CA1207030A - Communication set and method - Google Patents
Communication set and methodInfo
- Publication number
- CA1207030A CA1207030A CA000414155A CA414155A CA1207030A CA 1207030 A CA1207030 A CA 1207030A CA 000414155 A CA000414155 A CA 000414155A CA 414155 A CA414155 A CA 414155A CA 1207030 A CA1207030 A CA 1207030A
- Authority
- CA
- Canada
- Prior art keywords
- frequency
- call
- highway
- station
- carrier
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04Q—SELECTING
- H04Q11/00—Selecting arrangements for multiplex systems
- H04Q11/02—Selecting arrangements for multiplex systems for frequency-division multiplexing
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04M—TELEPHONIC COMMUNICATION
- H04M9/00—Arrangements for interconnection not involving centralised switching
- H04M9/02—Arrangements for interconnection not involving centralised switching involving a common line for all parties
- H04M9/022—Multiplex systems
- H04M9/027—Frequency division multiplex systems
Abstract
ABSTRACT
COMMUNICATION SET AND METHOD
A telephone communication method provides simul-taneoulsy duplex channels between respective pairs of stations over a single wire pair highway by frequency division multiplexing. Each duplex channel has a pre-determined pair of carrier frequencies, but only carrier frequency pairs of channels in use for communication are present on the highway at any time. On initiating a call, a station seeks for a free channel and reserves it by generating the "go" carrier of the free channel modulated with the call sign of the desired station, and also generating an alert signal. Quiescent stations respond-to the alert by seeking a "go" carrier with call sign data and, on identifying their own call sign, gene-rating the corresponding return carrier to set up the channel.
COMMUNICATION SET AND METHOD
A telephone communication method provides simul-taneoulsy duplex channels between respective pairs of stations over a single wire pair highway by frequency division multiplexing. Each duplex channel has a pre-determined pair of carrier frequencies, but only carrier frequency pairs of channels in use for communication are present on the highway at any time. On initiating a call, a station seeks for a free channel and reserves it by generating the "go" carrier of the free channel modulated with the call sign of the desired station, and also generating an alert signal. Quiescent stations respond-to the alert by seeking a "go" carrier with call sign data and, on identifying their own call sign, gene-rating the corresponding return carrier to set up the channel.
Description
-~ ~20703~
The present invention is concerned primarily with a communication method providing duplex communication between a plurality of pairs of stations on a single wire pair hiyhway by frequency division multiplexing. Frequency division multiplexing to pxovide several channels on a single pair of wires is known for telephony. However, in telephone systems employed hitherto, the various carrier frequencies providing the frequency division multiplexed channels on the single wire pair are provided continuously irrespective of whether a particular channel is busy. This arrangement is quite satisfactory for large scale telephone installations where power consumption is of only minor concern. However, to provide frequency division multi-plexing using known techniques for field telephone applica-tions, operating from battery power supplies, would make excessive demands on the battery supplies enabling only relativelv s~ort life operation. Also, such an arrangement would reduce the flexibility of the field telephone system since the various stations on the field telephone "net"
would have to operate through exchange apparatus which would provide channel routing and maintain the various frequency carrier signals.
According to a first aspect of the present invention, there is provided a communication method for providing duplex communication between a plurality of pairs of stations on a single wire pair highway by frequency division multiplexing, each station having a station-identi-fying call code, the highway being assigned a plurality of pairs of frequencies for communication thereover, each pair of frequencies including a go frequency and a re-turn frequency, said method comprising:
maintaining all presently non-communicating 7~30 stations in a quiescent mode in which each monitors the highway for alert signals;
activating a quiescent station desiring to transmit information as a caller station to a called station by having such caller station monitors frequency pairs on the highway to select a pair of presently unused frequencies and, upon selecting such a pair o~ frequencies, to apply an alert signal and the go frequency of the selected pair of frequencies to the highway, the go frequency being modulated by the call code of the called station;
activating all quiescent stations in response to receipt thereby of the alert signal for monitoring of call codes on the go frequency of the selected pair of frequencies;
initiating transmission on the highway, by that station which was activated by the alert signal and which corresponds to the call code, of the return fre-quency of the selected pair of frequencies, while return-ing all noncalled stations which were activated by the alert signal to the quiescent condition; and activating the caller station in response to receipt by it of the return frequency of the selected pair of frequencies to transmit on the highway the go frequency of the selected pair of frequencies modulated by the in-formation to be transmitted.
By eliminating the carrier signals which are notin use for communication, the power consumption of the arrangement can be greatly reduced and also the flexibility of operation especially in field telephone application can be greatly increased.
Further, the individual stations on the highway can themselves generate the various carrier frequency signals and first scan the existing carriers on the high-way to select a free channel.
~,,J
~207()~0 Preferably, each station activated by the alert signal monitors the highway for a go frequency modulated by a call code and upon receipt of a call code, compares the received call code with its own call code to determine whether it is the called station.
Thus, the stations not in use can be in the quiescent state with minimal if not zero power consumption.
However, they can be arranged to respond to the alert signal on the highway by seeking for the go frequency car-rier of the caller station and reading the call code.Only if the code is their own, do they remain non-quiescent and open the duplex channel by generating and transmitting to the highway the corresponding return frequency carrier.
The caller station preferably responds to receiving the retu~n ~requency from the called station also by can-celling the alert signal from the highway, causing all non-called stations which were activated by the alert signal to revert to the quiescent condition.
In accordance with a preferred characteristic of the method according to the invention, the quiescent sta-tions, upon being activated in response to receipt of the alert signal, monitor the pairs ol frequencies by scanning the return frequencies thereof to identify a return fre-quency absent from the highway, on locating an absent re-turn frequency tuning to the corresponding go frequencyof the respective pair of frequencies and, if the go fre-quency is present on the highway, checking for call code data on that go frequency, but otherwise continuing the scanning of the return frequencies. By this technique, the overall scanning time is reduced since go ~requencies are checked only if there is no corresponding return fre-quency. It will be understood that if there is a return frequency carrier already on the highway then this indicates that the particular channel is already in use and cannot be ., 1207(~3(~
the channel on which the new call is being placed.
According to a further preferred characteristic of the method of the invention, for use in telephony, the caller station modulates the go frequency with the call codes of selected called stations desired to join the call as a conference call and also a signal identifying the call as a conference call, the caller station terminating said go frequency generation and modulation after a predetermined time interval sufficient ~o permit the called stations to identify their respective call codes and then providing audio frequency communication with the highway, each called station responding to receipt of its call code and identifying that the call is a con-ference call by providing audio frequency communication with the highwav.
In accordance with another preferred charac-teristic of the invention, a selected pair o said pairs of frequencies is assigned as a priority channel for use only by a priority caller station in a priority mode to call a sta-tion already busy with an existing call or when all non-priority channels are busy, and the busy station called on the priority channel then responds by breaking contact with an existing call and moving to the priority channel to take the priority call. Preferably, in priority mode, a priority caller station checks the go frequency of the priority channel and, if such frequency is absent on the highway, generates and transmits the priority go frequency onto the highway, modulating such frequency with at least data defininy the call code of the desired called station, and simultaneously generates and impresses on the highway a priority call identifying signal, and each busy station xesponds to the priority call identifying signal by tuning to the go frequency of the priority channel, reading the ~LZC~ 30 call code modulated thereon, and comparing the call code with the respective call code assigned to the station, and then in response to identifying its own call code moving onto the priority channel but otherwise continuing with the existing call.
Preferably, in normal mode, the caller station maintains the alert signal in the absence of a received cor-responding return frequency for a predetermined maxlmum time, and, in priority mode, the priority call identifying signal comprises the alert signal and is maintained for a period of time in excess of the predetermined maximum time, and each busy station responds to the priority call iden-tifying signal only after the predetermined maximum time has elapsed.
The alert signal, and also the priority call identifying signal, may comprise a DC voltage impressed on the highway by the caller station. It will be appre-ciated that any non-busy station responds to the priority call identifying signal in the same way as to the alert signal, i.e. by reverting to a non-quiescent state and scanning the go carrier frequencies on the hi~hway for its own call code. All stations are advantageously arranged to scan all channels, including the priority channel in response to an alert signal, so that a priority channel call to a station which is not busy, will still be connected.
According to a secord aspect of the present invention, there is provided a communication set capable of providing , with other such sets at respective stations, duplex communication simultaneously between a plurality of pairs of stations on a single wire pair highway by fre-quency division multiplexing, wherein information i5 transmitt~d on the wire pair highway by modulation of pairs of predeiermined carrier frequencies, each pair of ~LZ~7~3~
said frequencies comprising a go frequency and a return frequency and providing a single channel duplex com-municatiGn between any selected pair of stations on the highway, each station being assigned a predetermined call code; the communication set comprising means for storing the call code assigned to the respective station, transmit-ter means energisable and controllable to generate and transmit to the highway carrier signals at a selected one of the predetermined carrier freqllencies, modulator means for modulating the generated carrier signal with information or data to be transmitted on the highway, tunable receiver means for selectively receiving carrier signals from the highway at any one of the predetermined carrier frequencies, demodulator means for demodulating information or data from the received carrier signal, operator input means enabling the operator of the set to initiate a call and key in the call code of a desired station, control means responsive to a call initiate signal from the input means to scan the tuning of the receiver means through said predetermined carrier frequencies until a vacant channel is identified, the re-spective pair of carrier frequencies for the channel being absent on the highway, and then to tune to the return fre-quency of the vacant channel, the control means including means to energise and control the transmitter means to transmit on to the highway a carrier signal at the go frequency of the vacant channel and simultaneously supply to the modulator means at least data from the input means defining the call code of the desired station so that the transmitted carrier signal is modulated with these data, the control means further including means responsive to reception by the receiver means of a carrier on the highway at the return frequenc~ of the vacant channel to inhibit further supply of the call code data to the modulator means, and an alert signal generator responsive to the control means on identifying a vacant channel to impress an alert signal on the highway until reception by the receiver means 703~
of said received frequency carrier.
In accordance with a preferred embodiment of the invention, the communication set comprises quiescent switching means arranged to switch the set to a quiescent state when not in use, but responsive to the presence of an alert signal on the highway to switch the set automa-tically to a non-quiescent state and means within the control means responsive on said switching to the non-quiescent state to scan the tuning of the receiver means to detect a go frequency carrier signal on the highway which is modulated with call code data and then to read these data and compare the received call code with that in said means for storing, the control means further including means responsive to the received call code matching that in said means for storing to hold the set in the non-quiescent state and to energise and control the transmitter means to tr~nsmit on to the highway a carrier signal at the return frequency of the channel including the detected go frequency carrier signal.
A non limitative example of the present invention will now be d~scribed with reference to the accompanying drawings in which: /
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~ ~21~703(~
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a block schematic dlagram illustrating a complete net incorporating a Dlurality of "subscriber"
sets connected to a sin~le wire pair highway;
Figure 2 is a block schematic diagram of a telephone "subscriber" set shown connected to a single wire pair highway;
Figure 3 illustrates an example of the telephone "subscriber" set provided as a single hand held unit an~
Figures 4, 5 and 6 are operational flow diagrams illustrating the sesuences of steps in operating the complete telephone syste~ in various different modes.
DETAILED DESCRIPTION OF A ~ ;KRED EX~lPLE
Figure 1 ill~ ~s a ccmplete tPl~rh~ net ~ r~t;ng in accor-dance with an P~m~nlP of the present invention. me net is foY~ed by a single hig~way cable 10 to~i~h are eonnected a n~r of "subscr ~ r"
sets 11-20. m2 highway cable 10 co~prises a sin~le wire pair typically a twisted pair or a co-axial eable with single core and sereen eonduetors. Eaeh "subseriber" set is conneeted to the highway eable ~y a link 21 whieh conneets the set to the two wires of the highway 10. The llnks 21 may be eonneeted to the highway 10 by means of eonnector elips whieh ~ake eonnection to the eonductors of the highway without breaking the highway at the conneetion point. A suitable ~orm of eonneetor whieh in one embodiment ~ 3L21~3(~
can connect the "subscribër" set linXs 21 to a c~-axial highway cable 10 is described in the specification o~
Canadian Patent Application n 414,768, filed on November 3, 1982.
The "subscriber" sets 11-20 may be of different types. In Figure 1, sets 12-1~ and 18 and 1~ are telephone "subscriber" sets for-use directly by usexs of the system. Mowever, sets 11, 17 and ~0 are interface uni$s of different kinds. Set 11 is an interface unit which enables callers on the net to interface with a radio telephone apParatus 22 . Set 17 ~rovides an interface with a magneto iele~hone exchange and set 20 provides an interface with another telephone net of the same kind as illustrated in Figure l. The detailed o~eration of interfaces 11, 17 and 20 will not be ~escribea in this s~ecification. It is sufficient to know that each inter-face a~ears.from the point of view of the telephone net-incorporating the highway 10 to mimic an ordinary teleDhone "subscriber" set,prcviding the sa~eresponses to enable a channel to be opened between the interface and another "subscriber" on the highway.
In oDeration, the various "subscriber" sets connected to the highway cable 10 can call each other and several communications between Dairs of sets can ~roceed simul-taneously on the sinyle highway cable 10 . A plurality .:, /d ~ ZO 70 3~
of communication channels are provided on the cable 19b~ frequency division multi?lexing (FD~) and the system is arran~ed so that the carrier frequencies in the FD~1 system are present on the highway cabl~ 10 only when the particular channel is being used for co~munication. The system includes no central exchange or control unit and all the carrier frequencies and control systems are provided in the various "subscriber" sets.
Referring now to Figure 2, a block circuit dia~ram is illustrated of a typical "subscriber" set incorporating microphone 30 and receiver 31 for use as a typical telephone. The entire circuitry illustrated in Figure 2 may be incorporated in a single housing with the microphone and receiver 31 to provide a single instrument as illustrated in Figure 3. The instrument incorporates a key pad 32 enabling a user of the instrument to control operation and insert the call codes of stations the user wishes to call up. Thus, the key ~ad 32 provides separate ke~ys for each of the decimal digits 0-9 and function control keys identified as follows:
STDY (standby), ON, CO~F (conference), P (priority call), and BATT TEST (battery test).
The hand set illustrated in Figure 3 also incorporates a visual alarm light 33 which can be actuated to flash in response to an incoming call instead of the usual audible " ~2~7~30 alarm tone. The alarm lam? 33 also doubles to provide a battery test indicator to provide an indication of battery state when khe BATT TEST key on the key pad 32 is depressed.
The hand set is powered by batteries provided within the casing of the unit.
A panel ,34 shown in Figure 1 can be removed to expose manually adjustable switches by which the hand set can be assigned the call code to which the hand set is to respond when on the telephone net.
The hand set can be connected to the cable highway 10 by means of a connector clip 35 as illustrated in Figure 1. The connector cliD 35 makes connection to the conductors of the hig,hway cable 10 without breaking the cable.
Referring now to the block schematic diagram of Figure 2 in'more detail, ,he various functions of the circuitry i~lustrated in Figure 2 are controlled by means of a controller 40 which receives data keyed into the set on the key pad ,32 ~ The controller 40 may typically be embodied as a microprocessor program~.ed to perform the various predetermined functions as required. To provide a functional programme for such a microprocessor controlled arrangement is well within the capacity of an experienced practitioner in this art without the need for lmdue experi-/~ 12C77~3C~
mentation. The circuit of Figure 2 can be connected to the highway cable 10 via a line inter.ace ~1 which transmits signals supplied to the line interface on lines 42 or 43 onto the highway cable 10 via c~nnecting link 21 and highway cable connector 35 . Similarly, signals from the highway cable are supplied from the line interface 41 on lines 4~ and Q5 . The line interface un.it 41 ensures that the "sl~scriber" set presents a high impedance across the conductors of the highway cable so as to minimise any effect on the ~ransrission ~roperties of the highway.
Carrier frequency signals from the highway are sup?lied from the line interface on line 44 to a tuned radio frequency amplifier 46 , the tuning of which is controlled by signals on a line 47 from the controller ~0 . The tuned radio frequency am~lifier 46 is controlled by the controller 40 to pass and am~lify only a band of frequencies centred on the particular carrier frequency to which the receiving ci.rcuits of the set are being tuned at any time.
The signals from the am~lifi~r 46 are then supplied to a mixer and intermediate frequency am~lifier g~` which receives a local oscillator signal on a line 49 . The local oscillator signal is derived by a synthesizer 50 under the control of the controller 40 . Thus, the controller can affect tuning of the receiver by controlling the ` /3 ~2(:~7~)3~
synthesizer 50 to synthesize a desired local oscillator frequency on line 49 which when ~ixed with the intended received carriex frequency produces a dirferenoe frequency at the intermediate frequency of the IF amplifier 48 .
The amplified IF carrier signal is supplied to a demodulator 51 wherein modulation on the carrier is detected. In the presently described system, the modulation on the various carrier frequency signals is fre~uency modulation and so the demodulator 51 may be any known type of FM detector, for example a quadrature detector.
The demodulator 51 provides a carrier detect signal on a line 52 to the controller 40 on detection of a carrier signal at the frequency to which the receiver is tuned. The demodulated information from the detected carrier is supplied on an outPut line 53 to the receiver 31 via a switch 54 which in normal operation of the apparatus is ~losed as shown in Figure 2. The output from the demodulator 51 is also supplied on a line :55 to the controller 40 whereby code signals modulated on the received carrier can be read anA decoded by the controller 40 as will be explained later.
Considering now transmission by the circuitry of Fi~ure 2, the carrier frequency of the transmission is derived also by the synthesizer ~0 subject to the control of the controller 40 . As ex~lained ~reviously, the complete LZ~:~7C~3~
radio tele~hone system is arranged to have predetermined pairs of carrier frequencies, one Dair defin.ing a duplex communication channel. Each pair of frequencies defining a channel com?rises a predetermined "go" frequency and a predetermined "return" freauency. All the various frequencies of the different channels available on the system are defined on setting u~ the system and may be stored in the controller 40 , typically in the memory of the micro-processor constituting the controller 40 . In operation, ~hen a caller station calls u. a called station, the caller station transmits carrier on the "go" frequency of a selected channel and the called station transmits back on the "return"
frequency. Thus, the controller 40 controls the synthesizer 50 to generate suitable signals on line 49 to the mixer and IF amplifier 48 and on a line 56 to a mo~ulator 57 , such that when a channel is established with another. station, the transmitted carrier is at one frequency of a predetermined pair and the receiver is tuned to the other frequency of the pair depending on whether the set was the caller station or the called station.
The transmitted carrier frequency fr~m the synthesizer is frequency modulated in the modulator 57 by signals from th~ microphone 30 and the modulated carrier is fed on a line 58 via a normally closed switch 5~ and a booster amplifier oO to the output line 42 to the line interface 6~J
/~ ~207(~3~
41 for transmission onto the highway 10 . The modulator 57 is also arranged to modulate the transmitted carrier with code signals provided from the controller 40 on a line 61 . As will be explained later, code si~nals are supplied by the controller 40 for modulation on the transmitted carrier frequency during t~e call-up ~rocedure and include the call code of the station being called up.
Also during the call-up procedure, as will be explained later, the controller 40 signals an alert generator 62 to generate an alert signal on the line A3 to impress the alert signal on the highway cable 10 . The alert signal is typically a DC voltage applied across the conductors of the highway 10 .
When the apparatus lS not in use for a call, the circuitry of the apparatus is in a quiescent state and is effectively switched off so that there is minimal or zero drain on the battery supPly of the set. A quiescent switch 6 3 iS illustrated symbolising the operation of the circuit in this respect. The quiescent switch Ç3 may operate to render the circuitry quiescent in res.onse to a signal fro~ the controller ~0 , typically in response to depressing the ST~Y key on the key pad 32 . ~owever the quiescent switch 63 is also arranged to operate auto~.atically following certain functions of the apparatus inclu~ing switching off the apparatus after a predetermined delay if ~6 ~C)703~) an intended call cannot be established.
If an alert signal is a~plied to the highway 10 by some other station, this signal is received b~ the line inter~ace 41 and a~plied to the line ~5 to an alert detector 64 . The alert signal, comprising a DC voltage is passed on by the alert detector 64 to the ~uiescent switch 63 causing the switch to put the circuitry of the a~aratus in a non-quiescent condition. At the same time, the alert detector 64 signals the controller 40 on a line 65 to show that there is an alert signal on the highway. As will be explainea in more detail later, the controller ao responds to the alert signal by checking to see if the particulax station is the one being called up, and if it is by identifying and sending the "return"
frequency carrier signal to establish the duplex c~mmnn;cation channel. ~n recognising a call intended for the ~articular station, the controller 40 also generates an alarm signal until a user answers the call. The alarm signal ~ay be the usual audible alarm tone supplied on line Sl to drive the microphone 30 , or mav alternatively be a visual alarm ~rom a light emitting diode 66 .
The controller 40 is arranged also to generate various other tones on a line 67 to drive the receiver 31 .
These tones ~ay include usual dial, ringing and engaged tones.
The dial and engaged tones are generated in the controller 40 /~ 1207~)3~
of the ap~aratus attempting to make the call. The ringing tone on the other hand is generated by the controller of the called station and modulated on the "return" carrier frequency sent by the called station.
Referring now to Figure 4, the functional operating procedure of the telephone system incorporating "subscriber"
sets as illustrated in Figure 2 is shown in the form of a flow diagram. A call is initiated at the caller station by the caller de?ressing key ON on the key pad 32 . This action powers up the callerls hand set and the controller 40 immediately beyins a search routine to identiEy a free channel for the call. In the search routine, the controller controls the synthesizer 50 to generate local oscillator frequencies on line 49, and simultaneously controls the tuned R~ amplifier by signals on the line ~7 so as to tune the receiver section of the set successively through the."go" frequencies of the various available channels. On tuning to a particular "go" frequency, the controller 40 responds to a carrier detect signal on line 52 by moving on to the next "go" frequency. If no carrier detect si~nal is observed at a particular "go" carrier frequency, the controller 4~ instructs the synthesizer 50 to generate a carrier on line 56 at this "go" frequency and this "go" frequency carrier is aDplied to the highway 10 .
However, if all available "go" frequency carriers are already /~ ~L2~)703~
on the hi~hway, the controller 40 continues to cycle through the channels looking for a free channel and during this period provides a distinct tone on the line 67 to the receiver 31 indicating that a free carrier is ~eing awaited. If no free carrier is identifie~ within thirty seconds, the controller 40 causes the set to switch off and the user must start again,-if desired, by pressing key ON. As soon as the controller 40 identi~ies a free "go" carrier and ap?lies that "go" carrier to the highway 10 , a dial tone is generated on line67tosignal the user of the apparatus. The user then keys in the code of the station which it is desired to call. The stations in the present example, each have ~ two digit code and on depressing the key for the seocnd digit of the Gode, the controller 40 generates a routing code on a line 61 which is modulated by the modulator 57 onto the "go" carrier frequency and sent on to the highway. At the same time, the controller 40 instructs the alert generator 62 to apply an alert signal to the highway 10 so as to alert quiescent stations connected to the highway.
Prior to sending the routing code and the alert signal, the apparatus may check the connecting link 21 to the highway 10 to ensure that the line is not shorted.
If a short is detected, the controller 40 generates an equi ment faulty tone on line 67 and after thirty seconds 37()3~
switches off.
The routing code generated by the controller 40 and transmitted on the "go" fre~uency carrier is transmitted repeatedly for the duration of the alert condition. The alert condition is termi~ated automatically by the controller if no reply is received from the called station within a predetermi~ed time, typically two seconds. ~owever, the alert is removed immediately on receipt of a reply from the called station in the form of detecting the "return"
frequency carrier on the same channel as the "go" freauency being transmitted.
The calling coae may comprise repeated frames made u~
of three eight bit b~tes followed by a control byte of typically at least two bits. The first eight bit byte of each frame is a synchronisation byte which may comprise four successive binary "l"'s followed by four successive-binary "O"'s. This synchronisation byte can be recognised as such at the various receiving stations to permit the subsequent data bytes to be read by the receiving stations in correct synchronisation. The next eight bit byte may comprise the calling code, i.e. the code of the station making the call~ The third eight bit byte may comprise the called code, i.e. the call code o~ the station being called up. The two bit control byte may include control data identifying the mode of the call as will becomé apparent ~, ~ZO'7~
later.
Considering now the apparatus of Figure 2 as the station on line in quiescent state. On receiving an alert signal from the highway 10 , the quiescent s~itch 3 automatically puts the a~paratus in a non-quiescent condition whereupon the controller 40 , in res~onse to the alert det~ct signal on line 65 instructs the synthesizer 50 to tune the receiver section sequentially through the various "return" frequencies o~ the available channels. On identifying a "return" frequency at which there is no carrier detected on line 52 , the controller 40 redirects the receiver to tune to the corresponding "go" frequency of that particular channel. If there is again no carrier signal ~resent, the controller 40 instructs the receiver to go on to the "return" freq~ency of the next channel. On detecting a "go" frequency carrier present on a channel on which there is no "return" frequency carrier present, the ~ontroller 40 monitors the output of the demodulator on line 55 and trys to read any code signals demodulated from the carrier. The controller 40 repeatedly trys to read code signals from the line 55 and looks for a match between the called code read from the line 55 and its own call code. If no match is identified after a ~redetermined time, say two hundred milisecon~s, the controller 40 instructs the receiver to moveon to the "return" frequency of the next channel. The controller 40 con~inues to scan ~J
o21 ~z~03C~
the channels until the alert signal is removed from the highway 10 .
On success~ully matching the called code read on the line 55 with its own call code, the controller 40 res~onds by instructing the synthesizer 50 to generate a carrier signal at the "return" carrier fre~uenc~ of the same channel as the received "go" frequency carrier. At the same time the controller 40 generates ringiny tone signals on line 51 which are modulated on the "return"
carrier and can be heard at the caller station. Also at the same time, the controller ~C of the called station sets up an alarm signal, either generating an alarm tone in the microphone 30 corresponding to the ringing tone trans-mitted on the "return" carrier, or by flashing the visual alarm represented by the LED 66 .
sack at the caller station, the receiving circuitry of the caller station's apparatus is already tuned to the "return" frequency of the channel being set u~ and generation of the "return" frequency by the distant called station is detected by the demodulator 51 and supplied as a carrier detect signal on line 52 to the controller 40 which reacts by removing the alert signal from the highway/ where-upon all other stations cease continuing to scan for their own call codes and revert to the quiescent condition.
In order to answer the alarm tone or light signal at r~
~, ~......
0~)3~
the called station, the user depresses the ON key of his set causing the controller ~0 of his set to terminate generating the ringing tone and alarm signal on line 61 .
Conversation can then proceed between the caller and called stations via the respective microphones 30 and receivers 31 . The conversation is frequency modulated and demodulated from the respective-"go" and "re-turn" frequency carrier signals.
On termination of the conversation, one or both parties presses the STBY key which causes his own set to revert to the quiescent condition removing its own generated carrier signal from the highway. Even if the other ~arty does not press the ST~Y key, his own set also reverts to quiescent condition, on detecting *hat the received carrier signal has been removea from the highway.
The present example of the ap?aratus provides a priority mode which allows certain designated priority callers to make calls even when all normal channels are busy and also when the station they are calling is busy with an existing call. In the priority mode, one vf the available channels of the system is set aside and is not used for normal inter-communication between the "subscriber" sets on the net. This channel set aside may be designated the priority channel and is used only for priority calls. In the articular arrangement described in this example, only certain "subscriber"
~.
.~ q 7~3~
sets are able to make priority calls. These are the "subscriber" sets with call co~es starting with "0". Thus there are up to ten codes available for priori-ty calling "subscriber" sets. The s~ste~ operation whereb~ the priority channel is set aside, may also be determined by the call codes assigned to the "subscriber" sets on the net. Thus, if all sets on the net have call codes between "00" and "39", then these sets will operate so that the priority channel is set aside for priority calls only ~rom the sets with call codes "00" to "09". On the other hand iL the sets on the net have call codes between 1~07~ and "99", then these sets are arranged to treat all channels available in the system equally so that there is no priorit~ mode available. The o~erational distinction between the ~arious call codes is performed by the controller 40 of the various sets in response to the call code assigned to the set.
In t~e normal operation i~ a priority caller wishes to call a paxticular station, the usual initial o~erations are carried out as with a normal call. As shown in Figure 5, the priorty procedure is used onlv if the ~riori-t~ caller cannot obtain a dial tone, indicating that all non~priority channels are busy, or on obtaining a dial tone and calling the desired 'Isubscriber''~ obtains a n~ber unobtainable tone indicating that the called station has not answered the call and is probably busy with an existing call. In either of ~J
37~3 13 these cases~ the priorit~ caller makes the priorit~ call bv pressing key ~ on his key pad. In response, the controller of his set tunes the receiver to the "go" freauency of the priority channel. If a carrier is detected at the "go" frequency, the controllPr 40 generates a priority busy tone. ~owever if the ?riority channel i5 not busy, the controller 40 controls the synthesizer 50 to generate the carrier signal on line 56 at the "go" frequency of the priority channel and produces a dial tone. ~he priority caller then dials the call code of the station to be called, whereupon the controller 40 sets up the alert signal on the highway 10 and sends data on line 61 for modulation on the "go" frequency carrier identifying the call code of the station being called and also containing control bits identifying that the call is a priority call If the "subscriber" being called is not busy with another call, his apparatus responds to the alert signal in the - usual way,determ;nes that the incoming call is on the priority channel and re~lies by sending the "return"
frequency carrier modulated with a ringing tone as usual.
Xowe~er, if the called "subscriber" is busy with another call, the controller 40 of his set does not immediately react to the alert signal on the highway. As mentioned previously, alert signals for normal non-priority calls have a maximum duration of typically two seconds. For a priority call, the ~lert signal is maintained for longer than this maximum duration, say three seconds. I~hen the set of the called "subscriber" recognises that the alert signal has been present on the highway for more than the normal time, indicating that the call is a priority call, the controller 40 ofthe called "subscriber" momentarily retunes its receiver circuits to the "go" ~requency oP the priority channel and tries to read the code modulated on the carrier at this freauency. It will be a~preciated that all busy stations will react to a priority call signal in this way and the various stations will continue to check the repeated code signals on the priori~y channel "go"
fre~uency carrier for a predetermined time, say two hun~red miliseconds, before reverting to their existing call if they cannot match the called code read Prom the carrier with their own call code. If they do match codes, the called "subscriber' apparatus responds by initially tuning back their receiViny circuit to the existing establish~d call but signalling to the person using the set by sending pips on line 67 to the receiver that they have a priority call. Typicallv there may be five pips at one second intervals follo~ling which the controller 40 automaticall~y retunes their receiving circuits to the "go" frequency of the priority ~h~nnel, In the meantime, the synthesizer 50 continues to generate the Prequencies keeping the transmitted carrier and local ~r~}~
oscillator signal on the existing operational channel. At the end of the five second delay, the controller 40 also instructs the synthesizer to generate on line 56 the "return" :frequency carrier of the priority channel.
~eanwhile, the priority caller is arranged to maintain the priority alert signal on the highway for the longer than usual duration, say three seconds whereupon the alert is automatically removed. However, the priority caller continues to wait for a period of time for any "return"
signal carrier to be received in case the called station was already busy in which case there is the five seconds delay before the called station generates the "return"
carrier. m us, the priority caller may wait a total of ten seconds following initiating the alert signal before providing an unobtainable tone. If during that ten seconds, the i'return" fre~uency carrier is received, the priority channel lin~ is completed and the intended conversation can proceed.
The apparatus of the present example may also provide a conference mode in which a number of stations may be able to talk to each other simultaneously in the manner of a conference. The conference mode employs audio fre~uency signalling on the highway. The functional flow diagram used in conference mode operation is shown in Figure 6.
Operation is as usual except that on hearing the dial tone, -~ . "
~ 7~3~1 the callin~ station presses the CONF key on his ~ey pad whereupon the controller 40 should generate the conference dial tone. The caller then keys the codes of the stations he wishes to call for the conference, -~ressing the COMF key once between each station call code. After the last call code keyed in, the caller presses the CONF button twice whereupon the controller 40 generates data on the line ~1 for modulation on a "go" carrier frequency of a ~ree channel, identi~ying all the call codes of the stations to be called.
The data modulated on the "go" carrier also includes control bits identifying that the call is a conference call. The call codes are transmitted on the "go" frequency carrier for a predetermined time set by the controller 40 and are then automatically terminated whereupon the controller 40 inhibits further generation of the "go" carrier frequency and sends control signals on line 70 to switch the switches 54 and 59 into the conference mode bypassing the modulation and demodulation circuits so that direct audio frequency signals from the microp'none 30 are transmitted to the hi~hway and received from the highway by the receiver 31.
Meanwhile, each called station reacts to the alert signal applied to the highway by the calling station in t'ne usual way scanning for a "go" frequency carrier with code modulation. On detecting its own call code, the called station also identifies from the received data that the r~
7~3~
call is a conference call and generates a special conference alarm tone to alert the user of the ap~aratus. No "return"
carrier signal is generated. When the user of the ap~aratus answers the alarm by pressing the O~ key, the a~paratus immediately reverts to the conference rode with the controller 40 operating the switches 5A and 59. At the same time, the controller 40 generates a short tone on line 61 which is impressed on the highway 10 to alert the caller station that a ~urther called "subscriber"
has come onto line.
On termination of the conference, each "subscriber"
depresses his STBY key in order to return his aparatus to - the quiescent state.
It will be appreciated that the above described arrangement permits a field telephone system to-be set up using a single wire pair highway but permitting multiple simultaneous duplex conversations bet~een di~ferent "subscriber" stations. The highway cable should be term;n~ted correctly at its ends with its characteristic impedance to avoid reflections. '~owever, the connections from the "subscribers" to the cable have substantially no effect on the propogation properties of the cable since the "subscriber" sets each present a ve~y hi~h impedance to the cable. Interface units may be connected to the cable enabling interfacing ol the particular cable net ~ ~2~7(~3~
witn other communication systems. For exam~le referring again to Figure 1, block 11 ~rovides an interface between the highway cable 10 and a remotely controllable radio transmitter 22. The interface 11 is designe~. to respond to signals on the highway 10 in the same manner as an ordinary "subscriber" set. However, on¢e a channel is estab~ished between a "subscriber" set and the interface ~1, control signals can also be transmitted on the hi~hway cable 10 for controlling operation of the radio 22. In this arrangement, the key pads of the various "subscriber" sets are continuously on line even during a conversation. ~hus, if any of the numerical keys is depressed during a conver-sation, the apparatus automatically transmits the relevant code for the depressed key suppressing the voice transmission.
Thus~ the key pad of each "subscriber" set can be used for controlling radio transmission by the radio 22 e.g. with one key providing a TRANSMIT instruction to the xadio and a second key providing a RECEIVE instruction.
The present invention is concerned primarily with a communication method providing duplex communication between a plurality of pairs of stations on a single wire pair hiyhway by frequency division multiplexing. Frequency division multiplexing to pxovide several channels on a single pair of wires is known for telephony. However, in telephone systems employed hitherto, the various carrier frequencies providing the frequency division multiplexed channels on the single wire pair are provided continuously irrespective of whether a particular channel is busy. This arrangement is quite satisfactory for large scale telephone installations where power consumption is of only minor concern. However, to provide frequency division multi-plexing using known techniques for field telephone applica-tions, operating from battery power supplies, would make excessive demands on the battery supplies enabling only relativelv s~ort life operation. Also, such an arrangement would reduce the flexibility of the field telephone system since the various stations on the field telephone "net"
would have to operate through exchange apparatus which would provide channel routing and maintain the various frequency carrier signals.
According to a first aspect of the present invention, there is provided a communication method for providing duplex communication between a plurality of pairs of stations on a single wire pair highway by frequency division multiplexing, each station having a station-identi-fying call code, the highway being assigned a plurality of pairs of frequencies for communication thereover, each pair of frequencies including a go frequency and a re-turn frequency, said method comprising:
maintaining all presently non-communicating 7~30 stations in a quiescent mode in which each monitors the highway for alert signals;
activating a quiescent station desiring to transmit information as a caller station to a called station by having such caller station monitors frequency pairs on the highway to select a pair of presently unused frequencies and, upon selecting such a pair o~ frequencies, to apply an alert signal and the go frequency of the selected pair of frequencies to the highway, the go frequency being modulated by the call code of the called station;
activating all quiescent stations in response to receipt thereby of the alert signal for monitoring of call codes on the go frequency of the selected pair of frequencies;
initiating transmission on the highway, by that station which was activated by the alert signal and which corresponds to the call code, of the return fre-quency of the selected pair of frequencies, while return-ing all noncalled stations which were activated by the alert signal to the quiescent condition; and activating the caller station in response to receipt by it of the return frequency of the selected pair of frequencies to transmit on the highway the go frequency of the selected pair of frequencies modulated by the in-formation to be transmitted.
By eliminating the carrier signals which are notin use for communication, the power consumption of the arrangement can be greatly reduced and also the flexibility of operation especially in field telephone application can be greatly increased.
Further, the individual stations on the highway can themselves generate the various carrier frequency signals and first scan the existing carriers on the high-way to select a free channel.
~,,J
~207()~0 Preferably, each station activated by the alert signal monitors the highway for a go frequency modulated by a call code and upon receipt of a call code, compares the received call code with its own call code to determine whether it is the called station.
Thus, the stations not in use can be in the quiescent state with minimal if not zero power consumption.
However, they can be arranged to respond to the alert signal on the highway by seeking for the go frequency car-rier of the caller station and reading the call code.Only if the code is their own, do they remain non-quiescent and open the duplex channel by generating and transmitting to the highway the corresponding return frequency carrier.
The caller station preferably responds to receiving the retu~n ~requency from the called station also by can-celling the alert signal from the highway, causing all non-called stations which were activated by the alert signal to revert to the quiescent condition.
In accordance with a preferred characteristic of the method according to the invention, the quiescent sta-tions, upon being activated in response to receipt of the alert signal, monitor the pairs ol frequencies by scanning the return frequencies thereof to identify a return fre-quency absent from the highway, on locating an absent re-turn frequency tuning to the corresponding go frequencyof the respective pair of frequencies and, if the go fre-quency is present on the highway, checking for call code data on that go frequency, but otherwise continuing the scanning of the return frequencies. By this technique, the overall scanning time is reduced since go ~requencies are checked only if there is no corresponding return fre-quency. It will be understood that if there is a return frequency carrier already on the highway then this indicates that the particular channel is already in use and cannot be ., 1207(~3(~
the channel on which the new call is being placed.
According to a further preferred characteristic of the method of the invention, for use in telephony, the caller station modulates the go frequency with the call codes of selected called stations desired to join the call as a conference call and also a signal identifying the call as a conference call, the caller station terminating said go frequency generation and modulation after a predetermined time interval sufficient ~o permit the called stations to identify their respective call codes and then providing audio frequency communication with the highway, each called station responding to receipt of its call code and identifying that the call is a con-ference call by providing audio frequency communication with the highwav.
In accordance with another preferred charac-teristic of the invention, a selected pair o said pairs of frequencies is assigned as a priority channel for use only by a priority caller station in a priority mode to call a sta-tion already busy with an existing call or when all non-priority channels are busy, and the busy station called on the priority channel then responds by breaking contact with an existing call and moving to the priority channel to take the priority call. Preferably, in priority mode, a priority caller station checks the go frequency of the priority channel and, if such frequency is absent on the highway, generates and transmits the priority go frequency onto the highway, modulating such frequency with at least data defininy the call code of the desired called station, and simultaneously generates and impresses on the highway a priority call identifying signal, and each busy station xesponds to the priority call identifying signal by tuning to the go frequency of the priority channel, reading the ~LZC~ 30 call code modulated thereon, and comparing the call code with the respective call code assigned to the station, and then in response to identifying its own call code moving onto the priority channel but otherwise continuing with the existing call.
Preferably, in normal mode, the caller station maintains the alert signal in the absence of a received cor-responding return frequency for a predetermined maxlmum time, and, in priority mode, the priority call identifying signal comprises the alert signal and is maintained for a period of time in excess of the predetermined maximum time, and each busy station responds to the priority call iden-tifying signal only after the predetermined maximum time has elapsed.
The alert signal, and also the priority call identifying signal, may comprise a DC voltage impressed on the highway by the caller station. It will be appre-ciated that any non-busy station responds to the priority call identifying signal in the same way as to the alert signal, i.e. by reverting to a non-quiescent state and scanning the go carrier frequencies on the hi~hway for its own call code. All stations are advantageously arranged to scan all channels, including the priority channel in response to an alert signal, so that a priority channel call to a station which is not busy, will still be connected.
According to a secord aspect of the present invention, there is provided a communication set capable of providing , with other such sets at respective stations, duplex communication simultaneously between a plurality of pairs of stations on a single wire pair highway by fre-quency division multiplexing, wherein information i5 transmitt~d on the wire pair highway by modulation of pairs of predeiermined carrier frequencies, each pair of ~LZ~7~3~
said frequencies comprising a go frequency and a return frequency and providing a single channel duplex com-municatiGn between any selected pair of stations on the highway, each station being assigned a predetermined call code; the communication set comprising means for storing the call code assigned to the respective station, transmit-ter means energisable and controllable to generate and transmit to the highway carrier signals at a selected one of the predetermined carrier freqllencies, modulator means for modulating the generated carrier signal with information or data to be transmitted on the highway, tunable receiver means for selectively receiving carrier signals from the highway at any one of the predetermined carrier frequencies, demodulator means for demodulating information or data from the received carrier signal, operator input means enabling the operator of the set to initiate a call and key in the call code of a desired station, control means responsive to a call initiate signal from the input means to scan the tuning of the receiver means through said predetermined carrier frequencies until a vacant channel is identified, the re-spective pair of carrier frequencies for the channel being absent on the highway, and then to tune to the return fre-quency of the vacant channel, the control means including means to energise and control the transmitter means to transmit on to the highway a carrier signal at the go frequency of the vacant channel and simultaneously supply to the modulator means at least data from the input means defining the call code of the desired station so that the transmitted carrier signal is modulated with these data, the control means further including means responsive to reception by the receiver means of a carrier on the highway at the return frequenc~ of the vacant channel to inhibit further supply of the call code data to the modulator means, and an alert signal generator responsive to the control means on identifying a vacant channel to impress an alert signal on the highway until reception by the receiver means 703~
of said received frequency carrier.
In accordance with a preferred embodiment of the invention, the communication set comprises quiescent switching means arranged to switch the set to a quiescent state when not in use, but responsive to the presence of an alert signal on the highway to switch the set automa-tically to a non-quiescent state and means within the control means responsive on said switching to the non-quiescent state to scan the tuning of the receiver means to detect a go frequency carrier signal on the highway which is modulated with call code data and then to read these data and compare the received call code with that in said means for storing, the control means further including means responsive to the received call code matching that in said means for storing to hold the set in the non-quiescent state and to energise and control the transmitter means to tr~nsmit on to the highway a carrier signal at the return frequency of the channel including the detected go frequency carrier signal.
A non limitative example of the present invention will now be d~scribed with reference to the accompanying drawings in which: /
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~ ~21~703(~
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a block schematic dlagram illustrating a complete net incorporating a Dlurality of "subscriber"
sets connected to a sin~le wire pair highway;
Figure 2 is a block schematic diagram of a telephone "subscriber" set shown connected to a single wire pair highway;
Figure 3 illustrates an example of the telephone "subscriber" set provided as a single hand held unit an~
Figures 4, 5 and 6 are operational flow diagrams illustrating the sesuences of steps in operating the complete telephone syste~ in various different modes.
DETAILED DESCRIPTION OF A ~ ;KRED EX~lPLE
Figure 1 ill~ ~s a ccmplete tPl~rh~ net ~ r~t;ng in accor-dance with an P~m~nlP of the present invention. me net is foY~ed by a single hig~way cable 10 to~i~h are eonnected a n~r of "subscr ~ r"
sets 11-20. m2 highway cable 10 co~prises a sin~le wire pair typically a twisted pair or a co-axial eable with single core and sereen eonduetors. Eaeh "subseriber" set is conneeted to the highway eable ~y a link 21 whieh conneets the set to the two wires of the highway 10. The llnks 21 may be eonneeted to the highway 10 by means of eonnector elips whieh ~ake eonnection to the eonductors of the highway without breaking the highway at the conneetion point. A suitable ~orm of eonneetor whieh in one embodiment ~ 3L21~3(~
can connect the "subscribër" set linXs 21 to a c~-axial highway cable 10 is described in the specification o~
Canadian Patent Application n 414,768, filed on November 3, 1982.
The "subscriber" sets 11-20 may be of different types. In Figure 1, sets 12-1~ and 18 and 1~ are telephone "subscriber" sets for-use directly by usexs of the system. Mowever, sets 11, 17 and ~0 are interface uni$s of different kinds. Set 11 is an interface unit which enables callers on the net to interface with a radio telephone apParatus 22 . Set 17 ~rovides an interface with a magneto iele~hone exchange and set 20 provides an interface with another telephone net of the same kind as illustrated in Figure l. The detailed o~eration of interfaces 11, 17 and 20 will not be ~escribea in this s~ecification. It is sufficient to know that each inter-face a~ears.from the point of view of the telephone net-incorporating the highway 10 to mimic an ordinary teleDhone "subscriber" set,prcviding the sa~eresponses to enable a channel to be opened between the interface and another "subscriber" on the highway.
In oDeration, the various "subscriber" sets connected to the highway cable 10 can call each other and several communications between Dairs of sets can ~roceed simul-taneously on the sinyle highway cable 10 . A plurality .:, /d ~ ZO 70 3~
of communication channels are provided on the cable 19b~ frequency division multi?lexing (FD~) and the system is arran~ed so that the carrier frequencies in the FD~1 system are present on the highway cabl~ 10 only when the particular channel is being used for co~munication. The system includes no central exchange or control unit and all the carrier frequencies and control systems are provided in the various "subscriber" sets.
Referring now to Figure 2, a block circuit dia~ram is illustrated of a typical "subscriber" set incorporating microphone 30 and receiver 31 for use as a typical telephone. The entire circuitry illustrated in Figure 2 may be incorporated in a single housing with the microphone and receiver 31 to provide a single instrument as illustrated in Figure 3. The instrument incorporates a key pad 32 enabling a user of the instrument to control operation and insert the call codes of stations the user wishes to call up. Thus, the key ~ad 32 provides separate ke~ys for each of the decimal digits 0-9 and function control keys identified as follows:
STDY (standby), ON, CO~F (conference), P (priority call), and BATT TEST (battery test).
The hand set illustrated in Figure 3 also incorporates a visual alarm light 33 which can be actuated to flash in response to an incoming call instead of the usual audible " ~2~7~30 alarm tone. The alarm lam? 33 also doubles to provide a battery test indicator to provide an indication of battery state when khe BATT TEST key on the key pad 32 is depressed.
The hand set is powered by batteries provided within the casing of the unit.
A panel ,34 shown in Figure 1 can be removed to expose manually adjustable switches by which the hand set can be assigned the call code to which the hand set is to respond when on the telephone net.
The hand set can be connected to the cable highway 10 by means of a connector clip 35 as illustrated in Figure 1. The connector cliD 35 makes connection to the conductors of the hig,hway cable 10 without breaking the cable.
Referring now to the block schematic diagram of Figure 2 in'more detail, ,he various functions of the circuitry i~lustrated in Figure 2 are controlled by means of a controller 40 which receives data keyed into the set on the key pad ,32 ~ The controller 40 may typically be embodied as a microprocessor program~.ed to perform the various predetermined functions as required. To provide a functional programme for such a microprocessor controlled arrangement is well within the capacity of an experienced practitioner in this art without the need for lmdue experi-/~ 12C77~3C~
mentation. The circuit of Figure 2 can be connected to the highway cable 10 via a line inter.ace ~1 which transmits signals supplied to the line interface on lines 42 or 43 onto the highway cable 10 via c~nnecting link 21 and highway cable connector 35 . Similarly, signals from the highway cable are supplied from the line interface 41 on lines 4~ and Q5 . The line interface un.it 41 ensures that the "sl~scriber" set presents a high impedance across the conductors of the highway cable so as to minimise any effect on the ~ransrission ~roperties of the highway.
Carrier frequency signals from the highway are sup?lied from the line interface on line 44 to a tuned radio frequency amplifier 46 , the tuning of which is controlled by signals on a line 47 from the controller ~0 . The tuned radio frequency am~lifier 46 is controlled by the controller 40 to pass and am~lify only a band of frequencies centred on the particular carrier frequency to which the receiving ci.rcuits of the set are being tuned at any time.
The signals from the am~lifi~r 46 are then supplied to a mixer and intermediate frequency am~lifier g~` which receives a local oscillator signal on a line 49 . The local oscillator signal is derived by a synthesizer 50 under the control of the controller 40 . Thus, the controller can affect tuning of the receiver by controlling the ` /3 ~2(:~7~)3~
synthesizer 50 to synthesize a desired local oscillator frequency on line 49 which when ~ixed with the intended received carriex frequency produces a dirferenoe frequency at the intermediate frequency of the IF amplifier 48 .
The amplified IF carrier signal is supplied to a demodulator 51 wherein modulation on the carrier is detected. In the presently described system, the modulation on the various carrier frequency signals is fre~uency modulation and so the demodulator 51 may be any known type of FM detector, for example a quadrature detector.
The demodulator 51 provides a carrier detect signal on a line 52 to the controller 40 on detection of a carrier signal at the frequency to which the receiver is tuned. The demodulated information from the detected carrier is supplied on an outPut line 53 to the receiver 31 via a switch 54 which in normal operation of the apparatus is ~losed as shown in Figure 2. The output from the demodulator 51 is also supplied on a line :55 to the controller 40 whereby code signals modulated on the received carrier can be read anA decoded by the controller 40 as will be explained later.
Considering now transmission by the circuitry of Fi~ure 2, the carrier frequency of the transmission is derived also by the synthesizer ~0 subject to the control of the controller 40 . As ex~lained ~reviously, the complete LZ~:~7C~3~
radio tele~hone system is arranged to have predetermined pairs of carrier frequencies, one Dair defin.ing a duplex communication channel. Each pair of frequencies defining a channel com?rises a predetermined "go" frequency and a predetermined "return" freauency. All the various frequencies of the different channels available on the system are defined on setting u~ the system and may be stored in the controller 40 , typically in the memory of the micro-processor constituting the controller 40 . In operation, ~hen a caller station calls u. a called station, the caller station transmits carrier on the "go" frequency of a selected channel and the called station transmits back on the "return"
frequency. Thus, the controller 40 controls the synthesizer 50 to generate suitable signals on line 49 to the mixer and IF amplifier 48 and on a line 56 to a mo~ulator 57 , such that when a channel is established with another. station, the transmitted carrier is at one frequency of a predetermined pair and the receiver is tuned to the other frequency of the pair depending on whether the set was the caller station or the called station.
The transmitted carrier frequency fr~m the synthesizer is frequency modulated in the modulator 57 by signals from th~ microphone 30 and the modulated carrier is fed on a line 58 via a normally closed switch 5~ and a booster amplifier oO to the output line 42 to the line interface 6~J
/~ ~207(~3~
41 for transmission onto the highway 10 . The modulator 57 is also arranged to modulate the transmitted carrier with code signals provided from the controller 40 on a line 61 . As will be explained later, code si~nals are supplied by the controller 40 for modulation on the transmitted carrier frequency during t~e call-up ~rocedure and include the call code of the station being called up.
Also during the call-up procedure, as will be explained later, the controller 40 signals an alert generator 62 to generate an alert signal on the line A3 to impress the alert signal on the highway cable 10 . The alert signal is typically a DC voltage applied across the conductors of the highway 10 .
When the apparatus lS not in use for a call, the circuitry of the apparatus is in a quiescent state and is effectively switched off so that there is minimal or zero drain on the battery supPly of the set. A quiescent switch 6 3 iS illustrated symbolising the operation of the circuit in this respect. The quiescent switch Ç3 may operate to render the circuitry quiescent in res.onse to a signal fro~ the controller ~0 , typically in response to depressing the ST~Y key on the key pad 32 . ~owever the quiescent switch 63 is also arranged to operate auto~.atically following certain functions of the apparatus inclu~ing switching off the apparatus after a predetermined delay if ~6 ~C)703~) an intended call cannot be established.
If an alert signal is a~plied to the highway 10 by some other station, this signal is received b~ the line inter~ace 41 and a~plied to the line ~5 to an alert detector 64 . The alert signal, comprising a DC voltage is passed on by the alert detector 64 to the ~uiescent switch 63 causing the switch to put the circuitry of the a~aratus in a non-quiescent condition. At the same time, the alert detector 64 signals the controller 40 on a line 65 to show that there is an alert signal on the highway. As will be explainea in more detail later, the controller ao responds to the alert signal by checking to see if the particulax station is the one being called up, and if it is by identifying and sending the "return"
frequency carrier signal to establish the duplex c~mmnn;cation channel. ~n recognising a call intended for the ~articular station, the controller 40 also generates an alarm signal until a user answers the call. The alarm signal ~ay be the usual audible alarm tone supplied on line Sl to drive the microphone 30 , or mav alternatively be a visual alarm ~rom a light emitting diode 66 .
The controller 40 is arranged also to generate various other tones on a line 67 to drive the receiver 31 .
These tones ~ay include usual dial, ringing and engaged tones.
The dial and engaged tones are generated in the controller 40 /~ 1207~)3~
of the ap~aratus attempting to make the call. The ringing tone on the other hand is generated by the controller of the called station and modulated on the "return" carrier frequency sent by the called station.
Referring now to Figure 4, the functional operating procedure of the telephone system incorporating "subscriber"
sets as illustrated in Figure 2 is shown in the form of a flow diagram. A call is initiated at the caller station by the caller de?ressing key ON on the key pad 32 . This action powers up the callerls hand set and the controller 40 immediately beyins a search routine to identiEy a free channel for the call. In the search routine, the controller controls the synthesizer 50 to generate local oscillator frequencies on line 49, and simultaneously controls the tuned R~ amplifier by signals on the line ~7 so as to tune the receiver section of the set successively through the."go" frequencies of the various available channels. On tuning to a particular "go" frequency, the controller 40 responds to a carrier detect signal on line 52 by moving on to the next "go" frequency. If no carrier detect si~nal is observed at a particular "go" carrier frequency, the controller 4~ instructs the synthesizer 50 to generate a carrier on line 56 at this "go" frequency and this "go" frequency carrier is aDplied to the highway 10 .
However, if all available "go" frequency carriers are already /~ ~L2~)703~
on the hi~hway, the controller 40 continues to cycle through the channels looking for a free channel and during this period provides a distinct tone on the line 67 to the receiver 31 indicating that a free carrier is ~eing awaited. If no free carrier is identifie~ within thirty seconds, the controller 40 causes the set to switch off and the user must start again,-if desired, by pressing key ON. As soon as the controller 40 identi~ies a free "go" carrier and ap?lies that "go" carrier to the highway 10 , a dial tone is generated on line67tosignal the user of the apparatus. The user then keys in the code of the station which it is desired to call. The stations in the present example, each have ~ two digit code and on depressing the key for the seocnd digit of the Gode, the controller 40 generates a routing code on a line 61 which is modulated by the modulator 57 onto the "go" carrier frequency and sent on to the highway. At the same time, the controller 40 instructs the alert generator 62 to apply an alert signal to the highway 10 so as to alert quiescent stations connected to the highway.
Prior to sending the routing code and the alert signal, the apparatus may check the connecting link 21 to the highway 10 to ensure that the line is not shorted.
If a short is detected, the controller 40 generates an equi ment faulty tone on line 67 and after thirty seconds 37()3~
switches off.
The routing code generated by the controller 40 and transmitted on the "go" fre~uency carrier is transmitted repeatedly for the duration of the alert condition. The alert condition is termi~ated automatically by the controller if no reply is received from the called station within a predetermi~ed time, typically two seconds. ~owever, the alert is removed immediately on receipt of a reply from the called station in the form of detecting the "return"
frequency carrier on the same channel as the "go" freauency being transmitted.
The calling coae may comprise repeated frames made u~
of three eight bit b~tes followed by a control byte of typically at least two bits. The first eight bit byte of each frame is a synchronisation byte which may comprise four successive binary "l"'s followed by four successive-binary "O"'s. This synchronisation byte can be recognised as such at the various receiving stations to permit the subsequent data bytes to be read by the receiving stations in correct synchronisation. The next eight bit byte may comprise the calling code, i.e. the code of the station making the call~ The third eight bit byte may comprise the called code, i.e. the call code o~ the station being called up. The two bit control byte may include control data identifying the mode of the call as will becomé apparent ~, ~ZO'7~
later.
Considering now the apparatus of Figure 2 as the station on line in quiescent state. On receiving an alert signal from the highway 10 , the quiescent s~itch 3 automatically puts the a~paratus in a non-quiescent condition whereupon the controller 40 , in res~onse to the alert det~ct signal on line 65 instructs the synthesizer 50 to tune the receiver section sequentially through the various "return" frequencies o~ the available channels. On identifying a "return" frequency at which there is no carrier detected on line 52 , the controller 40 redirects the receiver to tune to the corresponding "go" frequency of that particular channel. If there is again no carrier signal ~resent, the controller 40 instructs the receiver to go on to the "return" freq~ency of the next channel. On detecting a "go" frequency carrier present on a channel on which there is no "return" frequency carrier present, the ~ontroller 40 monitors the output of the demodulator on line 55 and trys to read any code signals demodulated from the carrier. The controller 40 repeatedly trys to read code signals from the line 55 and looks for a match between the called code read from the line 55 and its own call code. If no match is identified after a ~redetermined time, say two hundred milisecon~s, the controller 40 instructs the receiver to moveon to the "return" frequency of the next channel. The controller 40 con~inues to scan ~J
o21 ~z~03C~
the channels until the alert signal is removed from the highway 10 .
On success~ully matching the called code read on the line 55 with its own call code, the controller 40 res~onds by instructing the synthesizer 50 to generate a carrier signal at the "return" carrier fre~uenc~ of the same channel as the received "go" frequency carrier. At the same time the controller 40 generates ringiny tone signals on line 51 which are modulated on the "return"
carrier and can be heard at the caller station. Also at the same time, the controller ~C of the called station sets up an alarm signal, either generating an alarm tone in the microphone 30 corresponding to the ringing tone trans-mitted on the "return" carrier, or by flashing the visual alarm represented by the LED 66 .
sack at the caller station, the receiving circuitry of the caller station's apparatus is already tuned to the "return" frequency of the channel being set u~ and generation of the "return" frequency by the distant called station is detected by the demodulator 51 and supplied as a carrier detect signal on line 52 to the controller 40 which reacts by removing the alert signal from the highway/ where-upon all other stations cease continuing to scan for their own call codes and revert to the quiescent condition.
In order to answer the alarm tone or light signal at r~
~, ~......
0~)3~
the called station, the user depresses the ON key of his set causing the controller ~0 of his set to terminate generating the ringing tone and alarm signal on line 61 .
Conversation can then proceed between the caller and called stations via the respective microphones 30 and receivers 31 . The conversation is frequency modulated and demodulated from the respective-"go" and "re-turn" frequency carrier signals.
On termination of the conversation, one or both parties presses the STBY key which causes his own set to revert to the quiescent condition removing its own generated carrier signal from the highway. Even if the other ~arty does not press the ST~Y key, his own set also reverts to quiescent condition, on detecting *hat the received carrier signal has been removea from the highway.
The present example of the ap?aratus provides a priority mode which allows certain designated priority callers to make calls even when all normal channels are busy and also when the station they are calling is busy with an existing call. In the priority mode, one vf the available channels of the system is set aside and is not used for normal inter-communication between the "subscriber" sets on the net. This channel set aside may be designated the priority channel and is used only for priority calls. In the articular arrangement described in this example, only certain "subscriber"
~.
.~ q 7~3~
sets are able to make priority calls. These are the "subscriber" sets with call co~es starting with "0". Thus there are up to ten codes available for priori-ty calling "subscriber" sets. The s~ste~ operation whereb~ the priority channel is set aside, may also be determined by the call codes assigned to the "subscriber" sets on the net. Thus, if all sets on the net have call codes between "00" and "39", then these sets will operate so that the priority channel is set aside for priority calls only ~rom the sets with call codes "00" to "09". On the other hand iL the sets on the net have call codes between 1~07~ and "99", then these sets are arranged to treat all channels available in the system equally so that there is no priorit~ mode available. The o~erational distinction between the ~arious call codes is performed by the controller 40 of the various sets in response to the call code assigned to the set.
In t~e normal operation i~ a priority caller wishes to call a paxticular station, the usual initial o~erations are carried out as with a normal call. As shown in Figure 5, the priorty procedure is used onlv if the ~riori-t~ caller cannot obtain a dial tone, indicating that all non~priority channels are busy, or on obtaining a dial tone and calling the desired 'Isubscriber''~ obtains a n~ber unobtainable tone indicating that the called station has not answered the call and is probably busy with an existing call. In either of ~J
37~3 13 these cases~ the priorit~ caller makes the priorit~ call bv pressing key ~ on his key pad. In response, the controller of his set tunes the receiver to the "go" freauency of the priority channel. If a carrier is detected at the "go" frequency, the controllPr 40 generates a priority busy tone. ~owever if the ?riority channel i5 not busy, the controller 40 controls the synthesizer 50 to generate the carrier signal on line 56 at the "go" frequency of the priority channel and produces a dial tone. ~he priority caller then dials the call code of the station to be called, whereupon the controller 40 sets up the alert signal on the highway 10 and sends data on line 61 for modulation on the "go" frequency carrier identifying the call code of the station being called and also containing control bits identifying that the call is a priority call If the "subscriber" being called is not busy with another call, his apparatus responds to the alert signal in the - usual way,determ;nes that the incoming call is on the priority channel and re~lies by sending the "return"
frequency carrier modulated with a ringing tone as usual.
Xowe~er, if the called "subscriber" is busy with another call, the controller 40 of his set does not immediately react to the alert signal on the highway. As mentioned previously, alert signals for normal non-priority calls have a maximum duration of typically two seconds. For a priority call, the ~lert signal is maintained for longer than this maximum duration, say three seconds. I~hen the set of the called "subscriber" recognises that the alert signal has been present on the highway for more than the normal time, indicating that the call is a priority call, the controller 40 ofthe called "subscriber" momentarily retunes its receiver circuits to the "go" ~requency oP the priority channel and tries to read the code modulated on the carrier at this freauency. It will be a~preciated that all busy stations will react to a priority call signal in this way and the various stations will continue to check the repeated code signals on the priori~y channel "go"
fre~uency carrier for a predetermined time, say two hun~red miliseconds, before reverting to their existing call if they cannot match the called code read Prom the carrier with their own call code. If they do match codes, the called "subscriber' apparatus responds by initially tuning back their receiViny circuit to the existing establish~d call but signalling to the person using the set by sending pips on line 67 to the receiver that they have a priority call. Typicallv there may be five pips at one second intervals follo~ling which the controller 40 automaticall~y retunes their receiving circuits to the "go" frequency of the priority ~h~nnel, In the meantime, the synthesizer 50 continues to generate the Prequencies keeping the transmitted carrier and local ~r~}~
oscillator signal on the existing operational channel. At the end of the five second delay, the controller 40 also instructs the synthesizer to generate on line 56 the "return" :frequency carrier of the priority channel.
~eanwhile, the priority caller is arranged to maintain the priority alert signal on the highway for the longer than usual duration, say three seconds whereupon the alert is automatically removed. However, the priority caller continues to wait for a period of time for any "return"
signal carrier to be received in case the called station was already busy in which case there is the five seconds delay before the called station generates the "return"
carrier. m us, the priority caller may wait a total of ten seconds following initiating the alert signal before providing an unobtainable tone. If during that ten seconds, the i'return" fre~uency carrier is received, the priority channel lin~ is completed and the intended conversation can proceed.
The apparatus of the present example may also provide a conference mode in which a number of stations may be able to talk to each other simultaneously in the manner of a conference. The conference mode employs audio fre~uency signalling on the highway. The functional flow diagram used in conference mode operation is shown in Figure 6.
Operation is as usual except that on hearing the dial tone, -~ . "
~ 7~3~1 the callin~ station presses the CONF key on his ~ey pad whereupon the controller 40 should generate the conference dial tone. The caller then keys the codes of the stations he wishes to call for the conference, -~ressing the COMF key once between each station call code. After the last call code keyed in, the caller presses the CONF button twice whereupon the controller 40 generates data on the line ~1 for modulation on a "go" carrier frequency of a ~ree channel, identi~ying all the call codes of the stations to be called.
The data modulated on the "go" carrier also includes control bits identifying that the call is a conference call. The call codes are transmitted on the "go" frequency carrier for a predetermined time set by the controller 40 and are then automatically terminated whereupon the controller 40 inhibits further generation of the "go" carrier frequency and sends control signals on line 70 to switch the switches 54 and 59 into the conference mode bypassing the modulation and demodulation circuits so that direct audio frequency signals from the microp'none 30 are transmitted to the hi~hway and received from the highway by the receiver 31.
Meanwhile, each called station reacts to the alert signal applied to the highway by the calling station in t'ne usual way scanning for a "go" frequency carrier with code modulation. On detecting its own call code, the called station also identifies from the received data that the r~
7~3~
call is a conference call and generates a special conference alarm tone to alert the user of the ap~aratus. No "return"
carrier signal is generated. When the user of the ap~aratus answers the alarm by pressing the O~ key, the a~paratus immediately reverts to the conference rode with the controller 40 operating the switches 5A and 59. At the same time, the controller 40 generates a short tone on line 61 which is impressed on the highway 10 to alert the caller station that a ~urther called "subscriber"
has come onto line.
On termination of the conference, each "subscriber"
depresses his STBY key in order to return his aparatus to - the quiescent state.
It will be appreciated that the above described arrangement permits a field telephone system to-be set up using a single wire pair highway but permitting multiple simultaneous duplex conversations bet~een di~ferent "subscriber" stations. The highway cable should be term;n~ted correctly at its ends with its characteristic impedance to avoid reflections. '~owever, the connections from the "subscribers" to the cable have substantially no effect on the propogation properties of the cable since the "subscriber" sets each present a ve~y hi~h impedance to the cable. Interface units may be connected to the cable enabling interfacing ol the particular cable net ~ ~2~7(~3~
witn other communication systems. For exam~le referring again to Figure 1, block 11 ~rovides an interface between the highway cable 10 and a remotely controllable radio transmitter 22. The interface 11 is designe~. to respond to signals on the highway 10 in the same manner as an ordinary "subscriber" set. However, on¢e a channel is estab~ished between a "subscriber" set and the interface ~1, control signals can also be transmitted on the hi~hway cable 10 for controlling operation of the radio 22. In this arrangement, the key pads of the various "subscriber" sets are continuously on line even during a conversation. ~hus, if any of the numerical keys is depressed during a conver-sation, the apparatus automatically transmits the relevant code for the depressed key suppressing the voice transmission.
Thus~ the key pad of each "subscriber" set can be used for controlling radio transmission by the radio 22 e.g. with one key providing a TRANSMIT instruction to the xadio and a second key providing a RECEIVE instruction.
Claims (10)
1. A communication method for providing duplex communication between a plurality of pairs of stations on a single wire pair highway by frequency division mul-tiplexing, each station having a station-identifying call code, the highway being assigned a plurality of pairs of frequencies for communication thereover, each pair of fre-quencies including a go frequency and a return frequency, said method comprising:
maintaining all presently non-communicating stations in a quiescent mode in which each monitors the highway for alert signals;
activating a quiescent station desiring to transmit information as a caller station to a called sta-tion by having such caller station monitors frequency pairs on the highway to select a pair of presently unused frequen-cies and, upon selecting such a pair of frequencies,to apply an alert signal and the go frequency of the selected pair of frequencies to the highway, the go frequency being modu-lated by the call code of the called station;
activating all quiescent stations in response to receipt thereby of the alert signal for monitoring of call codes on the go frequency of the selected pair of frequencies;
initiating transmission on the highway, by that station which was activated by the alert signal and which corresponds to the call code, of the return frequency of the selected pair of frequencies, while returning all non-called stations which were activated by the alert signal to the quiescent condition; and activating the caller station in response to receipt by it of the return frequency of the selected pair of frequencies to transmit on the highway the go frequency of the selected pair of frequencies modulated by the in-formation to be transmitted.
maintaining all presently non-communicating stations in a quiescent mode in which each monitors the highway for alert signals;
activating a quiescent station desiring to transmit information as a caller station to a called sta-tion by having such caller station monitors frequency pairs on the highway to select a pair of presently unused frequen-cies and, upon selecting such a pair of frequencies,to apply an alert signal and the go frequency of the selected pair of frequencies to the highway, the go frequency being modu-lated by the call code of the called station;
activating all quiescent stations in response to receipt thereby of the alert signal for monitoring of call codes on the go frequency of the selected pair of frequencies;
initiating transmission on the highway, by that station which was activated by the alert signal and which corresponds to the call code, of the return frequency of the selected pair of frequencies, while returning all non-called stations which were activated by the alert signal to the quiescent condition; and activating the caller station in response to receipt by it of the return frequency of the selected pair of frequencies to transmit on the highway the go frequency of the selected pair of frequencies modulated by the in-formation to be transmitted.
2. A communication method as claimed in claim 1, wherein each station activated by the alert signal moni-tors the highway for a go frequency modulated by a call code and upon receipt of a call code compares the received call code with its own call code to determine whether it is the called station.
3. A communication method as claimed in claim 1, wherein the caller station responds to receiving the re-turn frequency from the called station by cancelling the alert signal from the highway, causing all non-called sta-tions which were activated by the alert signal to revert to the quiescent condition.
4. A communication method as claimed in claim 3, wherein the quiescent stations, upon being activated in response to receipt of the alert signal, monitor the pairs of frequencies by scanning the return frequencies thereof to identify a return frequency absent from the highway, on locating an absent return frequency tuning to the corre-sponding go frequency of the respective pair of frequencies and, if the go frequency is present on the highway, check-ing for call code data on that go frequency, but otherwise continuing the scanning of the return frequencies.
5. A communication method as claimed in claim 1, for use in telephony, wherein the caller station modulates the go frequency with the call codes of selected called stations desired to join the call as a conference call and also a signal identifying the call as a conference call, the caller station terminating said go frequency generation and modulation after a predetermined time interval suffi-cient to permit the called stations to identify their re-spective call codes and then providing audio frequency communication with the highway, each called station respond-ing to receipt of its call code and identifying that the call is a conference call by providing audio frequency communication with the highway.
6. A communication method as claimed in claim 1, further comprising assigning a selected pair of said pairs of frequencies as a priority channel for use only by a priority caller station in a priority mode to call a station already busy with an existing call or when all non-priority channels are busy, and the busy station called on the priority channel responds by breaking contact with the existing call and moving to the priority channel to take the priority call.
7. A communication method as claimed in claim 6, wherein, in priority mode, a priority caller station checks the go frequency of the priority channel and, if such frequency is absent on the highway, generates and transmits the priority go frequency onto the highway, modulating such frequency with at least data defining the call code of the desired called station, and simultaneously generates and impresses on the highway a priority call identifying signal, and wherein each busy station responds to the priority call identifying signal by tuning to the go frequency of the priority channel, reading the call code modulated thereon, and comparing the call code with the respective call code assigned to the station, and then in response to identifying its own call code moving onto the priority channel but otherwise continuing with the existing call.
8. A communication method as claimed in claim 7, wherein, in normal mode, the caller station maintains the alert signal in the absence of a received corresponding return frequency for a predetermined maximum time, and wherein, in priority mode, the priority call identifying signal comprises the alert signal and is maintained for a period of time in excess of the predetermined maximum time, and each busy station responds to the priority call identify-ing signal only after the predetermined maximum time has elapsed.
9. A communication set capable of providing, with other such sets at respective stations, duplex commu-nication simultaneously between a plurality of pairs of stations on a single wire pair highway by frequency division multiplexing, wherein information is transmitted on the wire pair highway by modulation of pairs of predetermined carrier frequencies, each pair of said frequencies comprising a go frequency and a return frequency and providing a single channel duplex communication between any selected pair of stations on the highway, each station being assigned a predetermined call code; the communication set comprising means for storing the call code assigned to the respective station, transmitter means energisable and controllable to generate and transmit to the highway carrier signals at a selected one of the predetermined carrier frequencies, modulator means for modulating the generated carrier signal with information or data to be transmitted on the highway, tunable receiver means for selectively receiving carrier signals from the highway at any one of the predetermined car-rier frequencies, demodulator means for demodulating infor-mation or data from the received carrier signal, operator input means enabling the operator of the set to initiate a call and key in the call code of a desired station, con-trol means responsive to a call initiate signal from the input means to scan the tuning of the receiver means through said predetermined carrier frequencies until a vacant chan-nel is identified, the respective pair of carrier frequencies for the channel being absent on the highway, and then to tune to the return frequency of the vacant channel, the control means including means to energise and control the transmitter means to transmit on to the highway a carrier signal at the go frequency of the vacant channel and simul-taneously supply to the modulator means at least data from the input means defining the call code of the desired sta-tion so that the transmitted carrier signal is modulated with these data, the control means further including means responsive to reception by the receiver means of a carrier on the highway at the return frequency of the vacant chan-nel to inhibit further supply of the call code data to the modulator means, and an alert signal generator responsive to the control means on identifying a vacant channel to impress an alert signal on the highway until reception by the receiver means of said received frequency carrier.
10. A communication set as claimed in claim 9, further comprising quiescent switching means arranged to switch the set to a quiescent state when not in use but responsive to the presence of an alert signal on the high-way to switch the set automatically to a non-quiescent state, and means within the control means responsive on said switching to the non-quiescent state to scan the tuning of the receiver means to detect a go frequency carrier signal on the highway which is modulated with call code data, and then to read these data and compare the received call code with that in said means for storing, the control means further including means responsive to the received call code matching that in said means for storing to hold the set in the non-quiescent state and to energise and control the transmitter means to transmit on to the high-way a carrier signal at the return frequency of the chan-nel including the detected go frequency carrier signal.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8133303 | 1981-11-04 | ||
| GB08133303A GB2112606B (en) | 1981-11-04 | 1981-11-04 | Communication set and method |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1207030A true CA1207030A (en) | 1986-07-02 |
Family
ID=10525638
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000414155A Expired CA1207030A (en) | 1981-11-04 | 1982-10-26 | Communication set and method |
Country Status (7)
| Country | Link |
|---|---|
| US (1) | US4513413A (en) |
| EP (1) | EP0078714B1 (en) |
| CA (1) | CA1207030A (en) |
| DE (1) | DE3268457D1 (en) |
| GB (1) | GB2112606B (en) |
| IN (1) | IN157852B (en) |
| ZA (1) | ZA827851B (en) |
Families Citing this family (22)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4646296A (en) * | 1984-07-09 | 1987-02-24 | Bard Technologies | Distributed telephone system |
| US4757496A (en) * | 1984-07-09 | 1988-07-12 | Bard Technologies | Distributed telephone system |
| US4682325A (en) * | 1984-12-27 | 1987-07-21 | Ncr Corporation | System for selectively coupling a plurality of stations into a single communications path |
| US4740967A (en) * | 1985-01-31 | 1988-04-26 | Georgalis Nicholas C | Dispersed switching telecommunication system |
| US4707832A (en) * | 1985-04-10 | 1987-11-17 | Harris Corporation | Switched point-to-point local area network control mechanism |
| WO1987001541A1 (en) * | 1985-08-28 | 1987-03-12 | Jose Manuel Soto | Distributed switching telecommunications system |
| US4813036A (en) * | 1985-11-27 | 1989-03-14 | National Exchange, Inc. | Fully interconnected spot beam satellite communication system |
| US4996709A (en) * | 1988-05-12 | 1991-02-26 | Tandy Corporation | Intercom telephone |
| ES2059913T3 (en) * | 1989-09-12 | 1994-11-16 | Siemens Ag | PROCEDURE FOR TELECOMMUNICATION BETWEEN SEVERAL SUBSCRIBER STATIONS AND EMPLOYABLE SUBSCRIBER STATION IN THIS CASE. |
| US5200951A (en) * | 1989-09-12 | 1993-04-06 | Siemens-Albis Ag | Apparatus and method for transmitting messages between a plurality of subscriber stations |
| US5212577A (en) * | 1990-01-19 | 1993-05-18 | Canon Kabushiki Kaisha | Optical communication equipment and optical communication method |
| EP0438155B1 (en) * | 1990-01-19 | 1997-05-02 | Canon Kabushiki Kaisha | Optical communication equipment |
| US6721419B1 (en) | 1999-06-09 | 2004-04-13 | Premisenet Incorporated | Method and system for selecting a frequency for communication within a premises network |
| US7039395B2 (en) | 2000-12-11 | 2006-05-02 | Cingular Wireless Ii, Llc | Method and apparatus for wireless auto-conferencing |
| FI114001B (en) * | 2001-11-09 | 2004-07-15 | Nokia Corp | Procedure for data communication and data transmission systems |
| IL154234A (en) * | 2003-01-30 | 2010-12-30 | Mosaid Technologies Inc | Method and system for providing dc power on local telephone lines |
| JP3746773B2 (en) * | 2003-06-03 | 2006-02-15 | 独立行政法人電子航法研究所 | Mobile station, mobile station side communication control method, base station, base station side communication control method, and communication system |
| JP4107432B2 (en) * | 2004-03-03 | 2008-06-25 | 独立行政法人電子航法研究所 | Mobile station, mobile station side communication control method, base station, base station communication control method, and communication system |
| WO2009075485A1 (en) * | 2007-12-13 | 2009-06-18 | Samsung Electronics Co., Ltd. | Apparatus and method for random access based on call priority in a mobile communication system |
| CN101742013B (en) * | 2009-12-22 | 2012-12-05 | 中兴通讯股份有限公司 | System and method for simulating user line access multiplexing |
| CA2847683A1 (en) * | 2014-03-28 | 2015-09-28 | Kapsch Trafficcom Ag | An electronic commerce transaction system using electronic toll collection transponders |
| KR102324960B1 (en) | 2015-06-25 | 2021-11-12 | 삼성전자 주식회사 | Communication device and electronic device including the same |
Family Cites Families (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| NL6617461A (en) * | 1966-12-13 | 1968-06-14 | ||
| FR1552870A (en) * | 1967-08-11 | 1969-01-10 | ||
| US3573379A (en) * | 1969-03-03 | 1971-04-06 | Bendix Corp | Communications system with frequency and time division techniques |
| US3809815A (en) * | 1972-05-04 | 1974-05-07 | Litton Systems Inc | Communication system utilizing frequency division multiplexing to link a plurality of stations each containing a switchable synthesizer |
| US4020289A (en) * | 1972-05-15 | 1977-04-26 | Teleplex, Inc. | Random access, multiple station communication system |
| US3864521A (en) * | 1973-10-25 | 1975-02-04 | Rockwell International Corp | Frequency division multiplex telephone system |
| FR2290103A1 (en) * | 1974-10-31 | 1976-05-28 | Thomson Csf | TELEPHONE ARTERY WITH MULTIPLE ACCESS POINTS AND NETWORK INCLUDING SUCH ARTERIES |
| US4262171A (en) * | 1979-01-08 | 1981-04-14 | Catalyst Research Corporation | Telephone system in which communication between stations is controlled by computers at each individual station |
| US4339816A (en) * | 1980-05-29 | 1982-07-13 | International Telephone And Telegraph Corporation | Conferencing apparatus and methods for a frequency division multiplex communications system |
-
1981
- 1981-10-27 ZA ZA827851A patent/ZA827851B/en unknown
- 1981-11-04 GB GB08133303A patent/GB2112606B/en not_active Expired
-
1982
- 1982-10-26 CA CA000414155A patent/CA1207030A/en not_active Expired
- 1982-11-02 US US06/438,450 patent/US4513413A/en not_active Expired - Lifetime
- 1982-11-03 DE DE8282305846T patent/DE3268457D1/en not_active Expired
- 1982-11-03 EP EP82305846A patent/EP0078714B1/en not_active Expired
- 1982-11-04 IN IN1297/CAL/82A patent/IN157852B/en unknown
Also Published As
| Publication number | Publication date |
|---|---|
| DE3268457D1 (en) | 1986-02-20 |
| IN157852B (en) | 1986-07-05 |
| GB2112606B (en) | 1985-01-23 |
| ZA827851B (en) | 1984-06-27 |
| GB2112606A (en) | 1983-07-20 |
| EP0078714B1 (en) | 1986-01-08 |
| EP0078714A1 (en) | 1983-05-11 |
| US4513413A (en) | 1985-04-23 |
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Legal Events
| Date | Code | Title | Description |
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| MKEX | Expiry |