1. Field of the Invention
The present invention relates to space-division multiplex communication method in which a plurality of rotationally radiated radio beams consisting of the same frequency are transmitted and received between a plurality of stations, thereby executing time-division multiplex communication.
2. Description of the Related Art
In general, a multiplex communication method of time-dividing a radio beam by using a radiation beam system in which radio beams having the same frequency and carrying different pieces of information are radiated in a plurality of directions and a method of performing interstation bidirectional multiplex communication by introducing a frequency-division system to the multiplex communication method have not yet been established.
An example of conventional techniques using the rotation of a beam is a radar. FIG. 5 shows an example of the radar.
Referring to FIG. 5, a station is provided to radiate and receive a radio beam. This station radiates a radio beam while rotating a beam. If an object is present in the radiation direction of the radiated radio beam, the radio beam is reflected by the object. The station receives the reflected radio beam and determines the position of the object in accordance with the incoming direction and the reception level of the received radio beam.
From a viewpoint of communication, a frequency- or time-division communication technique is available.
FIG. 6 is a view for explaining an arrangement of a conventional frequency-division multiplex communication system. Referring to FIG. 6, an information transmission station T for transmitting information is provided.
The information transmission station T non-directionally radiates a plurality of radio beams having different frequencies.
A plurality of receivers R1, R2, R3, . . . , Rn each for receiving a radio beam having a predetermined frequency are located within a distance range in that the above transmitted radio beams can be received. The receivers R1, R2, R3 , . . . , Rn receive radio beams having frequencies f1, f2, f3, . . . , fn, respectively.
In the above communication system, a frequency to be used in transmission performed by the information transmission station must be provided for each receiver. This goes for an arrangement in which a plurality of information transmission stations are provided.
FIG. 7 is a view for explaining an arrangement of a conventional time-division multiplex communication system, and FIG. 8 is a view showing transmission data used in the system. Referring to FIG. 7, radio beams are non-directionally radiated from an information transmission station for transmitting information.
A plurality of receivers R1, R2, R3, . . . , Rn for receiving the radiated radio beams are located within a distance range in that they can receive the above radiated radio beams. The receivers R1, R2, R3, . . . , Rn receive information at timings 1, 2, 3, . . . , n shown in FIG. 8, respectively. Referring to FIG. 8, information at timing 0 is a sync signal to be used by each receiver for information extraction.