Patent Abstract:
A communication device carries out communication using N number of communication channels, where N is an integer not less than 2. The communication device includes interleavers that shuffle a data series, which is meant to be transmitted over the N number of communication channels, in at least two directions from among a time direction, a space direction, and a frequency direction, and deinterleavers that shuffle the data series back to obtain the original data series.

Full Description:
BACKGROUND OF THE INVENTION 
     1) Field of the Invention 
     The present invention relates to an interleaver and a deinterleaver that respectively shuffle data and restore the order of data in a communication system. More particularly, the present invention relates to an interleaver, a deinterleaver, a communication device, and a method for trans-communication channel interleaving and deinterleaving, by which data can be sorted across a plurality of communication channels. 
     2) Description of the Related Art 
     A communication device deployed in a conventional communication system is explained first. Error bursts due to fading are common in communication systems like wireless LAN802.11 or HISWAN, etc. To counter the error bursts, these communication systems perform bit interleaving on the data that is subjected to an error correction coding. To be specific, an interleaver at the transmitter end shuffles the order of the data that is subjected to error correction coding, while a deinterleaver at the receiver end restores the original order of the data. The processes of interleaving and deinterleaving randomize the occurrence of burst errors and reduce data error. 
     A conventional communication system stipulated by the wireless LAN standards 802.11a set down by the United States (see Institute of Electrical and Electronic Engineers (IEEE) Standards 802.11a-1999) is explained next. The transmitter at the transmitting end subjects the information data to error correction coding, and shuffles the order of the data (conventional method of interleaving). The transmitter further modulates the shuffled data by a predetermined modulation method, and transmits the data. At the receiver end, the modulated data is demodulated, and the original order of the data is restored, after which the data is decoded. 
     However, the communication device in the conventional communication system has the following problems. 
       FIG. 8A  and  FIG. 8B  are drawings illustrating an interleaving method deployed in the conventional communication system. Specifically,  FIG. 8A  represents a Binary Phase Shift Keying (BPSK) interleaver that shuffles data by writing horizontally and reading vertically.  FIG. 8B  represents a Quadrature Phase Shift Keying (QPSK) interleaver, which also shuffles data like the BPSK interleaver, that is, by writing horizontally and reading vertically. The size and the shape of the interleaver created are specific to the modulation method, and closing of the interleaving process is independent of the communication channel. 
     However, in a communication involving a plurality of communication channels, if the interleavers are closed independently in all the communication channels as in the conventional communication system, deterioration in communication conditions in one of the communication channels (that is, if one of the communication channels is affected by interference, etc.) leads to a significant reduction in the throughput. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to at least solve the problem described above, and to provide an interleaver, an deinterleaver corresponding to the interleaver, and a communication device that includes the interleaver and the deinterleaver that shuffle data across a plurality of communication channels, and maintain a high throughput by averaging out the communication conditions of each of the communication channels. 
     To solve the above problem, and to achieve the objective mentioned above, an interleaver provided in a communication device that carries out communication using N number of communication channels, where N is greater than 2, includes a trans-communication channel interleaving unit that shuffles a data series to be transmitted to the N number of communication channels, in at least two directions from among a time direction, a space-division communication channel direction, and a frequency-division communication channel direction. 
     According to the present invention, a data series in the form of an output of a single error correcting encoder is transmitted by distributing the output to a plurality of frequency-division communication channels. Consequently, even if one communication channel is unable to communicate independently due to a sudden major interference, or the like, the errors are widely scattered due to the trans-communication channel interleaving, and therefore, error correction can be carried out. 
     According to the present invention, a data series meant for transmission is transmitted to a plurality of frequency-division communication channels. Consequently, even if one communication channel is unable to communicate independently due to a sudden major interference, or the like, the errors are widely scattered due to the trans-communication channel interleaving and deinterleaving. As a result, error correction can be carried out, and throughput is not adversely affected. 
     The other objects, features, and advantages of the present invention are specifically set forth in or will become apparent from the following detailed description of the invention when read in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  and  FIG. 1B  are drawings of a communication device in which an interleaver and a deinterleaver according to the present invention are deployed; 
         FIG. 2A  and  FIG. 2B  are drawings of configurations of the interleaver and deinterleaver; 
         FIG. 3A  and  FIG. 3B  are drawings illustrating an example of a shuffling method; 
         FIG. 4A  and  FIG. 4B  are drawings illustrating another example of the shuffling method; 
         FIG. 5  is a drawing of a configuration of a communication system in which the communication device shown in  FIG. 1  uses MIMO communication channels; 
         FIG. 6A  and  FIG. 6B  are drawings illustrating yet another example of the shuffling method; 
         FIG. 7  is a drawing illustrating yet another example of the shuffling method; and 
         FIG. 8A  and  FIG. 8B  are drawings illustrating an interleaving method deployed in a conventional communication system. 
     
    
    
     DETAILED DESCRIPTION 
     Exemplary embodiments of the interleaver, the deinterleaver, the communication device, and the method of interleaving and deinterleaving according to the present invention are explained next with reference to the accompanying drawings. The present invention is not limited to the embodiments described herein. 
     First Embodiment 
       FIG. 1A  and  FIG. 1B  are drawings of a communication device in which the interleaver and the deinterleaver according to the present invention are deployed. To be more specific,  FIG. 1A  is a drawing of the communication device at a transmitter end, and  FIG. 1B  is a drawing of the communication device at a receiver end. 
     The communication device according to the present embodiment is assumed to have N number of frequency-division communication channels. The transmitter end communication device shown in  FIG. 1A  includes M number of error correcting encoders  1 - 1  through  1 -M, an interleaver  2  that shuffles the data meant for different communication channels, and N number of modulating units  3 - 1  through  3 -N. The receiver end communication device shown in  FIG. 1B  includes-N number of demodulating units  4 - 1  through  4 -N, a deinterleaver  5  that shuffles the data meant for different communication channels, and M number of error correcting decoders  6 - 1  through  6 -M. 
     The error correcting encoders  1 - 1  through  1 -M perform a predetermined encoding process on the data meant for transmission (transmission data). The interleaver  2  shuffles the outputs from M number of error correcting encoders  1 - 1  to  1 -M (that is, performs interleaving between the outputs from the plural error correcting encoder). Each of the modulating units  3 - 1  through  3 -N modulates the shuffled transmission data by a predetermined modulation method assigned to the relevant communication channel, and outputs the modulated transmission data. Each of the demodulating units  4 - 1  through  4 -N of the receiver end transmission device demodulates the receiver signal of the relevant communication channel. The deinterleaver  5  shuffles the data back to the original order of the data (that is, restores the order of the data) shuffled by the interleaver  2 . Each of the error correcting decoders  6 - 1  through  6 -M decodes the original transmission data by a decoding method corresponding to the relevant error correcting encoders  1 - 1  through  1 -M. 
       FIG. 2A  is a drawing of a configuration of the interleaver according to the present invention, and  FIG. 2B  is a drawing of a configuration of the deinterleaver according to the present invention. The interleaver according to the present invention includes a distributing unit  11 , and N number of interleaving units  12 - 1  through  12 -N. The deinterleaver according to the present invention includes N number of deinterleaving units  13 - 1  through  13 -N, and a distributing unit  14 . 
     The distributing unit  11  distributes the outputs from M number of error correcting encoders  1 - 1  through  1 -M among N number of interleaving units  12 - 1  through  12 -N. The distributing unit  11  distributes, by a predetermined distribution method, the outputs from M number of error correcting encoders to each interleaving unit. The N number of deinterleaving units  13 - 1  through  13 -N shuffle the data back to restore its original order. The distributing unit  14  has an action that is the reverse of the distributing unit  11 , that is, distributes outputs from the N number of deinterleaving units  13 - 1  through  13 -N among M number of error correcting decoders  6 - 1  through  6 -M. 
       FIG. 3A  and  FIG. 3B  are drawings illustrating an example of a shuffling method according to the present embodiment. To be more specific,  FIG. 3A  is a drawing illustrating a process of writing to the interleaving units when M=2 and N=2.  FIG. 3B  is a drawing illustrating the outputs of the interleaving units. 
     It is assumed that a first communication channel corresponding to the interleaving unit  12 - 1  employs BPSK as the modulation method, and a second communication channel corresponding to the interleaving unit  12 - 2  employs QPSK as the modulation method, and that both the interleaving units  12 - 1  and  12 - 2  conform to the Wireless LAN Standard 802.11a. In other words, the interleaving unit  12 - 1  is assumed to employ the modulation method shown in  FIG. 8A , and the interleaving unit  12 - 2  is assumed to employ the modulation method shown in  FIG. 8B . The interleaving units that conform to standards or systems other than Wireless LAN 802.11a may also be used. In the example, both M and N are taken as 2. However, M may be any number equal to or more than 1, and N may be any number equal to or greater than 2, and if these conditions are fulfilled, M may be equal to, less than or greater than N. The modulation method of the communication channel is not limited to BPSK and QPSK, and may be any multiple value modulation. 
     The non-shaded numbers in  FIG. 3A  represent the output (for instance, bits) of the error correcting encoder  1 - 1 , and the shaded numbers represent the output of the error correcting encoder  1 - 2 . It is assumed in this example that the number of symbols transmitted by the first communication channel and the second communication channel is the same. However, because twice as much data can be sent by QPSK as by BPSK, the output of the interleaving unit  12 - 2  is twice that of the interleaving unit  12 - 1 . 
     In the distributing unit  11 , the outputs from the error correcting encoders  1 - 1  and  1 - 2  are written alternately starting from the rows, with the write numbers corresponding to the interleaving unit  12 - 1  (row with the write number  1 ) and the interleaving unit  12 - 2  (row with the write number  2 ) in the sequence of the write numbers ( 1  through  9 ). In this way, one-third of the output of the error correcting encoders  1 - 1  and  1 - 2  is written to the interleaving unit  12 - 1 , and the remaining two-thirds is written to the interleaving unit  12 - 2 . Because the outputs from the interleaving units  12 - 1  and  12 - 2  are read column-by-column, an intermingled output of the error correcting encoder  1 - 1  and the output of the error correcting encoder  1 - 2  emerge as the outputs from the interleaving units  12 - 1  and  12 - 2 , as shown in  FIG. 3B . 
       FIGS. 4A and 4B  are drawings illustrating another example of the shuffling method according to the present embodiment. To be more specific,  FIG. 4A  is a drawing illustrating a process of writing to the interleaving units when M=2 and N=2.  FIG. 4B  is a drawing illustrating the outputs of the interleaving units. The conditions for shuffling are the same as described with reference to  FIG. 3A  and  FIG. 3B . 
     In the distributing unit  11 , the outputs from the error correcting encoders  1 - 1  and  1 - 2  are written alternately between the interleaving units  12 - 1  and  12 - 2 , one bit each from the error correcting encoders  1 - 1  and  1 - 2  for the interleaving unit  12 - 1 , and two bits each from the error correcting encoders  1 - 1  and  1 - 2  for the interleaving unit  12 - 2 . This process is carried out until all the three rows are filled in the interleaving unit  12 - 1 , and all the six rows are filled in the interleaving unit  12 - 2 . Thus, bits from the error correcting encoders  1 - 1  and  1 - 2  are shuffled in a different way than that shown with reference to  FIG. 3A  and  FIG. 3B . 
     In the present embodiment, the first communication channel and the second communication channel are assumed to have the same number of transmission symbols. However, the number of transmission symbols in the two communication channels may be different. Further, the distribution of the bits to the interleaving units may not be equal. Moreover, any distribution method may be used, as long as the bits that are written to the interleaving units are reasonably shuffled. 
     Thus, in the present embodiment, a data series in the form of an output of a single error correcting encoder is transmitted by distributing the output to a plurality of frequency-division communication channels. Consequently, even if one communication channel is unable to communicate independently due to a sudden major interference, or the like, the errors are widely scattered due to the trans-communication channel interleaving and deinterleaving, and the error correcting decoders are able to carry out error correction. As a result, throughput is not adversely affected. Because the interleaver  2  consists of the distributing unit  11  and the interleaving units  12 - 1  through  12 -N, the conventional interleaver, which is modulation method-specific, may also be adaptable. 
     The communication in the communication device according to the present invention is explained with reference to a plurality of frequency-division communication channels. However, the present invention is not limited thereto, and a plurality of space-division communication channels (Multiple-Input Multiple-Output (MIMO) communication channels, corresponding to communication channels  7 - 1 ,  7 - 2 , and so on through  7 -N shown in  FIG. 5 ) may also be used.  FIG. 5  is a drawing of a configuration of a communication system in which the communication device shown in  FIG. 1  uses MIMO communication channels. Thus, if the shuffling method according to the present embodiment is deployed, the effect described earlier can be achieved even with MIMO communication channels. The MIMO communication channels may be realized by a plurality of antennae, or by beam forming, as long as they use space-division. 
     Further, in the present embodiment, the same effect described earlier can be achieved by using a plurality of both frequency-division communication channels and time-division communication channels (MIMO communication channels) for communication. 
       FIG. 6A  and  FIG. 6B  are drawings illustrating yet another example of the shuffling method of the interleaver  2  according to the present embodiment. To be specific,  FIG. 6A  and  FIG. 6B  are drawings illustrating shuffling in frequency direction and space direction. 
       FIG. 6A  is a drawing illustrating an output sequence when no shuffling is carried out by the interleaver.  FIG. 6B  is a drawing illustrating the output sequence after the interleaver performs interleaving. In this example, the communication channel is assumed to have four rows in the space direction and three columns in the frequency direction. However, there may be greater or fewer rows and columns. 
     In the shuffling method explained with reference to  FIG. 6A  and  FIG. 6B , the conventional time-direction interleaving unit may be jointly used either by connecting it in the beginning or at the end. 
       FIG. 7  is a drawing illustrating yet another example of the shuffling method of the interleaver  2  according to the present invention. To be specific,  FIG. 7  is a drawing illustrating an output order of the data prior to interleaving shown in  FIG. 6A , after it is shuffled in frequency direction, space direction, and time direction. In this example, the communication channel is assumed to have four rows in the space direction and three columns in the frequency direction. However, there may be greater or fewer rows and columns. 
     The interleaver described in the claims is essentially equivalent to the interleaver  2  described in the present embodiment, and a plurality of inter-communication channel interleaving units described in the claims are essentially equivalent to both the interleaver described in the claims and the interleaver  2 . 
     Although the invention has been described with respect to a specific embodiment for a complete and clear disclosure, the appended claims are not to be thus limited but are to be construed as embodying all modifications and alternative constructions that may occur to one skilled in the art that fairly fall within the basic teaching herein set forth.

Technology Classification (CPC): 7