GB2296988A

GB2296988A - Re-transmitting paging system

Info

Publication number: GB2296988A
Application number: GB9500369A
Authority: GB
Inventors: Alfred Caspers; Manfred Muller; Karl-Werner Hoffmann
Original assignee: Motorola GmbH
Current assignee: Motorola Solutions Germany GmbH
Priority date: 1995-01-10
Filing date: 1995-01-10
Publication date: 1996-07-17
Anticipated expiration: 2015-01-10
Also published as: GB2296988B; GB9500369D0

Abstract

A store and forward paging system having base stations which receive paging messages and re-transmit those messages, enabling wide-area coverage without expensive wire lines, comprises a first base station (10) having an input for receiving paging messages and a plurality of second base stations (13-17) each having a control and memory elements comprising an identification number and a path table. Each path table comprises a plurality of paths and each path comprises a series of sequential identifiers of the base stations in the path. Each base station extracts a path identifier from a received message and uses it to select the appropriate path from the table. The base station compiles a message that includes the identification number of the next base station in the selected path and re-transmits it. If it does not receive an acknowledgement, it tries another path from the table. The message contains a numeric/alphanumeric flag.

Description

RE-TRANSMITTING PAGING SYSTEM Field of the Invention This invention relates to a store and forward paging system having base stations which receive paging messages and re-transmit those messages, enabling wide-area coverage without expensive wire lines.

Background to the Invention Existing wide-area coverage paging systems are mainly reliant on wirebound feeder sections. The critical disadvantage of these systems is the high fees, e.g. for private postal lines. There is a general shortage of frequencies, and therefore radio feed sections cannot be used as a replacement.

Store and forward paging systems are known in which the frequency allocated for transmission to paging receivers is also used as a feeder frequency for distributing the paging messages to remote base stations across the wide area.

Pager calls are forwarded via digital alarm converters (DACs). These DACs operate on the store and forward principle. A master DAC centrally installed in the system distributes the pager calls to the various DACs, which retransmit the received signals. Owing to the range of DACs, there are relatively large overlapping zones, where evaluation by the alerted pagers is difficult.

Digital alarm converters of the type CAS 100 manufactured by Motorola Inc. are used for storing and forwarding of paging messages, for example, in a "token ring" system, in which DACs are arranged in a loop, each DAC in the loop having an address which is incremented with respect to the address of the immediately preceding DAC in the loop. When a DAC re-transmits a paging message or series of paging messages, it pre-pends the address of the next DAC in the loop for receipt and re-transmission of the paging messages. In this manner, the messages are relayed around the loop. By arranging the DACs in a loop, status and control information is relayed back to the starting point, so that the central station can check that the process has been completed correctly.

Should a DAC not receive the paging message relayed around the loop i.e. a break occurs in the loop occurs, the central station using the returned status and control information, is informed which DAC has not acknowledged receipt of the message. Such a prior art arrangement is inflexible in enabling the remaining DACs in the loop receive the message.

Summary of the Invention According to the present invention, a store and forward paging system is provided having a plurality of base stations each base station comprising an identification number and a memory element containing a table. Each table comprises a plurality of paths and each path comprises a series of sequential identifiers of the base stations in the path. Each base station further comprises message receiving and decoding elements arranged to receive a message, to extract therefrom a path identifier and to select the appropriate path from the table identified by the path identifier.Each base station further comprises message compiling and transmitting elements for compiling a message that includes the identification number of the next base station in the selected path and for re-transmitting the message with the identification number of the next base station in the path.

In this manner, each base station receives messages and decodes path information to select from the table the appropriate path for the subsequent base station to which the message is to be re-transmitted.

In a preferred arrangement, each base station is arranged to receive an acknowledgement from the next base station in the selected path, and in the event of not receiving such acknowledgement, it selects another path. This ensures that further base stations receive a given message should one base station in the loop not receive, or acknowledge receiving, the message. This in turn maximises the number of base stations successfully receiving a message. It is further arranged that the message compiling and transmitting elements of each base station, compile and transmit a message that includes the identification of a base station which has failed to acknowledge. It is further arranged for the message to indude a numeric flag to signify whether the message consists of numeric or alpha-numeric characters.

In another aspect of the invention a paging system is described comprising a receiving device capable of displaying numeric and alpha-numeric information and a transmitting station arranged selectively to transmit in a first aspect, numeric telegrams which include message information coded in a first format and which include a first type indicator and secondly alpha-numeric telegrams which include message information coded in a second format and which include a second type indicator.

A preferred embodiment of the invention will now be described, by way of example only, with reference to the drawings.

Brief Description of the Drawings FIG. 1 shows a paging system in accordance with the invention; FIG. 2 shows details the central station of the system of FIG. 1; FIG. 3 shows details of a DAC of the system of FIG. i; FIG. 4 shows details of frame 0 of a POCSAG paging batch for control of the system of FIG. 1; and FIG. 5 shows details of the fields of the data in frame 0 of a POCSAG paging batch for control of the system of FIG. 4.

Detailed Description of the Preferred Embodiment Referring to Fig. 1, a wide area paging system is shown comprising a central master station 10 having a standby master 11 for redundancy purposes and connected to a page entry terminal 12. The central master station is also labelled DAC 0, representing that it is digital alarm converter with address 0.

Surrounding central master station 10 are DACs 13, 14, 15, 16 and 17 (in anti-clockwise order) having, respectively, identification nos. 1, 2,3,4 and 5.

DACs 10 and 13 to 17 form a message loop.

Cirde 30 represents the area of coverage of the paging system.

The operation is as follows. A paging message or number of paging messages are entered at the page entry terminal 12 in a manner known in the art. These are sent over a standard ASCII interface to central master station 10.

Master station 10 compiles these messages into a POCSAG telegram which comprises an initial frame (frame 0) having system control information described below, seven frames of addresses, followed by a variable number of frames of text of the different messages. Master station 10 transmits this telegram throughout the coverage area 30 and the telegram is received by any paging receivers in that coverage area which are addressed specifically in address frames of the telegram. The telegram is also received by DACs 13 to 17.

Suitable apparatus for implementing the invention is illustrated in FIG. 2 and FIG. 3.

Referring to FIG. 2, details of the central station 10 are shown. The central station 10 comprises a radio transmitter 100, a radio receiver 101 and a control unit 102. The control unit 102 has an Input /Output (I/O) interface 103 for interfacing with the page entry channel 12 and has a POCSAG encoder 104 and a POCSAG decoder 105. A control and memory element 106 provides timing control and includes system configuration information.

In normal operation, pagers are entered at the page entry terminal 12, received through the interface 103 into the control unit 102, encoded in the encoder 104 and transmitted by the transmitter 100. Receiver 101 and POCSAG decoder 105 operate to receive test telegrams from remote DACs 13 to 17. Retransmission of the next telegram is controlled by the control and memory element 106.

Referring to FIG. 3, details of a DAC are shown. The DAC comprises a transmitter 200, a receiver 201 and a control unit 202. The control unit 202 comprises a POCSAG encoder 204, a POCSAG decoder 205, a read/write memory 206, a read only memory containing the station ID 208 and the path table 210 and a microprocessor 209.

In operation, paging telegrams are received by the receiver 201 and decoded in the POCSAG decoder 205. The paging telegram is temporarily stored in memory 206. Microprocessor 209 extracts from frame 0 of the telegram a path identifier. The path identifier indicates a particular path number on the path table to determine the next destination base station within the loop to which the telegram is to be re-transmitted. The microprocessor 209 inserts a station ID of the DAC from memory 208 into frame 0 of the telegram stored in memory 206. The microprocessor 209 causes the telegram to be encoded in encoder 204 and transmitted by transmitter 200. The DAC waits for an acknowledgement signal from the destination base station. If no acknowledgement is received a new path is extracted from the path table and the message is re-transmitted to a new base station. The station ID of the base station that did not acknowledge receipt of the message is included in the telegram when re-transmitted.

Referring to FIG. 4, an example of frame 0 of a paging telegram used in the operation of the system described with reference to FIGS. 1 to 3 is shown. In this telegram, certain data fields, such as CRC redundancy checks are shown as are well known in the art. Field 300 contains a numeric flag which is included to indicate whether the telegram contains numeric or alpha-numeric characters.

With the introduction of field 300 a pager can determine whether it should attempt to decode the message if it only operates on either numeric or alphanumeric characters. If a pager is capable of displaying both numeric and alphanumeric characters field 300 informs the pager which format to expect.

Field 302 is a 4-bit path control identifier offering 16 different paths for the message to be transmitted between the base stations. This field signifies the telegram transmission path between the base stations within the paging system.

Should the next base station not acknowledge receipt of the message the transmitting base station refers to the path table in the memory element to determine the next path and base station for the message re-transmission. In case this fallback station does not respond the base station will transmit the path number to the master station. The path table defines which is the next station in the loop and is provided as part of a code plug (i.e. non-volatile memory) of the station The introduction of field 302 to provide a list of preferred paths for the telegram to be sent between base stations allows much greater flexibility for ensuring that the maximum number of DACs in the loop receive the message.

Referring to FIG. 5, two tables are shown describing the field items of the frame 0 paging telegram of FIG. 4. The tables of FIG. 5 can be readily understood by one skilled in the art and need not be described in detail.

An example of a path name in the table 210 is shown below: Label Data Range Description Path~tabl $FF,$FF,$FF $00 - $1F ID of next station; ID of station in case of error; alternative path number (station IDs and path number = $FF if not used) The fifteen other path names use the same format.

Thus, a flexible arrangement is shown that maximises the number of DACs in the loop to receive the paging message.

Claims

1. A paging system comprising a plurality of base stations, each base station having: an identification number; a memory containing a table, where each table comprises a plurality of paths and each path comprises a series of sequential identifiers of base stations in the path, and message receiving and decoding elements arranged to receive a message, to extract therefrom a path identifier and to select the appropriate path from the table identified by the path identifier; and message compiling and transmitting elements for compiling a message including the identification number of the next base station in the selected path and for re-transmitting the message with the identification number of the next base station in the path

2. A paging system according to claim 1, wherein the table of each base station comprises a primary path and at least one default path.

3. A paging system according to claim 1 or 2, wherein each base station is arranged to receive an acknowledgement from the next base station in the selected path and, in the event of not receiving such acknowledgement, to select another path.

4. A paging system according to claim 3, wherein the message compiling and transmitting elements are arranged to compile and transmit a message including the identification of a base station which has failed to acknowledge.

5. A paging base station comprising: a memory containing a table comprising a plurality of paths, each path comprising a series of sequential identification numbers of base stations in the path, and a message receiving and decoding circuit arranged to receive a message, to extract therefrom a path identifier and to select a path from the table identified by the path identifier; and a message compiling and transmitting circuit for compiling a message including the identification number of the next base station in the selected path and for re-transmitting the message with the identification number of the next base station in the path.

6. A paging system comprising: a plurality of base stations, each base station having an identification number, means for receiving a paging message, means for storing path information and looking up an identification number of the next base station in a path and means for forwarding the message to the next base station, wherein the means for looking up comprises means for extracting a path identifier from the received message and for selecting a path from a number of pre-stored paths, according to the path identifier.

7. A paging system comprising a receiving device capable of displaying numeric and alphanumeric information and a transmitting station arranged selectively to transmit (a) numeric telegrams which include message information coded in a first format and which include a first type indicator and (b) alphanumeric telegrams which include message information coded in a second format and which include a second type indicator.

8. A paging system according to claim 7, where the telegrams are POCSAG telegrams.