United States Patent
`
`[19]
`
`[11] Patent Number:
`
`5,423,056
`
`
`
`[45] Date of Patent: Jun. 6, 1995
`Linquist et al.
`
`Usoos423056A
`
`[54] ADAPTIVE CELLULAR PAGING SYSTEM
`
`[75]
`
`Inventors:
`
`Roger D. Linguist; Malcolm M.
`Lorang, both of Dallas, Tex.
`
`[73] Assignee:
`
`Pagemart, Inc., Dallas, Tex.
`
`[21] Appl. No.: 236,247
`
`[22] Filed:
`
`May 2, 1994
`
`Related US. Application Data
`
`[63]
`
`Continuation of Ser. No. 661,078, Feb. 26, 1991, aban-
`doned.
`,
`
`Int. Cl.6 ............................................... H04B 7/26
`[51]
`[52] US. Cl. .................................. 455/33.l; 455/ 12.1;
`455/51.1; 455/56.1
`[58] Field of Search .................... 455/ 12.1, 13.2, 33.1,
`455/332, 33.4, 51.1, 51.2, 38.1, 56.1, 57.1, 54.1,
`54.2; 340/825.44, 311.1; 379/57, 59
`
`[56]
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`H610 3/1989 Focarile et al. ....................... 379/60
`4,398,192 8/1983 Moore et al.
`......
`. 340/825.44
`
`4,670,905 6/1987 Sandvos et a1.
`..... 455/33.4
`
`4,747,120 5/1988 Foley ................
`379/58
`
`.....
`4,747,122 5/1988 Bhagat et al.
`379/60
`4,829,554 5/1989 Barnes et al. ..................... 379/58
`
`..... 340/825.44
`4,918,437 4/1990 Jasinski et al.
`4,943,803 7/1990 Vrijakorte .............. 340/825.49
`
`......... 455/ 13.1
`4,956,875
`9/1990 Bernard et al.
`4,969,966 11/1990 Jasinski et al. ......... 340/825.44
`
`5,077,830 12/1991 Mallia ..................... 455/381
`
`6/1992 Cubley et al. ...................... 455/32.!
`5,122,795
`
`OTHER PUBLICATIONS
`
`Steven Ritter and J. McCoy, “Automatic Vehicle Lo-
`cation—An Overview”, IEEE Trans. on Veh. Tea, vol.
`VT—26, No. 1, Feb. 1977, pp. 7—9.
`M. Kihara, “Performance Aspects of Reference Clock
`Distribution for Evolving Digital Networks”, IEEE
`Communications Magazine, Apr. 1989.
`
`“Unwanted Calls? Turn on Pager Phone”, USA Today,
`Dec. 28, 1990, p. 8B.
`Gardner, W. A. and Chen C. K., “Interference—Toler-
`ant Time—Difference—Arrival Estiamteion fofr Modu-
`
`lated Signals”, IEEE Trans. on Acous, Speech and Sig.
`Proc., vol. 36, No. 9, Sep. 1988, pp. 1385-1395.
`D. C. Cox, “Universal Digital Portable Radio Commu-
`nications,” Proc. of the IEEE, vol. 75, No. 4, Apr. 1987,
`pp. 436—477.
`Telocator Bulletin, News and Analysis for the Mobile
`Telecommunications Industry, vol. 91, No. 3, Jun. 25,
`1991.
`
`M. Kihira, “Performance Aspects of Reference Clock
`Distribution for Revolving Digital Networks”, IEEE
`Comm. Magazine, Apr. 1989, pp. 24—34.
`
`Primary Examiner—Curtis Kuntz
`Assistant Examiner—Chi H. Pham
`Attorney, Agent, or Finn—Gregory M. Howison
`
`[57]
`
`ABSTRACI‘
`
`An adaptive paging system includes a paging terminal
`that is operable to receive paging signals and transmit
`them up to a satellite (28) and down through a downlink
`(312) to stick locations (314), (316), (318), (320) and
`(322). Each of the sticks (314)—(322) is associated with a
`given locale (324), (326), (328), (330) and (332). The
`sticks are operable in a simulcast mode and also in a
`cellular mode. In the cellular mode, each of the sticks
`(314)—(322) is Operable to receive a separate message
`that is distinct from the other cells. Pagers (36), having
`a known location at any of the locales (324)—(332) can
`then be selectively addressed and data transferred
`thereto. To prevent interference between adjacent RF
`locales, adjacent cells are not turned on during trans-
`mission to select cells in the cellular mode. These can be
`turned on at a different time. Orthogonal coding can be
`utilized such that adjacent cells can be turned on, thus
`increasing throughput.
`
`13 Claims, 9 Drawing Sheets
`
`
`
`CLEARWIRE 1010
`
`

`

`32
`
`44
`
`I 3 O
`
`PAGING
`
`DATA ENTRY
`UNIT
`
`US. Patent
`
`June 6, 1995
`
`Sheet 1 of 9
`
`5,423,056
`
`FIG.
`
`7
`
`TERMINAL 46
`
`
`

`

`US. Patent
`
`June 6, 1995
`
`Sheet 2 of 9
`
`5,423,056
`
`
`
`104
`
`PAGER/PLU
`
`so
`
`102
`
`|\
`
`BASE
`
`STATION
`
`

`

`US. Patent
`
`5,423,056
`
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`US. Patent
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`June 6, 1995
`
`Sheet 4 of 9
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`5,423,056
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`US. Patent
`
`June 6, 1995
`
`Sheet 5 of 9
`
`5,423,056
`
`244
`
`290
`
`
`START
`
`292
`REQUEST
` TRANSMISSION
`
`
`RX REQUEST
`
`294
`
`
`
`
`
`
`
`Tx LOC DATA &
`
`ID FROM PLU
`
`
`
`
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`RECEIVE PLU
`TRANSMISSION
`
`
`
`
`TIME TAG
`
`
`SEND ID & TIME TAG
`& STICK LOCATION TO
`
`CENTRAL PROCESSING
`
`
`
`295
`
`298
`
`300
`
`302
`
`
`COMPUTE LOCATION
`
`
`STORE LOCATION
`UPDATE DATABASE
`
`
`304
`
`
`
`
`306
`
`
`
`308
`
`1 0
`FIG.
`TIME OF ARRIVAL
`
`252
`
`TX STICK ID
`TO PLUR
`WITH PLU ID
`
`
`
`TX STICK ID
`TO PLUR
`WITH PLU ID
`
`262
`
`
`
`FIG. 9
`PLU FLOW CHART
`
`

`

`US. Patent
`
`June 6, 1995
`
`Sheet 6 of 9
`
`5,423,056
`
`314$ 316$ @318 $320 @322
`
`1206
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`

`US. Patent
`
`June 6, 1995
`
`Sheet 7 of 9
`
`5,423,056
`
`
`
`FIG. 14b
`
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`
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`PAGING
`
`SYSTEM
`
`

`

`US. Patent
`
`June 6, 1995
`
`Sheet 8 of 9
`
`5,423,056
`
`388
`
`FIG. 19
`
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`US. Patent
`
`June 6, 1995
`
`Sheet 9 of 9
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`5,423,056
`
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`

`1
`
`ADAPTIVE CELLULAR PAGING SYSTEM
`
`5,423,056
`
`This application is a Continuation, of application Ser.
`No. 07/661,078, filed Feb. 26, 1991, now abandoned.
`
`5
`
`TECHNICAL FIELD OF THE INVENTION
`
`The present invention pertains in general to a system
`for determining the receiving location of a paging re-
`ceiver and delivering data thereto and, more particu-
`larly, to a location detection system that operates in
`conjunction with an already existent paging system to
`determine location and adaptively divide the system
`into cells for delivery of messages to select cells.
`CROSS-REFERENCE TO RELATED
`APPLICATION
`
`This application is co-pending with US. patent appli-
`cation Ser. No. 08/088,400, entitled, “Personal Loca-
`tion Pager System”, filed concurrently herewith.
`BACKGROUND OF THE INVENTION
`
`Tracking the location of an individual or an object
`that can move in unknown directions has been a con-
`
`cern for a number of years. This has particularly been so
`for designers of urban communications systems. There
`are a large number of applications which require knowl-
`edge of the location of the object or person, such as fleet
`management, felons subjected to “house arrest”, track-
`ing of patients in health care units, the location of stolen
`or lost vehicles, the general location of any individual,
`etc. These systems have employed a variety of tech-
`niques including radio location, dead-reckoning and
`proximity systems.
`In one type of system termed “Automatic Vehicle
`Location” (AVL), various systems are employed to
`determine the location of a vehicle for the purpose of
`monitoring the location of a fleet or to find a lost or
`stolen vehicle. The systems have utilized a number of
`methods, one of which is the radio location method. In
`the radio location method, a number of towers are dis-
`posed at predetermined locations around a city to allow
`communication with vehicles in their vicinity. The lo-
`cation method typically utilizes triangulation which
`requires a comparison of a received signal from the
`vehicle with respect to a time base to determine the time
`of arrival of the signal at the receiving antennas. Typi-
`cally, these antennas have very high powered transmit-
`ters that are operable to turn on the transmitter in the
`vehicle from a remote location by transmitting a request
`for ID to the vehicle and that vehicle, having the corre-
`sponding ID, then transmitting back an answer. It is the
`receipt of this answer that allows the triangulation
`method to be facilitated. However, this type of system
`suffers from a number of disadvantages. First, only very
`few vehicles can be located in this manner and it is
`desired to determine the movements of large fleets of
`vehicles with this method. Second, they require a dedi-
`cated system, which requires a specific request for an
`ID and the assumption that the vehicle is within the
`vicinity of the transmitter. Therefore, any one locale
`would be limited to the number of transmitters and/or
`receivers that are disposed at that one locale. AVL
`Systems are described in Steven Ritter and Jan McCoy,
`“Automatic Vehicle Location—An Overview”, IEEE
`Transactions on Vehicular Technology, Vol. VT—26,
`No. 1, February 1977, which is incorporated herein by
`reference.
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`4O
`
`45
`
`50
`
`55
`,
`
`60
`
`65
`
`2
`location
`In another type of system, conventional
`systems such as Loran-C and GPS Systems are utilized
`which are satellite-based systems. These are very so-
`phisticated systems and have been typically utilized by
`large fleet management systems. These systems are
`typically expensive, but provide for fairly accurate lo-
`cation of a vehicle in substantially real time. Of course,
`these systems require some type of satellite receiver and
`obtain their accuracy by relying upon the very solid
`time base that is provided by the satellite.
`In another type of system, a person’s location is deter-
`mined by their proximity to a receiver, or their lack of
`proximity thereto. In health care units, transmitters are
`attached to an individual and when the individual leaves
`a pre-defined zone, a receiver fails to pick up the trans-
`mitted signal and sounds an alarm. This type of system
`is also utilized with house arrest pfograms for convicted
`felons that are not considered to be dangerous and are
`allowed to exist outside penal institutions. Other sys-
`tems require the felons to check in at random times and
`to interface a coded bracelet with the receiver on the
`
`telephone to confirm that they are, in fact, the individ-
`ual that has answered the phone. These sometimes can
`be combined with video systems.
`Once the location of an individual or an object is
`determined, this information is then useful in control-
`ling a paging system for selective delivery of messages.
`In some paging systems, the location of a paging re-
`ceiver in a paging system is defined in a database for one
`of a plurality of hubs. In this manner, throughput can be
`increased by transmitting different messages simulta-
`neously to two different hubs and two different defined
`sets of users. Of course, this assumes that a paging re-
`ceiver resides in the hub having the ID of the pager in
`its database. However, one problem in the past has been
`the mobility of the paging receivers which allows an
`individual to travel between various hubs. The only
`way to update the database at present is for the user to
`call in to a central station and have the paging terminal
`database updated with the new location. This, of
`course, needs to be done on a central level.
`
`SUMMARY OF THE INVENTION
`
`The present invention disclosed and claimed herein
`comprises an adaptive paging system for delivering
`messages to a paging receiver. The system includes first
`and second paging system for receiving messages, each
`of the first and second paging systems having a paging
`transmitter for transmitting the received messages over
`an RF link to ones of the paging receiver that are within
`a predetermined locale about the paging transmitter. A
`location system is provided for determining the pres-
`ence of a paging receiver within either of the first and
`second paging systems predetermined locales. A trans-
`mission device is also provided that generates and trans-
`mits the paging messages that are designated for prede-
`termined ones of the paging receivers. A transmission
`link is provided for connecting the transmission device
`to the first and second paging systems. Routing control
`circuitry controls the transmission device to transmit
`the messages only to the one of the first and second
`paging systems at which the location system has deter-
`mined the destination paging receivers to be located at.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`For a more complete understanding of the present
`invention and the advantages thereof, reference is now
`
`

`

`5,423,056
`
`5
`
`10
`
`15
`
`20
`
`25
`
`3O
`
`35
`
`3
`made to the following description taken in conjunction
`with the accompanying Drawings in which:
`FIG. 1 illustrates a perspective view of the paging
`system of the present invention;
`FIG. 2 illustrates a diagrammatic view of the triangu-
`lation method for detecting location;
`FIG. 3 illustrates a block diagram of the system;
`FIG. 4 illustrates a more detailed block diagram of
`the system illustrating one base station;
`FIG. 5 illustrates a detailed block diagram of the
`HUB;
`FIG. 6 illustrates a detailed block diagram of the
`personal location unit;
`FIG. 7 illustrates a block diagram of the boosting
`receiver;
`FIG. 8 illustrates a cross-sectional view of a building,
`illustrating a PTU and a PLU;
`FIG. 9 illustrates a flowchart for the operation of the
`PLU;
`FIG. 10 illustrates a flowchart for calculating the
`time-difference-of-arrival (TDA);
`FIG. 11 illustrates a diagrammatic view of the cellu-
`lar system‘for transmitting data to selective locations or
`cells;
`FIG. 12 illustrates a diagrammatic view of the vari-
`ous overlapping receive patterns;
`FIG. 13 illustrates diagrammatic view of the message
`string transmission;
`FIGS. 14a and 14b illustrate the arrangement of batch
`messages for transmission to cellular sites;
`FIG. 15 illustrates a diagrammatic view of the cellu-
`lar sites and further including localized building sites;
`FIG. 16 illustrates a block diagram for an alternate
`embodiment illustrating transmission of data over a
`phone line or CATV line;
`FIGS. 17a and 17b illustrate flowcharts for the sys-
`tem of FIG. 16;
`FIG. 18 illustrates a more detailed block diagram for _
`the system of FIG. 16;
`FIG. 19 illustrates a block diagram of the receiver in
`the PLU for receiving upper and lower sideband sig-
`nals, to allow orthogonal coding; and
`FIG. 20, illustrates a block diagram of an alternate
`embodiment for increasing the throughput of the sys-
`tem utilizing preceding.
`DETAILED DESCRIPTION OF THE
`INVENTION
`
`4
`information from a geosynchronous satellite 28 in a
`simulcast mode. Paging information is transferred to a
`satellite 28 from an uplink 30 and associated satellite
`transmitting antenna 32. Therefore, paging information
`can be queued up at the paging terminal 44 and then
`transmitted by the uplink 30 from the antenna 32 to the
`satellite 28 for re-transmission to all the antennas 22—26
`on sticks 10—14, respectively, in a simulcast manner. In
`this manner, the transmission arrives at each of the
`sticks 10-14 and their associated satellite receivers
`22—26, at substantially thesame time. Further, as will be
`described hereinbelow, the base station equipment asso-
`ciated with each of the sticks 10-14 has a clock that is'
`synchronized with the clock of a public switched net-
`work (PSN) 34, and which transmitted signal to the
`satellite 28 is also synchronized. Therefore, in addition
`to the time of arrival of the signal at the satellite receiv-
`ers 22—26 being the same, the data clocks are also syn-
`chronized and use for clock recovery synchronization
`at the base station. This negates the need for a highly
`stable local oscillator at each base station.
`
`A personal location unit (PLU) 36 is provided that is
`attached to either an individual or an object which can
`move relative to the fixed location of the sticks 10—14.
`The PLU 36 is essentially a modified pager that is of
`conventional construction. The PLU 36 is operable to
`receive a paging message in a conventional manner
`from the paging transmitter antennas 16-20, provided
`that it is within transmission range and the signal is
`above the noise level of the PLU 36. In a conventional
`manner, the PLU 36 will receive paging messages from
`the one of the paging transmitter antennas 16-20 that
`has the highest signal level, i.e., it locks onto the stron-
`gest signal. In this manner, there will be no contention
`for the reception of this information.
`A modification feature of the PLU 36 relative to a
`conventional pager is that the PLU 36 has stored inter-
`nal thereto sufficient memory to store the ID or call
`sign of the one of the paging transmitters associated
`with paging transmitter antennas 16—20 that it receives
`. information from. FCC regulations require that this call
`sign be transmitted on a periodic basis, typically every
`fifteen or thirty minutes, or once per transmission trans-
`action. The PLU 36 is sequenced on and looks for sync
`and paging messages or station ID transmitted thereto.
`If the sync word and paging message is the assigned
`vector stating that the following sequence is the station
`ID or call sign, the receiver will switch to call sign or
`station ID detection for the following period. The base
`station ID transmission is preceded by a POCSAG
`batch with an idle address plus data that is a unique
`vector designated to mean that the base station ID’s are
`to follow this POCSAG batch. An alternate to this is
`the modulo-two add a vector with the sync word to
`designate the following time slot for station call signs or
`IDs. Even though a message is not designated for the
`PLU 36, it does receive the ID of the one of the sticks
`10—14 that is closest thereto and which has the strongest
`signal, as will be described hereinbelow. This ID infor-
`mation is stored, and at a later time, a message can be
`transmitted to the PLU 36 via the conventional paging
`network and antennas 16-20 to request location infor-
`mation from the PLU 36. In response to this request, the
`PLU 36 transmits on another frequency the information
`to the system, which is received at each of the sticks
`10—14 on a receiving antenna 38, 40 and 42, respec-
`tively, assuming that the receiving antennas 38—42 are
`within the transmission range of the PLU 36. For power
`
`45
`
`Referring now to FIG. 1, there is illustrated a per-
`spective view of the system of the paging system of the
`present invention. Three antenna towers 10, 12 and 14
`_ are illustrated, which are referred to as “sticks”. The
`sticks 10—14 represent only three of a plurality of sticks
`that are utilized in a paging system. Essentially, each
`stick 10—14 has a predetermined coverage area which is
`provided from paging transmitter antennas 16, 18 and
`20, respectively. Each of the antennas operates to pro-
`vide a relatively even coverage in all directions from
`the antennas 16—20 with respect to signal strength. The
`patterns are designed such that they overlap. The gen-
`eral operation of the paging portion of the present in-
`vention is described in US. patent application Ser. No.
`612,064, filed ,Nov. 13, 1990, and entitled, “Satellite
`Control Link”, which is incorporated herein by refer-
`ence.
`Each of the sticks 10-14 has associated therewith a
`satellite receiver 22, 24 and 26, respectively. Each of the
`satellite receivers 22—26 is designed to receive paging
`
`50
`
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`
`65
`
`

`

`5,423,056
`
`6
`the sticks 10-14 and any other sticks that are operable to
`receive the transmission. Upon receipt of the transmit-
`ted data which includes the ID of the PLU 36, the data
`is time-marked. This time-marked data is then transmit-
`
`5
`
`10
`
`15
`
`ted to the PSN 34 for transmission back to the paging
`terminal 44 and there processed in accordance with
`various “time of arrival” algorithms. In this manner, a
`relatively precise measurement of location can be made,
`knowing the location of the sticks that receive the data.
`The general systems for determining a various Time-
`Difference-of-Arrival estimation is described in W. A.
`Gardner and C. K. Chen, “Interference-Tolerant Time-
`Difference-Of-Arrival Estimation for Modulated Sig-
`nals”, IEEE Transactions on Acoustics, Speech and
`Signal Processing, Vol. 36, No. 9, Sep. 1988, which is
`incorporated herein by reference.
`
`5
`considerations, it should be understood that the power
`level on the transmitter portion of the PLU 36 is rela—
`tively low.
`The information that is transmitted to the antennas
`
`38-42 provides the last received ID or call sign, which
`‘ was transmitted thereto on the periodic basis from one
`of the antennas 16—20. The information received by the
`receiving antennas 38—42 is transmitted to the PSN 34
`and then back to a paging terminal 44 through a data
`entry unit (DEU) 46. This information is utilized to
`determine the location of the PLU 36, as will be de-
`scribed in more detail hereinbelow.
`In the above described operation, two methods are
`utilized by which to determine the general location of
`the PLU 36. First, by knowing the general ID of the
`stick 10—20, a rough idea of the location of the PLU 36
`can be. determined. For example, in a paging system
`where specific hubs are defined around the country
`with each hub defining a different locale, it would be
`desirable to know which of the hubs the PLU 36 is in.
`To increase throughput, it is desirable to minimize the
`number of messages that are sent to any given hub, since
`it is only necessary to transmit the messages to the hub
`in which the PLU 36 is located. Present systems pro-
`vide for this, but these systems must assume which
`location the PLU 36 is in. Of course, the user of the
`PLU 36 could phone in a change of location and their
`ID could be redirected to a different hub. The present
`invention, however, provides for automatic determina-
`tion of the location of the PLU 36 for the purposes of
`transmitting messages thereto. Therefore, by knowing
`the ID of the sticks that are in the general vicinity of the
`PLU 36, the hub in which‘the PLU 36 resides can be
`determined and messages can be routed to that hub
`without requiring them to be routed to all of the hubs in
`the network, which significantly decreases throughput.
`Additionally, the system of the present invention also
`can determine that the PLU 36 is disposed within the
`transmission range of any one of the sticks 10—14 or the
`other sticks in the system. Of course, the accuracy of
`this determination depends upon the time lapse between
`transmission of the ID from the associated sticks 10—14
`and the time of the location determination and the time
`that a message is transmitted to the PLU 36. Of course,
`if the PLU 36 is associated with an individual or an
`object that has not moved in that time, then the integ-
`rity of the data is high. However, there is no knowledge
`as to the mobility of the PLU 36 and, therefore, as this
`time lapse increases, the integrity of the location data
`decreases. Therefore, to increase the integrity of the
`data, the sticks 10—14 are controlled to transmit their ID
`followed by a request for location for a given PLU 36.
`This method of locating provides a rough approxima-
`tion of which best radio link location the PLU 36 is in.
`Of course, by knowing only the location of the PLU 36
`relative to the one of the sticks 10—14 having the highest
`signal received by the PLU 36, the system is provided
`with the location of the PLU 36 within the radius of the
`transmitted energy from only one of the sticks 10—14.
`Since the, radius can be upward of five miles, this is a
`relatively inexact location method, and is primarily used
`to determine which of the hubs or stick the PLU 36 has
`best RF link communication in.
`A second method to further define the location of the
`PLU 36 is that utilizing a triangulation method. This is
`basically a radio location method. The PLU 36 is opera-
`ble to receive a request for transmission and transmit
`this request to the receiving antennas 38—42 at each of
`
`,
`
`20
`
`The basic Time-Difference-of-Arrival system (TDA)
`operates as illustrated in FIG. 2. Each of the sticks
`10—14 have associated therewith a transmission pattern,
`50, 52 and 54. The request signal is picked up by the
`PLU 36 as a result of it being in at least one of the
`transmission patterns 50—54. Of course, the signal hav-
`ing the highest amplitude will be captured by the PLU
`- 36 and only the message received from that associated
`25
`stick 10—14 will be processed and the message decoded
`therefrom. Thereafter, the internal transmitter in the
`PLU 36 will transmit the unique ID of the PLU 36 and
`the prestored call sign ID of the last received call sign
`ID back to the sticks 10-14. The call sign ID may be
`combinations of the FCC required station ID,
`the
`unique identifier and a unique vector during idle address
`and/or data. Of course, depending upon the power
`level and the transmission characteristics of the sur-
`rounding environment, other sticks in the proximity
`may also receive the signal. The receiving antennas
`associated with the sticks 10-14 are then operable to
`receive the transmitted message from the PLU 36 and
`time-stamp it. The clocks at each of the sticks 10—14 are
`synchronized to provide a very stable time base and
`therefore reduce error when the TDA algorithm esti-
`mation is made. The data is then transmitted from the
`sticks 10—14 back to a central processing center through
`the PSN 34. Since the message requesting data transmis-
`sion from the PLU 36 was transmitted in a particular
`time slot, the central system at the paging terminal 44
`can determine when the data for that particular PLU 36
`has been received.
`
`30
`
`35
`
`40
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`45
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`50
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`55
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`65
`
`Referring now to FIG. 3, there is illustrated a block
`diagram of the location portion of the present invention.
`The PLU 36 has associated therewith a location re-
`ceiver 60, paging receiver 62 and a transmitter 64. The
`PLU 36 is illustrated as having a separate antenna 66
`associated with a location receiver 60, an antenna 68
`associated with a paging receiver 62 and an antenna 70
`associated with the transmitter 64. In actuality,
`the
`antennas 66-70 are a single antenna, as will be described
`hereinbelow. However, for illustrative purposes, they
`are depicted as separate antennas.
`A request transmitter 72 is provided at a remotely
`disposed location from the PLU 36 for transmitting a
`request from a transmitting antenna 74 to the antenna 66
`associated with the location receiver 60. This request is
`interpreted by the PLU 36 as requesting transmission of
`ID information and location information. As described
`above, the location information is in the form of the
`location ID of the strongest one of the sticks, which ID
`was previously received and stored. In addition, the
`
`

`

`7
`PLU 36 has a paging receiver 62 that is operable to
`receive paging messages from one of a plurality of sticks
`78, 80, 82 or 84, which transmit the paging information
`therefrom on antennas 86, 88, 90 and 92, respectively.
`In the preferred embodiment, the request transmitter
`72 is identical to the paging transmitter in the sticks
`78—84, such that the antenna 74 is common with anten-
`nas 86—92. Additionally, the request is essentially a mes-
`sage that is transmitted in the conventional paging sys-
`tem, which message has data associated therewith that
`is interpreted by the PLU 36 as a request for an ID.
`Once a request has been received, the transmitter 64 of
`the PLU 36 transmits stored the location ID out to a
`receiving antenna 94 on a PLU receiver (PLUR) 96 in
`association with the unique ID of the PLU 36. PLUR 96
`is connected to a PLU processor 98, which also controls
`the request transmitter 72. The PLU processor 98 is
`operable to receive the information from the PLU 36
`and process this information. As described above, this
`information can merely be the stored location ID of the
`stick having the strongest signal received by the PLU
`36 during transmission of location ID from the sticks
`78—84. Alternately, the PLU processor 98 could receive
`multiple inputs from multiple PLURs 96, which have
`placed a time stamp on the received message from the
`transmitter 64. This time stamp is utilized to make a
`TDA estimation, and, knowing the location of the
`PLURs from which the information was received, de-
`termine with relative accuracy the location of the PLU
`36 at the time of transmission therefrom. Of course, this
`is a function of the time base that exists at each of the
`PLURs 96 and at the PLU processor 98.
`With the location portion of the present invention, it
`is important to notethat the first method of location
`utilizes the location ID of the one of the sticks 78—84
`having the strongest signal at the time of transmission of
`the location ID. This provides not only the ability to
`determine the location of a PLU 36 knowing the loca-
`tion of the stick, but it also determines the location of
`the PLU 36 as a function of its power reception capabil-
`ity. This is important as one aspect of the present inven-
`tion is directed toward locating the PLU 36 for the
`purposes of transmitting messages thereto. The actual
`spatial location of a PLU 36 for this purpose is insignifi-
`cant. Rather, it is important to know which of the sticks
`78—84 has the transmitted signal therefrom received
`with the highest signal strength by the PLU 36. Al-
`though the location of the stick is known, the actual
`transmission characteristics are not exactly known and,
`in fact, the spatial location is of no use in determining
`from which stick 78—84 information should be transmit-
`ted to be received at the PLU 36. Since the PLU 36 will
`
`capture the strongest signal from only one stick, it is
`that stick that should have a later message transmitted
`therefrom in order for the PLU 36 to receive it from
`only that stick. Conventional paging systems transmit
`information from all of the antennas 86—92, as they do
`not know which signal the PLU 36 will receive. This
`significantly decreases throughput. Rather, if it could be
`determined clearly that a given PLU 36 is associated
`with a given stick, then it is only necessary to transmit
`information from the selected stick during a given time
`slot to the desired PLU 36. The remaining sticks can
`transmit different messages to different PLUs. There-
`fore, it is important to have present in the system data-
`base location information for the PLU 36 in the form of
`which stick in the system will transmit the strongest
`signal to the PLU 36 for a later paging message, i.e.,
`
`10
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`15
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`20
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`25
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`30
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`35
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`4O
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`45
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`50
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`55
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`.
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`65
`
`5,423,056
`
`8
`which one will it “capture”. It is not of interest for this
`application whether the PLU 3,6 is located to the north
`or to the south of the stick but, rather, only that the
`PLU 36 will capture the signal from that stick as the
`strongest signal.
`Since the integrity of the location measurement is a
`function of time relative to the time at which the loca-
`tion ID was determined, it is necessary to coordinate
`requests for location information from the transmitter
`72 with the actual time at which the location ID was
`transmitted. The time that the location ID is transmitted
`is known in a system. Typically, this is transmitted as
`infrequently as possible, as it will reduce throughput.
`However, once it is transmitted, transmission requests
`can then be transmitted immediately thereafter, it being
`known that a certain time has elapsed before the re-
`quested PLUS 36 transmit back a response. For exam-
`ple, if it were desired to determine the location of five
`paging transmitters (64), the next five messages follow—
`ing the transmissibn of the location ID would be re-
`quests for these five PLUs to transmit back their loca-
`tion information. PLUR processor 98 would therefore
`expect to receive five sequential messages back from the
`five PLUS 36 in a predetermined time slot. The time lag
`would be known, and it would be on the order of a few
`seconds.
`In one application for the present invention, a large
`number of PLUs 36 can have a location thereof deter-
`mined for the purpose of increasing throughput for
`subsequent transmission of data. If, for example, one
`hundred PLUs 36 were located by the system of the
`present invention, this could be followed by transmis-
`sion of messages to all of the sticks in a parallel manner.
`If it were determined, for example, that all one hundred
`PLUs 36 were equally divided among four sticks,
`twenty-five to each, then twenty-five messages could be
`transmitted to each stick in a sequential and parallel
`manner to cover all one hundred PLUS 36 such that the
`
`throughput is increased by a fa