(12) United States Patent
`(10) Patent N0.:
`US 6,799,050 B1
`
`Krasner
`(45) Date of Patent:
`Sep. 28, 2004
`
`USOO6799050B1
`
`(54) REDUCING CROSS-INTERFERENCE IN A
`COMBINED GPS RECEIVER AND
`COMMUNICATION SYSTEM
`
`(75)
`
`Inventor: Norman E. Krasner, San Carlos, CA
`US
`(
`)
`
`(73) Assignee: Snaptrack, Inc., San Diego, CA (US)
`( * ) Notice:
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 557 days.
`
`(21) Appl. NO’: 09/874’747
`(22)
`Filed:
`Jun. 4, 2001
`
`Int. Cl.7 .................................................. H04Q 7/20
`(51)
`(52) US. Cl.
`................................ 455/456.1; 455/456.6;
`455/552.1; 455/550.1, 455/296; 342/357.06;
`342/357.1; 342/357.12
`(58) Field of Search ........................... 455/456.1, 456.6,
`455/63.1, 552.1, 553.1, 550.1, 296; 342/357.06,
`357.1, 357.12
`
`(56)
`
`.
`References Clted
`us. PATENT DOCUMENTS
`
`4/1994 Hirata
`5,301,368 A
`7/1998 lanky ...................... 342/3571
`5,786,789 A *
`5,825,372 A * 10/1998 Artieri .............. 345/566
`
`8/2000 Krasner .......
`6,107,960 A *
`342/35709
`..................... 455/427
`2002/0193108 A1 * 12/2002 Robinett
`
`2003/0045333 A1 *
`
`3/2003 Kimata et al.
`
`.............. 455/574
`
`EP
`W0
`
`FOREIGN PATENT DOCUMENTS
`1122554 A1 *
`8/2001
`............. G015/5/14
`WO 01/06669 A1
`1/2001
`OTHER PUBLICATIONS
`
`PCT International Search Report for PCT Int’l Appln No.
`U302 20302
`.1 dA . 10 2003
`7
`.
`/
`’ ma1 e
`pr
`’
`’ ( pages)
`* cited by examiner
`.
`.
`Przmary Examzner—Lee Nguyen
`Assistant Examiner—Minh D. Dao
`(74) Attorney, Agent, or Firm—Philip Wadsworth; Charles
`D. Brown; Donald Kordich
`
`(57)
`
`ABSTRACT
`
`A method of operating a mobile device is disclosed. A first
`activity of the mobile device is detected. The following two
`operations are executed upon detection of the first activity:
`(i) wireless transmission of data over a wireless data link
`from a communication unit of the mobile device is disabled
`
`is
`for a period of time, and (ii) a first control signal
`transmitted from a communication unit to a satellite osi-
`tioning system receiver of the mobile device, the first coIfitrol
`signal enabling processing of signal positioning system
`signals received by the receiver during this period of time.
`The size of this period of time may be predetermined or
`adaptable
`
`18 Claims, 6 Drawing Sheets
`
`100
`
`
`
`
`
`101
`
`CELLULAR TELEPHONE
`
`10
`
`2
`
`103
`
`109
`
`104
`
`
`
`DUPLEXER
`OR SWITCH
`
`RF T0 IF
`ONVERTER
`
`“9
`
`c
`
`
`DEMODU-
`LATOR
`
`MICRO-
`PROCESSOR
`
`E),
`
`
`
`O/FROM
`KEYPAD
`DISPLAY
`AND
`MICRO-
`PHONE
`
`
`
`130
`
`' ROCESSING
`CIRCUITRY
`
`120
`
`
`POSITION
`INFORMATION
`TO USER
`OR
`COMMUNICATION
`LINK
`
`|PR2020-01192
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`US. Patent
`
`Sep. 28, 2004
`
`Sheet 1 0f 6
`
`US 6,799,050 B1
`
`GPS
`ANTENNA
`
` GPS
`
`COMM.
`RECEIVER
`ANTENNA
`
`162
`
`
`COMMUNICATION
`TRANSCEIVER
`
`(CELLULAR TELEPHONE)
`
`
`19
`
`
`
`
`159
`
`BASE
`STATION
`
`
`
`COMBINED GPS RECEIVER m
`
`FIG.1
`
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`US. Patent
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`Sep. 28, 2004
`
`Sheet 2 0f 6
`
`US 6,799,050 B1
`
`MICRO-
`PROCESSOR
`
`TOFROM
`KEYPAD
`DISPLAY
`AND
`MICRO-
`PHONE
`
`GPS RECEIVER
`
`130
`
`M-CRO
`GPS
`RF-0IF
`.aAs
`_C - 'ROCESSING _C
`
`PR
`
`ESSOR
`
` 104
`
`WIT H
`
`ONVERTER
`
`SIGNAL
`
`CIRCUITRY
`
`FIG. 2
`
`POSITION
`INFORMATION
`ToggER
`COMMUNICATION
`LINK
`
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`US. Patent
`
`Sep. 28, 2004
`
`Sheet 3 0f 6
`
`US 6,799,050 B1
`
`ffl
`
`10100
`
` GPS
`RECEIVER
`
`
`§1_2
`
`
`
`
` GPS
`
`CELLULAR
`
`
`BASE
`
`SWITCHING
`STATION
`CENTER
`
`10
`
`
`
`3.05
`
`
`FIG. 3
`
`
`
`LAND-BASED
`PHONE
`NETWORK
`
`
`31_
`
`
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`US. Patent
`
`Sep. 28, 2004
`
`Sheet 4 0f 6
`
`US 6,799,050 B1
`
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`US. Patent
`
`Sep. 28, 2004
`
`Sheet 5 0f 6
`
`US 6,799,050 B1
`
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`US. Patent
`
`Sep. 28, 2004
`
`Sheet 6 0f 6
`
`US 6,799,050 B1
`
`
`
`
`ESTABLISH COMMUNICATION OVER
`
`
`COMMUNICATION LINK
`
`
`
`
`fiflQ
`
`
` IS ACTIVITY
`
`&
`
`DETECTED?
`
`
`
`
`
`(i) DISABLE TRANSMISSION OF VOICE DATA
`FOR A PERIOD OF TIME, AND
`(ii)TRANSMIT A CONTROL SIGNAL TO ENABLE
`PROCESSING OF SATELLITE POSITIONING
`SYSTEM SIGNAL DATA
`
`
`
`
`
`
`
`
`
`6%
`
`
`
`WHEN PERIOD OF TIME ELAPSES:
`0
`(iii) ENABLE TRANSMISSION OF VOICE DATA; AND
`
`
`(iv) DISABLE PROCESSING OF SATELLITE POSITIONING
`
`
`SYSTEM SIGNAL DATA
`
`
`
`5%
`
`FIG. 6
`
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`US 6,799,050 B1
`
`1
`REDUCING CROSS-INTERFERENCE IN A
`COMBINED GPS RECEIVER AND
`COMMUNICATION SYSTEM
`
`FIELD OF THE INVENTION
`
`The present invention relates generally to the field of
`satellite positioning system (SPS) receivers, and more par-
`ticularly to reducing cross-interference in a combined SPS
`receiver and communication system.
`BACKGROUND OF THE INVENTION
`
`The use of portable personal communication devices,
`such as cellular phones and pagers, has increased dramati-
`cally in recent years. Additionally,
`the use of portable
`navigational devices, such as Satellite Positioning System
`(SPS) receivers, has increased as these devices have become
`more widely available. Recent technological developments
`have allowed the combination of SPS receivers and com-
`
`munication systems in integrated units, such as a combina-
`tion SPS receiver and cellular phone unit. Such combined
`devices have many applications such as personal security,
`emergency response, vehicle tracking, and inventory con-
`trol. Some combination units combine separate SPS receiv-
`ers and communication systems using suitable electronic
`interfaces. Others use shared circuitry and packaging. These
`combined units feature the convenience advantages afforded
`by common housings and integrated user
`interfaces.
`However, such combined units may also exhibit certain
`shortcomings, such as increased power consumption and
`reduced performance.
`One marked disadvantage inherent in many combined
`SPS and communication devices is the decreased perfor-
`mance of the SPS receiver section of the combined unit. A
`
`common cause for this decreased performance is signal
`interference between the communication and SPS receiver
`
`stages. For example, in a combination cellular phone/SPS
`receiver, a cellular transmissions from the cellular telephone
`stage generate strong interference which can reduce the
`performance of the SPS receiver.
`Current approaches to overcoming the cross-interference
`between the communication and SPS stages involve the use
`of complicated filters or high dynamic range circuits in the
`front-end section of the SPS receiver to limit the in-band
`
`interference to acceptable ranges. These approaches,
`however, require the use of complex additional circuitry
`which can increase the cost and power consumption of the
`combined unit. For example, one method of reducing the
`cross-coupling in a combination cell phone/SPS receiver is
`to use several bandpass filters in the RF front end of the SPS
`transmitter to eliminate the radio frequency (RF) interfer-
`ence from the cellular transmitter. However, there are sev-
`eral problems with this approach. First, several filters may
`be required to provide adequate reduction of the signal
`energy coupled into the SPS receiver RF circuitry from the
`cellular transmitter. This may increase cost and size of the
`combined unit. Secondly,
`the use of filters increases the
`noise figure of the SPS receiver, making it less sensitive to
`the satellite navigational signals.
`It is therefore desirable to provide a system that reduces
`the cross-interference between the SPS and communication
`sections of a combined SPS/communication receiver.
`It is further desirable to provide a system that improves
`the SPS reception performance in a combined SPS/
`communication receiver without adversely impacting the
`cost and sensitivity characteristics of the SPS receiver.
`
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`2
`SUMMARY OF THE INVENTION
`
`Amethod of operating a mobile device is disclosed. Afirst
`activity of the mobile device is detected. The following two
`operations are executed upon detection of the first activity:
`(i) wireless transmission of data over a wireless data link
`from a communication unit of the mobile device is disabled
`
`is
`for a period of time, and (ii) a first control signal
`transmitted from the communication unit to a satellite posi-
`tioning system receiver of the mobile device, the first control
`signal enabling processing of signal positioning system
`signals received by the receiver during this period of time.
`The first activity may for example be due to an operation
`carried out by a user of the mobile device, such as the
`depression of a button on the mobile device or the absence
`of speech received by a microphone of the communication
`unit.
`
`Wireless transmission may be disabled and enabled in an
`alternating manner.
`Other features of the present invention will be apparent
`from the accompanying drawings and from the detailed
`description which follows.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`The present invention is illustrated by way of example
`and not by way of limitation in the figures of the accompa-
`nying drawings in which references indicate similar ele-
`ments and in which:
`
`FIG. 1 is a block diagram of a combined Global Posi-
`tioning System (GPS) receiver and communication system
`with a communication link to a basestation according to one
`embodiment of the present invention.
`FIG. 2 is a block diagram of the components comprising
`the GPS receiver and communication transceiver in a mobile
`
`device according to an embodiment of the present invention.
`FIG. 3 illustrates a mobile device used in a cellular
`
`telephone network according to one embodiment of the
`present invention.
`FIG. 4 is a time chart illustrating one method of operating
`a mobile device, according to the invention.
`FIG. 5 is a time chart illustrating another method of
`operating a mobile device according to the invention.
`FIG. 6 is a flow chart
`illustrating the operations of
`reducing cross-interference in a mobile device according to
`a method of the present invention.
`DETAILED DESCRIPTION
`
`Amethod and apparatus for reducing cross-interference in
`mobile device which is a combination of Satellite Position-
`
`ing System (SPS) receiver and communication device is
`described.
`In the following description, for purposes of
`explanation, numerous specific details are set forth in order
`to provide a thorough understanding of the present inven-
`tion. It will be evident, however, to one skilled in the art that
`the present invention may be practiced without these specific
`details.
`In other instances, well-known structures and
`devices are shown in block diagram form to facilitate
`explanation.
`In the following discussion, embodiments of the present
`invention will be described with reference to application in
`the United States Global Positioning Satellite (GPS) system.
`It should be evident, however, that these methods are equally
`applicable to similar satellite positioning systems, such as
`the Russian Glonass system. Thus, the term “GPS” used
`herein includes such alternative satellite positioning
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`US 6,799,050 B1
`
`3
`systems, including the Russian Glonass system. Likewise,
`the term “GPS signals” includes signals from alternative
`satellite positioning systems.
`Mobile device
`
`FIG. 1 is a block diagram of mobile device 150 which
`combines a communication transmitter/receiver
`(transceiver) with a GPS receiver for use in one embodiment
`of the present invention. The mobile device 150 is a portable
`hand-held unit that includes circuitry for performing the
`functions required for processing GPS signals as well as the
`functions required for processing communication signals
`transmitted and received through a communication link. The
`communication link, such as communication link 162, is
`typically a radio frequency communication link to another
`communication component, such as a basestation 160 hav-
`ing a communication antenna 164.
`The mobile device 150 contains a GPS receiver 130
`
`including an acquisition circuit and a processing section. In
`accordance with traditional GPS methods, GPS receiver 130
`receives GPS signals transmitted from orbiting GPS satel-
`lites and determines the times-of-arrival
`(so-called
`“pseudoranges”) of unique pseudo-random noise (PN) codes
`by comparing the time shifts between the received PN code
`signal sequences and internally generated PN signal
`sequences. GPS signals are received through GPS antenna
`111 and input to an acquisition circuit which acquires the PN
`codes for the various received satellites. The navigational
`data (e. g., pseudoranges) produced by the acquisition circuit
`are processed by a processor for transmission by commu-
`nication transceiver 109.
`The mobile device 150 also includes communication
`transceiver section 109. Communication transceiver 109 is
`
`coupled to communication antenna 100. Communication
`transceiver 109 transmits navigational data processed by
`GPS receiver 130 through communication signals (typically
`RF) to a remote basestation, such as basestation 160. The
`navigational data may be the actual latitude, longitude, and
`altitude of the GPS receiver, or it may be raw or partially
`processed data. Received communication signals are input
`to communication transceiver 109 and passed to a processor
`for processing and possible output through an audio speaker.
`According to one embodiment of the present invention, in
`the mobile device 150, pseudorange data generated by GPS
`receiver 130 is transmitted over communication link 162 to
`basestation 160. Basestation 160 then determines the loca-
`
`tion of combined receiver 150 based on the pseudorange
`data from the combined receiver,
`the time at which the
`pseudoranges were measured, and ephemeris data received
`from its own GPS receiver or other sources of such data. The
`location data can then be transmitted back to mobile device
`150 or to other remote locations. The communication link
`
`162 between mobile device 150 and basestation 160 may be
`implemented in a number of various embodiments including
`a direct link or cellular telephone link. In one embodiment
`of the present
`invention,
`the communication transceiver
`section 109 is implemented as a cellular telephone.
`FIG. 2 provides a more detailed block diagram of a
`combined cellular telephone and GPS receiver according to
`one embodiment of the present invention. It will be appre-
`ciated by those of ordinary skill in the art that the system
`illustrated in FIG. 2 is one embodiment, and that many
`variations in the design and construction of a combined GPS
`receiver in accordance with the teaching of the present
`invention are possible. For example, although the following
`discussion will assume that the communication section is
`
`embodied in a cellular telephone, it will be appreciated that
`the present invention may be embodied in other communi-
`
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`4
`cation devices, such as two-way pagers, and similar
`bi-directional communicators.
`
`In FIG. 2, the mobile device 150 comprises GPS receiver
`130 and GPS antenna 111 (together referred to as the “GPS
`section”), and cellular telephone 109 and cell phone antenna
`100 (together referred to as the “communication section”).
`The cellular telephone transmits and receives signals via
`antenna 100 to and from a remote base station (e.g., base
`station 160 in FIG. 1).
`GPS Section
`In the GPS receiver 130 of the mobile device 150, a
`received GPS signal is input from GPS antenna 111 through
`signal line 120 and switch 112 to a radio frequency (RF) to
`intermediate frequency (IF) converter 113. Frequency con-
`verter 113 translates the signal to a suitable intermediate
`frequency, for example 70 MHZ. It then provides a further
`translation to a lower intermediate frequency, for example 1
`MHZ. The output of the RF to IF converter 113 is coupled
`to the input of GPS signal processing circuit 114. GPS signal
`processing circuitry 114 includes an analog to digital (A/D)
`converter which digitizes the output signals from the RF to
`IF converter 113.
`
`In one embodiment of the present invention, GPS signal
`processing circuit 114 also includes a digital snapshot
`memory which is coupled to the output of the A/D converter
`and which can store a record of the data to be processed. The
`snapshot memory is used to process the GPS signals which
`are typically stored in a separate memory device coupled to
`GPS processing circuitry 114. The snapshot memory can
`also be employed for communication signals that are
`packetized, that is, signals consisting of bursts of data bits
`followed by long periods of inactivity. Continuous signaling,
`such as many cellular-type signals, may also be processed in
`a continuous manner by the processing circuitry.
`The output from GPS signal processing circuitry 114 is
`coupled to microprocessor 115. Microprocessor 115 further
`processes the satellite signals received in GPS receiver 130
`and outputs the processed signals for transmission directly to
`a user interface or through a communication link to a remote
`receiver (not shown).
`In one embodiment of the present invention, the GPS
`receiver 130 is a conventional GPS receiver that uses a set
`
`of correlators to demodulate the GPS signals. In a method of
`the present invention, a gating signal either activates or
`deactivates the GPS receiver. When actuated, a conventional
`GPS receiver can perform all of its normal functions,
`including demodulation of the 50 baud satellite data mes-
`sage. However, if the gating periods become a large fraction
`of the data baud period, then demodulation may be difficult
`or impossible. In this case, an alternative type of GPS
`receiver may be used. For example, one type of GPS
`receiver only finds the relative times of arrival of the
`multiple simultaneously received GPS signals, and transmits
`these relative times of arrival (so-called “pseudoranges”) to
`a remote location (see, for example, F. H. Raab, et al., “An
`Application of the Global Positioning System to Search and
`Rescue and Remote Tracking”, Journal of the Institute of
`Navigation, Vol. 24, No. 3, Fall 1977, pp. 216—227). The
`position of the mobile device is then determined by com-
`bining this pseudorange data with the GPS satellite infor-
`mation which it gathers using its own receivers or via some
`other source of such data. This configuration is especially
`useful in various emergency response and tracking applica-
`tions.
`
`Although embodiments of the present application are
`discussed with regard to a particular GPS receiver
`configuration, it will be apparent to those of ordinary skill in
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`US 6,799,050 B1
`
`5
`the art, that several different GPS receiver configurations
`exist which may take advantage of the cross-interference
`reduction methods of the present invention.
`Furthermore, although embodiments of the present inven-
`tion are described with reference to GPS satellites, it will be
`appreciated that
`the teachings are equally applicable to
`positioning systems which utilize pseudolites or a combi-
`nation of satellites and pseudolites. Pseudolites are ground
`based transmitters which broadcast a PN code (similar to a
`GPS signal) modulated on an L-band (or other frequency)
`carrier signal, generally synchronized with GPS time. Each
`transmitter may be assigned a unique PN code so as to
`permit identification by a remote receiver. Pseudolites are
`useful in situations where GPS signals from an orbiting
`satellite might by unavailable, such as tunnels, mines, build-
`ings or other enclosed areas. The term “satellite”, as used
`herein, is intended to include pseudolites or equivalents of
`pseudolites, and the term GPS signals, as used herein, is
`intended to include GPS-like signals from pseudolites or
`equivalents of pseudolites.
`Communication Section
`The communication section of the mobile device 150
`
`includes a receiver stage and a transmitter stage coupled to
`communication antenna 100 through a duplexer or transmit/
`receive switch 101. When a communication signal, such as
`a cellular telephone signal, is received from a communica-
`tion basestation (e. g., basestation 160), switch 101 routes the
`input signal
`to RF to IF converter 102. The RF to IF
`frequency converter 102-translates the communication sig-
`nal to a suitable intermediate frequency for further process-
`ing. The output of the RF to IF converter 102 is coupled to
`demodulator 103 which demodulates the communication
`
`signal in order to determine the commands in the commu-
`nication signal or other data in the communication signal
`(e.g., digitized voice, Doppler data or data representative of
`ephemeris of satellites in view). Demodulator 103 may be
`implemented as a digital demodulator. In this case, prior to
`input to demodulator 103, the frequency converted commu-
`nication signal may be passed through an analog to digital
`(A/D) converter which digitizes the output signals from the
`RF to IF converter 102.
`
`In one embodiment of the present invention, output from
`demodulator 103 is passed to microprocessor 104. Micro-
`processor 104 performs any processing required for the
`communication receive and transmit functions.
`
`The microprocessor 104 is also connected to a display and
`to a microphone. The microphone has the ability to convert
`speech to voice data and provide the voice data to the
`microprocessor 104. When a transmission is required
`through the communication link, microprocessor 104 gen-
`erates the data to be transmitted and baseband digital
`samples of the signal (or a representation thereof, such as a
`mathematical model of the signal). It then uses this data to
`modulate a carrier signal using modulator 106. Although
`analog modulation (such as frequency modulation) may also
`be used, in the latest systems, modulation is generally of a
`digital type, such as frequency shift keying or phase shift
`keying. In this case, the digital signal is converted from
`digital to analog in a D/A converter after modulation. The
`carrier frequency at which the modulation is performed in
`modulator 106 may or may not be at the final RF frequency
`of the communication signal;
`if it is at an intermediate
`frequency (IF), then an additional IF to RF converter 107 is
`used to translate the signal to a final RF frequency for the
`communication signal. A power amplifier 108 boosts the
`signal level of the communication signal, and this boosted
`signal is then transmitted to the communication antenna 100
`through switch 101.
`
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`In a method of the present invention, a communication
`signal containing data representative of position information
`(e.g., pseudoranges to various satellites, or a latitude and
`longitude of the mobile device 150) is transmitted to bas-
`estation 160, through communication link 162. Basestation
`160 may serve as a processing site for computing the
`position information of the portable GPS unit, or it may
`serve as a relay site and re-transmit the information received
`from the mobile device 150.
`
`In some cellular telephone systems, such as Time-
`Division Multiple Access (TDMA) systems (including, for
`example, GSM,
`the Global System for Mobile
`Communications), the transmission and reception times of
`the cellular signals are disjoint. In those cases, a simple
`switch 101 may be used to isolate the strong transmitted
`signal 118 provided by power amplifier 108 from the path
`119 connected to the sensitive front-end receiving circuitry
`(frequency converter 102). In particular, the receiving cir-
`cuitry 102 may contain a low noise amplifier (LNA) which
`may be destroyed or otherwise adversely affected if the
`signal from the power amplifier is transmitted to the LNA
`without significant attenuation.
`In other cellular systems, such as 18-95 North American
`based on Code Division Multiple Access (CDMA), there
`may be simultaneous transmission and reception of signals
`through the antenna 100. In order to isolate the RF circuitry
`of 102 from the high powered signal of 118 a device termed
`a “duplexer” is used instead of switch 101. Duplexer 101
`consists of two RF filters, one tuned to the transmission band
`of frequencies and the other to the received band. The power
`amplifier output 118 is passed through the transmission filter
`and then to antenna 100, while the received signal from the
`antenna is passed through the receive filter. Thus, the trans-
`missions are isolated from the RF circuitry 102 by an
`amount equal to the isolation that the receive filter provides
`at the transmission frequency.
`Signal Gating of Communication Transceiver
`In one embodiment of the present
`invention, mobile
`device 150 includes control circuitry which reduces cross
`interference between the GPS receiver and cellular trans-
`
`ceiver stages. In combined receivers, cross-interference is
`often an especially acute problem since satellite signals
`received in the GPS receiver are typically very weak.
`Cross-interference typically occurs due to a high degree of
`coupling between the transmitted cellular telephone signal
`through antenna 100 and the GPS receiving antenna 111.
`This is especially true in the case where the antenna units
`100 and 111 are collocated or share portions of their
`mechanical assembly in order to conserve physical space or
`reduce cost.
`
`invention, cross-
`In one embodiment of the present
`interference between the communication and GPS sections
`
`of the combined unit is reduced by lowering the power to the
`transmitter of the communication section (typically a cellu-
`lar telephone). Power of the transmitter is reduced for a
`period of time during which satellite positioning system
`signals may be processed, after which the transmitter is
`again powered up. A gating signal synchronizes the power
`control and GPS receiver operation. Reference is made to
`combined receiver of FIG. 2 for a description of the opera-
`tion of a gating signal according to one embodiment of the
`present invention.
`In the cellular telephone section 109 of the mobile device
`150, a power level control signal 105 is transmitted from
`microprocessor 104 to power amplifier 108. In one embodi-
`ment of the present invention, a first state of the power level
`control signal reduces power in the power amplifier, and a
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`US 6,799,050 B1
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`7
`second state of the signal restores normal power levels in the
`power amplifier. Alternatively,
`two signals are embodied
`within the power level control signal. A first signal reduces
`power in the power amplifier, and a second signal restores
`normal power levels in the power amplifier. Depending on
`the power level of amplifier 108 and the desired reduction in
`cross-interference, the power level control signal 105 can
`turn off power amplifier 108 completely, or reduce its
`amplification power by a predetermined amount.
`The power level control signal 105 is also transmitted to
`the GPS receiver 130. This signal is programmed to activate
`the GPS receiver to receive and process GPS signals in
`relation to the power level of the communication power
`amplifier 108. When the power level control signal 105
`reduces or cuts power to power amplifier 108,
`the GPS
`receiver 130 is activated to receive GPS signals. Conversely,
`when the power level control signal maintains normal power
`levels in power amplifier 108,
`the GPS receiver 130 is
`prevented from receiving GPS signals. Alternatively,
`the
`GPS receiver 130 may be programmed receive GPS signals
`but ignore such signals in its processing circuitry when the
`power level control signal indicates that the cellular tele-
`phone transmitter is at high power.
`In GPS receiver 130, gating signal 110,corresponds to
`power level control signal 105. In one embodiment of the
`present invention, gating signal 110 is transmitted to micro-
`processor 115 through line 122, and to GPS processing
`circuit 114 through line 116, and to switch 112 through line
`117. In one embodiment, switch 112 is controlled by gating
`signal 110 and power level control signal 105. When the
`power level control signal 105 reduces power to the cellular
`telephone power amplifier 108, switch 112 is turned on to
`allow data to pass from GPS antenna 111 to the GPS receiver
`circuits. Conversely, when the power level control 105
`signal maintains high power to the power amplifier 108,
`switch 112 is turned to off so that no data is passed through
`to the GPS receiver. Thus, GPS signals are gated out (or
`blocked) during cellular telephone transmissions at high
`power, while they may be received at all other times.
`In one embodiment of the present invention, switch 112 is
`a Gallium Arsenide (GaAs) switch. Because switch 112 is in
`the GPS input signal path, it will cause some attenuation of
`the input GPS signal. Use of a GaAs switch minimizes this
`attenuation. Moreover, current switch devices at the GPS
`frequency (1575.42 MHZ) provide an insertion loss of about
`0.5 dB.
`
`In an alternative embodiment of the present invention,
`gating signal 110 may be input only to the microprocessor
`115 instead of switch 117. In this configuration, micropro-
`cessor 115 directly controls switch 117 or GPS signal
`processing circuit 114 to gate the incoming GPS signals
`when the cellular telephone 109 is transmitting.
`In a further alternative embodiment of the present
`invention,
`the GPS receiver 130 may not include GaAs
`switch 112. This switch may be omitted if the RF front end
`circuitry of the GPS receiver 113 can withstand the high
`power from the cellular telephone transmitter (e.g., with
`some type of limiting circuitry). Omission of switch 112
`eliminates any potential signal attenuation through the
`switch. In this alternative embodiment, gating signal 110 is
`input to either or both GPS signal processing circuit 114 and
`microprocessor 115. This signal causes the input GPS sig-
`nals to be disregarded by the processing circuitry during
`periods in which the cellular telephone is transmitting, even
`though these signals are received by GPS receiver 130.
`Most modern digital cellular telephone systems have the
`ability to transmit at full power only a fraction of the time.
`
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`8
`Thus, the gating signal method described herein is appli-
`cable to a wide variety of digital cellular telephones. If
`cellular transmissions in these phones occur with a 1/8 duty
`cycle (as is the case of GSM digital cellular, or CDMA in
`reduced data throughput mode), then the loss in sensitivity
`of the GPS receiver due to such gating is only approximately
`0.5 dB.
`
`FIG. 4 illustrates one example of how the mobile device
`may operate. FIG. 4 is a time chart with times T1, T2, T3 etc.
`on the abscissa and actions such as “talk”, “transmit voice
`data”, and “process GPS data” on the ordinate.
`Beginning at time T1, a person may talk into a micro-
`phone until time T2 is reached. Voice data is continuously
`transmitted from the mobile device during this time.
`There may then be a break in speech from time T2 to time
`T3, after which speech is again resumed. Because the break
`from T2 to T3 is less than a predetermined minimum of, for
`example one-half second, voice data transmission is not
`interrupted.
`There may then again be a break (that is, a pause) in
`speech at time T4. The break in speech may last until time
`T7. Because the break or pause in speech is more than a
`minimum break of one-half seconds, voice data transmission
`is disabled after the minimum break at time T5. A control
`
`signal is transmitted at time T5 which enables GPS data
`processing. GPS data processing is continued until time T6.
`A difference between time T6 and time T5 is sufficiently
`large to enable processing of a required minimum amount of
`GPS data,
`typically one to two seconds. The minimum
`amount of GPS data is sufficient to triangulate a position of
`a mobile device.
`
`Speech is again resumed at time T7 and may continue
`until time T8, after which there is a break in speech from
`time T8 to time T10. The minimum break in speech of
`one-half seconds is reached at time T9, at which time voice
`data transmission is disabled. GPS data processing is
`enabled at time T9. At time T10, the user may again speak
`into the microphone and continue speaking until time T12.
`Voice data transmission is, however, de-activated until time
`T11. The difference between time T11 and