Method of detecting a paging channel in a multi-frequency radio pager network

Abstract: In order to detect a paging channel assigned to a pager in a shorter time in a frequency divided pager network system, a plurality of paging channels given priorities in channel searching are separately assigned to the paging areas in manner wherein reuse is avoided. A frequency subset number and frequency subset indicators related thereto, are memorized in a pager. Subsequently, paging channels available in the system are allocated to the frequency subset indicators. Further, a relationship between the frequency subset indicators and the corresponding paging channels is tabled and then stored in the pager. Then, the paging channels are assigned to the paging areas according to the relationship. The above mentioned paging channels given priorities in channel detection are monitored which are transmitted to the pager. In the event that the pager detects one of the paging channels with priorities, the pager is tuned to other paging channels according to the relationship.

Description: The present invention relates to methods of allocating and detecting a paging channel in a multifrequency radio pager network in which the overall service coverage is divided into a plurality of small paging areas. More specifically, the present invention relates to such a method in which the paging channel to be detected in a given paging area is dynamically assigned to one of a number of frequency subset indicators. The frequency subset indicators are related to one frequency subset number. It is known in the art that a radio pager is a device which alerts a subscriber to a call on a predetermined phone number by means of sound and/or flashing light. Recently, in order to transmit more pieces of information to a subscriber in one calling operation, a radio pager which is equipped with a display function has proved very popular and is gradually replacing the above-mentioned older-style pagers. A radio paging system currently in use is designed such that pager is able to receive its paging messages, via a predetermined paging channel, throughout an entire service coverage to which the subscriber has subscribed. In other words, there exists no radio pager system in which the service coverage is divided into a plurality of small paging areas and in which a pager uses different frequencies in different paging areas. However, merely by way of example, the European Telecommunications Standards Institute has proposed to provide frequency-divided network operations in the European Radio Message System (ERMES). This frequency-divided network operation implies that adjacent paging areas use different frequencies. Within one network a pager should use different frequencies in different paging areas. In the frequency-divided (viz., multifrequency) network, each of the pagers is informed on which channel to expect its messages. This is accomplished with a combination of a frequency subset indicator (FSI) transmitted in a system information partition to all pagers and a frequency subset number (FSN) permanently stored in the pager. Figure 1 is a chart which depicts the format of the paging signal which is transmitted to the pagers in the ERMES. The code format shown in Figure 1 starts with a synchronization part which consists of a preamble word (PR) and a synchronization word (SYN). A system information partition comes next which consists of two system information parts (SI, SI') and a supplementary system information part (SSI). The system information partition is followed by address and message partitions as shown. Figure 2 is a diagram which illustrates the relationship between frequency subset indicators (FSIs: 30 to 00) and frequency subset numbers (FSNs: 00 to 15), both of which have been proposed by the above-mentioned ERMES. Each of the pagers is assigned a signal FSN between 00 and 15. Each FSN defines a unique subset of five FSIs as indicated in Figure 2. It is intended that the FSIs are used in descending order. Thus, in the event that a single channel is used within a paging area, the transmitted FSI is set to 30. On the other hand, if two channels are used within a paging area, the transmitted FSIs are set to 28 and 29. The FSI(s) transmitted is located in the system information SI' in the code format of Figure 1. It is assumed that the number of frequency channels assigned to an overall service coverage is 16 and the frequency channels are depicted by F0 to F15. It should be noted that the FSIs do not correspond directly to frequency channel numbers. In more specific terms, the system operator allocates the 16 channels F0 to F15 to the thirty-one FSIs (viz., FSI values of 30 to 00). Thus, the FSI/FSN arrangement renders it possible to have a dynamic number of channels in use. The FSI broadcast on the paging channel indicates that messages will be transmitted for pagers with an FSN in the FSI's subset. For example, when the FSI on a channel equals 27, only messages to pagers with FSNs of 12, 13, 14 and 15 will be carried. Conversely, a pager with FSN=12 should look for its messages only on one of the channels broadcasting FSI values of 12, 22, 27, 29 or 30. These are linked by a heavy line in Figure 2. Merely for the convenience of description it is assumed that: (a) the pager with FSN=12 enters a given paging area; (b) the pager has previously stored FSI values of 12, 22, 27, 29 and 30 in a memory equipped therewith; and (c) four frequency channels F15, F10, F8 and F2 are used in the paging area in question and assigned respectively to the FSIs of 27, 26, 25 and 24. With these assumptions, the pager with FSN=12 has to detect channel F15 which has been assigned to FSI=27, and is then fixed to the channel F15. Thus, the pager begins to search for the channel F15 by subsequently changing the tuning frequencies in a predetermined order using a frequency synthesizer. It is further assumed that the channel searching is implemented in an ascending order (viz., from F0 to F15) by way of example. The pager is firstly tuned to the frequency F0. Since F0 is not in use in this particular case, the pager tuning proceeds to the next frequency F1 which is also unavailable in this case. Following this, the pager is tuned to F2. However, the FSI value of 24 transmitted on the channel F2 has not been assigned to the pager in question and accordingly, the pager is subsequently tuned to the following channel frequencies (viz., from F02 to F15). When the pager is tuned to the channel F15, it eventually detects the FSI=27 in the system information partition (Figure 1) on the channel F15 and is fixed to same and awaits the forthcoming message reception. The above mentioned prior art techniques have suffered from the difficulty in that the number of channel tuning operations is apt to be undesirably large before the assigned channel is detected, and in the worst cast is carried out 16 times. This problem is especially disagreeable in the case where a pager subscriber frequently moves from one paging area to another. Figure 3 schematically illustrates such a case wherein the service coverage is divided into 6 paging areas A1 to A6 by way of example. It is assumed that the paging areas A1 to A6 have been assigned the frequency channels F0, F2 to F4, F7 to F8, F10 to 12 and F14 to F15 as indicated. If a given pager moves from a point M to N along the broken line, as shown, the pager is required to search for the channel assigned thereto every time it enters the adjacent areas. As successively tuned to the channels in a predetermined order and, accordingly the tuning operations are time consuming. International Patent Application No. WO-A-90/03041 describes a multiple frequency message system which transmits coded messages on a plurality of channels. The transmitter system provides at least one channel to be assigned to each of a plurality of geographical areas. The coded message signals transmitted include individual channel identification information and message information being transmitted in a sequence of coded transmission slots on each of the plurality of channels. The sequence of coded transmission slots are transmitted offset in time such that any particular transmission slot is not simultaneously transmitted on any of the plurality of channels. The present invention is defined in the independent claims below, to which reference should now be made. Advantageous features of the invention are set forth in the appendant claims. A preferred embodiment of the invention is described below in which in order to detect a paging channel assigned to a pager in a shorter time in a frequency-divided pager network system, a plurality of paging channels given priorities in channel searching are separately assigned to the paging areas in a manner wherein re-use is avoided. The frequency subset number and frequency subset indicators related thereto are memorized in the pager. Subsequently, paging channels available in the system are allocated to the frequency subset indicators. Further, the relationship between the frequency subset indicators and the corresponding paging channels is stored in the pager. Then, the paging channels are assigned to the paging areas in accordance with this relationship. The above-mentioned paging channels given priorities in channel detection are transmitted to the pager which monitors them. In the event that the pager detects one of the paging channels with priorities, the pager is tuned to other paging channels according to the relationship. More specifically, the embodiment of the present invention is concerned with a frequency-divided pager network system whose service coverage is divided into a plurality of paging areas. A paging channel is separately determined for each of the paging areas in connection with each of the pagers. The pager is previously assigned to one of a plurality of frequency subset numbers. The paging channel is assigned to one of a plurality of frequency subset indicators which are related to the frequency subset number. A method embodying the present invention comprises the steps of: (a) selecting a plurality of priority paging channels (F0-F5) from among the N pager channels; (b) allocating the plurality of priority paging channels to the plurality of paging areas on a one-to-one basis such that no priority paging channel is assigned to two adjacent paging areas; (c) allocating the paging channels other than the priority paging channels to the FSIs corresponding to each of the paging areas; and (d) storing information in each of the pagers indicating the allocating of the paging channels to the FSIs corresponding to each of the plurality of paging areas. The features and advantages of the present invention will become more clearly appreciated from the following description taken in conjunction with the accompanying drawings in which like elements are denoted by like reference numerals and in which: Figure 1 is a chart depicting a format of the signals which are applied to a pager, this figure being applicable to both the prior art and the present invention and having been referred to in the opening paragraphs of the present disclosure; Figure 2 shows an FSI/FSN relationship which has been discussed in the opening paragraphs of the present disclosure; Figure 3 is an illustration depicting the movement of a subscriber into and out of a number of different subscriber areas; Figure 5 to 10 are diagrams each showing a respective FSI/channels relationship for illustrating the present invention; and Figure 11 is an illustration depicting allocation of paging channels in paging areas according to the present invention. Referring now to Figure 4, there is shown in block diagram form a hardware arrangement of a pager 10 to which the present invention is applicable. It is assumed that the pager 10 has not yet been tuned to the channel which has been assigned thereto. It is necessary, therefore, to ascertain the correct channel for enabling the pager 10 to receive paging messages directed thereto. This operation is required in the event that the pager 10 is initially energized due to the replacement of its battery or if the pager 10 is transported into an adjacent paging area, etc. As shown in Figure 4, a front end ( viz. , radio section) 12 is provided for amplifying and demodulating a code-modulated carrier wave ( viz., channel frequency) received by an antenna 14. The front end 12 comprises a high frequency amplifier, a frequency converter, an IF amplifier and a discriminator (not illustrated in Figure 4). The front end 12 is tuned to one of the above mentioned channels F0 to F15 (for example) under the control of a frequency synthesizer 13 and a controller ( viz., CPU (Central Processing Unit)) 22. In the event that the front end 12 is successfully tuned to an incoming carrier wave, the output of the front end 12 is applied to a decoder 16. Otherwise, the controller 22 instructs the front end 12 to proceed to the next channel frequency using the synthesizer 13. These operations are repeated until the front end 12 is successfully tuned to the incoming channel frequency. The decoder 16 is arranged to compare an FSI transmitted on the "tuned" channel with one of the FSIs which have previously been assigned to the pager 10 and stored in a memory 18. The FSI transmitted is located in the section SI' of the system information partition (Figure 1). The FSIs in the memory 18 are written thereinto from a non-volatile memory 20 when the pager 10 is switched on. The FSIs stored in the pager 10 will be referred to in more detail later. If the decoder 16 fails to detect a match of the aforesaid two FSIs, the controller 22 instructs the front end 12 to tune to the next channel using the synthesizer 13. On the other hand, if the decoder 16 detects that the received FSI on the "tuned" channel coincides with one of the FSIs stored in the pager 10, the controller 22 fixes the tuning frequency ( viz. , channel) at the front end 12 and thus terminates the channel search operations. Following this, the pager 10 enters into a standby mode for receiving any paging messages directed thereto within the paging area wherein the pager 10 has ascertained the coincidence of the two FSIs. After the pager 10 has entered into the standby mode, when it receives a signal transmitted over the paging channel which is fixed by the above mentioned operations, the decoder 16 proceeds to compare an incoming pager address code with a pager ID (Identification) code stored in the memory 18. The pager ID code in the memory 18 is written therein from the non-volatile memory 20 when the pager 10 is switched on. In the event that the incoming pager address code coincides with the pager ID code, the decoder 16 applies a message signal, which follows the coincident pager address code, to the controller 22. Subsequently, the controller 22 energizes a speaker 24 by way of a speaker driver 26. Although not shown in Figure 4, a light source such as an LED (Light Emitting Diode) or the like may be installed to provide a visible signal in addition to the audible one produced by the speaker 24. Further, the controller 22 stores the message in a RAM (Random Access Memory) 28 and simultaneously induces the same to appear on a display 30 using a display controller 32 in a manner known in the art. The controller 22 is arranged to control the overall operations of the pager 10 using a program which is previously stored in a ROM 34. The present invention will be discussed in more detail with reference to Figures 5 to 11. As mentioned in the opening paragraphs of the present specification, all pagers are assigned an FSN between 0 and 15. Thus, each FSN defines a unique subset of five FSIs as indicated in Figure 2. It is assumed that the service coverage of a multi-channel pager network is divided into six paging areas A1 to A6 as schematically shown in Figure 11. According to an embodiment of he present invention, each of the FSIs 00 to 03 and 14 to 30 is assigned a paging channel in each of the paging areas A1 to A6 as shown in Figures 5 to 10 respectively. The relationship of each of the FSIs and the corresponding paging channels shown in Figures 5-10 is previously allocated and stored, in the form of a look-up table, in the non-volatile memory 20 of each pager (Figure 4). Further, the paging channels F0 to F5 are priority paging channels which are separately assigned to the paging areas in a manner wherein re-use is avoided as shown in Figure 11, that is, no priority paging channel is assigned to two adjacent service areas. When the pager 10 in one of the paging areas A1 to A6 is required to ascertain the paging channel through which paging messages directed to the pager 10 are received, the pager 10 is sequentially tuned to the channels F0 to F5 in an ascending, descending or other suitably determined order. Since each paging area A1 to A6 is assigned to one of the channel F0 to F5, the pager is eventually tuned to one of the channels F0 to F5 after at most five channel searches. It is assumed in this example that the pager with FSN=12 initiates the channel search while located in the paging area A1 to which the main or priority channel F0 has been allocated (Figure 11). Accordingly, the pager 10 is tuned to the channel F0. In this instance, although F0 is in use as shown in Figure 11, the pager 10 with the FSN=12 fails to detect coincidence between the transmitted FSI=28 and any of the stored FSIs=30, 29, 27 and 22. Accordingly, the front end 12 is directly tuned to the channel F11 in the next step in this particular case, as it contains stored information indicating the allocation of the paging channels to the FSIs corresponding to each of the paging areas A1 to A6. Thus, the pager 10 detects the coincidence of the FSI=29 transmitted over the channel F11 with the FSI=29 stored in the pager. This means that the pager 10 is able to ascertain F11 as the channel assigned thereto. Subsequently, the pager 10 enters into a message waiting mode. It is noted in Figure 5 that a pager grouped into the FSN=00 is only tunable to the channel F0. Conversely, a pager related to the FSN=15 can be tuned to one of the five channels F0, F11, F13, F14 and F15. Therefore, many more pagers can be assigned to the FSN=15 relative to those assigned to the FSN=00. The above discussions are applicable to other pagers with FSNs other than FSN=12 and also to the other paging areas A2 to A6 to which main or priority channels F1 to F5 are assigned respectively. In the foregoing, the so-called priority channels which are firstly searched for are by no means limited to F0 to F5 and also the number thereof is not limited to six. Further, the relationships between the FSIs and the channels corresponding thereto, shown in Figures 5 to 10, are merely exemplary and not restricted thereto. That is to say, the FSI/channel relationship can be altered to comply with situations which require modifications. It will be understood that the above disclosure is representative of only one possible embodiment of the present invention and that the concept on which the invention is based is not specifically limited thereto.

Claims: A method of allocating pager channels (F0-F15) to a plurality of paging areas (A1-A6) in a multi-channel radio pager network system, wherein each pager is previously assigned one frequency subset number (FSN) from among a plurality of predefined FSNs, wherein N pager channels are available, each of the FSNs defining up to M frequency subset indicators (FSIs) and the FSIs being defined in the form of a tree with M levels; the method comprising the steps of: (a) selecting a plurality of priority paging channels (F0-F5) from among the N pager channels; (b) allocating the plurality of priority paging channels to the plurality of paging areas on a one-to-one basis such that no priority paging channel is assigned to two adjacent paging areas; (c) allocating the paging channels other than the priority paging channels to the FSIs corresponding to each of the paging areas; and (d) storing information in each of the pagers indicating the allocating of the paging channels to the FSIs corresponding to each of the plurality of paging areas. A method according to claim 1, further comprising the step of storing in a pager the frequency subset indicators which correspond to the frequency subset number assigned to that pager. A method according to claim 1 or 2, further comprising the steps of monitoring the priority paging channels transmitted to a pager, and tuning the pager to paging channels in accordance with the frequency subset indicators transmitted in a detected one of the priority paging channels. A method according to claim 1, 2 or 3, wherein there are N predefined FSNs. A pager for use in the method of claim 1, the pager being assigned an FSN and including a non-volatile memory (20) storing (i) between one and M FSIs defined by the assigned FSN, and (ii) information indicating the allocation of the paging channels to the FSIs for each of the plurality of paging areas.

Inventors: MATSUMOTO MARIKO, MATSUMOTO, MARIKO, MATSUMOTO, MARIKO, C/O NEC CORPORATION
Applicants: NIPPON ELECTRIC CO, NEC CORPORATION
Application year: 1992
Main classification: H04Q7
IPC codes: H04B7, H04W88