CA2036754C - Method and system for controlling radio channels to be used for cordless telephone systems - Google Patents

Abstract

In a key telephone system, a plurality of cordless telephone systems each including a pair of a connecting equipment 4 or 6 and a movable telephone set 5 or 7 are connected to a key service unit 3 as extension telephone sets. The key service unit 3 designates each speech channel of mutually different frequency selected from a plurality of predetermined speech channels as each speech channels to be used for each cordless telephone system, and indicates each designated speech channel to the connecting equipment 4 or 6 of each cordless telephone system. In each cordless telephone system, each designated speech channel is indicated from the connecting equipment 4 or 6 to the movable telephone set 5 or 7 using a predetermined control channel. After each designated speech channel has been indicated to each movable telephone set 5 or 7, the designated speech channel is mainly used for each cordless telephone system. Since the frequency of each designated speech channel for each cordless telephone system is different from each other, it is possible to simultaneously process outgoing or incoming calls of the plural cordless telephone systems.

Description

METHOD AND SYSTEM FOR CONTROLLING RADIO CHANNELS
TO BE USED FOR CORDLESS TELEPHONE SYSTEMS
BACKGROUND OF THE INVENTION
The present invention relates to a method and system for controlling radio channels to be used for cordless telephone systems. The present invention is preferably applicable to a telephone system such as a key telephone system or a home telephone system including a key service unit and a plurality of cordless telephone systems.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a block diagram showing a prior-art system configuration of a key telephone system including a plurality of cordless telephone systems as extension telephone sets;
Figure 2 is a diagram showing a connection operation sequence executed when an outgoing call is transmitted to an office line through the cordless telephone system of the prior-art key telephone system;
Figure 3 is a diagram showing a connection operation sequence executed when an incoming call is received from an office line through the cordless telephone system of the prior-art key telephone system;
Figure 4 is a timing chart showing the operation of the connecting equipment and the movable telephone set in the operation sequence shown in Figure 3;
Figure 5 is a block diagram for assistance in explaining the problem raised when two incoming calls arrive simultaneously at two cordless telephone systems of the prior-art key telephone system;

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Figure 6 is a block diagram showing the key service unit of an embodiment of the key telephone system according to the present invention;
Figure 7 is a block diagram showing the connecting equipment of the cordless telephone system of the key telephone system according to the present invention;
Figure 8 is a block diagram showing the movable telephone set of the key telephone system according to the present invention;
Figure 9 is a diagram showing a speech channel designation sequence in the same key telephone system;
Figure 10 is a view showing an example of a table formed in the RAM 16 shown in Figure 6;
Figure 11 is a view showing a speech channel selecting sequence in the same key telephone system;
Figure 12 is a diagram showing a connection operation sequence executed when an outgoing call is transmitted to an office line through the cordless telephone system of the same key telephone system;
Figure 13 is a diagram showing a connection operation sequence executed when an incoming call is received from an office line through the cordless telephone system of the same key telephone system; and Figure 14 is a diagram showing a connection operation sequence executed when the speech channel designated to the cordless telephone system at incoming call arrival is unusable.
A prior-art key telephone system including a plurality of cordless telephone systems as extension telephone sets will be 2a 2 0 3 6 7 5 4 20375-682 described with reference to Figure 1. This telephone system is composed of a key service unit 3 (referred to as KSU, hereinafter) connected to office lines 1 and 2 and provided with various control functions and a plurality of extension telephone sets connected to the key service unit 3. These extension telephone sets are wire electric key telephone sets (referred to as EKT, hereinafter) 8 and 9 and cordless telephone systems 4, 5, 6 and 7.
The cordless telephone system is composed of a movable telephone set (referred to as TEL, hereinafter) 5 or 7 and a connecting equipment (referred to as CE, hereinafter) 4 or 6 for communications between the TEL 5 or 7 and the KSU 3. Here, each pair of the CE 4 and TEL 5 or the CE 5 and the TEL 7 constitutes one cordless telephone system, respectively. In each cordless telephone system, outgoing calls, incoming calls and speech are enabled to office lines and other telephone sets via the KSU 3, in the same way as in the ordinary wire EKTs. Further, the KSU 3 including the CEs 4 and 6 is referred to as a base unit herein.
The channels usable for radio communications in the cordless telephone system are prescribed as shown in Table 1 below:

\ CE-Rx CE-Tx \ (UP-CHANNEL) (DOWN-CHANNEL) CHANNEL\ TEL-Tx TEL-Rx NAME
C-CH 254,9625 MHz 381,3125 MHz S-CH 1254,9500 MHz 381,3000 MHz S-CH 2254,9375 MHz 381,2875 MHz .
:

S-CH 41 254,4375 MHz 380,7875 MHz S-CH 42254,4125 MHz 380,7625 MHz S-CH 43254,4000 MHz 380,7500 MHz .
:
S-CH 86253,8625 MHz 380,2125 MHz In Table 1, the channel C-CH is referred to as a control channel, which is always used at each communication start at outgoing and incoming calls. On the other hand, the channels S-CH 1 to S-CH 86 are referred to as speech channels, each of which is used when the control channel is switched to one designated speech channel after each communication has been started.
Since a multichannel method is adopted with respect to the speech channels, it is possible to prevent interference with another cordless telephone system by designating any one of idling speech channels after the control channel has been used at each communication start.
A duplex radio communication is adopted for each cordless telephone system; that is, two different frequencies are allocated to the up- and down-channels, respectively for communications between the TEL and the CE. As listed in Table 1, whenever a speech channel number to be used is determined, the up-channel and down-channel frequencies can be determined unconditionally.
~~ 5 Further, FM or PM modulation technique~can be applied.
Fig. 2 shows a connection operation sequence executed when an outgoing call is transmitted through the prior-art cordless telephone system as shown in Fig. 1, in which communications between the TEL and the CE via the control channel are indicated by dashed lines and those via the speech channel are indicated by solid lines.
Before an outgoing call, since the cordless telephone system is in the standby state, the used lS channel is set to the control channel. In the standby state, when the TEL is set to an off-hook state, the TEL
transmits an outgoing call signal to the CE via the control channel as shown in Fig. 2. Since the outgoing call signal includes an identification code for the TEL, 20 the CE rrc~on~c~ to the outgoing call signal when the TEL
identification code matches an identification code for the CE itself, designates one speech channel to be used among a plurality of previously recognized idle speech channels, and returns the outgoing cal-l signal to the 25 TEL. This outgoing call response signal includes information indicative of the above-mentioned designated speech channel. Thereafter, the used channel between the CE and the TEL is switched from the control channel to the designated speech channel. After having confirmed 30 the idling state of the designated speech channel again, the TEL transmits a channel switch-end signal through the confirmed speech channel. This designated speech channel is used until the speech ends.
Fig. 3 shows a connection operation sequence 35 executed when an incoming call is received through the prior-art cordless telephone system as shown in Fig. 1, and Fig. 4 is a timing chart showing the operation of the TEL and the CE.
Before an incoming call, the cordless telephone system is in the standby state. In the standby state, 5 the TEL turns off a radio transmitting circuit (Tx) and intermittently turns on or off a radio receiving circuit (Rx) (e.g. turned off for 2 sec and on for 60 msec), in order to save a battery. On the other hand, the CE turns off a Tx and turns on a Rx.
Under these conditions, when an incoming call is received through the office line, as shown in Figs. 3 and 4, an incoming call command is transmitted from the KSU
to the CE. In response to this command, the CE
designates one channel to be used among a plurality of 15 previously recognized idle speech channels, and turns on the Tx to transmit an incoming call signal to the TEL
through the control channel. This incoming call signal includes information indicative of the above-mentioned designated speech channel. The incoming call signal is 20 repeatedly transmitted for a predetermined limited time period (e.g. 3.7 sec) until an incoming call response signal from the TEL is received by the CE.
The TEL maintains the turn-on state when an electric field is detected under the condition that the Rx is 25 turned on. In response to the incoming call signal, the TEL turns on the Tx to transmit an incoming call response signal to the CE through the control channel.
Thereafter, the TEL once turns off the Tx, switches the channel to be used to the designated speech channel, and 30 turns on the Tx again to transmit a channel switch-end signal.
In response to the incoming call response signal, the CE -stops transmitting the incoming call signal, 4~eæ
turns off the Tx, and switches the channel to be used to 35 the designated speech channel. Further, in response to the channel switch-end signal from the TEL, the CE turns on the Tx again, and repeatedly transmits an incoming call tone (bell) signal to the TEL whenever an incoming call tone command from the KSU is received. Further, the TEL generates a calling tone whenever the incoming call tone signal is received.
In the prior-art cordless telephone system as described above, however, the control channel is always used at every communication start. Therefore, there exists the case where the control channel is occupied by a single cordless telephone system for several seconds, in particular at incoming call arrival. Since only one control channel- is provided, the remaining cordless telephone systems cannot use the control channel when the control channel is being occupied by one cordless telephone system, thus resulting in the following 15 problems:
(l) where an incoming call arrives at a cordless telephone system, the remaining cordless telephone systems cannot transmit an outgoing call and receive an incoming call, for a little while immediately after the incoming call arrival at one cordless telephone system.
(2) where the TEL 5 of the first cordless telephone system is placed near the CE 6 of the second telephone system and additionally the TEL 7 of the second telephone system is placed near the CE 4 of the first system as 25 shown in Fig. 5 and further two incoming calls arrive at the two systems simultaneously, since each TEL receives a strong electromagnetic wave transmitted from each CE
placed in the vicinity of the TEL, an identification number will not match with each other, so that no call 30 tone is generated.
The similar problem arises between a plurality of independent cordless telephone systems used within a relatively small space, as well as between a plurality of cordless telephone systems used as the extension 5 telephone sets in a key telephone system.
SUMMARY OF THE INVENTION

Therefore, the ob~ect of the present lnventlon provldes a method and an apparatus for controlllng radlo channels to be used for cordless telephone systems 80 that two or more cordless telephone systems can slmultaneously transmlt an outgolng call and recelve an lncomlng call, respectlvely.
Accordlng to a broad aspect of the lnventlon there 18 provlded a method of selectlng and controlllng a channel from a predetermlned number of channels, to establlsh a speech llnk between a base unlt and a movable telephone set of a cordless telephone apparatus, comprlslng the steps of. detectlng ldle speech channels from a predetermlned number of speech channels ln the base unlt7 deslgnatlng one speech channel from the detected ldle speech channels as a speech channel to be used for the movable telephone set, and storlng lnformatlon lndlcatlve of the deslgnated speech channel; and controlllng the speech llnk by use of the deslgnated speech channel to enable speech, when a call 18 orlglnated/recelved by the cordless telephone apparatusl whereln the steps of detectlng the ldle speech channels, deslgnatlng the one speech channel and storlng the lnformatlon are performed before the call 18 orlglnated/recelved by the cordless telephone apparatus.
Accordlng to another broad aspect of the lnventlon there 18 provlded a method of selectlng and controlllng a channel from a channel band ln whlch a control channel for transmlttlng control slgnals to control a speech llnk and a predetermlned number of speech channels for transmlttlng speech slgnals are arranged wlthln a predetermlned frequency band, to establlsh a speech llnk between a base unlt and a movable telephone set of a cordless 203~754 8 _0375-682 telephone apparatus, comprlslng the steps of detectlng ldle speech channels from a predetermlned number of speech channels ln the base unlt;
designatlng one speech channel from the detected ldle speech channels as a speech channel to be used for the movable telephone set, and storlng lnformatlon lndlcatlve of the deslgnated speech channel;
transmlttlng the lnformatlon lndlcatlve of the deslgnated speech channel from the base unlt to the movable telephone set by use of the control channel, to store the lnformatlon ln the movable telephone set; and controlllng the speech llnk by use of the deslgnated speech channel, wlthout use of the control channel, to enable speech, when a call ls orlglnated/recelved by the cordless telephone apparatus;
whereln the steps of detectlng the ldle speech channels, deslgnatlng the one speech channel, storlng the lnformatlon and sendlng the lnformatlon are performed before the call ls orlglnated/recelved by the telephone apparatus.
Accordlng to another broad aspect of the lnventlon there ls provlded a system havlng a key servlce unlt and at least one cordless telephone apparatus havlng a base unlt and a movable telephone set, the apparatus belng connected to the unlt, for selectlng and controlllng a channel from a predetermlned number of channels, to e~tabllsh a speech llnk between the base unlt and the movable telephone set, comprlslng:
detectlng means for detectlng ldle speech channels from a predetermlned number of speech channels;
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deslgnatlng means provlded for deslgnatlng one speech channel from the ldle speech channels detected by sald detectlng means as a speech channel to be used for the movable telephone set;
communlcatlng means for establlshlng radlo communlcatlon between the base unlt and the movable telephone set; and control means for controlllng dlfferent speech channels to be used by sald base unlt and movable telephone set, whereln the deslgnated speech channel 18 transmltted from the base unlt to the movable telephone set before a call 18 0 orlglnated/recelved by the cordless telephone apparatus; and whereln, when the call 18 orlglnated/recelved by the cordless telephone apparatus, sald control means control sald communlcatlng means to use the deslgnated speech channel whlle controlllng the speech llnk between the base unlt and the movable telephone set.
Accordlng to another broad aspect of the lnventlon there ls provlded a system havlng a key servlce unlt and at least one cordless telephone apparatus havlng a base unlt and a movable telephone set, the apparatus belng connected to the unlt, for selectlng and controlllng a channel from a channel band ln whlch a control channel for transmlttlng control slgnals to control a speech llnk and a predetermlned number of speech channels for transmlttlng speech slgnals are arranged wlthln a predetermlned frequency band, to establlsh a speech llnk between the base unlt and the movable telephone set, comprlslng, detectlng means for detectlng ldle speech channels from a predetermlned number of speech channels;
deslgnatlng means for deslgnatlng one speech channel from the detected ldle speech channels as a speech channel to be used for - lo ~ 0 3 6 7 5 ~ 20375-682 the movable telephone set;
flrst storing means provlded for the base unlt, for storlng lnformatlon lndlcatlve of the deslgnated speech channel;
communlcatlng means for establlshlng radlo communlcatlons between the base unlt and the movable telephone set;
control means for controlllng dlfferent speech channels to be used by sald base unlt, and movable telephone set; and second storlng means provlded for the movable telephone set, for storlng the lnformatlon lndlcatlve of the deslgnated speech channel;
whereln the lnformatlon lndlcatlve of the deslgnated speech channel ls transmltted from the base unlt to the movable telephone set so as to be stored ln sald second storlng means vla the control channel, before a call ls orlglnated/recelved by the cordless telephone apparatus; and whereln, when the call orlglnatedtrecelved by the cordless telephone apparatus, sald control means control sald communlcatlng means to use the deslgnated speech channel whlle controlllng the speech llnk.
Accordlng to another broad aspect of the lnventlon there ls provlded a key telephone system ln whlch a cordless telephone system lncludlng a connectlng equlpment and a movable telephone ls connected to a key servlce unlt as an extenslon telephone set for mutual radlo communlcatlons, comprlslngz detectlng means provlded for the connectlng e~ulpment for detectlng ldle speech channels from a predetermlned number of speech channels and lndlcatlng the detected ldle speech channels to the key servlce unlt;

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deslgnatlng means provlded for the key servlce unlt, for deslgnatlng one speech channel from the ldle speech channels detected by sald detectlng means as a speech channel to be used for the key telephone system and lndlcatlng the deslgnated speech channel to the connectlng equlpment~
flrst communlcatlng means provlded for the connectlng equlpment, for establlshlng radlo communlcatlons between the connectlng equlpment and the movable telephone set~
flrst control means provlded for the connectlng equlpment, for controlllng a speech channel to be used by sald flrst communlcatlng means~
a second communlcatlng means provlded for the movable telephone set, for establlshlng radlo communlcatlons between the movable telephone set and the connectlng equlpment~ and second control means provlded for the movable telephone set, for controlllng a speech channel to be used by sald second communlcatlng means5 whereln the deslgnated speech channel lndlcated from the key servlce unlt to the connectlng equlpment 18 lndlcated from the connectlng equlpment to the movable telephone set vla radlo communlcatlons between sald flrst and second communlcatlng means, before a call 18 orlglnated/recelved by the cordless telephone system; and whereln, when the call 18 orlglnated/recelved by the cordless telephone system, sald flrst and second control means controls sald flrst and second communlcatlng means to use the deslgnated speech channel whlle controlllng a speech llnk between the connectlng equlpment and the movable telephone set.

DB~ ON OF TH13 ~n~r dRR~3D E ~D3ODIMI~NTS
An embodlment of the present lnventlon wlll be descrlbed herelnbelow wlth reference to the attached drawlngs.
Flgure 6, Flgure 7 and Flgure 8 show a key servlce unlt (KSU), a connectlng equlpment (CE) and a movable telephone set (TEL) accordlng to the present lnventlon, respectlvely whlch are all lncorporated ln a key telephone system as shown ln Flgure 1.

As shown in Fig. 6, the KSU 100 includes office line interface circuits 10 and 11, electric key telephone set (EKT) interface circuits 13 and 14, a switching circuit 12, a controller 15, a power supply circuit 24, etc.
Each office line interface circuit 10 or 11 is connected to each office line 1 or 2 and provided with various functions of detecting an incoming call signal transmitted through each office line and outputting it to the controller 15, acquiring each office line in accordance with a control data outputted from the controller 15, transmitting a select signal to the acquired office line in accordance with the control data from the controller 15, transmitting speech signals between the acquired office line and the switching circuit 12, etc.
Each EKT interface circuit 13 or 14 is connected to an extension telephone set such as a wire electric key telephone set (EKT), a cordless telephone system via speech signal lines 18 and 20 and control lines 19 and 21, and provided with various functions of supplying power to each extension telephone set, transmitting speech signals between each extension telephone set and the switching circuit 12, transmitting control data between each extension telephone set and the controller via a data interface circuit 17 including buffer memory and parallel/serial converting circuits.
The switching circuit 12 is connected to office line interface circuits 10 and 11 and the EKT interface circuits 13 and 14, and provided with a function of switching connections between an office line and an extension telephone set in accordance with control data from the controller 15. This switching circuit 12 is connected to an oscillator 22 for generating an extension dial tone (400 Hz). That is, in response to an outgoing call signal from an extension telephone set, this switching circuit 12 connects the oscillator 22 to an EKT
interface circuit generating an outgoing call signal to ,~ ,.

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;~ 2036754 transmit an extension dial tone to a telephone set to which the outgoing call signal is transmitted. However, any switching circuits can be applied to the key service unit.
The controller 15 is a microcomputer including a CPU
15a, a ROM 15b for storing control programs, a RAM 15c, etc. to control various system operations such as outgoing call, incoming call, connection, speech, speech end, etc. in accordance with the stored programs. In control operation, necessary control data are received/transmitted between the controller 15 and the various circuits such as the office line interface circuits 10 and 11, the EKT interface circuits 13 and 14, the speech switching circuit 12, etc.
The control programs include a program for designating a speech channel through which each cordless telephone system is used, and transmitting the designated speech channel to each cordless telephone system connected to the KSU 100. This program is executed by the CPU 15 as a part of the initial routines executed whenever the movable telephone set is turned on. The functions executed by the microcomputer in accordance-with this program are shown as a block diagram within the CPU 15a. Further, a RAM 16 iS connected to the 25 controller 15. This RAM 16 includes a table which records speech channels to be used by each cordless telephone system designated in accordance with the e~se~t ~ nvention, as shown in Fig. 10. The RAM 16 is ~ by a lithium battery 25, so that the table is 30 kept recorded even at power failure.
The power circuit 24 converts a commercial 100 V AC
supply voltage into a predetermined stabilized DC supply voltage and supplies it to the KSU 100. The converted supply voltage is also supplied to each extension 35 terminal set via each EKT interface circuit 13 or 14.

~ 2036754 With reference to Fig. 7, the connecting equipment (CE) of the cordless telephone system will be described hereinbelow.
The CE 200 is connected to the EKT interface circuit (e.g. 13) shown in Fig. 1 via a speech signal line (e.g.
18) and a control signal line 19, and provided with a hybrid circuit 30, a speech receiving circuit 31, a speech transmitting circuit 32, a radio transmitting circuit (Tx) 34, a radio receiving circuit (Rx) 38, a 10 controller 36, a power circuit 41, etc.
The hybrid circuit 30 converts two lines to 4 lines or vice versa between the speech signal line 18 connected to the KSU 100 and the speech signal lines connected to the speech receiving circuit 31 and the speech - 15 tra~smitting circuit 32. This hybrid circuit 30 includes ng ~network 33 to control a sidetone to an appropriate level by simulating the line impedance.
The speech receiving circuit 31 receives speech signals outputted from the hybrid circuit 30 and 20 transmits them to the Tx 34. ~ local oscillator signal ~ /oC~c~
is given from a PLL'~'circuit 35 to the Tx circuit 34. The carrier frequency of the local oscillator signal is controlled by the controller 36 so as to match one of down-channel frequencies (shown in Table 1) designated by 25 the KSU 100 as a speech channel for the cordless telephone system. However, in a specific case, the ~ carrier frequency of the Tx 34 is controlled so as to match that of the down-channel of the control channel, as described later. The output signal of the Tx circuit 34 30 is transmitted to an antenna 45 via an antenna sharing (duplex) device (DUP) 37 and then radio-transmitted to the TEL 300.
The signals transmitted from the TEL 300 are received via the antenna 45 and then inpu~ed to the Rx 35 38 via the antenna sharing device 37. ~ Rx 38 is composed of a control channel (C-CH) receive section 38a and a speech channel (S-CH) receive section 38b. The I~o . 203~5 C-CH receive section 38a is fixedly tuned to the up-channel frequency (shown in Table 1) of the control channel. On the other hand the S-CH receive section 38b receives a local oscillator signal from the PLL circuit 5 39. The frequency of the PLL circuit 52 is controlled by the controller 36 so that the S-CH receive section 38b is tuned to one of up-channel frequencies (shown in Table 1) designated by the KSU 100 as a speech channel to be used as the cordless telephone system. The speech 10 transmitting circuit 32 receives speech signals transmitted from the TEL 300 and received by the Rx 38 and control data, and transmits the speech signals to the hybrid circuit 30 and the control data to the controller 36.
The data line 19 from the KSU 100 is connected to a power circuit 41 and a data interface circuit 42 via a transformer 40. The power circuit 41 converts a power from the KSU 100 into a predetermined DC voltage level and then supplies it to the CE 200. The data interface 20 circuit 42 includes serial/parallel converters and buffer memory units to receive/transmit control data between the data line 19 and the controller 36.
- The ~ ntroller 36 is a microcomputer including a CPU
36a, a 36b for storing control programs, a RAM 36c, 25 etc. to control operations of the speech receiving circuit 31, speech transmitting circuit 32, Tx 34, PLL
circuits 35 and 39, etc. in accordance with stored programs. One of the control operations executed by this microcomputer is to control the afore-mentioned 30 frequencies of the Rx 31 and the Tx 34 in order to determine the radio channel used by this CE 200. The functions executed by the microcomputer in accordance with the program are shown as a block diagram within the CPU 36a. This controller 36 includes a radio data 35 interface circuit 36d having a modem. Therefore, the interface circuit 36d receives the speech frequency signal from the movable telephone set via the speech ~, - ~ 2036754 20375-682 transmitting circuit 32, demodulates the speech signal into control data and gives them to the CPU 36a. Further, the interface circuit 36d modulates control data to be transmitted from the CPU 36a to the movable telephone set into speech frequency signals and gives them to the speech receiving circuit 31. Further, the controller 36 receives/transmits control data from/to the KSU 100 via a data interface circuit 42.
An EEPROM (electrically erasable programmable read only memory) 43 and a speech channel clear switch 44 are connected to the controller 36. In this EEPROM 43, identification numbers of the cordless telephone systems and a speech channel number designated by the KSU 100 as a cordless telephone system to be used are recorded. With reference to the EEPROM, the CPU 36 controls the frequency of the PLL circuits 35 and 39. When turned on, the speech channel clear switch 44 erases the speech channel recorded in the EEPROM 43 as a channel to be used, so that the CE
200 is returned to an initial condition where a channel to be used is not yet designated. This switch 44 is used to designate the speech channel to be used again when the electric wave condition is poor at the designated speech channel. The same clear switch is also provided for the TEL 300. In case of poor electric wave condition, it is necessary to depress the clear switch of the telephone set, simultaneously.
With reference to Figure 8, the movable telephone set (TEL) 300 will be described hereinbelow.
The TEL 300 includes an antenna 30, a radio receiving circuit (Rx) 51, a speech receiving circuit 53, an earphone 54, a microphone 55, a speech transmitting circuit 56, a radio ~ 2036754 20375-682 transmitting circuit (Tx) 57, a controller 59, a sounder 63, a power circuit 66, dial and function keys 68.
Electric wave transmitted from the CE 200 is received by the antenna and inputted to the Rx via an antenna sharing (duplex) device (DUP) 50. The Rx 51 is composed of a control channel (C-CH) receive section 51a and a speech channel (S-CH) receive section 51b. The C-CH receive section 38a is fixedly tuned to the down-channel frequency (shown in Table 1) of the control 5 channel. On the other hand, the S-CH receive section 51b receives a local oscillator signal from the PLL circuit 52. The frequency of the PLL circuit 52 is controlled by the controller 59 so that the S-CH receive section 51b is tuned to one of down-channel frequencies (shown in Table 10 1) designated by the KSU 100 as a speech channel to be used as the cordless telephone system. The speech signals transmitted by the CE 20 and received by the Rx 51 and control data are given to the speech receiving circuit 53. The speech signals are transmitted to the 15 earphone 54 and the control data are transmitted to the controller 59. The speech signals from the microphone 55 are inputted to the speech receiv ~g circuit 56 and then transmitted to the Tx 57. The 57 ~eceives a local oscillator signal from the PLL circuit ~. The frequency 20 of the PLL circuit ~ is controlled by the controller 59 so that the carrier frequency of the Tx 57 matches one of up-channel frequencies (shown in Table 1) designated by the KSU 100 as a speech channel for the cordless telephone system. However, in a specific case, the PLL
25 circuit 58 is controlled so that the carrier frequency of the Tx 57 matches the up-channel frequency of the control channel, as described later. The output signal of the Tx 57 is transmitted to an antenna 73 via an antenna sharing (duplex) device (DUP) 50, and then transmitted to the CE
30 200.
The controller 59 is a microcomputer including CPU
59a, a ROM 59b for storing control programs, a RAM 59c, etc. to control operations of the speech receiving circuit 51, a radio receiving circuit 51, a speech 35 receiving circuit 53, a speech transmitting circuit 56, a radio transmitting circuit 57, PLL circuits 52 and 58, etc. in accordance with stored programs. One of the ., .

~b ~ 2036754 control operations executed by this microcomputer is to control the afore-mentioned frequencies of the Rx 51 and the Rx 57 in order to determine the radio channel used by this TEL 300. The functions executed by the 5 microcomputer in accordance with the program are shown as a block diagram within the CPU 59a. This controller 59 includes a radio data interface circuit 59d having a modem. Therefore, the interface circuit 59d receives the speech frequency signal (control data) from the CE 200 10 via the speech receiving circuit 53, demodulates, and transmits the speech signal to the CPU 59a. Further, the interface circuit 59d modulates control data to be transmitted from CPU 59a to the CE 200 into speech frequency signals and gives them to the speech receiving 15 circuit 56.
An EEPROM 60 and a speech channel clear switch 61 are connected to the controller 59. In the same way as in the connecting equipment 200, identification numbers of the movable key telephone sets and a speech channel 20 designated by the KSU 100 as a cordless key telephone system to be used are recorded in this EEPROM 60.
Further, when turned on, the speech channel clear switch 61 returns the movable key telephone set to an initial condition where a channel to be used is not yet 25 designated.
In addition, a sounder 63, dial and function keys 68, a hook key 69, a speech lamp 70, an unusable lamp 70 are connected to the controller 59. A call tone signal (when an incoming call arrives) or a confirmation tone 30 signal (when the dial and function keys 68 are depressed) are given from the controller 59 to the sounder 63 via an amplifier 62. The dial and function keys 68 are depressed when a dialing or a function selection is required. The hook-key 69 is a switch turned on when 35 once depressed and off when depressed again. Therefore, controller 59 recognizes an on-hook state of the movable telephone set when the hook key 69 is turned on and an off-hook state thereof when turned off. The controller 59 turns on the speech lamp 70 during speech and turns on the unusable lamp 71 when the movable telephone set is carried out of an area within which electric wave transmitted from the CE can reach.
The power circuit 66 regulates the output voltage of a nickel-cadmium battery 65 to a predetermined voltage level and supplies the regulated voltage to the movable telephone set (TEL) 300. Further, since the power circuit 66 is provided with a charge terminal 67, the battery 65 can be charged by connecting an external charger (not shown) to this terminal. The power switch 64 is used to turn off the power circuit 66 to prevent battery consumption when the movable key telephone sets 300 are all not used.
The operation of the key telephone system will be described hereinbelow.
After the system has been installed and the necessary wiring work has been completed by a worker, the 20 KSU 100 is turned on. Then, an initial routine is executed to initialize all the data (e.g. extension numbers of the telephone sets, various functions, etc.) required to operate the system. In this initial routine, a procedure of designating a speech channel to each 25 cordless key telephone system is of course included in the initial routine. Fig. 9 shows an operation sequence of the speech channel designation. The speech channel designating operation will be explained in further detail with reference to Figs. 6, 7, 8 and 9.
When the KSU 100 is turned on, a reset section 15g commands a table write section 15h to clear all the information recorded in a table (as shown in Fig. 10) in the RAM 16. This table clear signal is given- to a flag section 15i. This flag section 15i sets or resets a flag indicative of whether a speech channel to be used has already been designated or not for each cordless telephone system. In response to the table clear signal, . .,_ the flag section 15i sets a flag indicative of that all the speech channels for all the cordless telephone systems are not yet designated.
Further, when the KSU 100 is turned on, power is 5 supplied to the CE 200. Therefore, in the CE 200 as shown in Fig. 7, a reset section 36n of the controller 36 commands a ROM write section 36j to clear all the channel numbers previously stored in the EEPROM 43. The fact that the speech channel numbers are all cleared in the 10 EEPROM 43 is detected by a flag section 36g, so that the flag section 36g sets a flag indicative of that the speech channels are not yet designated. Further, a radio control section 36h turns on the radio receiving circuit 38 and the speech transmitting circuit 32. Further, in 15 response to a command from the reset section 36n, a channel scan section 36i scans the local oscillation frequencies all over the frequency range to search the idle/busy states of all the local speech channels at the spot where the connecting equipment is installed, on the 20 basis of a noise detection signal (ND) outputted from the speech transmitting circuit 32 at each frequency. The channel scan section 36i transmits idle/busy speech channel numbers (as shown in Table 1) obtained as a result of the scanning operation to a data transmit 25 section 36~. The data transmit section 36~ transmits the data to the KSU 100 via the control signal line 19. The above-mentioned data are referred to as local idle speech channel data, hereinafter. In the KSU 100 shown in Fig.
~, a table write section 15h of the controller 15 30 receives the local idle speech channel data from all the CEs via a data receive section 15e, sums up these data, and records the data into a table within the RAM 16.
Thereafter, when a clear key 61 of the TEL 300 as shown in Fig. 8 is depressed, a reset section 59j 35 commands a ROM write section 59h to clear all the speech channel numbers previously stored in the EEPROM 60. The fact that the speech channel numbers are all cleared in ~3 20367~4 the EEPROM 60 is detected by a flag section 59i, so that the flag section 59i sets a flag indicative of that the speech channels are not yet designated. Thereafter, the hook key 69 is depressed by a worker. Then, a hook-state 5 detect section 59g of the controller 59 recognizes an off-hook and indicates it to a radio data transmit section 59f and a radio control section 59g. Then, the radio control section 59g turns on the speech transmitting circuit 56 and the radio transmitting 10 circuit 57, and the radio data transmit section 59f transmits an outgoing call signal to the speech receiving circuit 56 via the radio data interface circuit 59d. In this transmission, the radio control section 59g determines a radio speech channel to be used in 15 accordance with the channel numbers stored in the EEPROM
60. In this case, when the channel numbers stored in the EEPROM 60 have been already cleared as described before, the radio control section 59g controls the PLL circuit 58 so that the control channel can be used. Since the 20 channel numbers have been already cleared in the EEPROM
43 in the CE 200, the radio control section 36h controls the PLL circuit 39 so that the control channel can be used. Accordingly, the outgoing call signal is transmitted from the TEL 300 to the CE 200.
The outgoing call signal received by the CE 200 as shown in Fig. 7 is transmitted from the speech transmitting circuit 32 to the radio data interface circuit 36d to compare the identification number of the TEL 300 included in the outgoing call signal with the 30 identification number read from the EEPROM 43. When both the identification numbers match each other, this outgoing call signal is transmitted to a radio data receive section 36e of the CPU 36a. In response to the outgoing call signal, the radio data receive section 36e 35 refers to the flag section 36g. As already described, the flag section 36g indicates the state where the speech channel is not yet designated. Therefore, the radio data receive section 36e transmits a speech channel designation request signal to the data transmit section 36e. The data transmit section 36e transmits the request signal to the KSU 100 via the control signal line 19.
In the KSU 100 shown in Fig. 6, the above channel designation request is transmitted to a data receive section 15e via the EKT interface circuit 13, and then given to a channel select section 15j. The channel select section 15j selects an idle speech channel from 10 among local idle speech channel data recorded in the RAM
16, and gives the selected idle speech channel number to a data transmit section 15d and a table write section 15h. The data transmit section 15d returns the channel number data to the CE 200 via the EKT interface circuit 15 13 as a designated speech channel data.
In the CE 200 shown in Fig. 7, a data receive section 36m receives this designated speech channel data, and gives it to a radio data transmit section 36f, a radio control section 36h and a ROM write section 36i.
20 The radio data transmit section 36f forms an outgoing signal response signal and transmits it to the TEL 300.
This outgoing call response signal includes the above-mentioned designated speech channel number data. This outgoing call response signal is transmitted via the 25 control channel. Therefore, the radio control section 36h controls the PLL circuits 35 and 39 so that the control channel is switched to the designated speech channel as a channel to be used.
In the TEL 300 shown in Fig. 8, in response to the 30 outgoing call response signal, a radio data receive section 59e refers to the flag section 59i. Since the speech channel is not yet designated, the designated speech channel number data is extracted from the outgoing call response signal, and then given to the radio control 35 section 59g and to ROM write section 59h. Then, the radio control section 59g controls the PLL circuits 35 -~ and 39 so that the channel to be used is switched from the control channel to the designated speech channel and subsequently the designated speech channel is checked as to whether the designated speech channel is idle on the basis of a carrier detection signal (CD) from the speech receiving circuit 53. If idle, the radio control section 59g gives its idle state to the radio data transmit section S9f. The radio data transmit section 59f forms a channel switch end signal and transmits its signal to the CE 200 via the designated speech channel. Thereafter, the ROM write section 59h writes the designated speech channel number data in the EEPROM 60, and commands the i~dlca~Jn 7 flag section 59i to set the flag indicaLi~ of that the channel has been designated. 3~ e In the CE 200, the radio data receive section ~ge receives the channel switch end signal from the TEL, and gives its signal to the data transmit section 36c, the radio data transmit section 36f and the ROM write section 36i. Therefore, the data transmit section 36e transmits an off-hook signal to the KSU 100, and the radio data transmit section 36f transmits a speech circuit turn-on signal to the TEL 300. Further, the ROM write section 36i writes the designated speech channel number data in the EEPROM 43, and gives its write end to the flag section 36g to set a flag indicative ~ that the speech 25 channel has been designated.
In the KSU 100 shown in Fig. 6, when the data receive section 15e receives the off-hook signal, the data receive section 15e knows that the speech channel is not yet designated with reference to the flag section 15i 30 and commands the table write section 15h to write the designated speech channel number data in a table within the RAM 16. Further, since the off-hook signal is given to a call control section 15f, the call control section 15f controls a switching circuit 12 so that an oscillator 22 is connected to the EKT interface circuit 13 to transmit an extension dial tone from the oscillator 22 to the CE 200 via the speech signal line 18. The CE 200 < ~
~ 20367S4 transmits the extension dial tone received through the speech signal line 18 to the TEL 300. In the TEL 300 shown in Fig. 8, the radio control section 59g receives the speech circuit turn-on signal via the radio data receive section 59e to turn on the speech circuit provided in the speech receiving circuit 53 and the speech transmitting circuit 56, respectively to connect the earphone 54 and the microphone 55 to the radio receiving circuit 51 and the radio transmitting circuit 57, respectively. Accordingly, the received extension dial tone is transmitted to the earphone 54. When hearing the extension dial tone, the worker knows that a speech channel to be used for this TEL has been designated and registered.
Thereafter, when the worker turns off the hook-key 69 of the TEL 300 again, a hook-state detect section 59k recognizes an on-hook state and transmits a speech end signal to the CE 200 via the radio data transmit section 59f. The CE shown in Fig. 7 receives the on-hook signal 20 and transmits it to the KSU 100, so that the KSU 100 recognizes that the channel designation procedure for the movable telephone set has been completed.
After the above-mentioned channel designation has been completed to one cordless telephone system, another 25 cordless telephone system is off-hooked and another speech channel is designated to the cordless telephone system in accordance with the same sequence as described above. That is, the similar sequence is repeated for all the cordless telephone systems.
Fig. 10 shows an example of a table formed in the RAM 16 of the KSU 100 after the speech channels have been designated to all the cordless telephone systems. This table includes a map indicative of designated speech channels for cordless telephone systems (a designated 35 speech channel map) and a map indicative of idle speech channels at cordless telephone system locations (a local idle speech channel map). In this example, four TELS

a~

~f~

having identification numbers 1 to 4 are listed, in which indicates a cordless telephone syst~em and "0"
indicates an electric key telephone set }~ the kind of telephone sets. In the designated speech channel map, "1" indicates a designated speech channel. In the local idle speech channel map, "0" indicates an idle speech channel. It is preferable to rewrite the local idle speech channel map occasionally so as to follow change in environment. For the purpose, in the CE 200 shown in Fig. 7, a channel scan section 36i scans the speech channels periodically in response to a synchronizing signal outputted from a timer 36k to transmit information as to local idle speech channels to the KSU 100. In the KSU 100 shown in Fig. 6, a table rewrite section 15h rewrites the local idle speech channel map within the RAM
16 on the basis of the local idle speech channel information periodically transmitted from the CE 200.
By the way, when each speech channel is designated to each cordless telephone system in sequence, it is necessary to prevent a speech channel from being designated to two or more cordless telephone systems.
For the purpose, the KSU 100 designates the speech channels in accordance with a selected sequence as shown in Fig. 11, for instance. In more detail, the speech channel No. 1 (S-CH 1) is designated to the first cordless telephone system; the speech channel No. 6 (S-CH
6) is designated to the second cordless telephone system;
the speech channel No. 11 (S-CH 11) is designated to the third cordless telephone system; and so on. That is, the speech channel is designated at intervals of five speech channel numbers. After the last speech channel No. 86 has been designated, the speech channel No. 2 is designated, and then other speech channels are designated at intervals of five speech channel numbers. In this designation, the speech channels now being used (indicated by "1" in the local idle speech channel map shown in Fig. 10) are passed without being designated.
-r Further, the relationship between the speech channelnumbers and the frequencies are listed in Table 1. The reason why the speech channels are designated to the cordless telephone systems at intervals of five channel numbers without being designated in the order of No. 1, No. 2, ... in sequence is to sufficiently increase difference in frequency of the channel to be used between the cordless telephone systems for prevention of radio interference with each other. However, it is also possible to adopt other methods of preventing the speech channels from being designated doubly.
The operation will be described, which is executed when an outgoing call is transmitted from the cordless telephone system to the office line or an incoming call is transmitted from the office line to the cordless telephone system after the initial routine has been completed.
Fig. 12 shows the connecting operation sequence executed when an outgoing call is transmitted from the cordless telephone system to the office line. The outgoing call operation will be explained with reference to Figs. 6 to 12. When the TEL 300 is off-hooked, an outgoing call signal is transmitted from the TEL 300 to the CE 200. In the TEL 300 and the CE 200, the radio control sections 59g and 36h have already set the used speech channel to the designated speech channel in accordance with the channel number stored in the EEPROMs and 43, respectively. Therefore, all the radio communications including the outgoing call signal transmission are always effected through the designated speech channel, without using the control channel.
Further, when transmitting the outgoing call signal, the radio control section 59g of the TEL 300 first confirms whether the designated speech channel can be used; that is, the frequency of the designated speech channel is not used for the other adjacent cordless telephone systems, on the basis of the carrier detection signal CD. When -q- -the idling state of the designated speech channel has been confirmed, this information is given to the radio data transmit section 59f to transmit the outgoing call signal.
In the CE 200 shown in Fig. 7, the radio data interface circuit 36d receives the outgoing call signal and checks whether the identification number of the TEL
300 included in the outgoing call signal matches its identification number stored in the EEPROM. If matches, the received outgoing call signal is transmitted to the radio data receive section 36e. The radio data receive section 36e transmits an off-hook signal to the KSU 100 via the data transmit section 36~ and further transmits an outgoing call response signal to the TEL 300 via the radio data transmit section 36f. In the TEL 300 shown in Fig. 8, in response to the outgoing call response signal, the radio control section 59g turns on the speech circuit on the basis of the command from the radio data receive section 59e. Further, in the KSU 100 shown in Fig. 6, in response to the off-hook signal, the call control section 15f controls the switch circuit 12 to transmit an extension dial tone to the CE 200. The CE 200 further transmits this dial tone to the TEL 300.
In the TEL 300 shown in Fig. 8, when the user hears the extension dial tone from the earphone 54, the user enters a predetermined number (e.g. "0") for calling an office line through the dial keys 68. Then, the dial signal of "0" is transmitted to the CE 200, and therefore the CE 200 transmits the corresponding dial data "0" to the KSU 100. In the KSU 100 shown in Fig. 6, the data receive section 15e receives this dial data "0" and gives it to the call control section 15f. The call control section 15f controls the office line interface circuit 10 to acquire an idle office line (e.g. 1) (to close a dc loop) and further controls the switching circuit 12 to connect the office line interface circuit 10 of the acquired office line to the EKT interface circuit 13 of 3 ;~
~''.~

the cordless telephone system which transmits an outgoing call signal.
When detecting the above acquisition, the telephone office transmits a dial tone (office line dial tone) to an office line 1, so that this dial tone is transmitted from the KSU 100 to the TEL 300 via the CE 200. When hearing this office line dial tone, the user enters a telephone number of a called subscriber through the dial keys 68. Therefore, the TEL 300 transmits the dial signals indicative of the called subscriber's number to the CE 200. The CE 200 transmits a dial data corresponding thereto to the KSU 100. The KSU 100 transmits the corresponding selection signal to the office line in the form of dial pulses or MF signals.
At the speech end, since the TEL 300 is on-hooked, a speech end signal is transmitted to the CE 200. In response to the speech end signal, the CE 200 transmits the on-hook signal to the KSU 100. In response to the on-hook signal, the KSU 100 opens the DC loop of the office line, so that the speech ends.
With reference to Figs. 6 to 8 and 13, the connecting operation sequence executed when an incoming call is transmitted to the cordless telephone system will be explained hereinbelow.
The call signal of 16 Hz, for instance is repeatedly transmitted intermittently from the telephone office to the KSU 100. In the KSU 100 shown in Fig. 6, in response to the first call signal, the call control section 15f transmits an incoming call command to the CE 200. Since the cordless telephone system is in the standby state before the incoming call arrival, in this state the radio receiving circuit 38 is turned on and the radio transmitting circuit 34 is turned off in the CE 200. In response to an incoming call command in this state, the radio control section 36h of the CE 200 turns on the radio transmitting circuit 34, and further the radio data transmit section 36f transmits an incoming call signal to the TEL 300. As already described, since the radio control section 36h allows the radio receiving circuit (Rx) 38 and the radio transmitting circuit (Tx) 34 to be set to the speech channel designated in accordance with the channel number stored in the EEPROM, all the radio communications including the incoming call signal transmission are always effected through the designated speech channel without using the control channel.
Further, when transmitting the incoming call signal, the radio control section 36h of the CE 200 first confirms whether the designated speech channel can be used; that is, the frequency of the designated speech channel is not used for the other cordless telephone systems, on the basis of the noise detection signal. When the idling state of the designated speech channel has been confirmed, the information is transmitted.
In the TEL 300, the radio control section 59g turns off the radio transmitting circuit 57 and intermittently turns on the radio receiving circuit 53 (e.g. turned off for 2 sec and on for 60 msec) in the standby state.
While the radio transmitting circuit 53 is turned on, if a carrier is detected, the radio control section 59 keeps the radio receiving circuit 53 in the turn-on state. In this state, when receiving the incoming call signal, the TEL 300 returns an incoming call response signal to the CE 200.
Thereafter, whenever a call signal arrives, the KSU
100 transmits an incoming tone command to the CE 200. In the CE 200, when the radio data receive section 36e receives the incoming call response signal from the TEL
300, this information is given to the radio data transmit section 36f to transmit an incoming call tone signal to the TEL 300. In the TEL 300, the sounder 63 is activated in response to the incoming call tone signal to generate a call tone (bell sound). The CE 200 keeps transmitting the incoming call tone command to the TEL 300 until the TEL 300 is off-hooked.
~ .

.

When the TEL 300 is off-hooked, an off-hook data is transmitted to the CE 200. In response to the off-hook data, the CE 200 transmits the off-hook signal to the KSU
100. In response to the off-hook signal, the call S control section 15f of the KSU 100 controls the office line interface circuit 10 to acquire the office line 1 and further controls the switching circuit 12 to connect the office line 1 to the cordless telephone system, so that speech begins.
The operation sequence of speech end is the same as that of the outgoing call.
As described above, in the method of the present invention, since radio communications can be always effected by use of each speech channel so designated as not to be overlapped with each other or not to be used doubly, it is possible to simultaneously process outgoing calls or incoming calls for a plurality of cordless telephone systems. In addition, since it is unnecessary to switch the channel to be used from the control channel to the speech channel at the start of the radio communications, being different from the prior-art method, it is possible to shorten the time interval from the start of an outgoing or incoming call to the end of the connection between the office line and the TEL.
By the way, there exist some cases where a speech channel once designated cannot be used because the same speech channel is being used for the other adjacent cordless telephone systems. In this case, an outgoing call is inhibited in the above embodiment. Further, an incoming call is transmitted to the TEL 300 by temporarily using the control channel.
Fig. 14 shows the operation sequence of the incoming call under these unusable conditions. In response to the incoming call command from the KSU 100, the CE 200 checks whether the designated speech channel is now idle or not.
If not idle or busy, the CE 200 requests the KSU 100 to designate a new idle speech channel. The KSU 100 refers -~ . 3~
~.

to the local idle channel map to designate another idle speech channel and indicates it to the CE 200. The CE
200 switches the channel of the Tx 34 to the control channel, and transmits the incoming call signal to the TEL 300 through the control channel. A data indicative of the newly designated idle speech channel is included in this incoming call signal. Therefore, the TEL 300 receives the incoming call signal of the C-CH receive section 51a of the Rx 51, and transmits it to the radio data receive section 59e. The radio data receive section 59e commands the radio control section 59g to switch the channel of the Tx 57 to the control channel. Therefore, the incoming call response signal is transmitted from the TEL 300 to the CE 200 through the control channel, and received by the C-CH receive section 38a of the Rx 38 in the CE 200. Thereafter, in both the CE 200 and TEL 300, the channel to be used is switched from the control channel to the newly designated speech channel. The TEL
300 checks whether the newly designated speech channel is idle or not. If idle, a channel switch end signal is transmitted from the TEL 300 to the CE 200 and further from CE 200 to the KSU 100. Then, the newly designated speech channel is stored in the KSU 100, the CE 200 and _ the TEL 300, so as to be used principally. ~ operation sequence after that is the same as that described with reference to Fig. 13.
As described above, when another channel is required to be designated because the designated channel is used doubly by another cordless telephone system, the user depresses the speech channel clear keys 44 and 61 of the TEL 300 and the CE 200. Then, in the TEL 300 and the CE
200, the reset sections 59j and 36n command the ROM write sections 59h and 36j to return the contents stored in the EEPROMS 60 and 43 to those stored before designated.
Further, the CE 200 indicates this reset operation to the KSU 100. Then, in the KSU 100, the reset section 15g is activated to execute again the afore-mentioned operation .

3~

sequence of designating a speech channel for the reset cordless telephone system. Therefore, the channel to be used for the cordless telephone system is designated again as a new speech channel.
The method and the apparatus of the present invention have been described of the key telephone system by way of example. Without being limited thereto, however, the present invention can be applied to home telephone systems or PBX systems. Further, the present invention can be applied to an independent cordless telephone system. In this case, however, the function of designating a channel to be used is provided for the CE, instead of the KSU.

Claims (18)

1. A method of selecting and controlling a channel from a predetermined number of channels, to establish a speech link between a base unit and a movable telephone set of a cordless telephone apparatus, comprising the steps of:
detecting idle speech channels from a predetermined number of speech channels in the base unit;
designating one speech channel from the detected idle speech channels as a speech channel to be used for the movable telephone set, and storing information indicative of the designated speech channel; and controlling the speech link by use of the designated speech channel to enable speech, when a call is originated/received by the cordless telephone apparatus;
wherein the steps of detecting the idle speech channels, designating the one speech channel and storing the information are performed before the call is originated/received by the cordless telephone apparatus.

2. The method of claim 1, wherein the step of detecting idle speech channels is executed when the cordless telephone apparatus is turned on.

3. The method of claim 2, wherein the step of detecting idle speech channels is executed periodically after the cordless telephone apparatus has been turned on.

4. The method of claim 1, which further comprises the step of continuously using the designated speech channel during the speech which has been enabled.

5. The method of claim 1, which further comprises the step of:
checking whether the designated speech channel is idle or not immediately before the speech link control operation; and if not idle, inhibiting the use of the designated speech channel.

6. The method of claim 5, which further comprises a step of controlling the speech link by use of a predetermined control channel, if the designated speech channel is not idle.

7. A method of selecting and controlling a channel from a channel band in which a control channel for transmitting control signals to control a speech link and a predetermined number of speech channels for transmitting speech signals are arranged within a predetermined frequency band, to establish a speech link between a base unit and a movable telephone set of a cordless telephone apparatus, comprising the steps of:
detecting idle speech channels from a predetermined number of speech channels in the base unit;
designating one speech channel from the detected idle speech channels as a speech channel to be used for the movable telephone set, and storing information indicative of the designated speech channel;

transmitting the information indicative of the designed speech channel from the base unit to the movable telephone set by use of the control channel, to store the information in the movable telephone set; and controlling the speech link by use of the designed speech channel, without use of the control channel, to enable speech, when a call is originated/received by the cordless telephone apparatus;
wherein the steps of detecting the idle speech channels, designating the one speech channel, storing the information and sending the information are performed before the call is originated/received by the telephone apparatus.

8. The method of claim 7, wherein the cordless telephone apparatus includes a plurality of movable telephone sets, and in the step of designating one speech channel, each of plural idle speech channels whose frequencies are not adjacent to each other is designated as each speech channel for each movable telephone set.

9. A system having a key service unit and at least one cordless telephone apparatus having a base unit and a movable telephone set, the apparatus being connected to the unit, for selecting and controlling a channel from a predetermined number of channels, to establish a speech link between the base unit and the movable telephone set, comprising:
detecting means for detecting idle speech channels from a predetermined number of speech channels;

designating means provided for designating one speech channel from the idle speech channels detected by said detecting means as a speech channel to be used for the movable telephone set;
communicating means for establishing radio communication between the base unit and the movable telephone set; and control means for controlling different speech channels to be used by said base unit and movable telephone set, wherein the designated speech channel is transmitted from the base unit to the movable telephone set before a call is originated/received by the cordless telephone apparatus; and wherein, when the call is originated/received by the cordless telephone apparatus, said control means control said communicating means to use the designated speech channel while controlling the speech link between the base unit and the movable telephone set.

10. A system having a key service unit and at least one cordless telephone apparatus having a base unit and a movable telephone set, the apparatus being connected to the unit, for selecting and controlling a channel from a channel band in which a control channel for transmitting control signals to control a speech link and a predetermined number of speech channels for transmitting speech signals are arranged within a predetermined frequency band, to establish a speech link between the base unit and the movable telephone set, comprising:
detecting means for detecting idle speech channels from a predetermined number of speech channels;
designating means for designating one speech channel from the detected idle speech channels as a speech channel to be used for the movable telephone set;
first storing means provided for the base unit, for storing information indicative of the designated speech channel;
communicating means for establishing radio communications between the base unit and the movable telephone set;
control means for controlling different speech channels to be used by said base unit, and movable telephone set; and second storing means provided for the movable telephone set, for storing the information indicative of the designated speech channel;
wherein the information indicative of the designated speech channel is transmitted from the base unit to the movable telephone set so as to be stored in said second storing means via the control channel, before a call is originated/received by the cordless telephone apparatus; and wherein, when the call originated/received by the cordless telephone apparatus, said control means control said communicating means to use the designated speech channel while controlling the speech link.

11. The system of claim 9 or 10, wherein said base unit is provided with said detecting means;
said designating means; and said communicating means;
said control means controlling the speech channel to be used by said base unit;
wherein said communicating means indicates the designated speech channel information to the movable telephone set via a predetermined control channel, before a call is originated/received by the cordless telephone apparatus; and wherein, when the call is originated/received by the cordless telephone apparatus, said control means controls said communicating means to use the designated speech channel while controlling a speech link between the base unit and the movable telephone set.

12. The system of claim 9 or 10, wherein said movable telephone set is provided with said communicating means, said control means controlling the speech channel to be used by said movable telephone set;
wherein said communicating means receives information indicative of the speech channel designated by the designating means via a predetermined control channel, before a call is originated/received by the cordless telephone apparatus; and wherein, when the call is originated/received by the cordless telephone apparatus, said control means controls said communicating means to use the designated speech channel while controlling a speech link between the base unit and the movable telephone set.

13. A key telephone system in which a cordless telephone system including a connecting equipment and a movable telephone is connected to a key service unit as an extension telephone set for mutual radio communications, comprising:
detecting means provided for the connecting equipment for detecting idle speech channels from a predetermined number of speech channels and indicating the detected idle speech channels to the key service unit;
designating means provided for the key service unit, for designating one speech channel from the idle speech channels detected by said detecting means as a speech channel to be used for the key telephone system and indicating the designated speech channel to the connecting equipment;
first communicating means provided for the connecting equipment, for establishing radio communications between the connecting equipment and the movable telephone set;
first control means provided for the connecting equipment, for controlling a speech channel to be used by said first communicating means;
a second communicating means provided for the movable telephone set, for establishing radio communications between the movable telephone set and the connecting equipments; and second control means provided for the movable telephone set, for controlling a speech channel to be used by said second communicating means;
wherein the designated speech channel indicated from the key service unit to the connecting equipment is indicated from the connecting equipment to the movable telephone set via radio communications between said first and second communicating means, before a call is originated/received by the cordless telephone system; and wherein, when the call is originated/received by the cordless telephone system, said first and second control means controls said first and second communicating means to use the designated speech channel while controlling a speech link between the connecting equipment and the movable telephone set.

14. The key telephone system of claim 13, wherein a plurality of pairs of the connecting equipment and the movable telephone set are included, said connecting equipments are connected to the key service unit, and said designating means in said key service unit receives information indicative of each group of idle speech channels detected by said detecting means in each connecting equipment, designates each speech channel included in each detected idle speech channel group and having a frequency different from each other as each speech channel for each pair, and indicates each designated speech channel to each connecting equipment.

15. The system of claim 9 or 10, wherein said key service unit is provided with said designating means and storing means for receiving information indicative of each idle speech channel group each detected from a predetermined number of speech channels by each cordless telephone apparatus, from each cordless telephone apparatus, and storing each idle speech channel group, wherein said designating means designates each speech channel including in each idle speech channel group stored in said storing means and having a frequency different from each other as each speech channel to be used for each cordless telephone apparatus, and said key service unit further comprises:

indicating means for indicating each designated speech channel to each cordless telephone apparatus, before a call is originated/received by each cordless telephone apparatus.

16. The method of claim 1 further comprising the steps of setting a flag indicative that the speech channel has been designated when the speech channel has been designated; and clearing the flag upon application of a reset signal, the flag thereby indicating that the speech channel has not been designated.

17. The method of claim 7 wherein the step of designating the one speech channel and storing the information includes the step of storing a flag value indicating that the speech channel has been designated.

18. A system as recited in claim 9 further comprising:
a first flag means provided for the base unit for indicating when the one speech channel has been designated for the movable telephone set;
first reset means for resetting the first flag means upon application of a reset signal to indicate that the one speech channel has not been designated;
a second flag means provided for the movable telephone set for indicating when the one speech channel has been designated;
and a second reset means for resetting the second flag means upon application of a reset signal to indicate that the one speech channel has not been designated.