WO1998020619A1

WO1998020619A1 - Apparatus and method for dynamically selecting a transmitter for directed message delivery

Info

Publication number: WO1998020619A1
Application number: PCT/US1997/019865
Authority: WO
Inventors: Slim Souissi; Samir A. Sawaya; Jheroen P. Dorenbosch; Alain Charles Louis Briancon; Gregory Lewis Cannon
Original assignee: Motorola Inc.
Priority date: 1996-11-05
Filing date: 1997-10-31
Publication date: 1998-05-14
Also published as: CN1235714A; AR010281A1; CN1154243C; CN1252945C; CN1497872A

Abstract

Apparatus and method for dynamically selecting a transmitter for directed message delivery in a messaging system (100) including plural transmitters (107-111) operating in a simulcast or non-simulcast mode. A communication system (1100) dynamically selects transmitters (1115) by sending transmission signals, receiving the transmission signals at a PMU (1105), calculating signal strengths of the transmission signals, transmitting a signal indicative of the signal strengths, receiving the signal and determining therefrom carrier-to-interference (C/I) values indicative of relative strengths of the transmission signals at a controller (1110), and delivering a message with a selected transmitter (1115) associated with a lowest C/I value that is chosen from the C/I values and that exceeds a C/I threshold value.

Description

Apparatus And Method For Dynamically Selecting A Transmitter For Directed Message Delivery

Field Of The Invention

The present disclosure concerns radio communications and more specifically apparatus and methods in communications systems for dynamically selecting a desirable transmitter for message delivery.

Background Of The Invention

Radio communications systems or messaging systems are known. Such systems ordinarily include transmitters for transmitting messages, messaging units (Mus) or portable messaging units (PMUs) for receiving the messages, controllers for controlling message delivery operations, and terminals or gateways coupled to public switched services such as the telephone or internet systems. Such systems routinely use a simulcast transmission mode for message delivery. This simulcast mode denotes a situation where all transmitters within a geographic area are active at the same time on the same radio frequency. To facilitate, indeed enable, successful communications in a simulcast mode, extreme care must be taken to insure that modulation on radio signals that originate from different transmitters and arrive at a location where the signal strength of each signal is equal are phase coherent or in phase. Equal is taken to mean within or approximating the capture ratio of a typical messaging unit or within about 6 dB for many messaging receivers when using frequency modulation.

Simulcast operation has proven to be very effective at reaching messaging receivers that are located at some unknown location within a large geographic area. However messaging systems that rely entirely on simulcast operation may be unduly capacity limited since the radio frequency used by the system can not be used at the same time for any purpose other than delivery or transmission of a single message anywhere in the system. Practitioners have realized that knowledge of a messaging unit location would allow a portion of the system, such as one transmitter, to transmit the message to the intended messaging unit. Concurrently other portions of the system, such as other transmitters may be used for other noninterfering duties, such as delivery of other messages to other messaging units, thus better utilizing system capacity. In recognition of this some systems use digital identification (ID) signals or codes that are unique to each transmitter providing coverage within a region. These digital identification signals or digital color codes are simulcast from each transmitter and a messaging unit with an address matching a simulcast transmitted message reports back to the system the digital ID it has received. The system thereafter attempts further or additional contemporaneous message delivery to this unit utilizing only the transmitter with that digital ID. This latter mode of operation is often designated directed or directed delivery or non-simulcast operation. While the use of digital color codes can provide a significant degree of directed message delivery and thus significant reuse of the system frequency by other transmitters within the system, certain drawbacks or limitations remain.

For example, if two signals are received each having approximately equal magnitude, the digital color codes will interfere with each other and neither may be accurately recovered. In this instance the messaging unit may not be able to determine which transmitter(s) are providing coverage. In any event, when a single digital ID is recovered it will represent the transmitter providing the best or strongest signal at the location of the messaging unit. Weaker signals with their respective digital IDs will be lost even when the weaker signal nevertheless has a completely adequate signal level. In this instance a potential opportunity for contemporaneous directed message delivery to two messaging units may be lost with a resultant reduction in system utilization. Clearly a need exists for methods and apparatus for dynamically selecting a suitable transmitter for directed message delivery that efficiently use system resources. Brief Description Of The Drawings

The features of the present invention that are believed to be novel are set forth with particularity in the appended claims. However, the invention together with further advantages thereof, may best be understood by reference to the accompanying drawings wherein:

FIG. 1 depicts in exemplary form, a messaging system in accordance with a preferred embodiment of the present invention;

FIG. 2 shows a spectrum plot of one exemplary identification signal;

FIG. 3 shows a spectrum plot of a second exemplary identification signal;

FIG. 4 depicts a preferred block diagram of a messaging unit suitable for use in the FIG. 1 system in accordance with the present invention; FIG. 5 shows a partial forward channel frame structure suitable for use in the FIG. 1 messaging system;

FIG. 6 depicts an exemplary received spectrum as detected at the FIG. 4 messaging unit suitable for use in the FIG. 1 system;

FIG. 7 depicts a flowchart of a preferred method of operation from the perspective of the FIG. 1 system; and

FIG. 8 depicts a flowchart of an alternative method embodiment from the perspective of the FIG. 4 messaging unit.

FIG. 9 is a flowchart of an operation of a sender included in the controller of FIG. 17 according to the present invention. FIG. 10 is an electrical block diagram of a PMU included in the communication system of FIG. 11 for calculating C/I values and providing an indication of transmitter groupings to the controller according to the present invention.

FIG. 11 is a diagram of a communication system for grouping transmitters into reuse groups according to carrier-to-interference (C/I) values associated with tones transmitted by the transmitters according to the present invention. FIGs. 12 and 13 are diagrams of different reuse groups into which the transmitters of FIG. 11 can be grouped according to the present invention.

FIG. 14 is an electrical block diagram of a portable messaging unit (PMU) for providing signal strengths of received tones to a controller included in the communication system of FIG. 11 according to the present invention.

FIG. 15 is a flowchart of an operation of a processor included in the PMU of FIG. 14 according to the present invention. FIG. 16 is a flowchart of an operation of a measurer included in the

PMU of FIG. 14 according to the present invention.

FIG. 17 is an electrical block diagram of a controller included in the communication system of FIG. 1 for calculating C/I values and grouping transmitters into reuse groups according to the present invention. FIG. 18 is a flowchart depicting an operation of a calculator included in the controller of FIG. 17 according to the present invention.

Detailed Description Of A Preferred Embodiment

The present disclosure concerns communications systems including messaging systems and selective messaging systems and messaging units (MUs) or portable messaging units (PMUs) for such systems together with methods within such systems all directed to an improved and inventive approach to determining or selecting a suitable transmitter or grouping of transmitters for directed message delivery to a subscriber messaging unit. A preferred method of selecting a transmitter for directed message delivery in a messaging system arranged and constructed to operate in a simulcast mode and the corresponding messaging system are discussed. The method includes; directing a first and a second transmitter to transmit in a simulcast mode, respectively, a first signal including a reference parameter and a first identification signal and a second signal including the reference parameter and a second identification signal, where the first identification signal and the second identification signal are distinguished from the reference signal by, respectively, a first and a second predetermined amount, and receiving an acknowledgment signal that includes a strength indication of the first identification signal relative to the second identification signal as determined at a messaging unit location, the strength indication corresponding to the preferred transmitter selected from the first and the second transmitter for a message delivery to the messaging unit in a non- simulcast mode. Having determined the preferred transmitter, further transmissions of messages to that messaging unit may be made from this transmitter in a non-simulcast mode. The preferred form of the reference parameter or reference signal and identification signals includes a reference tone and a plurality of identification (ID) tones where each such ID tone is uniquely assigned to a transmitter such that no two transmitters within communication range of a given messaging unit will have the same identification tone. The reference parameter or reference signal may alternatively be any signal attribute including only the carrier frequency in relatively high frequency stability systems, provided some characteristic of the reference signal is known, similar for all transmitters, and not subject to non-linear effects such as the capture effect encountered in phase modulated communications systems. The identification signals, while preferably tones, may be any orthogonal signal including for example a windowed tone.

Various forms of the strength indication are contemplated with each having certain utility. The first form compares all identification tones received at a messaging unit to a threshold and reports all or a plurality of those that are satisfactory while another merely reports the strongest or best tone as determined, preferably, by a weighted average over a plurality of transmissions and as a subset at least implicitly reports when none of the received transmitter ID tones are satisfactory. In the last case it may be assumed that further messages should be delayed or alternatively transmitted in a simulcast mode for a messaging unit reporting this circumstance.

An alternative preferred method of determining a desirable transmitter for a message delivery to a messaging unit and the corresponding messaging unit or selective messaging unit are also discussed. The method includes receiving a simulcast signal including a reference parameter or signal, a first identification signal, and a second identification signal, where the first identification signal and the second identification signal are distinguished, preferably spectrally spaced, from the reference signal by, respectively, a first and a second predetermined amount that corresponds, respectively, to a first transmitter and a second transmitter, comparing the first identification signal and the second identification signal to provide a strength indication, and transmitting a signal including a transmitter identification corresponding to this strength indication. For this method corresponding preferred forms of the reference and identification signals are used with corresponding results as further discussed below. A preferred messaging system in accordance with the present invention includes a plurality of transmitters arranged and constructed to operate in a simulcast mode or non-simulcast, reuse, mode. The system includes; a first transmitter for transmitting in a simulcast mode a first signal including a reference parameter or signal and a first identification signal distinguished or spectrally spaced from the reference signal by a first predetermined amount, a second transmitter for transmitting in a simulcast mode a second signal including the reference signal and a second identification signal spectrally spaced from the reference signal by a second predetermined amount, a base receiver for receiving an acknowledgment signal that includes a strength indication corresponding to a comparison of the first identification signal and the second identification signal as determined at a messaging unit location, where the strength indication corresponds to the preferred transmitter selected from the first and the second transmitter for a message delivery to the messaging unit in a non-simulcast mode. The system preferably additionally includes a controller coupled to all transmitters and base stations for controlling the system and scheduling or directing transmissions in simulcast or non-simulcast modes. Similar preferred forms of the reference and identification signals are used and directed to similar results.

For a clearer understanding of the present disclosure the reader is referred to the FIG. 1 depiction of a representative messaging system (100), preferably, selective messaging system. The messaging system includes a gateway or terminal (101) coupled to a message source such as the public switched telephone network (103). The terminal is available from Motorola as the WMG™ product as well as other manufacturers. The terminal is coupled to, often collocated with, a system controller (105), such as a Motorola RFC™ or CONDUCTOR. The terminal and system controller operate together to communicate messages with destination addresses to the system controller or various responses back to the terminal, thus PSTN and originator. The messaging system includes a plurality of transmitters with three depicted as a first, second and nth transmitter (107, 109, ... 111). The transmitters are available as Motorola NUCLEUS II™ transmitters and are coupled to the system controller by an outbound network channel (113). The outbound network channel is preferably leased telephone lines but may be any suitable media operating with any suitable networking or communication protocol including a radio link. The system, specifically controller and transmitters are arranged and constructed to operate in either a simulcast or non-simulcast mode. Operating in a simulcast mode as is generally known implies that the modulation on all carriers originating at all transmitter is substantially phase coherent and this is accomplished by insuring that all transmitters transmit the same message at the same time. Non-simulcast operation is operation of one or more transmitters in an independent fashion thus potentially increasing system capacity by virtue of the transmitter reuse. The particular equipment, such as a satellite or GPS based system typically used to provide the timing information with the degree of accuracy associated with or required for simulcast operation is, generally known, not further relevant nor further discussed, and not specifically shown. Generally the system controller provides control of the system, including scheduling messages intended for messaging units that are registered on or subscribe to the system's services, such as two depicted messaging units (115, 117). These messages are forwarded to the transmitters for subsequent transmission in accordance with a system protocol at a particular time on the forward or outbound radio channel (119). Additionally, the messaging system includes a plurality of base receivers, such as two depicted base receivers (121, 123) coupled by an inbound or network channel (125) to the system controller. Messages originating at the messaging units, either volitionally or responsive to a received message, are coupled by the reverse or inbound radio channel (127) to one or more of the base receivers where they are forwarded or relayed to the system controller on the inbound or network channel. The system controller may use these inbound messages for scheduling decisions or may forward them to the terminal, if, for example, they are intended for a user destination.

More specifically the messaging system in operation includes the first transmitter (107) transmitting in a simulcast mode a first signal, preferably an FM modulated radio signal on the forward channel (119). Referring to the FIG. 2 spectrum plot, the first signal includes or is modulated by a reference signal (201), preferably a reference tone of 1000Hz, and a first identification signal, preferably a unique first transmitter identification tone of 1200Hz, spectrally spaced from said reference signal by a first predetermined amount, preferably 200 Hz. Similarly included is the second transmitter (109) transmitting in a simulcast mode a second, preferably FM modulated radio signal on the forward channel. Referring to the FIG. 3 spectrum plot, the second signal includes or is modulated by the reference signal (201) and a second identification signal, preferably a second transmitter identification tone of 1400Hz spectrally spaced from the reference signal by a second predetermined amount, preferably 400Hz. Generalizing, many more base stations can be simulcasting their respective signals with their respective identification tones and a common reference parameter, here tone and yet each transmitter can be distinguished from the others by a receiver in a common coverage area that is operating in accordance with the inventive principles discussed here. As many as 30 different identification tones have been contemplated each separated from all others by, preferably, 200Hz.

Generally speaking in a practical messaging system the plurality of transmitters all transmit in a simulcast mode with each transmitter having a unique identification signal, preferably unique transmitter identification tone and a common reference parameter or reference signal, preferably reference tone. The system controller is responsible for assigning the unique identification signal to each base station within a cluster or grouping of base stations with same identification signals reassigned only within a different cluster using well known principles of reuse from spatial diversity systems such as cellular systems. The preferred system is a scheduled messaging system, such as a Motorola ReFLEX™ or inFLEXion™ system modified in accordance with the inventive principles disclosed herein. This system has a frame and time slot organized forward radio channel, such as depicted in FIG. 5.

FIG. 5 shows a preferred frame structure (500) that is transmitted in a simulcast mode from time to time, such as whenever the system has messages to be delivered and needs to know where the destination messaging units are located. The frame structure includes a first Sync portion (501), a second Sync portion (503), and the rest of the frame (505). The Sync portions provide sufficient information to allow for frame, word, and bit synchronization of the relevant messaging units to the forward radio channel together with other protocol dependent overhead information, such as zone identifiers, frame numbers, cycle numbers, and the like, that may be necessary for operation within the system however is not here further relevant. The rest of the frame includes messaging unit addresses and scheduling information for each messaging unit on the forward and reverse radio channel. The first Sync portion is 90 milliseconds (ms) long and is transmitted, preferably at 1600 Bps. This portion includes an identification or color code portion (507) that is 10 ms or the equivalent of 16 bits in duration. From testing the duration has been successfully varied from 5ms to as much as 40ms and may be included at any predetermined location within the frame structure The above mentioned identification signals, specifically a unique, within a given area or cluster of base stations, such signal for each base station are, preferably, simulcast transmitted during the portion (507).

The above simulcast signals will likely be received as a simulcast signal by a messaging unit (MU), such as messaging unit (117). Referring to the FIG. 4 block diagram, this MU is digital signal processor (DSP) based and arranged and constructed to determine a desirable transmitter for a message delivery and includes; a receiver (403) for receiving the simulcast signal including the reference signal (201) as detected after constructive addition, the first identification signal (203) as detected with path loss, and the second identification signal (303) as detected with path loss where all distinctions, such as spectral spacings between the reference parameter and identification signals preserved.

The MU also includes, here depicted as part of and coupled to the receiver (403) a buffer (405) and comparator (408) operating cooperatively to compare signal strengths or qualities, preferably the first identification signal and the second identification signal to provide an indication or strength indication signal at output (406). The comparator selects the appropriate indication signal, corresponding to an associated transmitter identification, and provides the indication signal to a MU transmitter (407). MU transmitter (407) transmits a signal including this indication or strength indication signal and thus transmitter identification on the reverse radio channel. In summary the system controller (105) then directs further messages destined for and thus received by this MU from a transmitter corresponding to the indication or transmitter identification in a non-simulcast mode. The receiver (403) is largely DSP based and is coupled to and controlled by a controller (409) that is based on a Motorola 68300 or similar series microprocessor. The controller (409) is executing software routines that are known or readily developed by one of ordinary skill given the inventive principles discussed here and takes care of radio management such as proper operational functions, timing, synthesizer frequency settings, and the like as generally well known. The receiver does include an RF frontend (411) coupled to an antenna (402) that operates to filter, amplify, and select given frequency carrier signals, and demodulate the carrier to provide a base band signal all as well known. When a message is received that is destined for user consumption, visual or aural, a switch (413) routes the message to a message processor (415) and to user I/O (417). Additionally all messages received are coupled in a baseband format to a well known analog to digital converter (419) where they are sampled at the rate of 51.2 thousand 8 bit samples per second. These samples or words are then processed in accordance with a 128 point or alternatively 256 point fast Fourier transform (FFT) function (421) as is well known. Preferably the received simulcast signal includes a reference tone version of the reference parameter or signal and a first and a second transmitter identification tone version of the first and second identification signals. If so, referring to FIG. 6 the results (600) of this FFT are buffered or stored by buffer (405). These results, preferably, include amplitude peaks (601) and the corresponding locations (603), for example the first, second, etc. identification signal spectral location, designated f_α - f₁₂, of the identification signals or tones relative to the spectral location (605) of the reference parameter (606) or reference tone. In the preferred form, at each operation of the FFT function the results are coupled to the buffer (405) where, preferably, a running or rolling weighted average or sum of the last plurality, for example eight, operations is maintained or stored. A simpler though likely less reliable approach is to store only the latest results.

The weighting allows for giving the more recent results or measurements greater effect while the plurality of measurements accounts for various anomalies of radio channels, such as fading. A simple linear weighting curve where the most recent measurement is given twice the weight of the oldest measurement with intermediate values receiving linearly related intermediate weights has been modeled with satisfactory results. More complex weighting curves, such as exponential or geometric, may be employed to more carefully mold the effects of newer and older measurements. As noted or implied earlier the comparator provides an indication or strength indication signal by scanning and comparing all received amplitude peaks or weighted sums thereof and selecting an appropriate or acceptable, preferably the best or strongest, one of these peaks or sums. As an alternative to the strongest peak being reported, all acceptable peaks or sums or indications may be reported.

By way of example and assuming the simple case of a single result from the FFT function, FIG. 6 by observation indicates that the strongest identification signal, here tone, is f, (607) with f₅ (609) and f₆ (611) being close seconds. Presuming a one to one correspondence, transmitter 1 (107) would appear to be the strongest, thus preferred transmitter. Alternative embodiments or comparisons would compare all received identification tones to a threshold (613) and then provide a strength indication signal that corresponds to all acceptable identification tones, here by observation (607, 609, 611) implying that corresponding transmitter 1, transmitter 5, or transmitter 6 would be acceptable. Note however that if the system controller attempts a directed message delivery to the MU, reporting this status, using either transmitter 5 or 6 and simultaneously attempts a message delivery to another MU using the other transmitter it is likely that the message delivery to the reporting MU will be unsuccessful since both transmitter 5 and 6 are apparently being received at the same level by the reporting MU. As a further alternative if the comparison of all received identification tones to the threshold showed that no identification tones were acceptable the MU may still report with an indication of that status. The system controller will know, implicitly, that communications is possible in a simulcast mode but not in a directed message mode.

More generally the MU transmitter (407) includes a translator (423) coupled to the indication at output (406) that incorporates this indication into an outbound transmit bit stream or information as generally known. This outbound bit stream may represent an acknowledgment message when the MU has been addressed by the system or may simply be a volitionally generated message. The translator is coupled to an encoder and modulator (425) that modulates as generally known the MU transmitter carrier with an encoded signal to provide a modulated carrier that is then amplified as known by power amplifier (427) and coupled to antenna (402). In this manner the MU, specifically MU transmitter transmits a signal that includes a transmitter identification corresponding to a strongest or best identification tone thus base or infrastructure transmitter, a plurality of acceptable identification tones thus such transmitters, or possibly no acceptable identification tones thus no acceptable transmitters as determined by a comparison of all identification signals including the first and the second transmitter identification tone to each other or to a predetermined threshold. When no acceptable identification tones have been observed the MU receiver may receive further transmissions, in a simulcast mode, using for example the first and the second transmitter.

These transmissions from the MUs will ordinarily be received by one or more of the base receivers (121, 123). Thus a base receiver will receive an acknowledgment signal that includes an indication corresponding to a comparison of all identification signals received at an MU including the first identification signal and the second identification signal as determined at the MU location and this indication will correspond to a preferred transmitter, selected from the first and the second transmitter, for a directed message delivery to said messaging unit. The base receiver forwards the indication to the system controller and further contemporaneous transmissions to this MU are directed by the controller to be undertaken by the preferred transmitter in a non- simulcast or directed delivery mode.

When the message or acknowledge message includes an indication corresponding to a strongest identification tone the corresponding transmitter will be used for the directed message delivery attempts. When the indication corresponds to a plurality of acceptable identification tones as determined by a comparison of said first and said second transmitter identification tone to a predetermined threshold at the messaging unit the system controller may select any one of the acceptable transmitters for subsequent directed messages. The particular selection in this case will likely depend on other system traffic considerations. If the indication corresponds to no acceptable identification tones the system controller will need to delay directed delivery messages for this MU or use simulcast attempts for further contemporaneous message delivery attempts for this particular MU. Referring to FIG. 7, a more detailed explanation of a method embodiment of the present invention will be provided. The setting is a messaging system including a plurality of transmitters arranged and constructed to operate in a simulcast mode such as the system discussed with reference to FIG. 1. The method is directed to selecting one of this plurality of transmitters for a directed or non-simulcast message delivery to an MU such as the MU discussed with reference to FIG. 4. The method begins at 700. Step (703) indicates that an identification (ID) signal is assigned to each transmitter. This ID signal is preferably a tone as earlier discussed and will be unique to each base station within a given geometrically proximate region. Approaches for providing such unique assignments are generally known from for example a similar problem with carrier frequencies in the cell phone industry. Generally the assignment is handled by the system operator using the system controller so as to facilitate any future system updates or modifications. Thereafter step (705) determines whether a new frame is starting or scheduled. The "new frame" may be any predetermined time period or event that occurs with some relative regularity. In any event if the new frame or other event is scheduled, step (707) directs a simulcast transmission of respective identification signals, preferably unique identification tones as modulation on a radio frequency carrier, including a reference parameter, preferably reference tone as modulation, from each of the transmitters. Preferably a system controller directs at least a first and a second transmitter to transmit in the simulcast mode, respectively, a first signal including a reference parameter and a first identification signal and a second signal including the reference parameter and a second identification signal, where the first identification signal and the second identification signal are distinguished from the reference parameter by, respectively, a first and a second predetermined amount. After step (707), the process moves to and returns from FIG. 8 at, respectively, A (709) and B (711) where preferably an MU detects and responds to the simulcast signals, as further discussed below. After B (711) step (713) receives an acknowledgment signal or other volitionally generated signal, preferably from an MU, having a relative indication of ID signals corresponding to a preferred transmitter. Preferably this signal at least includes an indication of the first identification signal relative to the second identification signal as determined at a messaging unit location where the indication corresponds to a preferred transmitter, selected from the first and the second transmitter, for a directed or non-simulcast message delivery to this messaging unit. This receiving step is preferably performed at a base receiver with the information received then being forwarded to and received by the system controller.

More specifically step (713) includes steps (715, 717, 719) each denoting different methodology depending on the particulars of the indication received. Step (715) is followed when the indication corresponds to the best or strongest ID signal determined at the MU location by a comparison of all received ID signals and is followed by step (721) where the transmitter having the corresponding ID signal is selected, preferably by the system controller. Note the indication from the MU may include or specify the preferred transmitter however allowing the system controller to do the correlation will usually provide greater future system flexibility. Then step (725) directs this preferred transmitter to send any further contemporaneous messages to the MU in a non- simulcast or directed delivery mode.

If the indication corresponds to a plurality of acceptable ID signals as determined at the MU by comparing all received ID tones to a threshold thus suggesting a plurality of acceptable transmitters for further directed message delivery attempts, step (717) is followed after which step (723) is directed to selecting one transmitter corresponding to one of the plurality of ID signals. Step (723) will be performed, preferably, by the system controller with the eventual selection depending, for example, on other system traffic requirements. After step (723) step (725) is performed. When the indication does not specify an ID signal thus indicating that no ID signal is acceptable when compared to a threshold, step (719) is followed and step (727) is then performed. Step (727) directs further contemporaneous transmissions to this MU in a simulcast mode. The method of FIG. 7, while set in a messaging system, is preferably executed at the system controller and is implemented with software routines readily modified or written by one of ordinary skill given the inventive principles discussed here

FIG. 8 starts at A (709) and depicts a method for determining a desirable transmitter for a message delivery to a messaging unit. This method is preferably practiced at an MU principally with readily available or readily modified software routines written in accordance with the principles discussed here so as to execute on the MU's controller or DSP. Step (801) receives a simulcast signal, preferably as transmitted at step (707). Specifically the simulcast signal includes at least a reference parameter, a first identification signal, and a second identification signal, the first identification signal and the second identification signal distinguished from the reference parameter by, respectively, a first and a second predetermined amount that corresponds, respectively, to a first transmitter and a second transmitter. At step (803) we determine whether the signal includes a message for a user and if so at step (805) process and provide that message to the user.

In either event Step (807) performs an FFT on the portion of the simulcast signal that includes the ID signals and reference parameter, preferably tones as earlier noted. The resulting amplitudes of the ID signals are buffered or stored at step (809). At optional step (811) the weighted rolling averages of the ID signals are updated. Step (813) performs a scanning and comparing procedure on the ID signals or weighted rolling averages and selects an appropriate indication. Step (813) includes steps (815, 817, 819, 821) and these are selectively performed depending on the particular embodiment.

Step (815) selects the strongest ID signal and corresponding indication of the same by comparing all of the ID signals, including in particular a first identification signal to a second identification signal, to provide an indication corresponding to the desirable transmitter. Alternatively step (817) will select a plurality of ID signals each of which satisfies a threshold and a corresponding indication thereof. If no ID signal satisfies the threshold as determined at step (819), step (821) selects a null indication. In any event after step (813) step (823) transmits an acknowledgment signal or a voiitionally generated signal that includes the selected indication from either step (815, 817, or 821) and the process goes to B (711). Summarizing, FIGs 7 and 8 depict inventive approaches for determining a desirable transmitter for delivery of a message in a non- simulcast mode. Having selected such a transmitter and having then made such a transmission the MU will receive this transmission, in a non-simulcast mode, including a message from this transmitter that corresponds to the indication.

The above described inventive approaches for determining a preferred and desirable transmitter for directed message delivery will now be further extended to grouping transmitters and selecting a desirable transmitter for directed message delivery to an MU or PMU within the group. The grouping will be accomplished, as explained below with reference to FIGs 9-18, in a manner that optimizes signal quality available for the message delivery while improving or enhancing efficiency of utilization of system resources.

FIG. 11 illustrates a communication system 1100 including one or more portable messaging units (PMUs) 1105, such as radio transceivers, for receiving and transmitting radio signals. The communication system 1100 further includes at least one radio frequency controller (RFC) 1110 for controlling operations of the system 1100. In particular, the RFC 1110 receives data, such as messages, for transmission to a PMU 1105. The RFC 1110 receives the data from, for example, conventional telephones or modems over a telephone network (not shown). The messages are then provided by the RFC 1110 to one or more transmitters 1115 included in the system 1100 for transmitting the messages as radio signals. A receiving device 1120 receives communications from PMUs 1105 and provides the communications to the RFC 1110 over a communication link, such as a dedicated wireline or a wireless communication channel.

Referring next to FIGs. 12 and 13, possible arrangements of transmitters 1115 within the system 1100 are depicted. As shown, the communication system 1100 comprises a plurality of cells grouped into clusters, each including a particular number of cells within which the transmitters 1115 send radio signals. The illustration of FIG. 12 shows a three-cells-per-cluster 1205, 1210 arrangement, i.e., reuse groups according to a reuse factor of three, while the illustration of FIG. 13 shows a seven- cell-per-cluster 1305, 1310 arrangement, i.e., reuse groups according to a reuse factor of seven. Each cell comprises a pre-defined area including a transmission range of the associated transmitter 1115, and cells are generally located at fixed distances from other cells. The distance between cells is determined by the cluster size and by the transmission range or ranges of the transmitters 1115. It will be appreciated that, within any given reuse group, only one transmitter 1115 at a time transmits over a particular communication channel, e.g., frequency. Other transmitters 1115 could, for instance, be turned off or transmit on different channels. Although FIGs. 12 and 13 depict fixed clusters of transmitters 1115, the transmitters 1115 included in each cluster can also be varied. For instance, referring to FIG. 12, the RFC 1110 could group TX1, TX3, and TX4 into a three-cell cluster. Referring to FIG. 13, the RFC 1110 could group TX3, TX4, TX5, TX6, TX7, TX10, and TX11 into a seven-cell cluster. This aspect of the present invention will be explained in greater detail below. In accordance with the present invention, the transmitters 1115 can be dynamically grouped into reuse groups including different numbers of transmitters 1115 based upon information supplied to the RFC 1110 by PMUs 1105 within the system 1100. Specifically, each transmitter 1115 within the system 1100 sends out a transmission signal at a reference frequency and a transmission signal at another frequency recognized by a PMU 1105. Preferably, a signaling protocol such as the well-known FLEX™ protocol is used for message delivery, and the transmission signals are sent out by the transmitters 1115 during predetermined times, such as during transmission of the "B" word of the synchronization code in selected or all frames of the radio signal. The PMU 1105 receives the transmission signals, or at least the portion that originates from in-range transmitters 1115. According to the present invention, the PMU 1105 is able to associate the received transmission signals with the transmitters 1115 that sent the transmission signals, such as by storing a listing of transmitter identification information (IDs) and frequencies associated therewith. The IDs can be programmed, for instance, manually by a service provider or by over-the-air programming.

The transmission signals that are provided by the transmitters 1115 need only be separable by receiving PMUs 1105 from other communications within the system 1100. Preferably, the transmission signals comprise orthogonal signals, such as tones. The transmission signals will hereinafter be referred to as tones, although other signal types can be alternatively utilized.

Bandwidths and frequency intervals for the tones can be varied to suit system needs. By way of example, the frequency tones sent by the transmitters 1115 could be located in a frequency bandwidth of 6.25 kilohertz (kHz) and separated by 150 Hz intervals. Therefore, according to the example, twenty-nine (29) tones would fit within a 6.25 kHz bandwidth. The number of tones can be doubled through time reuse. For instance, a first set of transmitters 1115 including twenty-eight (28) transmitters 1115 could transmit tones during one set of frames of the radio signal, while a second set of transmitters 1115 including another twenty-eight (28) transmitters 1115 could use another set of frames. By way of example, the two sets could be chosen to correspond to odd- numbered and even-numbered frames. When the number of transmitters 1115 within the system 1100, or within any particular zone of the system 1100, exceeds fifty-six (56), tones can be reused if necessary. According to a first embodiment of the present invention, the PMU 1105 receives tones from the transmitters 1115 and measures the power, i.e., the signal strength, of each received tone. The powers, in decibels, are provided directly to the RFC 1110 for calculation thereby of carrier-to-interference (C/I) values associated with the PMU 1105. The C/I values are indicative of relative strengths of the tones provided by the transmitters 1115 and are preferably calculated not only for each transmitter, but also for each possible transmitter grouping, i.e., each possible reuse factor. The RFC 1110 then determines from the C/I values which particular transmitter 1115 and which particular reuse factor are to be used for transmission of a message to the PMU 1105. The PMU 1105 can then, for example, be instructed as to which frequency will be used to transmit its messages. Alternatively, the PMU 1105 can scan to locate the proper frequency associated with the transmitter 1115 selected to transmit messages to the PMU 1105. When transmitters 1115 within the system 1100 are able to transmit on different frequencies, the RFC 1110 preferably also indicates to the selected transmitter 1115 which frequency is to be used for transmission.

According to a second embodiment of the present invention, the PMU 1105 computes the C/I values from the received tones. The C/I values are then sent by the PMU 1105 to the RFC 1110 so that the RFC 1110 can determine a reuse factor, e.g., three, five, seven, etc., that is indicative of the particular number of transmitters included in a reuse group and that is used for determining which transmitter 1115 is to be used to transmit a message to the PMU 1105. These two embodiments will be explained in greater detail below. FIG. 14 is an electrical block diagram of a PMU 1105 in accordance with the present invention. The PMU 1105 includes a transceiver 1405 for receiving tones transmitted by the transmitters 1115 (FIG. 11) and messages intended for reception by the PMU 1105. The tones and messages are processed by a processor 1420 coupled to the transceiver 1405 for controlling operations of the PMU 1105. A message memory 1415 stores the messages, a frequency database 1430 stores an indication of a reference frequency and frequencies at which tones are transmitted by the different transmitters 1115, and a tone database 1410 stores power measurements for received tones and transmitter IDs of transmitters 1115 associated therewith. A device memory 1425 stores an address associated with the PMU 1105, and a measurer 1435 measures signal strengths of the received tones. The measurer 1435 can be, for example, implemented in firmware stored in the device memory 1425 and executed by the processor 1420.

FIG. 15 is a flowchart illustrating an operation of the processor 1420 according to the present invention. When, at step 1505, the processor 1420 recognizes the synchronization word of the received radio signal, the measurer 1435 is activated, at step 1510. When, at step 1515, the synchronization word is over, the contents of the tone database 1410 (FIG. 14) are provided to the RFC 1110 (FIG. 11) via the transceiver 1405. When, at step 1635, reference to the frequency database 1430 indicates that further tones are to be located, processing continues at step 1615. Otherwise, the measurer 1435 awaits reactivation by the processor 1420, in which case processing continues at step 1605.

FIG. 16 is a flowchart of an operation of the measurer 1435 which, at step 1605, searches for a tone at the reference frequency. When, at step 1610, the reference frequency tone is found, the measurer 1435 attempts to locate a next tone, at step 1615. Thereafter, the power of the next located tone is measured, at step 1620, in a conventional manner. The frequency database 1430 is then referenced, at step 1625, to determine which of the transmitters 1115 is associated with the located tone, and an appropriate entry of the transmitter ID and signal strength is made in the tone database 1410, at step 1630. Referring next to FIG. 17, an electrical block diagram of an RFC 1110 according to the present invention is shown. The RFC 1110 includes a receiver 1745 for receiving the contents of the tone database 1410 from the PMU 1105, data ports 1705 for coupling to the transmitters 1115, and a central processing unit (CPU) 1710 for controlling operations of the RFC 1110. The data ports 1705 can also be coupled to a telephone network (not shown) for receiving messages intended for reception by PMUs 1105 within the system 1100 (FIG. 11).

A transmission database 1715 is coupled to the CPU 1710 for storing messages intended for reception by PMUs 1105, and a power database 1720 is coupled to the CPU 1710 for storing the power measurements, i.e., signal strengths, returned to the RFC 1110 by the different PMUs 1105 in the system 1100. A controller memory 1725 stores system parameters and system information, such as subscriber information, a C/I threshold value indicative of a calculated value for which messages are likely to be received properly by recipient PMUs 1105, and reuse information that includes different reuse factors. When the transmitters associated with each reuse group are fixed, the reuse information further includes transmitter groupings associated with each reuse group. The reuse information could include, for instance, an indication that TX9, TX10,

TX12, TX13, TX14, TX15, and TX24 form a single reuse group 1310 (FIG. 13) when the reuse factor equals seven. When the composition of the reuse groups can be varied, though, this information would be unnecessary. The RFC 1110 also includes a calculator 1730 for calculating, for each PMU 1105 that returned signal strengths of tones, C/I values indicative of relative signal strength for each transmitter 1115 and for each reuse group. A sender 1735 dynamically groups transmitters into appropriate reuse groups for transmission of messages in the system 1100. A reuse database 1740 is coupled to the CPU 1710 for storing the C/I values calculated by the calculator 1730. Preferably, the calculator 1730 and the sender 1735 are implemented in firmware stored in the controller memory 1725 and executed by the CPU 1710. Alternatively, hardware capable of performing equivalent operations can be used.

According to the present invention, the RFC 1110 receives signal strengths from the PMUs 1105 and calculates therefrom C/I values for each reuse factor utilized in the system 1100. By way of example, when the reuse factors are three, five, seven, nine, twelve, and thirteen (as shown), C/I values are calculated for each PMU 1105 for a transmitter reuse group that includes three transmitters 1115, then for a transmitter reuse group that includes five transmitters 1115, and so on, as explained in greater detail below. Additionally, as mentioned above, the transmitters 1115 included in each reuse group are not necessarily fixed. Therefore, C/I values can be calculated not only for different reuse factors but also, for each reuse factor, different combinations of transmitters 1115. Once the reuse database 1740 has been completed, the RFC 1110 determines, for each PMU 1105 awaiting message delivery, which reuse factor yields a lowest C/I value that still exceeds the C/I threshold value stored in the controller memory 1725. When, for instance, the C/I threshold value equals sixteen decibels (dB), a reuse factor of seven is chosen for message delivery to a first PMU 1105, e.g., PMU1, and a particular transmitter, e.g., TX2, in one of the seven-cell reuse groups is chosen to transmit the message to PMU1. Similarly, a reuse factor of five is chosen for message delivery to another PMU 1105, e.g., PMU3, and another transmitter, e.g., TX18, in one of the five-cell reuse groups is chosen to transmit the message to PMU3. After determining which reuse factor and which transmitter 1115 optimize the message delivery process for each PMU 1105 intended to receive a message, the RFC 1110 then groups together all outgoing messages having equivalent reuse factors for transmission during different time periods using different reuse groups. In this manner, the transmitters 1115 can be dynamically grouped for message delivery while still optimizing the C/I values to ensure proper message delivery. For illustrative purposes only, FIG. 17 shows a simplified reuse database 1740 that includes only the C/I values and selected transmitter 1115 for each reuse factor. It will be appreciated, however, that additional information will be included for systems in which the particular transmitters included in reuse groups vary. By way of example, a more complex reuse database could, in reality, also include an indication of which transmitters 1115 will be combined into a reuse group with the selected transmitter 1115 for each reuse factor entry in the database. In the reuse database 1740 of FIG. 17, for instance, the entry associated with PMU1 and with a reuse factor of three (3) could also designate that the selected reuse group would include TX11, TX13, and TX14. For purposes of simplicity, however, the system 1100 will be described below as if the transmitters 1115 included within each reuse group are fixed.

Referring next to FIG. 18, a flowchart illustrates an operation of the calculator 1730 in accordance with the present invention. When, at steps 1805, 1810, messages are stored in the transmission database 1715 for transmission, but a recipient PMU 1105 has not provided power measurements, the message for that particular PMU 1105 is held until a later time when power measurements have been received from the PMU 1105.

When, at steps 1805, 1810, there are messages for transmission and a recipient PMU 1105 has provided power measurements, a variable R_U (indicative of "reuse factor") is set, at step 1820, to equal the lowest reuse factor indicated by the reuse information stored in the controller memory 1725. Then, at step 1825, for each transmitter associated with a power measurement provided by the recipient PMU, the C/I value is calculated using the particular transmitter grouping associated with R_U. Specifically, the C/I value for a particular transmitter 1115 is calculated by summing the signal strengths of the tones transmitted by all corresponding transmitters 1115 within the system 1100. Corresponding transmitters 1115 are those transmitters 1115 that are to transmit on the same channel as the particular transmitter 1115 but that are in different reuse groups. The signal strength of the tone transmitted by the particular transmitter 1115 is then divided by the sum. This process is given by the following formula:

(1) C/IpMUπ ⁼ Strengthtransmitter m I ∑(strength_correSp_θnding transmitters) •

The following example operates on the assumptions that TXl, TX5, TX9, TX12, TX14, TX18, and TX12 are corresponding transmitters that transmit on the same channel in different reuse groups and that PMU1 received tones from TXl, TX5, TX9, TX12, TX14, TX18, and TX12. Given these assumptions and referring to FIG. 12 in conjunction with FIG. 18, when R_U = 3, the C/I value for TXl with respect to PMU1 is given by the following formula:

(2) C/IpMui = strength_Tχι / (strength_TX5 + strength_Tχ9 + strength_Tχi2

+ strengthτχi4 + strengthχχi8 + strengthτχ₂ι)-

The next example assumes that TX3, TX13, TX18, and TX25 are corresponding transmitters in different reuse groups and that PMU1 received tones from TX3, TX13, TX18, and TX25. Referring to FIG. 13 in conjunction with FIG. 18, when R_U = 7 (FIG. 13), the C/I value for TX13 with respect to PMU1 is given by the following formula:

(3) C/IPMUI = strength_Tχi₃ / (strength_TX3 + strength_TX18 + strength_Tχ2₅).

In both of the above examples, it will be appreciated that corresponding transmitters providing tones that were not received by the PMU 1105 will not be included in the denominator sum. Furthermore, when the system 1100 includes a greater number of reuse groups than shown in FIGs. 12 and 13, the denominator sum would account for additional corresponding transmitters as long as the PMU 1105 received the tones transmitted thereby.

Returning to FIG. 18, once all C/I values have been calculated for all transmitters 1115 with respect to the recipient PMU 1105 and with respect to the current setting of R_U, the highest C/I value and the ID of the transmitter associated therewith is stored, at step 1830, in the reuse database 1740 for the current reuse factor, as indicated by R_U. As mentioned above, the reuse database 1740 could further indicate which transmitters 1115 are included in each reuse group when the particular transmitters within each reuse group can be varied within the system 1100.

When, at step 1835, all of the reuse factors have not been considered in calculating C/I values for the recipient PMU 1105, R_U is incremented, at step 1840, to the next reuse factor. For instance, in the reuse database 1740 (FIG. 17), R_U would be incremented from three to five. Processing then continues at step 1825 to calculate, for the next value of R_U, C/I values for all transmitters 1115 with respect to the recipient PMU 1105.

When, at step 1835, all reuse factors have been considered in calculating C/I values for the recipient PMU 1105, the transmission database 1715 is referenced, at step 1815, to determine whether any messages for transmission to other PMUs 1105 are stored. When so, processing continues at step 1810. In this manner, the calculator 1730 fills, for each recipient PMU 1105, the reuse database 1740 with the most favorable C/I values and transmitter IDs associated therewith for each reuse factor.

It will be appreciated that less elaborate communication systems could always operate in a fixed reuse pattern, in which case messages for PMUs associated with insufficiently low C/I values could be held until a later time when higher C/I values are calculated. Alternatively, different reuse factors could be available but unused by a system under certain circumstances, such as when some transmitters are unavailable for use. Referring next to FIG. 9, a flowchart depicts an operation of the sender 1735 (FIG. 17) according to the present invention. When, at step 1905, messages are to be transmitted at the current time, e.g., when a frame corresponding to a home frame of a PMU 1105 has arrived, the variable R_U is set, at step 1910, to the lowest reuse factor, as indicated by the reuse information stored in the controller memory 1725. Then, at step 1915, when the C/I values for any recipient PMUs 1105 exceed the C/I threshold value stored in the controller memory 1725, the messages for those recipient PMUs 1105 are gathered and provided, at step 1920, to the transmitters 1115 for transmission thereby. Specifically, the RFC 1110 provides instructions for grouping the transmitters 1115 in the system 1100 into reuse groups in accordance with the reuse factor associated with the current value of R_U. Additionally, each message to be transmitted using the reuse factor associated with the current value of R_U is provided to the transmitter 1115 specified in the reuse database 1740 (FIG. 17), i.e., the transmitter 1115 that has been previously determined to yield the highest C/I value for the particular reuse group. Thereafter, the messages provided to the transmitters 1115 can be deleted, at step 1925, from the transmission database 1715 or marked as having been transmitted.

When, at step 1915, no C/I values in the database 1740 exceed the C/I threshold value for the reuse factor indicated by R_U, and all reuse factors have been considered, at step 1930, the sender 1735 awaits activation at a later time when processing continues at step 1905. When, at step 1930, all reuse factors have not yet been considered, the variable R_U is incremented, at step 1935, to the next reuse factor, and processing continues at step 1915.

As described in FIGs. 9, 14-18, the PMU 1105 calculates signal strengths of the received tones and returns the signal strengths to the RFC 1110 for calculation of the C/I values. Based on the C/I values, the RFC 1110 can then determine, for each message to be transmitted, the minimum number of transmitters that can be grouped into reuse groups while still ensuring delivery of a message that can be decoded without errors by the PMU 1105. Furthermore, the RFC 1110 can advantageously vary the number of transmitters in reuse groups for delivery of different messages. As a result, transmission resources are also efficiently utilized, since no message is transmitted using any higher reuse factor than necessary. Messages can therefore be provided without the delays and without the erroneous or missed messages that are often present in conventional messaging systems.

Additionally, the C/I values can be advantageously used for purposes other than grouping of the transmitters 1115 into reuse groups. For instance, data rate could be varied based upon the C/I values so that PMUs 1105 reporting high C/I values could receive messages at higher channel speeds, thereby further reducing system backlogs and delays. When C/I values for a PMU 1105 are sufficiently high, error correction could even be eliminated to reduce message length.

It will be appreciated by one of ordinary skill in the art that, when the RFC 1110 knows the system layout and transmitter characteristics, the RFC 1110 need not group the transmitters 1115 into groups based on fixed reuse factors at all. Instead, transmitters 1115 can be selected and/or grouped as necessary depending upon PMU locations and reported power measurements, from which the C/I values are calculated by the RFC 1110. By way of example, reference to calculated C/I values for recipient PMUs 1105 might reveal that transmission by selected transmitters 1105, with other transmitters 1115 turned off, adequately guarantees message delivery at a particular time, even without the formation of reuse groups within the communication system 1100. Alternatively, reuse groups could be formed using clusters of differing numbers of transmitters 1115. For instance, at one area within the system 1100, a reuse group could be formed by three transmitters 1115 while, at another area, a reuse group could be formed by seven transmitters 1115, with both reuse groups transmitting at the same time. Even in embodiments in which reuse groups of fixed numbers of transmitters 1115 are used, reuse factors do not necessarily have to be preprogrammed into the RFC 1110. Instead, the RFC 1110 can group the transmitters 1115 into reuse groups defined by any feasible reuse factor. For example, rather than using set reuse factors of 3, 5, 7, 9, 12, and 13 (as shown in FIG. 17), the RFC 1110 could calculate C/I values for reuse factors of 1, 2, 3, 4, 5, and so on until one of the reuse factors yields a

C/I value that exceeds the C/I threshold. In this manner, transmission of messages could be accomplished efficiently and quickly without jeopardizing reliability.

FIG. 10 is an electrical block diagram of a PMU 1105' that can be utilized in accordance with still another embodiment of the present invention. The PMU 1105' utilizes a transceiver 1405', a message memory 1415', a frequency database 1430', a measurer 1435', a tone database 1410', a device memory 1425', and a processor 1420' for performing operations similar to those performed by the PMU 1105 of FIG. 14. Additionally, the PMU 1105' includes a calculator 1950, which can be implemented in firmware, for calculating the C/I values for each reuse factor from the signal strengths of the received tones. A reuse database 1955 then stores the C/I values. Preferably, the device memory 1425' of the PMU 1105' includes the C/I threshold value and reuse information equivalent to that stored by the RFC 1110 of FIG. 17. However, it will be appreciated that, in this embodiment of the present invention, the particular transmitters included in each reuse group should be fixed for each reuse factor.

According to this embodiment of the present invention, the calculator 1950, for each reuse factor, computes the C/I values for the different transmitters 1115 and determines which transmitter 1115 yields the highest C/I value in a manner similar to that described with reference to FIG. 18. That C/I value and the ID of the particular transmitter 1115 are then stored in the reuse database 1955. Preferably, the processor 1420' references the stored C/I values to determine the lowest C/I value that exceeds the C/I threshold value and then activates the transceiver 1405' to transmit the selected reuse factor and transmitter ID to the RFC 1110. In this way, the PMU 1105' need only send a small amount of information; transmission of the entire contents of the tone database 1410' is unnecessary. As a result, less power and less time are required for transmission of the necessary information to the RFC 1110.

In summary, the communication system as described above includes a radio frequency controller (RFC) for controlling the system, portable messaging units (PMUs) for receiving messages, and transmitters for transmitting the messages to the PMUs. According to the present invention, the transmitters send out tones that are received by the PMUs, which subsequently calculate signal strengths of the received tones and transmit the signal strengths and associated transmitter IDs to the RFC. The RFC then calculates relative signal strengths, i.e., C/I values, of the tones received by the different PMUs for reuse factors associated with different reuse groups into which the transmitters can be grouped for message transmission. The C/I values are compared to a threshold value to determine, for each PMU intended to receive a message, which of several possible reuse groups will efficiently utilize system resources while maintaining messaging reliability. Thereafter, the messages to be transmitted are grouped according to reuse factors, and the RFC sends out the messages to be transmitted using different reuse groups during different time periods, respectively.

By way of example, when a first PMU sends a first signal indicative of first signal strengths, the RFC can calculate first C/I values associated with the first PMU. Then, a message to the first PMU can be transmitted during a first time period using a first selected transmitter determined from the first C/I values and included in a first reuse group characterized by a cluster of a first number of transmitters, i.e., a first reuse factor. When a second PMU sends a second signal indicative of second signal strengths, the RFC can calculate second C/I values associated with the second PMU. Subsequently, during a second time period, a message to a different PMU can be transmitted using a second selected transmitter determined from the second C/I values and included in a second reuse group characterized by a cluster of a second number of transmitters, i.e., a second reuse factor. In this manner, system performance can be optimized by dynamically altering reuse groups of transmitters based on the calculated C/I values.

Alternatively, each PMU could itself calculate its C/I values for each reuse group, then provide the RFC with a signal indicating the reuse group and the selected transmitter that are most appropriate for message transmission. This embodiment would require less time and less power for transmission of information from the PMU to the RFC.

Another advantages of calculating the C/I values is that data rate could be varied based upon the C/I values so that PMUs 1105 reporting high C/I values could receive messages at higher channel speeds, thereby speeding up message transmission. Also, error correction could be eliminated for PMUs 1105 with sufficiently high C/I values.

It will be appreciated by those of ordinary skill in the art that the apparatus and methods disclosed provide various approaches for determining a desirable transmitter for an optimized quality directed message delivery in a communications system that is set up for simulcast operation An approach has been shown that enhances efficiency of system resource utilization without unduly compromising any signal or system characteristics or otherwise unnecessarily burdening processing resources. These inventive structures and methods may be readily and advantageously employed in a wireless selective messaging system, system controller or messaging unit to provide directed message delivery and the resultant enhanced system capacity and efficiency. Hence, the present invention, in furtherance of satisfying a long-felt need of wireless communications, readily facilitates, for example, systems, receivers, and the like that require simulcast operation for hailing or initial unit location and thereafter directed message delivery to accommodate the requisite level of system traffic. Such information may by advantageously used to provide greater system capacity by facilitating, for example, more accurate directed message delivery or allowing more freedom from a messaging system perspective to provide directed message delivery.

It will be apparent to those skilled in the art that the disclosed invention may be modified in numerous ways and may assume many embodiments other than the preferred forms specifically set out and described above. For example many of the inventive procedures and apparatus described in a preferred form for FSK systems will work equally well for QAM systems, for example. Accordingly, it is intended by the appended claims to cover all modifications of the invention which fall within the true spirit and scope of the invention.

What is claimed is:

Claims

1. In a messaging system including a plurality of transmitters arranged and constructed to operate in a simulcast mode, a method of selecting a transmitter for directed message delivery, the method including the steps of; directing a first and a second transmitter to transmit in the simulcast mode, respectively, a first signal including a reference parameter and a first identification signal and a second signal including said reference parameter and a second identification signal, said first identification signal and said second identification signal distinguished from said reference parameter by, respectively, a first and a second predetermined amount, receiving an acknowledgment signal that includes a indication of said first identification signal relative to said second identification signal as determined at a messaging unit location, said indication corresponding to a preferred transmitter, selected from said first and said second transmitter, for a directed message delivery to said messaging unit.

2. The method of claim 1 wherein said first signal is transmitted with modulation including a reference tone and a first transmitter identification tone and said second signal is transmitted with modulation including said reference tone and a second transmitter identification tone.

3. The method of claim 2 wherein said step of receiving an acknowledgment signal further includes receiving an indication corresponding to a strongest identification tone as determined by a comparison of said first and said second transmitter identification tone at said messaging unit.

4. The method of claim 2 wherein said step of receiving an acknowledgment signal further includes receiving an indication corresponding to a plurality of acceptable identification tones as determined by a comparison of said first and said second transmitter identification tone to a predetermined threshold at said messaging unit.

5. A method of determining a desirable transmitter for a message delivery to a messaging unit, the method including the steps of; receiving a simulcast signal including a reference parameter, a first identification signal, and a second identification signal, said first identification signal and said second identification signal distinguished from said reference parameter by, respectively, a first and a second predetermined amount that corresponds, respectively, to a first transmitter and a second transmitter, comparing said first identification signal to said second identification signal to provide an indication corresponding to the desirable transmitter, transmitting a signal including said indication.

6. The method of claim 5 wherein said step of receiving a simulcast signal includes receiving a reference tone, a first transmitter identification tone and a second transmitter identification tone.

7. The method of claim 6 wherein said step of transmitting said signal further includes transmitting an indication corresponding to a strongest identification tone as determined by a comparison of said first and said second transmitter identification tone.

8. The method of claim 6 wherein said step of transmitting said signal further includes transmitting an indication corresponding to a plurality of acceptable identification tones as determined by a comparison of said first and said second transmitter identification tone to a predetermined threshold.

9. The method of claim 6 wherein said step of transmitting said signal further includes transmitting an indication corresponding to no acceptable identification tones as determined by a comparison of said first o and said second transmitter identification tone to a predetermined threshold.

10. A messaging system including a plurality of transmitters arranged and constructed to operate in a simulcast mode or non-simulcast mode, 5 the system comprising in combination; a first transmitter for transmitting in a simulcast mode a first signal including a reference parameter and a first identification signal spectrally spaced from said reference parameter by a first predetermined amount, a second transmitter for transmitting in a simulcast mode a second o signal including said reference parameter and a second identification signal distinguished from said reference parameter by a second predetermined amount, a base receiver for receiving an acknowledgment signal that includes an indication corresponding to a comparison of said first 5 identification signal and said second identification signal as determined at a messaging unit location, said indication corresponding to a preferred transmitter, selected from said first and said second transmitter, for a directed message delivery to said messaging unit.

0

11. The messaging system of claim 10 further including a system controller, coupled to said first transmitter, said second transmitter, and said base receiver, for directing a transmission, in a non-simulcast mode, of a message from said preferred transmitter.

12. The messaging system of claim 10 wherein said first transmitter transmits said first signal with modulation including a reference tone and a first transmitter identification tone and said second transmitter transmits said second signal with modulation including said reference tone and a second transmitter identification tone.

13. A messaging unit arranged and constructed to determine a desirable transmitter for a message delivery, the selective messaging unit comprising in combination; a receiver for receiving a simulcast signal including a reference parameter, a first identification signal, and a second identification signal, said first identification signal and said second identification signal distinguished from said reference parameter by, respectively, a first and a second predetermined amount that corresponds, respectively, to a first transmitter and a second transmitter, a comparator, coupled to said receiver, for comparing said first identification signal and said second identification signal to provide an indication signal, a transmitter, coupled to said comparator, for transmitting a signal including a transmitter identification corresponding to said indication signal.

14. The messaging unit of claim 13 wherein said receiver further receives a transmission, in a non-simulcast mode, of a message from a transmitter corresponding to said transmitter identification.

15. The messaging unit of claim 13 wherein said receiver receives a simulcast signal including a reference tone, a first transmitter identification tone and a second transmitter identification tone.

16. The messaging unit of claim 15 wherein said transmitter transmits a signal further including a transmitter identification corresponding to a strongest identification tone as determined by a comparison of said first to said second transmitter identification tone.

17. The messaging unit of claim 15 wherein said transmitter transmits a signal further including a transmitter identification corresponding to a plurality of acceptable identification tones as determined by a comparison of said first and said second transmitter identification tone to a predetermined threshold.

18. The messaging unit of claim 15 wherein said transmitter transmits a signal further including a transmitter identification corresponding to no acceptable identification tones as determined by a comparison of said first and said second transmitter identification tone to a predetermined threshold.

19. A method for dynamically selecting transmitters for message transmission in a communication system, the method comprising the steps of: sending transmission signals from the transmitters; calculating carrier-to-interference (C/I) values indicative of relative strengths of the transmission signals received by a portable messaging unit (PMU) included in the communication system; and determining, prior to message delivery, a selected transmitter for transmitting a message to the PMU, the selected transmitter associated with a lowest C/I value that is chosen from the C/I values and that exceeds a C/I threshold value.

20. The method of claim 19, wherein the calculating step comprises the step of: computing a C/I value associated with a particular transmitter by dividing a signal strength of a transmission signal transmitted by the particular transmitter with a sum of signal strengths of transmission signals transmitted by other transmitters not including the particular transmitter.

21. The method of claim 19, further comprising the steps of: calculating different C/I values indicative of relative strengths of the transmission signals received by a different PMU; and determining, prior to message delivery, a second selected transmitter for transmitting a second message to the different PMU, the second selected transmitter associated with a lowest C/I value that is chosen from the different C/I values and that exceeds the C/I threshold value.

22. The method of claim 19, wherein the calculating step comprises the step of: computing C/I values associated with a particular transmitter included in a cluster of transmitters defined by a particular reuse factor by dividing a signal strength of a transmission signal transmitted by the particular transmitter with a sum of signal strengths of transmission signals transmitted by other transmitters included within other clusters of transmitters defined by the particular reuse factor.

23. The method of claim 19, wherein the calculating step comprises the steps of: the PMU calculating signal strengths of the transmission signals; the PMU transmitting a signal indicative of the signal strengths to a controller included in the communication system; the controller computing the C/I values; and the controller determining the selected transmitter.

24. The method of claim 19, wherein the calculating step comprises the steps of: the PMU calculating signal strengths of the transmission signals; the PMU computing the C/I values; the PMU determining the selected transmitter; and the PMU transmitting a signal indicative of the selected transmitter to a controller included in the communication system.

25. A communication system for dynamically selecting transmitters for message transmission, the communication system comprising: the transmitters for sending transmission signals; a portable messaging unit (PMU) for receiving the transmission signals, calculating signal strengths of the transmission signals, and transmitting a signal indicative of the signal strengths; and a controller for receiving the signal, determining therefrom carrier- to-interference (C/I) values indicative of relative strengths of the transmission signals received by the PMU prior to message delivery to the PMU, and determining a selected transmitter for transmitting a message to the PMU, the selected transmitter associated with a lowest C/I value that is chosen from the C/I values and that exceeds a C/I threshold value.

26. A portable messaging unit (PMU) for receiving signals, the PMU comprising: a transceiver for receiving transmission signals transmitted by transmitters; calculating means coupled to the transceiver for calculating carrier- to-interference (C/I) values indicative of relative strengths of the transmission signals; and determining means coupled to the calculating means for determining, prior to message delivery to the PMU, a selected transmitter for transmitting a message to the PMU, the selected transmitter associated with a lowest C/I value that is chosen from the C/I values and that exceeds a C/I threshold value, wherein the transceiver transmits a signal indicative of the selected transmitter for subsequent use in transmitting the message to the PMU.

27. The PMU of claim 26, wherein the calculating means comprises: a measurer for calculating signal strengths of the transmission signals; and a calculator coupled to the measurer for computing the C/I values from the signal strengths.

28. The PMU of claim 27, wherein the determining means comprises a processor for comparing the C/I values to the C/I threshold value to determine the selected transmitter.

29. The PMU of claim 28, further comprising: a device memory coupled to the processor for storing the C/I threshold value.

30. The PMU of claim 28, further comprising: a frequency database coupled to the processor for storing frequencies at which the transmission signals are transmitted; a tone database coupled to the processor for storing the signal strengths of the transmission signals; and a reuse database coupled to the processor for storing the C/I values calculated by the calculator.

31. The PMU of claim 28, wherein the PMU is included in a communication system comprising: the transmitters for transmitting the transmission signals and the message; and a controller coupled to the transmitters for receiving the signal from the PMU and for providing the message to the selected transmitter indicated in the signal.

32. A controller for dynamically grouping transmitters for message transmission to portable messaging units (PMUs), the controller comprising: a receiver for receiving a first signal indicative of first signal strengths of transmission signals received by a first PMU and a second signal indicative of second signal strengths of transmission signals received by a second PMU; a calculator coupled to the receiver for computing first carrier-to- interference (C/I) values indicative of relative strengths of the transmission signals received by the first PMU and for computing second C/I values indicative of relative strengths of the transmission signals received by the second PMU; and a sender coupled to the calculator for determining, from the first C/I values and prior to message delivery to the first and second PMUs, a first selected transmitter and a first reuse factor for transmitting a first message to the first PMU, the first reuse factor included in a number of reuse factors used by the controller for grouping the transmitters for message delivery, and for determining, from the second C/I values, a second selected transmitter and a second reuse factor for transmitting a second message to the second PMU, the second reuse factor also included in the number of reuse factors.