Classifications

• • 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

Definitions

• the present invention relates to communications systems.
• the invention relates to a telephone system and the invention and its background will be described herein in relation to a telephone system.
• a pabx private branch exchange
• a pabx is, however, very expensive and cannot usually be justified for use in e.g. a domestic dwelling or in a small office.
• Many domestic dwellings, " and small offices have several telephones and it is likely that the numbers of telephones per dwelling or small office will increase.
• a telephone system in which a plurality of telephones are connected to a cable arrangement for transmitting telephone signals by one signalling device per telephone, the devices ' cooperating one with another to act as a telephone exchange distributed about the cable arrangement to automatically establish a communication link between telephones in response to selection by one of the telephones of another of the telephones-
• a signalling device for use in a system as specified in said one aspect, the device having a port for connection to a cable arrangement for transmitting telephone signals, a port for connection to a telephone , and means which is cooperable with other such means to act as a telephone exchange distributed about the cable arrangement to automatically establish a communication link between telephones connected to the means in response to the selection by one of the telephones of another of the telephones.
• a telephone system is to be connected to an external network e.g. a public telephone network ' such as the network owned in the UK by British Telecom PLC, then the system must not interfere with the operation of that network to the detriment of other users.
• an external network e.g. a public telephone network ' such as the network owned in the UK by British Telecom PLC.
• a communication system for which there is a defined maximum noise limit representing the maximum amount of signal noise which may be injected into the system, a communication subsystem in which an information signal of magnitude less than the noise limit is transmitted and received.
• system of the said one aspect constitutes the subsystem of the another aspect.
• the noise limit is defined at a maximum frequency of the information signal, and the frequency of the information signal is greater than the said maximum frequency.
• the frequency of the information signal is greater than 10 MHz e.g. 20 MHz.
• a communications system comprising
• each one of the devices being able to receive (or transmit) on one channel associated with itself, and transmit (or receive) on any one of a plurality of channels corresponding to the reception (or transmission) channels of the devices,
• the devices being responsive to the selection, at the said source associated with one of the devices, of another of the devices to automatically form a communication link between the said one and another devices in which each of the devices forming the link receives (or transmits) on the said one channel associated with itself, and transmits (or receives) on the said one channel associated with the device to which it transmits (or from which it receives).
• the device being arranged to receive (or transmit) on one channel associated with itself and transmit (or receive) on any selectable one of a plurality of channels corresponding to the reception (or transmission) channels of other such devices.
• the device being responsive to the selection at its associated information source of another such device to automatically form a communication link between itself and the said another such device in which the device receives (or transmits) on the said one channel associated with itself and transmits (or receives) on the said one reception (or transmission) channel associated with the another device or a further device intervening in the link.
• Such a system and signalling device may be used in the systems of the said one and another aspects.
• Figure 1 is a block schematic diagram of a telephone system according to an aspect . of the present invention.
• Figures 2a, 2b, and 2c are diagrams illustrating the operation of aspects of the system
• FIG. 3 is a block schematic diagram of a telephone control device according to another aspect of the present invention.
• Figure 4 is a block schematic diagram showing a transmitter
• Figure 5 is a block schematic diagram of a line/handset interface
• Figure 6 is a state diagram illustrating the operating states of the telephone system as implemented by the control logic in the telephone control devices.
• a telephone system comprising nine extension phones Til to 9 which are arranged in e.g. an office or a home.
• the number of phones may be 2 or more, and may be much ' greater than nine, but a maximum of nine has the advantage that single digit dialling of all the extensions is then possible.
• the phones TI 1 to 9 are shown in Figure 1 coupled by respective signalling or control devices CD 1 to 9 to a single pair of wires (or a coaxial cable) 20.
• signalling or control devices CD 1 to 9 to a single pair of wires (or a coaxial cable) 20.
• standard telephone company sockets SI to S9 e.g. British Telecom sockets together with BT wiring are used, and the control devices are in socket replicating boxes.
• control devices could be in any suitable boxes connected to the BT wiring; e.g. a box on which the telephone sits or even in the telephones themselves.
• the wiring may have any suitable configuration, e.g. star, branched, looped or any combination provided the wiring is continuous.
• the socket SI is a master socket to which the external telephone company line 21 is connected.
• that socket has two wires coming in from the external line, and four wires out:
• control devices allow:
• the system uses control signals and speech signals for use internally, having a magnitude less than the noise limit at the frequency of the signals.
• the frequency of the signals is above the maximum frequency for which a limit is associated.
• the frequency of the signals is chosen to be a frequency at which ambient noise levels are low; the illustrative system operates at approximately 20MHz. It should be appreciated that if the system is not connected to the telephone company line, or is used in a situation where noise limits are more relaxed or do not apply, signals of greater magnitude may be used.
• the control and speech signals are signals modulated onto a carrier of e.g. approximately 20 MHz.
• the form of modulation used in the illustrative system is frequency modulation (FM), because that allows reliable communication using the low signal levels ( ⁇ -70 dBm).
• FM frequency modulation
• the nine reception frequencies are in channels separated by 40 KHz each.
• the signals could all be amplitude modulated. It is possible to use amplitude modulation on several different frequencies to avoid the need to synchronise the local oscillators.
• the control devices CDl to CD9 each include a transmitter 22 and a receiver 23.
• each of the nine receivers can receive signals only of reception frequency uniquely associated with that receiver, and all the nine transmitters can transmit on all of the nine reception frequencies, although it should be appreciated that any one of the transmitters can transmit on only one reception frequency at any one time.
• each transmitter could be arranged to transmit on only one transmission frequency and the receivers could be arranged to receive all nine frequencies but that is not done in the illustrative system.
• Each of the control devices has a power supply 24 which in the illustrative system is a battery.
• each control device is powered-up intermittently e.g. for 10ms every 2s under the control of an intermittent actuation circuit 25.
• each device may be powered-up automaticaly when its associated phone is used, e.g. the hand piece is removed from its "hook".
• each device is powered-down automatically when use of its associated phone ceases although, power-down may be delayed depending on the circumstances.
• the control signals are tones in the frequency range lKHz to 3 KHz which are frequency modulated onto the 20 MHz carrier. Each tone is transmitted in a short burst of preset length e.g. 12 cycles.
• the tones are transmitted in sets called messages, many of which include tones representing the identity of the sender (i.e. the channel unique to the sender) and the identity of the intended recipient (i.e. the channel unique to the recipien ), and a tone representing a command.
• Incoming message of the form From, To, Command There are two sorts of message: Incoming message of the form From, To, Command; and outgoing messages of the form Frequency; From, To, Command.
• Con Con, Con (meaning connect).
• Commands include Discon (which means disconnect) and Conn (which means connect).
• Figure 6 is a state diagram, diagrammatically illustrating all states of one control device (called
• extension A eg extension 1
• extension X eg extension 2
• the logic unit 27 causes a "mute" to be applied via an interface 29 to the phone TI.
• a tone generator 28 under the control of logic unit 27 causes
• the 3 control tones transmitted on frequency X represent:
• identity of the sender eg extension 1
• identity of the receiver eg extension 2
• command connect ie the message has the form X: A, X, Conn.
• the 3 tones are transmitted in a sequence each tone lasting 12 cycles until either extension 1 hangs up or extension 2 responds.
• the control logic causes the mute to be applied to the phone TI2 and actuates a bleeper 31 eg a piezo electric resonator to indicate the call.
• the control logic 27 adjusts the carrier frequency of the transmitter of extension '2' so that it transmits on reception frequency '1 ' .
• A removes the ringing signal and 2-way communication is established.
• the users of the two extensions can then speak to each other via a modulated RF carrier, speech from the phones TI 1 and 2 being supplied by the interfaces to the transmitters via lines 32 and (demodulated) speech from the receivers being supplied to the phones via lines 33 and the interfaces 29.
• control logic When either user hangs up (goes on hook) the control logic causes the tone generator to transmit a sequence of 3 tones sender/recipient disconnect, eg X:A, X, Disconn if A hangs up, each of 12 cycles duration. That causes the control logic at the recipient (X) to revert t:o a power off condition. The control logic at the sender causes its control device to power down once the message has been transmitted.
• extension X If extension X is engaged when A calls, A produces an internally engaged signal, turns off its transmitter and receiver and when A goes on hook (OH) reverts to a power off condition. If X fails to answer after X has transmitted Con, Con, Con to A, when A hangs up (OH), A transmits X:A, X, Dis ⁇ onn and A and X power down.
• each extension can receive on only its own reception frequency, and that, at any one time, each transmitter can transmit on only one frequency.
• extension 1 transmits to extension 2 on reception frequency '2'
• extension 2 transmits to extension 3 on reception frequency '3'
• extension 3 transmits to extension 1 on reception frequency '1'.
• speech from extension 1 it is demodulated in extension 2 and remodulated in extension 2 onto reception frequency 3, even though that involves a reduction of the signal to noise ratio.
• Extension X receives the set of tones and applies the mute, and forwards on frequency Y: A, Y, Conn.
• X forwards to Y: A, Y, Discon,
• Extension X 2 hangs up (OH) Extension X transmits on frequency Y: X, Y, Discon; X powers down;
• Extension Y responds by retransmitting to A; X, Y, Discon. Extension A responds by changing its transmission frequency to Y. Extension A can then speak to extension Y.
• a ring detect circuit indicates the presence of a ring signal (RI) to the control logic and powers up (R2) the device and actuates the bleeper e.g. a piezo-electric resonator. All the control devices can thus indicate the presence of the call.
• Any of the other phones, eg X can then be connected to the call as if it were an internal call.
• the code number of the other extension which is to join the call is dialled.
• the dialling decoder 26 and the control logic 27 at the original extension respond to that code by causing the interface to put a dummy load on the BT line to hold it and the procedure described above for an internal call is then automatically followed.
• the control logic responds to the zero dialling to cause the interface circuit to reconnect the outside line to it and also transmits to the other phone X the message on frequency X, A, X, Discon which re-enables dialling and mutes the receiver at X. X then dials '0' to also directly access the outside line.
• the call is held at the extension eg
• the other extension X is called as if a normal internal connection was being made to inform the other extension X that there is an external call for it.
• the other extension X then dials '0'.
• the control logic and tone generator respond to the zero to automatically transmitting a set of tones on frequency A: X, A, Discon and to cause the interface circuit at X to connect X to the external line.
• X, A, Discon causes the extension A to assume the dialling enabled state.
• 'A' then powers down when A hangs up, leaving X connected directly to the line.
• a code Q_ is dialled and the control logic 27 responds by causing the interface circuit to connect the phone TI to the external line for a period of sixty seconds. In this sixty seconds all dialling is routed to outside lines. When the call is finished, the handset is replaced.
• the receiver 23 comprises a Plessey SI.6653 low power RF/IF/AF single chip mixer, IF amplifier and detector. Although the Plessey chip also incorporates an oscillator it is not used in this embodiment of the invention.
• an oscillator 35 (external to the Plessey chip) which produces a signal of frequency 455KHz higher or lower than the nominal reception frequency of the particular extension.
• the transmitter The transmitter
• the transmitter 22 comprises a phase-locked-loop (PLL) Frequency Synthesizer and an adjustable reference frequency divider 36.
• PLL phase-locked-loop
• the PLL comprises, as is known, a phase comparator 40 a loop filter 41, a voltage controlled oscillator 42 and a frequency divider 43.
• the frequency divider 43 is adjustable in integer steps.
• Adjustable frequency dividers 43 are well known.
• the control logic unit controls the frequency divider so that the output frequency of the VCO equals the desired carrier frequency.
• Tones from the tone generator 28 and audio from the interface circuit are applied to the VCO to frequency modulate its output.
• the Interface circuit (Fig 5)
• the line 20 or 21 is connected to a splitter network 50 which separates the RF signals from the conventional signals on the telephone company line. Downstream of the splitter 50 is a fullwave rectifer and surge arrester circuit 52 as known in the art.
• the interface circuit When making an external call, the interface circuit is powered from the telephone company line via the network 50 and the circuit 52. When making an internal call, the interface circuit is powered from a battery 56. To switch from battery to telephone company line powering, a switching circuit 57 is provided.
• the circuit is an electronic switching circuit, controlled via a control input 57, by the control logic 27 which in turn is responsive to the intermittent actuator 25.
• the phone TI is coupled between switch 57 and the OV rail via a series load resistor 51 of nominally lo ⁇ . resistance.
• the total resistance in series with the phone TI is limited by telephone company regulations to, eg 10Q .
• the resistance of resistor 51 may be slightly less than 10-2.
• the handset In order to make an internal call, the handset is lifted off its hook.
• the current flowing through the 180 _» ⁇ resistor is sensed by a power on sensor 55 which produces a power on signal indicating the handset is off the hook.
• the control logic responds to that signal by maintaining power to the control device. 'Ringing' of an internal call is audibly indicated by a buzzer 31 controlled by the control logic 27.
• the tones which are transmitted as described above are received by the interface circuit at the input RXAF. 33.
• the tones are passed via an amplifying circuit to the tone decoder 30 (Fig. 3). Speech from the handset varies the current in the resistor 51 and an amplifier 58 sends the resulting signals TX audio to the VCO of the transmitter 22 via a path 32 and a controllable signal combiner 65 as will be described hereinbelow.
• Demodulated speech received from the receiver 23 is input at RXAF (line 33).
• the signals are passed by an amplifier 53, to the handset.
• a mute 59 controlled by the control logic is applied to prevent a user hearing the tones which are transmitted and receiver noise when no carrier is present.
• the interface circuit comprises a further output TT audio from the amplifier 53 to a controllable signal combiner 65 which adds the speech from the telephone instrument TI to the speech received from another control device via the input RXAF (33) for transmission to a further control device via an output 66.
• the ringing signal is detected by the ring detector 61 upstream of the full wave rectifier.
• the detector actuates a buzzer 31.
• the ringing detector 61 has two outputs; RI and R2 (which differ only in amplitude) for indicating (RI) the ring to the logic circuit and for causing (R2) the intermittent actuation circuit to power-up the control device.
• the switching curcuit 57 connects the phone TI to the line 21 to be powered from the line.
• the outside code 0 is dialled and the dialling decoder and control logic respond to it to actuate the switch. 57 to connect the phone TI to the line 21.
• the dialling decoder and the control logic respond to a hold code e.g. the number of another extension to activate a load hold circuit 62 to place a line holding load across the line 21.
• a hold code e.g. the number of another extension to activate a load hold circuit 62 to place a line holding load across the line 21.
• a sound generator 64 is provided to inject sound signals into the phone TI via amplifier 53.
• the generator 64 is controlled by the control logic. The user will hear all dialling tones at low volume.
• the telephone instrument TI itself usually includes a hybrid circuit for that purpose.
• received speech is fed to the telephone instrument via the "top” (as shown in Fig.5) terminal 70, whilst transmitted speech current originating at the telephone is fed out to the load resistor 51 at the "bottom” terminal 71.
• the control logic unit may be a microprocessor, or an uncommitted logic array .
• dialling decoder (which is known in the art) needs to be chosen to suit the form of dialling used.
• the various aspects of the invention have been illustrated herein with respect to a telephone system at least some of the aspects can be applied to other systems.
• the technique of using very low level signals can be applied to the transmission of any information over any sort of signal line, such as alarm information of a burglar alarm system transmitted over the electrical mains cabling in a building.
• speech information could be replaced by other information provided it occupies the same or less bandwidth as the speech information.
• the telephones could then be replaced by other telephonic devices which act as information sources, such as facsimile machines,modems,etc although it should be appreciated that the term telephonic device as used herein does not cover equipment such as telephone exchanges.
• the system could be used as a network linking computers or computer terminals. If the cabling of the network is entirely independent of the telephone company cabling, then the signals used need not comply with telephone company regulations. For instance, the system of the invention could be used to link computers via mains wiring using high level signals.
• control or signalling devices CD1-9 as described herein are each adjusted at manufacture to their own respective reception frequencies and would be sold as nine differently marked devices.

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• Engineering & Computer Science (AREA)
• Signal Processing (AREA)
• Telephonic Communication Services (AREA)

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• 1987
  • 1987-01-09 GB GB878700458A patent/GB8700458D0/en active Pending
• 1988
  • 1988-01-08 WO PCT/GB1988/000012 patent/WO1988005240A1/en not_active Ceased
  • 1988-01-08 EP EP19880900575 patent/EP0340231A1/de not_active Withdrawn

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