Abstract:
By switching to a method that allocates frequency diversity as an independent signal sequence during the time when an influence of fading is small, adaptively corresponding to an increase and decrease of fading, performs stable wireless communication, and frequency resources are effectively utilized. A wireless communication system selects and performs quadruple diversity which is composed of space diversity using two uncorrelated antennas and frequency diversity using two waves of frequencies f 1  and f 2  or double diversity of only the space diversity. A matching filter  211  evaluates that the influence of fading is small when all tap information from adaptive matched filters  207  to  210  indicates a value greater than or equal to a threshold, and while switching selector switches  104  and  215  and performing only the space diversity, transmitting and receiving independent two transmission data that is respectively modulated by modulators  102  and  103.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a wireless communication device, a wireless communication method, and a wireless communication system, and particularly to a wireless communication device, a wireless communication method, and a wireless communication system that are provided with frequency diversity and space diversity and perform diversity transmission and reception. 
       BACKGROUND ART 
       [0002]    A wireless communication system which is provided with frequency diversity and space diversity and performs diversity transmission and reception is known (for example, see Patent Literature 1 and Patent Literature 2). Patent Literature 1 discloses a configuration in which, in a wireless communication system that is provided with the frequency diversity and the space diversity, when a receiving side evaluates that the status (line quality) of radio wave propagation is favorable based on a received electric field, a diversity operation is suspended, frequency bands are efficiently used, and the amount of data is doubled. 
         [0003]    Further, Patent Literature 2 discloses a wireless communication device with a configuration in which, on the receiving side that receives wireless signals modulated to at least two frequencies which are different from each other and realizes the frequency diversity and the space diversity, the same number of pairs of receivers as the number of frequency are included corresponding to each frequency, reception levels of all the receivers are compared and the receiver with the greatest reception level is selected, and furthermore the receiver with the greatest reception level among the plurality of receivers which receive the same reception frequency as the receiver is selected. 
       CITATION LIST 
     Patent Literature 
     Patent Literature 1 
       [0000]    
       
         Japanese Unexamined Patent Application Publication No. 2005-277910 
       
     
       Patent Literature 2 
       [0000]    
       
         Japanese Unexamined Patent Application Publication No. 9-307490 
       
     
       SUMMARY OF INVENTION 
     Technical Problem 
       [0006]    However, in a wireless communication system and a wireless communication device provided with the frequency diversity and the space diversity which are&#39;disclosed in Patent Literature 1 and 2, a diversity order is determined so as to maintain the line quality at the time when fading is the most severest, however as there is fluctuation in the short cycle and long cycle (seasonal unit or the like) in the fading, the determined diversity order may be excessive during the time when the influence of fading is small. 
         [0007]    Further, Patent Literature 2 discloses a wireless communication system that efficiently uses frequency bands, and doubles the amount of data when the radio wave propagation characteristics are favorable, however when the radio wave propagation characteristics are favorable, the diversity operation is suspended, thus it is necessary to repeat suspending and resuming the diversity operation for the fading that fluctuates in the short cycle, and there is a possibility that stable communication cannot be performed. 
         [0008]    The present invention is made in light of the above points, and aims to provide a wireless communication device, a wireless communication method, and a wireless communication system that, by switching to a method to allocate the frequency diversity as an independent signal sequence during the time when the influence of fading is small, adaptively correspond to an increase and decrease of fading to perform stable wireless communication, and effectively utilizes frequency resources. 
       Solution to Problem 
       [0009]    In order to achieve the abovementioned purpose, a wireless communication device according to the present invention includes a first wireless communication means by frequency diversity, a second wireless communication means by space diversity, a monitoring means that monitors radio propagation status and evaluates whether an influence of fading is large or not according to a reception signal, and a switching means that performs wireless communication by quadruple diversity which transmits and receives one transmission data by the first and the second wireless communications means in a period which is evaluated by the monitoring means that the influence of fading is large and performs wireless communication by double diversity which transmits and receives plurality of transmission data separately by the second wireless in a period which is evaluated by the monitoring means that the influence of the fading is small. 
         [0010]    Further, in order to achieve the abovementioned purpose, a wireless communication method according to the present invention includes performing first wireless communication by frequency diversity, performing second wireless communication by space diversity, monitoring radio propagation status and evaluating whether an influence of fading is large or not according to a reception signal, performing wireless communication by quadruple diversity which transmits and receives one transmission data by the first and the second wireless communications means in a period which is evaluated by the monitoring that the influence of fading is large and performing wireless communication by double diversity which transmits and receives plurality of transmission data separately by the second wireless communication means in a period which is evaluated by the monitoring that the influence of the fading is small. 
         [0011]    Furthermore, in order to achieve the abovementioned purpose, a wireless communication system according to the present invention for performing wireless communication between opposing wireless communication devices, in which each of the opposing wireless communication devices includes a first wireless communication means by frequency diversity, a second wireless communication means by space diversity, a monitoring means that monitors radio propagation status and evaluates whether an influence of fading is large or not according to a reception signal, and a switching means that performs wireless communication by quadruple diversity which transmits and receives one transmission data by the first and the second wireless communications means in a period which is evaluated by the monitoring means that the influence of fading is large and performs wireless communication by double diversity which transmits and receives plurality of transmission data separately by the second wireless communication means in a period which is evaluated by the monitoring means that the influence of the fading is small. 
       Advantageous Effects of Invention 
       [0012]    According to the present invention, when performing wireless communication by the frequency diversity and the space diversity, in the period when the influence of fading is large, the state is maintained in which the communication by both the frequency diversity and the space diversity is possible, and in the period when the influence of fading is small, while maintaining the state in which the communication only by the space diversity is possible, by increasing communication capacity for the amount not performing the frequency diversity, the frequency resources are effectively utilized, so that efficient communication can be stably performed. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0013]      FIG. 1  is a block diagram of one embodiment of a wireless communication device, a wireless communication method, and a wireless communication system according to the present invention; 
           [0014]      FIG. 2  is block diagram of an example of an adaptive matched filter; 
           [0015]      FIG. 3  is a block diagram of an important part of the wireless communication system of  FIG. 1  in a period when the influence of fading is large; and 
           [0016]      FIG. 4  is a block diagram of the important part of the wireless communication system of  FIG. 1  in a period when the influence of fading is small. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0017]    Next, exemplary embodiments of the present invention are described with reference to the drawings. 
         [0018]      FIG. 1  shows a block diagram of one embodiment of a wireless communication device, a wireless communication system, and a wireless communication system according to the present invention. The wireless communication system of this exemplary embodiment is composed of two opposing wireless communication devices, and for convenience,  FIG. 1  shows a wireless transmission device  100  in one of the wireless communication device and a wireless reception device  200  in the other wireless communication device. In one of the wireless communication device, a wireless reception device with the same configuration as the wireless reception device  200  is provided, and similarly in the other wireless communication device, a wireless transmission device with the same configuration as the wireless communication device  100  is provided. 
         [0019]    The wireless transmission device and the wireless reception device in the same wireless communication device may be connected to a circulator for separating transmission and reception, and two antennas  109  and  110 , and  201  and  202  may be shared for transmission and reception. The wireless communication system of this exemplary embodiment is a configuration example that selects and performs quadruple diversity composed of space diversity using two uncorrelated antennas and frequency diversity using two waves of frequencies f 1  and f 2 , or double diversity composed of only the space diversity. 
         [0020]    The wireless transmission device  100  includes a transmission interface  101 , modulators (MOD:Modulator)  102  and  103 , a selector switch  104 , and transmitters (TX)  105  and  106 , power amplifiers (HPA:High Power Amplifier)  107  and  108 , and antennas (antennas)  109  and  110 . The selector switch  104  selects one of each output signal of the modulators  102  and  103 , and inputs it into the transmitter  106 . 
         [0021]    On the other hand, the wireless reception device  200  includes antennas (antennas)  201  and  202 , receivers (RX)  203  to  205 , adaptive matched filters (AMF:Adaptive Matched Filter)  207  to  210 , a matching filter  211 , adders  212  to  214 , a selector switch  215 , demodulators (DEM:Demodulator)  216  and  217 , and a reception interface  218 . The adder  212  adds signals output from the adaptive matched filters  207  and  209 . The adder  213  adds signals output from the adaptive matched filters  208  and  210 . The selector switch  215  outputs the signal output from the adder  213  to the adder  214  or the demodulator  217 . 
         [0022]    The adaptive matched filters  207  to  210  are known adaptive filters which respectively estimate a time-varying transmission path impulse, convolve time-reversal complex conjugate of its impulse response with a reception signal, and perform S/N maximum ratio combining, and are usually considered as the configuration of the transversal filter. 
         [0023]      FIG. 2  shows a block diagram of an example of the adaptive matched filter. As shown in the drawing, the adaptive matched filter has a configuration including delay elements  301  and  302  which respectively delay an input signal by time τ and are cascaded, correlators  303 ,  305 , and  307  which calculate correlation between a signal at each tap (R 1 , R 2 , and R 3 ) and a demodulation signal, and outputs them as tap coefficients (wa, wb, and wc), multiplication circuits  304 ,  306 , and  308  which multiply the signal at each tap and the tap coefficient, a combiner  309  which combines each output signal of the multiplication circuits  304 ,  306 , and  308 , and a tap detection unit  310 . 
         [0024]    The time delay τ of the delay elements  301  and  302  is set to ½ of a symbol period T, for example. The correlators  303 ,  305 , and  307  respectively perform correlation operation between the signal at each tap R 1 , R 2 , and R 2  and the demodulation signal demodulated by the demodulators  216  and  217 , and supply their operation results to the multiplication circuits  304 ,  306 , and  308  as the tap coefficients wa, wb, and wc. When the values of the tap coefficients wa, wb, and wc are large, it indicates that the correlation with the demodulation signal is high. 
         [0025]    Note that in  FIG. 1 , the demodulation signal from the demodulator  216  is input to the adaptive matched filters  207  and  209 , to which a signal obtained by converting the reception signal of the frequency f 1  into a predetermined frequency is input, and the demodulation signal from the demodulator  217  is input to the adaptive matched filters  208  and  210 , to which a signal obtained by converting the reception signal of the frequency f 2  into a predetermined frequency is input. However, the demodulation signal from the demodulator  216  is input to all the adaptive matched filters  207  to  210  at the time of operation of the quadruple diversity described later. 
         [0026]    The multiplication circuits  304 ,  306 , and  308  multiply the signal at each tap R 1 , R 2 , and R 2  respectively by the tap coefficients wa, wb, and wc, and generate signals made by weighting the tap coefficients wa, wb, and wc on the signal at each tap R 1 , R 2 , and R 3 . The combiner  309  combines the signal output from the multiplication circuits  304 ,  306  and  308 , and outputs it to the subsequent stage of the adder  212  or  213 . Further, the tap detection unit  310  compares the tap coefficients wa, wb, and wc, and outputs, for example, the maximum tap coefficient to the matching filter  211  of  FIG. 1  as tap information W. 
         [0027]    Next, an operation of this exemplary embodiment shown in  FIG. 1  is explained. The transmission interface  101  supplies the input transmission data respectively to the modulators  102  and  103 . The modulator  102  modulates input first transmission data by the predetermined modulation technique, and supplies the obtained first modulated signal to the transmitter  105  and a first input terminal of the selector switch  104 . The modulator  103  modulates input second transmission data by the same predetermined modulation technique as the modulator  102 , and supplies the obtained second modulated signal to the transmitter  104  and a second input terminal of the selector switch  104 . 
         [0028]    The selector switch  104  is switched according to whether the fading is large or not, selects the first modulated signal or the second modulated signal, and supplies it to the transmitter  106 . The transmitter  105  frequency-converts the input first modulated signal into a first transmission signal having the frequency f 1  within a high frequency band such as a microwave band, and supplies the generated first transmission signal to the power amplifier  107 . On the other hand, the transmitter  106  frequency-converts the input first or the second modulated signal into a second transmission signal having the frequency f 2  within a high frequency band such as a microwave band, and supplies the generated second transmission signal to the power amplifier  108 . 
         [0029]    The power amplifier  107  amplifies the power of the input first transmission signal to a required level, and then transmits it to space from the antenna  109 . Similarly, the power amplifier  108  amplifies the power of the input second signal to the required level, and then transmits it to space from the antenna  120 . The transmission signals of two waves transmitted from the antennas  109  and  110 , respectively propagate two different propagation paths, and received by two antennas  201  and  202  of the wireless reception device, which are placed to be spatially uncorrelated. 
         [0030]    The signal received by the antenna  201  is split into the frequencies f 1  and f 2 , the reception signal of the frequency f 1  is supplied to the receiver  203 , and the reception signal of the frequency f 2  is supplied to the receiver  204 . Similarly, the signal received by the antenna  202  is split into the frequencies f 1  and f 2 , the reception signal of the frequency f 1  is supplied to the receiver  205 , and the reception signal of the frequency f 2  is supplied to the receiver  206 . 
         [0031]    While respectively amplifying the input reception signal, the receivers  203 ,  204 ,  205 , and  206  frequency-convert the reception signals into signals of the same predetermined frequency band (for example, an intermediate frequency signal of an intermediate frequency band), and then supply them to the adaptive matching filters  207 ,  208 ,  209 , and  210  which are provided correspondingly. While respectively performing S/N maximum ratio combining to the input signals by the known adaptive matching filtering process, which is explained along with  FIG. 2 , the adaptive matched filters  207 ,  208 ,  209 , and  210  supply tap information W 1 , W 2 , W 3 , and W 4 , which is maximum values of the tap coefficients among the used tap coefficients to the matching filter  211 . 
         [0032]    The adder  212  adds the signals which are obtained by performing the S/N maximum ratio combining by the adaptive matching filter  207  and  209  to the reception signals of the same frequency f 1 , which are received by different antennas  201  and  202 . Further, the adder  213  adds the signals which are obtained by performing the S/N maximum ratio combining by the adaptive matching filter  208  and  210  to the reception signals of the same frequency f 2 , which are received by different antennas  201  and  202 . 
         [0033]    The adder  214  outputs only a first addition signal output from the adder  212 , or when the second addition signal from the adder  213  is input via the selector switch  215 , generates and outputs a third addition signal, which is obtained by adding a second addition signal to the first addition signal. 
         [0034]    While demodulating the first addition signal or the third addition signal supplied from the adder  214  and supplying the demodulation signal to the reception interface  218 , the demodulator  216  supplies it to the adaptive matching filters  207  and  209  or the adaptive matching filters  207  to  210 . While demodulating the second addition signal input via the selector switch  215  and supplying the demodulation signal to the reception interface  218 , the demodulator  217  supplies it to the adaptive matching filters  208  and  210 . The reception interface  218  receives the first demodulation signal output from the demodulator  216 , and the second demodulation signal output from the demodulator  217  as input signals, and combines and outputs them. Note that when only the first demodulation signal is input, the reception interface  218  outputs only the first demodulation signal. 
         [0035]    Here, in this exemplary embodiment, switching the diversity order is automatically performed by monitoring radio propagation status. Specifically, in this exemplary embodiment, the tap information W 1  to W 4  input from the adaptive matched filters  207  to  210  is monitored by the matching filter  211 , whether the influence of fading is small or not is evaluated according to whether the tap information W 1  to W 4  is greater than or equal to a previously specified predetermined threshold or not, and an operation is performed by the quadruple diversity or double diversity. 
         [0036]    Firstly, in the period which is evaluated that the value of one or more tap information among four pieces of the tap information W 1  to W 4 , which are input from the AMPs  207  to  210 , indicates a value less than the previously specified predetermined threshold by the matching filter  211 , it is evaluated that the influence of fading is large, and the matching filter  211  controls the selector switch  215  to supply the second addition signal from the adder  213  to the adder  214 . 
         [0037]    Similarly, the wireless reception device with the same configuration as the wireless reception device  200  which is not shown and provided in the same wireless communication device as the wireless transmission device  100  receives two waves of transmission signals of frequencies f 3  and f 4  from the wireless transmission device with the same configuration as the wireless transmission device  100  provided in the same wireless communication device as the wireless reception device  200 , and by the similar operation as the wireless reception device  200 , when evaluating that it is the period when the influence of fading is large, controls the selector switch  104  to supply the first modulated signal from the modulator  102  to the transmitter  106 . 
         [0038]    Accordingly, when it is evaluated that is the period when the influence of fading is large, as shown in  FIG. 3 , since in the wireless transmission device  100 , the first modulated signal from the modulator  102  to be supplied to the transmitter  105  is selected by the selector switch  104  and supplied also to the transmitter  106 , the modulator  103  will not be used. Moreover, in the wireless reception device  200 , as shown in  FIG. 3 , the second addition signal from the adder  213  is selected by the selector switch  215  and supplied to the adder  214 , thus the demodulator  217  will not be used. Therefore, when it is evaluated that it is the period when the influence of fading is large, communication by the quadruple diversity is performed to maintain line quality. 
         [0039]    In this case, in the wireless transmission device  100 , the transmission interface  101  supplies transmission data which should be transmitted only to the modulator  102 . The modulated signals, which are the transmission data output from the modulator  201  and modulated, are respectively amplified and frequency-converted into the transmission signals of the wireless frequencies f 1  and f 2  by the transmitters  105  and  106 . Then, the transmission signals are transmitted from the antennas  109  and  110  via the power amplifiers  107  and  108 . The transmission signals of these two waves respectively propagate two different propagation paths, and are received by the antennas  201  and  202  of the wireless reception device  200 . 
         [0040]    In the wireless reception device  200 , as mentioned above, the reception signals of the frequency f 1  received by the antennas  201  and  202  are supplied to the adder  212  via the receivers  203  and  205  and the adaptive matched filters  207  and  209 , and will be the first addition signal of the predetermined frequency band. Further, the reception signal of the frequency f 2  is supplied to the adder  213  via the receivers  204  and  206  and the adaptive matched filters  208  and  210 , and will be the second addition signal of the same predetermined frequency band as above. 
         [0041]    As shown in  FIG. 3 , after these first and second addition signals are added by the adder  214  to be the third addition signal, it is supplied to the demodulator  216 . The third addition signal is a signal generated from two waves of the reception signals received by the antenna  201  and two waves of the reception signals received by the antenna  202 , and is a signal made by diversity combining four waves of the reception signals. The demodulator  216  demodulates the third addition signal, which is a signal made by diversity combining these four waves of the reception signals. When it is evaluated that the influence of fading is large in this way, communication by the quadruple diversity is performed in order to maintain the line quality. 
         [0042]    On the other hand, in the period when all the values of four pieces of the tap information W 1  to W 4  that are input from the adaptive matching filters  207  to  210  indicates greater than or equal to a previously specified predetermined threshold, it is evaluated that the influence of fading is small by the matching filter  211 , and the matching filter  211  controls the selector switch  215  to supply the second addition signal from the adder  213  to supply to the demodulator  217 . 
         [0043]    Similarly, the wireless reception device with the same configuration as the wireless reception device  200  which is not shown and provided in the same wireless communication device as the wireless transmission device  100  receives two waves of the transmission signals of the frequencies f 3  and f 4  from the wireless transmission device with the same configuration as the wireless transmission device  100  provided in the same wireless communication device as the wireless reception device  200 , and by the similar operation as the wireless reception device  200 , when evaluating that it is the period when the influence of fading is small, controls the selector switch  104  to supply the second modulated signal from the modulator  103  to the transmitter  106 . 
         [0044]    Accordingly, when it is evaluated that it is the period when the influence of fading is small, as shown in  FIG. 4 , in the wireless transmission device  100 , the second modulated signal from the modulator  103  is selected by the selector switch  104  and supplied to the transmitter  106 . Further, in the wireless reception device  200 , as shown in  FIG. 4 , the second addition signal from the adder  213  is selected by the selector switch  215  and supplied to the demodulator  217 , and the addition operation in the adder  214  will not be performed. Therefore, when evaluating that it is the period when the influence of fading is small, it is evaluated that it is the period when there is no influence of the line quality even when the diversity order is reduced, and communication by the double diversity is performed. At this time, the two waves of frequencies are used for transmission of separate data, and the transmission capacity is doubled. 
         [0045]    In this case, in the wireless transmission device  100 , the transmission interface  101  supplies the first transmission data, which is to be transmitted, to the modulator  102 , and supplies the second transmission data, which is to be transmitted, to the modulator  103 . The first and second modulated signals, which are output from the modulators  102  and  103  and modulated, are respectively amplified and frequency-converted into the transmission signals of the wireless frequencies f 1  and f 2  by the transmitters  105  and  106 . Then, the transmission signals are transmitted to space from the antennas  109  and  110  via the power amplifiers  107  and  108 . The transmission signals of these two waves respectively propagate two different propagation paths, and are received by the antennas  201  and  202  of the wireless reception device  200 . 
         [0046]    In the wireless reception device  200 , as mentioned above, the reception signal of the frequency f 1  received by the antennas  201  and  202  is supplied to the adder  212  via the receivers  203  and  205  and the adaptive matched filters  207  and  209 , and will be the first addition signal of the predetermined frequency band. Further, the reception signal of the frequency f 2  is supplied to the adder  213  via the receivers  204  and  206  and the adaptive matched filters  208  and  210 , and will be the second addition signal of the same predetermined frequency band as above. 
         [0047]    Among these first and second addition signals, as shown in  FIG. 4 , the first addition signal is supplied to the demodulator  216  via the adder  214 , and the first transmission data is demodulated. As shown in  FIG. 4 , the second addition signal is supplied to the demodulator  217  by the selector switch  215 , and the second transmission data is demodulated. 
         [0048]    As described above, when evaluating that it is the period when the influence of fading is small, according to the wireless communication system of this exemplary embodiment, double diversity communication is performed by separate space diversity in two paths between the modulator  102  and the demodulator  216 , and between the modulator  103  and the demodulator  217 , thus the transmission capacity can be doubled than at the time of the quadruple diversity communication. 
         [0049]    Although the present invention is explained with reference to the exemplary embodiments, the present invention is not limited by above. Various modification understood by a person skilled in the art within the scope of the invention can be made to the configuration and details of the present invention. 
         [0050]    The present application claims priority rights of and is based on Japanese Patent Application No. 2009-035988 filed on Feb. 19, 2009 in the Japanese Patent Office, the entire contents of which are hereby incorporated by reference. 
       REFERENCE SIGNS LIST 
       [0000]    
       
           100  WIRELESS TRANSMISSION DEVICE 
           101  TRANSMISSION INTERFACE 
           102  and  103  MODULATOR (MOD) 
           104  and  215  SELECTOR SWITCH 
           105  and  106  TRANSMITTER (TX) 
           107  and  108  POWER AMPLIFIER (NPA) 
           109 ,  110 ,  201 , and  202  ANTENNA 
           200  WIRELESS RECEPTION DEVICE 
           203  to  206  RECEIVER (RX) 
           207  to  210  ADAPTIVE MATCHED FILTER (AMF) 
           211  MATCHING FILTER 
           212  to  214  ADDER 
           216  and  217  DEMODULATOR (DEM) 
           218  RECEPTION INTERFACE 
           301  and  302  DELAY ELEMENT 
           303 ,  305 , and  307  CORRELATOR 
           304 ,  306 , and  308  MULTIPLICATION CIRCUIT 
           309  COMBINER 
           310  TAP DETECTION UNIT