United States Patent [19]
`Cameron et a].
`
`illllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllll
`5,754,946
`May 19, 1998
`
`USOO5754946A
`[11] Patent Number:
`[45} Date of Patent:
`
`[54] NATIONWIDE COMINICATION SYSTEM
`
`[75] Inventors: Dennis Wayne Cameron. Jackson.
`Miss; Walter Charles Roehr. Reston.
`
`Va; Rade Petrovic. Oxford. Miss.', Jai
`P. Bhagat. Jackson. Miss; Masood
`Garahi. Madison. Miss; William D.
`Hays. Jackson, Miss.; David W.
`Ackerman. Washington. DC.
`
`[73] Assignee: Mobile Telecommunication
`Technologies‘ Jackson_ Miss_
`
`.
`..
`2
`l.
`l 1] App NO 124319
`[22] F11ed:
`Sep. 21, 1993
`
`Related US‘ Application Data
`.
`.
`.
`[63] gzf'ggaggnééniggn of Ser‘ No‘ 973’918’ Nov‘ 12’ 1992’
`'6
`'
`'
`lnt. Cl. ..................................................... ..
`[5
`[52] US. Cl. ...................... .. 455/381, 455/517; 455/673;
`340/ 825-44
`[58] Field of Search ................................ .. 455/331. 54.1.
`455/54.2. 56.1. 69. 88. 422. 423. 424. 425.
`517. 524. 32.1. 38.1. 38.4. 67.1. 67.7; 370/953.
`235. 236. 252. 522; 340/82544. 311.1
`
`[56]
`
`References Cited
`U'S' PATENT DOCUMENTS
`
`2/1989 Willard et a1. ................... .. 340/82544
`4,803,487
`5,153582 10/1992 Davis ................................. .. 340/3111
`TENT
`U1 [EMT
`FOREIGN PA
`DOC
`S
`
`82715
`181241
`
`3/1989 Japan . . . . . .
`. . . . . . . . . . .. 455/69
`7/1989 Japan ..................................... .. 455/69
`
`OTHER PUBLICATIONS
`‘Telecommunications Protocols and Design" by Spragins et
`al Feb. 1991
`
`Primary Examiner—Reinhard J. Eisenzopf
`Assistant Examiner-Thanh Le
`Attorney, Agent, or Firm-Finnegan. Henderson. Farabow.
`Garrett & Dunner. L.L.P.
`[57]
`ABSTRACT
`
`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
`into Zonal assignments and broadcast in sil'nulcast
`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
`tern network dynamically alters zone boundaries to maxi
`mile 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
`a received message that contains errors.
`
`4,697,281
`
`9/1987 O’Sullivan ........................... .. 455/331
`
`9 Claims, 30 Drawing Sheets
`
`Moblle TFEIHSCGIVGI'
`
`I502
`TRANSHIT
`RECEIVE
`‘\j
`/
`
`1500
`/
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`I 1520
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`'
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`Transmltter {I5IB
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`40D l’il
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`/i506
`
`'
`
`
`
`Reoewer 150a
`
`Display and
`Storage Logic
`
`,‘525
`
`Transmit
`Logic
`
`)5“)
`Annuncialor
`
`,1512
`Display
`Controls
`
`[i514
`Display
`(LCD)
`
`{1516
`Input
`Switches
`
`Microsoft Ex. 1001
`Page 1 of 47
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`

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`U.S. Patent
`
`May 19, 1998
`
`Sheet 1 of 30
`
`5,754,946
`
`FIG. /
`PRIOR ART
`
`Transmitter
`
`N
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`I02 B
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`Tronsmiiter
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`\I'~§\
`
`104
`
`C
`
`Transmitter
`
`Microsoft Ex. 1001
`Page 2 of 47
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`

`
`US. Patent
`
`May 19, 1998
`
`Sheet 2 of 30
`
`5,754,946
`
`Microsoft Ex. 1001
`Page 3 of 47
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`

`
`U.S. Patent
`
`May 19, 1998
`
`Sheet 3 of 30
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`5,754,946
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`Microsoft Ex. 1001
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`Page 4 of 47
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`Microsoft Ex. 1001
`Page 4 of 47
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`Microsoft Ex. 1001
`Page 5 of 47
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`

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`5,754,946
`
`FIG‘. 5 PRIOR ART
`
`Microsoft Ex. 1001
`Page 6 of 47
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`

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`U.S. Patent
`
`May 19, 1993
`
`Sheet 6 of 30
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`5,754,946
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`Microsoft Ex. 1001
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`Page 7 of 47
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`Microsoft Ex. 1001
`Page 7 of 47
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`
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`

`
`US. Patent
`
`May 19, 1998
`
`Sheet 7 of 30
`
`5,754,946
`
`FIG. 7
`
`700
`\
`
`Generating a system information
`signal which inciudes a plurality of
`blocks of information
`
`702
`/
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`E Transmitting the system information
`l’ signai to the piuraiity of transmitters
`i
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`Transmitting by the ?rst and second
`706
`sets of transmitters a ?rst biock of
`information in simulcast during the first /
`time period
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`transmitters a third biock of
`I information during the second
`i time period
`L
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`1
`i
`
`i
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`i Transmitting by the ?rst set of
`1 transmitters a second block of
`‘ information during the second
`1 time period
`
`Microsoft Ex. 1001
`Page 8 of 47
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`US. Patent
`
`May 19, 1998
`
`Sheet 8 of 30 ‘
`
`5,754,946
`
`Fla 8
`
`800
`\
`
`Transmitting a message signal by a
`base transmitter servicing a zone
`where the mobile transceiver was last
`known to be located
`
`,802
`
`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
`base transmitter
`
`504
`
`Receiving the regional probe signal by r506
`the mobile transceiver
`
`Transmitting an acknowledgment
`signal by the mobile transceiver in
`response to the received regional
`probe signal
`
`,JOB
`
`7
`
`Receiving the acknowledgment signal
`from the mobile transceiver by a base f8")
`receiver
`
`___‘
`
`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
`
`J12
`
`Microsoft Ex. 1001
`Page 9 of 47
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`US. Patent
`
`May 19, 1998
`
`Sheet 9 of 30
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`Microsoft Ex. 1001
`Page 10 of 47
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`

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`U.S. Patent
`
`May 19, 1998
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`Sheet 10 of 30
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`5,754,946
`
`Fl 6‘. /0
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`Microsoft Ex. 1001
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`

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`US. Patent
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`May 19, 1998
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`Sheet 11 of 30
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`5,754,946
`
`FIG. 11
`
`} T00
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`f1122
`
`FREQUENCY
`CONTROL
`SIGNAL 1
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`
`Microsoft Ex. 1001
`Page 12 of 47
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`US. Patent
`
`May 19,1998
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`Sheet 12 of 30
`
`5,754,946
`
`FIG. 12
`
`CONTROL
`SIGNAL 1 % [r1202
`IN PHASE
`QUADRATURE
`
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`IN PHASE
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`
`Microsoft Ex. 1001
`Page 13 of 47
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`

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`Microsoft Ex. 1001
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`U.S. Patent
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`9
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`Page 15 of 47
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`Microsoft Ex. 1001
`Page 15 of 47
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`U.S. Patent
`
`May 19, 1993
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`Sheet 15 of 30
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`5,754,946
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`Page 16 of 47
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`Microsoft Ex. 1001
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`US. Patent
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`May 19,1998
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`Sheet 16 of 30
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`5,754,946
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`Microsoft Ex. 1001
`Page 17 of 47
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`US. Patent
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`May 19,1998
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`Sheet 17 of 30
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`5,754,946
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`FIG‘. /7
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`Mcbiie Receiver
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`Microsoft Ex. 1001
`Page 18 of 47
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`U.S. Patent
`
`May 19, 1998
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`Sheet 18 of 30
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`5,754,946
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`Microsoft Ex. 1001
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`Microsoft Ex. 1001
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`US. Patent
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`May 19, 1998
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`Sheet 19 of 30
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`5,754,946
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`FIG. /9
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`Microsoft Ex. 1001
`Page 20 of 47
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`U.S. Patent
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`May 19, 1998
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`Sheet 20 of 30
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`5,754,946
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`Microsoft Ex. 1001
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`U.S. Patent
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`May 19, 1993
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`Sheet 21 of 30
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`5,754,946
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`F/6'. 2/
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`
`Microsoft Ex. 1001
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`U.S. Patent
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`May 19, 1998
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`Sheet 22 of 30
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`5,754,946
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`Microsoft Ex. 1001
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`U.S. Patent
`
`May 19, 1993
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`Sheet 23 of 30
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`5,754,946
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`FIG. 23
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`Service Queue
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`Current Messages
`
`Microsoft Ex. 1001
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`Microsoft Ex. 1001
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`U.S. Patent
`
`May 19, 1993
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`Sheet 24 of 30
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`5,754,946
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`Microsoft Ex. 1001
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`U.S. Patent
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`May 19, 1993
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`Sheet 25 of 30
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`5,754,946
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`01
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`Microsoft Ex. 1001
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`Microsoft Ex. 1001
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`U.S. Patent
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`May 19, 1993
`
`Sheet 26 of 30
`
`5,754,946
`
`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
`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
`
`updated second set of base
`transmitters
`
`Transmitting substantialiy
`
`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
`
`
`2804
`
`2606
`
`Microsoft Ex. 1001
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`Page 27 of 47
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`Microsoft Ex. 1001
`Page 27 of 47
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`

`
`U.S. Patent
`
`M
`
`5,754,946
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`Microsoft Ex. 1001
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`Page 28 of 47
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`Microsoft Ex. 1001
`Page 28 of 47
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`
`
`
`
`

`
`U.S. Patent
`
`May 19, 1998
`
`Sheet 23 of 30
`
`5,754,946
`
`F/G. 28/4}
`
`2800
`
` Send a message to disable the
`
`2802
`
`registration feature
`
`
`
`
`Store the number of probe
`
`signals sent and a number of
`
`
`
`
`
`
`
`2804
`
`messages successfully
`
`delivered
`
`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
`
`
`
`
`
`
` Process the stored number of
`
`
`probe signals and number of
`
` 2806
`
`
`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
`
`Microsoft Ex. 1001
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`Page 29 of 47
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`Microsoft Ex. 1001
`Page 29 of 47
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`

`
`U.S. Patent
`
`May 19, 1998
`
`Sheet 29 of 30
`
`5,754,946
`
`F/G. 2678/
`
`28|0
`
`Send a message to enable the
`registration feature
`
`2312
`
`Store the number of registration
`
`signals received and a number
`
`of messages successfully
`delivered
`
`25”
`
`Process the stored number of
`
`
`
`registration signals and
`
`number of messages
`
`succesfully delivered to
`evaluate a likelihood that a
`
`
`
`
`
`
`
`
`
`2816
`
`
`
`
`
`
`
`
`
`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
`
`23m
`
`transceiver‘s capability to
`
`transmit a registration signal if
`the likelihood exceeds a
`
`selected value
`
`Microsoft Ex. 1001
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`Page 30 of 47
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`Microsoft Ex. 1001
`Page 30 of 47
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`

`
`U.S. Patent
`
`May 19, 1998
`
`Sheet 30 of 30
`
`5,754,946
`
`
`
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`Microsoft Ex. 1001
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`Page 31 of 47
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`Microsoft Ex. 1001
`Page 31 of 47
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`

`
`5,754,946
`
`1
`NATIONWIDE COMMUNICATION SYSTEM
`
`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.
`
`II. BACKGROUND OF THE INVENTION
`A. Field of the Invention
`
`The present invention relates to methods and systems for
`providing twoway 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 messaging systems often provide a
`variety of sm'vices 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 sys-
`tems is to provide a network of interconnected transmitters
`and receivers which provides suflicient 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 suffer 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
`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. Finther. such con-
`ventional 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.
`Sirnulcast
`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 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 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-
`
`5
`
`2
`mately equal. problems can arise because destructive inter-
`ference of signals occms 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 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 olfsetting 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.
`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-
`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 atfect 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.
`
`25
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`65
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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. 3(D) shows a linear graph 312 of the
`relative phase difl’erence caused by a slight carrier frequency
`difference between the signals from the first transmitter and
`the second transmitter. FIG. 3(E) shows a composite a.rnpli-
`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 i180°. 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 il80° 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 olfset
`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 ofl°set 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
`the
`
`etfect 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 difierent time slots to adjacent areas).
`or in frequency (e.g.. broadcasting the information si.multa-
`neously on dilferent 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 consump-
`tion.
`
`4
`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 ditferent 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 V2 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
`systems. more cells undesirably increases 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. Ifthe 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 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
`resources.
`
`III. SUMMARY OF THE INVENTION
`
`20
`
`25
`
`30
`
`35
`
`45
`
`50
`
`55
`
`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.
`
`65
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`5,754,946
`
`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 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 herein.
`the invention is directed to a mobile unit for transmitting and
`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 the 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 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
`signal from the mobile unit to the network. (e) receiving the
`request retransmission signal by the network. and (f) retrans-
`mitting the mes sage data by the network in the form