GB2110851A - Radiopaging systems - Google Patents

Abstract

In a radiopaging system comprising a plurality of receivers having respective addresses and a transmitter capable of sending paging signals comprising a plurality of successive codewords including at least one receiver address codeword and at least one control codeword, the transmitter in capable also of transmitting an 'all-call' signal for substantially simultaneously alerting some or all receivers, the 'all- call' signal comprising an 'all-call' address constituted by at least one said control codeword (SC,I), and some or all of the receivers comprise means to detect the receipt of a signal comprising the 'all-call' address. Normally a preamble is followed by batches of codewords, each batch being a synchronisation codeword (SC) followed by a mix of address, message and idle codewords. However, in an "all-call" signal, this mix is replaced by a particular sequence of synchronisation and idle codewords (SC,I) forming the "all-call" address each bit of which is represented by SC or I according to its value (Fig 2). Alternatively the mix may be replaced by one SC. <IMAGE>

Description

SPECIFICATION Radiopaging systems This invention relates to radiopaging systems.

Atypical modern digital radiopaging system comprises a plurality of receivers having respective addresses and a transmitter capable of sending paging signals comprising a plurality of successive codewords. The codewords typically comprise receiver address words, to signify to an associated receiver that it is being addressed, each receiver address word being followed by one or more message words representing some form of message to be presented to the user of the associated receiver, e.g. an alerting signal (audible and/or visual) and/or an alphanumeric or numeric message and/or speech. The codewords typically also comprise what may be collectively referred to as 'control codewords'. One form of control codeword may be a synchronisation codeword positioned at regular intervals in the sequence of codewords to provide word synchronisation of the receivers.For example, a synchronisation codeword may follow each 16 other words to divide a signal into batches each comprising a synchronisation codeword followed by 16 other codewords. Another form of control codeword may comprise a so-called idle codeword which is inserted into the transmission sequence in place of an address codeword or message codeword when no such word is transmitted but the signal is not to be terminated.

In use of a radiopaging system, it is often required that several related receivers be paged more or less simultaneously. This can be done by the provision of a so-called 'group call' facility, according to which a preselected group of receivers are calied in sequence by use of their respective address codes. Since it may take a few seconds to alert sequentially a few tens of receivers, a group call facility becomes of limited use when a large number of receivers are to be alerted, in particular when it is desired that ail the required receivers be alerted substantially simultaneously, for instance in an emergency situation.To caterforthis possibility, some radiopaging systems are provided with a so-called 'all-call' facility, by virtue of which all or at least a reasonably large number of the receivers of the system may be alerted substantially simultaneously by virtue of such receivers being provided with some form of common secondary address facility which will respond to an associated all-call signal containing information representing the secondary address.

According to the present invention there is provided a radiopaging system comprising a plurality of receivers having respective addresses and a transmitter capable of sending paging signals comprising a plurality of successive codewords including at least one receiver address codeword and at least one control codeword, wherein the transmitter is capable also of transmitting an 'all-call' signal comprising an 'all-call' address constituted by at least one said control codeword, and wherein at least some of the receivers comprise means to detect the receipt of a signal comprising the 'all-call' address.

A radiopaging system in accordance with the invention thus provides an 'all-call' facility by employing a control codeword or codewords already used by the system to make up a secondary 'all-call' address.

The invention will now be further described, by way of illustrative and non-limiting example, with reference to the accompanying drawings, in which: Figure lisa schematic representation of the format of a paging signal employed in normal operation in a radiopaging system embodying the invention; Figure 2 is a similar representation of a form of 'all-call' signal that can be used by the system; and Figure 3 is a view, similar to Figure 2, of a simpler form of 'all-call' signal.

A radiopaging system embodying the present invention comprises a plurality of receivers having respective addresses and a transmitter capable of sending digitally coded paging signals which typically, though not essentially, comprise bits modulated on a carrier signal by frequency shift keying. As shown in Figure 1, a paging signal comprises a preamble followed by at least one batch of codewords. The preamble comprises 576 bits in a predetermined format (e.g. 101010...), the receivers being responsive to receipt of the preamble (or the presence of carrier or other means to determine that the transmitter is transmitting) to switch themselves from an idle mode in which they draw little current from their batteries into a fully operational mode.

The receivers, once in the operational mode, use the preamble or other signals to attain bit synchronisation and to prepare to acquire word synchronisation once a synchronisation word is detected.

At the end of the preamble, a succession of 32-bit codewords are transmitted in batches each comprising a synchronising word SC followed by 16 other codewords. The synchronisation word SC is of a fixed format, i.e. a predetermined sequence of bits of value 1 or 0. Each receiver is capable of detecting a synchronisation codeword and is responsive thereto to provide word synchronisation with the received signal. The other 16 codewords in each batch comprise receiver address codewords, message codewords and idle codewords. A receiver address codeword, as the name implies, indicates that a particular receiver is addressed.Each receiver compares each address codeword with its respective address (stored therein) and, if there is coincidence, receives and acts in response to the message codeword or message codewords that may follow the address codeword in the sequence, e.g. by providing the user with an alerting signal (visual and/or audible) and/or an alphanumeric or numeric display of the message and/or speech. (The first bit of each address codeword is different from that of each message codeword whereby each receiver can tell whether a particular word is one or the other by examining the most significant bit.) If the address codeword is not intended for a particular receiver, it waits for and examines the next address codeword.

This process continues until the signal is terminated, which may take place at any word position in any batch when no more cails have to be made at the present time. If, however, the signal is not to be terminated, but there is no message or address word to be transmitted in a particular slot, a so-called idle word is instead transmitted. This, like the synchronisation word, is a 'dummy' word of a fixed format of bits of level 1 and level 0, though the format will of course be different from that of the synchronisation word.

Those skilled in the art will appreciate that the above-described paging signal format is similar to the standard POCSAG format of the British Post Office, save that it is rather simpler in that receiver framing is not employed. For a more detailed description of the POCSAG format, reference should be made to 'A Report of the Studies of the British Post Office Code Standardisation Advisory Group (POCSAG)', British Post Office, 1979.

As will be appreciated by those skilled in the art, paging signals of the general form described above are employed to page one or more of the receivers of the system, the precise form of the signal depending upon the number of receivers to be contacted and on the particular information, e.g. alerting signal (audible and/or visual) and/or alphanumeric message and/or speech, to be supplied thereto. A paging signal of the above format can, for example, be used to provide a 'group call' of the kind mentioned above by sending the same message in sequence to a predetermined group of receivers. Also, as will now be described, the system can be employed to transmit an 'all-call' signal enabling at least some of the receivers to be alerted substantially simultaneously.

The 'all-call' facility is provided by the use of a secondary address which is made up by sending synchronisation codewords and/or idle codewords (hereinafter collectively referred to as 'control codewords') in a predetermined array of at least one such codeword. For instance, as shown in Figure 2, the 16 words following the initial synchronisation word SC of the first batch can be transmitted in a predetermined array or pattern. Thus, if the synchronisation words SC are considered as representing a binary integer of one level and the idle words I are considered as representing a binary integer of the other level, tuhe above 16 words make up the bits of a 16-bit 'super-word'. The receivers are of necessity provided with means for detecting the synchronisation words.To enable them to recognise an all-call superword of the general form shown in Figure 2, they are provided also with an idle word detector together with means responsive to the outputs of the synchronisation word detector and idle word detector to determine whether such two words are being transmitted in the sequence or array indicating that an all-call signal has been received. If so, the receivers provide some form of alert or alarm, for example a four second bleep as shown in Figure 2.

The receivers may be operative automatically to switch the receivers into a speech reception mode at the end of the bleep, so that the nature of the call can be indicated to the receivers by means of speech.

To detect the 16 bit 'super-word' indicating the receipt of an all-call signal, the associated receivers are provided with means to store the 16-bit all-call address word so that they can compare it with a received word. The word can conveniently be stored therein by incorporation in a plug-in circuit conven tionally fitted to the receiver to programme it with its respective address code.

The use of a 16 bit all-call recording address word provides sufficient permutations to allow the use of approximately 65,000 different secondary 'all-call' addresses. This facility is thus sufficiently flexible to enable a very large number of different all-call facilities to be provided on a very large paging system, for example a nationwide system.

Naturally, it is not necessary to use an all-call address word of a length of 16 bits to provide the all-call facility. Neither is it necessary to use both synchronisation code words and idle codewords. For example, in a very simple arrangement shown in Figure 3 an all-call is signified simply by transmitting a onebit word, such one bit being represented by a single synchronisation word following the synchronisation word conventionally present at the beginning of the first batch. Thus, in that case, the receivers need only detect the presence of a synchronisation word in a position immediately following the usual synchronisation word following the preamble, an occurrence that would not normally take place.

CLAIMS (Filed on 19th November 1982) 1. A radiopaging system comprising a plurality of receivers having respective addresses and a transmitter capable of sending paging signals comprising a plurality of successive codewords including at least one receiver address codeword and at least one control codeword, wherein the transmitter is capable also of transmitting an 'all-call' signal comprising an 'all-call' address constituted by at least one said control codeword, and wherein at least some of the receivers comprise means to detect the receipt of a signal comprising the 'all-call address.

2. A radiopaging system according to claim 1, wherein said 'all-call' signal comprises at least one synchronisation codeword normally used by the receivers to achieve word synchronisation.

3. A radiopaging system according to claim 1 or claim 2, wherein said 'all-call signal comprises at least one idle codeword normally transmitted in a slot when a paging signal is not to be terminated but no message or address codeword is to be transmitted in that slot.

4. A radiopaging system according to claim 1, claim 2 or claim 3, wherein said 'all-cali' signal comprises a sequence of a plurality of different control codewords.

5. A radiopaging system according to any one of the preceding claims, wherein said 'all-call' signal comprises the occurrence of a control codeword at a position in a paging signal where it would not normally occur.

6. A radiopaging system according to claim 5, wherein said 'all-call' signal comprises the occurrence of a control codeword immediately after a like control codeword.

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

Claims (7)

**WARNING** start of CLMS field may overlap end of DESC **. present time. If, however, the signal is not to be terminated, but there is no message or address word to be transmitted in a particular slot, a so-called idle word is instead transmitted. This, like the synchronisation word, is a 'dummy' word of a fixed format of bits of level 1 and level 0, though the format will of course be different from that of the synchronisation word. Those skilled in the art will appreciate that the above-described paging signal format is similar to the standard POCSAG format of the British Post Office, save that it is rather simpler in that receiver framing is not employed. For a more detailed description of the POCSAG format, reference should be made to 'A Report of the Studies of the British Post Office Code Standardisation Advisory Group (POCSAG)', British Post Office, 1979. As will be appreciated by those skilled in the art, paging signals of the general form described above are employed to page one or more of the receivers of the system, the precise form of the signal depending upon the number of receivers to be contacted and on the particular information, e.g. alerting signal (audible and/or visual) and/or alphanumeric message and/or speech, to be supplied thereto. A paging signal of the above format can, for example, be used to provide a 'group call' of the kind mentioned above by sending the same message in sequence to a predetermined group of receivers. Also, as will now be described, the system can be employed to transmit an 'all-call' signal enabling at least some of the receivers to be alerted substantially simultaneously. The 'all-call' facility is provided by the use of a secondary address which is made up by sending synchronisation codewords and/or idle codewords (hereinafter collectively referred to as 'control codewords') in a predetermined array of at least one such codeword. For instance, as shown in Figure 2, the 16 words following the initial synchronisation word SC of the first batch can be transmitted in a predetermined array or pattern. Thus, if the synchronisation words SC are considered as representing a binary integer of one level and the idle words I are considered as representing a binary integer of the other level, tuhe above 16 words make up the bits of a 16-bit 'super-word'. The receivers are of necessity provided with means for detecting the synchronisation words.To enable them to recognise an all-call superword of the general form shown in Figure 2, they are provided also with an idle word detector together with means responsive to the outputs of the synchronisation word detector and idle word detector to determine whether such two words are being transmitted in the sequence or array indicating that an all-call signal has been received. If so, the receivers provide some form of alert or alarm, for example a four second bleep as shown in Figure 2. The receivers may be operative automatically to switch the receivers into a speech reception mode at the end of the bleep, so that the nature of the call can be indicated to the receivers by means of speech. To detect the 16 bit 'super-word' indicating the receipt of an all-call signal, the associated receivers are provided with means to store the 16-bit all-call address word so that they can compare it with a received word. The word can conveniently be stored therein by incorporation in a plug-in circuit conven tionally fitted to the receiver to programme it with its respective address code. The use of a 16 bit all-call recording address word provides sufficient permutations to allow the use of approximately 65,000 different secondary 'all-call' addresses. This facility is thus sufficiently flexible to enable a very large number of different all-call facilities to be provided on a very large paging system, for example a nationwide system. Naturally, it is not necessary to use an all-call address word of a length of 16 bits to provide the all-call facility. Neither is it necessary to use both synchronisation code words and idle codewords. For example, in a very simple arrangement shown in Figure 3 an all-call is signified simply by transmitting a onebit word, such one bit being represented by a single synchronisation word following the synchronisation word conventionally present at the beginning of the first batch. Thus, in that case, the receivers need only detect the presence of a synchronisation word in a position immediately following the usual synchronisation word following the preamble, an occurrence that would not normally take place. CLAIMS (Filed on 19th November 1982)

1. A radiopaging system comprising a plurality of receivers having respective addresses and a transmitter capable of sending paging signals comprising a plurality of successive codewords including at least one receiver address codeword and at least one control codeword, wherein the transmitter is capable also of transmitting an 'all-call' signal comprising an 'all-call' address constituted by at least one said control codeword, and wherein at least some of the receivers comprise means to detect the receipt of a signal comprising the 'all-call address.

2. A radiopaging system according to claim 1, wherein said 'all-call' signal comprises at least one synchronisation codeword normally used by the receivers to achieve word synchronisation.

3. A radiopaging system according to claim 1 or claim 2, wherein said 'all-call signal comprises at least one idle codeword normally transmitted in a slot when a paging signal is not to be terminated but no message or address codeword is to be transmitted in that slot.

4. A radiopaging system according to claim 1, claim 2 or claim 3, wherein said 'all-cali' signal comprises a sequence of a plurality of different control codewords.

5. A radiopaging system according to any one of the preceding claims, wherein said 'all-call' signal comprises the occurrence of a control codeword at a position in a paging signal where it would not normally occur.

6. A radiopaging system according to claim 5, wherein said 'all-call' signal comprises the occurrence of a control codeword immediately after a like control codeword.

7. A radiopaging system substantially as herein

described with reference to Figures 1, 2 and 3 of the accompanying drawings.