decision unit  230  will convert back to the original data block according to the output from the decoding module  220 .  
      Although the receiver  200  in  FIG. 2  has a single receiving antenna unit  202 , this does not limit the present invention as such. Anyone familiar with the technique may implement the required number of receiving antenna units accordingly. Furthermore, another receiving unit can easily replicate the aforesaid receiver. Hence, the present invention can obtain more multifarious gains.  
      In summary, the advantages of the present invention includes at least the following: 
          1. The present invention deploys the signal carrier frequency-band equalizing technique and is applicable to a multi-path channel with multiple frequency selection.     2. There is no need to perform channel estimation in either the transmitter end or the receiver end. Hence, the present invention is particularly adapted to a communication environment where the frequency attenuation conditions change rapidly.        

      It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.