Paging method and apparatus.

LOCATION METHOD AND APPARATUS

BACKGROUND

1 « Field of Invention

This invention pertains to location by communications, and particularly to a two-way location method and apparatus.

2» Related Technique and Other Considerations

Over the past few decades, pagers have proven to be important communication devices for contacting personnel in remote locations. While early pagers primarily provided only tone and/or vibration output, more modern pagers have improved output capabilities, such as alphanumeric visual displays that carry messages.

Location systems have historically been one-way systems. That is, the user receives a location message from a central terminal, but has no way to respond to that message with the locator. Attempts to provide two-way communication capabilities for a locator have included efforts to connect the locator to a telephone (e.g., a cell phone). See, for example, United States Patent Number RE 33,417 of Bhagat and collaborators (which combines a complete radio locator and a

-2.1:11 radiotelephone linked through an automatic dialer), and United States Patent Number 5,117,449 of Metroka and collaborators (which intends to combine location and cellular radiotelephone functions in a single unit).

Some locators have the ability to provide acknowledgment or feedback to a location signal. In some of these feedback recognition systems, a user operates a feedback input device (e.g., a toggle switch, a push-button switch, or a keypad) when being located. Typically, these feedback recognition systems involve a complex recognition transmission scheme, encompassing numerous frequencies or sub-frequency bands. The distribution of the locator, as it travels between different geographic regions or cells served by different central stations, becomes technically problematic when large frequencies are involved.

SUMMARY

A two-way locator system uses four local frequencies for transmissions between locator units and a central control station. A first local frequency carries a local clock; a second frequency

-3.III 1 local carries communication packets from the central control station to the locator units; a third local frequency carries communication packets from the locator units to the central control station;

A fourth local frequency carries status or request information from the locator units to the central control station. Transmissions on the fourth local frequency are based on a time-division slot allocation, divided among the locator units that have access to the central control station.

For a two-way locator 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 be different from cell to cell), and four of the frequencies used are lower power common frequencies or switching frequencies that are used to switch or distribute a locator unit that travels from one cell to another.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features, and advantages of the invention can be seen from the following more detailed description of the modalities

05 preferred, as illustrated in the accompanying drawings, in

-4lil.l where the reference characters refer to the same parts across different views. The drawings are not necessarily to scale, the emphasis being instead on illustrating the principles of the invention.

Figure 1 is a schematic view of a central control station included in a location system of a modality of the invention.

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

Figure 3 is a flowchart illustrating the steps executed by the central control station in Figure 1,

Figure 4 is a flowchart illustrating the steps executed by the locator unit of Figure 2 when it is in a transmit mode.

Figure 5 is a flowchart illustrating the steps performed by the locator unit in Figure 2 when it is in a receive mode.

^{20 The} Figure 6 is a timing diagram reflecting the communications between the central control station in Figure 1 and the locator unit in Figure 2.

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

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

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

Figure 10 is a flowchart illustrating the steps executed by the locator unit of Figure 8 in relation to a channel switching operation.

Figure 11 is a flowchart illustrating the steps executed by the central control station in Figure 7, in relation to a channel switching operation.

¹⁵ Figure 12 is a schematic view of a communications packet format used with modalities of the invention.

Figure 13 is a schematic view illustrating a split-time slot allocation technique of 20 in accordance with the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

Figure 1 shows a central control station 20 according to a first embodiment of the invention; Figure 2 shows a locating unit 22 suitable 25 for use with the central control station.1 2 0.

As shown in Figure 1, the central control station 20 includes a central computer 30; a transmitter 32; a receiver 34; and a computerized telephone answering system 36. The transmitter 32 transmits, by means of the transmitting antenna 42, two local frequencies, namely, frequency fj and frequency f₂Receiver 34 connects to receiving antenna 44 to receive two local frequencies, namely frequency f₃ and the frequency f₄The computerized telephone answering system 36 is connected to a telephone bank 48.

The central computer 30 of a central control station 20 comprises a conventional computer equipped with typical components, including a central processing unit (CPU) 50, an input/output interface 52; and memory 54. Although only generally shown 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, RAM, and read-only memory (ROM). Figure 1 shows that memory 54 contains (among other things) a locator log file 55 and a locator directory file 56. The locator files 55 and 56 are typically stored on a hard disk drive of the host computer 30, and upon booting, they can be loaded into a portion of memory 54 of the direct access memory (RAM).

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The central computer 30 of the central control station 20 further includes a decoder 57 (connected between the receiver 34 and the input/output interface 52 to decode incoming communications information from one or more locator units 22), as well as the encoder 58 (connected between the input/output interface 52 and the transmitter 32 to encode outgoing communications information).

The central control station 20 also includes a clock unit 59 that generates a local clock signal fl^eloj (which in turn is used to modulate the frequency fi)·

As further illustrated herein, the central processing unit (CPU) 50 of the central control station 20 prepares communication packets for transmission over frequency f₂As illustrated in general in Figure 12, the communication packets are of a predetermined format, which have fields for identification of the central control station, for identification of the receiving locator units 22, for an operation code, for alphanumeric information (optionally), and for other conventional packet type information such as checksum, error correction, and postamble. The preamble and postamble are specially selected patterns that can be recognized and

-8II 1 Distinguished data for the purpose of determining the beginning and end of a packet. The alphanumeric information may be in a customary 8-bit binary format. The format in Figure 12 is illustrative only, as this information, as well as the order of the fields, may vary in other formats.

The central control station 20 communicates with a plurality of locator units 22_1Λ 22₂, ... 22_NIn this illustration, only one locator unit is specifically illustrated and described, generically referenced as locator unit 22, it being understood that the construction and operation of the other locator units may be similar to those in the illustration.

As shown in Figure 2, locator unit 22 includes a receiving antenna for locator 60, which connects to the receiver of locator 62. The receiver of locator 62, in turn, connects via S/D converter 64 within the computer of locator 70. Receiver 62 receives the two local frequencies yf₂whose frequencies have been modulated to carry incoming communications information (described in more detail later) to the computer of locator 70. On the communications output side, the computer of locator 70 produces outgoing communications information to the transmitter of locator 72 by means of the

-9lili ι D/S converter 74. Transmitter 72 transmits, on the antenna of locator 76, the outgoing communications information on the two local frequencies f₃ yf₄.

As also shown in Figure 2, the locator computer 70 includes a locator microprocessor 80 that connects to each of an arithmetic processor 82; a memory system 84 (which includes both read-only memory (ROM) and direct access memory (RAM)); and the input/output interface 86. The input/output interface 86 connects to a clock unit 87. The input/output interface 86 is also connected to receive decoded input communications information from an 8-bit decoder 88, and to produce unencoded output communications information to an encoder.

8 bits 90. Decoder 88 is connected to receive encoded input communications information from S/D converter 64; encoder 90 is connected to produce encoded output communications information to D/f converter 74.

^{20 The} The clock unit 87 can be configured using appropriate inputs, such that the clock unit 87 generates a local clock signal f^clock with a frequency corresponding to its input. It should be understood that, in other configurations, the function of the clock unit 87 can be at least partially implemented by the

-1010 microprocessor 80, using a programmed execution.

The input/output interface 86 is also connected to provide an on/off signal on line 92 to the locator transmitter 72, as well as to facilitate input and output with numerous input/output devices. Input/output devices connected to the input/output interface 86 include the keypad 93; the pager 94; the vibrator 95; and the liquid crystal display (alphanumeric) 96.

During manufacturing, the locator unit 2 2 is pre-programmed with an identification serial number (e.g., a pre-assigned, alphanumeric 7-digit identification number), which is stored in memory 84 (read-only memory) (ROM). The locator unit 22 is activated (e.g., at the time of purchase) by inserting a time slot allocation (explained later), both in a predetermined memory address 84 of the locator unit 22, and in a directory file of locator 56 (stored in memory 54 of the central control station 20).

FIRST MODALITY OPERATION

Communication between central control station 20 and locator unit 22 occurs on all four local frequencies, particularly frequencies f_p F₂, f₃, yf₄ mentioned above. The first frequency (f^)

-11III 1 carries the local clock alignment signal from the central control station 20 to the locator unit 22. The second frequency (f₂) carries a locator command and alphanumeric data from the central control station 20 5 to the locator unit 22. The third frequency (f₃) carries the locator status data and alphanumeric data from locator unit 22 to central control station 20. The fourth frequency (f₄) carries a locator request signal from locator unit 22 to central control station 20. In the illustrated mode, the frequencies - f₄ Preferably, they are selected in such a way that fj * f₂ * f₃ * f₄.

As explained in more detail later, and as illustrated in Figure 13, in normal non-cellular switching operation, the locator request signal over frequency f₄ It is transmitted in a predetermined time slot assigned to locator unit 22. The predetermined time slot at frequency f₄ is related to the clock alignment signal (carried by the frequency f)₃), and is assigned in such a way that the fourth frequency can be used by a plurality of other locator units. For example, as shown in Figure 13, a first time slot over the frequency f₄It is assigned to a locator Pl; a second time slot is assigned to locator P2, and so on, up to slot 25

-12lll 1 of time n assigned to locator Pn. In the illustrated mode, the number of time slots (and consequently, the number of locators) can be as many as 10,000 or more.

Figure 3 shows the steps executed by the central processing unit (CPU) 50 of the central control station 20 during the communication process to and from one or more locator units. The steps illustrated in Figure 3 correspond to the instructions stored in a portion of memory 54 of the read-only memory (ROM) of the central control station 20.

When the central control station 20 is started (step 100), an initialization process is conducted (step 102). The initialization process includes the activation of transmitter 32 (so that transmitter 32 can transmit on both frequencies f₂ yf₂), and the activation of receptor 34 (in such a way that receptor 34 can receive both frequencies f₃ yf₄) . Moreover, the frequency f₂ It is modulated to carry the local clock alignment signal generated by local clock 59. Then, in step 104, the locator log file 55 and the locator directory file 56 are loaded from the hard drive into a memory section 54 of the direct attachment memory (RAM) (step 104).

After initialization and loading of the

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Files 55 and 56, the central processing unit (CPU) 50 repeatedly executes an instruction cycle 106. Cycle 106 involves checking to determine (in step 108) whether a telephone message is being received (via answering system 36 from one of the bank telephones 48), and checking to determine (in step 110) whether a pager message is being received (via transmitter 32 from one of the pager units 22).

As used herein, a message, whether originating from a telephone or a pager, may require a plurality of packets for its transmission from a central station to a pager or vice versa. In the following description, message transmission and reception assumes the transmission and reception of one or more packets. In general, message packet formation will be invisible to the user, meaning that a user enters a message without considering the number of packets that might be required to transmit it. The message typically ends with a message termination character or message delimiter character entered by the user. The transmitting device (either the central station 20 or the locator 22) assigns the message to one or more packets that have a format similar to that in Figure 12, with the last packet of the message carrying the message termination character 25. Alternatively, the

-1414 packets can be formatted in a way that indicates the number of consecutively related packets that emerge from a transmitter (e.g., there may be a separate packet field that indicates the continuation number of related packets).

The central computer 30 can distinguish between the reception of a telephone message (in step 108) and a pager message (in step 110) by virtue of the fact that the input/output interface 52 generates different types 10 of interrupts to the central processing unit (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 Figure 3 are executed.

In processing a received telephone message 15, in step 112, the central computer 30 extracts the outgoing communications information from the data entered into the telephone sequenced in a predetermined manner. The data entered into the telephone, entered by means of a keypad on a calling telephone (20 of the telephones in bank 48), conventionally includes an identification (e.g., a telephone number) of the calling telephone; an identification of the called Idealizer unit (e.g., the pre-assigned identification number, a seven-digit phanumeric code); and any character data for transmission, followed by a termination character.

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Outgoing communications information is received at the central computer 30 in a conventional DTMF format.

In step 114, using the called identification number (obtained in step 112), the central computer 30 checks the locator log file 55 and the directory file 56, to determine if the called locator unit is registered with the central control station 20. Assuming that the so-called accessor is so registered, in step 114, the central computer 10 30 also obtains from the locator directory file 56 the slot assignment for the accessed locator unit.

In step 116, the central control station 30 transmits communications information to the accessed locator unit 15. In this respect, the central control station 20 prepares and transmits (on frequency f)₂) a communications message that includes, among other things, the identification of the accessed locator unit and the character data received from the telephone for transmission 2 0 of locator unit 22. After step 116 is executed, the process returns to cycle 106.

If it is determined in step 110 that a message is being received from the locator, even-numbered steps 132-140 of Figure 3 are executed (before returning to cycle 106). As will be seen later in this document...

-1616 with respect to Figure 4, a dispatch locator unit 22 transmits, in its assigned time slot, a request signal on frequency f₄When the locator unit sending 22 wants to send a message, since the central control station 20 is always monitoring frequency f.₄, a request signal carried by the frequency f is noticeable₄From any locator unit 22. With reference to the local clock 59, in step 132, the central processing unit (CPU) 50 determines in which time slot on frequency f₄ The request signal is detected. Upon detecting the time slot in step 132, the central processing unit (CPU) 50, in step 134, consults the locator directory file 56 to determine the identification number of the particular locator unit 22 that originated the request signal 15.

Now that the identity of the requesting locator unit 22 is known, in step 13.6, the central control station 20 authorizes the requesting locator unit 22 to transmit its message. Specifically, the central processing unit (CPU) 50 directs the preparation of a communications message to be transmitted over frequency f.₂The particular communications packet prepared in step 13 6 includes an identification of the requesting locator unit (the recipient of the packet), 25 as well as an operation code (op code) that

-1717 orders/authorizes the requesting Idealizer unit 22 to send its message.

In step 138, central control station 20 receives a communications message on the 'frequency f'₃, sent from the dispatch locator unit (e.g., requester) 22. The communications message prepared and sent by the dispatch locator unit 22 includes packets of a format similar to that shown in Figure 12, and includes an identification of a locator to which the message is finally sent, as well as its own identification. In step 138, the central processing unit (CPU) 50 verifies to ensure that the final destination locator unit is registered in locator files 55 and 56. In step 140, the central processing unit (CPU) 50 performs any necessary reformatting and/or information substitution in the message, and causes the message to be transmitted on frequency f₂Transmission at frequency f₂ required by step 140, includes the identification of the final recipient (e.g., a locator unit 22), as well as an operation code indicating that the transmission includes a message relayed from another locator unit.

The steps performed by a locator unit 22 in relation to its transmission mode are illustrated in Figure 4. The steps performed by a locator unit 22 in relation to its reception mode are illustrated in Figure 5.

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;

5. The term "mode" as used herein does not connote exclusivity at any particular time, because it must be remembered that at all times locator unit 22 is receiving transmissions on the frequencies yf₂.

In its transmission mode (see Figure 4), after startup (step 200), the microprocessor 80 of the transmission locator unit 22 executes a cycle 202, in which it repeatedly searches (in step 204) for alphanumeric characters entered by the user (via keyboard 93), 10 until an end-of-message delimiter is detected (in step 206). As entered, the characters searched for in step 204 are displayed on the liquid crystal display 96. The entry of the delimiter character in step 206 causes the microprocessor 80 to exit cycle 202.

By convention, the message must include a recipient identifier, the recipient identifier of which is possibly the identifier of another of the locator units to which the message entered in step 204 is addressed.

After the message is entered, it waits for input from keyboard 93 of a transmit command at step 212. Assuming the transmit command is entered at step 212, microprocessor 80 prepares and sends a request signal on frequency f₄As indicated in point 25 above, the request signal is transmitted in the

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frequency f₄ in a time slot allocated to the requesting locator unit 22. It should be kept in mind that the locator unit 22, while receiving the local clock alignment signal on frequency f_lr It is everything that makes it possible for the 80 microprocessor to cause the transmission of the request signal over the frequency f₄ at a time corresponding to the specific time slot assigned to the particular shipment locator unit 22.

With regard to the above, in accordance with time division techniques, to each locator unit 22_±-22_n (e.g., the locators Pj-Pn in Figure 13), is assigned a selected slot of N number of time slots over the frequency f₄.

After the transmission of the request signal in step 214, the locator unit 22 awaits the receipt of a transmit command from the central control station 20. The preparation and transmission of the transmit command/authorization from control station 20 are described with reference to Figure 3. Upon receiving the transmission command/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 very similar to that in Figure 12. The recipient identification and the alphanumeric packet field of the communications message are

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They archive with the message entered in cycle 2 02. In step 220, the sending locator unit 22 transmits the communications packet over frequency f₃.

If no transmit command is entered in step 212, or after the message has been transmitted in step 220, the microprocessor 80 waits for input from at least one of several possible special function keys in step 222. For example, the user may press a function key that requires the storage of the message (whether or not it has been transmitted) [see step 228]. Alternatively, the user can press function keys to edit or delete the message (see steps 224 and 226, respectively). To end the message and begin working on other messages, a special function key for an exit operation must be pressed (step 230).

Figure 5 illustrates the steps executed by the microprocessor 80 of locator unit 22 when it is in receive mode. After startup (step 302), and as indicated by step 304, locator unit 22 receives transmissions from central control station 20 on frequency f₂Once a complete packet is received (determined in step 306), a verification is performed (in step 308) to see if the recipient ID in the communications packet (see packet format in Figure 12) is the locator unit ID.

-2121 receiver 22. If the determinations of step 306 or step 308 are negative, locator unit 22 waits for either the termination of the communications packet (in the case of step 306), or the reception of another communications packet (in the case of step 308) by returning the cycle to step 304.

Assuming the received communications packet is designated for this particular receive locator unit 22, in step 310, the microprocessor 80 consults the operation code field of the communications packet 10 (see Figure 12) to determine if the operation code indicates that the message includes a command. If the operation code indicates a command, a command processing routine (framed by the dashed lines in Figure 5) is executed.

Assuming for the moment that the operation code does not indicate a command, in step 314, the microprocessor 80 of .μ*—· the locator unit 22 stores the alphanumeric field portion of the communications packet (which at least partially forms the message) in a portion of memory 84 do 2 0 the direct access memory (RAM). Since a message communicated from the central processing station 20 may require several communication packets to complete the message (with subsequent communication packets providing continuations of the message content), the microprocessor 80 checks, in step 316, to ensure that

-2222 the entire message has been received. If not, processing continues back to step 304, for the reception of another communications packet.

Upon receiving a complete communications message, in step 318, the microprocessor 80 determines whether locator unit 22 is in beep mode or vibrate mode. There are numerous ways to set locator unit 22 to the desired mode, as >· >

either by means of a specially dedicated switch on locator unit 22, or by data input using keyboard 93. If locator unit 22 is in beep mode, processor 80 produces a signal that causes input/output interface 86 to emit an additional signal to activate beeper 94 (step 320). Alternatively, if locator unit 22 is in a vibration mode, microprocessor 80 produces a signal that causes input/output interface 86 to emit an additional signal to activate vibrator 95 (step 322).

In step 3 24, the microprocessor 80 directs the input/output interface 86 to send the alphanumeric message data to the liquid crystal display 96, so that the user can see the received message.

After notification to the user (either by means of the pager 94 and/or the vibrator 95), and deployment

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Visual (on the liquid crystal display 96) of the alphanumeric data received, the microprocessor 80 returns to step 304 to check if other communication packets are being received.

The command processing routine (framed by the dashed lines 312 in Figure 5) first determines (step 330) which particular operation is being ordered. This determination is based on the contents of the opcode, which differs for different types of commands. If the opcode indicates a failover, execution jumps to a failover subroutine that begins in step 340. If the opcode indicates a time slot change, execution jumps to a time slot change subroutine, which begins at step 350. If the opcode requires a transmitter deactivation, execution jumps to a transmitter deactivation subroutine, which begins at step 360. If the opcode requires a transmitter reactivation, execution jumps to a transmitter reactivation subroutine, which begins at step 370. If the opcode requires a clock reset, execution jumps to a clock reset subroutine starting at step 380.

Regarding the error-disable subroutine, in step 34 2, the microprocessor 80 obtains a

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The error type is indicated from the communications packet. The error type is stored in memory 84 (step 344), and then displayed on the liquid crystal display 96 (step 346). Then the microprocessor 80 issues a command (in step 348) to deactivate the locator unit 22, which is deactivated in step 349.

In relation to the time slot change subroutine, in step 352, the microprocessor 80 extracts, from the received communications packet 10, information indicating the new time slot assigned to the receive locator unit 22. The new time slot is put (in step 354) into memory 84, and is subsequently used (until another change) in relation to the transmission of request signals 15 at frequency f₄ (see, for example, step 214 in Figure 4). The time slot switching subroutine may also include other operations, if desired, including (for example) the removal of unused time slots (thereby increasing the tracing speed);

diagnosis and troubleshooting; and elimination of service interruption due to malfunction or failing equipment.

Regarding the transmitter deactivation subroutine, in step 362, the microprocessor 80 directs the input/output interface 86 to issue a command to

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OFF to transmitter 72. In relation to the transmitter rehabilitation subroutine, in step 372, the microprocessor 80 directs the input/output interface 86 to issue an ON command to transmitter 72.

Regarding the clock reset subroutine, in step 382, ​​the microprocessor 80 directs that clock 59 of locator unit 22 to be set.

After the execution of steps 354, 362, 372, or 382, ​​execution continues back to step 304 for processing of any additional potential communication packets. Therefore, unless an erroneous deactivation is noted, each entry of the command processing routine (framed by the dashed lines in Figure 5) is followed by a loop back to step 304.

Figure 6 is a time diagram showing the frequencies f_x - f₄, and the integration of the steps illustrated in Figures 3 to 5, particularly in the context of a request by a sending locator unit Pl, to send a message to a receiving locator unit P2. As employed in Figure 6, the computer refers to the central control station 20. It should be understood that the sending locator unit Pl, and the receiving locator unit P2, operate both in transmit mode as illustrated in Figure 4, and in receive mode as

-2626 is illustrated in Figure 5. In general, Figure 6 shows the transmission of a message from locator unit P1 (via central control station 20) to locator unit P2; the transmission of a confirmation message from locator unit P2 (via central control station 20) to locator unit Pl; and the transmission of a message from locator unit Pl to central control station 20, indicating that locator unit Pl received the confirmation message from locator unit P2.

STRUCTURE OF THE SECOND MODALITY

Figure 7 shows a central control station 420 according to a second embodiment of the invention; Figure 8 shows a locator unit 422 suitable for use with the central control station 420.

Figure 9 shows a wide-area localization system that includes a plurality of central control stations S1–S8 (each identical to central control station 420), each preferably geographically centered within a respective cell. Each central control station S1–S8 transmits its own local frequencies, as well as a set of common or switching frequencies C₁-C₄The common frequencies Cl - C₄ They are transmitted at a lower power, so their reception occurs only in a relatively small neighborhood.

-2727 small, or in a common frequency reception region (CFR) [also referred to as a “switching region”) around the central control station. Local frequencies are transmitted at a significantly higher power for reception substantially throughout the cell. For example, in Figure 9, the central control station SI transmits its lower power common frequencies Cj-C₄ towards the RRFC_1Z and its higher power local frequencies ^1^^4 towards the CELL; the central control station S2 transmits its lower power common frequencies towards the RRFC₂, and its highest local power frequencies f₅ - f₈ towards the CELL₂.

As also shown in Figure 9, the CELL^ and CELL₂, overlap in an overlap region shown in Figure 9. The SI station uses a set of local frequencies f₂ - f₄; station S2 uses a different set of local frequencies f₅ - f₈Both stations SI and S2 use the same set of common or switching frequencies Cj - C₄Therefore, each central control station uses two sets of frequencies, with four frequencies in each set, resulting in a total of eight frequencies distributed per station.

Therefore, the second embodiment of the invention is suitable for a system having a plurality 25 of 420 central control stations_x, _x = 1, 2, m^Each

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central control station 420_x transmits and receives a set of local frequencies f_L1, f l2 ' L3' ^4'^{in a} geographical area or associated cell, as well as the set of common or switching frequencies C_lz C₂, C₃, C₄. Although the 5 values ​​of the local frequencies f_L1, f_L2, f_L3, f_L4 They vary from cell to cell (e.g., they differ for different central control stations 420_x), the values ​​of the common or switching frequencies C_lr C₂, C₃, C₄ are uniform throughout the system (e.g., for all control stations 10 central 420_x).

Although not shown in Figure 9, it should be understood that the pattern of the central control stations repeats in a similar manner in all compass directions, in accordance with the prescribed geographical boundaries of the 15 location system. Furthermore, although not specifically illustrated in Figure 9, it should also be understood that each 420 central control station has an associated common frequency reception region.

Common or switching frequencies C₁ - C₄20 It has a function analogous to that of the corresponding local frequencies - f₄respectively. In this respect, the frequency Cj carries a clock frequency transmitted by the central control stations, although the clock speed over the common preferred frequency varies among the 25 central control stations. The frequency C₂ it is used

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to transmit information from the central control stations to the locator units; the frequency C₃ It is used to transmit information from a locator unit to a central control station; the 5 C frequency₄ It is used by the locator units to emit a request signal. The frequency C₂ It carries packages that have a format similar to that in Figure 12. In a manner analogous to the frequency f₂, the packets carried by the C frequency₂ They can have command codes. Among the 10 command codes of C₂, are a COMMAND CODE of

SYSTEM; a LOCAL FREQUENCY DOWNLOAD COMMAND CODE; a SLOT RECOGNITION COMMAND CODE; and a SLOT ASSIGNMENT COMMAND CODE.

As shown in Figure 7, the 15 central control station 420 resembles the 20 central control station of the modality in Figure 1 (assigning the same reference numbers to similar components for simplicity). However, the central control station 420 is augmented by the inclusion of another transmitter, known as the common frequency transmitter 432, along with its common frequency transmitting antenna 442, to transmit the common frequencies and C₂In contrast to the high-power transmitter 32, the transmitter 432 is a low-power transmitter. Furthermore, the 25-unit central control station 420 is enhanced by the inclusion of

-3030 another receiver, known as the 434 common frequency receiver, together with its 444 common frequency receiving antenna, for the reception of the C common frequencies₃ and C₄.

The central control station 420 of Figure 7.5 includes a clock unit 59* that generates two clock signals - a first local clock signal f_Lclock, and a second common clock signal ^clock . The local clock signal f_Lclock is used to modulate the frequency f_xThe common clock signal is used to modulate the common frequency C_T.

The 30 central computers of the 420 central control stations_xThey are connected in series with each other by means of a 486A output line and a 486B input line. In particular, although not expressly shown as such in Figure 7, computer 30 in Figure 7 (like the one in Figure 1) includes an input/output interface to which the serial 486A and 486B lines are connected. Serial lines 486A and 486B are used, for example, to update the contents of the locator 55 log file and the locator 56 directory file.

As shown in Figure 8, locator unit 422 resembles locator unit 22 of the modality in Figure 2 (similar components are again assigned the same part numbers for simplicity). However, locator unit 422 25 (similarly to central control station 420)

-3131 is augmented by the inclusion of an additional transmitter, known as the common frequency transmitter 572, along with its common frequency transmitting antenna 576, to transmit the common frequencies C₃ and C₄Furthermore, the central control station 420 is augmented by the inclusion of another receiver, known as the common frequency receiver 434, along with its common frequency receiving antenna 444, to receive the common frequencies C_xYC₂.

The operating frequencies of transmitter 72 and receiver 62 can be changed according to the values ​​transmitted over the frequency control lines from computer 70. In particular, the frequency control lines are connected to input/output interface 86 on computer 70. As described in more detail later, when a locator unit 422 migrates to a new common frequency receiving region, signals are applied on the frequency control lines in order to switch the locator unit 422 from the local frequencies of an old cell to the local frequencies of a new cell associated with the new common frequency receiving region to which the locator unit 422 migrates.

The 422 locator includes an 83' clock unit, which is capable of separately generating local clock signals

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F_Lclock, and the common clock signals f_clclock, to be used by the microprocessor 80. These clock signals are initiated, and their frequencies are set, by the appropriate respective inputs to the clock unit 83'.

Figure 8 also shows that the locator unit 422 has the data input/output unit 596, which includes both an alphanumeric graphic display and a pressure-sensitive typing keyboard. The alphanumeric graphic display is a dot-matrix device that can display characters and graphics. The typing keyboard has a 16 x 48 dot area.

SECOND MODALITY OPERATION

As shown in Figure 9, it is assumed that a localizer unit P1 has been operating in CELL^, and has previously received the common frequencies C_x - C₄ and the local frequencies f_x - f₂ From station SI. Now the localizer unit P1 travels on a route indicated by the dotted line with arrowhead ROUTE. Along the route, localizer unit P1 continues operating on local frequencies f₁ - f₂even when traversing through the cell overlap region. However, when the locator unit P1 enters a new common frequency reception region (i.e., CFRRR),₂), a switching or distribution operation occurs. In the operation of

-3333 switching, as explained in more detail later, the locator unit P1 obtains the common frequencies C_x C₄ from the central control station S2, and as a result, you can switch from the local frequencies fi - f₄ of the

CELL₁, up to the local frequencies f₅ - f_s of the CELL₂In order to carry out the switching or distribution operation, the locator unit P1 executes a channel switching routine; the central control station S2 executes a switching enable routine.

Regarding the channel switching routine and the switching enable routine, when the locator unit P1 moves into the RRFC₂The locator unit P1 receives the clock signal on the frequency from station S2. At this point, the locator unit

Pl will automatically align your clock unit with the clock signal from station S2.

Referring now to the channel switching routine executed by the Pl locator, subsequent to startup (step 500), in step 506, the Pl 20 locator unit obtains information that characterizes the system centered around station S2. This characterization information is referred to as system identification or system identification information.

In step 508, the Pl locator unit's microprocessor 80 checks to determine if there are any new

-3434 System identification information acquired on frequency C₂In other words, microprocessor 80 checks to determine if the system identification information regarding frequency C is being received.₂ (which can only occur in a common frequency reception region), and if so, it compares the system identification information with the system identification information immediately previously stored. If the previous and most recently acquired system identifications are the same, the locator unit P1 realizes that it is still within the jurisdiction of the same station (e.g., station SI). If this is not the case, locator unit P1 realizes that it has now entered the common frequency reception region of a new station (e.g., station S2), and in step 510, initiates a request on frequency C₄ to communicate with the central control station (for example, station S2) for the CELL₂.

With regard to the above, since the locator unit P1 has not yet been assigned a time slot for the CELL₂, the request regarding frequency C₄ It is done randomly. However, the locator unit P1 keeps track of the time slot in which it makes its request to the new central control station (e.g., station S2).

Subsequently, the locator unit P1 continues

-3535 monitoring (step 512) the communication packets from station S2 on frequency C₂, waiting for station S2 to transmit a message referencing the time slot in which the locator unit Pl made its request in step 510. In particular, the locator unit Pl is waiting for a message from station S2 on frequency C₂, which includes both a SLOT RECOGNITION COMMAND CODE, and the information stored in the same time slot that was randomly generated by the Pl locator unit.

Since the message that includes the SLOT ACKNOWLEDGMENT COMMAND CODE includes station S2 as the sender, and is a mirror of the slot randomly generated by the locator unit Pl, the locator unit Pl recognizes the message as sent to the locator unit Pl, and considers the issuance of this message by station S2 (see step 612 of Figure 11), to constitute authority for the locator unit Pl to further communicate with station S2. In this respect, in step 514, the Pl locator unit's microprocessor 80 determines whether there is a match between the time slot of a received message and the time slot in which the random request was made in step 510.

Assuming that a match is eventually found in step 514, in step 516 the localizer unit 25 Pl sends a communications packet in the

-36³⁶ frequency C₃ to station S2, including the communications packet the identification of the locator unit Pl. Using the locator log file 55, station S2 verifies that the identification of the locator unit Pl is a valid identification, and subsequently sends (over frequency C)₂) to the locator unit Pl, a message with the command code LOCAL FREQUENCY DOWNLOAD, which message informs the locator unit Pl about the values ​​of the local frequencies distributed by station S2 (for example, the frequencies f₅ - f₆). Subsequently, as also reflected in step 518, station S2 sends (on frequency C₂) to the locator unit Pl, a message with the command code of SLOT ASSIGNMENT COMMAND CODE, which message informs the locator unit Pl about its slot assignment on frequency f₈Then the microprocessor 80 changes its slot assignment through steps that are similar to those described with the previously mentioned time slot change routine (see steps 350, 352, and 354 of the

Figure 5). Step 518 of Figure 10 reflects the reception of the local frequency values ​​and the reception of the slot assignment.

After the acquisition of all local frequencies and the completion of slot allocation (step

520), the 80 microprocessor implements (in step 522) a

-3737 switch for the new local frequencies (e.g., the frequencies f₅ - f₈) . In this respect, the microprocessor 80 includes the input/output interface 86, to switch the transmitter 72 from the frequencies f₃, f₄, up to frequencies f₇, f₈; and to change receiver 62 from frequencies f_1F F₂, up to frequencies f₅, f₆The input/output interface 86 performs frequency changes by applying appropriate values ​​to the frequency control lines that connect the input/output interface 10 to the transmitter 72 and receiver 62, respectively.

After the switching to the new local frequencies in step 522, the microprocessor 80 cycles back to step 506, to finally determine 15 when any further switching may be required.

The steps involved in the switch-enable routine executed by a central control station (e.g., station S2) are illustrated in Figure 11. After boot (step 600), the central processing unit 2 0 (CPU) 50 determines the execution of a cycle 602 which enables the central processing unit (CPU) 50 to clear its locator directory file 56, and check if any new locator units have entered the cell it manages.

Specifically, in step 604, the processing unit

-3838 The central control unit (CPU) determines if its central control station (e.g., S2) has been inhabited by any other central control station (e.g., S3), and if a locator unit, previously under the control of its central control station (e.g., S2), has come under the control of the other central control station (e.g., S3). This warning occurs over serial links connecting the central control stations._x, and particularly the incoming serial link 486B. If this warning occurs, the identification for the locator that moved away from the locator directory file 56 for station S2 is suppressed (as reflected by steps 606 and 608).

In step 610, the central processing unit (CPU) causes messages with a SYSTEM COMMAND CODE to be transmitted over frequency S2. As stated earlier, messages transmitted over frequency C₂ They include packets that have a format such as that shown in Figure 12. The message with the SYSTEM COMMAND CODE particularly includes the central station identification number in its alphanumeric data field.

In step 612, the central control station 420 checks to determine if any locator unit 422 has transmitted a request signal on frequency C₄ (as happened, for example, in the context of the description of the 25th)

-39i.

Figure 10, particularly step 510). This request signal would possibly be emitted from a locator unit 422 that has entered the common frequency repeater region controlled by the central control station 5 (e.g., in the RRFC₂ controlled by station S2). If no request signal is detected, cycle 602 is repeated.

In the event that a request signal is detected in step 612, the central control station 420 notes 10 specifically the time slot on frequency C₄ in which the request was presented (step 614). At this point, that time slot is the only way the central control station 420 can identify the incoming locator unit 422. The central control station 420 wants the incoming locator unit 422 to transmit its identification (ID), but it cannot specifically address the incoming locator in any way other than by reference to the detected time slot. In accordance with the above, in step 616, the central control station 420 prepares and transmits a message on frequency C.₂, which has a SLOT AWARENESS COMMAND CODE. The message that includes the SLOT AWARENESS COMMAND CODE includes station S2 as the sender, and is a mirror of the slot randomly generated by locator unit P1 (for example, the 25th time slot in which the locator unit entered

-4040

422 (issued his request). This transmission on frequency C₂ constitutes an authority for the locator unit P1 to transmit its identification.

Step 618 denotes the acquisition by central control station 420 of the identification (ID) of the incoming locator unit 422. In step 620, central control station 420 checks its locator log file 55 to determine if the locator ID is valid. If it is not, an error message is generated and transmitted (in step 622), followed by a command to deactivate locator unit P1 (see step 624).

Assuming that the locator unit 422 ID was invalidated in step 620, the central processing unit 15 50 checks (in step 630) its locator directory file 56 to locate an available time slot for incoming locator unit 422, and then associates the available time slot with incoming locator unit 422 ID. Then, in step

632, using a message on frequency C₂ with a

LOCAL FREQUENCY DOWNLOAD COMMAND CODE, the central control station 420 sends the values ​​of its local frequencies (e.g., f₅, f₆, f₇, f¿) to the locator unit entering 422. Then the central control station (in step

634) assigns to the incoming locator unit 422, a new

-4141 time slot on its local frequencies, using a message on frequency C₂, with a SLOT ASSIGNMENT COMMAND CODE. The processing of the time slot change command by the locator unit entering 422, 5 is understood with an analogous reference to Figure 5, particularly steps 350, 352, and 354.

Upon completion of step 634, the locator unit entering 422 is fully initialized in its new cell (e.g., CELL₂), and has left the jurisdiction of its previous control station (e.g., CELL_x and SI station). In accordance with the above, in step 636, the central processing unit (CPU) 50 requests its input/output interface to issue a command over serial line 486A, advising (using the locator identification) that the incoming locator 422 is now under its jurisdiction, so that the former jurisdiction (e.g., SI) can delete its locator unit from its locator directory files 56. This deletion is understood with reference to steps 604-608 as described above.

In addition to illustrating the geographical location of the locator Pl, the SI and S2 stations, and the CELL^ and CELL cells₂Figure 9 shows the relative timing of communications occurring on common frequencies

C_x - C₄Figure 9 specifically relates the time of

-4242 the communications transmissions with the specific steps of the steps described above executed by the central control station 420 (the switching enable routine of Figure 11) and by the locator unit 422 5 (the channel switching routine of Figure 10).

Although the central control stations 4 2 0_xThey use the same common frequencies C₃ - c₄There is no interference or confusion of these signals transmitted from control stations 420_xThe common frequencies 10 Cj - C₄ They are transmitted at a relatively lower power than the local frequencies f_x - f₄, in such a way that the reception of the common frequencies C_x - C₄ They occur only in a limited neighborhood (common frequency reception region) around the central control station

420_xIn accordance with the above, the 422 locator units that travel through the system receive common frequencies C_x - C₄ only in limited and non-overlapping common frequency reception regions.

The operating characteristics of the system, such as cell diameter, common frequency reception region diameter, local frequency power level (e.g., f_x - f₄) , and the power level of common frequencies (C_x - C₄) , can be adjusted in the field to suit numerous factors, including particularly the terrain and topography of the region

-4343 geographic area covered by the system. As a non-limiting example, in one mode, the radius of each cell is on the order of approximately 32,180 kilometers; while the radius of each common frequency reception region is on the order of approximately 16,090 kilometers or less. In the same example, the power for transmitting local frequencies can be on a scale of approximately 3 watts to 1000 watts; while the power for transmitting common frequencies C_to - C₄ 10. Preference is less than 2 watts.

Therefore, the invention provides a two-way locator system that operates independently of a telephone system for wireless data communication between users. The invention minimizes the use of available frequencies permitted by the Federal Communications Commission (FCC), which uses only four local frequencies._T - f₄ for any given cell, and (for expanded multi-cell coverage) only four 20 common or switching frequencies C₁-C₄In order to minimize the number of frequencies (e.g., channels) used, time-division sharing and synchronization techniques are employed. A transmission power differential between the local frequencies and the common frequencies is also used. These techniques allow that

-44.11 i data transmission is kept separate from different locators, and therefore eliminates the merging of data.

The switching technique of the present invention 5 provides extensive geographical coverage, and minimizes location time by increasing the number of frequencies used in a cell, from four (e.g., the four local frequencies (up to eight) the four local frequencies plus the four common frequencies).

Regarding the verification of the locator identification, it should be understood that a single locator log file could be stored in a memory file, from only one of a plurality of central control stations, and that in that case, the verification would consist of issuing a search command (over serial links 486) to locate a locator identification in that (remote) memory file. with the result that the search is reported back to the inquisitorial central control station.

The keyboards illustrated herein, in some versions, may be multilingual keyboards, or typing keyboards that allow typing in languages ​​such as English, Chinese, or Japanese. The typing keyboard is especially useful in countries such as Japan, Thailand, and others.

The Middle East, or China, where alphabets like these are not used

-45.1.1 1 the English one. The typing keyboard could also be used for sketching and transmitting graphics. Furthermore, data compression/decompression techniques can be used in connection with data transfer.

Although the invention has been shown and described particularly with reference to preferred embodiments thereof, it will be understood by those skilled in the field that various alterations may be made to its form and details without departing from the spirit and scope of the invention. For example, it should be understood that repeaters may be employed within cells to facilitate transmission when a locator unit ventures far from a central control station.

-46[4 1.

NOVELTY OF THE INVENTION

Having described the preceding invention, it is considered novel, and therefore, the contents contained in the following are claimed as property: