Abstract:
A communication system having a radio master and a radio slave for communicating a communication signal and a control signal via a common channel is constructed by a receiver to receive a communication signal, a transmitter to transmit a control signal, and a limiter to limit an output of the signal received by the receiver for a period of time corresponding to a transmission of the control signal and a reception of a predetermined signal by the receiver. The limiter has a key to request the transmission of the control signal and limits the output of the reception signal in accordance with the key operation. The generation of an uncomfortable sound which is caused by a communication of the control signal can be prevented.

Description:
This is a continuation of application Ser. No. 08/428,776, filed on Apr. 24, 1995 now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a communication system which transmits a communication signal and a control signal through a common channel. 
     2. Related Background Art 
     In a radio telephone system, a timer of a predetermined time is provided in order to prevent an uncomfortable sound which is caused due to communication of control information before communication of speech when a key entry operation is performed in a radio slave terminal a voice circuit is closed for the predetermined time. 
     However, as shown in FIG. 4, in the case where communication of a control signal with a communication control device in association with a key operation in the radio slave takes longer than the predetermined closure time of the voice circuit because, for example, signal transmission is repeated since radio throughout is bad or there is a delay of processes in the communication control device or there are a number of control information, or the like, there is a problem in that an uncomfortable sound which is caused by the communication of the control information with the communication control device is heard from the radio slave. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to prevent audibility of a control signal which is communicated session during a communication. 
     Another object of the invention is to prevent generation of an uncomfortable sound associated with a control signal when the control signal is communicated during a-speech communication. 
     Still another object of the invention is to prevent audibility of a control signal transmitted when a signal according to a key operation is transmitted. 
     Yet another object of the invention is to prevent audibility of a control signal when transmission of the control signal is started from an own system and when transmission of the control signal is started from a communication partner. 
     A further object of the invention is to provide a communication system in which a countermeasure for noisiness of a reception signal is performed by a slave at a proper timing and a countermeasure for noisiness of a transmission signal is performed by a master at an arbitrary timing. 
    
    
     The above and other objects and features of the present invention will become apparent from the following detailed description and the appended claims with reference to the accompanying drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram showing the first embodiment of the invention; 
     FIG. 2 is a sequence chart showing the first operation of the first embodiment; 
     FIGS. 3A and 3B are flowcharts showing the first operation of the first embodiment; 
     FIG. 4 is a sequence chart showing the operation of a conventional system; 
     FIG. 5 is a sequence chart showing the second operation of the first embodiment; 
     FIGS. 6A and 6B are flowcharts showing the second operation of the first embodiment; 
     FIG. 7 is a block diagram showing the second embodiment of the invention; 
     FIG. 8 is a sequence chart showing the operation of the third embodiment of the invention; and 
     FIGS. 9A and 9B are flowcharts showing the operation of the third embodiment. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     An embodiment of the present invention will now be described in detail hereinbelow with reference to the drawings. 
     FIG. 1 is a block diagram showing an example of a first radio telephone system embodying the invention. The system comprises: a cordless slave (hereinafter, referred to as a slave) 1 as a radio slave; a cordless master (hereinafter, referred to as a master) 2 as a radio master; and a communication control device 3 to control a telephone line. The slave 1 has a communication unit 11, a control unit 12, a voice circuit 13, and a console unit 14. The voice circuit 13 includes a handset, a speaker, and the like. The master 2 has a communication unit 21 and a control unit 22. The communication control device 3 has an exchange unit 31 and a control unit 32. 
     FIG. 2 is a sequence chart showing an example of the operation of the radio telephone system of the embodiment. FIGS. 3A and 3B are flowcharts showing an example of the operation of the slave 1 and communication control device 3 of the radio telephone system of the embodiment. 
     For example, in the case where a holding key is depressed in the slave 1, control information regarding a display and control information regarding a state (during speech communication, during holding) are transmitted to the slave 1. 
     First, when a key operation such as a dial key or the like is performed in the console unit 14 of the slave 1 (S11), in order to prevent a user from hearing an uncomfortable sound due to the control information communication the control unit 12 closes the voice circuit 13 (on the speech reception side) of the slave 1 while using the key operation as a trigger (S12). It is not always necessary to completely turn off a speech reception output but to reduce a volume sufficiently. 
     Although the slave 1 and communication control device 3 execute the communication of the control information according to the key operation via the master 2, an uncomfortable sound in association with such a communication is not heard by the user (S13, S113). In this instance, since the control information in association with the key operation is transmitted from the slave 1, the control unit 32 of the communication control device 3 recognizes that the voice circuit 13 of the slave 1 was closed. When the control unit 32 detects the control information from the slave 1, the control unit 32 mutes a speech transmission signal from the slave 1, thereby preventing that the control information is transmitted to the speech communication partner. The control unit 32 releases the muting operation after completion of the reception of the control information from the slave 1. In this case as well, a volume can be also reduced without completely muting the speech transmission signal. In the case where the slave 1 returns a reception acknowledge signal in response to the control information from the master 2, the control unit 32 mutes the speech transmission signal from the slave 1 for a time duration during which a return of such a reception acknowledge signal is presumed. That is, the muting operation of the speech transmission signal and the muting operation of the speech reception signal are executed at different times. After that, the control unit 32 of the communication control device 3 checks to see if the communication of the control information has been completed or not after the control information was transmitted by the slave 1 via the master 2 (S114). When the communication of the control information is not completed, the state in step S113 is continued. 
     After completion of the communication of the control information, the control unit 32 of the communication control device 3 transfers a voice circuit release notification to the slave 1 via the master 2 (S115). After the voice circuit release notification was received (S14), the control unit 12 of the slave 1 releases the voice circuit 13 (S16). Thus, a speech communication can be executed. 
     In the above description, as shown in step S11, the voice circuit has been closed due to the key operation of the slave 1. Explanation will now be made with respect to the operation in the case where before starting the communication of the control information from the communication control device 3 to the slave 1 via the master 2, a voice circuit close notification is transmitted from the communication control device 3 to the slave 1 via the master 2, thereby closing the voice circuit. 
     FIG. 5 is a sequence chart showing an example of the operation of the radio telephone system in such a case. FIGS. 6A and 6B are flowcharts showing an example of the operation of the communication control device 3 and slave 1 of the radio telephone system. 
     First, in the case where the control information is generated from the communication control device 3 to the slave 1 (S311), before such control information is transmitted, the control unit 32 of the communication control device 3 transmits the voice circuit close notification via the master 2 (S312). After receiving the voice circuit close notification (S32), the control unit 12 of the slave 1 closes the voice circuit 13 (on the speech reception side) (S33). 
     Subsequently, the control information is communicated between the slave 1 and the communication control device 3 via the master 2 (S34, S314). Just after the completion of the communication was confirmed (S315), the control unit 32 of the communication control device 3 transmits the voice circuit release notification via the master 2 (S316). By receiving the voice circuit release notification, the control unit 12 of the slave 1 opens the voice circuit 13 (S37). Thus, an uncomfortable sound which is caused due to the communication of the control information is avoided. In this case, an uncomfortable sound in the communication of the control information due to a command of the communication control device 3 can be avoided. The control unit 32 mutes the speech transmission signal in a time zone during which a return of a reception acknowledge signal from the slave 1 is presumed in a manner similar to the foregoing case. 
     FIG. 7 is a block diagram showing an example of the second radio telephone system embodying the invention. The system is constructed by the cordless slave (hereinafter, referred to as a slave) 1 serving as a radio slave and the radio master 2 connected to a wire circuit. 
     FIG. 8 is a sequence chart showing an example of the operation of the radio telephone system of the embodiment. FIGS. 9A and 9B are flowcharts showing an example of the operation of the slave 1 and a master 20 in the radio telephone system of the embodiment. 
     First, when a key operation such as a dial key or the like is performed in the console unit 14 of the slave 1 (S21), the control unit 12 closes the voice circuit 13 (on the speech reception side) of the slave 1 by using the key operation as a trigger (S22) in order to prevent the user from hearing an uncomfortable sound which is caused by the communication of the control information. 
     Subsequently, the control information is communicated between the slave 1 and the master 20. However, an uncomfortable sound which is caused by such a communication is not heard by the user (S23, S213). In this instance, since the control information in association with the key operation is transmitted from the slave 1, a control unit 24 of the master 20 recognizes that the voice circuit 13 of the slave 1 was closed. The control unit 24 mutes the speech transmission signal in a manner similar to the control unit 32 of the foregoing embodiment. 
     After that, the control unit 24 of the master 20 judges whether communication of the control information has been completed or not (S214). When communication of the control information is not completed, the state in step S213 is continued. 
     After completion of communication of the control information, the control unit 24 of the master 20 transfers a voice circuit release notification to the slave 1 (S215). When receiving the voice circuit release notification, the control unit 12 of the slave 1 releases the voice circuit 13 (S26). 
     Although the present invention has been described above with respect to the preferred embodiments, the invention is not limited to the constructions of the above embodiments but many modifications and variations are possible within the spirit and scope of the appended claims of the invention. For example, the invention is not limited to the radio telephone system but can be also applied to a wired communication system in which a speech communication signal and a control signal are communicated using a common channel.