Abstract:
A wireless communication device including: a memory, and a processor coupled to the memory and configured to: wirelessly receive a packet including a header that is compressed by another wireless communication device, decompress the compressed header based on a set compression mode among a plurality of compression modes, each of the plurality of compression modes having a different amount of feedback information transmitted from the wireless communication device to the another wireless communication device, obtain a quality of a wireless channel from the another wireless communication device to the wireless communication device, and select the set compression mode based on the obtained quality of the wireless channel.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2014-157399 filed on Aug. 1, 2014, the entire contents of which are incorporated herein by reference. 
       FIELD 
       [0002]    The embodiments discussed herein are related to a wireless communication device, a wireless communication system, and a communication control method. 
       BACKGROUND 
       [0003]    A header compression method in communication using an internet protocol (IP) mainly via a wire has been proposed in related art with an objective of improving communication efficiency and reducing an error rate. In communication to which the header compression method is applied, a compressing unit of a communicating device on a transmitting side compresses the header of a packet, and transmits the packet including the compressed header. Then, a decompressing unit of a communicating device on a receiving side decompresses the received packet. Robust header compression (ROHC), for example, has been standardized as a standard for the header compression method. The header compression method uses redundancy in a field of the header. That is, for example, the value of an IP address field is usually fixed in packets of a same stream. Hence, the static field information (that is, a parameter scarcely varying in packet units) is transmitted by using an initial packet, and the transmission of the static field information can be omitted in subsequent packets. Relevant information in header fields may be referred to as a “context.” Incidentally, the above-described “decompression” refers to restoring the packet including the compressed header to a state before the header compression using the context. 
         [0004]    The following three operation modes are defined in ROHC. 
         [0005]    (1) U-Mode (Unidirectional Mode) 
         [0006]    In the U-mode, there is no feedback information from the decompressing unit to the compressing unit. Thus, while an amount of signaling is small, a degree of reliability of communication is low. 
         [0007]    (2) O-Mode (Bidirectional Optimistic Mode) 
         [0008]    In the O-mode, a feedback channel from the decompressing unit to the compressing unit is used for an error recovery request and an acknowledgment of a context update. 
         [0009]    (3) R-Mode (Bidirectional Reliable Mode) 
         [0010]    In the R-mode, the feedback channel is used more actively than in the O-mode. That is, in the R-mode, acknowledgments of all of context updates are transmitted using the feedback channel. 
         [0011]    As described above, the amount of feedback information is increased in order of the U-mode, the O-mode, and the R-mode, whereas the degree of reliability of communication is increased in order of the U-mode, the O-mode, and the R-mode. 
         [0012]    In related art, switching among the above-described three operation modes is performed on the basis of a “given switching pattern” set in advance. 
       PRIOR ART DOCUMENTS 
     Patent Documents 
       [0013]    [Patent Document 1] Japanese Laid-open Patent Publication No. 2010-199750 
         [0014]    [Patent Document 2] Japanese Laid-open Patent Publication No. 2012-169764 
       SUMMARY 
       [0015]    According to an aspect of the invention, a wireless communication device includes: a memory, and a processor coupled to the memory and configured to: wirelessly receive a packet including a header that is compressed by another wireless communication device, decompress the compressed header based on a set compression mode among a plurality of compression modes, each of the plurality of compression modes having a different amount of feedback information transmitted from the wireless communication device to the another wireless communication device, obtain a quality of a wireless channel from the another wireless communication device to the wireless communication device, and select the set compression mode based on the obtained quality of the wireless channel. 
         [0016]    The object and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the claims. 
         [0017]    It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention, as claimed. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0018]      FIG. 1  is a diagram illustrating an example of a wireless communication system according to a first embodiment; 
           [0019]      FIG. 2  is a block diagram illustrating an example of a wireless communication device on a transmitting side according to the first embodiment; 
           [0020]      FIG. 3  is a block diagram illustrating an example of a wireless communication device on a receiving side according to the first embodiment; 
           [0021]      FIG. 4  is a flowchart illustrating an example of processing operation of a wireless communication device on a receiving side according to the first embodiment; 
           [0022]      FIG. 5  is a diagram illustrating an example of a count table according to a second embodiment; 
           [0023]      FIG. 6  is a diagram illustrating an example of processing operation of a wireless communication system according to the second embodiment; 
           [0024]      FIG. 7  is a flowchart illustrating an example of processing operation of a wireless communication device on a receiving side according to the second embodiment; 
           [0025]      FIG. 8  is a diagram illustrating an example of processing operation of a wireless communication system according to a third embodiment; 
           [0026]      FIG. 9  is a flowchart illustrating an example of processing operation of a wireless communication device on a receiving side according to the third embodiment; and 
           [0027]      FIG. 10  is a diagram illustrating an example of hardware configuration of a wireless communication device. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0028]    The third generation partnership project long term evolution (3GPP LTE) standard as a wireless communication standard specifies that ROHC be applied to Layer 2 (data link layer). 
         [0029]    However, when a mode is switched in a fixed manner according to a “given switching pattern” as in the related art, the switching of the mode may cause a mismatch between the mode and conditions of a wireless communication channel, and decrease a degree of reliability of communication. This is attributable, for example, to more violent variations in communication channel conditions in a wireless communication channel than in a wire communication channel. 
         [0030]    The disclosed technology has been made in view of the above, and it is an object of the technology to provide a wireless communication device, a wireless communication system, and a communication control method that can reduce a decrease in a degree of reliability of communication. 
         [0031]    Embodiments of a wireless communication device, a wireless communication system, and a communication control method disclosed in the present application will hereinafter be described in detail with reference to the drawings. It is to be noted that the wireless communication device, the wireless communication system, and the communication control method disclosed in the present application are not limited by the embodiments. In addition, constitutions having identical functions in the embodiments are identified by the same reference symbols, and repeated description thereof will be omitted. 
       First Embodiment 
       [0032]    [Outline of Wireless Communication System] 
         [0033]      FIG. 1  is a diagram illustrating an example of a wireless communication system according to a first embodiment. In  FIG. 1 , the wireless communication system  1  includes a wireless communication device  10  and a wireless communication device  50 . The following description will be made supposing that the wireless communication device  10  is on the “transmitting side” of a compressed packet, and that the wireless communication device  50  is on the “receiving side” of the compressed packet. 
         [0034]    The wireless communication device  10  includes a compressing unit. The wireless communication device  10  transmits, to the wireless communication device  50 , a packet compressed according to a set “usage compression mode.” 
         [0035]    The wireless communication device  50  includes a decompressing unit. The wireless communication device  50  decompresses the received compressed packet according to the set “usage compression mode.” 
         [0036]    In addition, the wireless communication device  50  detects “communication quality” between the wireless communication device  50  and the wireless communication device  10 , and performs “switching control” that switches the “usage compression mode” among a plurality of “compression modes” on the basis of the detected “communication quality.” The “communication quality” may be detected on the basis of the number of times of retransmission, or may be detected on the basis of reception field strength, for example. The plurality of “compression modes” are different from each other in amount of feedback information from the decompressing unit to the compressing unit. That is, the plurality of “compression modes” are different from each other in degree of reliability of communication. The plurality of “compression modes” are for example the U-mode, the O-mode, and the R-mode described above. The following description will be made supposing that the three modes are used. 
         [0037]    For example, the wireless communication device  50  associates three “communication quality ranges” of different communication quality levels with the three compression modes (the U-mode, the O-mode, and the R-mode), respectively. For example, the U-mode is associated with a “high communication quality range” of highest communication quality levels, the O-mode is associated with a “medium communication quality range” of next highest communication quality levels, and the R-mode is associated with a “low communication quality range” of lowest communication quality levels. Then, the wireless communication device  50  identifies the “communication quality range” in which the value of the detected communication quality falls, and switches the “usage compression mode” to the compression mode associated with the identified “communication quality range.” That is, the wireless communication device  50  switches the usage compression mode of the decompressing unit in the wireless communication device  50  itself, and transmits information on the switched “usage compression mode” (which information may hereinafter be referred to as a “mode notification”) to the wireless communication device  10 . The usage compression mode of the compressing unit in the wireless communication device  10  is thereby switched. 
         [0038]    Because the wireless communication device  50  performs “switching control” based on the “communication quality” as described above, switching can be performed to the compression mode corresponding to a high degree of reliability of communication when the communication quality is low. As a result, a decrease in the degree of reliability of communication can be reduced. In addition, an amount of signaling can be reduced because switching can be performed to the compression mode corresponding to a small amount of feedback information when the communication quality is high. 
         [0039]    [Example of Configuration of Wireless Communication Device on Transmitting Side] 
         [0040]      FIG. 2  is a block diagram illustrating an example of a wireless communication device on a transmitting side according to the first embodiment. In  FIG. 2 , the wireless communication device  10  includes a transmission processing unit  11 , a wireless transmitting unit  12 , a wireless receiving unit  13 , and a reception processing unit  14 . 
         [0041]    The transmission processing unit  11  performs processing in Layer 2 (L2) and processing in Layer 1 (L1). Layer 2 includes for example a packet data convergence protocol (PDCP) layer, a radio link control (RLC) layer, and a medium access control (MAC) layer. The above-described ROHC layer is included in the PDCP layer. 
         [0042]    As illustrated in  FIG. 2 , for example, the transmission processing unit  11  includes a compressing unit  21 . The compressing unit  21  forms a compressed packet by compressing a transmission packet (that is, transmission data). This compression processing is processing in the above-described PDCP layer. In this case, the compressing unit  21  performs the packet compression processing using the “compression mode” indicated by the “mode notification” transmitted from the above-described wireless communication device  50 . 
         [0043]    In addition, the transmission processing unit  11  subjects the formed compressed packet to encoding processing and modulation processing, and outputs a resulting transmission signal to the wireless transmitting unit  12 . This encoding processing and this modulation processing are processing in the above-described Layer 1. 
         [0044]    The wireless transmitting unit  12  subjects the transmission signal received from the transmission processing unit  11  to given wireless transmission processing (for example digital-to-analog conversion, up-conversion, and the like), and transmits a resulting wireless signal to the wireless communication device  50  via an antenna. 
         [0045]    The wireless receiving unit  13  receives a signal transmitted from the wireless communication device  50  via the antenna. Then, the wireless receiving unit  13  subjects the received signal to given wireless reception processing (for example down-conversion, analog-to-digital conversion, and the like), and outputs a resulting signal to the reception processing unit  14 . 
         [0046]    The reception processing unit  14  subjects the signal received from the wireless receiving unit  13  to given reception processing (demodulation processing, decoding processing, and the like), and extracts a “mode notification” from resulting received data. Then, the reception processing unit  14  outputs the extracted “mode notification” to the compressing unit  21 . 
         [0047]    [Example of Configuration of Wireless Communication Device on Receiving Side] 
         [0048]      FIG. 3  is a block diagram illustrating an example of a wireless communication device on a receiving side according to the first embodiment. In  FIG. 3 , the wireless communication device  50  includes a wireless receiving unit  51 , a reception processing unit  52 , a communication quality obtaining unit  53 , a mode control unit  54 , a transmission processing unit  55 , and a wireless transmitting unit  56 . 
         [0049]    The wireless receiving unit  51  receives a signal transmitted from the wireless communication device  10  via an antenna. Then, the wireless receiving unit  51  subjects the received signal to given wireless reception processing (down-conversion, analog-to-digital conversion, and the like), and outputs a resulting signal to the reception processing unit  52 . 
         [0050]    The reception processing unit  52  performs processing in Layer 1 (L1) and processing in Layer 2 (L2). As described above, Layer 2 includes for example the PDCP layer, the RLC layer, and the MAC layer. In addition, the above-described ROHC layer is included in the PDCP layer. 
         [0051]    As illustrated in  FIG. 3 , for example, the reception processing unit  52  includes a decompressing unit  61 . The reception processing unit  52  reproduces a transmission packet by decompressing the signal (that is, a compressed packet) received from the wireless receiving unit  51  in the decompressing unit  61 . This decompression processing is processing in the above-described PDCP layer. In this case, the decompressing unit  61  performs the packet decompression processing using the “compression mode” indicated by the “mode notification” received from the mode control unit  54  which will be described later. 
         [0052]    In addition, the reception processing unit  52  outputs a signal (information) used to obtain communication quality (namely, quality of wireless channel) in the communication quality obtaining unit  53  which will be described later to the communication quality obtaining unit  53 . The signal (information) used to obtain communication quality may for example indicate the number of times of retransmission, or may indicate reception field strength. 
         [0053]    The communication quality obtaining unit  53  calculates (or detects) “communication quality” between the wireless communication device  10  and the wireless communication device  50  on the basis of the signal (information) received from the reception processing unit  52 . Then, the communication quality obtaining unit  53  outputs the value of the calculated (or detected) wireless quality to the mode control unit  54 . 
         [0054]    The mode control unit  54  identifies the compression mode corresponding to the value of the wireless quality which value is received from the communication quality obtaining unit  53  on the basis of the received value of the wireless quality and the above-described “correspondence relations” between the communication quality ranges and the compression modes. Then, the mode control unit  54  generates a “mode notification” including information on the identified compression mode, and outputs the generated “mode notification” to the decompressing unit  61  and the transmission processing unit  55 . 
         [0055]    The transmission processing unit  55  subjects the mode notification received from the mode control unit  54  to encoding processing and modulation processing, and outputs a resulting transmission signal to the wireless transmitting unit  56 . This encoding processing and this modulation processing are processing in the above-described Layer 1. 
         [0056]    The wireless transmitting unit  56  subjects the transmission signal received from the transmission processing unit  55  to given wireless transmission processing (for example digital-to-analog conversion, up-conversion, and the like), and transmits a resulting wireless signal to the wireless communication device  10  via the antenna. 
         [0057]    [Example of Operation of Wireless Communication System] 
         [0058]    Description will be made of an example of processing operation of a wireless communication system having the above configuration. The following description will be made particularly of processing operation of a wireless communication device on a receiving side.  FIG. 4  is a flowchart illustrating an example of processing operation of a wireless communication device on a receiving side according to the first embodiment. The wireless communication device  50  illustrated in  FIG. 3  may perform the processing operation illustrated in  FIG. 4 . Incidentally, the processing operation illustrated in  FIG. 4  may be performed repeatedly in given cycles. 
         [0059]    The communication quality obtaining unit  53  obtains “communication quality” between the wireless communication device  10  and the wireless communication device  50  on the basis of a signal (information) received from the reception processing unit  52  (step S 101 ). 
         [0060]    The mode control unit  54  identifies the communication quality range in which the communication quality obtained in the communication quality obtaining unit  53  falls. That is, the mode control unit  54  determines whether or not the obtained communication quality falls in the high communication quality range (step S 102 ). 
         [0061]    When the obtained communication quality falls in the high communication quality range (affirmative in step S 102 ), the mode control unit  54  sets the usage compression mode to the U-mode (step S 103 ). That is, the mode control unit  54  generates a “mode notification” indicating the U-mode, and outputs the generated “mode notification” to the decompressing unit  61  and the transmission processing unit  55 . 
         [0062]    When the obtained communication quality does not fall in the high communication quality range (negative in step S 102 ), the mode control unit  54  determines whether or not the obtained communication quality falls in the medium communication quality range (step S 104 ). 
         [0063]    When the obtained communication quality falls in the medium communication quality range (affirmative in step S 104 ), the mode control unit  54  sets the usage compression mode to the O-mode (step S 105 ). 
         [0064]    When the obtained communication quality does not fall in the medium communication quality range (negative in step S 104 ), the mode control unit  54  sets the usage compression mode to the R-mode (step S 106 ). 
         [0065]    As described above, according to the present embodiment, in the wireless communication device  50 , the communication quality obtaining unit  53  detects “communication quality” between the wireless communication device  10  and the wireless communication device  50 . Then, the mode control unit  54  performs switching control that switches among the plurality of compression modes corresponding to the respective different amounts of feedback information on the basis of the communication quality detected in the communication quality obtaining unit  53 . For example, the mode control unit  54  switches to a compression mode corresponding to a larger amount of feedback information as the communication quality detected in the communication quality obtaining unit  53  becomes lower. 
         [0066]    The configuration of the wireless communication device  50  can reduce a decrease in the degree of reliability of communication. In addition, an amount of signaling can be reduced because switching can be performed to the compression mode corresponding to a small amount of feedback information when the communication quality is high. 
       Second Embodiment 
       [0067]    In a second embodiment, the “number of pieces of data in each range of the number of times of retransmission” is used as an index of “communication quality.” Incidentally, main configurations of wireless communication devices in the second embodiment are the same as the main configurations of the wireless communication devices  10  and  50  in the first embodiment, and will therefore be described with reference to  FIGS. 2 and 3 . In addition, the wireless communication device on the transmitting side in the second embodiment is not different from the wireless communication device on the transmitting side of the first embodiment, and therefore the following description will be made mainly of the wireless communication device on the receiving side. 
         [0068]    [Example of Configuration of Wireless Communication Device on Receiving Side] 
         [0069]    In the wireless communication device  50  according to the second embodiment, the communication quality obtaining unit  53  reads the number of times of occurrence of hybrid automatic repeat request (HARQ) retransmission of each piece of received data, and counts the number of pieces of data for each number of times of occurrence of HARQ retransmission. Then, the communication quality obtaining unit  53  outputs the counted number of pieces of data for each number of times of occurrence of HARQ retransmission to the mode control unit  54 . Incidentally, the communication quality obtaining unit  53  may create a “count table” as illustrated in  FIG. 5 .  FIG. 5  is a diagram illustrating an example of a count table according to the second embodiment. 
         [0070]    The mode control unit  54  calculates the number of pieces of data in each “range of numbers of times of retransmission” on the basis of the number of pieces of data for each number of times of occurrence of HARQ retransmission, the number of pieces of data for each number of times of occurrence of HARQ retransmission being received from the communication quality obtaining unit  53 . For example, a range of numbers of times of retransmission in which range the number of times of retransmission is less than seven (“first threshold value”) is set as a “first range of numbers of times of retransmission,” a range of numbers of times of retransmission in which range the number of times of retransmission is seven (“first threshold value”) or more is set as a “second range of numbers of times of retransmission,” a range of numbers of times of retransmission in which range the number of times of retransmission is one (“second threshold value”) or more is set as a “third range of numbers of times of retransmission,” and a range of numbers of times of retransmission in which range the number of times of retransmission is less than one, that is, no retransmission has occurred is set as a “fourth range of numbers of times of retransmission.” Then, the mode control unit  54  calculates the respective numbers of pieces of data in the “first range of numbers of times of retransmission,” the “second range of numbers of times of retransmission,” the “third range of numbers of times of retransmission,” and the “fourth range of numbers of times of retransmission.” Incidentally, suppose in the following that the number of pieces of data in the “first range of numbers of times of retransmission” is “Count A,” that the number of pieces of data in the “second range of numbers of times of retransmission” is “Count B,” that the number of pieces of data in the “third range of numbers of times of retransmission” is “Count C,” and that the number of pieces of data in the “fourth range of numbers of times of retransmission” is “Count D.” In the example of  FIG. 5 , Count A=a1+a2+a3+a4+a5+a6+a7. In addition, Count B=a8+a9+a10. In addition, Count C=a2+a3+a4+a5+a6+a7+a8+a9+a10. In addition, Count D=a1. 
         [0071]    Then, the mode control unit  54  identifies a compression mode corresponding to communication quality on the basis of the respective numbers of pieces of data in the “first range of numbers of times of retransmission,” the “second range of numbers of times of retransmission,” the “third range of numbers of times of retransmission,” and the “fourth range of numbers of times of retransmission,” a “communication quality range identifying rule,” and the above-described “correspondence relations.” 
         [0072]    The “communication quality range identifying rule” is as follows, for example. 
         [0073]    (1) When Count D&gt;0 and Count C=0, the communication quality range is the “high communication quality range.” 
         [0074]    (2) When Count A&lt;Count B, the communication quality range is the “low communication quality range.” 
         [0075]    (3) When Count A≧Count B&gt;0, the communication quality range is the “medium communication quality range.” 
         [0076]    The mode control unit  54  identifies the communication quality range on the basis of the respective numbers of pieces of data in the “first range of numbers of times of retransmission,” the “second range of numbers of times of retransmission,” the “third range of numbers of times of retransmission,” and the “fourth range of numbers of times of retransmission” and the above-described “communication quality range identifying rule.” Then, the mode control unit  54  sets the compression mode corresponding to the identified communication quality range as the usage compression mode. Then, the mode control unit  54  generates a “mode notification” including information on the usage compression mode, and outputs the generated “mode notification” to the decompressing unit  61  and the transmission processing unit  55 . 
         [0077]    [Example of Operation of Wireless Communication System] 
         [0078]    Description will be made of an example of processing operation of a wireless communication system according to the second embodiment having the above configuration.  FIG. 6  is a diagram illustrating an example of processing operation of a wireless communication system according to the second embodiment.  FIG. 7  is a flowchart illustrating an example of processing operation of a wireless communication device on a receiving side according to the second embodiment. 
         [0079]    The wireless communication device  10  transmits an ROHC packet to the wireless communication device  50  (step S 201 ). Suppose that in this stage, the usage compression mode is the U-mode. 
         [0080]    The ROHC packet transmitted from the wireless communication device  10  is received by the reception processing unit  52  of the wireless communication device  50 . 
         [0081]    In the reception processing unit  52 , the ROHC packet is input to the decompressing unit  61  via a physical layer (PHY) unit and a MAC processing unit (steps S 202  and S 203 ). 
         [0082]    The MAC processing unit of the reception processing unit  52  outputs HARQ information to the communication quality obtaining unit  53  (step S 204 ). 
         [0083]    The communication quality obtaining unit  53  counts the number of pieces of data for each number of times of occurrence of HARQ retransmission (step S 205 ). The communication quality obtaining unit  53  then outputs the counted number of pieces of data for each number of times of occurrence of HARQ retransmission to the mode control unit  54  (step S 206 ). 
         [0084]    The mode control unit  54  determines the usage compression mode on the basis of the number of pieces of data for each number of times of occurrence of HARQ retransmission, the number of pieces of data for each number of times of occurrence of HARQ retransmission being received from the communication quality obtaining unit  53  (step S 207 ). 
         [0085]    For example, as illustrated in  FIG. 7 , the mode control unit  54  calculates the respective numbers of pieces of data in the “first range of numbers of times of retransmission,” the “second range of numbers of times of retransmission,” the “third range of numbers of times of retransmission,” and the “fourth range of numbers of times of retransmission” on the basis of the number of pieces of data for each number of times of occurrence of HARQ retransmission, the number of pieces of data for each number of times of occurrence of HARQ retransmission being received from the communication quality obtaining unit  53  (steps S 301 , S 302 , S 303 , and S 304 ). The mode control unit  54  then determines whether or not “Count D&gt;0 and Count C=0” is satisfied (steps S 305  and S 207 ). 
         [0086]    When “Count D&gt;0 and Count C=0” is not satisfied (negative in step S 305 ), the mode control unit  54  determines whether or not “Count A&lt;Count B” is satisfied (steps S 306  and S 207 ). 
         [0087]    When “Count A&lt;Count B” is satisfied (affirmative in step S 306 ), the communication quality range is the “low communication quality range.” The mode control unit  54  can therefore determine that the usage compression mode may be switched to the R-mode. Then, the mode control unit  54  determines whether or not the present usage compression mode is the R-mode (step S 307 ). When the present usage compression mode is not the R-mode (negative in step S 307 ), the mode control unit  54  performs control that switches the usage compression mode to the R-mode (step S 308 ). That is, the mode control unit  54  generates a mode notification indicating the R-mode (step S 208 ), and sends out the generated mode notification to the decompressing unit  61  and the wireless communication device  10  (steps S 209  and S 210 ). Then, the decompressing unit  61  switches the usage compression mode to the R-mode (step S 211 ). The compressing unit  21  of the wireless communication device  10  similarly switches the usage compression mode to the R-mode. 
         [0088]    When “Count A&lt;Count B” is not satisfied (negative in step S 306 ), the communication quality range is the “medium communication quality range.” The mode control unit  54  can therefore determine that the usage compression mode may be switched to the O-mode. The mode control unit  54  then determines whether or not the present usage compression mode is the O-mode (step S 309 ). When the present usage compression mode is not the O-mode (negative in step S 309 ), the mode control unit  54  performs control that switches the usage compression mode to the O-mode (step S 310 ). That is, the mode control unit  54  generates a mode notification indicating the O-mode (step S 208 ), and sends out the generated mode notification to the decompressing unit  61  and the wireless communication device  10  (steps S 209  and S 210 ). The decompressing unit  61  then switches the usage compression mode to the O-mode (step S 211 ). The compressing unit  21  of the wireless communication device  10  similarly switches the usage compression mode to the O-mode. 
         [0089]    When “Count D&gt;0 and Count C=0” is satisfied (affirmative in step S 305 ), the communication quality range is the “high communication quality range.” The mode control unit  54  can therefore determine that the usage compression mode may be switched to the U-mode. Then, the mode control unit  54  determines whether or not the present usage compression mode is the U-mode (step S 311 ). When the present usage compression mode is not the U-mode (negative in step S 311 ), the mode control unit  54  performs control that switches the usage compression mode to the U-mode (step S 312 ). That is, the mode control unit  54  generates a mode notification indicating the U-mode (step S 208 ), and sends out the generated mode notification to the decompressing unit  61  and the wireless communication device  10  (steps S 209  and S 210 ). Then, the decompressing unit  61  switches the usage compression mode to the U-mode (step S 211 ). The compressing unit  21  of the wireless communication device  10  similarly switches the usage compression mode to the U-mode. Incidentally, when the present usage compression mode is the R-mode (affirmative in step S 307 ), when the present usage compression mode is the O-mode (affirmative in step S 309 ), and when the present usage compression mode is the U-mode (affirmative in step S 311 ), the processing flow of  FIG. 7  is ended. 
         [0090]    As described above, according to the present embodiment, in the wireless communication device  50 , the mode control unit  54  performs switching control that switches among the plurality of compression modes corresponding to the respective different amounts of feedback information on the basis of “communication quality.” The mode control unit  54  uses the “number of pieces of data for each range of numbers of times of retransmission” as an index of “communication quality.” 
         [0091]    The configuration of such a wireless communication device  50  can also provide effects similar to the effects of the first embodiment. 
       Third Embodiment 
       [0092]    In a third embodiment, “reception field strength” is used as an index of “communication quality.” Incidentally, main configurations of wireless communication devices according to the third embodiment are the same as the main configurations of the wireless communication devices  10  and  50  according to the first embodiment, and will therefore be described with reference to  FIGS. 2 and 3 . In addition, the wireless communication device on the transmitting side according to the third embodiment is not different from the wireless communication device on the transmitting side of the first embodiment, and therefore the following description will be made mainly of the wireless communication device on the receiving side. 
         [0093]    [Example of Configuration of Wireless Communication Device on Receiving Side] 
         [0094]    In the wireless communication device  50  according to the third embodiment, the communication quality obtaining unit  53  detects (or measures) reception field strength. The communication quality obtaining unit  53  then outputs the value of the measured reception field strength to the mode control unit  54 . 
         [0095]    The mode control unit  54  identifies a compression mode corresponding to the value of the reception field strength which value is received from the communication quality obtaining unit  53  on the basis of the received value of the reception field strength and “correspondence relations” between reception field strength ranges (corresponding to the above-described communication quality ranges) and the compression modes. In the “correspondence relations,” the U-mode is associated with a “high strength range” of highest reception field strength levels, the O-mode is associated with a “medium strength range” of next highest reception field strength levels, and the R-mode is associated with a “low strength range” of lowest reception field strength levels. 
         [0096]    Then, the mode control unit  54  generates a “mode notification” including information on the identified compression mode, and outputs the generated “mode notification” to the decompressing unit  61  and the transmission processing unit  55 . 
         [0097]    [Example of Operation of Wireless Communication System] 
         [0098]    Description will be made of an example of processing operation of a wireless communication system according to the third embodiment having the above configuration.  FIG. 8  is a diagram illustrating an example of processing operation of a wireless communication system according to the third embodiment.  FIG. 9  is a flowchart illustrating an example of processing operation of a wireless communication device on a receiving side according to the third embodiment. 
         [0099]    A PHY unit of the reception processing unit  52  outputs information on reception field strength to the communication quality obtaining unit  53  (step S 401 ). 
         [0100]    The communication quality obtaining unit  53  measures the reception field strength on the basis of the information on the reception field strength (step S 402 ). Then, the communication quality obtaining unit  53  outputs the value of the measured reception field strength to the mode control unit  54  (step S 403 ). 
         [0101]    The mode control unit  54  determines a usage compression mode on the basis of the value of the reception field strength which value is received from the communication quality obtaining unit  53  (step S 404 ). 
         [0102]    For example, as illustrated in  FIG. 9 , the mode control unit  54  determines in which of the “high strength range,” the “medium strength range,” and the “low strength range” the value of the reception field strength which value is received from the communication quality obtaining unit  53  falls (steps S 501  and S 502 ). 
         [0103]    When the value of the reception field strength falls in the “low strength range” (negative in step S 501  and negative in step S 502 ), the mode control unit  54  can determine that the usage compression mode may be switched to the R-mode. Then, the mode control unit  54  determines whether or not the present usage compression mode is the R-mode (step S 503 ). When the present usage compression mode is not the R-mode (negative in step S 503 ), the mode control unit  54  performs control that switches the usage compression mode to the R-mode (step S 504 ). That is, the mode control unit  54  generates a mode notification indicating the R-mode (step S 405 ), and sends out the generated mode notification to the decompressing unit  61  and the wireless communication device  10  (steps S 209  and S 210 ). Then, the decompressing unit  61  switches the usage compression mode to the R-mode (step S 211 ). The compressing unit  21  of the wireless communication device  10  similarly switches the usage compression mode to the R-mode. 
         [0104]    When the value of the reception field strength falls in the “medium strength range” (negative in step S 501  and affirmative in step S 502 ), the mode control unit  54  can determine that the usage compression mode may be switched to the O-mode. Then, the mode control unit  54  determines whether or not the present usage compression mode is the O-mode (step S 505 ). When the present usage compression mode is not the O-mode (negative in step S 505 ), the mode control unit  54  performs control that switches the usage compression mode to the O-mode (step S 506 ). That is, the mode control unit  54  generates a mode notification indicating the O-mode (step S 405 ), and sends out the generated mode notification to the decompressing unit  61  and the wireless communication device  10  (steps S 209  and S 210 ). Then, the decompressing unit  61  switches the usage compression mode to the O-mode (step S 211 ). The compressing unit  21  of the wireless communication device  10  similarly switches the usage compression mode to the O-mode. 
         [0105]    When the value of the reception field strength falls in the “high strength range” (affirmative in step S 501 ), the mode control unit  54  can determine that the usage compression mode may be switched to the U-mode. Then, the mode control unit  54  determines whether or not the present usage compression mode is the U-mode (step S 507 ). When the present usage compression mode is not the U-mode (negative in step S 507 ), the mode control unit  54  performs control that switches the usage compression mode to the U-mode (step S 508 ). That is, the mode control unit  54  generates a mode notification indicating the U-mode (step S 405 ), and sends out the generated mode notification to the decompressing unit  61  and the wireless communication device  10  (steps S 209  and S 210 ). Then, the decompressing unit  61  switches the usage compression mode to the U-mode (step S 211 ). The compressing unit  21  of the wireless communication device  10  similarly switches the usage compression mode to the U-mode. Incidentally, when the present usage compression mode is the R-mode (affirmative in step S 503 ), when the present usage compression mode is the O-mode (affirmative in step S 505 ), and when the present usage compression mode is the U-mode (affirmative in step S 507 ), the processing flow of  FIG. 9  is ended. 
         [0106]    As described above, according to the present embodiment, in the wireless communication device  50 , the mode control unit  54  performs switching control that switches among the plurality of compression modes corresponding to the respective different amounts of feedback information on the basis of “communication quality.” The mode control unit  54  uses “reception field strength” as an index of “communication quality.” 
         [0107]    The configuration of such a wireless communication device  50  can also provide effects similar to the effects of the first embodiment. 
       Other Embodiments 
       [0108]    The constituent elements of the units illustrated in the first to third embodiments do not necessarily need to be physically configured as illustrated in  FIGS. 1 to 9 . That is, specific forms of distribution and integration of the units are not limited to the forms illustrated in  FIGS. 1 to 9 , but the whole or a part of the units can be configured to be distributed or integrated functionally or physically in arbitrary units according to various kinds of loads, usage conditions, and the like. 
         [0109]    Further, the whole or an arbitrary part of various kinds of processing functions performed in the respective devices may be performed on a central processing unit (CPU) (or a microcomputer such as a micro processing unit (MPU) or a micro controller unit (MCU)). In addition, the whole or an arbitrary part of the various kinds of processing functions may be performed on a program analyzed and executed by the CPU (or the microcomputer such as the MPU or the MCU), or performed on hardware by wired logic. 
         [0110]    The wireless communication devices according to the first to third embodiments can be realized by the following hardware configuration, for example. 
         [0111]      FIG. 10  is a diagram illustrating an example of hardware configuration of a wireless communication device. As illustrated in  FIG. 10 , the wireless communication device  100  includes a processor  101 , a memory  102 , and a radio frequency (RF) circuit  103 . Each of the wireless communication devices  10  and  50  according to the first to third embodiments has the hardware configuration illustrated in  FIG. 10 . A CPU, a digital signal processor (DSP), a field programmable gate array (FPGA), or the like is cited as an example of the processor  101 . In addition, a random access memory (RAM) such as a synchronous dynamic random access memory (SDRAM), a read only memory (ROM), a flash memory, or the like is cited as an example of the memory  102 . 
         [0112]    Then, the various kinds of processing functions performed in the wireless communication devices according to the first to third embodiments may be implemented by executing, by a processor, programs stored in various kinds of memory such as a nonvolatile storage medium. That is, programs corresponding to respective pieces of processing performed by the transmission processing unit  11  and the reception processing unit  14  may be recorded in the memory  102 , and each program may be executed by the processor  101 . In addition, the wireless transmitting unit  12  and the wireless receiving unit  13  are realized by the RF circuit  103 . In addition, programs corresponding to respective pieces of processing performed by the reception processing unit  52 , the communication quality obtaining unit  53 , the mode control unit  54 , and the transmission processing unit  55  may be recorded in the memory  102 , and each program may be executed by the processor  101 . In addition, the wireless receiving unit  51  and the wireless transmitting unit  56  are realized by the RF circuit  103 . 
         [0113]    Incidentally, it is assumed in this case that the various kinds of processing functions performed in the wireless communication devices according to the first to third embodiments are performed by one processor  101 . However, the various kinds of processing functions performed in the wireless communication devices according to the first to third embodiments are not limited to this, but may be performed by a plurality of processors. 
         [0114]    All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although the embodiments of the present invention have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.