Paging method and apparatus

ES 2 227 551 T3

DESCRIPTION

People search method and apparatus.

Background of the invention

1. Scope

The present invention relates to the search for persons in communications, and in particular to an apparatus and a bidirectional method of searching for persons.

two. Related art and other considerations

During the last decades, paging devices have proven to be an important communication device for contacting people far away. While early paging devices basically provided only acoustic and / or vibratory output, many modern paging devices have improved their output capabilities such as alphanumeric displays that carry a message.

People search systems have historically been one-way systems. That is, the user receives a paging message from a central terminal but has no way of responding to that message with the paging device. Prior art attempts to provide two-way communication capabilities to a paging device have included efforts to connect the paging device to a telephone (eg, a mobile radiotelephone). See, for example, US RE 33,417 to Bhagat et al. (combining a complete paging device and a radiotelephone, connected by an automatic dialer) and US Patent 5,117,449 to Metroka et al. (proposing to combine cellular radiotelephony and paging functions in a single unit).

Some paging devices have the ability to provide an acknowledgment, or response, to a paging signal. In some "acknowledged" systems of this type, a user operates a device to respond to an input (eg, a toggle switch, pushbutton switch, or keyboard) when searched. Typically, acknowledged systems of this type involve a complex acknowledged transmission scheme, involving numerous frequencies or frequency subbands. Inter-station handover of the paging device, as the paging device moves between different geographic regions or "cells" served by different central stations, becomes technically cumbersome when multiple frequencies are involved.

US-A-5 111 197 (D1 for short), discloses a paging system comprising a predetermined number of paging terminals, each producing a subscriber identification number, a zone signal service, and a frequency signal, corresponding respectively to a subscriber number, to a pager processor to distribute subscriber identification numbers received from paging terminals to a predetermined number of pager service areas and to a predetermined number of time slots, in accordance with the signals service area and frequency, and to a predetermined number of transmitters for radioing the paging signals arranged in each of the paging service areas, so that at least two paging signals having different frequencies, which have been Obtained by modulating at least two of the subscriber identification numbers, they are radiated in two adjacent paging service areas in one of the time slots. In the paging system according to D1, ringing signals of the same frequency of the paging signal can be used in more than two service areas.

Document US-A-5,206,855 (D2 for short), discloses a transmitter system for transmitting encoded message signals on a plurality of channels of which at least one channel is to be assigned to each of a plurality of geographic areas. The encoded message signals include channel and identification information and message information, being transmitted in a sequence of encoded transmission slots on each of the plurality of channels. The sequence of coded transmission slots is transmitted with a time offset such that a particular transmission slot is not transmitted substantially simultaneously on any channel of the plurality of channels. Also, a receiver capable of receiving the scrambled message signals during a scrambled transmission slot that is transmitted on the plurality of channels is described. The receiver includes a channel selector circuit capable of responding to the detection of a predetermined channel identification information, transmitted during the predetermined coded transmission slot on the predetermined channel, to maintain reception during the predetermined coded transmission slot on the channel. predetermined. The receiver also includes a memory for storing active channel information for a given geographic area, and the channel selector circuit is capable of responding to the active channel information to select the reception only of the active channels in the particular geographic area, when the channel identification information detected during the predetermined encoded transmission slot in the predetermined channel does not match a predetermined channel identification information.

US-A-5,276,703 (D3 for short) discloses a local area network that includes at least one hub unit, at least one associated station unit, and a wireless communication link between each concentrator unit and its associated station units. The communication link includes a downstream wireless channel for transferring information from each hub unit to its associated station units and an upstream wireless channel for transferring information from each station unit to its associated hub unit. Communication is performed according to a combination of time division multiplexing and a collision-based protocol. A common and synchronized time slotted frame between each concentrator unit and its associated station units is imposed by the concentrator unit.

Document US-A-5,297,144 (D4 for short), discloses a wireless data communications network that has a user number

ES 2 227 551 T3 rios communicating from remote individual stations to a central station over an infrared optical single channel using a non-collision-based two-stage multiple access communications protocol. During the first stage of the reservation-based interrogation protocol, the central station provides a synchronization signal to the remote station to define the start of a "reservation request period," and distributes fixed time slots, during which any station remote that has a data message to transmit, it can request access and reserve a part of the channel for its data messages. During the second stage or "interrogation data transfer period", the central station interrogates only those remote stations that have a data message to transmit and that have requested access to the channel. In response to the polling, the polled remote stations transmit their data messages in their previously reserved data slots. If desired, the central station can also return an acknowledgment signal to remote stations after successful reception of each data message.

Document US-A-5,521,925 (D5 for short), describes a system that integrates a terminal traffic in a cellular digital voice radio communication system. Data is transported from remote data stations and from remote radiotelephone stations over a reverse channel TDMA frame. The distribution of the time slots in the reverse channel TDMA frame is controlled at the base station. The base station gives priority to radiotelephones that have digitized voice traffic. The base station allocates time slots within the reverse channel TDMA frame based on distribution requests received from the radiotelephone stations and from the remote data stations. Remote data stations can collide in random access for a minority of a set of time slots in the reverse channel data frame. In addition, they can request an allocated slot by inserting a dispatch request into a control slot of the reverse channel data frame. The base station distributes the time slots according to a voice radiotelephone priority, and allocates any excess time slots to the data stations waiting to access the reverse channel.

Data Networks publication, pages 312-317, by Dimitri Bertsekas and Robert Gallagher, Prentice Hall, Inc., Upper Saddle River, New Jersey 07458,2^to 1992 edition (D6 for short), describes multiple access reservations, and in particular a way to increase the overall data transfer rate of multiple access channels. D6 also describes a simple satellite reservation system.

Summary

A two-way pager system uses four local frequencies for transmissions between pager units and a central control station. A first local frequency carries a local clock; a second local frequency carries communication packets from the central control station to the paging units; a third local frequency carries communication packets from the paging units to the central control station; and a fourth local frequency carries a request or status signal from the paging units to the central control station. The transmissions on the fourth local frequency are in accordance with a time-divided slot distribution among the pager units accessing the central control station.

For a bi-directional paging system having a plurality of central control stations serving a corresponding plurality of cells, a total of eight frequencies are used within any cell. Four of the frequencies used are local frequencies, (which may differ from cell to cell), and four of the frequencies used are common lower power frequencies or switching frequencies that are used for switching or handover of a unit of power. search for people moving from one cell to another.

Brief description of the drawings

These and other objects, features, and advantages of the invention will become more apparent from the following more particular description of the preferred embodiments, as illustrated in the accompanying drawings, in which the reference characters indicate the same parts through all the different views. The drawings are not necessarily to scale, emphasis being placed on illustrating the principles of the invention.

Figure 1 is a schematic view of a central control station included in a paging system of an embodiment of the invention.

Figure 2 is a schematic view of a pager unit included in a pager system for use with the central control station of Fig. 1.

Figure 3 is a flow chart showing the steps performed by the central control station of Figure 1.

Fig. 4 is a flow chart showing the steps executed by the pager unit of Fig. 2 when it is in a transmission mode.

Fig. 5 is a flow chart showing the steps executed by the pager unit of Fig. 2 when it is in a receiving mode.

Figure 6 is a timing diagram reflecting the communications between the central control station of Figure 1 and the paging unit of Figure 2.

Figure 7 is a schematic view of a central control station included in a paging system of a second embodiment of the invention.

Figure 8 is a schematic view of a pager unit included in a pager system for use with the central control station of Fig. 7.

Figure 9 is a hybrid of a schematic view and a timing diagram, to represent switching operations for the paging system of the second embodiment of the invention.

Fig. 10 is a flow chart showing the steps executed by the pager unit of Fig. 8 in relation to a channel switching operation.

ES 2 227 551 T3

Figure 11 is a flow chart showing the steps performed by the central control station of Figure 7 in relation to a channel switching operation.

Figure 12 is a schematic view of a communication packet format used with different embodiments of the invention.

FIG. 13 is a schematic view illustrating a time split slot distribution technique in accordance with the invention.

Detailed description of the figures

Figure 1 shows a central control station 20, according to a first embodiment of the invention; Figure 2 shows a pager unit 22 suitable for use with the central control station 20.

As shown in Figure 1, the central control station 20 comprises a central computer 30; a transmitter 32; a receiver 34; and a computerized answering telephone system 36. Transmitter 32 transmits, through transmitting antenna 42, two local frequencies, namely frequency fi and frequency f₂. Receiver 34 is connected to receiving antenna 44 to receive two local frequencies, namely frequency f₃ and the frequency f₄. The computerized answering telephone system 36 is connected to a bank of telephones 48.

The central computer 30 of the central control station 20 comprises a conventional computer equipped with typical components, including a CPU 50; an I / O interface 52; and a memory 54. Although shown only generally in Figure 1, it should be understood that memory 54 includes a number of memory devices not illustrated, including (for example) a hard disk drive, a RAM, and a ROM. . FIG. 1 shows that the memory 54 has stored therein (among other things) a log file 55 of the pager device and a directory file 56 of the pager device. Files from pager 55 and 56 are typically stored on a host computer hard disk drive 30, and after startup are loaded into a RAM portion of memory 54.

The central computer 30 of the central control station 20 further includes a decoder 57 (connected between the receiver 34 and the I / O interface 52 to decode an incoming communication information from one or more pager units 22), thus as an encoder 58 (connected between I / O interface 52 and transmitter 32 to encode outgoing communication information).

The central control station 20 also includes a clock unit 59 that generates a local clock signal f₁clk (which, in turn, is used to modulate the fi frequency).

As further illustrated in this case, the CPU 50 of the central control station 20 prepares the communication packets for transmission on the frequency f2. As generally illustrated in figure 12, the communication packets are of a predetermined format, having fields for the identification of the central control station, for the identification of the paging unit (s) 22 addressed (s), for an operation code, for (optionally) alphanumeric information, and for other conventional packet type information such as a checksum, an error correction, and a postamble. The preamble and postamble are specially selected patterns that can be recognized and distinguished from the data for the purpose of determining the beginning and end of a packet. The alphanumeric information can be in a custom 8-bit binary format. The format of Figure 12 is only illustrative, since this type of information, as well as the order of the fields, can be varied in other embodiments.

Central control station 20 communicates with a plurality of pager units 22₁, 22₂,... 22_n. Only such a people search unit, generally referred to as people search unit 22, is specifically illustrated and described in this case, it being understood that the construction and operation of other people search units may be similar to that illustrated.

As shown in FIG. 2, pager unit 22 includes a receiver antenna 60 of the pager device that is connected to receiver 62 of the pager device. Receiver 62 of the pager device is, in turn, connected via S / D converter 64 within computer 70 of the pager device. Receiver 62 receives the two local frequencies f1 and f2, which frequencies have been modulated to carry incoming communication information (described in more detail below) to a computer 70 of the paging device. On a communications broadcast side, the paging device computer 70 broadcasts outgoing communications information to a paging device transmitter 72 through the D / S converter 74. Transmitter 72 radiates, through antenna 76, outgoing communication information on the two local frequencies fs and f4.

As also shown in FIG. 2, the paging device computer 70 includes a paging device microprocessor 80 that is connected to each of the arithmetic processors 82; a memory system 84 (including both a ROM and a RAM); and an I / O interface 86. The I / O interface 86 is connected to a clock unit 87. The I / O interface 86 is also connected to receive incoming decoded communications information from an 8-bit decoder 88 and to output outgoing decoded communications information to an 8-bit encoder 90. Decoder 88 is connected to receive incoming scrambled communications information from S / D converter 64; encoder 90 is connected to broadcast outgoing encrypted communications information to a D / S converter 74.

The clock unit 87 is adjustable by means of appropriate inputs thereto, so that the clock unit 87 generates a local clock signal f₁clk which has a frequency corresponding to its input. It should be understood that, in other embodiments, the function of the clock unit 87 can be performed, at least partially, by the microprocessor 80, using a scheduled execution.

I / O interface 86 is also wired to supply an on / off signal on line 92 to transmitter 72 of the pager device.

ES 2 227 551 T3 nas, as well as to facilitate entry and exit with numerous input / output devices. The input / output devices connected to the I / O interface 86 include a keyboard 93; a buzzer 94; a vibrator 95; and an LCD display (alphanumeric) 96.

After its manufacture, the person search unit 22 is pre-programmed with a plurality identification number (eg, a 7-digit pre-assigned alphanumeric ID number) that is stored in memory 84 (ROM). The people search unit 22 is activated (for example, at the time of purchase) by inserting a time slot assignment (explained below) both at a predetermined address in the memory 84 of the people search unit persons 22 and within the directory file 56 of the paging device (stored in the memory 54 of the central control station 20).

Operation of the first embodiment

Communication between the central control station 20 and the paging unit 22 occurs on the four local frequencies, in particular, the frequencies f₄, f₂, f₃ and f₄ mentioned above. The first frequency (f) carries the local clock synchronization signal from the central control station 20 to the pager unit 22. The second frequency (f₂) carries a paging device instruction and alphanumeric data from central control station 20 to paging unit 22. The third frequency (f₃) carries paging device status data and alphanumeric data from paging unit 22 to central control station 20. The fourth frequency (f4) carries a paging device request signal from paging unit 22 to the central control station 20. In the illustrated embodiment, the frequencies I ', -f₄ are preferably selected such that f ^ f₂^ f₃^ f₄.

As explained in greater detail below and as illustrated in Figure 13, in normal operation without cell switching, the request signal from the paging device on frequency f4 is transmitted in a predetermined time slot assigned to the unit. people search 22. The default time slot on frequency f₄ is related to the clock synchronization signal (carried by the frequency f₄) and assigned such that the fourth frequency is usable by a plurality of other pager units. For example, as shown in Figure 13, a first time slot on frequency f4 is assigned to a paging device P1; a second slot is assigned to a pager device P2, and so on, up to time slot n assigned to a pager device P_n. In the illustrated embodiment, the number of time slots (and, accordingly, the number of paging devices) can be as much as ten thousand or more.

Figure 3 shows the steps executed by the CPU 50 of the central control station 20 in the process of communications to and from one or more pager units. The steps shown in Figure 3 are indicative of instructions stored in a ROM portion of memory 54 of central control station 20.

When the central control station 20 comes into operation (step 100), an initialization procedure is performed (step 102). Included in the initialization procedure is the activation of transmitter 32 (so that transmitter 32 can transmit on both frequencies f, and f₂) and the activation of the receiver 34 (so that the receiver 34 can receive the two frequencies f₃ and f₄). In addition, the frequency f, is modulated to carry the clock synchronization signal generated by the local clock 59. Next, in step 104, the paging device log file 55 and the paging device directory file 56 are loaded. from the hard disk into the RAM section of memory 54 (step 104).

After initialization and loading of files 55 and 56, CPU 50 repetitively executes an instruction loop 106. Loop 106 involves a check to determine (at step 108) if a phone message is being received (through answering system 36, from one of the phones in bank 48) and a check to determine (at step 110) if a message is being received from the paging device (through the transmitter 32 from one of the paging units 22).

As used in this case, a message, whether originated from a telephone or from a paging device, may require a plurality of packets for transmission from a central control station 20 to a paging unit 22 or vice versa. . In the ensuing discussion, transmission and reception of messages means transmission and reception of one or more packets. In general, the division of messages into packets will be transparent to the user, meaning that a user enters a message without taking into account the number of packets that will be required to transmit the message. The message typically ends with a message completion character or with a user-entered message separator character. The transmitting device (either the central station 20 or the paging device 22), distributes the message according to one or more packets that have a format similar to that of figure 12, with the last packet in the message carrying the termination character message. Alternatively, the packets may be formatted in a way that indicates the number of consecutively related packets leaving a transmitter (eg, there may be a separate packet field indicating the continuation number of the related packets).

The central computer 30 can distinguish between the receipt of a telephone message (at step 108) and a message from the paging device (at step 110) as to the fact that the I / O interface 52 generates different types of interrupts to CPU 50, depending on the type of message received. If it is determined in step 108 that a telephone message is being received, steps 112, 114 and 116 of FIG. 3 are executed.

In the process of a received telephone message, in step 112 the central computer 30 extracts the outgoing communication information from the data entered by telephone in a predetermined sequence. The data entered by telephone, entered through a keyboard of

ES 2 227 551 T3 a phone of bank 48 that is calling, includes by convention an identification (for example, the telephone number) of the called pager unit (for example, the alphanumeric number previously assigned 7-digit ID) ; and any character data for transmission followed by an end character. This outgoing communication information is received at the central computer 30 in the standard DTMF format.

In step 114, using the ID number of the called paging device (obtained in step 112), the central computer 30 checks the log file 55 and the directory file 56 of the paging device, to determine whether the paging unit call is registered with central control station 20. Assuming that the called paging device is registered in this way, in step 114 the central computer 30 also obtains, from the directory file 56 of the paging device, the time slot distribution of the called pager unit.

In step 116, the central control station 30 transmits communication information to the called paging unit. In this regard, the central control station 20 prepares and transmits (on the frequency f₂) a communications message including, among other things, the ID of the called paging unit and the character data received from the telephone for transmission of the paging unit 22. After the execution of the step 116, the procedure returns to loop 106.

If it is determined in step 110 that a message is being received from the paging device, the even numbering steps 132-140 of FIG. 3 are executed (before returning to loop 106). As will be seen hereinafter with respect to FIG. 4, a transmitting paging unit 22 transmits, in its assigned time slot, a request signal on the frequency f₄ when the sending pager unit 22 wishes to send a message. Since the central control station 20 is always monitoring the frequency f₄, a request signal carried on frequency f4 from any paging unit 22 is indicated. Relative to local clock 59, in step 132, CPU 50 determines in which time slot, at frequency f₄, the request signal is detected. After detection of the time slot in step 132, in step 134 the CPU 50 queries the directory file 56 of the paging device to determine the identification number of the particular sending pager unit 22 that originated the signal. of request.

With the now known identity of the requesting pager unit 22, in step 136 the central control station 20 authorizes the requesting pager unit 22 to transmit its message. In particular, CPU 50 governs the preparation of a communications message for transmission on frequency f2. The particular communications packet prepared in step 136 includes an identification of the requesting person search unit (the recipient of the packet), as well as an operation code (code "op") that commands / authorizes the search unit of requesting 22 people sending your message.

In step 138, the central control station 20 receives a communications message on frequency f₃ sent from the sending pager unit 22 (for example, to make a request). The communications message prepared and sent by the sending pager unit 22 includes packets of a format similar to that shown in figure 12, and includes an identification of a paging device to which the message is ultimately destined, as well as its own identification. At step 138, CPU 50 performs a check to ensure that the final recipient pager unit is registered in the paging device files 55 and 56. At step 140, CPU 50 performs any reformatting and / or replacement. information necessary in the message, and causes the message to be transmitted on the frequency f₂. Transmission on frequency f₂ required by step 140 includes the identification of the final recipient (eg, a pager unit 22), as well as an operation code indicating that the transmission includes a message relayed from another pager unit.

The steps performed by a pager unit 22 in relation to its transmission mode are shown in FIG. 4. The steps executed by a pager unit 22 in relation to its reception mode are shown in FIG. 5. The term "mode", as used in this case, does not have the connotation of exclusivity at any particular time, so it should be remembered that at all times the pager unit 22 is receiving transmissions on the frequencies fi and f₂.

In its transmission mode (see Figure 4), after startup (step 200), the microprocessor 80 of the transmitting pager unit 22 executes a loop 202 in which some alphanumeric user characters (entered through the keyboard 93) are repeatedly extracted (at step 204) until an end-of-message separator is detected (at step 206). As entered, the characters extracted at step 204 are displayed on LCD 96. Entering the separator character at step 206 causes microprocessor 80 to exit loop 202. By convention, the message must include a recipient ID. , Recipient ID which is probably the ID of another of the search units of persons to which the message entered in step 204 is destined.

After the input of the message, the input from the keyboard 93 of a transmission instruction in step 212 is awaited. Assuming that the transmission instruction is entered in step 212, the microprocessor 80 prepares and sends a request signal in the frequency f4. As indicated above, the request signal is transmitted on frequency f4 in a time slot assigned to the requesting pager unit 22. It should be noted that the paging unit 22 is all the time receiving the clock synchronization signal on the frequency fi, which allows the microprocessor 80 to cause the transmission of the request signal on the frequency f4 at a corresponding time. to the specific time slot assigned to the particular broadcast pager unit 22.

In this regard above, in accordance with the technical

ES 2 227 551 Time division t3, each person search unit 22₁ -22_N (for example, paging devices P₁ -P_n in figure 13) is assigned to a selected one of a number N of time slots at frequency f₄.

After the transmission of the request signal in step 214, the paging unit 22 awaits the reception of a transmission instruction from the central control station 20. The preparation and transmission of the transmission order / authorization from central control station 20 is described in relation to figure 3. After receiving the transmission order / authorization from the central control station 20 (step 216), the microprocessor 80 prepares (in step 218), a communications message with one or more packets that have a format more like that of figure 12. The recipient ID and the alphanumeric field of the communications message packets is adapted to the message entered in loop 202. In step 220, the broadcast paging unit 22 broadcasts the communications packet on the frequency f₃.

If no transmission instruction is entered in step 212, or after transmission of the message in step 220, the microprocessor 80 waits for the entry of at least one of several possible special function keys in step 222. For example, the user may press a function key that requests storage of the message (whether or not it has been transmitted) [see step 228]. Alternatively, the user can press function keys that make it easy to edit or delete the message (see steps 224 and 226, respectively). To complete the message and start working on another message, a special function key must be pressed for an output operation (step 230).

Figure 5 shows the steps executed by the microprocessor 80 of the paging unit 22 when it is in receiver mode. After startup (step 302), and as indicated by step 304, pager unit 22 receives transmissions from central control station 20 on frequency f₂. Once a complete packet has been received (determined in step 306), a check is made (in step 308) as to whether the recipient ID in the communications packet (see the packet format of Figure 12) is the ID of the receiving paging unit 22. If the determinations of both steps 306 and 308 are negative, the paging unit 22 waits either for the communication packet to be completed (in the case of step 306), or for the reception of another packet of calls. communications (in the case of step 308) by looping back to step 304.

Assuming that the received communications packet is designated for this particular receiving pager unit 22, in step 310 the microprocessor 80 queries the opcode field of the communications packet (see Figure 12), to determine if the code Operation indicates that the message includes an instruction. If the opcode indicates an instruction, an instruction processing routine is executed (framed by dashed lines 312 in FIG. 5).

Assuming for the moment that the opcode does not indicate an instruction, in step 314 the microprocessor 80 of the people search unit 22 stores the alphanumeric field portion of the communications packet (which forms the message, at least in a partial) in a RAM portion of memory 84. Because a message communicated from central control station 20 may require multiple communication packets to complete the message (with subsequent communication packets providing a continuation of the message content), microprocessor 80 checks in step 316 for ensure that the entire message has been received. Otherwise, the process continues to return to step 304 to receive an additional communication packet.

After receipt of a complete communications message, in step 318 the microprocessor 80 determines whether the pager unit 22 is in a buzzer mode or a vibrator mode. In this regard, there are many ways to set the pager unit 22 to the desired mode, both by means of a specially dedicated switch on the pager unit 22, and by entering data using the keyboard 93. If the pager unit 22 is in a buzzer mode, the microprocessor 80 outputs a signal that causes the I / O interface 86 to output an additional signal to activate the buzzer 94 (step 320). Alternatively, if the pager unit 22 is in a vibrator mode, the microprocessor 80 outputs a signal that causes the I / O interface 86 to output an additional signal to activate the vibrator 95 (step 322).

In step 324, the microprocessor 80 governs the I / O interface 86 to send the alphanumeric message data to the LCD screen 96, so that the received message can be viewed by the user.

After notification to the user (both through buzzer 94 and / or vibrator 95), and display (on LCD 96) of the received alphanumeric data, microprocessor 80 returns to step 304 to check if it has been received. additional communications packages.

The instruction processing routine (outlined by dashed lines 312 in FIG. 5) first determines (step 330) which particular operation is being commanded. This determination is based on the content of the opcode, which is different for different types of instruction. If the opcode indicates a shutdown due to error, execution proceeds to a shutdown due to error subroutine starting at step 340. If the opcode indicates a timeslot change, execution proceeds to a timeslot change subroutine starting at step 350. If the opcode requires the transmitter to be turned off, execution proceeds to a timeslot subroutine. Transmitter shutdown beginning at step 360. If the opcode requires transmitter wake-up, execution proceeds to a transmitter wake-up subroutine beginning at step 370. If the opcode requires a clock reset, execution proceeds to a clock reset subroutine starting at step 380.

Regarding the subroutine shutdown due to error, in step 342 the microprocessor 80 obtains an indication of the type of error from the communications packet. The type of error is stored in the

ES 2 227 551 T3 memory 84 (step 344) and then is displayed on the LCD screen 96 (step 346). Next, the microprocessor 80 issues an instruction (in step 348) to turn off the pager unit 22, which takes place in step 349.

In relation to the time slot change subroutine, in step 352 the microprocessor 80 extracts, from the received communications packet, information indicative of the new time slot assigned to the receiving person search unit 22. The new one time slot is entered (in step 354) into memory 84 and then used (up to a further change) in connection with the transmission of request signals on frequency f₄ (see, for example, step 214 of FIG. 4). The timeslot change subroutine may also include other operations, if desired, including (for example) removing unused timeslots (thereby increasing the scan speed); performing a fault diagnosis and repair; and avoiding interruption of service due to equipment being damaged or malfunctioning.

In relation to the transmitter shutdown subroutine, in step 362 the microprocessor 80 governs the I / O interface 86 to issue an OFF instruction to the transmitter 72. In relation to the transmitter reactivation subroutine, in step 372 microprocessor 80 governs I / O interface 86 to issue a power ON instruction to transmitter 72.

In relation to the clock reset subroutine, in step 382 the microprocessor 80 governs that the clock 59 of the paging unit 22 is set.

After execution of steps 354, 362, 372, or 382, ​​execution continues to return to step 304 to process potential additional communication packets. In this manner, unless an error shutdown is indicated, each entry of the instruction processing routine (framed by dashed lines 312 in FIG. 5) is followed by a loop back to step 304.

Figure 6 is a timing diagram showing the frequencies fi -f₄, and the integration of the steps shown in Figures 3 to 5, in particular in the context of a request by a sending person search unit P1 to send a message to a recipient person search unit P2. As used in Figure 6, "computer" refers to central control station 20. It should be understood that the sending pager unit P1 and the recipient pager unit P2 operate both in transmission mode, as shown in Fig. 4, and in reception mode, as shown in Fig. 5. In general, Figure 6 shows the transmission of a message from the pager unit P1 (through the central control station 20) to the pager unit P2; transmitting a confirmation message from the pager unit P2 (through the central control station 20) to the pager unit P1; and transmitting a message from the pager unit P1 to the central control station 20 indicating that the pager unit P1 has received the confirmation message from the pager unit P2.

Structure of the second embodiment

Figure 7 shows central control station 420 in accordance with a second embodiment of the invention; Figure 8 shows a pager unit 422 suitable for use with the central control station 420.

Figure 9 shows a wide area paging system including a plurality of central control stations S1-S8 (each identical to central control station 420), each geographically centered, preferably, within a respective cell. . Each central control station S1-S8 broadcasts its own local frequencies, as well as a set of common or switching frequencies C₁-C₄. Common frequencies C₁ -C₄ are radiated at a lower power so that reception occurs only in a relatively small neighborhood or common frequency reception region (CFRR) [also referred to as a "switching region"] around the central control station . The local frequencies are radiated at a significantly higher power, to have reception substantially throughout the cell. For example, in Figure 9, the central control station S1 radiates its lower power common frequencies C₁-C₄ to the CFRR₁ and their common frequencies f₁-F₄ of higher power to CELL1; the central control station S2 radiates its common frequencies C₁-C₄ lower power than CFRR₂ and their higher power local frequencies f₅-F₈ to the CELL₂ .

As also shown in figure 9, the CELL₁ and the CELL₂ overlap in a common coverage region shown in Figure 9. Station S1 uses a different set of local frequencies f₁ -F₄; station S2 uses a set of local frequencies f₅-F₈. Both stations S1 and S2 use the same set of common or switching frequencies C₁-C₄. In this way, each central control station uses two sets of frequencies, with four frequencies remaining in each set, resulting in a total of eight frequencies handled per station.

In this way, the second embodiment of the invention is suitable for a system having a plurality of central control stations 420_{XiX = 1}, 2, .. M · Each central control station 420_xtransmits and receives a set of local frequencies f_L1, f_L2, f_L3, f_L4, in an associated geographic area or cell, as well as the common or switching frequency set C₁, C₂, C₃, C₄. While the values ​​of the local frequencies f_L1, f_L2, f_L3, f_M vary from cell to cell (e.g. differs for different central control stations 420_x), the values ​​of the common or switching frequencies C₁, C₂, C₃, C₄are uniform throughout the system (for example, for all 420 central control stations_x).

Although not shown in Figure 9, it should be understood that the pattern of central control stations is similarly repeated in all cardinal directions in accordance with the prescribed geographic boundaries of the pager system. Furthermore, although not specifically illustrated in FIG. 9, it should also be understood that each central control station 420 has an associated CFRR.

The common or switching frequencies C1 C4 have a function analogous to the corresponding local frequencies f₁-F₄, respectively. To this

With respect to ES 2 227 551 T3, the frequency Ci carries a clock frequency transmitted by the central control station (s), although the clock rate on the common frequency Ci varies preferably according to the central control stations . The frequency C₂ It is used to transmit information from the central control station (s) to the paging units); frequency C₃ It is used to transmit information from a paging unit to the central control station; frequency C₄it is used by paging units to issue a request signal. The C2 frequency carries packets that have a format similar to that of figure 12. In a manner analogous to that of the f2 frequency, the packets transported by the C2 frequency can have instruction codes. Between the C instruction codes₂ there is a SYSTEM INSTRUCTION CODE; a LOCAL FREQUENCY DISCHARGE INSTRUCTION CODE; a SLOT RECOGNITION INSTRUCTION CODE; and a SLOT ASSIGNMENT INSTRUCTION CODE.

As shown in Figure 7, central control station 420 resembles central control station 20 of the embodiment of Figure 1 (similar components have been assigned the same reference numerals for simplicity). However, the central control station 420 is expanded by including an additional transmitter, known as a common frequency transmitter 432, in conjunction with its common frequency transmitting antenna 442, to transmit the common frequencies Ci and C2. Unlike the high power transmitter 32, the transmitter 432 is a low power transmitter. Additionally, the central control station 420 is expanded by including an additional receiver, known as the common frequency receiver 434, in conjunction with its common frequency receiver antenna 444, to receive the common frequencies C₃ and C₄.

The central control station 420 of FIG. 7 includes the clock unit 59 'that generates two clock signals, a first or local clock signal f_Lclk and a second or common C clock signal₁clk. The local clock signal fLclk is used to modulate the frequency f₁; the common clock signal C₁clk is used to modulate the common frequency C₁.

Central computers 30 of central control stations 420_x they are connected in plurality to each other, by an outlet line 486A and an outlet line 486B. In particular, although not shown as expressly as in Figure 7, the central computer 30 of Figure 7 (like that of Figure 1) includes an I / O interface to which the plurality lines 486A and 486B are connected. The plurality lines 486A and 486B are used, for example, to update the contents of the paging device log file 55 and paging device directory file 56.

As shown in Figure 8, the people search unit 422 resembles the people search unit 22 of the embodiment of Figure 2 (similar components have been reassigned to the same reference numbers for simplicity ). However, the pager unit 422 (similarly to the central control station 420) is expanded by including an additional transmitter, known as a common frequency transmitter 572, in conjunction with its common frequency transmitter antenna 576, for the transmission of common frequencies C3 and C4. Additionally, central control station 420 is expanded by including an additional receiver, known as common frequency receiver 434, in conjunction with its common frequency receiving antenna 444, to receive common frequencies C1 and C2.

The operating frequencies of transmitter 72 and receiver 62 are changeable according to values ​​transmitted on "frequency control" lines from computer 70. In particular, the frequency control lines are connected to the I / O interface. S 86 on computer 70. As described in more detail below, when a pager unit 422 transitions to a new CFRR, signals are applied on the frequency control lines to switch pager unit 422 from the local frequencies of a old cell at the local frequencies of a new cell associated with the new CFRR, to which it passes to pager unit 422.

The pager unit 422 includes a clock unit 83 'that is capable of separately generating the local clock signals f_Lclk and common clock signals f_c1clk for use by the microprocessor 80. These clock signals are initiated and their frequencies are set by respective appropriate inputs to the clock unit 83 '.

FIG. 8 also shows that the pager unit 422 has an I / O interface 596 that includes both an alphanumeric graphic display and a pressure sensitive electronic writing surface. The alphanumeric graphic display is a dot matrix device that can display characters and graphics. The keyboard surface has an area of ​​16 x 48 dots.

Operation of the second embodiment

As shown in figure 9, it is assumed that a paging unit P1 has been operating in CELL1 and that it has previously received the common frequencies C₁ -C₄ and the local frequencies f₁-F₂ from station S1. Now, the people search unit P1 travels along a route indicated by a dashed line ending in an arrowhead ROUTE. In traveling along ROUTE, the paging unit P1 continues to operate on the local frequencies f1 f2, even as it travels through the cellular region of common coverage. However, when the paging unit P1 enters a new common frequency receiving region (i.e. the CFRR₂), a switching or handover operation takes place. In the switching operation, as described in more detail below, the paging unit P1 obtains the common frequencies C₁-C₄ from the central control station S2 and as a result you can switch from the local frequencies f_1x-F₄ CELL₁, at local frequencies f₅-F₈ CELL₂. To perform the handover or handover operation, the paging unit P1 executes a channel switching routine; the central control station S2 executes a switching activation routine.

Regarding the channel switching routine and

In the switching activation routine, when the paging unit P1 moves within the CFRR2, the paging unit P1 will receive the clock signal on the frequency Ci from the station S2. At this point, the paging unit P1 will automatically synchronize its clock unit with the clock signal from station S2.

In relation now to the channel switching routine executed by the paging device P1, after it starts up (step 500), in step 506 the paging unit P1 obtains information that characterizes the system centered around station S2. This type of characterizing information is referred to as system identification or system ID information.

In step 508, the microprocessor 80 of the paging unit P1 performs a check to determine if there is any new acquired system ID information on frequency C2. That is, the microprocessor 80 performs a check to determine if the system ID information is received on the C2 frequency (which can only occur in a CFRR) and, if so, compares the system ID information with the information. system ID stored immediately before. If the previous system IDs and the most recently acquired IDs are the same, the paging unit P1 recognizes that it is still in the jurisdiction of the same station (eg, station S1). Otherwise, the paging unit P1 recognizes that it has passed into a CFRR of a new station (for example, station S2) and, in step 510, initiates a request on frequency C4 to communicate with the station. control center (eg station S2) for CELL2.

With respect to the foregoing, since the paging unit P1 has not yet been assigned a time slot for CELL2, the request on frequency C4 is made randomly. However, the paging unit P1 records the time slot in which it makes its request to the new central control station (eg station S2).

Next, the paging unit P1 continues the supervision (step 512) of the communication packets from the station S2 on the frequency C2, waiting for the station S2 to issue a message which is referred to the time slot in the which person search unit P1 made its request from step 510. In particular, the paging unit P1 waits for a message from the station S2 on the frequency C2 that includes both a SLOT RECOGNITION INSTRUCTION CODE, and information stored in the same time slot as the paging unit. P1 has generated randomly. Since the message including the SLOT RECOGNITION INSTRUCTION CODE includes station S2 as the sender and retransmits the slot randomly generated by the pager unit P1, the pager unit P1 recognizes the message as destined towards the paging unit P1 and considers that the emission of such a message by the station S2 (see step 612 of figure 11) grants authority, to the paging unit P1, to further communicate with the station S2. In this regard, in step 514 the microprocessor 80 of the paging unit P1 determines whether there is a match between the time slot of a received message and the time slot to which the random request was made in step 510.

Assuming that a match is finally found in step 514, in step 516 the paging unit P1 sends a communications packet on frequency C₃ to the station S2, with the communication packet including the identifier or ID of the paging unit P1. Using the paging device log file 55, the station S2 verifies that the ID of the paging unit P1 is a valid ID, and then sends (on the frequency C2), to the paging unit P1, a message with the instruction code LOCAL FREQUENCY DOWNLOAD, a message which informs the paging unit P1 of the values ​​of the local frequencies handled by the station S2 (for example, the frequencies f₅ -F₈). Next, as also reflected in step 518, the station S2 sends (on the frequency C2), to the paging unit P1, a message with the instruction code SLOT ASSIGNMENT INSTRUCTION CODE, message which informs to the people search unit P1 of its slot distribution at frequency f8. Next, the microprocessor 80 changes its slot distribution by steps that are similar to those discussed with respect to the previously mentioned time slot change routine (see steps 350, 352, and 354 of FIG. 5). Step 518 of FIG. 10 reflects the reception of the local frequency values ​​and the reception of the slot distribution.

After the acquisition of all local frequencies and the slot assignment has been completed (step 520), the microprocessor 80 implements (in step 522) a switch to the new local frequencies (for example, the frequencies f₅F₈). In this regard, the microprocessor 80 commands the I / O interface 86 to switch to the transmitter 72 from the frequencies f₃, f₄ at frequencies f₇, f₈; and to switch to receiver 62 from frequencies f₁, f₂ at local frequencies f₅, f₆. The I / O interface 86 performs the frequency changes by applying appropriate values ​​to the frequency control lines connecting the I / O interface to the transmitter 72 and to the receiver 62, respectively.

After switching to the new local frequencies in step 522, the microprocessor 80 loops back to step 506, finally to determine when any additional switching may be required.

The steps involved in the switching activation routine executed by a central control station (eg, station S2) is shown in Figure 11. After startup (step 600), CPU 50 executes a loop 602 which allows CPU 50 to clean up its paging device directory file 56 and check if any new paging units have passed into the cell it manages.

In particular, in step 604 the CPU determines whether the central control station (for example, S2) has been notified by any other central control station.

ES 2 227 551 T3 control (for example, S3) that a paging unit, previously under the control of its central control station (for example, S2) has come under the control of the other central control (for example, S3). This type of notification has occurred in the plurality links that connect the central control stations 420_x, and particularly, at the input plurality link 486B. If such notification occurs, the ID for the outgoing paging device is deleted from the directory file 56 of the paging device of station S2 (as reflected by steps 606 and 608).

In step 610, CPU 50 causes messages with a SYSTEM INSTRUCTION CODE to be transmitted on frequency C2. As indicated before, the messages transmitted on the C2 frequency include (s) a packet (s) having (are) a format such as that shown in figure 12. The message with the INSTRUCTION CODE OF SISTEMA includes, in particular, the identification number of the central station in its alphanumeric data field.

In step 612, central control station 420 makes a determination as to whether a request signal has been transmitted by any pager unit 422 on frequency C4 (as occurred, for example, in the context of the discussion of FIG. 10, in particular step 510). This type of request signal would probably be emitted from a person pager unit 422 that has just passed within the CFRR controlled by the central control station (for example, within the CFRR₂ controlled by station S2). If no such request signal is detected, loop 602 is repeated again.

In the event that a request signal is detected in step 612, the central control station 420 specifically indicates the time slot on frequency C4 in which the request occurred (step 614). At this point, such a timeslot is the only way that central control station 420 can identify incoming paging unit 422. Central control station 420 desires incoming paging unit 422 to transmit its identification (ID), but cannot specifically address an incoming paging device other than the one pertaining to the detected time slot. Accordingly, in step 616, the central control station 420 prepares and transmits a message on frequency C2 having a SLOT RECOGNITION INSTRUCTION CODE. The message including the SLOT RECOGNITION INSTRUCTION CODE includes station S2 as the sender and retransmits the slot randomly generated by the paging unit P1 (for example, the time slot in which the paging unit inbound page 422 has issued its request). This transmission on frequency C2 grants authority for the paging unit P1 to transmit its identification.

Step 618 indicates the acquisition by the central control station 420 of the identification (ID) of the incoming paging unit 422. In step 620, the central control station 420 checks its registration file 55 of the paging device for Determine if the ID of the paging device is a valid ID. Otherwise, an error message is generated and transmitted (in step 622), followed by an instruction to the paging unit P1 to turn it off (see step 624).

Assuming that the identification of the pager unit 422 was validated in step 620, the CPU 50 checks (in step 630) its directory file 56 of the pager device to locate an available time slot for the incoming pager unit. 422, and then associates the available timeslot with the ID of the incoming paging unit 422. Next, in step 632, using a message on frequency C2 with a LOCAL FREQUENCY DOWNLOAD INSTRUCTION CODE, the central control station 420 sends the values ​​of its local frequencies (for example, f₅, f₆, f₇, f₈) to the incoming paging unit 422. The central control station then (in step 634) assigns the incoming paging unit 422 a new time slot on its local frequencies, using a message on frequency C2 with a SLOT ASSIGNMENT INSTRUCTION CODE. The process of the time slot change instruction by the incoming paging unit 422 is understood with analogous reference to FIG. 5, in particular steps 350, 352 and 354.

After completing step 634, the incoming paging unit 422 is fully started within its new cell (e.g., CELL₂), and has left the jurisdiction of its previous control station (for example, CELL1 and S1 station). Accordingly, at step 636, CPU 50 requests its I / O interface to issue a command on a plurality line 486A that notifies (using the ID of the paging device) that the incoming paging unit 422 is now under their jurisdiction, so that the above jurisdictions (eg S1) may delete this pager unit from their directory files 56 of the pager device. Such an erasure is understood in relation to steps 604 to 608 as described above.

In addition to illustrating the geographic location of the paging device P1, the stations S1 and S2, and the cells CELL1 and CELL2, Figure 9 shows the relative timing of the communications that occur on common frequencies C1-C4. Figure 9 specifically relates the timing of communication transmissions with the specific steps of the steps described above, executed by the central control station 420 (the switch activation routine of Figure 11) and by the search unit for people 422 (the channel switching routine of FIG. 10).

Although central control stations 420_xuse the same common frequencies C₁ -C₄, there is no interference or confusion of these signals transmitted from the central control stations 420_x. Common frequencies C₁-C₄ they are radiated at a power relatively lower than that of the local frequencies f1 -f4, so that the reception of the common frequencies C1 -C4 occurs only in a limited neighborhood (CFRR), around the central control station 420x. Based on the above, 422 people search units traveling

ES 2 227 551 T3 through the system receive the common frequencies Ci -C₄ only on limited and non-overlapping CFRRs.

Operating characteristics, such as cell diameter, CFRR diameter, power level of local frequencies (for example, f₁-F₄), and the power level of the common frequencies (Ci -C4) can be adjusted on the ground to suit the many factors of the gw ps 6/22/94, including in particular the terrain and topography of the region geographic area covered by the system. By way of non-limiting example, in one embodiment, the radius of each cell is on the order of about 20 miles; while the radius of each CFRR is of the order of approximately 10 miles or less. In the same example, the power for transmitting the local frequencies can be in the range of between about 3 watts to 1000 watts; while the power for the transmission of the common frequencies C₁ -C₄ it is preferably less than 2 watts.

Thus, the invention provides a two-way paging system that operates independently of a telephone system, for wireless data communication between users. The invention minimizes the use of available frequencies allowed by the Federal Communications Commission (FCC), using only four local frequencies f1 -f4 for any given cell and (for expanded multicellular coverage) only four common or switching frequencies C1 -C4. To minimize the number of frequencies (eg channels) used, time division sharing and synchronization techniques are used. A transmit power difference between local frequencies and common frequencies is also used. These techniques allow data transmissions from different paging devices to be kept separate, thus eliminating data mixing.

The switching technique of the present invention provides extended geographic coverage and minimizes paging time by increasing the number of frequencies used in a cell from four (for example, the four local frequencies) to eight (the four local frequencies). local plus the four common frequencies).

In relation to the verification of the ID of the paging device, it should be understood that a single log file of the paging device may be stored in a memory file of only one of a plurality of central control stations, and that in such case, the verification would constitute issuing a search instruction (on plurality lines 486) to locate an ID of the paging device in the single (remote) memory file, with the search results being delivered back to the requesting central control station.

The keyboards illustrated in this case may, in some embodiments, be multi-language keyboards or electronic writing surfaces, which allow typing in the English, Chinese or Japanese languages, for example. The electronic writing surface is especially useful in such countries as Japan, Thailand, the Middle East or China, where alphabets similar to English are not used. The electronic writing surface could also be used to draw and transmit graphics. In addition, compression / decompression techniques can be used in connection with data transfer.

Although the invention has been particularly shown and described in relation to preferred embodiments thereof, it will be appreciated by those skilled in the art that various alterations may be made thereto, in form and in detail, without thereby departing from the scope of the invention. invention. For example, it should be appreciated that repeaters may be used within cells to facilitate transmission when a paging unit ventures away from a central control station.