Ulllted States Patent [19]
`Crimmins et al.
`
`US005917425A
`[11] Patent Number:
`[45] Date of Patent:
`
`5,917,425
`Jun. 29, 1999
`
`[54] IR/RF LOCATOR
`
`[75] Inventors: James W. Crimmins, Wilton; James L.
`Saulnier, NeWtOWn, both of Conn
`
`-
`
`.
`
`-
`
`[73] Asslgnee' girceless iommgmanons Products’
`’
`an my’ on“
`
`-
`
`-
`
`5,204,687
`
`4/1993 Elliott et al. .......................... .. 343/702
`
`5,239,296
`
`8/1993 Jenkins . . . . . . . .
`
`. . . .. 340/936
`
`356/139-06
`5,268,734 12/ 1993 Parker et a1~
`........... .. 455/9
`5,301,353
`4/1994 Borras et 'al.
`5,317,309
`5/1994 Vercellotti et al. .............. .. 340/825.54
`5,627,524
`5/1997 Frederickson et al.
`340/825.07
`5,689,229 11/1997 Chaco e161. ....................... .. 340/573.1
`
`5,479,408 12/1995 Will ...................................... .. 370/941
`
`Primary Examiner—Brian Zimmerman
`Assistant Examiner—Yves Dalencourt
`Attorney, Agent, or Firm—St. Onge Steward Johnston &
`Reens LLC
`[57]
`
`ABSTRACT
`
`An infrared (IR) article or person locator system is described
`Wherein a plurality of stationary units are distributed in
`Zones throughout an enclosure. The article or person carries
`a portable device so that the infrared communication link
`can derive local information as to Where the article or person
`is and an RF link is used, instead of cables, to transfer the
`local information to a central processor or station. In one
`embodiment local stationary beacons generate location
`codes at an IR carrier frequency and IR portable devices
`carry transceivers made of an IR receiver and a portable RF
`transmitter transmits the location code and a PIN code
`associated With the portable device to the central station.
`Techniques are described for reducing electrical poWer
`demands on the portable device’s battery While enhancing
`the speed With Which the central station can be alerted of a
`change in the location of the portable device.
`
`22 Claims, 7 Drawing Sheets
`
`[21] Appl. No.: 08/999,184
`[22]
`Filed:
`Dec. 29, 1997
`
`Related US. Application Data
`
`[63] Continuation-in-part of application No. 08/551,133, J an. 22,
`1996, abandoned.
`
`[51] Int. C1.6 ..................................................... .. G08B 5/00
`
`[52] U.S.Cl. .............................. .. 340/825.49;340/825.34;
`340/825.36; 340/825.72; 340/539, 340/5731,
`340/573.4, 359/145, 359/152, 359/172
`[58] Field Of Search ....................... .. 340/82549, 825.36,
`340/82572, 825.34, 825.54, 539, 572, 573.1,
`5734, 359/145, 152, 172
`
`[56]
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`2/1988 Emik Avakian ...................... .. 359/172
`4,727,600
`2/1991 Guest et al.
`340/573
`4,990,892
`5,062,151 10/1991 Shipley ...... ..
`359/154
`5,103,108
`4/1992 Crimmins
`250/3381
`5,153,584 10/1992 Engira .............................. .. 340/870.18
`
`RF
`RECEIVER
`
`DECODER
`
`45
`
`48
`
`28 56
`
`PROCESSOR
`
`Sonitor Exhibit 1008
`IPR of U.S. Patent No. 9,622,030
`
`

`

`U.S. Patent
`
`Jun. 29, 1999
`
`Sheet 1 of7
`
`5,917,425
`
`mm .
`
`“Q n mm
`
`3
`
`mommwuomm mv
`
`“3m. 53 .24
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`
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`5mm 9%
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`5.4
`
`V
`
`

`

`U.S. Patent
`
`Jun. 29, 1999
`
`Sheet 2 of7
`
`5,917,425
`
`IR
`
`\,\
`
`15
`
`L.U
`'
`IR
`32
`22
`DETECTOR _’ ‘Eggs; / /
`J
`44
`30
`5
`i
`PIN
`MULTIPLEX
`STORE “a SAMPLER _’ MODULATOR
`5
`36
`{/38 f
`34
`DIVIDER <—— osc
`
`Y7
`45¢
`
`FIG. 2
`
`40‘
`
`4‘2
`
`A
`
`<—— 1'X
`
`1000T x
`T
`
`>{
`
`LUn
`
`PINn
`
`M
`
`I F
`
`LUn
`
`PINn
`
`990T x
`LUn+1 PlNn+1 <-—-——h_r” LUn+1 PlNn+1
`
`ll
`
`F/G. 3
`
`

`

`U.S. Patent
`
`Jun. 29, 1999
`
`Sheet 3 of7
`
`5,917,425
`
`\l\
`
`32
`
`i
`
`/22 45
`
`IR
`DETECTOR
`F
`30
`9
`3 ‘A INTERVAL
`9
`TIMER
`
`-—-H MICROPROCESSOR
`W’TH MULTIPLE)‘ I-—-> MODULATOR
`+ 3
`44
`
`t
`34
`P'" f”
`
`40w OMOER
`
`T
`
`437
`
`42w OSCILLATOR
`
`'
`
`RF
`
`-* CARR’ER
`
`FIG. 4
`
`

`

`U.S. Patent
`
`Jun. 29, 1999
`
`Sheet 4 of 7
`
`5,917,425
`
`POL
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`

`

`U.S. Patent
`
`Jun. 29, 1999
`
`Sheet 5 of7
`
`5,917,425
`
`H7
`
`/,112
`
`114
`
`N0
`
`ENTER DATA
`
`'3
`DATA PACK
`VALID '2
`
`130
`;
`
`READ TIME
`T
`NEW
`
`100
`L
`
`1151‘
`
`READ TIME
`TNEW
`118
`l
`j
`STORE AREA CODE
`AcNEW
`
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`___ T
`T
`OLD
`NEW
`A
`
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`A0
`= AC ?
`NEW
`OLD
`
`TNEW ' TOLD
`?
`
`122
`
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`
`132
`
`TNEW - TOLD > K2
`'7
`
`134
`3
`RF Tx PIN AND
`LOCATION
`UNKNOWN CODES
`l
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`
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`
`136i
`
`1
`126
`sET /
`ACOLD : ACNEW
`
`124
`RF Tx
`PIN coDE & I
`
`

`

`U.S. Patent
`
`Jun. 29, 1999
`
`Sheet 6 of7
`
`5,917,425
`
`742
`
`140
`
`STARTUP
`
`732'
`
`'5 TIME S'NCE
`LAST VALID
`
`YES
`
`AC > K1?
`
`K 144
`
`L/ RESET IDLE TIMER T1
`
`‘L
`‘
`
`WAIT FOR DATA PACKET
`
`146
`
`IS THERE A
`VALID
`DATA PACKET ?
`
`160 148-7
`STORE AREA CODE AcNEW
`STORE TIME T2
`REsET IDLE TIMER T1
`
`ACTIVATE
`06”“
`
`150
`
`YES
`
`Is AcNEW A
`STABLE NEW
`LOCATION ?
`152 7
`No
`ASSEMBLE PACKET
`UP ? I
`
`IS
`IDLE TIME
`
`ENTER
`‘OLE MODE
`
`I £156
`
`RI= TRANSMIT AREA
`+ PIN CODES
`
`1154
`
`FIG. 7
`
`164
`S
`DETERMINE TIME
`LAPSE AT SINCE
`LAST RF TX
`
`YES
`
`I
`
`RF TRANSMIT
`NO IR SIGNAL
`CODE
`PIN CODE
`
`v
`NO
`
`1134'
`
`

`

`U.S. Patent
`
`Jun. 29, 1999
`
`Sheet 7 0f 7
`
`5,917,425
`
`A+
`‘
`IR/ASK
`BEACON x1701
`
`t1
`
`*f; 172
`1;
`
`174
`/
`
`_THRESHOLD
`CIRCUIT
`__I 182
`
`104
`L
`
`178
`9
`MICRO _’ RF
`PROC
`TX
`I A
`-'
`
`d102
`
`190
`H
`
`8
`
`18a
`'5 —
`IR/ASK
`\\
`—% }“ RECEIVER S
`/l/‘
`75
`I
`IRIASK
`176
`BEACON 1170 2
`M72 186/ S&H AID
`|<—t2—>1 t
`__ J
`DUMP
`
`188
`K
`[184
`
`1.94
`
`S
`192
`
`INITIALIZE VARIABLES a 196
`
`————»x
`
`RECEIVE Ac1 ~ 198 / 193
`
`200
`
`YES —————--> DUMP
`4r
`STORE AC1, s1 /1/ 202
`
`NO
`
`204
`
`0
`
`YES
`
`YES
`SET s2 = 31 ; AC2 = AC1 xv 206
`+
`IS 9cmT = A02 '2 >208
`{, NO
`SET AcLAST = AC2
`+
`TRANSMIT ACLAST, PIN M212 FIG 9
`J
`
`210
`
`

`

`5,917,425
`
`1
`IR/RF LOCATOR
`
`PRIOR APPLICATION
`
`This application is a continuation in part of US. patent
`application Ser. No. 08/551,133, ?led Jan. 22, 1996, entitled
`IR/RF Locator by James W. Crimmins and James Saulnier
`and assigned to the same assignee as for this application noW
`abandoned.
`
`FIELD OF THE INVENTION
`
`This invention relates to a method and apparatus for
`locating a device or person inside an enclosure such as an
`of?ce building, hospital or factory and the like. More spe
`ci?cally this invention relates to an apparatus for the deter
`mination of the location of a person or device inside a
`building using infrared and radio frequency (rf) signals.
`
`BACKGROUND OF THE INVENTION
`
`In US. Pat. Nos. 4,275,385 and 5,103,108 infrared com
`munication systems are described Wherein a person or
`device carries a portable infrared transceiver With Which
`signals can be relayed via ceiling located modules. This
`infrared communication technique has been extended so that
`a central locating facility can determine the location of the
`portable infrared transceiver, see for example US. Pat. No.
`5,319,191. This is done by placing an infrared communica
`tor in each room of an enclosure and providing suitable
`cabling from each room located module to a central control
`facility. The latter may then determine from the code signals
`from the portable infrared device Where the person or
`apparatus is located.
`A problem With such infrared communication system is
`that each of the room located infrared modules needs to be
`connected by cable to a central control. The cabling is
`expensive to install and available cabling is not alWays
`suitable for communication at the desired transmission rate.
`The cabling costs can constitute betWeen 30 to 60 percent of
`the costs for an entire infrared communication system.
`Another problem is found to arise in areas Where a
`multiple of ?xed IR units are used. In such a situation a
`portable device may be reported to be in more than one area
`at a time by different responding ?xed IR units. To resolve
`such ambiguity, the infrared signal strength is measured and
`reported along With the identi?cation codes to enable a
`central processor to determine the most likely location for
`the portable device. To enable a reliable determination of the
`location or When a portable device has left an area, an
`impracticably accurate (i.e. +/—1 db) logarithmic signal
`strength measurement is required. Such measurements
`impose expensive hardWare requirements, Which in the face
`of the high cabling costs for the Wiring of the ?xed IR units
`drive the price of an IR locator system too high for many
`applications.
`When an IR locator system employs a regularly transmit
`ting IR portable badge to a ?xed IR receiving unit, frequent
`location updates, of the order of 20 times a minute, are
`needed to keep track of the IR portable device. Such updates
`determine the time before one can note that a person or
`apparatus bearing the badge has changed location. Since,
`several seconds for such determination can be too long, an
`increase in the transmission rate Would be needed. In such
`case, hoWever, the drain on the portable device’s battery
`increases and its corresponding useful life or recharge inter
`val is unacceptably reduced. One can increase the battery
`siZe, but this also represents an undesirable expense and an
`overly heavy badge.
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`2
`RF devices for locating and monitoring people are
`described in US. Pat. Nos. 4,598,275; 4,814,751; 5,153,
`584; and 5,317,309. Such systems tend to propagate through
`Walls of a room so that the precise room location of a person
`is not alWays available. Such RF systems are prone to
`interference from extraneous sources and from other users at
`the same frequencies.
`These shortcomings of the prior art IR locator systems are
`avoided With an IR locator system in accordance With the
`invention.
`
`SUMMARY OF THE INVENTION
`
`With a communication system in accordance With the
`invention, advantages of infrared and RF communications
`are advantageously combined to provide an accurate and
`convenient-to-install person or apparatus locator. This is
`achieved, as described for one embodiment in accordance
`With the invention, by providing portable transceivers Which
`have infrared receivers and RF transmitters. The portable
`transceivers receive infrared location coded signals from
`enclosure or room located infrared transmitters and retrans
`mit these at RF carrier frequencies to a central unit after
`combining the location coded signals With personal identi
`?cation number (PIN) signals. These PIN signals are
`assigned to the person or apparatus Whose location in a
`building is to be monitored.
`With a communication system in accordance With the
`invention reliance upon the need for cabling is advanta
`geously eliminated and reliable communication is obtained.
`The stationary infrared transmitters are distributed through
`out a building to regularly transmit an infrared location
`coded signal that is prearranged to identify a particular Zone
`or room. The portable transceivers detect IR location signals
`from the respective stationary IR transmitters, combine
`location codes With the portable’s PIN number and as
`necessary, retransmit these at an RF carrier frequency to a
`central unit. The RF transmission is done in either repeated
`short bursts or With loW duty cycles, and preferably With
`random spacing in time, so that a plurality of portable
`transceivers can utiliZe the same carrier frequency even
`When at times the RF transmissions from the portable
`transceiver may occur at the same time.
`As described herein for one embodiment in accordance
`With the invention a unique rapid and sensitive technique for
`determining changes in location of a portable IR transceiver
`device is provided. This is obtained by utiliZing ?xed IR
`beacons Which transmit IR location signals at a continuously
`active and common IR carrier frequency. A portable IR
`receiver is used With an FM receiver section, having the
`usual FM characteristics. Hence, the IR FM receiver cap
`tures and responds to the strongest IR beacon signal When
`ever several beacon signals are simultaneously incident
`upon the portable IR receiver. With such an IR receiver,
`vastly improved discrimination betWeen different IR beacon
`signals is obtained so that the most likely location of a
`portable IR device can be much more accurately and cost
`effectively determined.
`Since the use of a portable transceiver having an IR
`receiver section and an RF transmitter tends to demand a
`relatively high amount of battery poWer, if the RF transmis
`sion is to be transmitted at regular short intervals, a preferred
`technique is used to limit RF transmission to those occasions
`When they are needed. For example, in one technique in
`accordance With the invention the continued presence of an
`IR portable device at the same location is sensed and as long
`as this continues an RF transmission is not needed. When a
`
`

`

`5,917,425
`
`3
`change in location occurs and this is sensed by RF trans
`mission control circuitry inside the IR portable device, an
`RF transmission of the neW location is made.
`Because the IR transmitter is stationary and has access to
`much more poWer than the conventional “IR transmitting
`portable” approach, it is possible to have it transmit a
`continuous FM stream of repeating data packets containing
`the location code. These packets can repeat every feW
`milliseconds. Such an arrangement offers great advantages
`for the portables: First, each portable can be programmed to
`revieW its location as often as is desired for that application.
`Aportable attached to a piece of equipment for example may
`be programmed to revieW its location only once a minute
`thus saving battery poWer. Aportable on a fast moving fork
`lift truck may be programmed to revieW its location every
`tenth of a second. The stationary IR transmitter is unchanged
`for both applications. Secondly, because there is no need to
`Wait for an IR location packet, a great deal of battery drain
`is conserved because the portable can Wake up, energiZe its
`receiver, read its location, decide Whether to transmit an RF
`burst and go back to a timed sleep all Within a feW milli
`seconds. Doing this, it is possible to reduce battery current
`to a fraction of What is currently required.
`Because the proposed architecture uses a stationary IR
`transmitter and a portable RF link to the central equipment,
`it is uniquely advantageous for incorporation in indoor
`Wireless PBX systems having RF handsets. In this case the
`required RF update packet transmission is accomplished as
`part of the handset’s normal RF handshaking With the
`system and the controller function is incorporated in the
`handset’s controller. Only a miniature IR receiver needs to
`be added.
`It is, therefore, an object of the invention to provide a
`reliable IR locator system Which can be provided at reason
`able costs and provides accurate and timely locating capa
`bility and can be operated With extended battery life for the
`IR portable device.
`It is, a further object of the invention to provide a method
`and system for determining the location of a person or
`apparatus Within a building Without requiring an expensive
`cumbersome installation of additional communication
`cables to each of a plurality of individual Zones in the
`building.
`These and other advantages and objects of the invention
`can be understood from the folloWing description of several
`illustrative embodiments in accordance With the invention as
`shoWn in the draWings.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 is a schematic representation of a building in Which
`a locating system in accordance With the invention is
`installed;
`FIG. 2 is a block diagram vieW of a portable transceiver
`and locating system in accordance With the invention for use
`in the system shoWn in FIG. 1;
`FIG. 3 is a timing diagram of RF transmission bursts from
`several transceivers in accordance With the invention to
`illustrate a minimiZation of signal interference;
`FIG. 4 is a more detailed block diagram vieW of a portable
`system in accordance With the invention;
`FIG. 5 is a schematic block diagram of still another
`embodiment in accordance of the invention;
`FIG. 6 is a How chart illustrating one example for the
`operation of a microprocessor used in an IR portable device
`of this invention;
`
`4
`FIG. 7 is a more detailed ?oW chart illustrating additional
`steps used in a program for operating a microprocessor used
`in an IR portable device in accordance With the invention;
`FIG. 8 is a block diagram vieW of a portable IR trans
`ceiver in accordance With the invention and using an ASK IR
`transmission technique;
`FIG. 9 is a How chart for the operation of a microproces
`sor used in an ASK IR transceiver technique as shoWn in
`FIG. 8.
`
`DETAILED DESCRIPTION OF DRAWINGS
`
`In FIG. 1 a building 10 is illustrated having a plurality of
`separate Zones 12, Which typically coincide With the indi
`vidual rooms or Zones Within the building 10. The use of
`decimals after numbers signify like items but at different
`locations. Each of the rooms 12 is provided With an infrared
`transmitter 14, identi?ed as, a beacon signal generating local
`unit (L.U.), and Which typically sends out very short bursts
`of infrared (IR) location signals at regular intervals. The
`intervals are preferably randomly selected by setting appro
`priate components during the manufacture of the transmit
`ters 14.
`The IR transmitters 14 may be mounted from the ceilings
`16 or on the Walls 18 of the rooms or mounted at an ac
`receptacle as in Zone 12.5. The IR transmitters can be battery
`poWered or When mounted at ac receptacles be activated
`from available ac poWer. When an IR transmitter 14 is
`located at a loW room level as shoWn in room 12.5 and a
`large obstruction such as 20 is nearby, IR communication is
`still possible by virtue of IR re?ections from a ceiling 16.5
`and/or a Wall as shoWn for room 12.5.
`Each IR transmitter beacon 14 sends out a unique IR ID
`(identi?cation) signal from a memory store and Which can
`be identi?ed at a central control as originating from a
`particular Zone or room 12, FIG. 1. The IR location or ID
`signals may, for example, be transmitted at an IR carrier
`frequency that is typically above 400 KHZ so as to avoid
`signal interference from ?uorescent lamps and be in the
`form of bursts of the order of about 3 milliseconds long at
`intervals of once every 5 seconds. Different burst durations
`and repetition intervals can be accommodated.
`Portable transceivers 22, or badges as they are sometimes
`called, are provided for persons or apparatuses. These trans
`ceivers each include an IR receiver 24 and an RF transmitter
`26 Which are coupled to each other. Hence, RF transmitters
`26 can re-transmit received IR location signals at an RF
`carrier frequency to a remote central control system 28.
`These transmissions do not alWays have to occur at the rate
`that IR location code signals are received if the resulting RF
`transmissions from multiple RF transmitters creates inter
`ference problems.
`As shoWn in FIGS. 2 and 4 each portable transceiver 22
`includes an IR detector Which detects the infrared location or
`ID signals from the various IR stationary transmitters 14 and
`temporarily stores the detected location code in a memory
`15 of a microprocessor 32. Apersonal identi?cation number,
`a PIN, associated With a particular person or equipment, is
`stored in a memory 34 for as long as the person or equipment
`is associated With the particular transceiver 22.
`A multiplexer, Which can be a part of the signal processor
`32, is activated at predetermined intervals by a pulse on a
`line 38 from an interval timer 39. The timer is activated by
`pulses from a divider netWork 40 driven by a signal from an
`oscillator 42. The microprocessor 32 transfers the location
`code detected by the IR detector 30 and the PIN signal from
`memory 34 in sequence to a modulator 44 to modulate an RF
`
`10
`
`15
`
`25
`
`35
`
`45
`
`55
`
`65
`
`

`

`5,917,425
`
`15
`
`25
`
`5
`carrier signal obtained from a carrier signal generator 43
`driven by oscillator 42.
`The modulated carrier signal is transmitted by an antenna
`45 to an antenna 47 of an RF receiver 46 in the central
`control station 28, see FIG. 1. The output from receiver 46
`is decoded by a decoding netWork 48 to reproduce the
`location signal on line 50 and the personal identi?cation
`signal on line 52. These signals are associated With each
`other and so used in the signal processor 56 to determine
`Where a particular person or piece of equipment is located.
`In the system of FIGS. 1 and 2 the bursts of RF trans
`missions from a transceiver occur as shoWn in FIG. 3
`separated by intervals T. It should be understood, hoWever,
`that the portable devices can do either such store and
`forWarding or immediately transmit received IR local Zone
`codes folloWed by PIN codes. The intervals T are preferably
`slightly different for each transceiver 22 so that in the
`aggregate relatively feW instances of interference from
`simultaneously transmitted bursts occur. For example, if the
`duration of a burst is designated as TX and the time betWeen
`bursts is for example 10,000Tx then for different transceivers
`22 different repetition rates are employed such as 9,990Tx
`9,970Tx etc. In this manner the chances for any one trans
`mission to step on that from another transceiver is reduced
`to a very loW level even When a substantial number of
`transceivers 22 are employed at one facility 10.
`With an IR/RF locator system in accordance With the
`invention the Wiring of the various IR transmitters 14 to a
`central control can be avoided. The common RF frequency
`employed can be designated particularly for the facility 10
`and interference from other RF sources minimiZed With
`appropriate isolation techniques.
`Having thus described several embodiments of the inven
`tion its advantages can be appreciated. Variations from the
`described embodiments can be made Without departing from
`the scope of the invention. For example, the embodiment
`described herein for FIGS. 1—4 employed portable systems
`formed of an RF transmitter and an IR receiver and a
`stationary IR location transmitter. This arrangement can be
`reversed Whereby the portable unit 22 is formed of an IR
`PIN code transmitter only and the stationary local unit 14
`has an IR receiver such as 24 and an RF transmitter such as
`26. The portable unit 22 then transmits its PIN code at
`regular intervals, and the stationary unit 14 receives and
`detects this PIN code and transmits this With its stored
`location or ID code to the base system 28 using RF.
`In the embodiment illustrated in FIG. 5 portable IR
`transceivers 70 are used as portable badges or devices and
`communicate With ?xed IR beacons 72 located in a manner
`as previously described in connection With FIG. 1. The IR
`beacons 72 transmit using a common IR carrier as illustrated
`at 74 With a location code 76 FM modulating the carrier 74.
`Other signals can of course also be transmitted by the
`beacons 72 to portable devices 70. The IR beacons’ repeti
`tion intervals preferably are smaller, of the order of several
`times a second.
`The IR portable device 70 detects the IR and FM modu
`lated carrier 74 With an appropriate photo diode 75 sensitive
`to the IR radiation and in a manner as is Well knoWn in the
`art. The detected carrier is converted to an electrical FM
`carrier signal Which is demodulated in an FM receiver
`section 78, Which has a mixer stage 80, an IF (intermediate
`frequency) stage 82 using standard FM circuitry and a
`standard discriminator stage 84. The standard IF stage
`produces an RSSI signal on an output line 86, Which signal
`in turn is representative of the amplitude of the IR carrier at
`the input to the photo diode 75 of the IR portable device 70.
`
`6
`The FM signal is detected With a standard discriminator,
`Which detects the location code 76 and applies this onto an
`output line 88 together With such error correction coding
`(CRC) as may be used to enhance the correct detection of the
`location code by a microprocessor 90 in portable device 70.
`The FM receiver section 78 has the Well knoWn capture
`effect Whereby Weaker interfering signals are suppressed and
`the larger signal preferentially selected. As a result, When an
`IR portable device 70 receives beacon signals from different
`beacons 72.1 and 72.2, the beacon signal that is larger tends
`to be selected and With an effectiveness that depends upon
`the capture ratio for the FM receiver stage 82. Since the
`capture ratio can be substantial, a small IR signal amplitude
`difference, such as caused by the movement aWay from one
`beacon 72.1 and closer to another such as 72.2, can be
`detected as a change in location of the IR portable device.
`Hence, a more sensitive response to position changes can be
`obtained and a more reliable reporting of a neW location can
`be made to a central signal processor such as 56 shoWn in
`FIG. 1. The FM receiver section 78, therefore , has a
`sufficient capture ratio so as to optimiZe the FM receiver’s
`capability in isolating and selecting the stronger of the
`infrared signals from different infrared transmitters.
`Another aspect of the IR transceiver device 70 of this
`invention involves a reliable detection of the beacon signals
`76. This can be done With the use of a squelch circuit 92 or
`With the use of an adequate amount of error correction
`coding or a combination of both. In the embodiment of FIG.
`5 the squelch circuit 92 includes a threshold generator 94
`Which applies a signal, indicative of a minimum desired
`level of the IR signal at the photo detector 75, to a com
`parator 96. This compares the threshold signal With the RSSI
`signal on line 86 to control enablement of an AND gate 98
`interposed betWeen the output on line 88 of receiver 78 and
`the microprocessor 90.
`Once the IR signal incident on diode 75 is sufficiently
`large to overcome the squelch signal threshold level and
`AND gate 98 has been enabled, the received signal burst
`from a beacon is entered into microprocessor 90. This then
`enters an RF transmission control routine 100 to analyZe the
`received location code 76 and, When a change in location is
`sensed, it produces an output signal for RF transmission via
`transmitter 102 and RF antenna 104 to the central processor
`56, see FIG. 1. The RF transmission includes at least the neW
`beacon location code and the PIN signal identifying the
`particular IR portable device Which sensed a change in
`location.
`The RF transmission control routine 100 provides for a
`technique to determine When a change in location is to be
`transmitted as Well as recogniZe a need to transmit a signal
`When no beacon signal has been received for a predeter
`mined time. The routine 100 begins at 106 by monitoring the
`strongest beacon signal and as long as this remains the same,
`refrains from sending an RF signal burst. Then, When at 108
`a change in beacon signals is sensed, an RF transmission is
`made occur. In the event no beacon signal has been received
`for a long time a special idle code indicative of this condition
`is generated by the processor 90 and transmitted via RF to
`the central processor With the PIN code at 110 in the routine
`100. This idle code is transmitted at a sloW rate, i.e. With
`long intervals betWeen transmissions, for as long as a beacon
`signal is not being received and provided the IR portable
`device is on.
`FIG. 6 illustrates With more detail illustrative steps
`involved in the routine 100 for a microprocessor 90. At 111
`registers and variables are initialiZed. At 112 data from the
`
`35
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`45
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`55
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`65
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`5,917,425
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`10
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`15
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`7
`FM receiver, or such other receiver as may be used by the
`IR portable device, is entered, using standard techniques,
`into the processor 90. Entered data is then examined for
`validity at 114. This typically involves using an error cor
`rection code appended to the transmission from a beacon 72.
`The CRC’s length determines hoW rigorous the validity
`examination is and if sufficiently long can be relied upon to
`delete any squelch circuitry such as 92.
`If the data is deemed to be valid, a timer is read at 116 and
`stored in a location identi?ed as Tnew together With the area
`code de?ned by the beacon’s location code and stored as
`ACMW at 118. A test is made at 120 Whether there has been
`a change in area location by the IR portable device as
`indicated by a change in the beacon signal’s location code.
`This test is done by comparing the just received location
`code ACMW With a previously stored location code ACOld at
`120. If there has been no change in the location code a test
`is made at 122 Whether the elapsed time betWeen Tnew and
`Told, representative of a previous time, exceeds a maximum
`duration K1. If not, a return is made to step 112 to aWait the
`next beacon signal. If so, then at 124 an RF transmission is
`sent to the central processor 56 of the IR portable device’s
`PIN code and the neW location code ACMW.
`In the event the test at 120 indicated that there Was a
`change in the sensed location code, then after setting AC0ld=
`AC at 126, the IR portable device’s PIN code and the neW
`location code AC are sent at 124 and a return is made to
`step 112 to aWait the next beacon signal detection.
`Since it is possible that for some reason there is no
`reception of a beacon signal, for example if the IR portable
`device is in a closet or bath room, a need exists to recogniZe
`this condition. This is done Whenever the validity test at 114
`does not identify valid data or Whenever a particular time
`interval has been exceeded. Hence, at 130, in response to not
`?nding valid data at 114, a timer is read and stored as TMW
`and a test is done at 132 Whether the interval since the last
`valid beacon signal Was received exceeds a particular maxi
`mum K2. If not a return is made to step 112 and if so, an RF
`transmission is made at 134 of the IR portable device’s PIN
`code and a “location-unknown” code. This “location
`unknoWn” code can be such code as identi?es the fact that
`no IR location code signal has been received by the par
`ticular IR portable device for a predetermined interval. A
`return is then made to step 112 after setting TMW equal to a
`value Told at 136.
`With the routine 100 as set forth in FIG. 6, RF transmis
`sions are signi?cantly reduced because there is no need to
`transmit current location codes to the central processor at
`regular intervals. Transmissions are only made When
`needed. As a result the battery life of the IR portable device
`is increased, transmission spectrum is preserved and RF
`transmissions from different IR portable devices are less
`likely to step on each other resulting in a more reliable RF
`communication.
`Further battery poWer conservation can be obtained by
`implementing an idle mode. For example, the beacons 72
`may be transmitting an IR location code rapidly separated by
`short intervals. This Would enable an IR portable device to
`more quickly determine When there has been a change in
`location. For some IR portable devices 70 such rapid analy
`sis of beacon signals may not be needed and battery poWer
`conserved by de-poWering part of the circuit used to detect
`IR beacon signals and activating the idled circuit at certain
`intervals for certain time periods.
`FIG. 7 illustrates an example for a routine 140 incorpo
`rating an idle interval. After start up at 142, involving an
`
`8
`initialiZing of registers and variables, an idle timer T1 is set
`at 144. Atest is then entered at 146 Whether received beacon
`signals represent valid data, and, if so, the location code is
`stored at 148 as ACMW together With time time T2. The idle
`time is again reset and a test is entered at 150 as to Whether
`the location is neW or different. If neW, an RF transmission
`of the location code and PIN code is made at 152 after
`assembling the data packet to be transmitted at 154. An idle
`mode is then entered at 156. This mode de-poWers the IR
`portable device, except for its timer, for a certain interval. At
`158 the idle timer is monitored to determine Whether the idle
`interval has expired. If so the portable device is activated at
`160 and a return made to step 146.
`Other steps in routine 140 include similar steps as
`described in connection With FIG. 6 as suggested With the
`use of primed similar numbers. In addition a special timer
`controlled test is conducted at 164 as to Whether there has
`been an excessive time lapse since the last RF transmission
`of a location code.
`The techniques in FI