RADIO COMMUNICATION SYSTEM AND ITS CONTROL METHOD

Abstract: Wireless communication equipment of the multichannel access system which detects a vacant wireless channel out of a plurality of wireless channels to transmit and receive voice or data. When a call is received through a wire, a signal for designating a speech channel and a signal for designating a representative out of a plurality of wireless terminals are sent to a plurality of wireless terminals. Under the condition where a channel switch completion signal is received from the representative wireless terminal equipment, a signal for generating calling sound is transmitted to a plurality of wireless terminals simultaneously, such that calling sound is generated simultaneously from the plurality of wireless terminals.

Description: The present invention relates to a radio communication system of the multi-channel access type in which an idle one of a plurality of radio channels is detected to perform transmission and reception of voice signals, data signals or the like, and also to a method of controlling the radio communication system. Fig. 3 is a block diagram showing an arrangement of a prior art radio communication system of the type referred to the above. In the drawing, a base unit 1 is to be coupled, at its one side, through a radio communication circuit to a radio telephone set 2 as a radio terminal apparatus; while the base unit is also connected, at the other side, to a wired telephone line 3. A signal sent from the wired telephone line 3 is supplied through a line relay 10 and a hybrid circuit 11 to a transmitter 12 as its modulation input. Electromagnetic waves subjected to a modulation at the transmitter 12 are transmitted from an antenna 14 to the radio telephone set 2 through antenna duplexer 13. Electromagnetic waves transmitted from the radio telephone set 2, on the other hand, are received at the antenna 14 and sent through the antenna duplexer 13 to a receiver 15 to be demodulated thereat. A signal subjected to a demodulation at the receiver 15 is send through the hybrid circuit 11 onto the wired telephone circuit 3. A synthesizer 16 applies to the transmitter 12 and the receiver 15 a signal of a frequency corresponding to radio channels, that is, speech and control channels. The receiver 15 has a function of demodulating a data signal included in the received demodulation wave signal, that is, demodulating an identification signal determined by a combination of the base unit 1 and the radio telephone set 2, and the receiver 15 applies the demodulated identification signal (ID code) to a controller 17. The controller 17 per se is used to control the synthesizer 16 in such a manner that the switching of the radio channels is controlled and a transmission data signal is applied to the transmitter 12 as its modulation input. A ringing-signal detecting circuit 18 detects a ringing signal of 16Hz received from the wired telephone line 3. The identification signal of the radio telephone set 2 is previously stored in a ROM 19. As in the base unit 1, the radio telephone set 2 also has an antenna 20, a receiver 21, an antenna duplexer 22, a transmitter 23 and a synthesizer 24, a demodulated output of the receiver 21 being output to a handset receiver 30. A voice input through a handset transmitter 25 is applied to the transmitter 23 as its modulation input, sent to the antenna duplexer 22 and further transmitted from the antenna 20. The synthesizer 24 and a ROM 26 are substantially the same as those in the base unit 1. A controller 27 performs the entire control over the radio telephone set 2. A loudspeaker 28 is a sounder which generates a ringing tone at the time of receiving an incoming signal. The control of this prior art radio communication system in its incoming signal mode is schematically carried out in accordance with such a flowchart as shown in Fig. 4. The base unit 1, when detecting at the ringing-signal detecting circuit 18 an incoming signal received from the wired telephone line 3 in its wait mode (step 30), sets the oscillation frequency of the synthesizer 16 at a control channel frequency, turns ON the receiver 15 to receive electromagnetic waves on a control channel (C-CH), and in the absence of the received electromagnetic waves, judges that the control channel is idle and transmits the incoming signal from the transmitter 12 (steps 31 and 32). In this case, the incoming signal contains a speech channel (S-CH) designation signal. In the radio telephone set 2 in its wait mode, on the other hand, the synthesizer 24 is turned ON, the oscillation frequency of the synthesizer is set at the control channel frequency, and the receiver 21 is intermittently turnend ON. When the receiver 21 is turned ON (step 50), the transmitter 23 is turned ON under a condition that the ID code contained in the incoming signal coincides with the ID code stored in the ROM 26, so that the transmitter transmits an incoming-signal answering signal including its own ID code (step 51) and the speech channel (S-CH) is switched to the specified one (step 52). In the case where the radio telephone set 2 receives no incoming signal, the receiver 21 is turned OFF and the radio telephone set is put back in its wait mode. The base unit 1 is monitoring the arrival of the incoming-signal answering signal from the radio telephone set 2 for a time of T1. If the base unit 1 receives the incoming-signal answering signal within the time of T1 (steps 33 and 34), then the base unit stops the transmission of the incoming signal therefrom, compares the ID code contained in the incoming-signal answering signal with the ID code stored in the ROM 19, and when finding an ID code coincidence, switches the speech channel (S-CH) to the one specified by the incoming signal (step 35). If the base unit fails to find an ID code coincidence, then the unit awaits the disappearance of the ringing signal from the wired telephone line 3 and returns to the wait mode, since this incoming-signal answering signal is from another undesired radio telephone. Even when the base unit 1 fails to receive the incoming-signal signal within the time T1, the unit returns to the wait mode. The radio telephone set 2, on the other hand, switches the current speech channel to the one specified by the base unit 1. When the switched speech channel is already being used, the radio telephone set 2 returns to the wait mode (step 53). When the switched speech channel is not being used, the radio telephone set 2 transmits a channel switching completion signal toward the base unit 1 (step 55). Meanwhile, the base unit 1 is monitoring the arrival of the channel switching completion signal from the radio telephone set 2 for a time of T2. When the base unit 1 fails to monitor the arrival of the channel switching completion signal within the time of T2, the base unit regards the radio telephone set 2 as having judged that the speech channel is in use, and returns to the wait mode. When the base unit 1 detects the arrival of the channel switching completion signal within the time T2 (steps 36 and 37), the base unit transmits a bell ringing signal (step 38). The radio telephone set 2, when receiving the bell ringing signal (step 56), causes the loudspeaker 28 to generate a ringing tone (step 57). Responsive to the ringing tone, if the telephone user turns OFF a hook switch 29 to provide an off-hook operation to the radio telephone set 2 (step 58), then this causes the radio telephone set 2 to transmit an off-hook signal (step 59) and then to be put in its speech mode (step 60). The base unit 1, when receiving the off-hook signal (step 39), stops the transmission of the bell ringing singal, closes the line relay 10 to establish a speech loop with the wired telephone line 3, and thus enters into its speech mode (step 40). The following is the operation of the radio communication system when it is desired to give a call from the radio telephone set 2. That is, when the telephone user turns OFF the hook switch 29 for the purpose of giving a call to the wired telephone line 3, this causes the controller 27 to judge on the basis of the switch 29 turned OFF that the radio telephone set should be moved to its signal transmission mode, lock the oscillation frequency of the synthesizer 24 at that of the control channel, and turn ON the receiver 21 to receive electromagnetic waves on the control channel (C-CH). And when the intensity of electric field received on the control channel is lower than a predetermined constant value, the controller judges that the control channel is idle and turns ON the transmitter 23 to transmit therefrom a calling signal including the ID code assigned to its own telephone set. The base unit 1, when receiving the ID code, decides whether or not the received ID code coincides with the ID code assigned to the combination between the radio telephone set 2 and the base unit 1. If the base unit 1 finds an ID code coincidence, then it turns ON the transmitter 12 to transmit an answering signal (including the ID code and speech channel (S-CH) designation information) therefrom toward the radio telphone set 2. The radio telephone set 2 receives the answering signal from the base unit 1 on the control channel, and determines whether or not the ID code included in the received answering signal coincides with its own one. If the radio telephone set determines an ID code coincidence, then it causes the oscillation frequency of the synthesizer 24 to be switched to the frequency of the speech channel specified by the base unit 1. Meanwhile, the base unit 1 itself, after having transmitted the answering signal, causes the oscillation frequency of the synthesizer 16 to be switched to the frequency of the speech channel specified for the speech. As a result, the radio telephone set 2 is interconnected with the base unit 1 through the speech channel specified by the base unity 1. Thereafter, user's dialing operation with use of a dial key (not shown) enables the calling of the party telephone and the realization of speech with the party. In the aforementioned radio communication system, such an arrangement is considered that n (n ≧ 2) of the radio telephone sets are provided for a single base unit so that, when the base unit receives an incoming call from the wired telephone line, not only one radio telephone set but all the radio telephone sets generate ringing tones to improve the possibility of answering the incomging call. In this case, the incoming signal including a speech-channel designation signal is transmitted to all the radio telephone sets to generate the ringing tones at all the radio telephone sets. As will be clear from a flowchart shown in Fig. 4, each of the radio telephone sets switches the current speech channel to the one specified by the base unit, checks the idle or non-idle state of the speech channel, and when finding the idle state, transmits the channel switching completion signal. Such operation proceeds simultaneously with respect to all the n radio telephone sets. For this reason, the channel switching completion signals will be transmitted substantially at the same time from all the radio telephone sets, which may cause radio interference at the base unit. To avoid such radio interference, such an arrangement is necessary that the channel switching completion signals be transmitted from the respective radio telephone sets in slightly mutually shifted timing relationship therebetween, and only when the base unit receives all the channel switching completion signals from all the radio telephone sets, the base unit should transmit the bell ringing signal. In the case where the channel switching completion signals are transmitted to the base unit at different timings, however, the base unit must wait for the transmission of the bell ringing signal until the base unit receives all the channel switching completion signals from the n radio telephone sets. For this reason, the prior art radio communication system has such a problem that the generation of the ringing tones at the respective radio telephone sets is delayed and thus user's response is also delayed. A similar system is disclosed in EP-A-0214810. A radio telephone system comprises one master apparatus and a plurality of radio telephone sets, and when a call is received from a communication line, the master apparatus sequentially transmits an incoming signal containing channel designation information to the plurality of radio telephone sets in a predetermined priority order so as to sequentially guide the radio telephone sets to a speech channel. It then transmits a bell ringing signal to the radio telephone sets through the speech channel. By way of background also, EP-A-0180178 discloses a cordless telephone system which allows a plurality of mobile stations to be connected to a single base station, in which the mobile stations are classified into a master and slaves. In this system, however, the master station is capable of originating and receiving a telephone call, the others are only capable of receiving a telephone call. It is an object of the present invention to provide a radio communication system which, when it is desired to generate ringing tones at the same time at a plurality of radio telephone sets as radio terminal apparatuses, can generate such ringing tones in a short time, and also to provide a method of controlling the radio communication system. The invention provides a radio communication system according to Claim 1, and a method according to Claim 11 of controlling a radio communication system. When the base unit receives the incoming call from the wired line, only a representative one of the plurality of radio terminal apparatuses which is specified by the base unit can send the speech channel switching completion signal to the base unit. And when the base unit receives the channel switching completion signal from the representative radio terminal apparatus, it transmits a ringing signal for generation of the ringing tones such that the ringing tones can be generated at the same time from the plurality of radio terminal apparatuses. Thus, the base unit no longer has to delay the transmission of the ringing signal until the base unit has received all the channel switching completion signals from the plurality of radio terminal apparatuses. As a result, the ringing tones can be generated at the same time from the plurality of radio terminal apparatuses and in a shorter time than before. Brief Description of Drawings: Fig. 1 is a block diagram showing an embodiment of the present invention; Fig. 2 is a flowchart showing the incoming-call operation of the embodiment; Fig. 3 is a block diagram showing an arrangement of a prior art radio communication system; and Fig. 4 is a flowchart showing the incoming-call operation of the prior art system. Referring to Fig. 1, there is shown a block diagram of an embodiment of the present invention, in which two radio telephone sets 2 and 2' as radio terminal apparatuses are provided for a single base unit 1. Parts enclosed by broken lines in the two radio telephone sets 2 and 2' have an identical arrangement, but ROMs for storage of ID code provided in the telephone sets are distinguishably shown as denoted by 26 and 26', because the ROMs store respectively different ID codes assigned to the respective radio telephone sets 2 and 2'. ROMs in the base unit 1 are correspondingly shown distinguishably as denoted by 19 and 19'. The incoming call operation of this embodiment is shown by a flowchart in Fig. 2. Explanation will be made as to the operation of the embodiment when receiving an incoming call from a wired telephone line 3, by referring to the flowchart of Fig. 2. First, the base unit 1, when receiving an incoming call from a wired telephone line 3, checks the idle or non-idle state of the control channel and in the case of the idle state, transmits an incoming signal, as in the prior art system. In this connection, although the incoming signal contains the speech-channel designation signal and the ID code of the radio telephone set in the prior art, the incoming signal containing only the ID code is transmitted so that the ID code prescribes the returning timing of an incoming-signal answering signal to be returned from the radio telephone sets 2 and 2' in the present embodiment. The radio telephone set 2 or 2', when receiving the incoming signal containing the ID code that coincides with the ID code assigned to the telephone set (step 50), returns the incoming-signal answering signal to the base unit 1 at a timing prescribed by the ID code (step 51). The base unit 1 is monitoring the arrival of the incoming-signal answering signal from the telephone sets for the time T1 after having transmitted the incoming signal. The base unit 1, when receiving the incoming-signal answering signals from both or at least one of the radio telephone sets 2 and 2' (steps 41 and 42), transmits a speech channel designation signal to the radio telephone sets and then switches its own speech channel to the one specified by the speech channel designation signal (steps 43 and 35). Here, the channel designation signal contains a channel code indicative of the specified speech channel as well as an ID code signal specifying a representative one of the plurality of radio terminal sets which responds to the incoming signal and returns a channel switching completion signal to the base unit. The radio telephone set 2 or 2' is monitoring the arrival of the channel designation signal for a time of T3 (steps 61 and 62). If the radio telephone set receives the channel designation signal, then it switches the current speech channel to the specified one (step 52) and checks the idle or non-idle state of the specified speech channel (step 53). When the specified channel is not in the idle state, the radio telephone set returns to its wait mode; whereas, when the specified channel is in the idle state, the telephone set examines whether the telephone set itself is selected to be the representative one. If the radio telephone set is selected to be the representative one (step 54), then only the representative radio telephone set transmits the channel switching completion signal (step 55). If the radio telephone set is not selected to be the representative one, then it awaits the reception of a bell ringing signal. The base unit 1, when receiving the channel switching completion signal from the radio telephone set 2 or 2' as the representative one (steps 36 and 37), transmits the bell ringing signal (step 38) to the radio telephone sets 2 and 2' to cause the two radio telephone sets 2 and 2' to generate ringing tones at the same time. As criterions on the basis of which the base unit 1 selects representative one of the radio telephone sets, the following conditions can be considered. 1 ○ One of the radio telephone sets which has first transmitted the incoming-signal answering signal. 2 ○ One of the radio telephone sets having transmitted the incoming-signal answering signal and having the minimum or maximum value among the ID codes of these telephone sets. 3 ○ One of the radio telephone sets which has been the maximum in the intensity of received electric field of the incoming-signal answering signal. When the other one of the two radio telephone sets 2 and 2', e.g. radio telephone set 2', which has not been selected to be the representative one fails to receive the incoming signal for some reasons, for example, due to the fact that the radio telephone set 2' is located out of its wave arrival range, the telephone set 2' returns to its wait mode and thus will not generate a ringing tone. Although explanation has been made as to the radio telephone sets, as an example, in the foregoing embodiment, the present invention may be applied to various sorts of radio terminal apparatuses for data transmission and so on. Industrial Applicability: As has been explained in the foregoing, in the present invention, when it is desired to generate ringing tones at a plurality of radio terminal apparatuses at the same time, a representative one of the plurality of radio terminal apparatuses is selected and a base unit, only when receiving a channel switching completion signal from the representative radio terminal apparatus, transmits a signal for generation of the ringing tones. As a result, it can be eliminated that the base unit must await the reception of the channel switching completion signals from all the radio terminal apparatuses, and all the radio terminal apparatuses which have responded to the incoming signal can generate the ringing tones at the same time and in a short time.

Claims: A radio communication system, comprising a base unit (1) connected to a wired line (3) and a plurality of radio terminal units (2) to be coupled through a radio circuit (14, 20) with the base unit, in which the base unit is arranged to transmit (12) an incoming signal to the plurality of radio terminal units (2) through a control channel when the base unit receives an incoming call from the wired line; the radio terminal units (2) being arranged to return (23) through the control channel an incoming signal answering signal to the base unit in response to the incoming signal; the base unit (1) being arranged to transmit a channel designation signal to the plurality of radio terminal units in response to the reception of the incoming signal answering signal and to switch a reception channel of its own to a communication channel designated by the channel designation signal; each radio terminal unit being arranged, on receipt of the channel designation signal to switch (27) a reception channel of its own to a communication channel designated by the channel designation signal and to transmit a channel switching completion signal to the base unit; and the base unit (1), in response to the reception of the channel switching completion signal, being arranged to transmit a ringing signal through the switched communication channel to the plurality of radio terminal units (2), CHARACTERIZED IN THAT: the base unit is arranged to select (17) a representative one of the radio terminal units which have returned the incoming signal answering signals and to transmit representative radio terminal identification information for identifying the selected representative radio terminal unit together with the channel designation signal to the plurality of radio terminal units; the arrangement is such that only the said one representative radio terminal unit (2) which is identified by the representative radio terminal identification information transmits the channel switching completion signal to the base unit (1); and the base unit is arranged, in response to the channel switching completion signal received from the representative radio terminal unit, to transmit the ringing signal to the plurality of radio terminal units. A radio communication system according to Claim 1, wherein each of the radio terminal units (2) is a radio telephone set. A radio communication system according to Claim 1 or 2, wherein the base unit (1) is arranged to transmit the incoming signal to the plurality of radio terminal units (2) together with an identification code for identifying each radio terminal unit. A radio communication system according to Claim 1, 2 or 3, wherein the radio terminal units (2) are arranged to transmit the incoming signal answering signals to the base unit (1) with a mutually shifted timing relationship between the plurality of the radio terminal units (2). A radio communication system according to Claim 3, wherein each of the radio terminal units (2) is arranged to transmit the incoming signal answering signal to the base unit (1) at a timing specified by the identification code. A radio terminal system according to Claim 4, wherein the base unit (1) is arranged to select, as the representative radio terminal unit, the radio terminal unit (2) from which the incoming signal answering signal is received first. A radio communication system according to Claim 3, wherein the base unit (1) is arranged to select the representative radio terminal unit (2) on the basis of the identification code. A radio communication system according to Claim 3, wherein the base unit (1) is arranged to select, as the representative radio terminal unit, the radio terminal unit (2) from which the highest level of the incoming signal answering signal is received. A radio communication system according to any preceding claim, wherein the base unit (1) is arranged to transmit the channel designation signal either when it has received the incoming signal answering signals from all the radio terminal units (2) within a predetermined time or else when it has received the incoming signal answering signal from at least one of the plurality of radio terminal units (2) and the predetermined time has elapsed. A radio communication system according to any preceding claim, wherein each of the radio terminal units (2) is arranged to return to a wait mode when it has failed to receive the channel designation signal within a predetermined time after transmission of the incoming signal answering signals. A method of controlling a radio communication system comprising a base unit (1) connected to a wired line (3) and a plurality of radio terminal units (2) to be coupled through a radio circuit (14, 20) with the base unit, in which the base unit transmits an incoming signal to the plurality of radio terminal units through a control channel when the base unit receives an incoming call from the wired line; at least one of the plurality of radio terminal units which has received the incoming signal returns through the control channel an incoming signal answering signal to the base unit in response to the incoming signal; the base unit transmits a channel designation signal to the plurality of radio terminal units in response to the reception of the incoming signal answering signal and switches a reception channel of its own to a communication channel designated by the channel designation signal; at least one of the plurality of radio terminal units which has received the channel designation signal switches a reception channel of its own to a communication channel designated by the channel designation signal and transmits a channel switching completion signal to the base unit; and the base unit, in response to the reception of the channel switching completion signal, transmits a ringing signal through the switched communication channel to the plurality of radio terminal units, CHARACTERIZED IN THAT the method comprises: a first step of selecting a representative radio terminal unit from the radio terminal units (2) which have returned the incoming signal answering signals; a second step of transmitting representative radio terminal identification information for identifying the selected representative radio terminal unit (2) togehter with the channel designation signal from the base unit to the plurality of radio terminal units; a third step of transmitting the channel switching completion signal to the base unit (1) from only the representative radio terminal unit which is identified by the representative radio terminal identification information; and a fourth step of transmitting the ringing signal from the base unit (1) to the plurality of radio terminal units (2) in response to the channel switching completion signal received from the representative radio terminal unit.

Inventors: FUSE SHOJI, OHTA YUJI, ONO KOJI, SAEGUSA NOBORU, SHIMURA YUKIHIRO, TOYAMA HIDEKI, FUSE, SHOJI, OHTA, YUJI, ONO, KOJI, SAEGUSA, NOBORU, SHIMURA, YUKIHIRO, TOYAMA, HIDEKI, ONO, KOJI 605, HACHIOJI-HAZAMA-JUTAKU, SAEGUSA, NOBORU NEC CORPORATION, SHIMURA, YUKIHIRO NEC CORPORATION
Applicants: NIPPON ELECTRIC CO, NIPPON TELEGRAPH & TELEPHONE, TOSHIBA KK, KABUSHIKI KAISHA TOSHIBA, NEC CORPORATION, NIPPON TELEGRAPH AND TELEPHONE CORPORATION, NTT MOBILE COMMUNICATIONS NETWORK INC.
Application year: 1989
Main classification: H04M1
IPC codes: H04J3, H04B7, H04Q7, H04M1