Signal receiving apparatus and method

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.sub.A, T.sub.B and T.sub.C, from three transmitters 11.sub.A, 11.sub.B and 11.sub.C, by multiplexing communication via three different paths P.sub.A, P.sub.B and P.sub.C, using a transmission antenna unit 12. A signal receiving device 20 receives the three different information items T.sub.A, T.sub.B and T.sub.C, transmitted via three different paths P.sub.A, P.sub.B and P.sub.C, by receivers 22.sub.A, 22.sub.B, 22.sub.C, using a receiving antenna unit 21, for obtaining three different items of the reception information, namely the reception information items R.sub.A, R.sub.B and R.sub.C.

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.

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.sub.A, T.sub.B and
 T.sub.C from transmitters 11.sub.A, 11.sub.B and 11.sub.C over a
 transmission antenna 12 through three different paths P.sub.A, P.sub.B and
 P.sub.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.sub.A,
 P.sub.B and P.sub.C by receivers 22.sub.A, 22.sub.B and 22.sub.C using a
 reception antenna 21 for producing three different items of the received
 information R.sub.A, R.sub.B and R.sub.C.
 The three items of the transmitted information T.sub.A, T.sub.B and T.sub.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.sub.A, 12.sub.B and 12.sub.C and hence has
 three different directivities. A receiving antenna unit 21 of the signal
 transmission device 20 also has three directive antennas 21.sub.A,
 21.sub.B and 21.sub.C and hence has three different directivities.
 The transmission side directive antennas 12.sub.A, 12.sub.B and 12.sub.C
 have directivities set in meeting with directive paths of the associated
 receiving directive antennas 21.sub.A, 21.sub.B and 21.sub.C respectively.
 The receiving directive antennas 21.sub.A, 21.sub.B and 21.sub.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.sub.A, P.sub.B
 and P.sub.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.sub.A, P.sub.B and P.sub.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.sub.A, P.sub.B and P.sub.C That is, a set of directive antennas is
 allocated to the path P.sub.A, while another set of directive antennas is
 allocated to the path P.sub.B and a further set of directive antennas is
 allocated to the path P.sub.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.sub.A, P.sub.B and
 P.sub.C. That is, the directive antennas 12.sub.A and 21.sub.A are
 allocated to the path P.sub.A, while the directive antennas 12.sub.B and
 21.sub.B are allocated to the path P.sub.B and the directive antennas
 12.sub.C and 21.sub.C are allocated to the path P.sub.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.sub.A, 21.sub.B
 and 21.sub.C and those of the transmission side directive antennas
 12.sub.A, 12.sub.B and 12.sub.C need to be set appropriately in the
 directions of the paths P.sub.A, P.sub.B and P.sub.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.sub.A, 21.sub.B or 21.sub.C to follow up with changes in the paths
 P.sub.A, P.sub.B or P.sub.C relative to changes in the arriving
 directions, the receiving side directive antennas 21.sub.A, 21.sub.B and
 21.sub.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)=.vertline.Y(t).vertline..sup.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 S1, an initial value of the motor
 control pulse C is set to 1 (C=1). Then, at step S2, 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 S4
 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 S5 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 S2 to step S5 then is
 repeated.
 If there are plural, such as two, directive antennas, it suffices if a
 reception power detecting circuit 37A or a reception power detecting
 circuit 37B and a motor control pulse generating circuit 38A or a motor
 control pulse generating circuit 38B are provided for each set of the
 antenna 35A or 35B and the servo motor 36A or 36B, 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.sub.A, 22.sub.B and 22.sub.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.sub.A, 11.sub.B and 11.sub.C in the order of the
 decreasing magnitude of the C/N ratio of the paths P.sub.A, P.sub.B and
 P.sub.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.sub.D by a serial/parallel converter 46
 into three parallel signals for path-division multiplexing transmission
 from three transmitters 47.sub.A, 47.sub.B and 47.sub.C over three
 different paths P.sub.A, P.sub.B, P.sub.C using the directivity antennas
 48.sub.A, 48.sub.B and 48.sub.C of the transmitting antenna unit 48.sub.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.sub.A, P.sub.B,
 P.sub.C by path-division multiplex transmission, with receivers 52.sub.A,
 52.sub.B and 52.sub.C using directive antennas 51.sub.A, 51.sub.B and
 51.sub.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.sub.D.
 Similarly to those of the first embodiment, the transmission directive
 antennas 48.sub.A, 48.sub.B and 48.sub.C of the signal
 transmission/reception device 45 have directivities set in meeting with
 the directive paths of the reception detective antennas 51.sub.A 51.sub.B
 and 51.sub.C of the associated signal receiving device 50. The receiving
 side directive antennas 51.sub.A, 51.sub.B and 51.sub.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.sub.D is first converted into three
 parallel information items which are then sent by path-division
 multiplexing transmission over three independent paths P.sub.A, P.sub.B
 and P.sub.C. The receiving side then converts the three parallel
 information items into a sole serial information item R.sub.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.sub.A, 51.sub.B and
 51.sub.C to follow up with changes in the paths P.sub.A, P.sub.B or
 P.sub.C or changes in the arrival direction, these receiving side
 directive antennas 51.sub.A, 51.sub.B and 51.sub.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.sub.A and T.sub.B from two transmitters
 63.sub.A, 63.sub.B using a transmission array antenna 64 over two
 different paths P.sub.A and P.sub.B, and a signal reception device 70 for
 receiving the two different items of transmission information T.sub.A and
 T.sub.B by path-division multiplex transmission over the two different
 paths P.sub.A and P.sub.B by receivers 76.sub.A, 76.sub.B using a
 receiving array antenna 71 for producing two different items of the
 received items of information R.sub.A and R.sub.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.sub.1,
 66.sub.2, . . . , 66n, for multiplying the transmission information
 T.sub.A from the transmitter 63.sub.A with coefficients G.sub.A1,
 G.sub.A2, G.sub.An and coefficient multipliers 67.sub.1, 67.sub.2, . . . ,
 67n, for multiplying the transmission information T.sub.B from the
 transmitter 63.sub.B with coefficients G.sub.B1, G.sub.B2, . . . ,
 G.sub.Bn. The transmission array antenna 64 also includes adders 68.sub.1,
 68.sub.2, . . . , 68.sub.n for summing together the results of
 multiplication obtained on multiplication with the coefficients by the
 coefficient multipliers 66.sub.1 67.sub.1, 66.sub.2, 67.sub.2, 66.sub.n
 and 67.sub.n. The transmission array antenna 64 also includes sensor array
 elements 69.sub.1, 69.sub.2, . . . , 69.sub.n for multiplying the sum
 outputs of these adders 68.sub.1, 68.sub.2, . . . , 68.sub.n with the
 coefficients G.sub.A1, G.sub.A2, . . . , G.sub.An, to output the resulting
 outputs (one outputs) via path P.sub.A to the reception array antenna 71
 as electric waves, and for multiplying the sum outputs of these adders
 68.sub.1, 68.sub.2, . . . , 68n with the coefficients G.sub.B1, G.sub.B2,
 . . . , G.sub.Bn to output the resulting outputs (other outputs) via path
 P.sub.B to the reception array antenna 71 as electric waves.
 The reception array antenna 71 includes sensor array elements 72.sub.1,
 72.sub.2, . . . , 72.sub.n, for converting the transmission information
 T.sub.A and the transmission information T.sub.B transmitted via paths
 P.sub.B and P.sub.A and the electric waves concerning the information
 T.sub.A and T.sub.B into information signals, and coefficient multipliers
 73.sub.1, 73.sub.2, . . . , 73.sub.n for multiplying n parallel outputs
 from the sensor array elements 72.sub.1, 72.sub.2, . . . , 72.sub.n with
 coefficients G.sub.A1, G.sub.A2, . . . , G.sub.An The reception array
 antenna 71 also includes coefficient multipliers 74.sub.1, 74.sub.2, . . .
 , 74.sub.n for multiplying n parallel outputs with coefficients G.sub.B1,
 G.sub.B2, . . . , G.sub.Bn and an adder 75.sub.A for synthesizing outputs
 of the coefficient multipliers 73.sub.1, 73.sub.2, . . . , 73.sub.n and an
 adder 75.sub.B for synthesizing outputs of the coefficient multipliers
 74.sub.1, 74.sub.2, . . . , 74.sub.n.
 The array antenna 71 for reception adjusts the coefficients G.sub.A1,
 G.sub.A2, . . . , G.sub.An so as to give directivity indicated by a solid
 line for the path P.sub.A. The array antenna 71 for reception also adjusts
 the coefficients G.sub.B1, G.sub.B2, . . . , G.sub.Bn so as to give
 directivity indicated by a solid line for the path P.sub.B. The solid-line
 directivity for the path P.sub.A has a null point for the path P.sub.B,
 while the broken-line directivity for the path P.sub.B has a null point
 for the path P.sub.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.sub.A1, G.sub.A2, . . . , G.sub.An and the
 coefficients G.sub.B1, G.sub.B2, . . . , G.sub.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.sub.A1, G.sub.A2, . . . , G.sub.An are
 adjusted so that the array antenna for reception 71 will have directivity
 as shown by a solid line for the path P.sub.A. The above coefficients
 G.sub.B1, G.sub.B2, . . . , G.sub.Bn are adjusted so that the array
 antenna for reception 71 will have directivity as indicated by a broken
 line for the path P.sub.A. The solid-line directivity for the path P.sub.B
 has a null point for the path P.sub.B, while the broken-line directivity
 for the path P.sub.B has a null point for the path P.sub.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.sub.1, . . . , 72.sub.n are x.sub.Ai (t), an
 output voltage x.sub.Ai (t) output by the adder 75.sub.A is given by
EQU y.sub.A (t)=.SIGMA.G.sub.Ai.times.x.sub.Ai (t)
 where i denotes 1 to n.
 On the other hand, if the input voltages from the sensor array elements
 72.sub.1, 72.sub.2, . . . , 72.sub.n are x.sub.Bi (t), an output voltage
 y.sub.B (t) output by the adder 75.sub.B is given by
EQU y.sub.B (t)=.SIGMA.G.sub.Bi.times.x.sub.Bi (t)
 where i denotes 1 to n.
 In the receiver 76.sub.A, the reception information R.sub.A is obtained
 from the output voltage y.sub.A (t), whereas, in the receiver 76.sub.B,
 the reception information R.sub.B is obtained from the output voltage
 y.sub.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.sub.A1, G.sub.A2, . . . , G.sub.An G.sub.B1,
 G.sub.B2, . . . , G.sub.Bn are used in the coefficient multipliers
 66.sub.1, 66.sub.2, . . . , 66.sub.n, 67.sub.1, 67.sub.2, . . . , 67.sub.n
 and a sole sensor array element 69 is used.
 The sensor array element 72.sub.n accords suitable coefficients G.sub.A1,
 G.sub.A2, . . . , G.sub.An by the coefficient multipliers 73.sub.1,
 73.sub.2, . . . , 73.sub.n for matching the directivity to the optimum
 path P.sub.A of the paths P.sub.B and P.sub.A.
 On the other hand, the sensor array element 72.sub.n accords suitable
 coefficients G.sub.B1, G.sub.B2, . . . , G.sub.Bn by the coefficient
 multipliers 74.sub.1, 74.sub.2, . . . , 74.sub.n for matching the
 directivity to the optimum path P.sub.B of the paths P.sub.B and P.sub.A.
 This completes setting of the directivity of the reception antenna.
 The directivity of the transmission antenna is then set as shown in FIG.
 10B. 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.sub.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 .epsilon.(t), that is the mean square value of the difference
 .epsilon.(t)=y(t)-.gamma.(t), where .gamma.(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. 11A. The transmission and
 reception are then interchanged, as shown in FIG. 11B. 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.sub.A and the transmitting
 information T.sub.B entering the transmitters 63.sub.A and 63.sub.B may be
 the information converted in parallel during the preceding stage.
 Specifically, the transmitting information T.sub.A and the transmitting
 information T.sub.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.sub.A
 and the transmitting information T.sub.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.sub.A and P.sub.B. The signal reception
 device 70 synthesizes the reception information R.sub.A and the reception
 information R.sub.B obtained by the receivers 76.sub.A and 76.sub.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.sub.A and 76.sub.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.sub.A and 63b in the order of decreasing
 C/N ratio.