JPH0984133A - Digital cordless phone - Google Patents

Abstract

(57) [Abstract] [PROBLEMS] A BCC transmitted from a parent device of its own station and a parent device of another station when a plurality of parent devices are within the same service range.
To obtain a digital cordless telephone capable of avoiding collision between H and PCH. SOLUTION: The master unit of the own station monitors the BCCH of the master unit of another station, obtains the minimum mt1 or nt2 of t3 + mt1 +625 μsec> nt2, and controls the timing before sending the BCCH102 after m superframes from the present time. The BCCH 103 by changing the transmission timing by the unit 7
Is sent. This allows BC after m superframes.
Avoid collision with CH201.

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, and more particularly to a transmission signal control system of a base unit of a personal handyphone system (hereinafter referred to as PHS).

[0002]

2. Description of the Related Art First, when the master units of a plurality of digital cordless telephones are used in almost the same place, the same frequency may be used for the control channel of each master unit. If the same frequency is used, since the master units are not synchronized with each other, the BCCH (Broad Cast Control) that each master unit transmits to the slave units.
Channel), PCH (Paginng Chan)
(nel) will eventually collide with the passage of time.
In the case of a collision, the mobile device cannot normally receive the incoming call data, and thus the incoming call may be missed.

Here, the BCCH is a downlink unidirectional broadcast channel for broadcast of control information from the master unit to the slave unit.
Transfers information about channel structure, system information, etc. Further, the PCH is a point-multipoint downlink unidirectional simultaneous paging channel for simultaneously transmitting the same information from the master to all the slaves.

FIG. 9 is a block diagram of a master unit of a digital cordless telephone, FIG. 10 is a diagram showing a sequence of a conventional BCCH or PCH transmission control system, and FIG. 11 is a conventional BC.
It is a figure which shows the sequence of the transmission control system of CH or PCH. In the figure, 1 is an antenna, 2 is a line control unit that performs an interface for connecting to a public line, and 3 is a radio unit that transmits and receives radio waves.

Reference numeral 4 is a digital signal for receiving an analog voice signal from an analog voice signal processing unit 5 which will be described later and processing it into a predetermined digital signal, and for processing the digital signal received by the radio unit 3 to process it into an analog signal. Processing unit,
Reference numeral 5 is an analog signal processing unit that performs level conversion and signal addition between the signal input / output from the digital signal processing unit 4 and the line control unit 2, and 6 is a reference clock unit that creates a clock that is the reference of the digital cordless telephone system. Is.

Reference numeral 7 is a timing control unit for controlling the time of the radio unit 3 and the digital signal processing unit 4 according to the clock from the reference clock unit 6, 8 is a master unit control unit for controlling the entire master unit, 9 is a display unit, 10 Is an operation unit, 102 is an LCCH (L
The original control channel is the BCCH of the master unit of its own station whose period of the superframe (hereinafter referred to as the superframe) is t1, and 201 is the BCCH of the master unit of another station whose period of the superframe is t2.

Next, the operation will be briefly described with reference to FIG. The radio unit 3 transmits radio waves using a digital signal to a slave (not shown) via the antenna 1 and transmits various kinds of information. Here, regarding the transmission of the digital signal to the slave unit, the timing control unit 7 controls the radio unit 3 and the digital signal processing unit 4 based on the clock based on the reference clock 6.
By controlling the transmission timing of the digital signal by the radio wave, the radio wave of the digital signal is transmitted from the radio unit 3 to the slave unit by the BCCH and PCH via the antenna 1.

Next, referring to FIGS. 10 and 11, BCCH, P
The CH collision will be described. First, at a certain time point, the time difference between the BCCH of the base unit of the own station and the BCCH of the base unit of another station is t.
3 After that, the transmission timings of the BCCH 102 and the BCCH 201 overlap with the passage of time due to a slight deviation between the cycles t1 and t2 of the superframes of the parent device of the own station and the parent device of the other station.

FIG. 10 shows the rear part of the BCCH 102 and the BCC.
This is the case where the front portion of H201 overlaps and collides, and the hatched portion A indicates the collision portion. Further, in FIG. 11, the front portion of the BCCH 102 and the BCCH 20
This is a case where the rear portion of No. 1 overlaps and collides, and the hatched portion A indicates the collision portion. Also,
The data length of BCCH is 625 μsec. Therefore, the conditions under which two BCCHs collide after m superframes are integers m and n, whereas in FIG.

[0010]

[Equation 1]

In FIG. 11,

[0012]

[Equation 2]

[0013] Further, since the PCH collision is the same as the BCCH, detailed description thereof will be omitted.
As with H, due to a slight deviation between the superframe cycles t1 and t2 of the parent station of the own station and the parent station of the other station, the PCH of the parent station of the own station and the PCH of the parent station of the other station change with time. The sending timings overlap and a collision occurs.

As another conventional example, FIG. 12 is a block diagram of a multiple transmission phase synchronization system disclosed in Japanese Patent Laid-Open No. 63-27133. A detailed description is given in the publication, but it is an invention in which one of the base stations is used as a reference station and each of the other base stations synchronizes by adjusting a timing delay with respect to a transmission signal timing of the reference station. However, considering the application of the PHS to the master unit, it is difficult to arrange the phase synchronization receiver 11 in the wireless zone and control each master unit.

[0015]

The base unit of the conventional digital cordless telephone is configured as described above, and the BC
In the CH / PCH transmission control method, the transmission timing is always fixed, so if multiple PHS masters are within the same service range, BCCH and PCH will collide and the incoming call to the slave will fail. However, there is a problem in that the synchronization between the master unit and the slave unit may be lost.

The present invention has been made in order to solve the above problems, and when the master devices of a plurality of PHSs are within the same service range, the master device of the own station and the master device of another station It is an object of the present invention to obtain a digital cordless telephone that can avoid the collision of transmitted BCCH and PCH.

[0017]

A digital cordless telephone according to the present invention is a digital signal processing unit for processing digital signals transmitted / received to / from a slave unit, and a radio unit for transmitting / receiving digital signals to / from the slave unit by the digital signal processing unit. Department,
The radio unit has a master unit having a timing control unit for controlling the timing of channels for transmitting / receiving digital signals to / from the slave unit, and monitors the channel used by the master unit of another station and monitors the other station. If the timing of the channel that transmits the digital signal to the slave unit of the master unit of the other station and the timing of the channel that transmits the digital signal to the slave unit of the local station of the local station collide, the timing control unit causes the parent station of the local station before the collision. Is to change the timing of the channel for transmitting a digital signal to the child device.

Further, when the timing of the channel for transmitting the digital signal to the child device by the parent device of the other station and the timing of the channel for transmitting the digital signal to the child device by the parent device of the own station conflict, the parent device of the own station By changing the superframe structure of the channel that transmits the digital signal to the slave, the timing of the channel that transmits the digital signal to the slave by the master of the own station is changed, and the slave is notified of this timing change. It is a thing.

Further, when the timing of the channel for transmitting the digital signal to the slave unit by the master unit of the other station and the timing of the channel for transmitting the digital signal to the slave unit by the master unit of the own station conflict, the master unit of the own station By temporarily changing the superframe structure of the channel that transmits the digital signal to the slave unit,
The timing of the channel for transmitting a digital signal to the child device by the parent device of the own station is moved, and thereafter the superframe structure is restored.

Further, a reference clock unit for generating a clock as a reference for the entire system is provided, and a superframe structure of a digital signal transmission channel to a slave unit by a master unit of another station and a slave unit by a master unit of the own station. , The digital signal transmission channel has the same superframe structure, and the digital signal transmission channel to the slave unit by the master unit of another station and the digital signal to the slave unit by the master unit of the local station due to the slight difference in the clocks by the reference clock unit. When the timings of the transmission channels collide, the timing control unit adjusts the clock by the reference clock unit to change the timing of the digital signal transmission channel to the slave unit by the master unit of the own station before the collision. .

Further, when there is a master unit of another station having a different superframe structure, the slave unit is notified of the timing change of the digital signal transmission channel to the slave unit by the master unit of the own station, and then the own station. This is to change the superframe structure for moving the timing of the digital signal transmission channel from the parent device to the child device.

Further, when there is a master unit of another station having a different superframe structure, the slave unit is notified of the timing change of the digital signal transmission channel to the slave unit by the master unit of the own station, and then the own station. The master frame temporarily changes the superframe structure for moving the timing of the digital signal transmission channel to the slave unit, and then restores the superframe structure.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiment 1. FIG. 1 is a diagram showing a sequence of a BCCH or PCH transmission control method of a digital cordless telephone according to Embodiment 1 of the present invention, and FIG. 2 is a BCC of a digital cordless telephone according to Embodiment 1 of the present invention.
It is a figure which shows the sequence of the transmission control system of H or PCH. Since the block diagram of the master unit in the digital cordless telephone is the same as the conventional example, FIG. 9 is used.

In the figure, 101 is the BCCH, 201, 2 of the superframe of the parent device of the own station whose cycle is t1.
02 is the BCCH of the super frame of the master of the other station whose cycle is t2, and the BCC of the master of the own station at a certain point.
The time difference between H101 and BCCH201 is t3. Further, 102 is the BCCH of the parent device of the own station when the transmission timing is not changed, and the hatched part A is the BCCH.
The collision part with 202 is shown, and in FIG. 1, the rear part of the BCCH 102 collides, and in FIG. 2, the front part of the BCCH 102 collides. Reference numeral 103 is the BCCH of the parent device of the own station when the transmission timing is changed.

Next, the avoidance of BCCH collisions transmitted from the master unit of the own station and the master unit of another station will be described. B
Since the length of CCH data is 625 μsec, m
The conditions under which two BCCHs collide after a superframe are integers m and n, whereas in FIG.

[0026]

(Equation 3)

And in FIG.

[0028]

[Equation 4]

Is as follows. Therefore, the master unit of the own station monitors the BCCH of the master unit of the other station by the master unit control unit 8 via the antenna 1, the wireless control unit 3, and the digital signal processing unit 4, and sets the minimum m
Calculate t1 or nt2. Then, the parent device of the own station changes the transmission timing by the timing control unit 7 and transmits the BCCH 103 before transmitting the BCCH 102 m frames after the present time. This makes it possible to avoid collision with the BCCH 202 after m superframes. Although the description has been made using the BCCH,
Collision can be avoided by performing the same for BCCH, PCH, and PCH.

Embodiment 2 FIG. FIG. 3 is a diagram showing a sequence of a BCCH or PCH transmission control system of the digital cordless telephone according to the second embodiment of the present invention.
In the figure, the same or corresponding parts as those of the first embodiment are designated by the same reference numerals and the description thereof will be omitted. 104 is BCCH20
2 is the BCCH of the parent device of the own station immediately before the collision, 105 is the BCCH of the parent device of the own station when the transmission timing is changed, 10
6 is B of the base unit of the own station when the transmission timing is not changed
It is a CCH, and the hatched portion A indicates a collision portion with the BCCH 202.

Next, the avoidance of BCCH collisions transmitted from the master unit of the own station and the master unit of another station will be described. m
The condition under which two BCCHs collide after the superframe is the same as in the first embodiment. Therefore, the parent device of the own station informs the child device of the change of the superframe structure from the superframe having the period t1 to the superframe having the period t4 by using the BCCH 104 after the (m-1) superframe. And instruct. As a result, BCCH 105 is transmitted after m superframes and BC
A collision with CH202 can be avoided. Although the above description has been made using BCCH, BCCH, PCH, PC
Collision can be avoided by performing the same for Hs.

Embodiment 3. FIG. 4 is a diagram showing a sequence of a BCCH or PCH transmission control system of the digital cordless telephone according to the third embodiment of the present invention.
In the figure, parts that are the same as or correspond to those in the first and second embodiments are assigned the same reference numerals and explanations thereof are omitted. Reference numeral 106 denotes the BCCH of the parent device of the own station when the transmission timing is changed again.

Next, the avoidance of BCCH collisions transmitted from the master station of the own station and the master station of another station will be described. In the second embodiment, in order to avoid the collision between BCCHs, the superframe structure is changed from the superframe having the cycle t1 to the superframe having the cycle t4, but in the third embodiment, the BCCH 105 is changed by this change.
BCCH105 after avoiding the collision of
Is used to re-change the superframe structure from the superframe having the cycle t4 to the superframe having the cycle t1 again, and the initial superframe structure is notified to the slave unit and instructed. It should be noted that although the above description has been made using the BCCH, the same applies to the PCH.

Embodiment 4 FIG. 5 is a diagram showing a sequence of a BCCH or PCH transmission control method of a digital cordless telephone according to Embodiment 4 of the present invention, and FIG. 6 is a BCCH or PCH transmission control method of a digital cordless telephone according to Embodiment 4 of the present invention. Is a diagram showing a sequence of the above, and in the figure, the same or corresponding parts as those of the first to third embodiments are designated by the same reference numerals and the description thereof will be omitted. In FIG. 5, the rear part of BCCH 106 is BCCH 202.
And the front portion of the BCCH 106 in FIG. 6 will collide.

Next, the avoidance of BCCH collisions transmitted from the master unit of the own station and the master unit of another station will be described. When the superframe of the cycle t1 of the master station of the own station and the superframe of the cycle t2 of the master station of the other station have the same superframe structure, the cycle t1 and the cycle t2 are almost equal, and the deviation between them is It is equal to the deviation of the clock by the reference clock unit 6. Therefore, the condition under which two BCCHs collide after m superframes is that for the integer m, if t1 <t2 in FIG.

[0036]

(Equation 5)

Further, in the case of t1> t2 in FIG.

[0038]

(Equation 6)

Is as follows. Therefore, the master unit of the own station monitors the broadcast channel of the master unit of the other station and knows the reference clock deviation from the cycle t1 and the cycle t2. Then, the master unit of the own station corrects the reference clock so that the cycle t1 (k) of the superframe becomes {t1 (k-1) + t2} / 2 in order to adjust the reference clock, and avoids collision.

Here, when the other base unit uses the same algorithm, the cycle of the superframe is (t1
+ T2) / 2 matches. Further, without such an algorithm, the superframe cycle of the master of the own station gradually approaches the cycle t2 of the superframe of the master of the other station, and substantially coincides with each other, causing a collision.

Since the periods of the superframes match as described above, it is possible to prevent the BCCHs from colliding with each other due to the periods being gradually shifted. Although the above description has been made using BCCH, BCCH, PCH, PCH
Collisions can be avoided by performing the same for CHs.

Embodiment 5 FIG. FIG. 7 is a diagram showing a sequence of a BCCH or PCH transmission control system of a digital cordless telephone according to a fifth embodiment of the present invention.
In the figure, the same or corresponding parts as those of the first to fourth embodiments are designated by the same reference numerals, and the description thereof will be omitted. Reference numeral 301 denotes a master unit of the other station and a master unit of the other station (hereinafter, master unit B) having a superframe structure of a cycle t5 different from the superframe of the master unit of the own station and one of the other stations (hereinafter, referred to as master unit A). BCCH1 of the parent device of the own station at a certain time.
01 and the BCCH301 of the master unit B of another station have a time difference of t6
It is.

Next, the collision avoidance of the BCCHs respectively transmitted from the master unit of the own station and the master units A and B of the other stations will be described. First, the avoidance of the BCCHs transmitted from the parent device of the own station and the parent device A of the other station is avoided by performing the same as in the fourth embodiment. On the other hand, the cycle t5
For the base unit B having the super frame structure, the BCCH 106 of the base unit of the own station is the base unit B of the other station under the same conditions m, n, t1 (m → ∞), t5, and t6 as in the first embodiment. B
It collides with CCH302.

Therefore, in this case, the parent device of the own station is (m-
1) Using the BCCH 104 after the superframe, the slave unit is instructed to change the superframe structure from the superframe having the cycle t1 to the superframe having the cycle t4. As a result, BCCH 105 is transmitted after m superframes, and collision with BCCH 302 can be avoided. It should be noted that, although the above description has been made using the BCCH, it is possible to avoid the collision by performing the same for the BCCH, the PCH, and the PCHs.

Embodiment 6 FIG. FIG. 8 is a diagram showing a sequence of a BCCH or PCH transmission control system of a digital cordless telephone according to a sixth embodiment of the present invention.
In the figure, parts that are the same as or correspond to those in the first to fifth embodiments are assigned the same reference numerals, and description thereof will be omitted.

Next, the collision avoidance of the BCCHs respectively transmitted from the master unit of the own station and the master units A and B of the other stations will be described. First, the collision avoidance of the BCCHs respectively transmitted from the master unit of the own station and the master unit A of the other station is performed and avoided in the same manner as in the fourth embodiment. Then, the collision avoidance of the BCCHs transmitted from the parent device of the own station and the parent device B of the other station is performed in the same manner as in the fifth embodiment, and the BCCH 10
5 avoids collision with BCCH 302.

After that, using the BCCH 105, the cycle t4
The superframe structure is changed again to the superframe having the cycle t1 and the initial superframe structure is instructed to the slave unit. It should be noted that although the above description has been made using the BCCH, the same applies to the PCH.

[0048]

As described above, according to the present invention, the channel used by the master unit of another station is monitored, and the channel for transmitting a digital signal to the slave unit by the master unit of the other station and the channel of the own station. When the timing of the channel for transmitting the digital signal to the slave unit by the master unit conflicts, the timing control unit changes the timing of the channel for transmitting the digital signal to the slave unit by the master unit of the own station before the collision. Therefore, it is possible to obtain a digital cordless telephone capable of avoiding a collision, establishing stable synchronization between the master and slave, and receiving an incoming call.

When the timing of the channel for transmitting a digital signal to the slave by the master of the other station and the timing of the channel for transmitting the digital signal to the slave by the master of the own station collide, the master of the own station By changing the superframe structure of the channel that transmits the digital signal to the slave, the timing of the channel that transmits the digital signal to the slave by the master of the own station is changed, and the slave is notified of this timing change. Thus, there is an effect that a collision can be avoided, a stable cordless handset can be established, and a digital cordless telephone capable of receiving an incoming call can be obtained.

Further, when the timing of the channel for transmitting the digital signal to the slave unit by the master unit of the other station and the timing of the channel for transmitting the digital signal to the slave unit by the master unit of the own station conflict, the master unit of the own station By temporarily changing the superframe structure of the channel that transmits the digital signal to the slave unit,
Since the timing of the channel for transmitting a digital signal to the slave unit by the master unit of the own station is moved, and thereafter the superframe structure is restored, the collision can be avoided while maintaining the optimum superframe structure, There is an effect that it is possible to obtain a digital cordless telephone capable of establishing stable synchronization between the base unit and the slave unit and receiving an incoming call.

Further, a reference clock unit for generating a clock that serves as a reference for the entire system is provided, and the superframe structure of the digital signal transmission channel to the slave unit by the master unit of another station and the slave unit by the master unit of the own station. , The digital signal transmission channel has the same superframe structure, and the digital signal transmission channel to the slave unit by the master unit of another station and the digital signal to the slave unit by the master unit of the local station due to the slight difference in the clocks by the reference clock unit. When the timings of the transmission channels collide, the timing control unit adjusts the clock by the reference clock unit to change the timing of the digital signal transmission channel to the slave unit by the master unit of the own station before the collision. Therefore, it is said that it will be possible to obtain a digital cordless telephone that can avoid collisions, establish stable synchronization between the master and slave units, and make incoming calls. There is an effect.

When there is a master unit of another station having a different superframe structure, the slave unit is notified of the timing change of the digital signal transmission channel to the slave unit by the master unit of the own station, and then the own station. By changing the superframe structure for moving the timing of the digital signal transmission channel to the slave unit by the master unit, it is possible to avoid collisions, establish stable synchronization between the master and slave units, and receive incoming calls. There is an effect that a digital cordless telephone capable of performing the above can be obtained.

When there is a master unit of another station having a different superframe structure, the slave unit is notified of the timing change of the digital signal transmission channel to the slave unit by the master unit of the local station, and then the local station. Maintains the optimal superframe structure by temporarily changing the superframe structure to move the timing of the digital signal transmission channel from the master device to the slave device and then restoring the superframe structure. On the other hand, there is an effect that a collision can be avoided, a stable cordless handset can be established, and a digital cordless telephone capable of receiving an incoming call can be obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing a sequence of a BCCH or PCH transmission control system of a digital cordless telephone according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a sequence of a BCCH or PCH transmission control system of the digital cordless telephone according to the first embodiment of the present invention.

FIG. 3 is a diagram showing a sequence of a BCCH or PCH transmission control method of the digital cordless telephone according to the second embodiment of the present invention.

FIG. 4 is a diagram showing a sequence of a BCCH or PCH transmission control system of a digital cordless telephone according to a third embodiment of the present invention.

FIG. 5 is a diagram showing a sequence of a BCCH or PCH transmission control method of a digital cordless telephone according to a fourth embodiment of the present invention.

FIG. 6 is a diagram showing a sequence of a BCCH or PCH transmission control system of a digital cordless telephone according to a fourth embodiment of the present invention.

FIG. 7 is a diagram showing a sequence of a BCCH or PCH transmission control method of a digital cordless telephone according to a fifth embodiment of the present invention.

FIG. 8 is a diagram showing a sequence of a BCCH or PCH transmission control system of a digital cordless telephone according to a sixth embodiment of the present invention.

FIG. 9 is a block diagram of a base unit of a conventional digital cordless telephone.

FIG. 10: BCC of conventional digital cordless telephone
It is a figure which shows the sequence of the transmission control system of H or PCH.

FIG. 11: BCC of conventional digital cordless telephone
It is a figure which shows the sequence of the transmission control system of H or PCH.

FIG. 12 is a configuration diagram of a conventional multiple transmission phase synchronization system.

[Explanation of symbols]

3 radio equipment section, 4 digital signal processing section, 6 reference clock section, 7 timing control section

Claims (6)

[Claims] 1. A digital signal processing unit for processing a digital signal transmitted / received to / from a slave unit, a radio unit for transmitting / receiving a digital signal to / from the slave unit by the digital signal processing unit, and a digital unit to the slave unit by the radio unit. A digital cordless telephone having a master unit having a timing control unit for controlling the timing of channels for transmitting and receiving signals, the channel being used by the master unit of another station is monitored and the slave unit of the master unit of the other station is used. When the timing of the channel for transmitting a digital signal to the local station and the timing of the channel for transmitting a digital signal to the local station of the local station collide with each other, the timing control section causes the local station to transmit the digital signal to the secondary station before the collision. A digital cordless telephone characterized by changing the timing of a channel for transmitting a digital signal. 2. When the timing of the channel for transmitting a digital signal to the slave unit by the master unit of the other station and the timing of the channel for transmitting the digital signal to the slave unit by the master unit of the own station conflict, the master unit of the own station By changing the superframe structure of the channel that transmits the digital signal to the slave unit,
2. The digital cordless telephone according to claim 1, wherein the timing of the channel for transmitting the digital signal to the slave by the master of the own station is changed and the slave is notified of the timing change. 3. When the timing of the channel for transmitting the digital signal to the slave unit by the master unit of the other station and the timing of the channel for transmitting the digital signal to the slave unit by the master unit of the own station conflict, the master unit of the own station By temporarily changing the superframe structure of the channel for transmitting the digital signal to the child device by the above, the timing of the channel for transmitting the digital signal to the child device by the parent device of the own station is moved, and then the superframe structure is used as the original. The digital cordless telephone according to claim 1, wherein 4. A digital signal processing unit for processing a digital signal transmitted to and received from a slave unit, a radio unit for transmitting and receiving a digital signal by the digital signal processing unit to and from the slave unit, and a digital unit including the slave unit by the radio unit. A digital cordless telephone having a master unit having a timing control unit for controlling the timing of channels for transmitting and receiving signals, and a reference clock unit for generating a clock as a reference for the entire system, which is a slave unit of a master unit of another station. The superframe structure of the digital signal transmission channel to the device and the superframe structure of the digital signal transmission channel to the child device by the parent device of the own station are the same, and the parent device of another station due to the slight difference in the clock by the reference clock Timing of the digital signal transmission channel to the slave unit and the digital signal transmission channel to the slave unit of the local master unit In the case of collision, the timing control unit adjusts the clock by the reference clock unit to change the timing of the digital signal transmission channel to the slave unit by the master unit of the own station before the collision. Cordless phone. 5. When a master unit of another station having a different superframe structure exists, the slave unit is notified of the timing change of the digital signal transmission channel to the slave unit by the master unit of the own station, and then the own station. 5. The digital cordless telephone according to claim 4, wherein the superframe structure is changed to shift the timing of the digital signal transmission channel from the master unit to the slave unit. 6. When a master unit of another station having a different superframe structure exists, the slave unit is notified of the timing change of the digital signal transmission channel to the slave unit by the master unit of the own station, and then the own station. 5. The digital cordless according to claim 4, wherein the superframe structure is temporarily changed to move the timing of the digital signal transmission channel by the master unit to the slave unit, and then the superframe structure is restored. Telephone.