United States Patent
`
`[19]
`
`[11] Patent Number:
`
`5,754,946
`
`Cameron et al.
`[451 Date of Patent:
`May 19, 1998
`
`
`US00575494-6A
`
`[54] NATTONWHJE COMMUNICATION SYSTEM
`
`340f8?5.44
`211989 Vfillard at al.
`4,803,487
`5.153582 10l199Q Davis ................................... 3-1-0f3ll.l
`
`[75]
`
`Inventors: Dennis Wayne Cameron. Jackson.
`Miss.'. Walter Charles Ra-ehr. Reston.
`Va.: Rude Petrovic. Oxford. MiS5.: Jll
`P. Bnag-at. Jackson. Miss-.; Masood
`Gm-nlai. Madison. Miss.', William D.
`Hays. Jackson. Miss; David W.
`Aclternnn. Washington. D.C.
`
`[13] Assignee: Mobile Telecommuniclfion
`Technogoggem lac-k5Ou_ Mis_.,_
`
`[211 A991‘ N“ ‘"319
`[223
`rues:
`Sep. 21, 1993
`
`ETEN-I. DOC”! IENTS
`
`FOREIGN P
`82715
`3Il989
`Japan
`131241
`7.11989
`Japan
`OIHER PUBLICATIONS
`‘Telecornmunications Protocols and Design“ by Spragins et
`al Feb. 1991
`
`-l55!69
`4551169
`
`_
`_
`_
`_
`Primary Exarmner—Retnl1ard J. Ersenzopf
`Assistarzt Examiner-—'['haI1h Le
`Attorney, Agent, or Firm-—-Finnegan. Henderson. Farabow.
`Garrett & Dunner. LLP.
`[57]
`ABSTRACT
`
`Rehwd U5‘ APP““‘fi°“ D'‘‘‘
`_
`_
`_
`[63] C°'"m“m°“"”"P’“ °f 5"’ N°' 97333‘ NM‘ 12' 1992'
`N . S 90.
`.
`Pat
`0 5 403
`Int. (16
`[51]
`[52] U.S. Cl.
`
`H04]! 7N0
`455.68.]: 45515 17; 45557.7;
`34{1‘825.44
`
`A two-way communication system for communication
`between a system network and a mobile unit. The system
`network includes a plurality of base transmitters and base
`,
`_
`_
`,
`receivers included 1]] the network. The base transmitters are
`divided into zonal assignments and broadmst in simulcast
`using rI1u1ti-carrier modulation techniques. The system net-
`work controls the base transmitters to broadcast in simulcast
`
`45583.1. 54.1.
`[53] Field of Search
`4ssr54.2. 56.1.39. 33. 422. 423. 424. 425.
`517. 524. 32.1. 38.1. 38.4. 67.1. 67.7: 37(if95.3.
`235. 236. 252. S22; 340I825.44. 311.1
`
`during both systemwidc and zonal time intervals. The sys-
`tern network dynamically alters zone boundaries to maxi-
`mize information throughput. The system also uses a mobile
`unit which receives messages from the network and trans-
`mits messages to the network. The mobile unit includes a
`switch that allows a user to request the network to retransmit
`References Cited
`U S PATENT m a received message that contains errors.
`
`[56]
`
`4.691281
`
`9:193‘: 0‘Su.l1ivan ............................ 45533.1
`
`9 Claims. 30 Drawing Sheets
`
`Mobile Transceiver
`
`/l500
`
`
`
`E
`1520
`1503
`I522
`,I_..._ ..-..J./’__._.__._.___
`H
`
`Fleoewer
`;:'.‘:...:.___]
`3 Transmitter
`
`
`1502
`rrmrsrur
`
`rrscrwa
`
`U‘
`
`
`
`
`
`
`Transmit
`
`Logic
`
`
`
`Display and
`Storage Logic
`
`
`input
` Display
`
`Jrnnuncialor
`Controls
`Switches
`
`
`1
`
`GOOGLE 1001
`
`GOOGLE 1001
`
`1
`
`

`
`U.S. Patent
`
`May 19, 1993
`
`Sheet 1 of 30
`
`5,754,946
`
`F/6'. /
`
`PRIOR ART
`
`Transmitter
`
`2
`
`

`
`May 19, 1993
`
`Sheet 2 of 30
`
`5,754,946
`
` U.S.Patent
`
`3
`
`

`
`U.S. Patent
`
`May 19, 1993
`
`Sheet 3 of 30
`
`5,754,946
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`

`
`U.S. Patent
`
`May 19, 1998
`
`Sheet 5 of 30
`
`5,754,946
`
`FIG.5PRIORART
`
`6
`
`

`
`U.S. Patent
`
`May 19, 1993
`
`Sheet 6 of 30
`
`5,754,946
`
`$0mmqm
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`

`
`US. Patent
`
`May 19, 1993
`
`Sheet 7 of 30
`
`5,754,946
`
`FIG. 7
`
`i’00
`
`
`it Generating a system information
`.'
`signal which inciudes a piurality of
`
`
`blocks of information
`
`
`702
`
`
`
`! Transmitting the system information
`-'
`signal to the pluraiity of transmitters
`
`‘(G4
`
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`
`II T
`
`ransmitting by the first and second
`sets of transmitters a first block of
`
`
`
`
`
`
`information in simulcast during the first
`time period
`
`
`
` g Transmitting by the first set of
`
`Transmitting by the second set of
`"
`transmitters a second biock of
`transmitters a third block of
`
`
`
`information during the second
`time period
`
`,.
`
`
`
`information during the second
`time period
`
`:
`
`8
`
`

`
`U.S. Patent
`
`May 19, 1993
`
`Sheet 3 of 30
`
`‘
`
`5,754,946
`
`Fl G 8
`
`800
`
`\
`
`Transmitting a message signal by a
`
`base transmitter servicing a zone
`
`[.802
`
`_ where the mobile transceiver was last
`
`‘ known to be locatedi
`base transmitter[
`
`&%
`
`Tfiansrnitting a regional 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
`
`E
`I
`I
`L 804
`
`,e__._...L.....__.__._.__
`l
`
`Receiving the regional probe signal by {L395
`
`the mobile transceiver
`
`Transmitting an acknowledgment
`signal by the mobile transceiver in
`response to the received regional
`probe signal
`
`B03
`
`Receiving the acknowledgment signal
`from the mobile transceiver by a base
`receiver
`
`3:0
`
`
`
`Updating the data to reflect the zone
`I of the base receiver that received the
`'- acknowledgment signal as the last
`known location of the mobile
`transceiver
`
`
`
`5
`
`812
`
`
`
`9
`
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`
`10
`
`

`
`U.S. Patent
`
`May 19, 1998
`
`Sheet 10 of 30
`
`5,754,946
`
`FIG. /0
`
`11
`
`11
`
`

`
`U.S. Patent
`
`May 19, 1993
`
`Sheet 11 of30
`
`5,754,946
`
`FREQUENCY
`CONTROL
`SIGNAL1
`
`FREQUENCY
`CONTROL
`OONAL2
`
`FREQUENCY
`CONTROL
`OONRL3
`
`FREQUENCY
`CONTROL
`3|GN1.-_~1|_4
`
`FIG. 11
`
`j——-——:.
`1102
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`® MODULATOR
`
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`4110
`'
`MODULATOR
`
`r‘\,
`
`«H20
`
`12
`
`12
`
`

`
`U.S. Patent
`
`May 19, 1993
`
`Sheet 12 of 39
`
`5,754,946
`
`FIG. 12
`
`CONTROL
`SIGNAL1 "9 {.1202
`
`IN PHASE
`
`QUADRATURE
`
`1200
`
`/
`
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`
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`
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`
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`
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`IN PHASE
`
`OUADRATURE
`
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`suems *—+ r1206
`
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`
`F3
`
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`
`QUADRATURE
`
`FOUR CARRIER QUADRATURE MODULATOR
`
`13
`
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`

`
`U.S. Patent
`
`May 19, 1998
`
`Sheet 15 of 30
`
`5,754,946
`
`m_m_®.m_®_mF©Fm.®Fo.
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`

`
`U.S. Patent
`
`May 19, 1993
`
`Sheet 17 of 30
`
`5,754,946
`
`FIG‘. /7
`
`Mobile Receiver
`
`I700
`
`I706
`
`Receiver
`
`I708
`
`Display and
`Storage Logic
`
`
`
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`
`U.S. Patent
`
`May 19, 1993
`
`Sheet 19 of 30
`
`5,754,946
`
`1808
`
`
`
`Regional
`
`
`.
`PFOCGSSIDQ
`Circuitry
`
`FIG. /9
`
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`21
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`

`
`US. Patent
`
`May 19, 1993
`
`Sheet 21 of 30
`
`5,754,946
`
`2'02
`
`2104
`
`2l06
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`
`_______________|_____
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`
`22
`
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`
`May 19, 1998
`
`Sheet 22 of 30
`
`5,754,946
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`
`U.S. Patent
`
`May 19, 1993
`
`Sheet 23 of 30
`
`5,754,946
`
`FIG. 23
`
`Service Queue
`
`Current Messages
`l
`Data Location
`
`24
`
`24
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`

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`May 19, 1998
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`
`U.S. Patent
`
`May 19, 1993
`
`Sheet 26 of30
`
`5,754,946
`
`FIG‘. 26
`
`£600
`
`Transmitting substantially
`
`simultaneously a first information
`
`signal and a second information
`
`signal, 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
`
`2602
`
`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, thereby creating an updated
`first set of base transmitters and an
`
`2304
`
`updated second set of base
`transmitters
`
`Transmitting substantiaily
`
`simultaneously a third 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
`
`2606
`
`being transmitted in simulcast by the
`updated second set of base
`transmitters
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`
`

`
`U.S. Patent
`
`May 19, 1998
`
`Sheet 23 of 30
`
`5,754,946
`
`F/GI 28(4)
`
`2800
`
`2802
`
`2304
`
`
`
`
` Send a message to disable the
`
`registration feature
`
`Store the number of probe
`
`signals sent and a number of
`
`
`
`
`messages successfully
`
`delivered
`
`
`
`
`
`
` Process the stored number of
`probe signals and number of
`
`
`
`
`
` 2306
`
`
`messages succesfully
`
`delivered to evaluate a
`
`likelihood that a probe signal
`will be required to be sent by
`the network to locate the mobile
`
`
`
`transceiver
`
`unit to enable the mobile
`
`transceivers capability to
`
` Send a message to the mobile
`
`
`2808
`
`
`transmit a registration signal if
`
`
`the likelihood exceeds a
`'
`
`selected value
`
`29
`
`29
`
`

`
`U.S. Patent
`
`May 19, 1993
`
`Sheet 29 of 30
`
`5,754,946
`
`F/6‘. 28(8)
`
`2310
`
`Send a message to enable the
`registration feature
`
`23[2
`
`Store the number of registration
`
`signals received and a number
`
`of messages successfully
`delivered
`
`35”
`
`Process the stored number of
`
`registration signals and
`
`number of messages
`
`succesfully delivered to
`evaluate a likelihood that a
`
`M6
`
`registration signal will be
`
`received by a base receiver in
`
`the network that will not be
`
`used by the network to
`determine a set of base
`
`transmitters to be operated to
`
`transmit a message to the
`mobile transceiver
`
`Send a message to the mobile
`unit to disable the mobile
`
`23”;
`
`transceivers capability to
`
`transmit a registration signal if
`the likelihood exceeds a
`
`selected value
`
`30
`
`30
`
`

`
`mmPQMnu
`
`May 19, 1998
`
`sheet 30 of 30
`
`5,754,946
`
`
`
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`
`5 .754, 946
`
`1
`NATIONWIDE COMMUNICATION svsmsr
`
`I. CROSS-REFERENCE TO RELATED
`APPLICATIONS
`
`This application is a continuation-in-part of application
`Ser. No. 07./973.918. filed Nov. 12. 1992. U.S. Pat. No.
`5.590.403. the contents of which is hereby incorporated by
`reference.
`
`IL BACKGROUND OF THE INV'EN'l"ION
`A. Field of the Invention
`
`The present invention relates to methods and systems for
`providing two-way cornmunicalion 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
`eflicient use of system resources.
`B. Description of the Related Art Conventional two-way
`poltablelmobile wireless messaging systems often provide a
`variety of services to subscribu's. 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 sys-
`tems is to provide a network of interconnected transmitters
`and receivers which provides sulficient transmitted signal
`strength and receive capability to uniformly cover a geo-
`graphic region. Some conventional messaging systems pro-
`vide the message to the user on a small viewing screen on
`the mobile unit.
`
`However. such conventional systems often suifer from
`problems associated with low system throughput. evidenced
`by slow message delivery and message size limitations and
`do not provide an 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
`¢.u'ing a given period of time divided by the frequency
`bandwidth necessary to transmit the message data and may
`be measured in bits transferred per Hz. Further. such con-
`ventional systems sufier 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 lransrnitta‘ 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 gener-
`ally 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) transrnitter dominates (e.g.. areas
`A. B. and C in FIG. 1). simulcast is effective because the
`other transmitters do not significantly alfect 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 approxi-
`
`2
`rnately equal. problems can arise because destructive inter-
`ference of signals occ1.n's 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 ca.rrier frequen-
`cies of all simulcast transmitters does not overcome the
`problem because points (Le. nodes) at which destructive
`summing occurred persisted for long periods of time. At
`such points. a mobile receiver can not receive the simulcast
`signal.
`Deliberately offsetting the can-ier frequencies of adjacent
`transmitters can ensure that deslnlctive interference does not
`persist at one point for an extended period of time. The slight
`errors in frequency displayed by high quality reference
`Oscillators (e.g.. 20 hertz errors in 100 MHz signals or a few
`parts in 10’) render deliberate otfserting unnecessary.
`Further. merely offsetting the carrier frequencies could not
`guarantee acceptable quality demodulafion 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 wavefonns are synchronized and
`includes coverage boundary 202 from a first transmitter and
`a second transmitter coverage boundary 204 from a second
`adjacent transmitter. An eqni-signal boundary 200 exists
`where the signals from the first and second transmitters have
`approximately equal signal strengths. A more realistic equi-
`signal bonndmy would take into account natural and man-
`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 ocean’ 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 allect the synchronization. In
`general. there are at least three sources which cause the
`signals from the firs: transmitter and the second transmitter
`to be out of synchronization: (I) timing shifts in the delivery
`of the modulating waveform to each of the transmitters: (2)
`timing slulfts intern.al to each transmitter; and (3) tirning
`shifts caused by propagation distances and anomalies. From
`the perspective of a receiver located in an overlap area. these
`three sotuces of timing shifts combine to produce an overall
`timing shifts between the received signals from the firs’: and
`second Iransrnitters. In cI.n'rent commercial prarxice. the
`summation of these three components results in time shifts
`of about 200 microseconds. The tirning shift present in
`simulcast systems disadvantagcously limits the baud rate at
`which information may be transferred. In geueraL 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. 303). 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
`band 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.
`
`S
`
`35
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`

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`5.754.946
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`3
`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. 30)) shows a linear graph 312 of the
`relative phase dilference caused by a slight carrier frequency
`difierence between the signals from the first transmitter and
`the second transmitter. FIG. 363) shows a composite ampli-
`tude signal 314. A noise threshold is indicated by the
`horizontal dashed line 304 in FIG. 3(E).
`Of intaest. FIG. 303) 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 tl80°. as shown in FIG. 3(D)). As can be seen from FIG.
`3(E). the anti-phase condition 302 caused by the slight phase
`shift between uansrniner 1 and transmitter 2 will not cause
`any loss of data because the anti-phase condition persists for
`ouly a small portion of the baud interval
`The slight ofl°set 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 :l:l80° out of phase. the ternporary dip
`in the amplitude signal may cause the loss of a few bits in
`the composite signal. at worst. These errors can be counter-
`acted with a conventional error correcting code. such as is
`commonly lcnown.
`FIG. 4 shows a set of similar signals to those in FIG. 3.
`but wherein the signal 402 from the firs: transmitter is ofiset
`lirorn. or out of synchronization with. the signal 404 from the
`second transmitter by a full band. In particular. signal 404
`lags signal 402 by one baud interval. As previously
`discussed. the oifset of signals 402 and 40-1 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 unde-
`sirably covers several entire baud intervals and. therefore.
`successful demodulation is impossible during those baud
`intervals. If the baud interval were increased to
`the
`
`eifect 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 altanafivc to simulcast for wide area coverage is
`assignment of orthogonal. non-overlapping subdivisions of
`the available system capacity to adjacent areas. Subdivisions
`can be made in time (e.g.. broadcasting the information on
`the same frequency in dilferent time slots to adjacent areas).
`or in frequency (e.g.. broadcasting the information simulta-
`neously on dilferent frequencies in adjacent areas].T'here are
`several problems with such orthogonal systems. however.
`First. orthogonal assignments require tuning the receiver to
`the assigned tirequency 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 ccrrect
`channel for their favorite programs. Simulcast opaation
`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 consump
`tion.
`
`4
`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 syst.ern.s. This waste of capacity is somewhat
`recouped if the same infortnation 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 difiereut data to
`be transmitted to difierent 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 transruitter and operates in a diiferent frequency or
`time division within the cotmuunicalion 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 cells increases.
`the lilrelihood 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 952 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 50%! 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 sys-
`tems total
`iltforrnation tl'a.nsfer.
`In frequency division
`systems. more cells undesirably increases the frequency
`bandwidth required. Therefore. system throughput in bits
`per Hz is decreased as the number of cells increases.
`Ftrrthermae. 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 u-ansmitters
`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. Ifthe mobile unit determines that the blockhas 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
`reassernbies the block into the proper portion of the mes-
`sage. 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
`resotn-ces.
`
`III. SUMMARY OF THE N
`
`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 for communicating mes-
`sages to a mobile unit. which decreases costs and conserves
`system resources.
`Another object of the invention is to reduce the needless
`retransmission of some message blocks.
`
`45
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`
`5,754,946
`
`6
`FIG. 9 is a schematic diagram of a frequency spectrum for
`rnulti-carrier modulation;
`FIG. 10 is a schematic diagram of an onloil’ keying
`modulator:
`FIG. 11 is a schematic diagram of a frequency shift keying
`modulator;
`FIG. 12 is a schematic diagram of a four can'ier quadra-
`ture modulator;
`FIG. 13 is a schematic diagram of a first embodiment of
`a base l:l'ansmitte1':
`
`FIG. 14 is a schematic diagram of a second embodiment
`of a base transmitter;
`FIG. 15 is a schematic diagram of a mobile transceiver;
`FIG. 16 is a pictorial representation of a mobile trans-
`cerver;
`
`FIG. 17 is a schematic diagram of a mobile receiver:
`FIG. l8(A) is a schematic diagram of an analog base
`x. receiver;
`FIG. 1803) is a schematic diagram of a digital base
`receiver;
`FIG. 19 is a schematic diagram of a base receiver with a
`store and forward feature;
`
`15
`
`30
`
`FIG. 20 is a schematic diagram of a network operations
`center;
`
`FIG. 21 is a schematic diagram of a database structure:
`FIG. 22 is a schematic diagram of a lrafic database;
`FIG. 23 is a schematic diagram of a service queue;
`FIG. 24 is a schematic diagram of a base transrnittcr
`database:
`
`5
`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 die 5
`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 herein.
`the invention is directed to a mobile unit for transmitting and 10
`receiving radio frequency signals to and from a communi-
`cations network comprising means for receiving radio fre-
`quency messages from the network. switch means for allow-
`ing 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 to 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 transmit-
`ting radio frequency signals containing message data to a
`mobile unit. means for receiving radio frequency signals
`from lhe mobile unit instructing the network to retransmit
`the message data to the mobile unit. and means for retrans-
`mitting 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 signms
`containing the message data at the mobile unit. (c) receiving
`at the mobile unit a request from a user to retransmit the
`message data.
`(:1)
`transmitting a request retransmission
`signal from the mobile unit to the network. (e) receiving the
`request retransmission signal by the network. and (1) retrans-
`mitling the message date 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 exem-
`plary and explanatory only and are not restrictive of the
`invention. as claimed.
`
`35
`
`FIG. 25 is a schematic diagram of dynarnically changing
`zonal assignntents;
`FIG. 26 is a flow chart of a preferred method of dynami-
`cally zonal reassignment;
`FIG. 2’)'(A) is a schematic diagram of the cycle protocol:
`FIG. 27(3) is a schematic diagram of the forward batch
`-to interval protocol;
`FIG. 2‘7{C) is a schematic diagram of the individual batch
`protocol;
`FIG. 28(A) is a flow Chan of a preferred method to enable
`the registration feartn-e of a mobile unit:
`FIG. 2803) is a flow chart of a preferred method to disable
`the registration feanne of a mobile unit;
`FIG. 29(A) is a flow chart of a preferred evaluation
`method used to enable the registration feature; and
`FIG. 29(1)) is a flow chart ofa preferred method used to
`disable the registration feature.
`
`IV. BRIE? DFSCRIPITON OF Tl-IE 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
`wav