GB2110850A - Radiopaging arrangements - Google Patents

Abstract

A radiopaging arrangement comprises a plurality of adjacent radiopaging systems each comprising a transmitter and a plurality of receivers. The transmitters are operated at the same frequency and each transmitter is arranged to commence each transmission with a digitally coded preamble recognisable by the receivers of the associated system. The receivers are responsive to recognition of the preamble signal to switch from an idle mode to an operational mode. To ensure that a transmission in any one system will not cause switching of the receivers of the other system or systems into the operational mode, the coding of the preamble is different for each said system. Typical different preambles for different systems are shown at (a) to (d) in Figure 3. <IMAGE>

Description

SPECIFICATION Radiopaging arrangements This invention relates to radiopaging arrangements.

Atypical modern digital radiopaging system com prises a plurality of receivers and a transmitter arranged to commence each transmission with a digitally coded preamble recognisable by the receivers, the receivers being responsive to recognition of the preamble signal to switch from an idle mode to an operational mode. In the idle mode, the current consumption of each receiver is minimal. At intervals (e.g. one second intervals) each receiver looks for a transmission by determining whether it is receiving the preamble signal. If the preamble signal is not being received, the receiver reverts to a quiescent state, i.e. remains in the idle mode. If, however, the preamble signal is detected, the receivear adopts an operational mode ready to determine whether a subsequent message is intended for itself or for another receiver.An advantage of the foregoing arrangement is that current drain on the receiver batteries is minimised. That is to say, in the absence of a transmission the receivers will remain in the minimal power consumption idle mode and are only switched to the operational mode, in which more current is consumed, when they detect a transmission.

With increasing use of radiopaging, it is becoming increasingly common for radiopaging systems to be installed adjacent to one another, that is to say that they have operational areas which are near one another or which wholly or partly overlap. For instance, several different radiopaging systems may be installed in a single shopping, industrial or commercial complex or so as to cover the same geographical area. A problem can arise, in this case, if the transmitters of the different systems operate on the same radio channel or frequency. While the use of the same channel or frequency is in general undesirable, there is at present little effective alternative in many countries, where the relevant authorities restrict the number of channels available to radiopaging to a very small number.The problem does not reside so much in message security, since it can be ensured that transmissions of one system are not directed to receivers of another system by arranging that the receivers of the different systems do not have common addresses, i.e. that the address coding of a receiver in any one system will not be identical with that of a receiver in any of the other systems. It has in fact been realised that a problem arises in a different respect. The problem is that, if the different systems are made by the same manu facturer,theywould in general use the same preamble coding.They will in fact generally adopt the same coding if made by different manufacturers, since at least in the UK there is now a standard code format which includes a form of preamble. (See 'A Report of the Studies of the British Post Office Code Standardisation Advisory Group (POCSAG)', British Post Office, 1979.) Thus, unbeknown to their users, the receivers of all of the systems will or may switch from the idle to the operational mode in response to a transmission from another system of a message or messages intended only for one or more of the receivers of the other system. Thus, the current drain on the batteries of the receivers is greatly increased and the battery life may therefore be reduced.

According to the present invention there is pro vided a radio paging arrangement comprising a plurality of adjacent radiopaging systems each com prising a transmitter and a plurality of receivers, wherein the transmitters are operated at the same frequency and each transmitter is arranged to com mence each transmission with a digitally coded preamble recognisable by the receivers of the asso ciated systems, the receivers being responsive to recognition of the preamble signal to switch from an idle mode to an operational mode, and wherein the coding of the preamble is different for each said system such that a transmission in any one system will not cause switching of the receivers of the other system or systems into the operational mode.

Thus, with an arrangement embodying the invention, the above-described problem can be at least alleviated. Further, this can be done in a manner that need not involve undue compiexity in design and construction, in that the various different systems can be generally the same except that the transmitter and receiver coding is different between the different systems.

The invention will now be further described, by way of illustrative and non-limiting example, with reference to the accompanying drawing, in which: Figure 1 is a diagrammatic representation of a radiopaging system; Figure2 is a diagrammatic representation of a form of signal transmitted by a transmitter of the radiopaging system; and Figure 3 represents examples of different preamble codes that can be used in the different radio paging systems of a radio paging arrangement embodying the invention.

Figure 1 shows a radiopaging system comprising a transmitter X and a plurality of paging receivers P.

In a manner well known in the art, the transmitter X can pass a message, which can be an alerting sound or light signal, an alphanumeric or numeric message for a visual display, or a speech message, to any selected one of the receivers P. It does this by transmitting a digitally coded signal which is typically, though not essentially, in the form of bits modulated on a carrier signal by frequency shift keying. As shown in Figure 2, the signal typically comprises a preamble followed by codewords. The preamble, as mentioned above, causes the various receivers P to switch from an idle mode to an operational mode, after which the receivers use the preamble signal to attain bit synchronisation and to prepare the acquire word synchronisation once the codewords arrive.In the above-mentioned POCSAG format, the preamble comprises 576 bits transmitted at a rate of 512 bits/second, whereby the preamble lasts for slightly longer than one second. Each receiver looks for the preamble at a rate of about once per second, whereby it should never miss a transmission. Once the receivers P have detected a transmission and are all in the operational mode, and once the preamble has ended, the codewords arrive. The codewords comprise a group of multi-bit (e.g. 32 bit) words that typically includes synchronisation words, address words to indicate which receiver or receivers P is or are being addressed, and message words. The selected receiver or receivers then receives the message and directs it to the user in the form of an alerting signal (audible and/or visual) and/or an alphanumeric message and/or speech.

As mentioned above, if a plurality of such systems are installed adjacent one another, i.e. are near one another or have operational areas that wholly or partially overlap, and if the transmitters of at least some of such systems are constrained to operate at the same frequency, the emission of a signal by any one of the transmitters of such systems will cause the receivers of all such systems to be switched into the operational mode, thereby unnecessarily energising the receivers of the other system or systems and thereby increasing the current demand on their batteries, whereby the battery life can be reduced.

This problem can be alleviated in an arrangement embodying the invention, which arrangement comprises a plurality of like systems as described above arranged adjacent one another, by arranging for the preamble coding of the adjacent systems to be different. For example, if there are four such systems, they can have the four different preamble codes shown at (a), (b), (c) and (d) in Figure 3. These different preamble sequences are encoded at the transmitters and receivers of the various systems, this being a simple task, in particular as regards the receivers since they will already comprise a plug-in logic circuit or the like enabling their respective address codes to be programmed therein. With this arrangement, only the receivers of the associated system will respond to a transmission, whereby the battery life of the receivers of the various systems is maximised.In other words, different systems working in the vicinity of one another on the same frequency will have a battery economy which should be as good as they would have if they were widely separated. The above arrangement also provides protection against receivers responding to transmissions from other systems that create modulation resembling the standard POCSAG preamble, which is that shown in Figure 3(a).

CLAIMS (Filed on 19th Nov. 1982) 1. A radiopaging arrangement comprising a plurality of adjacent radiopaging systems each comprising a transmitter and a plurality of receivers, wherein the transmitters are operated at the same frequency and each transmitter is arranged to commence each transmission with a digitally coded preamble recognisable by the receivers of the associated systems, the receivers being responsive to recognition of the preamble signal to switch from an idle mode to an operational mode, and wherein the coding of the preamble is different for each said system such that a transmission in any one system will not cause switching of the receivers of the other system or systems into the operational mode.

2. A radiopaging arrangement substantially as herein described with reference to Figures 1,2 and 3 ofthe accompanying drawing.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (2)

**WARNING** start of CLMS field may overlap end of DESC **. and once the preamble has ended, the codewords arrive. The codewords comprise a group of multi-bit (e.g. 32 bit) words that typically includes synchronisation words, address words to indicate which receiver or receivers P is or are being addressed, and message words. The selected receiver or receivers then receives the message and directs it to the user in the form of an alerting signal (audible and/or visual) and/or an alphanumeric message and/or speech. As mentioned above, if a plurality of such systems are installed adjacent one another, i.e. are near one another or have operational areas that wholly or partially overlap, and if the transmitters of at least some of such systems are constrained to operate at the same frequency, the emission of a signal by any one of the transmitters of such systems will cause the receivers of all such systems to be switched into the operational mode, thereby unnecessarily energising the receivers of the other system or systems and thereby increasing the current demand on their batteries, whereby the battery life can be reduced. This problem can be alleviated in an arrangement embodying the invention, which arrangement comprises a plurality of like systems as described above arranged adjacent one another, by arranging for the preamble coding of the adjacent systems to be different. For example, if there are four such systems, they can have the four different preamble codes shown at (a), (b), (c) and (d) in Figure 3. These different preamble sequences are encoded at the transmitters and receivers of the various systems, this being a simple task, in particular as regards the receivers since they will already comprise a plug-in logic circuit or the like enabling their respective address codes to be programmed therein. With this arrangement, only the receivers of the associated system will respond to a transmission, whereby the battery life of the receivers of the various systems is maximised.In other words, different systems working in the vicinity of one another on the same frequency will have a battery economy which should be as good as they would have if they were widely separated. The above arrangement also provides protection against receivers responding to transmissions from other systems that create modulation resembling the standard POCSAG preamble, which is that shown in Figure 3(a). CLAIMS (Filed on 19th Nov. 1982)

1. A radiopaging arrangement comprising a plurality of adjacent radiopaging systems each comprising a transmitter and a plurality of receivers, wherein the transmitters are operated at the same frequency and each transmitter is arranged to commence each transmission with a digitally coded preamble recognisable by the receivers of the associated systems, the receivers being responsive to recognition of the preamble signal to switch from an idle mode to an operational mode, and wherein the coding of the preamble is different for each said system such that a transmission in any one system will not cause switching of the receivers of the other system or systems into the operational mode.

2. A radiopaging arrangement substantially as herein described with reference to Figures 1,2 and 3 ofthe accompanying drawing.