NZ201827A

NZ201827A - Scanning radiophone system

Info

Publication number: NZ201827A
Application number: NZ201827A
Authority: NZ
Inventors: K Kerschbaumer; H Resch; F Machl; H Ullrich
Original assignee: Portaphone Ag
Priority date: 1981-09-08
Filing date: 1982-09-07
Publication date: 1985-01-31
Also published as: DK159355B; ES8306429A1; ES515536A0; IE53438B1; NO823048L; FI75716B; PT75522B; AU555241B2; DK159355C; FI823070L; PT75522A; FI823070A0; NO155368B; JPS5854743A; AT391234B; DE3262435D1; EP0074940A1; CH647631A5; FR2512621A1; DK396082A

Description

201827 Patents Form No. 5.

Patents Act 1953 COMPLETE SPECIFICATION "TELECOMMUNICATION SYSTEM WITH RADIO LINK" WE, PORTAPHONE AG, a company organised and existing under the laws of Switzerland, of Bahnhofstrasse 16, CH-8&08 Pfaffikon SZ, Switzerland, hereby declare the invention, for which we pray that a patent may be granted to us,,and the method by which it is to be performed, to be particularly described in and by the following statement 201827 The present invention relates to a telephone or other telecommunication system wherein a multiplicity of subscribers are served by one or more central offices through a wired network terminating at fixed relay stations which communicate by radio links with associated subscriber stations.

In such a system the subscriber stations will be movable relatively to their relay stations within a range whose radius is determined by the power of the transmitters at each end of the respective links. In order to insure the necessary privacy, each subscriber station conventionally operates on a radio frequency individually assigned thereto. In practice, an operating range with a radius of about $0 meters will allow telephone calls to be received and transmitted anywhere in a subscriber's house. With only a limited number of radio frequencies available, the same frequency will have to be allocated to stations spaced sufficiently far apart to prevent possible cross-talk or listening-in; in rural areas, for example, 40 communication channels may suffice to. cover a region of about 3 km in radius. In multidwelling urban housing, however, such a channel allocation would be inadequate.

The object of the present invention is to provide a telecommunication - especially telephone - system in which the problem of channel allocation to radio links between mobile subscriber stations and fixed relay stations in densely populated areas is solved.

In a system according to the present invention, each relay station connected to a branch of a wired network is uniquely 201827 identified by an individual call number assigned to an associated subscriber station coupled therewith through a radio link, the combination of a relay station and a subscriber station being referred to hereinafter as a post; it should be understood, however, that the subscriber station of any post may encompass several extensions reached for example through a common switchboard. The subscriber station of each post comprises a first radio transmitter and a first radio receiver which are tunable to any one of a plurality of communication channels available to a group of such posts, the first radio receiver being provided with first scanning means for cyclically exploring these channels in an idle state of the subscriber station to determine their free or busy condition. The subscriber station further comprises first coding means and first comparison means, the latter being connected to the first radio receiver and to the first coding means for detecting an identity between a locally generated reference code and a code received on any of the channels in order to cause the first radio transmitter to send out a first verification signal on the same channel upon detection of such identity. The subscriber station additionally includes selector means for initiating an outgoing call by triggering the first radio transmitter to send out a locally generated identification code, on a channel found idle by the first radio receiver, preparatorily to the emission of a call signal to the wired network in response to reception of a second verification signal on the channel found idle. In an analogous manner, the associated relay station comprises a second radio transmitter and a second radio receiver tunable to the same channel, the second radio receiver being provided with second scanning means for cyclically exploring these channels in an idle state of the relay station to determine their free or busy condition. The relay station further comprises second coding means and second comparison means, the latter being connected to the second radio receiver and to the second coding means for detecting an identity between a locally generated reference code and a code received on one of the channels and for causing the second radio transmitter to send out the aforementioned second verification signal upon detection of such identity, the second radio transmitter being triggerable by an incoming call signal from the network to send out a locally generated identification code on a channel found idle by the second radio receiver preparatorily to seizing the idle channel in response to reception of the aforementioned first verification signal over the channel for enabling an extension of the incoming call to the associated subscriber station.

In the field of use more specifically contemplated, and as particularly described hereinafter, the selector means of the subscriber station will be part of a telephone set. only Such a system will not/insure the necessary privacy but also prevent a subscriber from channelling an outgoing call through a relay station of an adjacent post whose subscriber would then be falsely charged for that call.

The reference code generated by the first coding means matches the identification code generated by the second coding means but need not be identical with the identification code generated by the first coding means or the reference code generated by the second coding means., A diversity of the two reference codes used by the ~two stations, of a post will in fact provide additional safeguards against invasion of privacy or unauthorised channelling of outgoing calls through unrelated relay stations.

In telephone systems with mobile stations on automotive vehicles it is known to use address codes for discriminating among different satellite stations aboard vehicles within range of a central relay station. In such a system, however, the address codes are the equivalent of call numbers individually assigned to the various mobile satellite stations. This .contrasts with the present system in which a code (e.g. a 15-bit word) is used strictly for verification since no relay station can communicate with any subscriber station other than the one forming part of the same post.

A preferred embodiment of the invention will novv be described in detail by way of example only, with reference to the accompanying drawing the sole Figure of which shows a post adapted to communicate through a branch of a wired telephone netwoik with a central office.

The post shown in the drawing comprises a mobile subscriber station 1 and a fixed relay station 2 communicating with each other through a radio link. Subscriber station 1 includes a receiver 3 having means for cyclically scanning (in an idle state of the station) a multiplicity of radio-frequency channels allocated to a group of such posts, and a transmitter Receiver 3 has two output terminals 5 and 8, the latter serving to deliver a l$-bit code word encountered on any channel during the scanning thereof. Such a code word may appear, upon demodulation, in a low-frequency band reserved for voice' transmission and separated 201827 from a narrow frequency band of the same channel on which a pilot signal appears when the channel is busy. When a channel is found to be idle and carries no code word, receiver 3 energizes its output 5 to unblock a gate 10 for enabling the initiation of an outgoing call by a subscriber with the aid of a keyboard 6; the selection signals from the keyboard then reach the transmitter 4- A code word appearing on terminal B is fed to a comparator 9 which receives a locally generated reference code from a coder 7 connected thereto. Coder 7 also delivers a 15-bit identification code, which may be different from the aforementioned reference code, to transmitter 4 whenever that transmitter is triggered to seize an idle channel upon a lifting of a handset 21 by the subscriber wishing to initiate an outgoing call. The transmitter 4 then sends out the locally generated identification code by way of the radio link using the hereto fore idle channel, to relay station 2 where that code arrives at a receiver 13 which also cyclically scans the available communication channels. Receiver 13 has two output terminals 15 and 18, similar to terminals 5 and & of receiver 3> the first of which serves to unblock a gate 20 upon detection of an idle channel while the second one delivers an incoming identification code to a comparator 19 also receiving from a coder 17 a locally generated reference code. A transmitter 14 in relay station 2 receives from coder 17 a locally generated 15-bit identification code, identical with the reference code emitted by coder 7 of subscriber station 1, for emission via the radio link whenever an incoming call addressed to post 1, 2 arrives over a line 22 by which station 2 is connected to the otherwise 201827 nonillustrated telephone network. The use of 15-bit words enables discrimination among more than 30,000 posts to which the same set of, say, 40 communication channels is available. Naturally, the scanner of each receiver 3, 13 remains connected long enough to any channel found to be idle, i.e. one that lacks the pilot signal serving to indicate its busy condition, to receive the entire 15-bit code word recurrently sent out by transmitter 14 or 4 upon the arrival of an incoming call or the initiation of an outgoing call, respectively.

When comparator 9 detects an identity between an identification code received from station 2 and the locally generated reference code, it enables ...via handset 21 in the illustrated embodiment .. the transmitter 4 to send out the identification code generated by coder 7 which in turn is relayed by receiver 13 via terminal 18 to comparator 19, the latter thereupon checking its identity with the reference code generated by coder 17. When that check has a positive outcome, transmitter 14 is enabled to send a "handshake" signal to receiver 3 and to extend an incoming call waiting on line 22 to subscriber station 1 which in turn can now transmit messages to relay station 2 for establishment of full-duplex communication between line 22 and station 1.

Comparator 1$, similarly, enables the transmitter 14 (through the intermediary of line 22 and the central office connected thereto) to send the locally generated identification code to subscriber station 1 whose receiver 3 feeds it to comparator 9 for checking against the reference code generated by coder 7. When identitiy is found to exist, a "handshake" signal is sent to relay station 2; the subscriber then receives dial tone and can now proceed to select the call number of the 2018 27 remote station by means of keyboard 6.

The 40 or so available channels may be modulated upon a carrier of 900 MHz, for example, with sidebands spread over 45 MHz A transmitting power of 10 mW will allow radio communication between subscriber station 1 and relay station 2 over a radius of about 50 meters. The two stations may each comprise a crystal-controlled master oscillator and a voltage-controlled oscillator slaved thereto by a phase-locking loop (PLL) stabilizing its operating frequency at, say, 70 MHz. That frequency is stepped down in a mixer working into an adjustable frequency divider which under the control of a programmed sequencer, successively emits the several channel frequencies to a scanner within receiver 3 or 13. The stabilized VCO signal of 70 MHz is fed via respective buffer amplifiers to a receiving-side multiplier and to a trans-mitting-side mixer. The receiving-side multiplier has an output frequency of' about $50 MHz fed via a multipole filter, which removes unde.sirable- controlled transmitting oscillator operates with approximately SO MHz. Its output signal is phase-modulated with the suitably amplified message signals from handset 21 or from line 22. The modulation product is additively combined in the transmission-side mixer with the VCO signal, the result being stepped up in a transmission-side multiplier to the carrier frequency of about 900 MHz. Upon amplification in a final stage a power of +10 dBm is available for transmission. Band-pass filters at the antenna output and in the output of the transmission-side multiplier are necessary for proper suppression of undesirable frequencies. With the high operating frequencies utilized, only so-called helix filters will be suitable for this purpose in order to provide the necessary circuit quality with compact dimensions, 201827 low series attenuation and high selectivity. Despite the relatively high cost of such filters, they insure an optimum suppression of interference from harmonics or image frequencies.

The receiver operates by the dual-heterodyning principle. With simple conversion it would be necessary to employ a rather high intermediate frequency (100 to 150 MHz) in order to avoid image frequencies as much as possible. The amplification and demodulation of high intermediate frequencies is, however, difficult on account of limited stability and low electrical efficiency.

The first and second intermediate frequencies may be fixed at 75 and 10.7 MHz, respectively. The receiver should be of highly integrated structure.

After a preselection in a two-stage band-pass filter the level of the useful signal is raised in a preamplifier whose output is fed via a further band-pass filter to the first mixer. The second mixer transposes the 75-MHz signal to 10.7 MHz whereupon the signal is delivered to a limiting amplifier and, after demodulation, is fed to handset 21 or to line 22.

Each receiver further comprises a noise barrier whose threshold is adjustable. This insures that a connection is established only when the signal-to-noise ratio exceeds a certain minimum value. If a connection already exists, that connection is maintained for several seconds after a drop below the aforementioned minimum threshold; if the signal does not rise above the threshold during that interval, the connection is terminated. 201827

Claims

WHAT WE CLAIM IS;

1. A telecommunication system comprising a wired network and a multiplicity of posts served by said network for selectively communicating with one another, each of said posts being uniquely identified by an individual call number and comprising a relay station connected to a branch of said network and a mobile subscriber station coupled with said relay station by a radio link of limited range; said subscriber station comprising a first radio transmitter and a first radio receiver tunable to any one of a plurality of communication channels available to a group of said posts, said first radio receiver being provided with first scanning means for cyclically exploring said channels in an idle state of the subscriber station to determine their free or busy condition, said subscriber station further comprising first coding means and first comparison means connected to said first radio receiver and to said first coding means for detecting an identity between a locally generated reference code and a code received on one of said channels and for causing said first radio transmitter to send out a first verification signal on the same channel upon detection of such identity said subscriber station additionally including selector means for initiating an outgoing call by triggering said first radio transmitter to send out a locally generated identification code on a channel found idle by said first radio receiver preparatorily to the emission of a call signal to said network in response to reception of a second verification signal on the channel found idle, - 10 - 201827 said relay station comprising a second radio transmitter and a second radio receiver tunable to said channels, said second radio receiver being provided with second scanning means for cyclically exploring said channels in an idle state of the relay station to determine their free or busy condition, said relay station further comprising second coding means and second comparison means connected to said second radio receiver and to said second coding means for detecting an identity between a locally generated reference code and a code received on one of said channels and for causing said second radio transmitter to send out said second verification signal upon detection of such identity, said second radio transmitter being triggerable by an incoming call signal from said network to send out a locally generated identification code on a channel found idle by said second radio receiver preparatorily to seizing the idle channel in response to reception of said first verification signal thereover for enabling an extension of the incoming call to said subscriber station.

2. A telecommunication system as defined in Claim 1 wherein said selector means is part of a telephone set.

3. A telecommunication system as defined in Claim 1 or 2 wherein the reference code generated by said first coding means matches the identification code generated by said second coding means but is different from the identification code generated by said first coding means, the latter matching the reference code generated by said second coding means. - 11 - ZoiZll

4. A telecommunication system as defined in Claim 1 or 2 wherein each of said radio receivers comprises a crystal-controlled oscillator, a voltage-controlled oscillator slaved in a phase-locking loop to said crystal-controlled oscillator, and frequency-dividing means connected to an output of said voltage-controlled oscillator, each of said scanning means comprising a sequencer connected to a control input of the respective frequency-dividing means f°r carrying out a step-down ratio thereof.

5. A telecommunication system substantially as hereinbefore described with reference to and as shown in the accompanying drawing. PORTAPHONE AG by their authorised agents: P.L.BERRY '& ASSOCIATES per: