Abstract:
A signal transmitting/receiving method and apparatus freed of the drawback of the conventional information multiplexing method (FDMA, TDMA or CDMA) that information multiplexing needs a bandwidth broader than the bandwidth of the original information, such that, if the bandwidth is scanty, the number of channels that can be accommodated is decreased. A signal transmission device  10  sends three different items of the transmission information, namely the transmission information items T A , T B  and T C , from three transmitters  11   A   , 11   B  and  11   C , by multiplexing communication via three different paths P A , P B  and P C , using a transmission antenna unit  12.  A signal receiving device  20  receives the three different information items T A , T B  and T C , transmitted via three different paths P A , P B  and P C , by receivers  22   A   , 22   B   , 22   C , using a receiving antenna unit  21,  for obtaining three different items of the reception information, namely the reception information items R A , R B  and R C .

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a signal transmitting/receiving method and apparatus, applied with advantage to a portable telephone system, a cordless telephone system and an inside radio communication system. 
     2. Related Art 
     Since the bandwidth of radio communication is finite, attempts have so far been made for developing a radio system having high frequency utilization efficiency. For this reason, a multiplication technique of synthesizing plural different items of the information and transmitting the resulting multiplexed signal has become widely known. Among the multiplexing techniques, there are a frequency-division multiplexing access (FDMA) system, a time-division multiplexing access (TDMA) system and a code-division multiplexing access (CDMA) system. 
     The FDMA system is such a communication method in which each modulation wave modulates a separate sub-carrier wave having its frequency separated a certain width. That is, in FDMA, signals occupying non-overlapping frequency ranges are summed together. By using different frequency bands, two or more separate signals can be transmitted by one and the same transmission channel. A desired signal can be taken out by a filter. This multiplexing system is not in need of synchronization. 
     The TDMA is a communication system in which a transmission device uses the common channel intermittently and a channel is established in a specified receiver device by an automatic distribution function. Specifically, signals compressed to high-speed burst signals are arranged in specified time slots in such a manner as to evade temporal overlap. The desired signal is reproduced on extracting the time slots. The system is synchronized because timing reference is required. 
     The CDMA is a multiplexing communication method employing insignia (identifiable properties or codes) proper to the signals. Demultiplexing is by utilizing code correlation characteristics with previously known reference signals. The signals handled with this system are usually digital signals. 
     If, in the above-described FDMA, TDMA or CDMA, the information is multiplexed, there is needed a band broader than the bandwidth of the original signals. If it is attempted with these systems to transmit 4-channel signals, for example, with 32 kbps, a band of 32 kbps is required, thus leading to an extremely high transmission rate. 
     In the conventional practice, if it is attempted to transmit the information simultaneously within one and the same band from the same site to some other same site, the band needs to be enlarged as compared to the bandwidth of the original information. Thus, if the bandwidth is limited, the number of channels that can be accommodated is restricted. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide a signal transmission method and apparatus whereby multiplexing is realized using the same frequency without enlarging the information bandwidth for improving the frequency utilization efficiency for realization of a large-capacity radio communication system. 
     In one aspect, the present invention provides a signal transmission/reception device including a transmitting antenna having N directivities, N transmission means associated with the directivities of the transmission antenna, a receiving antenna having N directivities associated with the respective directivities of the transmitting antenna and N reception means associated with the directivities of the receiving antenna, wherein N different information items transmitted from the N transmission means via N different paths associated with the N directivities of the transmitting antenna are received via receiving antennas with the N directivities as multiplexed signals. With the signal transmission/reception device of the present invention, signal multiplexing can be realized with the same frequency without enlarging the information bandwidth for increasing the frequency utilization efficiency while realizing a large-capacity radio communication system. 
     In another aspect, the present invention provides a signal transmission/reception method wherein N different information items are transmitted via N different paths associated with N directivities of a transmission antenna and wherein the transmitted information is received as multiplexed signal by a receiving antenna having N directivities associated with N directivities of the transmission antenna. With the signal transmission/reception method of the present invention, signal multiplexing can be realized with the same frequency without enlarging the information bandwidth for increasing the frequency utilization efficiency while realizing a large-capacity radio communication system. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram showing a first embodiment of the signal transmission/reception device and method according to the present invention. 
     FIG. 2 illustrates the principle of the operation of the first embodiment of the signal transmission/reception system. 
     FIG. 3 illustrates, similarly to FIG. 2, the principle of the operation of the first embodiment of the signal transmission/reception system. 
     FIG. 4 is a schematic view showing a controller for mechanically rotating a receiving side antenna in the first embodiment. 
     FIG. 5 is a flowchart for illustrating the operation of the controller shown in FIG.  4 . 
     FIG. 6 is a schematic view of a controller for coping with two receiving side antennas. 
     FIG. 7 is a block diagram showing a second embodiment of the signal transmission/reception device and method according to the present invention. 
     FIG. 8 is a block diagram showing a third embodiment of the signal transmission/reception device and method according to the present invention. 
     FIG. 9 is a graph showing directivity characteristics of a receiving array antenna employed in the third embodiment. 
     FIGS. 10A and 10B illustrate a typical sequence of setting the array antenna directivity in the third embodiment. 
     FIGS. 11A,  11 B and  11 C illustrate another typical sequence of setting the array antenna directivity in the third embodiment. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring to the drawings, preferred embodiments of a signal transmission/reception device and method according to the present invention will be explained in detail. 
     The first embodiment, directed to a signal transmission/reception system for transmitting three different transmission information items from a given site to some other site by the same frequency, at the same time point and within one and the same band, is now explained. 
     Referring to FIG. 1, this signal transmission/reception system  1  includes a signal transmitting device  10  for multiplexed transmission of three different items of the transmission information T A , T B  and T C  from transmitters  11   A ,  11   B  and  11   C  over a transmission antenna  12  through three different paths P A , P B  and P C . The signal transmission/reception system also includes a signal reception device  20  for receiving the three multiplexed different items of the information transmitted through the three different paths P A , P B  and P C  by receivers  22   A ,  22   B  and  22   C  using a reception antenna  21  for producing three different items of the received information R A , R B  and R C . 
     The three items of the transmitted information T A , T B  and T C  are transmitted by electrical waves of the same frequency. If the transmission route is the same, these electrical waves interfere with one another, so that it is difficult to realize transmission with high signal quality. On the other hand, the multiplexed transmission by the above-mentioned FDMA, TDMA and CDMA is in need of a bandwidth broader than the original information bandwidth. 
     With this in view, the present signal reception system uses a multiplexing method which may be termed a path-division multiplexing method in which paths are independently different and different items of the information are carried on electric waves passing through the different paths. 
     A transmission antenna unit  12  of the signal transmission device  10  has three directive antennas  12   A ,  12   B  and  12   C  and hence has three different directivities. A receiving antenna unit  21  of the signal transmission device  20  also has three directive antennas  21   A ,  21   B  and  21   C  and hence has three different directivities. 
     The transmission side directive antennas  12   A ,  12   B  and  12   C  have directivities set in meeting with directive paths of the associated receiving directive antennas  21   A ,  21   B  and  21   C  respectively. The receiving directive antennas  21   A ,  21   B  and  21   C  suppress the intensity of the signals passing through the different paths to a sufficiently low level. 
     The principle of the path-division multiplexing method is now explained, with reference to FIGS. 2 and 3. In a portable telephone or a cordless telephone system, the electric waves arriving at the receiving antenna pass through plural paths, instead of through a sole path. 
     It is assumed, as an example, that three different paths P A , P B  and P C  are present in a room  30 . A receiving side non-directive antenna  32  receives a signal which is composed of three signals transmitted through three paths P A , P B  and P C  independent from a transmitting side non-directive antenna  31 , these three signals being overlapped together. 
     Thus, one set each of directive antennas are allocated at a transmission point  33  and at a reception point  34  to each of the three independent paths P A , P B  and P C  That is, a set of directive antennas is allocated to the path P A , while another set of directive antennas is allocated to the path P B  and a further set of directive antennas is allocated to the path P C  for transmitting respective independent information items, This secures an independent communication path for the antenna on the same site using the same frequency. 
     In the above-described first embodiment of the signal transmission/reception system  1 , one set each of directive antennas are allocated at the signal transmission device  10  and at the signal reception device  20  to each of the three independent paths P A , P B  and P C . That is, the directive antennas  12   A  and  21   A  are allocated to the path P A , while the directive antennas  12   B  and  21   B  are allocated to the path P B  and the directive antennas  12   C  and  21   C  are allocated to the path P C , for having different information items carried by the electric waves passing through three different paths for multiplex transmission of the three different information items using the same frequency. 
     Thus, with the present signal transmission/reception system  1 , the communication capacity can be increased without enlarging the frequency domain under suppression of interference. This increases the frequency utilization efficiency in proportion to the number of paths. 
     With the above-described signal transmission/reception system  1 , reception directivities of the reception side directive antennas  21   A ,  21   B  and  21   C  and those of the transmission side directive antennas  12   A ,  12   B  and  12   C  need to be set appropriately in the directions of the paths P A , P B  and P C  respectively. A sequence of setting the directivities at the communication start time is required, while haphazard directivity setting cannot lead to successful communications. 
     If an antenna of fixed directivity, such as Yagi antenna, is used, it is possible for the transmitting side to rotate an element in search of a proper direction of reception by the receiving side, which then is non-directive. Thus, with the present method, the direction of the transmission antenna directivity can be set first. It is not critical which side antenna directivity is to be set first. 
     In order for the directivities of the receiving side directive antennas  21   A ,  21   B  or  21   C  to follow up with changes in the paths P A , P B  or P C  relative to changes in the arriving directions, the receiving side directive antennas  21   A ,  21   B  and  21   C  can be rotated mechanically by a servo motor. 
     FIG. 4 shows a control device for mechanically rotating a directive antenna  35  by a sole servo motor  36 . In this control device, a reception signal Y(t) from the antenna  35  is fed to a reception power detecting circuit  37  for calculating a reception power detecting output y(t)=|Y(t)| 2 . A motor control pulse generating circuit  38  generates a motor control pulse C(t), based on the reception power detecting output y(t), for supplying the generated pulse to the servo motor  36 , which then is responsive to the motor control pulse C(t) to rotate the antenna  35  at a pre-set pitch towards left or right. 
     The motor control pulse generating circuit  38  constitutes a control circuit and controls the operation of the control device in accordance with the flowchart of FIG.  5 . First, at step S 1 , an initial value of the motor control pulse C is set to 1 (C=1). Then, at step S 2 , the motor control pulse is transmitted to the servo motor  36 . 
     The servo motor  36  then rotates the antenna  35  clockwise by one pitch. It is noted that clockwise rotation of the antenna occurs when the motor control pulse C(t) is +1, while counterclockwise rotation thereof occurs when the motor control pulse C(t) is −1. 
     On rotation of the antenna  35 , the motor control pulse generating circuit  38  judges whether or not the reception power detecting output y(t) as detected by the reception power detecting circuit  37  has been increased. If the reception power detecting output y(t) is found to have been increased, the motor control pulse generating circuit  38  at step S 4  updates the motor control pulse C. On the other hand, if the reception power detecting output y(t) cannot be found to have been increased, the motor control pulse generating circuit  38  at step S 5  increments the motor control pulse C by +1, for example, for controlling the rotation of the servo motor  36  to control the rotation of the servo motor  36  to rotate the antenna  35  by one pitch. The processing as from step S 2  to step S 5  then is repeated. 
     If there are plural, such as two, directive antennas, it suffices if a reception power detecting circuit  37 A or a reception power detecting circuit  37 B and a motor control pulse generating circuit  3   8 A or a motor control pulse generating circuit  38 B are provided for each set of the antenna  35 A or  35 B and the servo motor  36 A or  36 B, as shown for example in FIG.  6 . 
     As for directivity of the transmission antenna unit  12 , it suffices if, after setting the directivity of the receiving antenna unit  21 , the directivity antennas of the transmission antenna unit  12  are rotated under control by the control unit shown in FIG. 4 or  6  for maximizing the carrier to noise (C/N) ratio of each receiver. 
     Each of the three receivers  22   A ,  22   B  and  22   C  has a C/N measurement circuit. The results of comparison are compared by a C/N comparator circuit  23 . The signal transmission device  10  allocates the information in the order of the decreasing value of priority to the transmitters  11   A ,  11   B  and  11   C  in the order of the decreasing magnitude of the C/N ratio of the paths P A , P B  and P C . 
     The second embodiment is now explained. This second embodiment is directed to a signal transmission/reception system for transmitting three different parallel-converted information items from a given point to another given point with the same frequency, at the same time point and within the same area. 
     Referring to FIG. 7, this signal transmission/reception system  40  includes a signal transmission/reception device  45  for converting a given serially transmitted information item T D  by a serial/parallel converter  46  into three parallel signals for path-division multiplexing transmission from three transmitters  47   A ,  47   B  and  47   C  over three different paths P A , P B , P C  using the directivity antennas  48   A ,  48   B  and  48   C  of the transmitting antenna unit  48   C  respectively. The signal transmission/reception system  40  also includes a signal receiving unit  50  for receiving the three parallel transmitted information items, sent over the three different paths P A , P B , P C  by path-division multiplex transmission, with receivers  52   A ,  52   B  and  52   C  using directive antennas  51   A ,  51   B  and  51   C  of the reception antenna unit  51 , and converting the received information items by a parallel/serial converter  53  into a sole serial reception information item R D . 
     Similarly to those of the first embodiment, the transmission directive antennas  48   A ,  48   B  and  48   C  of the signal transmission/reception device  45  have directivities set in meeting with the directive paths of the reception detective antennas  51   A    51   B  and  51   C  of the associated signal receiving device  50 . The receiving side directive antennas  51   A ,  51   B  and  51   C  suppress the intensity of the signals passed through the different paths to a sufficiently small level. 
     Thus, with the present signal transmission/reception system  40 , a sole transmission information item T D  is first converted into three parallel information items which are then sent by path-division multiplexing transmission over three independent paths P A , P B  and P C . The receiving side then converts the three parallel information items into a sole serial information item R D . Thus, one-third bandwidth suffices for transmitting the information for the same information rate, while the information volume can be trebled for the same bandwidth. That is, with the present signal transmission/reception system  40 , the frequency utilization efficiency can be increased in proportion to the number of paths. 
     It should be noted that, with the present signal transmission/reception system  40 , transmission directivity of the directive antenna for transmission and reception directivity of the directive antenna for reception need to be appropriately set in the respective path directions. At the communication start time, the sequence of operation for setting the directivity is required which is similar to that of the first embodiment of the the signal transmission/reception system  1 . 
     In order for the receiving side directive antennas  51   A ,  51   B  and  51   C  to follow up with changes in the paths P A , P B  or P C  or changes in the arrival direction, these receiving side directive antennas  51   A ,  51   B  and  51   C  an also be mechanically rotated by a servo motor, as explained with reference to FIGS. 4 to  6 . 
     It should be noted that, after setting the directivity of the receiving antenna unit  51 , the directivity of the transmission antenna unit transmission antenna unit  48  can be set for maximizing the C/N ratio of each receiver by rotating the directive antennas of the transmission antenna unit transmission antenna unit  48  under control by the control unit analog signals shown in FIGS. 4 and 6. 
     The third embodiment is now explained. This third embodiment is directed to a signal transmission/reception system for transmitting two different information items with the same frequency at the same time point in one and the same area from a given point to another given point with the use of an array antenna in each of the transmission and reception sides. 
     The signal transmission/reception system  60  includes a signal transmission device  62  for path-division multiplex transmission of two different items of transmission information T A  and T B  from two transmitters  63   A ,  63   B  using a transmission array antenna  64  over two different paths P A  and P B , and a signal reception device  70  for receiving the two different items of transmission information T A  and T B  by path-division multiplex transmission over the two different paths P A  and P B  by receivers  76   A ,  76   B  using a receiving array antenna  71  for producing two different items of the received items of information R A  and R B . 
     The array antenna means such an antenna comprised of an array of plural sensor array elements and having the function of adaptively changing the directivity to the prevailing electric wave environment in which the antenna is put by adjusting gain coefficients afforded to each sensor array element. 
     A transmission array antenna  64  includes coefficient multipliers  66   1 ,  66   2 , . . . ,  66   n , for multiplying the transmission information T A  from the transmitter  63   A  with coefficients G A1 , G A2 , G An  and coefficient multipliers  67   1 ,  67   2 , . . . ,  67   n , for multiplying the transmission information T B  from the transmitter  63   B  with coefficients G B1 , G B2 , . . . , G Bn . The transmission array antenna  64  also includes adders  68   1 ,  68   2 , . . . ,  68   n  for summing together the results of multiplication obtained on multiplication with the coefficients by the coefficient multipliers  66   1    67   1 ,  66   2 ,  67   2 ,  66   n  and  67   n . The transmission array antenna  64  also includes sensor array elements  69   1 ,  69   2 , . . . ,  69   n  for multiplying the sum outputs of these adders  68   1 ,  68   2 , . . . ,  68   n  with the coefficients G A1 , G A2 , . . . , G An , to output the resulting outputs (one outputs) via path P A  to the reception array antenna  71  as electric waves, and for multiplying the sum outputs of these adders  68   1 ,  68   2 , . . . ,  68   n  with the coefficients G B1 , G B2 , . . . , G Bn  to output the resulting outputs (other outputs) via path P B  to the reception array antenna  71  as electric waves. 
     The reception array antenna  71  includes sensor array elements  72   1 ,  72   2 , . . . ,  72   n , for converting the transmission information T A  and the transmission information T B  transmitted via paths P B  and P A  and the electric waves concerning the information T A  and T B  into information signals, and coefficient multipliers  73   1 ,  73   2 , . . . ,  73   n  for multiplying n parallel outputs from the sensor array elements  72   1 ,  72   2 , . . . ,  72   n  with coefficients G A1 , G A2 , . . . , G An  The reception array antenna  71  also includes coefficient multipliers  74   1 ,  74   2 , . . . ,  74   n  for multiplying n parallel outputs with coefficients G B1 , G B2 , . . . , G Bn  and an adder  75   A  for synthesizing outputs of the coefficient multipliers  73   1 ,  73   2 , . . . ,  73   n  and an adder  75   B  for synthesizing outputs of the coefficient multipliers  74   1 ,  74   2 , . . . ,  74   n . 
     The array antenna  71  for reception adjusts the coefficients G A1 , G A2 , . . . , G An  so as to give directivity indicated by a solid line for the path P A . The array antenna  71  for reception also adjusts the coefficients G B1 , G B2 , . . . , G Bn  so as to give directivity indicated by a solid line for the path P B . The solid-line directivity for the path P A  has a null point for the path P B , while the broken-line directivity for the path P B  has a null point for the path P A , as shown in FIG.  9 . That is, the lobe need not be sharp for the opposite side paths since the directivity need only be sufficient to attenuate the signals of the opposite side paths to a sufficient amplitude. 
     The above coefficients G A1 , G A2 , . . . , G An  and the coefficients G B1 , G B2 , . . . , G Bn  are adjusted so that the array antenna for reception  71  will have directivity as indicated in FIG.  9 . 
     That is, the above coefficients G A1 , G A2 , . . . , G An  are adjusted so that the array antenna for reception  71  will have directivity as shown by a solid line for the path P A . The above coefficients G B1 , G B2 , . . . , G Bn  are adjusted so that the array antenna for reception  71  will have directivity as indicated by a broken line for the path P A . The solid-line directivity for the path P B  has a null point for the path P B , while the broken-line directivity for the path P B  has a null point for the path P A . That is, the lobe need not be sharp for the opposite side paths since the directivity need only be sufficient to attenuate the signals of the opposite side paths to a sufficient amplitude. 
     In the array antenna for reception  71 , if the input voltages from the sensor array elements  72   1 , . . . ,  72   n  are x Ai (t), an output voltage x Ai (t) output by the adder  75   A  is given by 
     
       
           y   A ( t )=Σ G   Ai   ×x   Ai ( t ) 
       
     
     where i denotes 1 to n. 
     On the other hand, if the input voltages from the sensor array elements  72   1 ,  72   2 , . . . ,  72   n  are x Bi (t), an output voltage y B (t) output by the adder  75   B  is given by 
     
       
           y   B ( t )=Σ G   Bi   ×x   Bi ( t ) 
       
     
     where i denotes 1 to n. 
     In the receiver  76   A , the reception information R A  is obtained from the output voltage y A (t), whereas, in the receiver  76   B , the reception information R B  is obtained from the output voltage y B (t) 
     It should be noted that the above coefficients are set for maximizing the C/N ratio of the signal of the required path and for minimizing the BER. At this time, the directivity is set for enlarging the gain in the arrival direction of the desired waves and for diminishing the gain in the direction of the arriving waves passing through a different path which will be smaller at the above-mentioned null point. 
     With the array antenna, a non-directive pattern can be produced using only a sole sensor array element. The sequence of operations for setting the transmission directivity and reception directivity appropriately for respective paths is carried out beginning from the directivity of the reception antenna because of the excessively large degree of freedom of the directive pattern. The reason is that it is not clear at the outset which pattern should be set in the transmission pattern, that is in which direction transmission should occur strongly and in which direction transmission should cease to occur. 
     In the case of the array antenna, a non-directive pattern can be produced using only a sole sensor array element. It is possible to transmit signals non-directively and to select several suitable directivities on the receiving side. Then it is sufficient if the directivity of the transmitting antenna is set properly for sending out the separate information in the directions of the respective paths. 
     Referring to FIG. 10, an illustrative example of setting the directivity of the transmission side and the reception side sets of the array antennas is explained. This method sets the transmission and reception antenna pairs so that these antenna pairs will have opposite directivities. 
     First, the directivity of the reception antenna is set. Referring to FIG. 10A, suitable coefficients G A1 , G A2 , . . . , G An  G B1 , G B2 , . . . , G Bn  are used in the coefficient multipliers  66   1 ,  66   2 , . . . ,  66   n ,  67   1 ,  67   2 , . . . ,  67   n  and a sole sensor array element  69  is used. 
     The sensor array element  72   n  accords suitable coefficients G A1 , G A2 , . . . , G An  by the coefficient multipliers  73   1 ,  73   2 , . . . ,  73   n  for matching the directivity to the optimum path P A  of the paths P B  and P A . 
     On the other hand, the sensor array element  72   n  accords suitable coefficients G B1 , G B2 , . . . , G Bn  by the coefficient multipliers  74   1 ,  74   2 , . . . ,  74   n  for matching the directivity to the optimum path P B  of the paths P B  and P A . This completes setting of the directivity of the reception antenna. 
     The directivity of the transmission antenna is then set as shown in FIG.  10 B. The directivity of the reception antenna is that previously set by the above sequence of operations. 
     The pre-set coefficients are accorded to the transmission antenna as coefficients and a training sequence is sent in order to find the C/N ratio of the reception output at this time. 
     Other coefficients are accorded to the transmission antenna as coefficients for similarly finding the C/N ratio of the reception output. This sequence of operations is repeated several times to select two coefficients which will give optimum C/N for setting the selected coefficients on the sensor array elements  69   n . 
     In order for the directivity of the array antenna for transmission array antenna  64  to be such directivity capable of securing sufficient C/N on the receiving side for each path, the error information such as BER or the C/N ratio on the receiving side needs to be fed back to the transmission side. 
     For controlling the array antenna directivity, a least mean square error (LMS) method, a constrained power minimization (CPM) method or a constant modulus algorithm (CMA) method, may be used. 
     Here, the LMS method is used, that is, a training sequence is sent as described above in order to find the C/N ratio of the reception output at this time. The training sequence is found as a time waveform as instantaneous voltage values. If the training sequence at this time is r(t), the receiving side controls the coefficients for minimizing the error ε(t), that is the mean square value of the difference ε(t)=y(t)−γ(t), where γ(t) denotes the training sequence and y(t) is an actual output. 
     As a method for setting directivities of the transmitting and receiving side antenna sets, there is an illustrative method which will be hereinafter explained with reference to FIG.  11 . FIG. 11 shows an instance in which the transmitting frequency is equal to the receiving frequency and transmission and reception occur alternately. 
     First, the transmitting side TX is set to be non-directive and the directivity of the receiving side RX has its directivity set by controlling its coefficients, as shown in FIG.  11 A. The transmission and reception are then interchanged, as shown in FIG.  11 B. The coefficients used for reception are used as coefficients for the transmitting side TX. Since the antenna used so far on the transmitting side is now changed over to the receiving side, its coefficients are found. The transmission and reception are then again interchanged, as shown in FIG. 11C, and the coefficients are used for the transmission side. 
     In the signal transmission reception system, according to the third embodiment, the transmitting information T A  and the transmitting information T B  entering the transmitters  63   A  and  63   B  may be the information converted in parallel during the preceding stage. Specifically, the transmitting information T A  and the transmitting information T B  are inherently the same serial information and are converted by the preceding stage serial/parallel converter into two parallel information items, namely the transmitting information T A  and the transmitting information T B , which are transmitted by the transmission array antenna  64  to the signal reception device  70  so as to be passed through the paths P A  and P B . The signal reception device  70  synthesizes the reception information R A  and the reception information R B  obtained by the receivers  76   A  and  76   B  by a parallel/serial converter of the succeeding stage to obtain a sole reception information item. 
     In this case, the frequency utilization efficiency can be improved in proportion to the number of paths, as in the signal transmission/reception system  40  described above. 
     The two receivers  76   A  and  76   B  each have a C/N ratio measurement circuit. The results of comparison by these circuits are compared by the C/N comparator circuit, The signal transmission device signal transmission device  62  allocates the information of higher order in transmission sequence to the transmitters  63   A  and  63   b  in the order of decreasing C/N ratio.