Per
`
`WORLD INTELLECTUAL PROPERTY ORGANIZATION
`International Bureau
`
`(51) International Patent Classification 5 :
`
`(11) International Publication Number:
`
`INTERNATIONAL APPLICATION PUBLISHED UNDER THE PATENT COOPERATION TREATY (PCT)
`wo 94/11960
`26 May 1994 (26.05.94)
`
`H04H3/00
`
`A2
`
`(43) International Publication Date:
`
`-•
`
`(21) International Application Number:
`
`PCT/US93/10713
`
`(22) International Filing Date:
`
`12 November 1993 (12.11.93)
`
`(74) Agents: TURNER, John, B. eta!.; Finnegan, Henderson,
`Farabow, Garrett & Dunner, 1300 I. St., N.W., Washing-
`ton, DC 20005-3315 (US).
`
`(30) Priority data:
`07/973,918
`08/124,219
`
`12 November 1992 (12.11.92) US
`21 September 1993 (21.09.93) US
`
`(71) Applicant: MOBILE TELECOMMUNICATION TECH(cid:173)
`NOLOGIES [US/US]; P.O. Box 2469, Jackson, MS
`39225 (US).
`
`(72) Inventors: CAMERON, Dennis, Wayne ; 29 Polo Drive,
`Jackson, MS 39211 (US). ROEHR, Walter, Charles, Jr. ;
`11317 South Shore Road, Reston, VA 22090 (US). PE(cid:173)
`TROVIC, Rade ; 406 Redbud Lane, Oxford, MS 38655
`(US). BHAGAT, Jai, P. ; 155 Rolling Meadows, Jack(cid:173)
`son, MS 39211 (US). GARAHI, Masood ; 454 Morning
`Forest Lane, Madison, MS 39110 (US). HAYS, William,
`D. ; 2345 Twin Lake Circle, Jackson, MS 39211 (US).
`ACKERMAN, David, W. ; 3730 W Street, N.W., Wash(cid:173)
`ington, DC 20007 (US).
`
`(81) Designated States: AT, AU, BB, BG, BR, BY, CA, CH,
`CZ, DE, DK, ES, FI, GB, HU, JP, KP, KR, KZ, LK,
`LU, LV, MG, MN, MW, NL, NO, NZ, PL, PT, RO,
`RU, SD, SE, SK, UA, UZ, VN, European patent (AT,
`BE, CH, DE, DK, ES, FR, GB, GR, IE, IT, LU, MC,
`NL, PT, SE), OAPI patent (BF, BJ, CF, CG, CI, CM,
`GA, GN, ML, MR, NE, SN, TD, TG).
`
`Published
`Without international search report and to be republished
`upon receipt of that report.
`
`(54) Title: MOBILE TWO-WAY COMMUNICATION SYSTEM
`
`A~L
`10~
`
`TRANSMITTER
`
`(57) Abstract
`
`A two-way communication system for communication between a system network and a mobile unit. The system network in(cid:173)
`cludes a plurality of base transmitters and base receivers included in the network. The base transmitters are divided into zonal as(cid:173)
`signments and broadcast in simulcast using multi-carrier modulation techniques. The system network controls the base transmit(cid:173)
`ters to broadcast in simulcast during both systemwide and zonal time intervals. The system network dynamically alters zone
`boundaries to maximize information throughput. The system also uses a mobile unit which receives messages from the network
`and transmits messages to the network. The mobile unit includes a switch that allows a user to request the network to retransmit a
`received message that contains errors.
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`FOR THE PURPOSES OF INFORMATION ONLY
`Codes used to identify States party to the Per on the front pages of pamphlets publishing international
`applications under the PCf.
`
`AT
`AU
`88
`BE
`BF
`8G
`BJ
`BR
`BY
`CA
`CF
`CG
`CH
`Cl
`CM
`CN
`cs
`cz
`DE
`OK
`ES
`Fl
`FR
`GA
`
`Austria
`Australia
`Barbados
`Belgium
`Burkina Faso
`Bulgaria
`Benin
`Bra.:t.il
`Belarus
`Canada
`Central African Republic
`Congo
`Switzerland
`Cote d'lvoirc
`Cameroon
`China
`Czechoslovakia
`Czech Republic
`Germany
`Denmark
`Spain
`Finland
`France
`Gabon
`
`G8
`GE
`GN
`GR
`HU
`IE
`IT
`JP
`KE
`KG
`KP
`
`KR
`KZ
`Ll
`LK
`LU
`LV
`MC
`MD
`MG
`ML
`MN
`
`United Kingdom
`Georgia
`Guinea
`Greece
`Hungary
`Ireland
`Italy
`Japan
`Kenya
`Kyrgystan
`Democratic People's Republic
`of Korea
`Republic of Korea
`Kazakhstan
`Liechtcnstei n
`Sri Lanka
`Luxembourg
`Latvia
`Monaco
`Republic of Moldova
`Madagascar
`Mali
`Mongolia
`
`MR
`MW
`NE
`NL
`NO
`NZ
`PL
`PT
`RO
`RU
`so
`SE
`Sl
`SK
`SN
`TO
`TG
`TJ
`TT
`UA
`us
`uz
`VN
`
`Mauritania
`Malawi
`Niger
`Netherlands
`Norway
`New Zealand
`Poland
`Portugal
`Romania
`Russian Federation
`Sudan
`Sweden
`Slovenia
`Slovakia
`Senegal
`Chad
`Togo
`Tajikistan
`Trinidad and Tobago
`Ukraine
`United States of America
`Uzbekistan
`VietNam
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`Description
`
`MOBILE TWO-WAY COMMUNICATION SYSTEM
`
`Background Of The Invention
`Field of the Invention
`A.
`The present invention relates to methods and systems for
`providing two-way communication capability between a central
`network and a mobile unit over a relatively large area, and
`more particularly to such methods and systems which allow for
`rapid communication of large messages and efficient use of
`system resources.
`
`B. Description of the Related Art
`Conventional two-way portable/mobile wireless messaging
`systems often provide a variety of services to subscribers.
`Conventional messaging systems in particular provide one-way
`services using store and forward techniques to mobile
`receivers carried by the subscriber. A fundamental goal of
`two-way messaging systems is to provide a network of
`interconnected transmitters and receivers which provides
`sufficient transmitted signal strength and receive capability
`to uniformly cover a geographic region. Some conventional
`messaging systems provide the message to the user on a small
`viewing screen on the mobile unit.
`However, such conventional systems often suffer from
`problems associated with low system throughput, evidenced by
`slow message delivery and message size limitations and do not
`provide an acknowledgment feature wherein the mobile unit
`transmits an acknowledgment signal to the system to
`acknowledge receipt of the message from the system.
`Generally, system throughput refers to the overall
`communication capability of a system as defined by the total
`amount of message data from the system to the mobile units
`transferred by the system during a given period of time
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`divided by the frequency bandwidth necessary to transmit the
`message data and may be measured in bits transferred per Hz.
`Further, such conventional systems suffer from technical
`problems preventing consistent wide area coverage and would
`require extremely wide portions of valuable frequency
`bandwidth to achieve acceptable system throughput rates.
`Simulcast technology in communication systems was
`originally developed to extend transmitter coverage beyond
`that which could be obtained from a single transmitter. Over
`time, however, simulcasting has evolved into a technique
`capable of providing continuous coverage to a large area.
`Generally, simulcast technology provides multiple
`transmitters, operating on substantially the same frequencies
`and transmitting the same information positioned to cover
`extended areas. As shown in Fig. 1, transmitter 100
`generally provides coverage over area A, D, and E,
`transmitter 102 generally provides coverage over area B, D,
`and E, and transmitter 104 generally provides coverage over
`area C, E, and F.
`In some cases, the coverage area of a
`first transmitter may be entirely enclosed within the
`coverage area of another transmitter, such as in building
`interiors and valleys.
`In areas where one (and only one)
`transmitter dominates (e.g., areas A, B, and C in Fig. 1),
`simulcast is effective because the other transmitters do not
`significantly affect receivers in those areas.
`However, in "overlap" areas D, E, and F shown in Fig. 1,
`where the signals from two or more transmitters are
`approximately equal, problems can arise because destructive
`interference of signals occurs in these overlap areas such as
`areas D, E, and F. Destructive interference occurs when the
`two signals are equal in magnitude and 180° out of phase and
`completely cancel each other. While there were some
`successes, reliable design procedures were not available.
`Attempting to precisely synchronize the carrier
`frequencies of all simulcast transmitters does not overcome
`the problem because points (i.e. nodes) at which destructive
`summing occurred persisted for long periods of time. At such
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`points, a mobile receiver can not receive the simulcast
`signal.
`Deliberately offsetting the carrier frequencies of
`adjacent transmitters can ensure that destructive
`interference does not persist at one point for an extended
`period of time. The slighb errors in frequency displayed by
`high quality reference oscillators (e.g., 20 hertz errors in
`100 MHz signals or a few parts in 10 7 ) render deliberate
`offsetting unnecessary. Further, merely offsetting the
`carrier frequencies could not guarantee acceptable quality
`demodulation because proper alignment of the modulating
`signals in time is also required.
`Fig. 2 displays the situation at, for example, point D
`in Fig. 1 when modulating waveforms are synchronized and
`includes coverage boundary 202 from a first transmitter and a
`second transmitter coverage boundary 204 from a second
`adjacent transmitter. An equi-signal boundary 200 exists
`where the signals from the first and second transmitters have
`approximately equal signal strengths. A more realistic
`equi-signal boundary would take into account natural and man(cid:173)
`made topography and propagation conditions, and therefore
`would probably not be a straight line.
`Figs. 3 and 4 generally illustrate various signals as
`they may occur at or near the equi-signal boundary 200 as
`shown in Fig. 2.
`In particular, Figs. 3 and 4 illustrate
`various aspects of modulation synchronization and how
`altering transmission parameters may affect the
`synchronization.
`In general, there are at least three
`sources which cause the signals from the first transmitter
`and the second transmitter to be out of synchronization:
`(1) timing shifts in the delivery of the modulating waveform
`to each of the transmitters; (2) timing shifts internal to
`each transmitter; and (3) timing shifts caused by propagation
`distances and anomalies. From the perspective of a receiver
`located in an overlap area, these three sources of timing
`shifts combine to produce ~n overall timing shifts between
`the received signals from the first and second transmitters.
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`. .
`
`In current commercial practice, the summation of these three
`components results in time shifts of about 200 microseconds.
`The timing shift present in simulcast systems
`disadvantageously limits the baud rate at which information
`may be transferred.
`In. general, Figs. 3 and 4 will also
`illustrate how timing shifts prevents high baud rate
`transmissions.
`A time line representation of a signal 306 from a first
`transmitter is shown in Fig. 3(A) and a signal 308 from a
`second transmitter is shown in Fig. 3(B), both from the
`perspective of a receiver located in an overlap area.
`Vertical dashed lines 300 represent baud intervals on the
`time axis. As can be seen from Figs. 3(A) and (B), the
`signals 306 and 308 are frequency modulated between a high
`and a low frequency value and the signals 306 and 308 are
`exactly in phase. As will be appreciated, the timing shift
`between signals 306 and 308 must be small when compared to
`the baud interval shown in Figs. 3(A) and (B) .since signals
`306 and 308 are in synchronization. Of course, as the baud
`interval decreases, the timing shifts will likely cause
`signals 306 and 308 to be out of synchronization.
`Figs. 3(C), (D), and (E) show the summation of these two
`signals 306 and 308 at an equi-signal boundary, such as
`boundary 200 in Fig. 2. Fig. 3(C) shows a composite signal
`310 indicating that the frequency information remains
`unchanged, Fig. 3(D) shows a linear graph 312 of the relative
`phase difference caused by a slight carrier frequency
`difference between the signals from the first transmitter and
`the second transmitter. Fig. 3(E) shows a composite
`amplitude signal 314. A noise 'threshold is indicated by the
`horizontal dashed line 304 in Fig. 3(E).
`Of interest, Fig. 3(E) shows the composite amplitude
`signal 314 dipping below the noise threshold 304 at an
`anti~phase condition 302 (e.g., when the relative phase angle
`is± 180°, as shown in Fig. 3(0)). As can be seen from
`Fig. 3(E), the anti-phase condition 302 caused by the slight
`phase shift between transmitter 1 and transmitter 2 will not
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`cause any loss of data because the anti-phase condition
`persists for only a small portion of the baud interval.
`The slight offset of the carrier frequencies between the
`first and second transmitters causes a slow drift of the
`relative phase of the two signals, as shown in Fig. 3(D).
`When the signals are ± 180° out of phase, the temporary dip
`in the amplitude signal may cause the loss of a few bits in
`the composite signal, at worst. These errors can be
`counteracted with a conventional error correcting code, such
`as is commonly known.
`Fig. 4 shows a set of similar signals to those in
`Fig. 3, but wherein the signal 402 from the first transmitter
`is offset from, or out of synchronization with, the signal
`404 from the second transmitter by a full baud.
`In
`particular, signal 404 lags signal 402 by one baud interval.
`As previously discussed, the offset of signals 402 and 404
`may be caused by various timing shifts in the delivery of
`both signals 402 and 404 to a receiver in an overlap area.
`Figs. 4(A) and (B) illustrate the extreme case where the sum
`of these timing shifts is equal to the baud interval shown by
`dashed lines 400. As can be seen in Fig. 4(C), composite
`signal 406 includes a period of indeterminate frequency which
`undesirably covers several entire baud intervals and,
`therefore, successful demodulation is impossible during those
`baud intervals.
`If the baud interval were increased to
`minimize the effect of these timing shifts, data loss would
`be less likely. Therefore, it can be seen that the baud rate
`at which good data transfer can be accomplished is limited by
`the timing shifts between signals delivered to receivers in
`overlap areas.
`Through these examples, it can be seen that high degrees
`of modulation synchronization make it possible to obtain good
`data demodulation in a simulcast system. However, the baud
`rate limitation of simulcast systems is a significant
`drawback and limits system throughput.
`An alternative to simulcast for wide area coverage is
`assignment of orthogonal, non-overlapping subdivisions of the
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`available system capacity to adjacent areas. Subdivisions
`can be made in time (e.g., broadcasting the information on
`the same frequency in different time slots to adjacent
`areas), or in frequency (e.g., broadcasting the information
`simultaneously on different frequencies in adjacent areas).
`There are several problems with such orthogonal systems,
`however. First, orthogonal assignments require tuning the
`receiver to the assigned frequency or time channel for the
`area in which the receiver currently resides.
`In the
`broadcast services every traveler has experienced the
`frustration of finding the correct channel for their favorite
`programs. Simulcast operation avoids the need for scanning
`and re-tuning as the mobile unit moves between areas. Such
`scanning and re-tuning also disadvantageously increases
`mobile unit power consumption.
`Second, and more serious, the orthogonal assignment
`approach drastically reduces the system throughput capacity
`as measured in bits per Hz because anywhere from 3 to 7, or
`possibly more, orthogonal assignments are required to obtain
`continuous area coverage in most conventional orthogonal
`systems. This waste of capacity is somewhat recouped if the
`same information is not needed throughout the service area
`because a given piece of information is sent only to those
`cells where it is needed.
`Conventional cellular radio service is a typical example
`of an orthogonal system.
`In cellular, the same frequencies
`are reused in spatially separated cells to allow different
`data to be transmitted to different mobile units. An example
`of three cellular arrangements is shown in Fig. 5 where the
`number of cells (N) is equal to 3, 4, and 7. Each cell
`(i.e., A, B, C, . . . ) in conventional cellular service
`usually only includes a single transmitter and operates in a
`different frequency or time division within the communication
`protocol. As shown in Fig. 5, cellular service generally
`locates transmitters utilizing the same division (all the "A"
`transmitters) far enough apart to reduce the likelihood of
`interference between such transmitters. As the number of
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`cells increases, the likelihood of interference decreases.
`For example, with N=3 as shown by arrangement 500 in Fig. 3,
`the distance between the coverage area of "A" cells is about
`~ cell width, with N=4 in arrangement 502, the distance
`between the coverage areas of "A" cells is slightly larger,
`and with N=7 in arrangement 504 the distance between "A"
`cells is larger than the width of one cell.
`However, as the number of cells increases, the length of
`the individual time intervals per cell decreases for time
`division multiplexed systems, thereby decreasing the systems
`total information transfer.
`In frequency division systems,
`more cells undesirably i?creases the frequency bandwidth
`required. Therefore, system throughput in bits per Hz is
`decreased as the number of cells increases. Furthermore,
`cellular systems often require an electronic "handshake"
`between system and mobile unit to identify the specific cell
`(i.e. transmitter) in which the mobile unit is located to
`allow capacity reuse.
`In a conventional communication system, the transmitters
`transmit messages in blocks to a mobile unit, each block
`including an error correcting code. When a block is received
`by the mobile unit, the mobile unit uses the error correcting
`code to determine whether the block has been received
`correctly.
`If the mobile unit determines that the block has
`not been received correctly, the mobile unit automatically
`sends a message back to the communication system requesting
`retransmission of that particular block. The system then
`retransmits the block to the mobile unit and the mobile unit
`reassembles the block into the proper portion of the message.
`This technique ensures that messages are accurate, but
`consumes a great deal of air time, driving up the costs of
`mobile messaging, often needlessly. Therefore, it would be
`desirable to reduce the needless retransmission of some
`message blocks to reduce costs and conserve system resources.
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`Summary Of The Invention
`The systems and methods of the present invention have a
`wide variety of objects and advantages. The systems and
`methods of the present invention have as a primary object to
`provide a communication system with wide area coverage and
`high message throughput while minimizing frequency bandwidth
`usage.
`It is an object of the invention to provide a simulcast
`communication system with a high data transfer rate which
`does not exceed the baud rate limitations of simulcast
`transmission.
`It is a further object of the present invention to
`provide a communication system which provides for superior
`data communication integrity.
`Yet another object of the invention is to provide a
`mobile transceiver unit which prevents unnecessary RF
`interference, particularly on commercial aircraft.
`Still further, it is an object of the invention to
`provide a zone based communication system which may
`dynamically redefine zone boundaries to improve information
`throughput.
`Another object of the invention is to provide a zone
`based simulcast communication system which can effectively
`communicate with both mobile transceiver units located near
`the center of each zone as well as mobile transceiver units
`located within the overlap areas between two or more zones.
`Another object of the invention is to reduce the
`needless retransmission of some message blocks.
`Additional objects and advantages of the invention will
`be set forth in part in the description which follows, and in
`part will be obvious from the description, or may be learned
`by practicing the invention. The objects and advantages of
`the invention will be realized and attained by means of the
`elements and combinations particularly pointed out in the
`appended claims.
`To achieve the objects and in accordance with the
`purpose of the invention, as embodied and broadly described
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`herein, the invention is directed to a method for information
`transmission by a plurality of transmitters to provide broad
`communication capability over a region of space, the
`information transmission occurring during at least both a
`first time period and a second time period and the plurality
`of transmitters being divided into at least a first and
`second set of transmitters, the method comprising the steps
`of (a) generating a system information signal which includes
`a plurality of blocks of information, (b) transmitting the
`system information signal to the plurality of transmitters,
`(c) transmitting by the first and second sets of transmitters
`a first block of information in simulcast during the first
`time period, (d) transmitting by the first set of
`transmitters a second block of information during the second
`time period, and (e) transmitting by the second set of
`transmitters a third block of information during the second
`time period.
`In another embodiment, the invention is directed to a
`multi-carrier simulcast transmission system for transmitting
`in a desired frequency band a message contained in an
`information signal, the system comprising a first transmitter
`means for transmitting an information signal by generating a
`first plurality of carrier signals within the desired
`frequency band and by modulating the first plurality of
`carrier signals to convey the information signal, and a
`second transmitter means, spatially separated from the first
`transmitter, for transmitting the information signal in
`simulcast with the first transmitter by generating a second
`plurality of carrier signals at substantially the same
`frequencies as the first plurality of carrier signals and by
`modulating the second plurality of carrier signals to convey
`the information signal.
`In another embodiment, the invention is directed to a
`communication method implemented in a computer controlled
`communication network for locating a mobile transceiver
`within a region of space, the region of space being divided
`into a plurality of zones with each zone serviced by at least
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`one base transmitter and at least one base receiver, the
`network storing data corresponding to a zone where the mobile
`transceiver was last known to be located, the communication
`method comprising the steps of (a) transmitting a message
`signal by a base transmitter servicing a zone where the
`mobile transceiver was last known to be located,
`(b) transmitting a systemwide probe signal by a plurality of
`base transmitters servicing a plurality of zones if the
`mobile transceiver does not indicate receipt of the message
`signal from the base transmitter, (c) receiving the regional
`probe signal by the mobile transceiver, (d) transmitting an
`acknowledgment signal by the mobile transceiver in response
`to the received regional probe signal, (e) receiving the
`acknowledgment signal from the mobile transceiver by a base
`receiver, and (f) .updating the data to reflect the zone of
`the base receiver that received the acknowledgment signal as
`the last known location of the mobile transceiver.
`In yet another embodiment, the invention is directed to
`a method of communicating messages between a plurality of
`base transmitters and mobile receivers within a region of
`space divided into a plurality of zones with each zone having
`at least one base transmitter assigned thereto, the
`communication method comprising the steps of (a) transmitting
`substantially simultaneously a first information signal and a
`second information signal to communicate messages to the
`mobile receivers, the first information signal being
`transmitted in simulcast by a first set of base transmitters
`assigned to a first zone, and the second information signal
`being transmitted in simulcast by a second set of base
`transmitters assigned to a second zone, (b) dynamically
`reassigning one or more of the base transmitters in the first
`set of base transmitters assigned to the first zone to the
`second set of base transmitters assigned to the second zone
`as a function of the messages to be communicated in an area,
`thereby creating an updated first set of base transmitters
`and an updated second set of base transmitters, and
`(c) transmitting substantially simultaneously a third
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`information signal and a fourth information signal, the third
`information signal being transmitted in simulcast by the
`updated first set of base transmitters, and the fourth
`information signal being transmitted in simulcast by the
`updated second set of base transmitters to communicate
`additional messages to said mobile receivers.
`In another embodiment, the invention is directed to a
`mobile transceiver unit for transmitting messages to and
`receiving messages from a network comprising input means for
`allowing the user to input a user message to the unit,
`transmitter means for transmitting a radio frequency signal
`including the user message from the mobile unit to the
`network, receiver means for receiving radio frequency signals
`having a message from the network, signal detector means for
`detecting at least one type of electromagnetic signal
`generated external to the mobile unit and the network, and a
`circuit, connecting the signal detector means to the
`transmitter means, for disabling the transmitter means upon
`detection of the electromagnetic signal, thereby preventing
`unwanted radio frequency transmission.
`In another embodiment, the invention is directed to a
`communication method for controlling a mobile transceiver
`which may communicate with a communication network controlled
`by a computer, the network including a plurality of base
`transmitters for transmitting messages from the network to
`the mobile transceiver and base receivers for receiving
`messages from the mobile transceiver, the mobile transceiver
`being capable of sending a registration signal to be received
`by a base receiver in the network to identify the mobile
`transceiver's location and the plurality of base transmitters
`in the network being capable of sending a probe signal to the
`mobile transceiver to cause the mobile transceiver to
`transmit a signal to a base receiver to identify its
`location, the method comprising the steps of (a) sending a
`message from the network to the mobile transceiver to disable
`the mobile transceiver's capability to transmit a
`registration signal, (b) storing the number of probe signals
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`sent by the network to the mobile transceiver during a first
`period of time and the number of messages successfully
`delivered to the mobile transceiver by the network during a
`second period of time, (c) processing by the computer the
`stored number of probe signals and number of messages
`successfully delivered to evaluate a likelihood that a probe
`signal will be required to be sent by the network to locate
`the mobile unit to deliver a message, and (d) sending a
`message to the mobile unit to enable the mobile transceiver's
`capability to transmit a registration signal if the
`calculated likelihood exceeds a selected value.
`In another embodiment, the invention is directed to a
`communication method for controlling a mobile transceiver
`which may communicate with a communication network controlled
`by a computer, the network including a plurality of base
`transmitters for transmitting messages to the mobile
`transceiver and base receivers for receiving messages from
`the mobile transceiver, the mobile transceiver being capable
`of sending a registration signal to be received by a base
`receiver in the network to identify the mobile transceiver's
`location, the network using received registration signals to
`determine a set of base transmitters to be operated to
`transmit a message to the mobile transceiver, the method
`comprising the steps of (a) sending a message from the
`network to the mobile transceiver to enable the mobile
`transceiver's capability ~o transmit a registration signal,
`(b) storing the number of registration signals from the
`mobile transceiver to the network during a first period of
`time and the number of messages successfully delivered to the
`mobile transceiver by the network during a period of time,
`(c) processing the stored number of registration signals and
`number of messages successfully delivered to evaluate a
`likelihood that a registration signal from said mobile unit
`will not be used by the network to determine a set of base
`transmitters, and (d) sending a message to the mobile unit to
`disable the mobile transceiver's capability to transmit a
`
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`

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`WO 94/11960
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`-13-
`
`PCf /US93/1 0713
`
`registration signal if the likelihood exceeds a selected
`value.
`In another embodiment, the invention is directed to a
`mobile unit for transmitting and receiving radio frequency
`signals to and from a communications network comprising means
`for receiving radio frequency messages from the network,
`switch means for allowing a user to request retransmission of
`at least parts of the message from the communications
`network, and means for transmitting, upon actuation of the
`switch means, a signal to the communications network
`requesting retransmission of the at least portions of the
`message.
`In another embodiment, the invention is directed tb a
`communications network for transmitting radio frequency
`signals to a mobile unit and for receiving radio frequency
`signals from a mobile unit comprising means for transmitting
`radio frequency signals containing message data to a mobile
`unit, means for receiving radio frequency signals from the
`mobile unit instructing the network to retransmit the message
`data to the mobile unit, and means for retransmitting radio
`frequency signals containing the message data to the mobile
`unit.
`In yet another embodiment, the invention is directed to
`a method for transmitting messages from a communications
`network to a mobile unit comprising (a) transmitting radio
`frequency signals containing message data from the network to
`the mobile unit, (b) receiving the radio frequency signals
`containing the message data at the mobile unit, (c) receiving
`at the mobile unit a request from a user to retransmit the
`message data, (d) transmitting a request retransmission
`(e) receiving the
`signal from the mobile unit to the network 1
`request retransmission signal by the network, and (f)
`retransmitting the message data by the network in the form of
`radio frequency signals.
`It is to be understood that both the foregoing general
`description and the following detailed description are
`
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`Juniper v MTel891
`
`

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`wo 94/11960
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`-14-
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`PCf /US93/ 10713
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`exemplary and explanatory only and are not restrictive of the
`invention, as claimed.
`
`Brief Description Of The Drawings
`The accompanying drawings, which are incorporated in and
`constitute a part of this specification, illustrate several
`embodiments of the invention and together with the
`description, serve to explain the principles of the
`invention.
`Fig. 1 is a schematic diagram of an arrangement of
`simulcast transmitters;
`Fig. 2 is a schematic diagram of uniform smooth earth
`propagation;
`Fig. 3 is a schematic diagram of synchronized modulated
`waveforms;
`Fig. 4 is a schematic diagram of modulated waveforms
`offset a full baud;
`Fig. 5 is a schematic diagram of cellular system
`coverage;
`Fig. 6 is a schematic diagram of a communication system;
`Fig. 7 is a flow chart of a preferred method of
`communication;
`Fig. 8 is a flow chart of a preferred method of sending
`a regional probe signal;
`Fig. 9 is a schematic diagram of a frequency spectrum
`for multi-carrier modulation;
`Fig. 10