GB2173674A

GB2173674A - Paging system

Info

Publication number: GB2173674A
Application number: GB08508839A
Authority: GB
Inventors: Alexander Poliakoff; Sydney Richard Pitkin
Original assignee: Multitone Electronics PLC
Current assignee: Multitone Electronics PLC
Priority date: 1985-04-04
Filing date: 1985-04-04
Publication date: 1986-10-15
Also published as: GB2173674B; GB8508839D0

Abstract

A paging system includes a local transmitter 15 for transmitting local paging signals to paging receivers 16 over a limited range. An external transmission detector 14 is arranged to detect external area wide transmissions from an external transmitter 18 operating at the same frequency as the local transmitter 15. When such an external transmission is detected, an on-site encoder 11 which includes a memory 12 storing local paging signals inhibits transmission of the local paging signals until the external transmission has stopped. Thus a single paging receiver 16 can be used to receive both external, area wide transmissions and also local transmissions. <IMAGE>

Description

SPECIFICATION Paging system The present invention relates to a paging system, and in particular to a paging system capable of dual purpose operation.

Area wide paging systems are now prevalent in which a central organisation, such as British Telecom in the United Kingdom, provides transmissions composed of message signals intended for specific paging receivers which respond to the particular received message signals to provide an alarm tone, display or the like. These transmissions are broadcast over wide areas to that the message signals can be received relatively independently of the specific geographical location of the paging receiver at the time that the particular message signal is broadcast.

Most developed countries now have such countrywide or city-wide paging systems working on dedicated frequencies. All large systems now use digital codes to select specific receivers, the circuits of which include battery economy arrangements which require a preamble to be sent out before transmission of individual calls to receivers. Thus the transmission system is arranged to store all calls to be sent out, and then to transmit the messages in batches preceded by the preamble.

In addition to these area wide systems, so-called on-site paging systems are available in which the purpose is to be able to reach paging receivers over a much smaller range than in area wide systems, it generally being sufficient to provide coverage over a single building or group of buildings, such as in a hospital.

On-site paging systems have previously worked in different frequency bands from the area wide systemps which generally operate at very high frequencies, whereas the on-site systems have utilised lower transmission frequencies. Previously, if an individual required both area-wide and on-site paging facilities, it was necessary to have two paging receivers.

According to the invention, there is provided a paging system comprising a local transmitter for transmitting local paging signals over a limited range to paging receivers such that each particular receiver responds to its individual paging signal, and an external transmission detector arranged to reveive external transmissions at the same frequency as the local paging signals and to inhibit the local transmitter when such external transmissions are detected.

Such a system therefore permits an off-site (area wide) paging receiver to be used on-site without interference between the two systems.

In the preferred arrangement, the on-site transmission from the local transmitter is limited to the site by means of reduced E.R.P., low aerials and/or leaky feeders or the like, and is controlled by the detector which responds to all area-wide transmissions on the given frequency. The on-site calls are stored in a memory of the on-site encoding equipment, and are preferably transmitted as soon as the first area wide transmission stops. Should that transmission start up again before the on-site calls have been completed, the on-site transmitter is immediately switched off and the call is repeated in the next interval. If the on-site call does not follow immediately an area wide transmission, then the on-site system has to transmit a preamble signal identical with the area wide preamble, in order to activate the receivers.

The invention will now be described by way of example, with reference to the accompanying drawing which shows a block diagram of one embodiment of a paging system according to the invention.

Referring to the drawing, an on-site system 10 includes an encoder 11 having a memory 12, the encoder 11 being responsive to an area wide transmission detector 14 to inhibit calls being sent to an on-site transmitter 15, such local transmissions therefore being prevented during an area wide transmission. The drawing shows a single paging receiver 16 (although of course a number of such receivers will be in use) and also a distant area wide transmitter 18. The paging receiver 16 will be capable of receiving paging signals from the area wide transmitter 18. When the area wide transmission stops, local calls stored in the memory 12 are fed to the on-site transmitter 15 and sent under reduced power (or other range limiting means being utilised, as described above), again being received by the paging receiver 16.The local calls are however retained in the memory 12 in the event that the area wide transmission should start up again before the on-site calls have been completed. In that case, the on-site transmitter 15 is immediately switched off and the local call is repeated in the next interval. Thus the contents of the memory 12 have to be preserved until a complete batch of local calls has successfully been transmitted.

When the on-site calls immediately follow an area wide transmission, the paging receiver 16 should successfully receive the on-site calls since it will still be powered up. It it is desired to send on-site calls at other times, not necessarily following area wide transmissions, the encoder 11 should be capable of producing a preamble signal for transmission identical to the area wide preamble, so as to power up the receiver.

In the situation where an area wide transmission starts during an on-site transmission, it is necessary for the area wide detector 14to be able to distinguish between the transmissions so as to detect correctly that an area wide transmission is being received.

Since both transmissions will be present under these circumstances, one way of achieving this is to sense a beat note between the two transmissions, presence of the beat note acting to inhibit on-site transmission.

The advantage of a dual purpose system of this type is that, in most establishments provided with an on-site system, only a small proportion of people supplied with paging receivers need to be called outside their site so that most receivers need not be part of the area wide system and thus qo not generally require the same high sensitivity and other stringent specification parameters of the off-site receivers. Equally, many facilities of on-site systems are totally unavailable off-site, such as automatic triggering, priorities and other facilities. Therefore a significant cost saving can be achieved by supplying paging receivers in accordance with the user's requirements, in other words, whether or not the receiver is to be capable of being used off-site to receive area wide transmissions, as well as on-site for local calls.

Claims

1. A paging system comprising a local transmit ter for transmitting local paging signals over a limited range to paging receivers such that each particular receiver responds to its individual paging signal, and an external transmission detector arranged to receive external transmissions at the same frequency as the local paging signals and to inhibit the local transmitter when such external transmissions are detected.

2. A paging system according to claim 1, comprising a memory for storing local paging signals prior to transmission and means for enabling transmission of the local paging signals upon termination of an external transmission.

3. A paging system according to claim 2, including means for inhibiting transmission of the local paging signals should the external transmission re-commence, and for repeating transmission of the local paging signals upon termination of the recommenced external transmission.

4. A paging system according to claim 1, claim 2 or claim 3, wherein the local transmitter range is limited by means of one or more of reduced E.R.P., low aerials and leaking feeders.

5. A paging system according to any one of the preceding claims, wherein the external transmission detector comprises means for detecting a beat note between the local and external transmissions.

6. A paging system substantially as hereinbefore described with reference to the accompanying drawing.