JPH07212838A - Digital cordless telephone equipment - Google Patents

Abstract

PURPOSE:To satisfactorily perform the transmission processing of a control signal from each master set in the digital cordless telephone provided with plural master sets even in the case that communication with the other master sets is impossible. CONSTITUTION:In the digital cordless telephone equipment where transmission and reception of digital data are shifted from each other with respect to time to perform speaking between master sets 1, 2, and 3 and slave sets 4, 5... and a system call code common to respective master sets 1, 2, and 3 is set to realize speaking between all master sets 1, 2, and 3 and slave sets 4, 5..., the control signal from the master set 1 as the reference out of plural master sets is received by the other master sets 2 and 3, and control signals are transmitted from the other master sets 2 and 3 synchronously with the reception timing of this control signal, and the other master sets 2 and 3 transmit control signals at independent timings if failing reception of the control signal from the master set 1 as the reference.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital cordless telephone device in which communication between a base unit and a handset is performed by transmitting / receiving digital data.

[0002]

2. Description of the Related Art A digital cordless telephone system is constructed, for example, as shown in FIG. In FIG. 9, reference numeral 1 denotes a base unit that serves as a base station, and the base unit 1 is connected to a telephone line and includes an antenna 1a for communicating with a handset. A plurality of (three in this case) slaves capable of communicating with the master 1 are prepared. That is, the slaves 4, 5, 6 are prepared, the antennas 4a, 5a, 6a are attached to the slaves 4, 5, 6 respectively, and the antenna 1a of the master 1 and the antennas of the slaves 4, 5, 6 are installed. 4a, 5a, 6
Wireless transmission is performed with a.

When a call is made with each of the slaves 4, 5 and 6 to the master 1 (or the other party connected to the master 1 via a telephone line), the master 1 sends a connection control signal of a predetermined format.
Then, the voice data converted into digital data is transmitted to the base unit 1 in a time division manner with the base unit 1 to make a call.

In such a digital cordless telephone device, transmission and reception are performed at the same frequency, and so-called ping-pong transmission is performed in a TDD system (time division duplex system) or a TDMA / TDD system (time division multiple access / time division). There are some that are adopted.

That is, in the case of the TDD system, for example, as shown in A of FIG. 10, one channel (frequency) is temporally divided into a transmission slot T and a reception slot R, and these slots T and R alternate. And a guard time (not shown) is provided between these slots T and R. In this case, for example, each slot T, R is 1 m
The guard time is set to several tens of microseconds. Then, the mobile phone (slave unit) communicates with the base station (master device) in the transmission slot T and receives from the base station in the reception slot R.

In the case of the TDMA / TDD system,
As shown in FIG. 10B, in the communication between one child device and the parent device, the transmission slot T and the reception slot R in one channel are used only once every several cycles, and the same channel is used. The other transmission slot T and the reception slot R are used for communication between another child device and the parent device, and are multiplexed so that communication can be performed between a plurality of communication devices on one channel. is there.

By being multiplexed in this way, the frequency band prepared for the cordless telephone can be used efficiently. By the way, in the case of performing such communication, the transmission of the control signal from the master unit to each slave unit is performed according to a fixed format every predetermined period. That is, for example, as shown in A of FIG. 11, the control signal d1 is transmitted to each slave unit for 625 μs every 125 msec. Then, for example, when any one of the slave units is called by an extension call from the master unit, the individual number of the corresponding slave unit is transmitted by the control signal d1 and the corresponding slave unit is called. Then, during the standby operation in which each slave unit waits for being called by the control signal from the master unit, as shown in B of FIG. 11, only this control signal is transmitted in a predetermined cycle (for example, 1 every 1.5 seconds). By intermittently turning on the power supply of the reception unit so that the reception is intermittently performed, the power consumption required for reception in the reception standby state can be reduced. In addition, the reception of the control signal once,
Basically, it only needs to be performed for 625 μsec, but in actuality, considering the rise time of the receiving unit, etc., about 10 m at a time
Only receive for a second. So, for example, 10 every 1.5 seconds
If the reception is performed every m seconds, the time during which the receiving unit is operating is about 0.67%, and the power consumption can be significantly reduced compared to the case where the reception is continuously performed.

[0008]

By the way, as a system configuration for such a digital cordless telephone,
As shown in FIG. 1, a system having a plurality of parent devices is considered. That is, in FIG. 1, reference numerals 1, 2 and 3 indicate respective cordless telephone master units, and the respective master units 1, 2 and 3 are individually connected to a telephone line and are connected to a cordless handset. Antennas 1a and 2 for communication
a, 3a. Then, it is assumed that slave units 4,5, 6, 7, 8 ... Which are capable of communicating with the respective master units 1, 2, 3 are prepared. At this time, each of the slaves 4, 5, ... Is capable of wireless communication with any of the masters 1, 2, 3, and is also capable of making a call through any of the masters. With this configuration, each mobile device can send an outside line through which master device and can answer when there is an incoming call on any master device. Spreads.

However, if the slaves can communicate with a plurality of masters in this way, each slave must receive control signals from all masters during standby operation.
Intermittent reception during the standby operation described above is not possible,
It was difficult to reduce the power consumption during the standby operation. That is, in each of the slave units 4, 5, ...
There is a possibility that it will be called by a control signal even from a few
The control signal transmitted from the first base unit 1 and the second base unit 2
It is necessary to receive all of the control signal transmitted from the control unit and the control signal transmitted from the third master unit 3. Here, the control signals are periodically transmitted from the respective master units 1, 2, and 3, but the respective control signals transmitted from the three master units 1, 2, 3 are completely compatible with each other. It doesn't matter. Therefore,
When the slave units 4, 5 ... Are in standby mode,
In order to receive the control signal from any of the base units, it is necessary to make the receiving unit of each handset power on for a very long time.

In this case, it is possible to detect the timings at which the control signals are transmitted from all the master units 1, 2, and 3 and turn on the power supply of the receiving unit of each slave unit at each transmission timing. In this case, the number of times of turning on / off is three times (when there are three parent devices) compared with the case of turning on only at the timing when the control signal is transmitted from one parent device as shown in FIG. However, the on / off control of the receiver becomes complicated.

In order to solve this inconvenience, the present applicant first made one master unit 1 a master master unit and another master unit a slave master unit from slave master units 2 and 3. Has proposed a cordless telephone system in which the transmission of control signals from the master unit 1 is synchronized with the control signal transmitted from the master unit 1 so that the control signals are continuously transmitted from each unit. No. 159484).

However, when the system is constructed in this way, when the slave master units 2 and 3 suffer some reception failure and cannot receive the control signal from the master master unit 1, the control signal is transmitted. I don't know the timing. If the transmission timing of the control signal is unknown, it becomes impossible to transmit the control signal from the slave master devices 2 and 3, and the slave master device does not function as a master device of the cordless telephone.

In view of the above, the present invention provides a cordless telephone apparatus of this type in which a control signal transmission process from each master unit in the case of a system having a plurality of master units cannot communicate with other master units. But there is to be good.

[0014]

According to the present invention, for example, as shown in FIG. 1, a plurality of parent machines 1, 2, 3 and child machines 4, 5 ,.
.. and the slave units 4,5, ... Make a call by differently transmitting and receiving digital data with respect to each other, and make a call. , 3 to set a common system call code, all base units 1,
In a digital cordless telephone device capable of communicating between the second and third handset units 4, 5, ..., The control signal transmitted from the base unit 1 serving as a reference among a plurality of base units is transmitted to other parent units. The masters 2 and 3 receive the signals, and the control signals are transmitted from the other masters 2 and 3 in synchronization with the reception timing of the control signal. When the control signal to be transmitted cannot be received, the control signal is transmitted at its own timing.

Further, in this case, after a predetermined time elapses after the control signal transmitted from the reference master device 1 cannot be received, the other master devices 2 and 3 transmit the control signal from the reference master device 1. When the control signal is received and the control signal can be received, the control signal is transmitted from the other master units 2 and 3 in synchronization with the reception timing of the control signal.

Further, the process of receiving the control signal from the base unit 1 serving as the reference is repeated every time a predetermined time elapses until the control signal can be received.

[0017]

According to the present invention, while the control signal transmitted from the reference master unit can be received, each master unit transmits the control signal in synchronism with the control signal. The timing is always constant. Then, when some failure occurs and the other master cannot receive the control signal transmitted from the reference master, each master transmits the control signal at its own timing. The control signal from the parent device can be received, and the child device can access the parent device in any case.

In this case, after a lapse of a predetermined time after the control signal transmitted from the reference master device cannot be received, another master device receives the control signal transmitted from the reference master device. , When this control signal can be received, the control signal is transmitted from another master unit in synchronization with the reception timing of this control signal, so that the process of restoring the synchronization with the reference master unit is performed. Well done.

Further, the reception process of the control signal from the base unit as a reference is repeated every time a predetermined time elapses until the control signal can be received, so that there is no obstacle in the communication state between the base units. Then, the synchronous state can be immediately restored.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS.

In this example, as in the conventional example, TDMA is performed.
It is applied to a digital cordless telephone device of the / TDD system. First, the system configuration is shown in FIG. In this example, three master units are prepared, and the first, second, and third master units 1, 2, and 3 are individually connected to the telephone line and are connected to the slave unit. 1a, 2 for communicating with
a, 3a. A plurality of slave units 4, 5, 6, 7, 8 ... Which can communicate with the respective master units 1, 2, 3 are provided, and each slave unit 4, 5 ,. Are provided with antennas 4a, 5a ...
At this time, each of the slaves 4, 5, ... Is capable of wireless communication with any of the masters 1, 2, 3, and is also capable of making a call through any of the masters.

In this case, a common system call code is set for each master unit 1, 2, 3 and the common system call code is set for the control signal transmitted from each master unit 1, 2, 3. It is added that each slave unit is commonly used,
The system call code can be used for discrimination. Explaining the configuration of this system call code, first, the downlink control signal transmitted from each master unit is shown in FIG.
It is configured as shown in. That is, first, a preamble PR which is synchronous data in which a fixed pattern continues for a predetermined period is provided, and in the following, a unique word UW of a specific pattern indicating a control signal, a channel type C for communication are performed.
1, control data CAC indicating control contents, and parity CRC for error detection.

Then, the identification code shown in FIG. 8 is transmitted by using a predetermined bit in the control data CAC. As the identification code, the system call code is transmitted using the first half 29 bits, and the additional ID is transmitted using the second half 13 bits. With this additional ID, an ID set individually for each parent device is transmitted. Note that FIG.
The control signal shown in (1) is transmitted once in 625 μsec.

In this example, the first master unit 1 of the three master units prepared is the master master unit, and the other master units 2 and 3 are slave master units. Then, the slave master units 2 and 3 receive the control signal transmitted from the master master unit 1, and the control signals from the slave master units 2 and 3 are synchronized with the reception timing of the control signal. I am trying to send you. Specific control of this transmission timing will be described later.

Next, the configuration of each of the master units 1, 2, and 3 will be described. The master unit 1 of the master and the slave units of the master units 2 and 3 have the same circuit configuration, as shown in FIG. Composed. That is, the wireless unit 32 receives and processes the data received from the slave unit by the antenna 31, supplies the data to the modulator / demodulator 33, and demodulates the received data. Then, the demodulated received data is supplied to the ADPCM codec section 35 via the communication control section 34, the ADPCM digital data obtained by reception is used as an analog audio signal, and this analog audio signal is supplied to the line interface section 36. , Analog telephone line connection terminal 3
Send to 7 side.

Further, an analog voice signal obtained from the analog telephone line connection terminal 37 side is supplied to the ADPCM codec unit 15 via the line interface unit 36, and A
The DPCM digital data is supplied to the modulation / demodulation unit 33 via the communication control unit 34 to be modulated for transmission, and the modulated data is wirelessly transmitted from the antenna 31 connected to the wireless unit 32.

Further, the handset 38 is directly connected to the line interface unit 36 so that the handset 38 can communicate with the outside line side through the analog telephone line connection terminal 37, and the handset 38 can be connected to the ADPCM codec unit 15 side to make a child. It is possible to make extension calls with the machine. Further, the key input unit 39 is connected to the line interface unit 36 so that various controls such as transmission to an outside line can be performed.

Then, in the communication control unit 34 of this master unit,
A dedicated channel (frequency band) prepared for control signal transmission is used to transmit control signals at predetermined intervals, and this control signal is used to call other slave units. In this case, the same system call code is added to the control signal transmitted from each master unit, and the distinction between the master and the slave is notified by the additional ID transmitted following the system call code.

In this example, the communication control unit 34 of the slave master units 2 and 3 controls so as to receive the control signal transmitted from the master master unit 1. That is, the control signal including the system call code to which the master ID is added is received and determined. Then, basically, the communication control unit 34 controls so that the control signals are periodically transmitted from the master units 2 and 3 of each slave in synchronization with the timing of receiving the control signal from the master. In this case, in this example, the master units 2 and 3 of the respective slaves are synchronized with each other based on the timing of receiving the preamble as the synchronization data, which is the first signal transmitted as the control signal. However, when the slave master units 2 and 3 cannot receive the control signal from the master master unit 1, the communication control unit 34 of each master unit controls the transmission timing of the control signal at its own timing.

Next, FIG. 3 shows the construction of the slaves 4, 5, ... Used in the cordless telephone of this example. In FIG. 3, reference numeral 11 denotes an antenna, and the radio unit 12 receives and processes data received from the master unit or another slave unit by the antenna 11, and supplies the data to the modulation / demodulation unit 13 to demodulate the received data. Then, the demodulated received data is sent to A via the communication control unit 14.
AD obtained by receiving and receiving the DPCM codec section 15
The PCM digital data is used as an analog audio signal, and this analog audio signal is output from the speaker 16.

The audio signal picked up by the microphone 17 is AD
It is supplied to the PCM codec section 15 to be ADPCM digital data, and this digital data is sent to the communication control section 14
The data is supplied to the modulation / demodulation unit 13 via the wireless LAN and modulated for transmission, and the modulated data is wirelessly transmitted from the antenna 11 connected to the wireless unit 12.

Further, the key input section 18 is connected to the ADPCM codec section 1 via the man-machine interface section 19.
5, and the operation information of the key input unit 18 is supplied to the communication control unit 14 side. Further, the display unit 20 is connected to the man-machine interface unit 19 so that the operating state and the like are displayed.

Then, the communication control unit 14 controls the receiving operation so as to receive only the control signal transmitted from the master unit on a predetermined control channel at a predetermined interval when in the standby state. . In this case, the system call code included in the control signal is discriminated to judge whether or not it is the control signal of the system to which this slave belongs. Further, the control signal transmitted from the master base unit 1 is discriminated by the additional ID transmitted after the system call code, and the control signal is periodically transmitted based on the reception timing of the control signal from the master base unit 1. It is designed to perform intermittent reception. This receiving process will be described later.

When the received control signal is the control signal of the system to which the slave unit belongs, the content of the received control signal is discriminated and the slave unit receives the connection request signal included in the control signal. When it is determined that it has been called, this slave unit is caused to perform the corresponding operation. When each cordless handset is called by this connection request signal, it communicates with the base unit for internal or external telephone calls, and communicates with other cordless handsets for internal telephone calls. There are cases when In addition, when you want to make a call from each cordless handset for an external call or an extension call (extension call with the base unit and call between the handset), use the control channel to send a connection request signal to the base unit. I am sending it.

Next, the state in which the control signal is transmitted from each of the parent devices 1, 2, 3 having the above-described configuration to each of the child devices 4, 5, ... The transmission by the master device 1 is performed in the state shown in A of FIG. That is, the transmission of the control signal once for 625 μs is continuously performed at a cycle of 125 ms. The period in which the waveform of A in FIG. 4 rises is the period in which the control signal is transmitted.

The slave master units 2 and 3 receive the control signal transmitted from the master master unit 1 and transmit the control signal in synchronization with the reception timing. Here, the control signal is transmitted from the second master unit 2 5 msec after starting to receive the master control signal (see B in FIG. 4), and the third master unit 3 10 msec later. The control signal is transmitted from the device (see C in FIG. 4). Therefore, [10 msec + 625μ
[Second], the control signals are continuously transmitted from the three master units 1, 2, and 3.

In each of the slave units 4, 5, ... In the standby state, the power supply of the receiving section (the wireless section 12 etc.) is turned on only at the transmission timing when this series of control signals is continuously transmitted. It is turned on periodically. Here, as shown in D of FIG. 4, the first (master) base unit 1
From the start of the transmission of the control signal from the third master unit 3
The power supply of the receiving unit is turned on only during the period T _ON when the transmission of the control signal is completed. However, in actuality, it takes some time (for example, 25 μs) for the receiving unit to start up. Therefore, the time T _ON for turning on once is the above-mentioned time [10 msec + 625].
[μsec] to which a rise time of approximately 25 μsec is added. By performing such control, the operating time in the standby state of each of the slave units 4, 5, ... Can be significantly reduced.

By the way, the reason why such control is possible is as follows.
This is the case where the slave master units 2 and 3 can receive the control signal transmitted from the master master unit 1, but the control signal transmitted from the master master unit 1 due to some failure occurs and is transmitted to the slave master unit 1. There is a possibility that the devices 2 and 3 cannot receive the data. For example, when the master base unit 1 fails and stops transmitting control signals, or some kind of radio interference occurs, the control signals transmitted from the master base unit 1 are transmitted to the slave base units 2 and 3. It may be impossible to receive correctly.

In such a case, the slave master units 2 and 3 of this example transmit the downlink control signal at their own timing. The specific processing will be described below. First, as shown in FIG. 5A, the master base unit 1
It is assumed that the control signal is not transmitted at a predetermined timing T ₁ (or is being transmitted but cannot be received by the slave side) while the downlink control signal is being transmitted at an interval of 125 msec.

The reception of this control signal is the slave master unit 2,
When it becomes impossible in step 3, the slave master units 2 and 3 of the respective slaves cannot obtain the reference synchronization data as shown in FIG. To stop. That is, B of FIG. 5 shows the transmission state of the control signal in the second master unit 2, and after the timing T ₁ at which the control signal is not transmitted from the master master unit 1, the slave master unit 2 transmits the control signal. The control signal transmission is also stopped. In this example, if the slave master units 2 and 3 cannot receive control signals from the master master unit 1 for 5 consecutive seconds, control of the communication control unit 34 of the slave master units 2 and 3 is performed. Then, the downlink control signal is transmitted at 125 msec intervals at its own timing. That is, for example, in the second base unit 2, as shown in B of FIG. 5, the transmission of the downlink control signal is restarted at 125 msec intervals from the timing T _{2 when} approximately 5 seconds have elapsed since the reception from the master became impossible. To do.
At this time, the control signal transmitted from the slave master unit is a control signal having the same data structure as the control signal transmitted when the master unit was in the synchronous state with the master.

In this way, the master units 2 and 3 of each slave
By transmitting the downlink control signal at its own timing,
Each slave unit 4, 5 ... Can receive a control signal from at least this slave master unit 2, 3 and respond to an incoming call, for example, in a state where no control signal is transmitted from the master master unit 1. Even if it occurs, the system configuration as a cordless telephone is secured, and it becomes possible for the slave unit to receive the outside line received by the slave master units 2 and 3.

Then, in this way, the slave master units 2 and 3
When the transmission of the control signal from the master unit 1 is started at a unique timing, the communication control unit 34 in the slave unit of the master unit receives the control signal from the master unit 1 of the master unit every predetermined time (here, every 10 seconds). Perform processing. That is, for example, as shown in A of FIG. 6, in a state where the control signal is not transmitted from the first base unit 1, as shown in B of FIG. When the control signal of 125 msec interval is being transmitted, if the control signal of 125 msec interval is transmitted for 10 seconds at this unique timing, the transmission of this control signal is temporarily stopped, and shown in C of FIG. As described above, the control signal reception process (setting of the reception channel for the control signal and determination of the reception data) is performed for 500 msec. That is, the master device of this example has a configuration in which transmission and reception are performed in a time-sharing manner as shown in FIG. 2, and it is necessary to stop the transmission process during the reception process. It should be noted that C in FIG. 6 shows a period in which the high level period is in the process of receiving the control signal from the master base unit 1.

When the control signal from the master unit 1 of the master cannot be received in the reception processing for 500 msec,
As shown in FIG. 6B, 125 m at unique timing
Restart transmission of control signals at intervals of seconds. After that, this 10
The transmission of the control signal at intervals of 125 msec and the reception process of the control signal for 500 msec are repeatedly performed.

When a control signal is received from the master unit 1 of the master during the control signal receiving process for 500 msec, the control signal receiving process is stopped and the preamble included in the received control signal is received. The control signal transmission process is performed based on the timing. For example, second
When the control signal transmitted at the timing T ₃ shown in A of FIG. 6 can be received by the parent device 2 of FIG. 6, the reception processing of the control signal at this time is immediately stopped as shown in C of FIG. The transmission of the control signal synchronized with the control signal of the master device 1 of the master is started after a predetermined time T ₄ (see B in FIG. 6) required for the process of synchronizing with the control signal received at this time has elapsed. After that, as long as the control signal from the master can be received, the control signal is transmitted at 125 msec intervals with the synchronization being secured.

As described above, when the control signals are transmitted from the slave master units 2 and 3 at their own timings, it is judged at every predetermined time whether or not the control signals from the master can be received. Since the process is returned to the process synchronized with the master, an appropriate control signal transmission process is always performed, and the slave unit can always be controlled well.

As for the control signal receiving process in the standby state in each of the slave units 4, 5, ..., When the control signal from the master unit 1 of the master cannot be received, the synchronization with the master unit is lost. Since the determination is made and the process of synchronizing again with the control signal transmitted from the master unit is performed, at this time, the control signal transmitted from the master units 2 and 3 of the respective slaves is synchronized, which can be dealt with.

In the above embodiment, the case where the number of parent devices is three has been described, but the number of parent devices and child devices is not limited as long as the system is composed of a plurality of parent devices. Also,
The configuration of the control signal and the setting of the interval of the transmission / reception processing shown in the above-mentioned embodiments are merely examples, and the present invention is not limited to the above-mentioned embodiments.

[0048]

According to the present invention, when some trouble occurs in the transmission of the control signal from the reference master unit and another control unit cannot receive the control signal transmitted from the reference master unit, Since each master unit sends control signals at its own timing, the slave unit can receive control signals from one of the master units, and the slave unit can access the master unit in any case. The system configuration as a cordless telephone is secured.

In this case, after a lapse of a predetermined time after the control signal transmitted from the reference master device cannot be received, the reception process of the control signal transmitted from the reference master device is performed by another master device. , When this control signal can be received, the control signal is transmitted from another master unit in synchronization with the reception timing of this control signal, so that the process of restoring the synchronization with the reference master unit is performed. Well done.

Further, the reception process of the control signal from the base unit as a reference is repeated every time a predetermined time elapses until the control signal can be received, so that there is no obstacle in the communication state between the base units. Then, the synchronous state can be immediately restored.

[Brief description of drawings]

FIG. 1 is a system configuration diagram of a cordless telephone according to an embodiment of the present invention.

FIG. 2 is a configuration diagram of a parent device according to an embodiment.

FIG. 3 is a configuration diagram of a child device according to an embodiment.

FIG. 4 is a timing diagram illustrating a transmission / reception state of control signals according to an embodiment.

FIG. 5 is a timing diagram showing a downlink control signal transmission state when a failure occurs in one embodiment.

FIG. 6 is a timing diagram showing a synchronization recovery processing state between the master units according to the embodiment.

FIG. 7 is an explanatory diagram showing a configuration of a control signal according to an embodiment.

FIG. 8 is an explanatory diagram showing a configuration of an identification code according to an embodiment.

FIG. 9 is a configuration diagram showing a system configuration of a conventional cordless telephone device.

FIG. 10 is a configuration diagram showing a communication method.

FIG. 11 is a timing diagram showing a conventional transmission / reception state of control signals.

[Explanation of symbols]

 1 1st master unit (master master unit) 2 2nd master unit (slave master unit) 3 3rd master unit (slave master unit) 4, 5, 6, 7, 8 Slave unit 12, 32 Radio unit 13,33 Modulation / demodulation unit 14,34 Communication control unit

Claims (3)

[Claims] 1. A plurality of base units and a handset unit are provided, and a call is made between the base unit and the handset unit while making transmission and reception of digital data different from each other in time. In the digital cordless telephone device in which a common system call code is set to all of the above-mentioned base units to enable communication between all the base units and the slave units, Control signal transmitted from the other master unit, in synchronization with the reception timing of this control signal, while transmitting the control signal from the other master unit, the other master unit, in the above A digital cordless telephone device that transmits a control signal at its own timing when it cannot receive the control signal transmitted from the parent device. 2. After a lapse of a predetermined time after the control signal transmitted from the reference master unit cannot be received,
When the control signal transmitted from the reference master unit is received by the other master unit, and when this control signal can be received, it is synchronized with the reception timing of this control signal from the other master unit. The control signal is transmitted.
The described digital cordless telephone device. 3. The digital cordless telephone device according to claim 2, wherein the process of receiving the control signal from the base unit as the reference is repeated every time the predetermined time elapses until the control signal can be received.