United States Patent [19]
`Cameron et al.
`
`l|Il|lllllllll|||llllllllllllgLllllslllllllllllllllllllllllllllllllllllll
`
`90403A
`
`[11]
`Patent Number: '
`[45] Date of Patent:
`
`5,590,403
`Dec. 31, 1996
`
`[54] METHOD AND SYSTEM FOR EFFICIENTLY
`PROVIDING TWO WAY COMMUNICATION
`BETWEEN A CENTRAL NETWORK AND
`MOBILE UNIT
`
`[75] Inventors: Dennis W. Cameron, Jackson, Miss.;
`Walter C. Roehr, Jr., Reston, Va.;
`Rade Petrovic, Oxford; Jai P. Bhagat,
`Jackson, both of Miss.; Masood
`Garahi, Madison; William D. Hays,
`Jackson, both of Miss.; David W.
`Ackerman, Washington, DC.
`
`[73] Assignee: Destineer Corporation, Jackson, Miss.
`
`[21] App]. No.: 973,918
`[22] Filed:
`Nov. 12, 1992
`
`[51] Int. Cl.6 ..................................................... .. H04B 7/06
`[52] US. Cl. ..................... .. 455/51.2; 455/33.4; 455/34.1;
`455/56.1; 455/59; 455/101; 375/299
`[58] Field of Search ................................ .. 455/33.1, 33.2,
`455/33.4, 34.1, 34.2, 51.2, 54.1, 54.2, 59,
`56.1, 63, 101, 102, 103; 370/953, 77; 375/260,
`267, 299
`
`[56]
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`4,490,830 12/1984 Kai et al. ................................ .. 455/59
`4,570,265
`2/1986 Thro ............. ..
`455/59
`4,968,966 11/1990 Jasinki et al. ........................ .. 45551.2
`
`FOREIGN PATENT DOCUMENTS
`
`WO91/18458 11/1991 WIPO .................................. .. 455/101
`WO9211707 7/1992 WIPO ................................. .. 455/33.1
`
`Primary Examiner~Reinhard J. Eisenzopf
`Assistant Examiner-Thanh Le
`Attorney, Agent, or Firm—-Finnegan, Henderson, Farabow,
`Garrett & Dunner, L.L.P.
`
`ABSTRACT
`[57]
`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 in the network. The base transmitters are
`divided into zonal assignments and broadcast in simulcast
`using multi-carrier modulation techniques. The system net
`work controls the base transmitters to broadcast in simulcast
`during both systemwide and zonal time intervals. The sys
`tem network dynamically alters zone boundaries to maxi
`mize information throughput. The preferred mobile unit
`includes a noise detector circuit to prevent unwanted trans
`missions. The system network further provides an adaptive
`registration feature for mobile units which controls the
`registration operations by the mobile units to maximize
`information throughput.
`
`4,223,405
`4,392,242
`
`9/1980 Hattori et a1. .......................... .. 455/59
`7/1983 Kai ................ ..
`455/34.1
`
`12 Claims, 30 Drawing Sheets
`
`Generating a system information
`signal which includes a plurality of
`blocks of information
`
`")2
`/
`
`Transmitting the system information
`signal to the plurality of transmitters
`
`A04
`
`Transmitting by the ?rst and second
`sets of transmitters a ?rst block of
`information in simulcast during the first
`time period
`
`706
`
`708
`
`TIO
`
`Transmitting by the first set of
`transmitters a second block of
`information during the second
`time period
`
`Transmitting by the second set of
`transmitters a third block of
`information during the second
`time period
`
`1
`
`TMO1005
`
`

`
`US. Patent '
`
`Dec. 31, 1996
`
`Sheet 1 of 30
`
`5,590,403
`
`Transmitter
`
`transmitter
`
`2
`
`

`
`US. Patent
`
`Dec. 31, 1996
`
`Sheet 2 of 30
`
`5,590,403
`
`3
`
`

`
`U.S. Patent
`
`Dec. 31, 1996
`
`Sheet 3 of 30
`
`5,590,403
`
`E:HWWWW.53mesaH.H.__¢mE_s_mz<E
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`_>_oEWWm.8TmézoatoWWEEGm_m<:n_.9wasNEm>E:mm_mHm<Ezo:<s__>5m
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`
`4
`
`
`

`
`U.S. Patent
`
`5,590,403
`
`
`
`m,WWWWWE:.___:mE__>_mz<E:3most
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`
`5,590,403
`
`
`
`FIG‘. 5 PRIOR ART
`
`6
`
`

`
`U.S. Patent
`
`Dec. 31, 1996
`
`Sheet 6 of 30
`
`5,590,403
`
`4<zo_wm_m
`
`Em
`
`M95
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`
`
`

`
`US. Patent
`
`Dec. 31, 1996
`
`Sheet 7 of 30
`
`5,590,403
`
`'F/G.7
`
`700
`
`Generating a system information
`signal which includes a plurality of
`blocks of information
`
`702
`/
`
`Transmitting the system information
`signal to the plurality of transmitters
`
`/‘(()4
`
`Transmitting by the ?rst and second
`706
`sets of transmitters a first block of
`information in simulcast during the first /
`time period
`
`‘7
`
`/?08
`
`V
`
`/7l0
`
`Transmitting by the first set of
`transmitters a second block of
`information during the second
`time period
`
`Transmitting by the second set of
`transmitters a third block of
`information during the second
`time period
`'
`
`8
`
`

`
`US. Patent
`
`Dec. 31, 1996
`
`Sheet 8 of 30
`
`5,590,403
`
`FIG: 8
`
`800
`\
`
`Transmitting a message signal by a
`base transmitter servicing a zone
`where the mobile transceiver was. last
`known to be located
`
`,802
`
`V
`
`Transmitting 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 i304
`base transmitter
`'
`
`7
`
`Receiving the regional probe signal by
`the mobile transceiver
`
`806
`
`V
`
`Transmitting an acknowledgment
`signal by the mobile transceiver in
`response to the received regional
`probe signal
`
`#308
`
`7
`
`Receiving the acknowledgment signal
`from the mobile transceiver by a base
`receiver
`
`8'0
`
`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
`
`/8|2
`
`9
`
`

`
`US. Patent
`
`Dec. 31, 1996
`
`Sheet 9 0f 30
`
`[Iv NE» All
`
`\ \
`
`8m . NNm 2m 3m 2
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`mg 3w Km 0% m6 m6 8m
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`
`10
`
`

`
`US. Patent
`
`Dec. 31, 1996
`
`Sheet 10 of 30
`
`5,590,403
`
`F l6‘. I0
`
`1002
`SW1
`F1 @ \(IOIZ
`
`1004
`SW2
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`
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`/
`
`A022
`
`‘006
`
`SW3
`
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`
`.SWn
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`
`11
`
`

`
`US. Patent
`
`Dec. 31, 1996
`
`Sheet 11 of 30
`
`5,590,403
`
`FIG. 11
`
`FREQUENCY
`CONTROL
`SIGNAL 1
`
`FREQUENCY
`CONTROL
`SIGNAL 2
`
`FREQUENCY
`CONTROL
`SIGNAL 3
`
`FREQUENCY
`CONTROL
`SIGNAL 4
`
`FREQUENCY
`CONTROL
`SIGNAL n
`
`1102
`
`1
`
`1104
`
`1106
`
`1108
`
`@— MODULATOR 1112
`@— MODULATOR 1114
`{1116
`®—— MODULATOR
`@— MODULATOR (1118
`
`f
`
`f
`
`} 1100
`
`I112
`
`1
`
`1
`
`1
`
`1110
`
`1
`
`®—~ MODULATOR
`
`f
`1120
`
`12
`
`

`
`U.S. Patent
`
`Dec. 31, 1996
`
`Sheet 12 of 30
`
`5,590,403
`
`F1
`
`F2
`
`CONTROL
`slGNAL 1
`
`CONTROL
`S|GNAL2
`
`CONTROL
`SIGNAL 3
`
`CONTROL
`SIGNAL 4
`
`FIG. 12
`
`1202
`IN PHASE
`QUADRATURE
`
`1204
`IN PHASE
`QUADRATURE
`
`1206
`IN PHASE
`
`QUADRATURE
`
`1208
`IN PHASE
`m QUADFIATUFIE
`
`1200
`f
`
`f1210
`
`2 ———*~
`
`FOUR CARRIER OUADRATURE MODULATOR
`
`13
`
`

`
`U.S. Patent
`
`Dec. 31, 1996
`
`Sheet 13 of 30
`
`5,590,403
`
`oom_I82
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`
`14
`
`14
`
`
`
`

`
`US. Patent
`
`Dec. 31, 1996
`
`Sheet 14 of 30
`
`5,590,403
`
`33
`
`EEQEOQ
`
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`
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`
`US. Patent
`
`Dec. 31, 1996
`
`Sheet 16 of 30
`
`5,590,403
`
`82
`
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`
`17
`
`

`
`US. Patent
`
`Dec. 31, 1996
`
`Sheet 17 of 30
`
`5,590,403
`
`FIG. /7
`
`Mobile Receiver
`
`I700
`
`n02
`‘(woe
`Receiver
`
`/
`
`W08
`Display and
`Storage Logic
`
`Annuncialor
`
`Display
`
`Controls '
`
`Display
`(LCD)
`
`18
`
`

`
`US. Patent
`
`Dec. 31, 1996
`
`Sheet 18 of 30
`
`5,590,403
`
`82
`
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`
`5508mm
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`19
`
`

`
`US. Patent
`
`Dec. 31, 1996
`
`Sheet 19 of 30
`
`5,590,403
`
`FIG‘. /9
`
`EH00
`Anaiog /l802
`Receiver
`
`/i8|0
`Demodulator
`
`I906
`Error ‘
`Correction /
`Circuit
`
`I908
`Store &
`Forward /
`Circuit
`
`‘9m
`/
`
`[I808
`
`Regional
`Processing
`Circuitry
`
`20
`
`

`
`U.S. Patent
`
`Dec. 31, 1996
`
`Sheet 20 of 30
`
`5,590,403
`
`cs
`
`
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`21
`
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`
`U.S. Patent
`
`Dec. 31, 1996
`
`Sheet 21 of 30
`
`5,590,403
`
`FIG’. 2/
`
`2|02
`
`2104
`
`2|06
`
`User 1
`
`ID#
`
`NO
`
`Button Format
`
`User 2
`
`Last
`Location
`
`Transmit
`Capability?
`
`Service Area
`
`Button Format
`
`User Database
`
`22
`
`22
`
`

`
`U.S. Patent
`
`Dec. 31, 1996
`
`Sheet 22 of 30
`
`5,590,403
`
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`
`U.S. Patent
`
`Dec. 31, 1996
`
`Sheet 23 of 30
`
`5,590,403
`
`FIG‘. 23
`
`Service Queue
`
`Current Messages
`
`24
`
`24
`
`

`
`U.S. Patent
`
`Dec. 31, 1996
`
`Sheet 24 of 30
`
`5,590,403
`
`SE
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`

`
`U.S. Patent
`
`Dec. 31, 1996
`
`Sheet 26 of 30
`
`595909403
`
`FIG. 26
`
` 2600
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`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
`2602
`second zone
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`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
`updated second set of base
`transmitters
`
`
`
`
`
`
`
`
`
`
`
`2604
`
`
`
`Transmitting substantially
`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
`
`
`being transmitted in simulcast by the
`
`updated second set of base .
`transmitters
`
`
`
`2606
`
`27
`
`27
`
`

`
`U.S. Patent
`
`Dec. 31, 1996
`
`Sheet 27 of 30
`
`5,590,403
`
`co_EmEoO
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`
`28
`
`
`
`
`
`

`
`U.S. Patent
`
`Dec. 31, 1996
`
`Sheet 28 of 30
`
`5,590,403
`
`FIG. 28(4)
`
`2800
`
`Send a message to disable the
`
`2802
`
`registration feature
`
`Store the number of probe
`signals sent and a number of
`
`messages successfully
`delivered
`
`2804
`
`Process the stored number of
`
`probe signals and number of
`
`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
`
`Send a message to the mobile
`
`unit to enable the mobile
`
`transceiver's capability to
`transmit a registration signal if
`the likelihood exceeds a
`
`selected value
`
`29
`
`2806
`
`2808
`
`29
`
`

`
`U.S. Patent
`
`Dec. 31, 1996
`
`Sheet 29 of 30
`
`5,590,403
`
`FI6‘. 28/3}
`
` Send a message to enable the
`
`
`28|0
`
`/
`
`28l2
`
`registration feature
`
`
`
`
`
`
`
`
`
`Store the number of registration
`signals received and a number
`of messages successfully
`delivered
`
`
`
` Process the stored number of
`registration signals and
`
`
`
`number of messages
`succesfully delivered to
`
`
`
`
`
`
`
`
`
`evaluate a likelihood that a
`
`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
`
`
`
` 28l4
`
`28l6
`
`
`
`
`
`
`
`
`
`
`
`
`
` Send a message to the mobile
`
`
`
`
`unit to disable the mobile
`
`transceiver's capability to
`transmit a registration signal if
`the likelihood exceeds a
`
`
`
`
`
`28|8
`
`
`
`selected value
`
`30
`
`30
`
`

`
`U.S. Patent
`
`Dec. 31, 1996
`
`Sheet 30 of 30
`
`5,590,403
`
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`

`
`5,590,403
`
`1
`METHOD AND SYSTEM FOR EFFICIENTLY
`PROVIDING TWO WAY COMMUNICATION
`BETWEEN A CENTRAL NETWORK AND
`MOBILE UNI'I'
`
`BACKGROUND OF THE INVENTION
`
`A. Field of the Invention
`
`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
`eflicient use of system resources.
`B. Description of the Related Art
`
`Conventional two-way portable/mobile wireless messag-
`ing systems often provide a variety of services to subscrib-
`ers. 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
`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 cover-
`age and would require extremely wide portions of valuable
`frequency bandwidth to achieve acceptable system through-
`put rates.
`
`technology in communication systems was
`Simulcast
`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 trans-
`mitters, 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) 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 approxi-
`mately equal, problems can arise because destructive inter-
`ference of signals occurs in these overlap areas such as areas
`
`2
`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 suc-
`cesses, reliable design procedures were not available.
`Attempting to precisely synchronize the carrier frequen-
`cies 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 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 slight
`errors in frequency displayed by high quality reference
`oscillators (e.g., 20 hertz errors in 100 MHz signals or a few
`parts in 107) render deliberate offsetting unnecessary. Fur-
`ther, 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 2.02 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-
`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 an overall
`timing shifts between the received signals from the first and
`second transmitters. 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
`
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`5,590,403
`
`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 ampli-
`tude 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 il80°, 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 transmitter 1 and transmitter 2 will not 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 i180° 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 counter-
`acted 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 dis-
`cussed, the oifset 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 unde-
`sirably 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 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 simulta-
`neously 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 charmel for the area in which
`the receiver currently resides. In the broadcast services every
`traveler has experienced the frustration of finding the correct
`charmel 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 consump-
`tion.
`
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`
`the orthogonal assignment
`Second, and more serious,
`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 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 1/2 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 sys-
`tems total information transfer. In frequency division sys-
`tems, more cells undesirably increases the frequency band-
`width 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.
`
`II. 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 interfer-
`ence, 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 through-
`put.
`
`Another object of the invention is to provide a zone based
`simulcast communication system which can effectively
`communicate with both mobile transceiver units located
`
`33
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`

`
`5,590,403
`
`5
`near the center of each zone as well as mobile transceiver
`units located within the overlap areas between two or more
`zones.
`
`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.
`
`10
`
`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 method for information trans-
`mission by a plurality of transmitters to provide broad
`communication capability over a region of space, the infor-
`mation 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 infonnation 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 fre-
`quency 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 trans-
`mitter, 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 con-
`trolled communication network for locating a mobile trans-
`ceiver within a region of space, the region of space being
`divided into a plurality of zones with each zone serviced by
`at least 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 com-
`munication 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
`
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`
`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 commu-
`nication method comprising th