JPH0292121A - Cordless telephone - Google Patents

Abstract

PURPOSE:To suppress the generation of cross modulation by opening only a call channel not to give the cross modulation interference to a control channel for calling. CONSTITUTION:Idle channel information is held at areas ECH 1 to ECH 3 of an RMA, and a call channel is opened between handsets 1A to 1H based on the idle channel information. Further, when the idle channel information is registered to the areas ECH 1 to ECH 3, it is checked whether or not the call channel is a channel to give the cross modulation to a control channel, and when it is the channel to give the cross modulation, the registration to the areas ECH 1 to ECH 3 is prohibited. Thus, it is eliminated to give the cross modulation interference to the control channel, and in the base station 2, a command signal CMND can be correctly received.

Description

[Detailed description of the invention] The explanation will be given in the following order.

A. Industrial application field B. Summary of the invention C Conventional technology D Problems to be solved by the invention E. Means to solve the problem (Figure 1) F. Effect G Example G. First embodiment (Figures 1 to 4) G2 other examples Effect of H invention A. Industrial application field This invention relates to cordless telephones.

B. Summary of the Invention The present invention is a multi-cordless telephone in which communication channels are managed to prevent interference due to cross-modulation on the control channel.

C. Conventional Technology A low-power type cordless telephone uses the MCA system, and has 87 communication channels and 2 control channels.

Therefore, a so-called multi-cordless telephone, in which a plurality of slave units can be used in combination with one base unit, has been considered as an extension of the functions of such a cordless telephone.

FIG. 2 shows an example of such a multi-cordless telephone. However, in this example, two outside lines, up to eight handsets can be supported, and only one control channel is used.

In FIG. 2, (IA) to (IH) indicate first to eighth handsets (slave units). These handsets (I
Since A) to (IH) have the same configuration, (110) will be explained using the handset (IA) as a representative.
is a transmitting circuit, and (120) is a receiving circuit. The transmitting circuit (110) converts the audio signal Sr and command signal CMND (details will be described later) into an upstream channel FM signal Su and transmits the same, and the receiving circuit (120) converts the downstream channel FM signal Su. Sd
is received and demodulated into audio signal St and command signal CMND.

Also, (131) is a dial key, (132)
This talk key (132) is a non-locking type bush switch, and this key (132) is an inferior talk key.
132) Each time you press , the handsera) (IA> is
Switches alternately between standby mode and talk mode. Note that when the handset controller (18) is in standby mode, the receiving circuit (120) is in a reception standby state on the downlink control channel.

Furthermore, (133) to (137) are auxiliary keys such as extension keys configured with non-locking type bush switches, (139) is a ringer speaker,
(140) is a micro combinator for system control. In this microcomputer (140), a command signal CMND to be transmitted by a transmitting circuit (110) is formed, and a receiving circuit (140) generates a command signal CMND.
20> is determined. In addition, in the microcontroller (140),
Permission/prohibition of transmission of the transmission circuit (110), transmission circuit (1
A control signal TCTLSRCTL for controlling the channel through which the receiver circuit (10) and receiver circuit (120) perform transmission and reception is also formed.

Furthermore, (141) is a RAM, and this RAM (
141) stores a 25-bit system identification code 5YID for identifying this multi-cordless telephone from other cordless telephones. Furthermore, the handsets (IA) to (IH) are provided with "1" to "1" to identify them from each other.
The handset number "8" is assigned (the order of assignment is arbitrary), and the handset number is R as a 4-bit handset identification code H3ID.
It is stored in A M (141). In addition, when the identification code (handset number) 15ID is "0", 1 is for all handset sets (18) to (IH).
corresponds.

In addition, (2) is the base station (master unit), (3A
) (3B) indicates a telephone line (external line). Then, base station (2) (Gotai, (218) ~ (21C)
) indicates the base unit, and these base units (21A) to (2IC) are the handset (IA).
It has a transmitting circuit (210) and a receiving circuit (220) similar to the transmitting circuit (110) and receiving circuit (120) in ~(IH). The receiving circuits (220) to (220) of these base units (21A) to (21C) are also on standby on the uplink control channel when not on a call.

Furthermore, at the base station (2), (22)
is a call switch circuit, (23A) and (23B) are external line interface circuits, and (24) is a micro combinator for mask control. In this case, the switch circuit (22) is connected between the pace unit (21A) to (21C) and between the base unit (21A) to (21C) and the interface circuit (23A) according to the purpose of communication.

(23B). In addition, the interface circuits (23A) and (23B) are
4-wire/2-wire conversion circuit (231) Switch circuit (232) compatible with the hook switch of general telephones,
Dial tone signal (DTI, IP double signal formation circuit)
233), ring tone signal detection circuit (234>
etc., respectively.

Furthermore, the microcomputer (24) is connected to the handset (IA)
(IH) performs the same processing as the microcontroller (140) in handsets (IA) to (III).
, call channel, base unit (21A) ~(
2IC), line (3A).

(3B) is used to manage the entire operation of this cordless telephone, such as the usage status. Further, (241) is a ROM, and a system identification code 5YID is written in this ROM (241).

FIG. 3 shows an example of the signal format of the command signal CMNO. This signal CMND has a 24-bit bit synchronization signal BSYN at the beginning, followed by a 16-bit freight synchronization signal FSYN. In this case, these signals BSYN, FSYN are for example BSYN=
“101010・・・・・・・・・10″FS
YN-“1100010011010110”...
FSYN for upstream channel = “1001001100110110”・
...has a specific bit pattern indicated for the downstream channel.

Further, the command signal CMNO includes, following the signal FSYN, a 25-bit system identification code 5YID and a 12-bit error correction code C for this code 5YID.
C in order, and 5 following C)'ECC.
It has a byte control code CTRL.

In this case, the control code CTRL is
LI is a code indicating the control contents of the handset (IA) to (IH) and the base station (2), and the second
Byte CTL2 to fifth byte CTL5 are the first byte C
These are parameters or data related to TLI.

Example Eva, the base station (2) is connected to the handset (I).
When informing one of A) to (IH) of the channel number of the call channel, CT number: Code indicating that it is a call channel notification CTL2: Handset identification code of the other party's handset H3ID CTL3: Call channel Channel number CTL4.
CTL5: Considered a dummy. Note that in most cases, the second byte CTL2 is the handset identification code H3ID as described above.

When the handset (IA) to (IH) or base unit (21A) to (2IC) receive this command signal CMNO, the microcomputer (
140) Or in (24), the signal CM
Identification code 5YID (and H3ID) included in ND
is your RAM (141) or ROM (
241) Identification code 5YID (
and H3ID), and only when they match, the command signal CMNO is made valid, and when they do not match, it is made invalid.

Calls from handseras (IA) to (IH) are made as follows.

In other words, for example, when the handsera (LA) is in standby mode, if you press its talk key (132), this will be detected by the microcomputer (140),
A transmission control signal TCTL is supplied from the microcomputer (140) to the transmitting circuit (110), and as a result, the transmitting circuit (110) is permitted to transmit on the upstream control channel, and the microcomputer (140)
, a command signal C whose control code CTRL indicates a request to make a call and its handset identification code ll5ID
MND is formed, and this signal CMND is sent to the transmitting circuit (
110).

Therefore, in the transmitting circuit (110), the signal C
MNO is an FM signal (F
SK signal) Su and this signal Su is transmitted to the base station (2) through the antenna (100).

Then, in the base station (2), the signal (radio wave) Su is received by the antenna (200), and this received signal Su is transmitted to the base unit (2).
18) to (21C). In this case, for example, if the base unit (21 people) is vacant, the receiving circuit (220) of the base unit (21A) is in the receiving state of the uplink control channel, so this receiving circuit ( 220), the command signal CMNO is demodulated from the FM signal Su, this signal CMNO is supplied to the microcomputer (24), and the identification code 5YID included in the signal CλINO is
It is checked whether it matches the identification code 5YID of the ROM (241). In this case, since there is a match and the call is requested from the handset (IA), the transmission circuit (210) is sent from the microcomputer (24).
A transmission control signal TCTL is supplied to the transmitter circuit (210), which permits transmission on the downlink control channel, and a control code CTRL is supplied to the microcomputer (24) for permission to make a call, handset identification code H3ID and A command signal CMNO indicating the channel number of the communication channel is generated and supplied to the transmitting circuit (210).

Therefore, the base circuit (21A) transmitter circuit (2
10) The signal CMND is converted into the FM signal Sd of the downlink control channel, and this signal S
(l is transmitted through the antenna (200) to the handsets (IA) to (IH).

In the handsera (IA), when an FM signal Sd is transmitted from the base station (2) through the downlink control channel, it is received by the antenna (100) and sent to the receiving circuit (120).
), and the command signal CMNO is taken out from the receiving circuit (120) and sent to the microcomputer (140).
supplied to

Then, since the identification codes 5YIS and H3ID included in the command signal CMND match the identification codes 5YIS and H3ID stored in the RAM (141), the transmitting circuit (1i0) and the receiving circuit (12
0) is set by the control signal TCTLRCTL to the communication channel of the channel number indicated by the control signal CTRL in the received command signal CMND, and reception is also permitted.

In addition, in the base unit (21A), when the command signal CMNO instructs the handset (IA) to a communication channel, the microcomputer (24) sends the transmission control signal TCTL and The reception control signal RCTL is supplied to the transmission circuit (210) and the reception circuit (220).
is permitted to be transmitted and received on the communication channel whose channel number is specified by the microcomputer (24) to the wireless terminal (IA).

Turn around and put the handset (LA) and base unit (
21A) A communication channel has been opened between the two parties.

At this time, the remaining handsets (IB) to (IH)
, the FM signal Sd transmitted from the base station (2) is received, but the transmitted handset identification code (IsID) does not match the own, so the reception standby state ( remain in standby mode).

Furthermore, in the base station (2), among the interface circuits (23A) and (23B),
In the case of the vacant interface circuit shown in the figure, the interface circuit (23A) is selected, its Sui-Sochi circuit (232) is turned on (off-hook state), and the switch circuit (22) is controlled to turn the base off. unit) (21A) transmitting circuit (210)
and the receiving circuit (220) are connected to the conversion circuit (231) of the interface circuit (23A) through the switch circuit (22).

Therefore, in this case, the base unit (21A) includes the switch circuit (22) and the interface circuit (21A).
3A), and the handset (IA) is connected to the line (3A) through the circuit (218>, (2
2), it is connected to line (3A) through (23A).

Therefore, when the caller enters the telephone number of the other party using the dial key (131) on the handset (IA),
A command signal CMNO indicating that the control code CTRL is the transmission of a telephone number and the telephone number is formed, and this signal CMNO is converted by the base station (2) into an FM signal Su of the designated communication channel. Sent.

Therefore, at base station (2), Sonocommand (W CMNO is the base unit) (21
The control code CTRL of this signal CMNO is obtained from the receiving circuit (220) in A), and since the control code CTRL of this signal CMNO indicates that a telephone number is to be sent and that telephone number, the formation circuit (233) is obtained from the microcomputer (24). A dial tone signal corresponding to the telephone number sent from the handset cell (LA) is formed under control according to the telephone number, and this signal is sent to the telephone via the conversion circuit (231) and further through the switch circuit (232). line (3
A).

When the other party answers the phone, the voice signal Sr from the other party is transmitted to the base unit (21A) through the signal line of line (3A) → switch circuit (232) → conversion circuit (231) → switch circuit (22). The transmitting circuit (
210). Therefore, the signal Sr is converted into the FM signal Sd of the downlink communication channel, and this signal Sd is transmitted from the antenna (200).

Then, this signal Sd is received by the handset cell (LA) and sent from the receiving circuit (120) to the audio signal S.
r is taken out, and this signal Sr is sent to the receiver (121).
supplied to

Furthermore, when transmitting a call, the audio signal St from the transmitter (111) is supplied to the transmitting circuit (110) and converted into the FM signal Su of the uplink communication channel, and this signal Su is transmitted from the antenna (100) to the base station. (2).

Then, in the base station (2), the signal Su is received by the base unit (21A) and the signal St is taken out from the receiving circuit (220), and this signal St is transferred from the switch circuit (22) to the interface circuit (23A). ) conversion circuit (231) →
The signal is supplied to the line (3A) through the signal line of the switch circuit (232) and sent to the other party's telephone.

A call and a conversation are made as described above.

Then, when the call ends, press the talk key (132) on the handset (IA) to receive the control code CTR.
A command signal CMN[l is formed indicating that L is the end of the call and the handset controller)gl&another:]-do) ISID;
This signal CMNO is transmitted to the base station (2) by the FM signal Su of the communication channel.

Then, the pace unit) (21> receiving circuit (220)
), and the microcomputer (24) determines that the call is over. As a result, the transmitter circuit (21A) of the base unit (21A)
0) is prohibited by the control signal TCTL, and the receiving circuit (220) is placed in a standby state for receiving the uplink control channel by the control signal RCTL. Further, the switch circuit (232) of the interface circuit (238) is also turned off (on-hook state).

Furthermore, in the handset (IA), after transmitting the command signal CMNO indicating the end of the call, the transmitting circuit (110) is prohibited from transmitting by the control signal TCTL, and the receiving circuit (120) is prohibited from transmitting by the control signal RC. The control channel is in standby mode.

In this way, the handset (LA), the base unit (
21A) and interface circuit (23A)
is in standby mode.

On the other hand, incoming calls to (IA) to (IH)
This is done as follows.

That is, when a telephone call is received through the line (3A), for example, the ring tone signal is detected by the detection circuit (234) of the interface circuit (23A), and this detection signal is supplied to the microcomputer (24).

Surt, the base unit (21) by the microcomputer (24)
A vacant base unit (21A) from among A) to (21C) is selected, and the transmission circuit (21A) of this base unit) (21A) is selected.
10) The control signal TCTL permits transmission on the downlink control channel, and the control code CTRL indicates that there is an incoming call and that the handset (I
A command signal CMND indicating the identification code H3ID of the vacant handset among A) to (IH) and the channel number of the communication channel is formed, and this command signal C
MND is supplied to a transmitting circuit (210).

Therefore, F with this command signal CM N O
The M signal Sd is transmitted to the handsets (IA) to (IH) through a downlink control channel.

Now, if the identification code H3ID included in the control code CTRL in the command signal C1, IND indicates, for example, a handset cell (LA), then the signal C is sent from the receiving circuit (120) of the handset (IA>).
MND is obtained and its identification code is 5YID, H3ID
matches the identification code 5YIDHSID stored in the RAM (141) of the handset (IA), and the control code C of the command signal C1, IN
Since the TRL indicates an incoming call, the microcomputer (140)
The oscillation circuit (138) is controlled by the oscillator circuit (138) to form a ringer signal, and this signal is supplied to the speaker (139), which produces a bell sound indicating an incoming call.

Therefore, when the user of the handset (IA) presses the talk key (132), the ringer signal of the oscillation circuit (13B) is turned off and the bell sound is stopped, and then the transmission circuit (110) is turned off by the control signal TCTL. Transmission on the uplink control channel is permitted, and
A command signal CllN0, in which the control code CTRL indicates an incoming call response and the handset identification code H3ID, is formed and supplied to the transmitting circuit (110).

Therefore, a command signal CMND indicating an incoming call response is transmitted to the base station (2) by the FM signal Sd on the control channel.

When this transmission is finished, the control signals TCTL and RCTL from the microcomputer (140) cause the transmission circuit (1
10) and the receiving circuit (120) are the base unit)
(21A) The communication channel is switched to the channel number specified by (21A).

In addition, the base unit (21A) receives the FM signal Su of the command signal CMND indicating an incoming call response from the handset (LA).
When the control signals TCTL and RCTL are received, the transmitting circuit (210) and the receiving circuit (220)
When the call arrives, the call channel is switched to the channel number specified by the handset (LA).

Therefore, from this point on, a communication channel has been opened between the base unit (218) and the handset (IA).

Furthermore, in the base station (2), the switch circuit (22) is controlled by the microcomputer (22), and the transmission circuit (210) of the base unit (21A) is controlled by the microcomputer (22).
and the receiving circuit (220>) is the switch circuit (22)
It is connected to the conversion circuit (231) of the interface circuit (23A) through the interface circuit (23A), and the switch circuit (232) is turned on.

Therefore, the base unit (21A) includes the switch circuit (22) and the interface circuit (23A).
This means that it is connected to the line (3A) through.

Therefore, the base station (IA) is
The user is now connected to the line (3A) through the connection (2), and can thereafter make a call in the same manner as when making a call as described above.

Then, when you finish the call, if you press talki-coo (132), the call will end in the same way and the phone will go back to standby mode.

Furthermore, a telephone call between any two handsets (IA) to (IH), that is, an extension telephone call, is performed as follows.

That is, for example, when the handsera (IA) is in standby mode, the auxiliary keys (133) to (137)
), press the extension key (133), then press the number key (131) corresponding to the handset number (this is equal to the handset identification code H3ID) of the handset you want to make an extension call to. In case 1 (110), transmission on the control channel is permitted, and the control code CTRL is
However, one of the keys (133) to (137) was pressed, and the pressed key was the extension key (133).
, the number key pressed among the dial keys (131) (other party's handset) Ilb separate code (HDIS) and own handset identification code (ISI)
A command signal CMNO indicating D is formed and sent to the transmitting circuit (
110).

Therefore, this command signal CMNO is transmitted to the base station (2) by the FM signal Su on the uplink control channel.

For example, if base unit) (21A) is vacant, this base unit) (21 people)
The command signal CMND is taken out from the receiving circuit (220) of the handset (IA), and it is determined that it is a request for an extension call from the handset (IA). )
A communication channel will be opened between them.

Furthermore, in the base station (2), a vacant base unit and a vacant communication channel are selected by the microcomputer (24). For example, if the base unit (21B) is vacant, this base unit (21B) The FM signal Sd of the command signal CMNO is transmitted through the downlink control channel.However, at this time, the command signal CMND
The control code CTRL in is an extension call;
Handset identification code HSID of the party with whom the (IA) wishes to make an extension call.

and data indicating the channel number of the communication channel.

Then, the FM signal Sd of this command signal CMNO is
When the call is received by the handset of the desired party (LA), for example, the handset (IH), a bell will sound from the speaker (139) of the handset (IH) in the same manner as in the case of an incoming call. When the other party presses the talk key (131) on the handset (IH), the handset (LH) and base unit (21B)
A calling channel is opened during the call.

At the base station (2), since it is an internal call, the switch circuit (22) is controlled by the microcomputer (24).
are controlled and the transmitting circuit (210) and receiving circuit (220) of the base unit) (21A) are connected to the base unit) (21B) through the switch circuit (22).
receiving circuit (220) and transmitting circuit (210)
connected to.

Therefore, the handset (IA) is connected to the handset (IH) through the base station (2),
Thereafter, extension calls can be made between the handset (LA) and (IH).

Then, end the call, handset) (IA), (
11 (), for example, when the handset (LA) presses the talk key (131), the handset (LA) and the base unit (2LA) will end the call in the same way as ending a call with an outside line. These are placed in standby mode. In addition, the base unit (21
B) to handsera) (IH), control code C
A command signal CMND indicating that the TRL is terminated and the identification code H3ID of the handset (IH) is sent, and the handset (IH) and base unit) (21B
) However, the call termination process is performed and these also go into standby mode.

In addition, similar protocols allow transfer of an outside line from one handset to another, and even a single call between an outside line and two handsets.

D Problem to be solved by the invention However, as mentioned above, one base station (two
) transmits and receives two or more channels of radio waves at the same time, problems may occur due to cross modulation.

That is, now, for example, the base unit) (21A).

(21B) through handsera) (IA) and (1
)1), and at this time, base units) (21A), (21B)
As shown by the solid line in Fig. 4, the frequency of the communication channel (carrier frequency) used by
Suppose that

At this time, in the receiving circuit (220) of the base unit (21C), the frequencies f,, fy become f8-fa-(fb-f6), as shown by the broken line in FIG. (i)fy=
fb+(fb −f,) −−−−・−(ii
) are generated as cross-modulation signals SX and SV (higher-order cross-modulation components are also generated, but their energy is small, so they are ignored).

Therefore, if this frequency f8 or fy matches or approaches the frequency of the control channel,
Base unit) (21C) receiving circuit (220)
is the upstream FM signal Su through the control channel.
When receiving the FM signal Su, the signal Sx or Sy causes cross-modulation interference, and as a result, the receiving circuit (220) of the base unit) (2IC>
cannot demodulate the command signal CMND correctly,
This may cause problems such as the base unit (21C) not being able to open channels.

As long as a plurality of transmitting circuits and receiving circuits are provided close to each other as in the base station (2) described above, it is technically difficult to suppress the occurrence of cross modulation as described above.

However, this invention attempts to solve such problems.

E Means for Solving the Problem By the way, in the above-mentioned multi-cordless telephone, an unoccupied base unit among the base units (21A) to (21C) repeatedly scans all call channels to determine whether they are unoccupied. Detects the call channel and stores the channel number of the free call channel.
It is held as free channel information in the RAM (not shown) of the microcomputer (24).

However, at this time, the vacant channel information held is the base unit of base station (2) (21A).
~(21C) Taking into account the number of channels, for example, there are three channels.

When opening a communication channel between the handset and the base station (2) due to a call, etc.,
Based on the free channel information held in RAM,
The channel number of the call channel is determined.

The present invention focuses on such points, and when an empty base unit scans the communication channels and registers (retains) the channel number of the empty communication channel in the RAM of the microcomputer (24), the empty communication channel is , when transmitting on that free channel, it is checked to see if it is a channel that causes cross modulation on the control channel, and if it is a channel that does not cause cross modulation, the channel number of that free channel is stored as "vacant channel information". As the RAM of the microcomputer (24)
It was designed to do so.

F Effect Only speech channels that do not cause cross-modulation interference to the control channel are opened for speech.

An example of a receiving circuit (220) is shown in which an up-channel FM signal Su is received by an antenna (200) and supplied to a china circuit (221).

This china circuit (221>) has a high frequency amplifier to a second mixer circuit and is configured in a double super hetero gain system, and its receiving channel is a microcomputer (221).
4), the FM signal 7Su of the channel according to this signal RCTL is frequency-converted into a second intermediate frequency signal Si and taken out.

Then, this signal Si is transmitted to the second intermediate frequency amplifier (22
2) is supplied to the FM demodulation circuit (223) through which the audio signal St or command CMNO is extracted.

This audio signal St is supplied to the switch circuit (22) through the amplifier (224), and the command signal CMNO is supplied to the microcomputer (24) through the shaping circuit (225).

Further, an intermediate frequency signal Si is taken out from the amplifier (222), and this signal Si is sent to the detection circuit (226).
For example, by performing AM detection and shaping, a signal CDET indicating the presence or absence of the signal S1 is extracted.
This signal CDET is supplied to the microcomputer (24). Note that since the signal rDET is a signal that indicates the presence or absence of the signal Si, it is also a signal that indicates whether or not the FM signal Su is present on the upstream channel specified by the control signal RCTL. It is also a signal indicating whether or not the channel is free.

Furthermore, in the microcomputer (24), (240) is the CPU, (241) is the ROM in which the system identification code 5YID is written as described above, and (2
42) is the ROM in which the program is written,
(243) is RAM for work area, (2
44) is an input port, (245) is an output port, and these circuits (241) to (245> are bus (2
46) to the CPU (240).

In addition, the RAM (243) has an area (address) that holds information on available channels for, for example, 3 channels.
ECHI to EC) 13 are prepared, and areas tlcH1 to UCH that hold the channel numbers of the call channels currently in use for three channels correspond to the number of pace units) (21 people) to (21C).
3 will also be available.

Then, by making a call, etc., the handset (18) to (I)
When a communication channel is opened between H) and the base station (2), the channel number of the communication channel is stored in the RAM (
243) is written in any of the areas [ICH1 to 1ICl13. In addition, when the previously used call channel is closed due to the end of a call, the in-use channel information indicating the channel number is stored in areas IICHI to UCII of RAM (243>).
Deleted from 3.

Furthermore, as mentioned above, for example, the base unit (21C
) is vacant, this base unit ) (
In the reception circuit (220) of the 2IC), the communication channels are repeatedly scanned by the control signal RCTL, and during this scanning, the signal CD[iT is checked in the microcomputer (24) for each communication channel, and the communication channel is If it is an empty channel, three channels of the channel number of the empty call channel are stored in the RAM as empty channel information.
(243) in areas ECHI to EC)13, and previously written in areas ECHI to ECH3 in RAM (243), if the communication channel indicated by the vacant channel information is being used at the time of the current scan. The free channel information is rewritten to another free channel information.

That is, the vacant channel information in areas εCHI to ECH3 is updated to the latest information every time a call channel is scanned.

However, in this invention, RAM (243)
When writing vacant channel information to areas EiCH1 to 1EcH3, the following processing is performed.

That is, now, f: Frequency of the free call channel indicated by the free channel information of areas ECHI to ECH3 (for 3 channels) fu: Frequency of the busy call channel indicated by the busy channel information of areas LIC) 11 to 1JcII3 ( 3 channels) When fc is the frequency of the control channel, the communication channel of frequency f is f + (f - f, ) = f.

f+ (f-fu)=f.

When either f - (f - fe) - fc f - (f - fu) = fc is satisfied, the channel number of the communication channel with frequency f is stored in RAM ( 243) Prohibits writing to areas ECHI to EC)13 as vacant channel information.

According to such a configuration, R is used as free channel information.
A M (243) area IEc) II ~ ECH
The frequency f8 of the communication channel written in 3 does not satisfy the above equations (i) and (ii), so R
Even if a channel is opened using the communication channel written in areas BCHI to EC113 of AM (243), cross-modulation signals SX, S) are sent to the control channel.
l will not occur. Therefore, the base station (2) receives the command signal C on the control channel.
When receiving MND, it can be received reliably and processing according to the command signal CMND can be performed normally.

Thus, according to the invention, RMA (243)
Free channel information is held in areas ECHI to ECH3, and based on this free channel information, communication channels are opened between handsets (IA) to (IH) and base station (2), and communication channels are held in areas ECHI to ECH3.
When registering vacant channel information in ECH3, it is checked whether the call channel is a channel that gives cross modulation to the control channel, and if it is a channel that gives cross modulation to the control channel, it is registered in areas ECHI to BCH3.
Since registration to the command signal CMND is prohibited, there is no cross-modulation interference on the control channel, and the base station (2) can correctly receive the command signal CMND.

Moreover, there is no need to add special hardware for this purpose, and only a partial change in the software of the ROM (242) is required, so there is no increase in costs.

G2 Other embodiments In the above description, when scanning a call channel,
Although it is assumed that all communication channels are scanned, this scan may be performed for communication channels recognized by the handsets (IA) to (IH) and the base station (2).

Furthermore, when scanning communication channels, it is possible to skip scanning of communication channels that are already being used by the base station (2).

Furthermore, regarding cross-modulation interference on a communication channel, when scanning an empty communication channel, cross-modulation signals SX and SL are already present in the communication channel, and the detection circuit (226) determines that this is a channel in use. Therefore, no problem will occur.

Effects of the Invention According to this invention, vacant channel information is held in the areas ECHI to BCH3 of RMA (243), and the handset (IA)
~' (1) 1) Open a communication channel with base station (2) and
When registering vacant channel information in Cll3, it is checked whether the call channel is a channel that gives cross modulation to the control channel, and if it is a channel that gives cross modulation, then the area EC) 11 to Mi C is checked.
Since registration to H3 is prohibited, the base station (2) can correctly receive the command signal CMND without causing cross-modulation interference on the control channel.

Moreover, there is no need to add special hardware for this purpose, and only a partial change in the software of the ROM (242) is required, so there is no increase in costs.

[Brief explanation of the drawing]

1 and 2 are system diagrams of an example of the present invention, and FIGS. 3 and 4 are diagrams for explaining the same. (IA) to (IH) are handsets, (2) is a base station, (3A) to (3B) are telephone lines, (21A
) ~ (21B) is Base Uni Soto, (238),
(23B) is an interface circuit. Agent Paige Ito
Hide Mori Matsukuma Figure 4

Claims (1)

[Claims] An MCA system in which a base unit has a plurality of sets of transmitting circuits and a receiving circuit, and communication channels can be opened simultaneously between the base unit and a plurality of slave units. In the cordless telephone, the receiving circuit of the base unit sequentially scans the call channels and registers data indicating the vacant call channels in the memory as vacant channel information, and between the base unit and the handset, When opening the above call channel, the channel is opened with the call channel indicated by the free channel information registered in the above memory, and when the data indicating the above free call channel is registered in the above memory as free channel information, When a channel is opened as a communication channel, it is checked whether cross-modulation interference occurs on the control channel, and if the channel causes cross-modulation interference, data indicating that communication channel is prohibited from being registered in the above memory. A cordless telephone.