Patent Publication Number: US-6907269-B2

Title: Mobile communication base station equipment

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to a base station equipment of a mobile communication system which is intended to enable a communication with a mobile station with a narrow angle directivity (narrow angle beam) antenna in order to reduce the quantity of interferences. 
   An adaptive array antenna in a conventional mobile communication base station equipment is constructed by providing a plurality of receivers for each communication channel, adjusting an antenna weight to control the direction of a principal beam in the antenna directivity response, extracting an optimal received signal, and employing the antenna weight which is used for the optimal signal in controlling the direction of a principal beam in the directivity response of a transmitting antenna. However, this practice requires a plurality of transmitters/receivers for each channel for both the transmission and the reception, disadvantageously increasing the scale of the equipment. 
   To accommodate for this problem, there is proposed a technique as illustrated in  FIG. 1  where a beam switcher  12  selectively connects a transmitter  13  to one of a plurality of antennas  11 - 1  to  11 - 4  having narrow beam angle directivities  35 - 1  to  35 - 4  in mutually different directions through respective duplexers  36 - 1  to  36 - 4  while a beam switcher  14  selectively connects a receiver  15  to one of the antennas, thus minimizing the number of transmission/reception network paths. According to this technique, receivers  16 - 1  to  16 - 4  are used to measure the signal strength from respective narrow beam antenna  11 - 1  to  11 - 4  to allow a beam selection control circuit  17  to switchably control the beam switchers  12 ,  14  so that transmitter  13  and the receiver  15  may be connected to one of the antennas having the maximum received signal power. With this technique, to scan the arriving direction of a received radiowave, a number of direction finder receivers  16 - 1  to  16 - 4  are necessary which is equal to the number of antenna branches, which is four in FIG.  1 . When the technique is applied to the mobile communication, which represents a multi-path environment, a difficulty is encountered in establishing an accurate beam switching because of a variation in the signal strength which occurs independently on each antenna branch. (See Tadashi Matsumoto, Seiji Nishioka and David J. Hodder, “Beam-Selection Performance Analysis of a Switched Multibeam Antenna System in Mobile Communications Environments,” IEEE Trans., VT, Vol. 46, No. 1 (February 1997).) 
   A high resolution signal processing technique such as MUSIC is known in the art to estimate the arriving direction of a radiowave (DOA; Direction of Arrival), but requires a complex treatment including the calculation of a correlation matrix, resulting in a tremendous length of time as the number of antennas increases. (See R. O. Schmidt, “Multiple Emitter Location and Signal Parameter Estimation,” IEEE Trans. AP. Vol-34, No. 3 (March 1986).) The treatment of this technique is even more complicated when plural antenna having different directivities are used. For this reason, it necessitates the provision of an array antenna including antenna elements  18 - 1  to  18 - 4  having a common directivity for direction finding purpose, separately from communication antennas, as shown in FIG.  2 . Received signals from the antenna elements  18 - 1  to  18 - 4  are fed to the receivers  16 - 1  to  16 - 4 , outputs of which are processed in a circuit  19  according to the MUSIC procedure to determine the direction on which the transmitting mobile station is located, thus controlling the beam switchers  12  and  14 . 
   In the actual operation of the mobile communication, there are users (mobile stations) who move rapidly during the communication intervals and who frequently change the channels on one hand, and there are many users who complete the communications without substantial movements on the other hand. Because the mobile communication base station equipment premises that every user (mobile station) be serviced during a rapid movement thereof, it uses antenna which exhibit a common wide angle directivity response for a plurality of frequency channels and time slots. Thus, when commencing a communication with a particular user (mobile station), the base station equipment is radiating radio waves in directions of its service area such as a sector area, for example, other than the direction on which the user is located, and this represents a wasteful power dissipation. It will thus be seen that the use of antennas which exhibit a common angle directivity response for every frequency channel and time slot is problematic from the standpoints of radio wave environment and power saving. There is then a proposal which uses an array antenna to produce a narrow beam angle directivity response separately for each frequency channel and time slot so that a narrow angle beam be always directed to a user, thus tracking it. The proposed technique is excellent when viewed from above standpoints, but presents problems in that an increased area must be provided for installation of antennas and the equipment must be scaled up. In addition, a complex signal processing system is needed. 
   A conventional arrangement of base station equipment is shown in  FIG. 3. A  receiving antenna  111  and a transmitting /receiving antenna  112  are oriented in a common direction and have directivity responses indicated by principal beams  161  and  162 , respectively, which are 120° wide. The receiving antenna  111  is directly connected to a combiner and distributor  26  while the transmitting/receiving antenna  112  is connected thereto through a duplexer  36 . Each transmitter  13  of transmitter/receiver assemblies  115 - 1  to  115 -L for frequency channels f 1 s to f 1 L inclusive of control channels and communication channels is connected to the transmit port of the combiner and distributor  26  while receivers  15 - 1  and  15 - 2  are connected to the respective receive port of the combiner and distributor  26  for the antennas  111  and  112 , thus allowing the transmission and the reception of the control channel and the communication channel. Communication channel transmitter/receiver assemblies  121 - 1  to  121 M for frequency channels f 21  to f 2 M each include a transmitter  122  which is connected to the transmit port of the combiner and distributor  26  and also each include receivers  123  and  124  which are connected to the respective receive port of the combiner and distributor  26  for the antennas  111  and  112 , thus allowing the transmission and the reception of the communication channels. Each of the receivers  15 - 1  and  15 - 2  is adapted to diversity reception as is each of the receivers  123  and  124 . 
   Time slots which are utilized by the transmitter/receiver assemblies  115 - 1  to  115 -L are shown in FIG.  4 A and time slots which are utilized by the transmitter/receiver assemblies  121 - 1  to  121 -M are shown in FIG.  4 B. The beam  162  of the antenna which is used in each transmission has a width of 120°, and this means that a common beam is used for every frequency channel and time slot. A base station controller  126  allocates a channel which is used by either one of the transmitter/receiver assemblies  115 - 1  to  115 -L and  121 - 1  to  121 -M during a particular time slot. 
   As discussed, the arrangement which employs the direction finding of the mobile station and a result of such scan is used in switching a transmit/receive beam suffers from the accuracy of directional finding, the scale of equipment and the quantity of calculations. 
   It will also be seen that because a wide angle beam antenna is fixedly assigned to every channel in a conventional base station equioment, this means that the equipment dissipates a wasteful radiation power in directions in its service area (such as a sector, for example) other than the direction on which a desired mobile station is located, contributing to increasing the quantity of interferences with other base stations. It is an object of the invention to provide a mobile communication base station equipment which enables a communication with a mobile station with a narrow angle beam by performing a direction finding of an arriving radio wave at a higher accuracy with a minimum scale of equipment and with a minimum volume of calculations. 
   It is another object of the invention to provide a mobile communication base station equipment which allows the quantity of interferences caused by radiated power to be reduced as compared with the prior art. 
   According to a first aspect of the present invention, there are provided a pair of wide angle beam antennas located close to each other for substantially covering a service area which is covered by an entire assembly including a plurality of narrow angle beams. One of the antennas of the pair is connected to a communication receiver while the other antenna is connected to a direction finder receiver. The direction on which a mobile station transmitting a particular received radio wave is located is determined on the basis of phases of received signals from the both receivers. The function of the wide angle beam antenna may be served by one of the plurality of antennas which are used to form the narrow angle beams. 
   According to a second aspect of the present invention, there are provided a single wide angle beam antenna and a plurality of narrow angle beam antennas which collectively cover a service area of the wide angle beam antenna. A traveling speed of a mobile station and the direction of a narrow angle beam on which the mobile station is located are detected. On the basis of such information, when the traveling speed is high, one of communication channel transmitters/receivers capable of feeding transmitting power is allocated to the wide angle beam antenna while when the traveling speed is low, one of the communication channel transmitters/receivers capable of feeding transmitting power is allocated to the narrow angle beam antenna corresponding to the direction on which the mobile station is located. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a block diagram of a conventional mobile communication base station equipment; 
       FIG. 2  is a block diagram of another example of conventional mobile communication base station equipment; 
       FIG. 3  is a block diagram of a further example of conventional base station equipment; 
       FIGS. 4A and 4B  are diagrams illustrating relationships between time slots and antenna beams in a conventional base station equipment; 
       FIG. 5A  is a block diagram of an embodiment according to a first aspect of the present invention; 
       FIG. 5B  graphically shows a relationship between a phase difference and an angle of an arriving radio wave; 
       FIG. 5C  is a block diagram of a specific example of a direction measuring unit shown in  FIG. 5A ; 
       FIG. 6  is a block diagram illustrating the application of the embodiment shown in  FIG. 5A  to a plurality of communication channels; 
       FIG. 7A  is a block diagram of an embodiment according to the first aspect of the present invention when a narrow angle beam and a wide angle beam use an antenna in common; 
       FIG. 7B  illustrates a relationship between the plurality of narrow angle beams and the wide angle beam shown in  FIG. 7A ; 
       FIG. 8  is a block diagram of an example in which the embodiment shown in  FIG. 7A  is applied to a plurality of communication channels; 
       FIGS. 9A , B and C are illustrations of the principle of operation for obtaining a reliable measured direction; 
       FIG. 10  is a schematic view showing a functional arrangement of a direction measuring unit  23  which is based on the principle illustrated in  FIG. 9 ; 
       FIG. 11  is a flow chart of an exemplary processing procedure according to the principle illustrated in  FIG. 9 ; 
       FIGS. 12A , B and C are illustrations of another principle of operation for obtaining a reliable measured direction; 
       FIG. 13  is a schematic view showing a functional arrangement of a direction measuring unit  23  which is based on the principle illustrated in  FIG. 12 ; 
       FIG. 14  is a flow chart of an exemplary processing procedure according to the principle illustrated in  FIG. 12 ; 
       FIGS. 15A , B and C are illustrations of a further principle of operation for obtaining a reliable measured direction; 
       FIG. 16  is a schematic view showing an exemplary functional arrangement of a direction measuring unit  23  which is based on the principle illustrated in  FIG. 15 ; 
       FIG. 17  is a flow chart of an exemplary processing procedure according to the principle illustrated in  FIG. 15 ; 
       FIG. 18  is a schematic view showing a functional arrangement of a direction measuring unit  23  according to a further embodiment of obtaining a reliable measured direction; 
       FIG. 19  is a flow chart of an exemplary processing procedure used by the direction measuring unit  23  shown in  FIG. 18 ; 
       FIG. 20  is a schematic view showing a general functional arrangement of a direction measuring unit  23  for obtaining a reliable measured direction; 
       FIG. 21  graphically shows a result of experiments determining an instantaneous direction; 
       FIG. 22  graphically shows a result of experiments in which instantaneous directions measured are averaged to determine a mean direction; 
       FIG. 23  graphically shows a result of experiments in which the reliable direction is determined to be the direction being measured; 
       FIG. 24  is a block diagram of an embodiment according to the second aspect of the present invention; 
       FIG. 25A  shows examples of time slots of control and communication channel transmitters/receivers and prevailing antenna directivity responses which occur in the embodiment shown in  FIG. 24 ; 
       FIGS. 25B and C  show two examples of time slots of communication channel transmitters/receivers and prevailing antenna directivity responses which occur in the embodiment shown in  FIG. 24 ; 
       FIG. 26A  is an illustration of a procedure of determining the traveling speed caused by a fading pitch of a mobile station and selecting a particular beam; 
       FIG. 26B  illustrates an exemplary relationship between an antenna beam width (layer) and transmitted power; 
       FIG. 27  is a schematic view of another embodiment according to the second aspect of the present invention in which a narrow angle beam communication channel transmitter/receiver is connected to a narrow angle beam antenna during a time slot which is assigned depending on the direction of a mobile station; 
       FIG. 28A  is a schematic view showing an exemplary relationship between time slots for control and communication channel transmitters/receivers and prevailing antenna beams which occur in the embodiment shown in  FIG. 27 ; 
       FIG. 28B  is a schematic illustration of another relationship between time slots of communication channel transmitters/receivers and prevailing antenna beams which occur in the embodiment shown in  FIG. 27 ; 
       FIG. 29  is a schematic view showing another specific example of a beam selection information detector unit  154  shown in  FIG. 24 ; and 
       FIG. 30  is a schematic view of an embodiment which results when the diversity function is removed from the embodiment shown in FIG.  24 . 
   

   DETAILED DESCRIPTION OF EMBODIMENTS 
     FIG. 5A  shows an embodiment according to the first aspect of the present invention, and corresponding parts to those shown in  FIG. 1  are designated by like reference characters as used in  FIG. 1 , it being understood that throughout the description to follow, a similar convention is followed. In this embodiment, there are provided a pair of antennas  21 - 1  and  21 - 2  which exhibit a wide angle directivity response (or wide angle beam). Each of the wide angle beam antennas  21 - 1  and  21 - 2  is capable of substantially covering a service area which is collectively covered by narrow angle beam antennas  11 - 1  to  11 - 4 . It is to be understood that the both antennas  21 - 1  and  21 - 2  are located close to each other so as to be within the order of one-half the wavelength (λ) of radio waves involved, and have wide angle beams  20 - 1  and  20 - 2  having central axes which are parallel to each other. 
   A direction finder receiver  22  is connected to one of the wide angle beam antennas,  21 - 1 , while a communication receiver  15  is connected to the other wide angle beam antenna  21 - 2 . A received signal form the communication receiver  15  and a received signal from the direction finder receiver  22  are input to a direction measuring unit  23 , which determines the direction of a mobile station transmitting the radio wave of the received signal on the basis of a phase difference between the both received signals. A result of the measurement is input to a beam selection control circuit  24 , which controls a beam switcher  12 , thus connecting a transmitter  13  to one of the narrow angle beam antennas  11 - 1  to  11 - 4  having the direction of a beam  35 -i (where i=1,2,3 or 4) which is aligned with the determined direction. 
   Channel information, synchronization information or a channel estimation information which is received by the communication receiver  15  is received under the same terms and conditions as the direction finder receiver  22 . Since the wide angle beam antennas  21 - 1  and  21 - 2  are located close to each other, it follows that the correlation between the received signals from the wide angle beam antennas  21 - 1  and  21 - 2  is close to 1. Accordingly, by detecting the phase difference between the both received signals and adjusting the phase so that these signals cancel each other, namely choosing these signals to be of opposite phases, it is possible to estimate the arriving direction on the basis of the phase difference is alone since the correlation between the signals is substantially equal to 1 with a minimal amplitude difference. By way of example, as illustrated in  FIG. 5C , the received signal from one of the receivers,  15 , is fed to a variable phase shifter  201 , the output of which is added with the output signal from the other receiver  22  in a combiner circuit  202 . A phase shift which occurs in the variable phase shifter  201  is controlled in accordance with an output from the combiner circuit  202  so that the combiner circuit  202  delivers a zero output. It is to be understood that the both inputs to the combiner circuit  202  are pre-processed to an equal amplitude. Accordingly, when the both inputs to the combiner circuit  202  are of opposite phases to each other, it provides an output of zero, and a phase shift which prevails in the variable phase shifter  201  represents a phase difference θ between the both received signals, which is then delivered to the beam selection control circuit  24 . 
   Thus, because the spacing between the antennas  21 - 1  and  21 - 2  are equal to λ/2 or less, the phase difference (or phase shift) θ has a one-to-one correspondence with respect to the arriving angle, as shown in FIG.  5 B. When the phase difference (or phase shift) θ is equal to π, the arriving direction of the radio wave forms an angle of 0 with respect to a perpendicular or a bisector of a line joining the antennas  21 - 1  and  21 - 2 . As the phase difference (or adjusted phase shift) θ becomes less than π, the arriving direction shifts to the left from the perpendicular, and conversely as the phase difference (or adjusted phase shift) θ becomes greater than π, the arriving direction shifts to the right from the perpendicular. Accordingly, the beam switcher  12  is operated to connect the transmitter  13  to the antenna  11 -i having the narrow angle beam  35 -i which corresponds to the arriving direction which has been estimated by the phase difference (or adjusted phase shift) θ. In this manner, the transmitting beam  35 -i of the base station equipment can be made to track the direction of the mobile station as it travels. It should be noted that the arriving direction of the radio wave can be detected merely by determining the phase difference (or adjusting the phase shift) without resort to adaptive signal processing and/or inverse matrix calculation. 
   Where there exist a plurality of communication channels, an arrangement as shown in  FIG. 6  is used where parts corresponding to those shown in  FIG. 5A  are designated by like reference characters as used before. What differs from the arrangement of  FIG. 5A  is only the addition of a plurality of transmitters/receivers  25 - 1  to  25 -L each including a beam switcher  12 , a transmitter  13  and a receiver  15 , a combiner and distributor  26  and a switch assembly  203 . Outputs corresponding to respective narrow angle beams of the beam switchers  12  of the transmitters/receivers  25 - 1  to  25 -L are combined together in the combiner and distributor  26  to be fed to corresponding ones of the narrow angled antennas  11 - 1  to  11 - 4 . A received signal from a wide angle antenna  21 - 2  is distributed by the combiner and distributor  26  to be fed to respective communication receivers  15  of the transmitters/receivers  25 - 1  to  25 -L. The channel allocation which determines which channels are used by the respective transmitters/receivers  25 - 1  to  25 -L for purpose of communication is controlled by a base station controller  126 . The base station controller  126  repeats sequentially establishing the channel which is allocated to one of the transmitters/receivers  25 - 1  to  25 -L in the direction finder receiver  22 , and each time the channel is established therein, it derives the received signal from the communication receiver  15  of one of the transmitters/receivers  25 - 1  to  25 -L for which this channel has been allocated by controlling the switch assembly  203  to be fed to the direction measuring unit  23 . The beam selection control circuit  24  includes output parts  53 - 1  to  53 -L in a manner corresponding to the respective transmitters/receivers  25 - 1  to  25 -L. A result of measurement of the direction on which a mobile station with which each of the transmitters/receivers  25 - 1  to  25 -L is in communication is located is stored in the output parts  53 - 1  to  53 -L, and the measured direction which is stored in the output parts  53 - 1  to  53 -L is fed to the beam switcher  12  of the respective transmitter/receiver  25 - 1  to  25 -L. 
   The direction finder receiver  22  is arranged to operate in arbitrary channel in a time division manner, and the phase difference θ of its received signal with respect to the corresponding receiver  15  in one of the transmitters/receivers  25 - 1  to  25 -L is determined in the direction measuring unit  23 , thus estimating the arriving direction of the received radio wave. The beam selection control circuit  24  controls the beam switcher  12  in one of the transmitters/receivers  25 - 1  to  25 -L for which the channel has been established, thus selecting the narrow angle beam for purpose of transmission. In this manner, as a mobile station which is in communication with one of the transmitters/receivers  25 - 1  to  25 -L travels, the transmitted beam may be made to track the direction of that mobile station. The embodiments shown in  FIGS. 5A and 6  represent an arrangement in which the narrow angle antennas  11 - 1  to  11 - 4  form the narrow angle beam forming antenna assembly  205  and the wide angle antennas  21 - 2  form the wide angle beam forming antennas  26 . 
   An example in which part of antennas which forms a plurality of narrow angle beams also serves as a wide angle beam antenna will now be described. This example is shown in  FIG. 7A  where a multi-beam antenna  33  is formed by an array antenna  31  including wide angle beam antenna elements  31 - 1  to  31 - 4  and a beam former  32  which may comprise Butler matrix, for example. The antenna elements  31 - 1  to  31 - 4  are arrayed at a spacing on the order of one-half the wavelength (λ) of the radio wave involved and each exhibit a wide angle directivity response (as indicated by a wide angle beam)  34  shown in broken lines in FIG.  7 A. The multi-beam antenna  33  has a plurality of narrow angle directivity responses (narrow angle beams)  35 - 1  to  35 - 4  which are directed in mutually different directions. As shown in  FIG. 7B , the service area of the wide angle beam  34  can be substantially covered by the narrow angle beams  35 - 1  to  35 - 4  collectively. 
   A switched output from the beam switcher  12  can be fed through duplexers  36 - 1  to  36 - 4 , respectively, to any one of the four ports of the beam former  32 . For example, when the four ports of the beam former  32  are fed from the duplexers  36 - 1  to  36 - 4 , each input forms a transmitted wave as represented by one of the narrow angle beams  35 - 1  to  35 - 4 . In this manner, the output from the duplexer  36 - 1  forms the transmitted wave corresponding to the narrow angle beam  35 - 1 , for example. 
   A received output from the multi-beam antenna  33  (corresponding to a signal from the input port during the transmission) is fed through the duplexers  36 - 1  to  36 - 4  to a beam former  37  which may comprise Butler matrix, for example, to be converted back to the received signal according to the directivity response of the wide angle beam antenna elements  31 - 1  and  31 - 2 , for example, or corresponding to the wide angle beam  34 . One of the received signals corresponding to the antenna elements  31 - 1  and  31 - 2  is fed to the communication receiver  15  while the other is fed to the direction finder receiver  22 . It is to be noted that a coordination is made so that channel information, synchronization information and/or channel estimation information which is received by the communication receiver  15  is also received by the direction finder receiver  22  under the same terms and conditions. 
   A spacing between the antenna elements  31 - 1  and  31 - 2  is on the order of one-half the wavelength or less, and accordingly, the arriving direction of the radio wave can be estimated by detecting the phase difference between the both received signals by the direction measuring unit  23 , generally in the similar manner as described above in connection with FIG.  5 A. Thus, an output from the transmitter  13  can be fed to the narrow angle beam which is oriented in this direction. 
   Where there are a plurality of communication channels, a resulting arrangement will be as shown in  FIG. 8 , and what differs from  FIG. 7A  is the addition of a plurality of transmitters/receivers  25 - 1  to  25 -L each including a beam switcher  12 , a transmitter  13  and a receiver  15 , a combiner and distributor  26 , a distributor  26   a  and a switch assembly  203 . Corresponding outputs from the respective beam switchers  12  are combined in the combiner and distributor  26  to be fed to corresponding ones of the duplexers  36 - 1  to  36 - 4 . Outputs from the beam former  37  which are to be fed to the communication receivers  15  are distributed by the distributor  26   a  to the communication receivers  15  of the respective transmitters/receivers  25 - 1  to  25 -L. 
   The direction finder receiver  22  is arranged to operate in an arbitrary channel in a time division manner, and a phase difference between the received signal from the direction finder receiver  22  and the received signal from the communication receiver  15  for that channel is detected by a direction measuring unit  23 , which selects and establishes a narrow angle beam to be used for the transmission from the transmitter  13  which forms a pair with this communication receiver  15 . In this manner, as a mobile station which is in communication with one of the transmitters/receivers  25 - 1  to  25 -L travels, it is possible to cause the transmitted beam to track the mobile station in the direction in which it travels. The embodiment shown in  FIGS. 7 and 8  represent an arrangement in which the multi-beam antenna  33  comprises a narrow angle beam forming antenna assembly  205  while the combination of the multi-beam antenna  33  and the beam former  37  forms the wide angle beam forming antenna assembly  206 . 
   Preferred examples of the direction measuring unit  23  shown in  FIGS. 5  to  8  will now be described. The principle of operation for one example is shown in  FIG. 9. A  received signal which is input to the direction measuring unit  23  has a received power which undergoes a variation due to a fading effect or the like, as indicated by a curve  41  in  FIG. 9A , for example. The determination of an i-th reliable measured direction Φi will be described. An instantaneous received power is measured a plurality of times (which are chosen to be N=five times in  FIG. 9 ) at a time interval of T to determine values ai 1  to aiM. A typical value is obtained as a mean power Ai of ai 1  to aiM (FIG.  9 A). At the same time, an instantaneous phase difference between the both received signals is measured to obtain an instantaneous measured direction φi 1  to φiM, and a typical value is obtained as a mean measured direction Φi of φi 1  to φiM (FIG.  9 B). In this manner, a mean power and a mean measured direction are obtained as A 1 , A 2 , . . . Φ 1 , Φ 2 , . . . at the time interval of T. A plurality of values (which are N=3 in  FIG. 9 ) for the mean power and the mean measured direction are stored in a memory. By way of example, at time t 3 , it is determined that the reliable measured direction is the mean measured direction Φ 2  which is obtained at time t 2  when the maximum mean power A 2  is obtained among the three stored mean powers A 1 , A 2  and A 3  in the memory (it will be noted that the mean power A 2  at time t 2  is greater than the remaining values A 1  and A 3 ). This memory is sequentially updated by new data in a first-in and first-out (FIFO) manner. Thus, at time t 4 , the mean power A 1  and the mean direction Φ 1  at time t 1  are discarded while mean power A 4  and mean direction Φ 4  which are obtained anew are stored. At time t 4 , the mean powers A 2 , A 3  and A 4  stored in the memory are compared against each other again, thus determining a new reliable direction according to the described algorithm (it will be seen that in  FIG. 9 , the reliable direction is determined to be Φ 2 ). The time interval T and the number of data N which is used in determining the maximum are chosen such that the correlation between the mean powers is minimized. The fading structure which occurs is determined from the plurality of mean powers (which is N=3 in the present example) which are compared against each other, and a choice is made so that a mean direction which lies in a depression caused by the fading effect is not selected. By choosing the parameters T and N suitably, the selection of a measured direction which occurs during a depression in the received power where a large error is likely to occur as the reliable direction is avoided. In the example shown in  FIG. 9 , Φ 5  is not selected as the reliable direction because the received mean power A 5  is low. For each measurement which takes place at the time interval of T, a decision is rendered whether or not the reliable direction is to be updated on the basis of the mean powers obtained during past several measurements, (which is N=3 in FIG.  9 ).  FIG. 9B  shows the mean measured direction and  FIG. 9C  shows the reliable direction determined and the direction in which the determination has occurred. 
   As mentioned above, it is preferred that the time interval T between successive measurements be determined to provide a reduced correlation between the mean powers obtained so that the fading structure can be recognized from N received mean powers and so that a comparison between the received powers in a depression zone is avoided. It will be seen that a longer time interval is preferred for T, but when a longer time interval is chosen, an updating of the measured direction is slowed down in a corresponding manner, degrading the tracking capability for a mobile station which travels rapidly. It is preferred that the time interval T be chosen in accordance with the traveling speed of the mobile station or the period of the fading effect. The number N of the mean powers which are used in detecting the maximum mean power is preferably chosen to avoid a depression zone in the received power and to enable the fading structure to be recognized from the mean powers being compared. For these reasons, the number of mean powers is chosen in a range from 3 to 10. The mean powers are measured a plurality of times (M-times) at the time interval of T in order to reduce the influence of noises, and should be made a plurality of times as close to each other as possible. The number M of measurements may be on the order of 10 to 20, for example. 
   An exemplary functional arrangement which is used to determine the reliable direction is shown in FIG.  10 . Both received signals which are input to a direction measuring unit  23  are applied to a pair of terminals  42  and  43  of an instantaneous direction measuring unit  44  where an instantaneous phase difference between the both received signals is measured a plurality of times (or M-times) to determine an instantaneous direction on the basis of the instantaneous phase difference. M values of the instantaneous measured direction are averaged in a direction averager 4, and a resulting mean direction is stored in a direction FIFO memory  46 . 
   The received signals applied to the terminals  42  and  43  are also input to an instantaneous power measuring unit  47  where the instantaneous power is measured M-times, and M values of the instantaneous power are averaged in a power averager  48 , and a resulting mean power is stored in a power FIFO memory  49 . The measurement of the instantaneous power may take place with respect to only one of the received signals applied to the terminals  42  and  43 , or may take place with respect to a sum or a mean value thereof. A controller  51  operates the instantaneous direction measuring unit  44  and the instantaneous power measuring unit  47  at the time interval of T, and the outputs from the direction averager  45  and the power averager  48  are stored in the direction FIFO memory  46  and the power FIFO memory  49 , respectively. The time of measurement when a maximum one of the mean powers which are stored in the power FIFO memory  49  is obtained is detected by a maximum power time detector  52 , and the mean direction which prevails at this point in time is read out from the direction FIFO memory  46  to be delivered as the reliable direction from an output part  53 , and as an output representing the measured direction determined by the direction measuring unit  23 . 
     FIG. 11  shows a processing procedure which takes place in the arrangement of FIG.  10 . Initially, the instantaneous direction and the instantaneous power are measured (S 1 ). The measurement is repeated until the measurement takes place a given number of times M (S 2 ). After the given number of measurements, a mean direction from M values of the instantaneous measured direction is calculated to be stored in the direction FIFO memory  46  (S 3 ). A mean power of M values of the instantaneous measured power is calculated to be stored in the power FIFO memory  49  (S 4 ). A point in time when a maximum one of M values of the mean power which are stored in the power FIFO memory  49  is retrieved (S 5 ), and the mean direction which prevails at the retrieved point in time is read out from the direction FIFO memory  46  to be delivered as the reliable measured direction from the direction measuring unit  23  (S 6 ). Then, the elapse of the time interval T is waited for, subsequently returning to step S 1  (S 7 ). 
   Another principle of operation for obtaining a reliable measured direction will now be described with reference to FIG.  12 . The determination of an i-th reliable measured direction Φi will be described. The instantaneous received power is measured M times (which is equal to five times in  FIG. 12 ) at the time interval of T to obtain values ai 1  to aiM, and a typical value is obtained as a mean power Ai of ai 1  to aiM (FIG.  12 A). At the same time, an instantaneous measured direction φi 1  to φiM is measured from the phase difference between the both received signals, and a typical value is obtained as a mean measured direction Φi of φi 1  to φiM (FIG.  12 ). The mean value and the mean measured direction are obtained at the time interval of T in this manner. Assume that a mean power M 3  is obtained at time t 3 , and if A 3  is greater than a threshold value Th A , the mean measured direction Φ 3  which prevails at time t 3  is determined to be a reliable measured direction and is used to update an output measured direction, while if A 3  is less than the threshold value Th A , the measured direction is not updated. When the time interval T and the threshold value Th A  are suitably chosen, a measured direction which occurs during a depression in the received power where a large error in the measured direction is likely to occur cannot be selected as the reliable measured direction. By way of example, in  FIG. 12 , the mean received power A 5  which prevails at time t 5  is less than the threshold value Th A , and thus, the mean measured direction Φ 5  cannot be adopted as the reliable measured direction. Instead, the direction measuring unit  23  delivers an output of Φ 4  at time t 4 , and does not deliver an output or again delivers Φ 4  at time t 5 . In the example shown in  FIG. 12 , only those mean directions shown in  FIG. 12C  are delivered as the reliable measured direction. 
   An exemplary functional arrangement for a direction measuring unit  23  which should operate to carry out the principle of operation mentioned above is shown in  FIG. 13  where the parts corresponding to those shown in  FIG. 10  are designated by like reference characters as used before. The instantaneous direction is measured by an instantaneous direction measuring unit  44  M times, and a mean direction is calculated by a direction averager  45 . The instantaneous power is measured M times by an instantaneous power measuring unit  47 , and a mean power is calculated in a power averager  48 . The mean power is compared against a threshold value Th A  fed from a threshold presetter  56  in a comparator  55 . If it is equal to or greater than the threshold value Th A , the mean direction delivered from the direction averager 45 is used to update the measured direction which is retained in an output part  53 , whereby it is delivered as a reliable measured direction. If it is found in the comparator  55  that the mean power is less than the threshold value Th A , the measured direction retained in the output part  53  is not updated. 
   An exemplary processing procedure which is used for the arrangement shown in  FIG. 13  is shown in FIG.  14 . The instantaneous direction and the instantaneous power are measured a given number of times (M times) (S 1  and S 2 ). A mean direction for M values of the instantaneous direction and a mean power for M values of the instantaneous power are calculated (S 3  and S 4 ). An examination is made to see if the mean power is equal to or greater than the threshold value Th A  (S 5 ), and if the mean power is equal to or greater than Th A , the output measured direction is updated (S 6 ) while if the mean power is less than Th A , the output measured direction is not updated, thus waiting for the time interval T to pass, whereupon the operation returns to step S 1  (S 7 ). 
   A further principle of operation for obtaining a reliable measured direction is illustrated in FIG.  15 . The determination of an i-th reliable direction Φi will be described. The instantaneous measured direction is measured M times (which is equal to five times in  FIG. 15 ) at the time interval of T to obtain values φi 1  to φiM, and a typical value is obtained as a mean measured direction Φi of φi 1  to φiM (FIG.  15 B). A plurality of mean measured directions (which is assumed to be N=2 in this example) are stored in a memory. At time t 3 , a mean measured direction Φ 3  is obtained and is stored in a memory. A difference between Φ 3  and a mean measured direction Φ 2  for two values stored in a memory or |ΔΦ|=|Φi−Φi−1|is then calculated. If the difference |ΔΦ| is less than a threshold value Thφ, the mean measured direction Φ 3  which is now obtained, is determined to be a reliable measured direction. The memory is sequentially updated in a first-in and first-out manner. For example, at time t 4 , the mean measured direction Φ 2  obtained at time t 2  is discarded from a memory while a new mean measured direction Φ 4  is stored. At time t 4 , the difference between the two mean measured directions Φ 3  and Φ 4  in the memory is obtained, and the difference |ΔΦ| is compared against the threshold value Thφ. In this example,|ΔΦ|&lt;Thφ, and accordingly the output measured direction is updated to Φ 4  (FIG.  15 C). By suitably choosing the time interval T and the threshold value Thφ for the difference of the mean measured direction, a mean measured direction which occurs during a depression in the received power where a large error in the measured direction is likely to occur cannot be adopted as a reliable measured direction. In the present example, the mean measured direction Φ 5  obtained at time t 5  occurs for a low received level A 5 , and a difference over the mean measured direction Φ 4  increases to cause |ΔΦ| to exceed the threshold value Thφ, whereby it cannot be adopted as the reliable measure direction, as indicated in FIG.  15 C. 
   It is to be noted that when the received power is low, a mean phase difference increases or the mean phase difference increases as a result of the received power being buried into the noise. 
   An exemplary functional arrangement of this direction measuring unit  23  is shown in  FIG. 16  where parts corresponding to those shown in  FIG. 10  are designated by like reference characters as used before. An instantaneous direction is measured from the phase difference between the both received signals by an instantaneous direction measuring unit 44 M times at a time interval of T. Resulting M values of the instantaneous measured direction is averaged in an averager 45 to be stored in an FIFO memory  46 . The difference |ΔΦ| between the two mean measured directions contained in the FIFO memory  46  is calculated by a difference circuit  58 , and the difference |ΔΦ| (is compared against the threshold value Thφ supplied from a threshold presetter  61  in a comparator  59 . If |ΔΦ|≦Thφ holds, the mean measured direction Φi which is then stored in the memory  46  is used to update the measured direction which is retained by an output part  53 . On the contrary, if |ΔΦ|&gt;Thφ, the output part  53  is not updated. 
   An exemplary processing procedure which is used with the arrangement shown in  FIG. 16  is shown in FIG.  17 . An instantaneous direction is measured on the basis of a phase difference between both received signals a given number of times (M times) (S 1  and S 2 ). M values of the instantaneous measured direction are averaged to be stored in a memory (S 3 ). A difference |ΔΦ| between the current and the previous mean measured value is calculated (S 4 ), and an examination is made to see if |ΔΦ| is equal to or less than the threshold value Thφ (S 5 ). If |ΔΦ|≦Thφ, the measured direction from the output part  53  is updated by the latest mean measured direction. If |ΔΦ|≦Thφ does not hold, the measured direction retained in the output part  53  is not updated, but the elapse of the time interval T is waited for, whereupon the operation returns to step S 1  (S 7 ). 
   An additional functional arrangement for the direction measuring unit  23  which obtains a reliable measured direction is shown in  FIG. 18  where parts corresponding to those shown in  FIG. 16  are designated by like reference characters as used before. The instantaneous direction is measured M times by an instantaneous direction measuring unit  44  at time interval of T, and M values of the instantaneous measured direction are averaged in an averager  45  to be stored in a FIFO memory  46 . Thus, the FIFO memory  46  stores four latest mean measured directions Φi+1, Φi, Φi−1 and Φi−2, for example, thus storing a time sequence of four latest values of the mean measured direction. 
   Differences between each pair of adjacent mean measured directions in the time sequence are calculated by difference circuits  58   1 ,  58   2  and  58   3 . A minimum one of these differences |ΔΦ 1 |=|(Φi+1)−Φi|, |ΔΦ 2 |=|Φi (Φi−1)| and |ΔΦ 3 |=|(Φi−1)−(Φi−2)| is detected by a minimum value detector  63 . One of the two mean measured directions which are used in forming the difference having the minimum value is chosen as a reliable measured direction, and thus is read out from the FIFO memory  46  to be delivered to an output part  53 . For example, if the output difference |ΔΦ 2 | from the difference circuit  58   2  is a minimum value, one of the mean measured directions Φi and Φi−1 which are used in deriving the difference, preferably the latest one Φi, is read out from the memory  46  to be delivered to the output part  53 . Alternatively Φi−1 may also be delivered. 
   An exemplary processing procedure which is used with the arrangement shown in  FIG. 18  is shown in FIG.  19 . The instantaneous measured direction is measured M times (S 1  and S 2 ), and M values of the instantaneous direction is averaged to be stored in the FIFO memory  46  (S 3 ). Differences (absolute values) between each pair of adjacent mean measured directions in the time sequence stored in the FIFO memory  46  are calculated (S 4 ), and a minimum one of these differences is located. A latest one Φi of the two mean measured directions Φi and Φi−1 which are used in reaching the difference of the minimum value is delivered as a measured direction (S 6 ). Subsequently, the operation returns to step S 1  after waiting for the time interval T to pass (S 7 ). Alternatively, Φi−1 may be delivered at step S 6 . 
   As discussed above for various embodiments, the direction measuring unit  23  is designed to be controlled by a controller  51 , as shown in  FIG. 20 , such that an instantaneous direction measuring unit  44  measures an instantaneous phase difference between both received signals to determine an instantaneous direction on the basis of such phase difference, the measurement of the instantaneous direction is preferably repeated a plurality of times and a mean value of the plurality of instantaneous directions is obtained in a direction averager 45. Alternatively, the instantaneous phase difference is measured a plurality of times and a mean value over these instantaneous phase differences is determined, and a mean direction may be determined on the basis of the mean phase difference. In a reliability presence/absence decision unit  65 , the presence or absence of the reliability in the mean direction is determined according to one of the techniques illustrated in  FIGS. 9  to  19 , and the direction which has been determined to be reliable is delivered to an output part  53  as a measured direction. In the embodiments shown in  FIGS. 9 and 12 , the instantaneous power of received signals has been measured, but alternatively, the instantaneous amplitude of the received signals may be measured. 
   As an example,  FIG. 21  shows a result of experiments which determined a measured direction by the instantaneous direction measuring unit  44 . In  FIG. 21 , the abscissa represents time in terms of the number of symbols, and the ordinate represents the measured direction. In the example shown, the actual arriving direction of the radio wave is equal to 45°. However, it will be noted that the result of experiments shown indicates the presence of a significant variation in the measured direction. It is believed that this is partly because the measured direction cannot remain constant, but undergoes a large variation under the influence of receiver noises. For this reason, values of the instantaneous measured direction which are obtained by M=10 repetitions are averaged in order to suppress the influence of noises. In this instance, a result of experiments for the mean measured direction or the output from the direction averager  45  for the received signals which are under the same conditions as for  FIG. 21  is as shown in FIG.  22 . It will be seen from the results shown in  FIG. 22  that a variation in the measured direction can be reduced by averaging values of the instantaneous measured direction. However,  FIG. 22  shows that there still remains a large variation which cannot be suppressed even after the averaging operation. It is believed that this is due to a substantial reduction in the received power, namely during a deep depression in the received power or due to a depression caused by a fading effect when the arriving radio wave has an extended spatial reach. 
   By contrast, when the techniques illustrated in  FIGS. 11 ,  14 ,  17  and  19  are used to determine and deliver a reliable measured direction, experiments conducted for received signals of the same conditions indicate a result as shown in  FIG. 23  for each of these techniques where there is no rapid variation or there is no large error, and the actual arriving direction of 45° is obtained in a fairly stabilized manner. The experiments have been conducted with M=10 and N=8. It is seen from such result that the techniques illustrated in  FIGS. 11 ,  14 ,  17  and  19  allow a stabilized measured direction to be obtained while reducing the probability that a mean measured direction which is obtained during a substantial depression in a received power is determined to be reliable, thus providing noise resistance as well as interference resistance. 
   In the above description, the measured direction which is retained in the output part  53  of direction measuring unit  23  is updated. However, rather than retaining the measured direction in the output part  53 , information may be retained in the beam selection control circuit  24  and may be updated by an output from the output part  53 . 
   Referring back to  FIG. 5B , when the output from one of the receivers  15  and  22 , for example, receiver  22 , is inverted in polarity in a polarity inverter  231 , as indicated in broken lines, the amount of control which must be applied to the variable phase shifter  201  can be reduced. The direction measuring unit  23  may determine the arriving angle on the basis of an output level of a phase difference between those received signals which is detected by an analog phase difference detection circuit. It is necessary to invert the polarity of one of the both received signals in order to achieve the response as shown in  FIG. 5B  in this instance. A phase difference between both received signals can be determined by converting each received signal into a complex digital signal and determining the phase of each received signal to derive a difference therebetween. It is to be note that the relationship between the phase difference and the arriving angle need not be as illustrated by the relationship shown in FIG.  5 B. In other words, a phase difference between both received signals can be determined without inverting the polarity of one of the both received signals. In this instance, the phase difference θ is equal to 0 for the arriving angle of 0° in a direction of the perpendicular. 
   It is to be understood that despite the above description, the number of narrow angle beams is not limited to four, but any desired number of beams may be used. The function of the direction measuring unit  23  can be served by causing a computer to execute a program. 
   As discussed above, according to the first aspect of the present invention, one of received signals from a pair of received wide angle beams is fed to a communication receiver while the other is fed to a direction finder receiver. By measuring a phase difference between signals from these receivers, the arriving direction of the received radio wave is detected. By controlling a beam switcher so that an output from a transmitter is fed to one of a plurality of transmitting narrow angle beams, the transmitting power can be reduced (due to a high gain of the antenna) and the interference can be reduced (due to the narrow angle beam). In addition, the arriving direction of the radio wave can be detected by simple means of detecting a phase difference. Because the transmitting narrow angle beam is switched in accordance with a change in the arriving direction of a received signal from a mobile station, it is possible to allow the transmitting narrow angle beam to substantially track the direction of the mobile station. A single direction finder receiver is used for purpose of finding the arriving direction of a received radio wave while utilizing other communication receivers for the purpose of finding the direction. As a consequence, the entire arrangement is greatly simplified as compared with the prior art shown in FIG.  2 . In particular, as shown in  FIGS. 6 and 8 , a single direction finder receiver can be used with transmitters/receivers for a plurality of communication channels. 
   When a reliable measured direction is determined, it is possible to direct a transmitting narrow angle beam always accurately without failure. 
     FIG. 24  shows an embodiment according to a second aspect of the present invention. In this instance, a pair of 60° beam (narrow angle beam) forming antenna assemblies  205  cover a 120° sector service area and a 120° beam (wide angle beam) antenna  21 - 2  covers the 120° sector service area while a combination of antennas  31 - 1  and  31 - 2  of the narrow angle beam forming antennas assembly  205  and the antennas  21 - 2  enables a diversity reception. The antennas  31 - 1  and  31 - 2  are connected through a hybrid  134  and through duplexers  36 - 1  and  36 - 2  to a combiner and distributor  26  while the 120° beam antennas  21 - 2  is connected through a duplexer  36 - 3  to the combiner and distributor  26 . As viewed toward the antennas  31 - 1  and  31 - 2  from ports  134   a  and  134   b  of the hybrid  134  where it is connected to the duplexers  36 - 1  and  36 - 2 , respectively, each of the principle beams  35 - 1  and  35 - 2  of the combined directivity response has a beam width of 60° and are directed to the left and to the right, respectively, while the antenna  21 - 2  has a wide angle beam  20 - 2  having a beam width of 120°, substantially covering the narrow angle beams  35 - 1  and  35 - 2 . In this manner, the combination of the antennas  31 - 1  and  31 - 2  and the hybrid  134  constitute the narrow angle beam forming assembly  205  which forms the pair of 60° beams (narrow angle beams)  35 - 1  and  35 - 2 . 
   Each of transmitters/receivers  137 - 1  to  137 -L for channels f 1 l to f 1 L inclusive of control and communication channels includes a transmitter  138  which can feed transmitting power directly to the 120° beam (wide angle beam) antenna  21 - 2  through the combiner and distributor  26  and the duplexer  36 - 3 , receivers  139  and  141 , each of which can be fed with a received signal from each 60° beam port of the hybrid  134  through the combiner and distributor  26  and the duplexers  36 - 2  or  36 - 1 , and a receiver  142  which can be fed with a received signal from the 120° beam antenna  21 - 2  through the combiner and distributor  26  and the duplexer  36 - 3 . 
   Each of the communication channel transmitters/receivers  143 - 1  to  143 -L for channels f 21  to f 2 M includes a receiver  144  which can feed a transmitting power to the 60° beam port  134   a  of the hybrid  134  through the combiner and distributor  26  and the duplexer  36 - 1 , a receiver  145  which can be fed with a received signal from the both 60° beam ports  134   a  and  134   b  of the hybrid  134  through the hybrid  147 , the combiner and distributor  26  and the duplexers  36 - 1  or  36 - 2 , and a receiver  146  which can be fed with a received signal from the 120° beam antenna  21 - 2  through the combiner and distributor  26  and the duplexer  36 - 3 . 
   Each of communication channel transmitters/receivers  148 - 1  to  148 -M for channels f 3 l to f 3 M includes a transmitter  149  which can feed transmitting power to the 60° beam port  134   b  of the hybrid  134  through the combiner and distributor  26  and the duplexer  36 - 2 , a receiver  151  which can be fed with a received signal from either 60° beam port  134   a  or  134   b  of the hybrid  134  through the combiner and distributor  26  and the duplexer  36 - 1  or  36 - 2 , and a receiver  152  which can be fed with a received signal from the 120° beam antenna  21 - 2  through the combiner and distributor  26  and the duplexer  36 - 3 . 
   Another wide angle beam antenna  21 - 1  which covers the service area in the similar manner as the wide angle beam antenna  21 - 2  is disposed close thereto within a distance of one-half the wavelength and is directed in the same beam direction. A received signal from the antenna  21 - 1  is received by a receiver  22 . 
   A received output from a control channel receiver  142  is fed to a beam selection information detection system  154 , which obtains direction information Φ as both received signals from the receiver  142  and the receiver  22  are fed to a direction measuring unit  23  which is responsive thereto to determine whether the direction on which a mobile station, which provided the received signals, is located in the direction of the 60° beam  35 - 1  or in the direction of the 60° beam  35 - 2 , and also obtains information Tf representing the traveling speed of the mobile station which is derived by a traveling speed detector  211  on the basis of a variation in the reception level of the receiver  142  or fading pitch Tf. It is to be noted that any one of various direction measuring units mentioned above can be used for the direction measuring unit  23  of this embodiment. As described above in connection with the embodiment of  FIG. 6 , a base station controller  126  controls a switch assembly  203  so that the received signal from the receiver  142  of one of the transmitters/receivers  137 - 1  to  137 -L be fed to the direction measuring unit  23  and the traveling speed detector  211 , and also controls the receiver  22  to establish a channel therein. 
   The total time slots of the 120° beam control and communication channel transmitters/receivers  137 - 1  to  137 -L are in the 120° beam (wide angle beam)  20 - 2 , as shown in FIG.  25 A. The time slots of the 60° beam communication channel transmitters/receivers  143 - 1  to  143 -M are assigned to the right beam (narrow angle beam)  35 - 2  as shown in  FIG. 25B  while time slots of the 60° beam communication channel transmitters/receivers  148 - 1  to  148 -N are assigned to the left beam (narrow angle beam)  35 - 1  as shown in FIG.  25 C. The operation will now be described. 
   The base station controller  126  interrogates the beam selection information detection system  154  for the traveling speed information (fading pitch Tf) and beam (direction) information φ when it assigns a communication channel as during a call request or termination. In response to the response information Tf and Φ, the base station controller  126  operates in a manner shown in FIG.  26 A. If Tf is greater than a given value, it is determined that a mobile station is in the course of rapidly traveling and thus one of the transmitters/receivers  137 - 1  to  137 -L having a communication channel in the 120° beam (wide angle beam) is assigned for the intended communication (S 2 ). On the other hand, if it is found at step S 1  that Tf is less than the given value, it is determined that the mobile station remains stationary or is moving slowly, and a reference is made to the direction information φ (S 3 ) and one from either the transmitters/receivers  143 - 1  to  143 -M or  148 - 1  to  148 -N having a communication channel in the 60° beam (narrow angle beam) which includes the referred direction in its service area is assigned (S 4 ). Because the transmitters/receivers  143 - 1  to  143 -M or  148 - 1  to  148 -N are assigned to a communication with a mobile station, for which the traveling speed is determined to be slow, the probability that a channel switching operation occurs during the communication with this mobile station is low. Accordingly, the beam selection information detection system  154  is not connected to the transmitters/receivers  143 - 1  to  143 -M or  148 - 1  to  148 -N. However, as indicated by broken lines in  FIG. 26A , the beam selection information detection system  154  may be connected to the transmitters/receivers  143 - 1  to  143 -M and  148 - 1  to  148 -N so that subsequent to the completion of the steps S 2  and S 4 , the operation may return to step S 1  where the traveling speed may be detected to switch between a wide angle beam transmitter/receiver and a narrow angle beam transmitter/receiver in an adaptive manner. 
   It is possible to suppress the beam division loss to the lowest possible limit by adaptively choosing the relative proportions of the numbers of the transmitters/receivers  137 - 1  to  137 -L,  143 - 1  to  143 -M and  148 - 1  to  148 -N depending on the traffic and the distribution of the traveling speeds. In the present embodiment, the transmitting beam comprises a 120° beam and a pair of 60° beams, but it is also possible to use a 120° beam and a pair of 60°beams for the receiving beam in the similar manner as for the transmitting beam. It will be noted that in  FIG. 24 , the hybrids  147  and  153  are used to form a 120° beam for reception. The transmitters/receivers  143 - 1  to  143 -M and  148 - 1  to  148 -N which use 60° beam are capable of transmitting with a high gain antenna, and accordingly use a transmitting power which is 3 dB lower than the transmitting power used with the 120° beam transmitters/receivers  137 - 1  to  137 -L. As shown in  FIG. 26B , the transmitting power can be reduced by increasing the layers used such as a coverage of the service area by the 120° beam (layer  1 ), a coverage of the service area by the pair of 60° beams and a coverage of the service area by narrower beams such as four 30° beams (layer  3 ). In the arrangement of  FIG. 26B , the transmitting power may choose 0 dB for the layer 1, −3 dB for the layer  2  and −6dB for the layer  3 . 
   As an alternative, one of 60° communication channel transmitters/receivers shown in  FIG. 24 , namely,  148 - 1  to  148 -N, may be omitted and the transmitter  144  of the remaining 60° communication channel transmitters/receivers  143 - 1  to  143 -M may feed a transmitting power to the 60° beam ports  134   a  and  134   b  in a switched manner. Such an arrangement is shown in FIG.  27 . Each transmitter  144  can be switchably connected to the 60° beam ports  134   a  and  134   b  through a switch  158  and through the combiner and distributor  26 . 
   The total time slots of 120° beam control and communication channel transmitters/receivers  137 - 1  to  137 -L are in the 120° beam  20 - 2 , as shown in  FIG. 28A  while the time slots of the 60° communication channel transmitters/receivers  143 - 1  to  143 -M are assigned to the left beam  35 - 1  for the first three slots and assigned to the right beam  35 - 2  for the second three slots, as shown in FIG.  28 B. Its operation will be described below. 
   A base station controller  126  interrogates a beam selection information detection system  154  for the traveling speed information (fading pitch Tf) and the direction information Φ when assigning a communication channel as during a call request or termination. In response to such information, if Tf is greater than the given value, the base station controller  126  determines that a mobile station is rapidly traveling, and accordingly, assigns one of the transmitters/receivers  137 - 1  to  137 -L having a communication channel in the 120° beam. On the other hand, if Tf is less than the given value, the controller determines that the mobile station remains stationary or slowly traveling, and thus assigns one of the transmitters/receivers  143 - 1  to  143 -M having a 60° beam communication channel. During the process, the direction on which the mobile station is located is detected on the basis of a phase difference between received signals from the receiver  142  and the antenna  21 - 1 , and a selection of either the right beam  35 - 2  or the left beam  35 - 1  is determined in accordance with such Φ information, and a corresponding time slot is assigned to this communication. The base station controller  126  switches a beam changing switch  158  in synchronism with the beam switching timing of the time slot. Because the transmitters/receivers  143 - 1  to  143 -M are assigned only to a mobile station which has been determined to be traveling with a slow speed, the possibility that a channel switching operation occurs during the communication is low, and thus, the beam selection information detection system  154  is not connected to the transmitters/receivers  143 - 1  to  143 -M. 
   Any one of the arrangements described above with reference to  FIGS. 5B and 9  to  20  may be used as the direction measuring unit  23  used within the beam selection information detection system  154  shown in FIG.  24 . 
   In the embodiments shown in  FIGS. 24 and 27 , the antenna  21 - 1  and the receiver  22  may be omitted, and a level comparator  213  shown in  FIG. 29  may be used in place of the direction measuring unit  23  in the beam selection information detection system  154 , thus determining the narrow angle beam which is directed on the direction on which a mobile station transmitting the received radio wave is located. Received signals from the receivers  139 ,  141  and  142  in the 120° beam control and communication channel transmitters/receivers  137 - 1  to  137 -L are fed to the beam selection information detection system  154  including a switch assembly  203  where the received signal from the receivers  139 ,  141  and  142  of one of the transmitters/receivers  137 - 1  to  137 -L are selected. Received signals from the receivers  139  and  141  are fed to the level comparator  213  where the levels of the both received signals are compared against each other. If the received signal level of the receiver  139  is greater than the received signal level from the receiver  141 , it is determined that the mobile station is located in the service area of the narrow angle beam  35 - 2 . On the contrary, if the received signal level from the receiver  141  is higher, it is determined that the mobile station is located in the service area of the narrow angle beam  35 - 1 . Beam (direction) information indicating the narrow angle beam thus determined is delivered. In the event the traveling speed information of the mobile station remains below a given value, the base station controller  126  assigns one of the communication channel transmitters/receivers including a communication channel transmitter which feeds a transmitting power to the narrow angle beam which has been determined by the level comparator  213 . When this technique is applied to the embodiment shown in  FIG. 24 , if the beam information indicated by the beam selection information detection system  154  indicates the narrow angle beam  35 - 1 , one of the communication transmitters/receivers  143 - 1  to  143 -M is assigned, and if the beam information indicates the narrow angle beam  35 - 2 , one of the communication transmitters  148 - 1  to  148 -N is assigned. When the beam selection information detection system  154  shown in  FIG. 29  is used in the embodiment of  FIG. 27 , the base station controller  126  assigns one of the communication channel transmitters/receivers  143 - 1  to  143 -M if the traveling speed is equal to or less than a given value, and assigns a time slot to the communication which is chosen in accordance with the relationship between the time slot and the narrow angle beam shown in  FIG. 28B  depending on the beam information from the level comparator  213 , namely, whether it indicates the right beam  35 - 2  or the left beam  35 - 1 . 
   One embodiment which uses the beam selection information detection system  154  shown in  FIG. 29 , but in which the diversity arrangement is removed from the arrangement shown in  FIG. 24  is shown in  FIG. 30  where corresponding parts to those described before are designated by like reference characters. Specifically, in this embodiment, the 120° beam antennas  21 - 1  and  21 - 2 , the duplexer  36 - 3  and the receivers  22 ,  142 ,  146  and  152  are omitted from the arrangement of FIG.  24 . Each transmitter  38  in the 120° beam control and communication channel transmitters/receivers  137 - 1  to  137 -L is capable of feeding a transmitting power to the both 60° beam ports  134   a  and  134   b  of the hybrid  134  through a hybrid  156 , and through the combiner and distributor  26  and the duplexers  36 - 1  and  36 - 2 , thus feeding transmitting power to the 120° beam (wide angle beam) antenna assembly  215 . In other words, in addition to feeding transmitting power to (and receiving received signals from) a plurality of narrow angle beams  35 - 1  and  35 - 2 , a plurality of narrow angle beam antennas  31 - 1  and  31 - 2  may be used to perform the transmission and the reception through a single wide angle beam. 
   In the arrangement shown in  FIG. 27  also, the 120° beam antenna  21 - 1  and  21 - 2  may be omitted, and the beam selection information detection system  154  shown in  FIG. 29  may be used to cause the pair of 60° beam antenna  31 - 1  and  31 - 2  to serve as the 120° beam antennas, in the similar manner as shown in FIG.  30 . 
   The wide angle beam is not limited to 120° as described above, but may cover 360°, for example. Instead of covering a service area which is covered by a wide angle beam by a pair of narrow angle beams, three or more narrow angle beams may be used to cover the service area of the wide angle beam. 
   According to the second aspect of the present invention as described above, a narrow angle beam can be assigned to a mobile station which is traveling slowly, without irradiating unnecessary radio waves in directions other than the direction on which a desired mobile station is located. The transmitting power from the base station equipment can be reduced in a corresponding manner, and the interferences can also be reduced because a dispersion of radio waves can be suppressed.