United States Patent [19]
`Krasner
`
`[54] GPS RECEIVER UTILIZINGA
`COMMUNICATION LINK
`
`[75] Inventor: Norman F. Krasner, San Carlos, Calif.
`
`[73] Assignee: SnapTrack, Inc., San Jose, Calif.
`
`[21] Appl. No.: 612,582
`[22]
`Filed:
`Mar. 8, 1996
`
`Related US. Application Data
`
`[60]
`
`Provisional application No. 60/005,318 Oct. 9, 1995.
`
`[51] Int. Cl. 6 ............................ .. H04B 7/185; G01S 5/02
`[52] US. Cl. ......................... .. 342/357; 701/213; 701/214
`[58] Field of Search ....................... .. 342/357; 364/4497,
`364/4499, 449.95; 701/213, 214
`
`[56]
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`342/357
`4/1984 Taylor et al. .
`4,445,118
`364/602
`7/1986 Kilvington
`4,601,005
`375/1
`4,701,934 10/1987 Jasper ...... ..
`4,785,463 11/1988 Jane et al. ................................. .. 375/1
`
`(List continued on neXt page.)
`
`FOREIGN PATENT DOCUMENTS
`
`0444738 4/1991 European Pat. Off. .
`0508405 10/1992 European Pat. Off. .
`0601293 6/1994 European Pat. Off. .
`4424412 12/1994 Germany .
`2308033 11/1997 United Kingdom .
`WO9714049 4/1994 WIPO .
`9414081 6/1994 WIPO
`WO9615636 5/1996 WIPO
`9740398 10/1997 WIPO
`
`OTHER PUBLICATIONS
`
`PCT International Search Report for Int’l Appln No. PCT/
`US97/21260, mailed 20 Nov. 1997.
`US. Patent Application Serial No. 08/759,523, ?led Dec. 4,
`1996 and entitled “An Improved GPS Receiver Utilizing a
`Communication Link”, 47 pages and 14 sheets of draWings.
`
`US005874914A
`[11] Patent Number:
`[45] Date of Patent:
`
`5,874,914
`Feb. 23, 1999
`
`“RTCM Recommended Standards for Differential Navstar
`GPS Service, Version 2.0” Radio Technical Commission for
`Maritime Services, Jan. 1, 1990.
`“Animal—borne GPS: Tracking the Habitat”, Rogers &
`Anson, GPS World, pp. 21, 22, Jul., 1994.
`“Navstar GPS User Equipment, Introduction”, NATO, Feb.
`1991.
`“Navigation Journal of the Institute of Navigation, vol. 25,
`No. 2” The Institute of Navigation, 1978 (entire edition).
`“GPS Receiver Structures”, Petterson et al., ION—GPS—95,
`Session C4, Land Vehicular Applications, Palm Springs, CA
`Sep. 1995.
`“An Application of the Global Positioning System to Search
`and Rescue and Remote Tracking”, Raab, et al. Navigation
`Journal of Institute of Navigation, vol. 24, No. 3, 1977.
`
`Primary Examiner—Theodore M. Blum
`Attorney, Agent, or Firm—Blakely, Sokoloff, Taylor &
`Zafman
`
`[57]
`
`ABSTRACT
`
`A GPS receiver in one embodiment includes an antenna
`Which receives GPS signals at an RF frequency from in vieW
`satellites; a doWnconverter coupled to the antenna for reduc
`ing the RF frequency of the received GPS signals to an
`intermediate frequency (IF); a digitiZer coupled to the doWn
`converter and sampling the IF GPS signals at a predeter
`mined rate to produce sampled IF GPS signals; a memory
`coupled to the digitiZer storing the sampled IF GPS signals
`(a snapshot of GPS signals); and a digital signal processor
`(DSP) coupled to the memory and operating under stored
`instructions thereby performing Fast Fourier Transform
`(FFT) operations on the sampled IF GPS signals to provide
`pseudorange information. These operations typically also
`include preprocessing and post processing of the GPS sig
`nals. After a snapshot of data is taken, the receiver front end
`is poWered doWn. The GPS receiver in one embodiment also
`includes other poWer management features and includes, in
`another embodiment the capability to correct for errors in its
`local oscillator Which is used to sample the GPS signals. The
`calculation speed of pseudoranges, and sensitivity of
`operation, is enhanced by the transmission of the Doppler
`frequency shifts of in vieW satellites to the receiver from an
`external source, such as a basestation in one embodiment of
`the invention.
`
`36 Claims, 11 Drawing Sheets
`
`G PS Antenna
`
`4o
`
`MOBILE OH REMOTE UNlT
`
`42
`
`44
`
`4B
`
`RF '0 ‘F
`Convener
`
`Analog lo
`Digital Converter(s)
`
`
`Digital
`
`Snapshot Memory
`
`|-- <)
`
`15
`
`34
`
`32
`
`Determines Position
`Intormation
`General Purpose
`
`Programmable DSP Chip
`
`39
`
`383
`Frequency
`Synthesizer
`
`g
`f 2‘
`1
`i
`L/ C
`i
`Write
`“ ---- """y: .‘
`,r---(--‘--
`A dress
`i
`'
`I
`FdPGA
`L05 43“ 21b 1
`i
`' m
`35
`Sample Clk
`Batter/E Power ,,,,,,,,,,,,,,,,,,,,,,, ,,_
`Regulawr 8‘
`
`ziep
`
`48
`
`-/33
`sglellitelnlkzlromBBase
`osition n ov lo ase
`
`GPS Antenna
`
`‘2'
`
`Transmit Doppler
`‘‘
`Shilts, and Other Signal Parameters
`/
`Transmit Computed Position
`‘4 W 24
`Modem
`22
`Data Link 16
`
`-
`x Serial
`25
`HO
`
`Satellite
`Pararrielers
`
`Baseslation '\ i0
`
`20
`
`Legend:
`— — — Controlled Power Lines 21
`Data and Signal Paths
`
`GOOGLE 1032
`Page 1
`
`

`
`5,874,914
`Page 2
`
`US. PATENT DOCUMENTS
`
`477977677
`1/1989 MaCDOran 6‘ al- ~~~~~~~~~~~~~~~~~~~ ~~ 342/352
`4,910,752
`3/1990 Yester, Jr. et a1. .
`. 375/75
`479597656
`9/1990 Kum‘“ """"" "
`" 342/418
`233%; 2133; 1842;‘
`____ N
`323325
`5:223:844
`6/1993 Mansell et a1‘
`" 342/357
`572257842
`7/1993 Brown et a1~ “
`_ 342/357
`
`1/1995 Brown et a1. ......................... .. 364/449
`5,379,224
`1/1995 Fernandes et a1. ....................... .. 375/1
`5,379,320
`5389 934 2/1995 Kass ...................................... .. 342/357
`5,416,797
`5/1995 G?housen et a1‘
`' 375/7O5
`5,420,592
`5/1995 Johnson ................................ .. 342/357
`5,430,759
`7/1995 Yokev et a1. ......................... .. 375/202
`5,483,549
`1/1996 Weinberg et a1. .................... .. 375/200
`5,512,902
`4/1996 Guthrre et a1. ........................ .. 342/357
`
`1/1994 DeCarlo eta.
`5,280,744
`5/1994 Brown .......... ..
`5,311,194
`5317323 5/1994 Kennedy et a1_ _
`5,323,163
`6/1994 Maki ____________ __
`5,323,322
`6/1994 Mueller et a1.
`
`.. 89/419
`.. 342/357
`__ 342/457
`__ 342/357
`.. 364/449
`
`~- 342/357
`9/1996 Brickell
`5,554,993
`-- 342/455
`5,574,469 11/1996 H511 ------- --
`5,592,173
`1/1997 Lau et a1. .............................. .. 342/357
`5,594,453
`1/1997 Rodal et a1. .......................... .. 342/357
`5,600,329
`2/1997 Brenner ....... ..
`.. 342/357
`
`5,334,987
`
`8/1994 Teach . . . . . . . . . . . .
`
`. . . . . . . . . . . . . .. 342/357
`
`5,626,630
`
`5/1997 Markowitz et a1.
`
`607/60
`
`5,365,450 11/1994 Schuchman et 211.
`5,379,047
`1/1995 Yokev et a1. ......................... .. 342/457
`
`5,633,799
`5,650,770
`
`364/449.9
`5/1997 Dussell ............ ..
`7/1997 Schlager et a1. ...................... .. 340/573
`
`GOOGLE 1032
`Page 2
`
`

`
`U.S. Patent
`
`Feb. 23, 1999
`
`Sheet 1 of 11
`
`5,874,914
`
`
`
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`GOOGLE 1032
`Page 3
`
`

`
`U.S. Patent
`
`Feb. 23, 1999
`
`Sheet 2 of 11
`
`5,874,914
`
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`GOOGLE 1032
`Page 4
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`

`
`U.S. Patent
`
`Feb. 23, 1999
`
`Sheet 3 of 11
`
`5,874,914
`
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`GOOGLE 1032
`Page 5
`
`

`
`U.S. Patent
`
`.eB
`
`99913:2h.
`
`Sheet 4 of 11
`
`5,874,914
`
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`
`GOOGLE 1032
`Page 6
`
`

`
`U.S. Patent
`
`Feb. 23, 1999
`
`Sheet 5 0f 11
`
`5,874,914
`
`3 E0822
`
`/ k
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`
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`
`HHN|IHIIHIH|
`
`GOOGLE 1032
`Page 7
`
`

`
`U.S. Patent
`
`Feb. 23, 1999
`
`Sheet 6 of 11
`
`5,874,914
`
`Receive Fix
`Command and x100
`Doppler Data
`From Base
`
`Power Down and
`Wait for New Fix ’\ 132
`Command
`+
`
`/\
`
`102
`
`“104
`
`..
`
`1
`.
`if“ / 30
`F'ng
`Complete Position ~QLn/Off DSP
`Calculation
`
`pro?lssed
`Satellites?
`
`128
`
`i
`Find Oscillator
`?gsjrfjfiinc
`Tum on
`RCVR Here\/+
`K PN Frames,
`Collect
`K Typically 10o
`Snapshot of
`to 1000
`GPS Signal
`Tum O? ?
`RCVR Here,
`Get PN Code for
`Turn 0" DSP
`First/Next N 106
`interpolate Peak
`Salem“?
`hi Location to Find N126
`Pseudorange
`Multiply First/Next N
`Consecutive PN
`Frames by Doppler \108
`Correction Exponential
`+
`Sum First/Next N
`Consecutive PN ‘\11()
`Frames
`¢
`
`Data
`Processed for this
`
`Satellite?
`
`2048 Words
`Add Data to Sum_
`of Data
`of Previous Data \\/
`122
`i
`Find Magnitude
`Squared of Data \120
`+
`Find Inverse
`FFT
`
`\118
`
`I
`N Typically 10
`K/N PN
`Frames Are Left
`
`F'
`FFT f
`gl?'mmedo
`112 / Frames
`+
`Multiply by
`K FFT of PM
`Code
`114
`
`FFT Based
`Matched Filtering
`Against PN Code
`
`‘
`
`Multiply by
`
`Exponential to
`Compensateior ,\
`DopplerTimeShift
`116
`FIE-*3
`
`GOOGLE 1032
`Page 8
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`

`
`U.S. Patent
`
`Feb. 23, 1999
`
`Sheet 7 of 11
`
`5,874,914
`
`:<—— Data=0 -——->:<-—— Data=1I---—>}<j Dara=o—>r
`I Frame ,' Frame I Frame I Frame I Frame: Frame I Frame I Frame 1 Frame I Frame I Frame I Frame '
`|0'1'2'3'4'5'6'7 8'
`'_10'
`
`Baseband PN Signal, Frame Length = 7, Data Period = 4 Frames
`E‘ I E _ 4 A
`
`I
`I<——— Data=0 ———>t<—— Data=1———->I<—— Data=O ——>.
`I Frame: Frame: Frame I Frame I Frame I Frame I Frame I Frame I Frame I Frame I Frame I Frame I
`.0'1'2'3 4‘5'6'7I8'9'10'11
`
`Output Atter Summing Groups of 4 PN Frames
`I'IE_4I:]1
`
`Frame I Frame I Frame I Frame I FrameI Frame I Frame I Frame
`0
`1
`2
`3
`4
`5
`6
`7
`I
`I
`I
`I
`I
`I
`
`Frame Frame I Frame IFrame I
`B
`9
`I
`I
`
`Output After FFT Based Matched Filter
`
`:4-—-— Data: 0 ———>}<—-—- oa1a=1 ——-—-->{<——— Dara: o -———->}
`I Frame I Frame I Frame I Frame I Frame I Frame I Frame IFrame I Frame I Frame I Frame I Frame I
`0
`I
`1
`I
`2
`I
`3
`I
`4
`I
`5
`I
`6
`I
`7
`I
`8
`I
`9
`I
`I
`I
`
`OutpuI After Squaring Matched Filter Outputs
`II?‘ I I3 __ 4 ID
`
`i<— Data=0 ———>i<———— Data=1 ——>i<— Data=0 ——>I
`I Frame I Frame I Frame IFrame I Frame I Frame I Frame I Frame I Frame I Frame I Frame I Frame I
`o'1'2's 4'5'e'7 a'9'1o'11
`Pseudorange
`
`I :
`
`I
`
`_/ Maximum Possible
`Pseudorange
`
`Output After Summing Outputs of D
`II.’-'II}_4l]E:
`
`GOOGLE 1032
`Page 9
`
`

`
`U.S. Patent
`
`Feb. 23, 1999
`
`Sheet 8 0f 11
`
`5,874,914
`
`( 505
`
`4
`Disciplined
`Local Oscillator ‘
`
`Time Reference Signal
`K 510
`
`GPS
`Receiver
`
`Doppler and/or
`Other Satellite Data
`
`8
`
`506 \
`
`l
`
`\ 51 1
`
`Modulator
`
`/\ 512
`
`501a
`
`\
`501
`
`( 513
`
`503a M
`< 503
`To Mobile
`Unit
`
`> Transmitter
`
`514
`(
`
`T
`
`504a W
`.
`504
`From Mobile
`/
`Unit
`
`4
`
`Receiver
`
`502
`\
`
`l
`
`V
`
`Data
`Processing
`Unit
`
`508 \3
`
`( 507
`
`-
`D'Sp'ay
`
`Mass Storage
`with GIS Software
`
`FIE__EA
`
`GOOGLE 1032
`Page 10
`
`

`
`U.S. Patent
`
`Feb. 23, 1999
`
`Sheet 9 0f 11
`
`5,874,914
`
`( 551
`
`( 552
`
`Log‘jf‘gjg?jtor
`-
`(e.g. Cesium Standard)
`
`Source of Doppler and/or
`( Other Satellite Data Information
`e.g. rom e ecommunication Link
`or Radio Link)
`
`506 \
`
`l
`
`Doppler and/or
`Other Satellite Data
`
`"
`
`K
`553
`
`Modulator
`
`/\ 512
`
`503a M
`< 503
`To Mobile
`Unit
`
`>
`
`Transmitter
`
`A
`
`( 514
`
`504a
`
`504
`/
`
`4
`
`Receiver
`
`W .
`From Mobile
`Unit
`
`( 513
`
`502
`\
`
`l
`
`v
`
`Data
`Processing
`Unit
`
`508 w
`
`( 507
`
`-
`D'sp'ay
`
`Mass Storage
`with GIS Software
`
`FII;_EB
`
`GOOGLE 1032
`Page 11
`
`

`
`U.S. Patent
`
`Feb. 23, 1999
`
`Sheet 10 0f 11
`
`5,874,914
`
`GPS
`Antenna
`
`613
`
`(614
`
`GPS
`Downconverter
`
`(618
`(616
`Digital
`Analog to
`DSP
`.
`.
`—> Digital —> Snapshot —>
`Convener
`M em Ory
`Component
`
`(620
`
`610
`(
`
`T
`I
`:
`:
`
`I
`< 605
`|
`|
`610a
`Comparator ———--§-____J
`
`A
`
`x 604
`
`612
`
`609 \
`
`Frequency
`Synthesizer
`
`4
`‘
`
`A
`’\ 607
`
`608
`
`GPS
`Local
`Oscillator
`
`’\
`606
`
`601
`
`(602
`
`(603
`
`Modern
`
`AFC
`
`P'IE_E
`
`GOOGLE 1032
`Page 12
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`

`
`U.S. Patent
`
`Feb. 23, 1999
`
`Sheet 11 of 11
`
`5,874,914
`
`701 N Initialize Components and Place in Reduced Power State
`V
`Communication Receiver at Full Power
`
`703 N
`
`705 ’\/
`
`707 N
`
`713 N
`
`715 N
`
`717
`
`Receiving Request from Base Unit for Location Information
`V
`Alerting Power Management Circuit
`V
`709 N Returning Communication Receiver to Reduced Power
`V
`711 ’\/ Power Management Circuit Returning GPS Receiver to Full Power
`V
`GPS Receiver Receiving GPS Signal
`V
`Buffering GPS Signal
`V
`Returning GPS Receiver to Reduced Power
`V
`Returning Processing System to Full Power
`V
`Processing GPS Signal
`V
`723 N Returning Processing System to Reduced Power
`V
`725 N Returning Communication Transmitter to Full Power
`V
`727 N Transmitting Processed GPS Signal to Base Station
`V
`729 N Returning Communication Transmitter to Reduced Power
`V
`Delay for a Period of Time
`V
`Returning Communication Receiver to Full Power
`
`719 N
`
`721 N
`
`731 N
`
`733 ’\/
`
`GOOGLE 1032
`Page 13
`
`

`
`5,874,914
`
`1
`GPS RECEIVER UTILIZING A
`COMMUNICATION LINK
`
`RELATED APPLICATIONS
`
`This application is related to tWo patent applications ?led
`by the same inventor on the same date as this application;
`these tWo applications are: An Improved GPS Receiver and
`Method for Processing GPS Signals (Ser. No. 08/612,582);
`An Improved GPS Receiver Having PoWer Management
`(Ser. No. 08/613,966).
`This application is also related to and hereby claims the
`bene?t of the ?ling date of a provisional patent application
`by the same inventor, Norman F. Krasner, Which application
`is entitled LoW PoWer, Sensitive Pseudorange Measurement
`Apparatus and Method for Global Positioning Satellites
`Systems, Ser. No. 60/005,318, ?led Oct. 9, 1995.
`A portion of the disclosure of this patent document
`contains material Which is subject to copyright protection.
`The copyright oWner has no objection to the facsimile
`reproduction by anyone of the patent document or the patent
`disclosure, as it appears in the Patent and Trademark Of?ce
`patent ?le or records, but otherWise reserves all copyright
`rights Whatsoever.
`
`BACKGROUND OF THE INVENTION
`
`1. Field of the Invention
`The present invention relates to receivers capable of
`determining position information of satellites and, in
`particular, relates to such receivers Which ?nd application in
`global positioning satellite (GPS) systems.
`2. Background Art
`GPS receivers normally determine their position by com
`puting relative times of arrival of signals transmitted simul
`taneously from a multiplicity of GPS (or NAVSTAR) sat
`ellites. These satellites transmit, as part of their message,
`both satellite positioning data as Well as data on clock
`timing, so-called “ephemeris” data. The process of searching
`for and acquiring GPS signals, reading the ephemeris data
`for a multiplicity of satellites and computing the location of
`the receiver from this data is time consuming, often requir
`ing several minutes. In many cases, this lengthy processing
`time is unacceptable and, furthermore, greatly limits battery
`life in micro-miniaturiZed portable applications.
`Another limitation of current GPS receivers is that their
`operation is limited to situations in Which multiple satellites
`are clearly in vieW, Without obstructions, and Where a good
`quality antenna is properly positioned to receive such sig
`nals. As such, they normally are unusable in portable, body
`mounted applications; in areas Where there is signi?cant
`foliage or building blockage; and in in-building applications.
`There are tWo principal functions of GPS receiving sys
`tems: (1) computation of the pseudoranges to the various
`GPS satellites, and (2) computation of the position of the
`receiving platform using these pseudoranges and satellite
`timing and ephemeris data. The pseudoranges are simply the
`time delays measured betWeen the received signal from each
`satellite and a local clock. The satellite ephemeris and timing
`data is extracted from the GPS signal once it is acquired and
`tracked. As stated above, collecting this information nor
`mally takes a relatively long time (30 seconds to several
`minutes) and must be accomplished With a good received
`signal level in order to achieve loW error rates.
`Virtually all knoWn GPS receivers utiliZe correlation
`methods to compute pseudoranges. These correlation meth
`ods are performed in real time, often With hardWare corr
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`elators. GPS signals contain high rate repetitive signals
`called pseudorandom (PN) sequences. The codes available
`for civilian applications are called C/A codes, and have a
`binary phase-reversal rate, or “chipping” rate, of 1.023 MHZ
`and a repetition period of 1023 chips for a code period of 1
`msec. The code sequences belong to a family knoWn as Gold
`codes. Each GPS satellite broadcasts a signal With a unique
`Gold code.
`For a signal received from a given GPS satellite, folloW
`ing a doWnconversion process to baseband, a correlation
`receiver multiplies the received signal by a stored replica of
`the appropriate Gold code contained Within its local
`memory, and then integrates, or loWpass ?lters, the product
`in order to obtain an indication of the presence of the signal.
`This process is termed a “correlation” operation. By sequen
`tially adjusting the relative timing of this stored replica
`relative to the received signal, and observing the correlation
`output, the receiver can determine the time delay betWeen
`the received signal and a local clock. The initial determina
`tion of the presence of such an output is termed “acquisi
`tion.” Once acquisition occurs, the process enters the “track
`ing” phase in Which the timing of the local reference is
`adjusted in small amounts in order to maintain a high
`correlation output. The correlation output during the track
`ing phase may be vieWed as the GPS signal With the
`pseudorandom code removed, or, in common terminology,
`“despread.” This signal is narroW band, With bandWidth
`commensurate With a 50 bit per second binary phase shift
`keyed data signal Which is superimposed on the GPS Wave
`form.
`The correlation acquisition process is very time
`consuming, especially if received signals are Weak. To
`improve acquisition time, most GPS receivers utiliZe a
`multiplicity of correlators (up to 12 typically) Which alloWs
`a parallel search for correlation peaks.
`Some prior GPS receivers have used FFT techniques to
`determine the Doppler frequency of the received GPS signal.
`These receivers utiliZe conventional correlation operations
`to despread the GPS signal and provide a narroW band signal
`With bandWidth typically in the range of 10 kHZ to 30 kHZ.
`The resulting narroW band signal is then Fourier analyZed
`using FFT algorithms to determine the carrier frequency.
`The determination of such a carrier simultaneously provides
`an indication that the local PN reference is adjusted to the
`correct phase of the received signal and provides an accurate
`measurement of carrier frequency. This frequency may then
`be utiliZed in the tracking operation of the receivers.
`US. Pat. No. 5,420,592 to Johnson discusses the use of
`FFT algorithms to compute pseudoranges at a central pro
`cessing location rather than at a mobile unit. According to
`that method, a snapshot of data is collected by a GPS
`receiver and then transmitted over a data link to a remote
`receiver Where it undergoes FFT processing. HoWever, the
`method disclosed therein computes only a single forWard
`and inverse Fast Fourier Transform (corresponding to four
`PN periods) to perform the set of correlations.
`As Will be evident from the folloWing description of the
`present invention, higher sensitivity and higher processing
`speed can be achieved by performing a large number of FFT
`operations together With special preprocessing and postpro
`cessing operations.
`In this patent the terms correlation, convolution and
`matched ?ltering are often utiliZed. The term “correlation”
`When applied to tWo series of numbers means the term by
`term multiplication of corresponding members of the tWo
`series folloWed by the summation of the series. This is
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`3
`sometimes referred to as “serial correlation” and results in
`an output that is a single number. In some circumstances, a
`succession of correlation operations are performed on suc
`cessive groups of data.
`The term “convolution” as applied to tWo series of
`numbers is the same as that commonly used in the art and is
`equivalent to a ?ltering of the second series of length m With
`a ?lter, corresponding to the ?rst series, having an impulse
`response of length n. The result is a third series of length
`m+n—1. The term “matched ?ltering” refers to a
`convolution, or ?ltering, operation in Which the aforemen
`tioned ?lter has an impulse response Which is the time
`reversed complex conjugate of the ?rst series. The term “fast
`convolution” is utiliZed to indicate a series of algorithms that
`computes the convolution operation in an ef?cient manner.
`Some authors utiliZe the terms correlation and convolu
`tion interchangeably; for clarity, hoWever, in this patent, the
`term correlation alWays refers to the serial correlation opera
`tion described above.
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`FIG. 1C is a block diagram of another alternative GPS
`mobile unit.
`FIGS. 2A and 2B provide tWo alternatives for the RF and
`IF portions of a receiver Which is an embodiment of the
`present invention.
`FIG. 3 shoWs a How chart of the major operations (e.g.
`softWare operations) performed by the programmable DSP
`processor in accordance With the methods of the present
`invention.
`FIGS. 4A—4E illustrate the signal processing Waveforms
`at various stages of processing according to the methods of
`the present invention.
`FIG. 5A illustrates a basestation system in one embodi
`ment of the present invention.
`FIG. 5B illustrates a basestation system in an alternative
`embodiment of the present invention.
`FIG. 6 illustrates a GPS mobile unit having, according to
`one aspect of the present invention, local oscillator correc
`tion or calibration.
`FIG. 7 is a How chart Which shoWs a poWer management
`method for a mobile unit according to one embodiment of
`the present invention.
`
`SUMMARY
`
`One embodiment of the present invention provides a
`method for determining the position of a remote GPS
`receiver by transmitting GPS satellite information, including
`Doppler, to the remote unit or mobile GPS unit from a
`basestation via a data communication link. The remote unit
`uses this information and received GPS signals from in vieW
`satellites to subsequently compute pseudoranges to the sat
`ellites. The computed pseudoranges are then transmitted to
`the basestation Where the position of the remote unit is
`calculated. Various embodiments of apparatuses Which can
`perform this method are also described.
`Another embodiment of the present invention provides a
`GPS receiver having an antenna for receiving GPS signals
`from in vieW satellites; and a doWnconverter for reducing
`the RF frequency of the received GPS signals to an inter
`mediate frequency
`The IF signals are digitiZed and
`stored in memory for later processing in the receiver. This
`processing typically is accomplished, in one embodiment of
`the invention, using a programmable digital signal processor
`Which executes the instructions necessary to perform fast
`convolution (e.g. FFT) operations on the sampled IF GPS
`signals to provide pseudorange information. These opera
`tions also typically include preprocessing (prior to fast
`convolution) and post processing (after fast convolution) of
`stored versions of the GPS signals or processed and stored
`versions of the GPS signals.
`Yet another embodiment of the present invention provides
`a method of poWer management for a GPS receiver and also
`provides a GPS receiver having poWer management fea
`tures. PoWer dissipation is reduced over prior systems by
`receiving GPS signals from in vieW satellites; buffering
`these signals; and then turning off the GPS receiver. Other
`poWer management features are described.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`The present invention is illustrated by Way of example
`and not limitation in the ?gures of the accompanying
`draWings in Which references indicate similar elements and
`in Which:
`FIG. 1A is a block diagram of the major components of
`a remote or mobile GPS receiving system utiliZing the
`methods of the present invention, and shoWs data links that
`may exist betWeen a basestation and the remote.
`FIG. 1B is a block diagram of an alternative GPS mobile
`unit.
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`DETAILED DESCRIPTION OF THE
`INVENTION
`
`This invention concerns apparatuses and methods for
`computing the position of a mobile, or remote, object in a
`manner that results in the remote hardWare having very loW
`poWer dissipation and the ability to operate With very loW
`received signal levels. That is, poWer consumption is
`reduced While receiver sensitivity is increased. This is made
`possible by the implementation of the remote receiving
`functions, as shoWn in FIG. 1A, as Well as the transmission
`of Doppler information from a separately located basestation
`10 to the remote or GPS mobile unit 20.
`It should be noted that pseudoranges may be used to
`compute the remote’s geographical position in many differ
`ent Ways. Three examples are:
`1. Method 1: By re-transmitting the satellite data mes
`sages to the remote 20 from the basestation 10, the remote
`20 may combine this information With the pseudorange
`measurements to compute its position. See, for example,
`US. Pat. No. 5,365,450, Which is incorporated herein by
`reference. Typically, the remote unit 20 performs the com
`putation of position in the remote 20.
`2. Method 2: The remote 20 may gather the satellite
`ephemeris data from the reception of GPS signals in the
`normal manner that is commonly practiced in the art. This
`data, Which typically is valid for one to tWo hours, may be
`combined With pseudorange measurements to complete,
`typically in the remote unit, the position calculation.
`3. Method 3: The remote 20 may transmit over a com
`munications link 16 the pseudoranges to the basestation 10
`Which can combine this information With the satellite
`ephemeris data to complete the position calculation. See, for
`example, US. Pat. No. 5,225,842, Which is incorporated
`herein by reference.
`In approaches (or Methods) 1 and 3, it is assumed that the
`basestation 10 and remote 20 have a common vieW of all
`satellites of interest and are positioned close enough to one
`another to resolve a time ambiguity associated With the
`repetition rate of the GPS pseudorandom codes. This Will be
`met for a range betWeen basestation 10 and remote 20 of 1/2
`times the speed of light times the PN repetition period (1
`millisecond), or about 150 km.
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`In order to explain the current invention, it is assumed that
`method 3 is utilized to complete the position calculation.
`However, upon revieW of this Speci?cation, it Will be
`appreciated by those skilled in the art that the various aspects
`and embodiments of the present invention could be used
`With any of the above three Methods as Well as other
`approaches. For eXample, in a variation of Method 1,
`satellite data information such as data representative of
`satellite ephemeris may be transmitted by a basestation to a
`remote unit, and this satellite data information may be
`combined With pseudo ranges, computed according to the
`present invention from buffered GPS signals, to provide a
`latitude and longitude (and in many cases also an altitude)
`for the remote unit. It Will be appreciated that the position
`information received from the remote may be limited to
`latitude and longitude or may be eXtensive information
`Which includes latitude, longitude, altitude, velocity and
`bearing of the remote. Moreover, the local oscillator cor
`rection and/or the poWer management aspects of the present
`invention may be utiliZed in this variation of Method 1.
`Furthermore, Doppler information may be transmitted to the
`remote unit 20 and utiliZed by the remote unit 20 in
`accordance With aspects of the present invention.
`Under Method 3, the basestation 10 commands the remote
`20 to perform a measurement via a message transmitted over
`a data communications link 16 as shoWn in FIG. 1A. The
`basestation 10 also sends Within this message Doppler
`information for the satellites in vieW, Which is a form of
`satellite data information. This Doppler information typi
`cally is in the format of frequency information, and the
`message Will typically also specify an identi?cation of the
`particular satellites in vieW or other initialiZation data. This
`message is received by a separate modem 22 that is part of
`the remote unit 20, and it is stored in a memory 30 coupled
`to a loW-poWer microprocessor 26. The microprocessor 26
`handles data information transfer betWeen the remote unit
`processing elements 32—48 and the modem 22, and it
`controls poWer management functions Within the remote
`receiver 20, as Will be evident in the subsequent discussion.
`Normally, the microprocessor 26 sets most or all remote unit
`20’s hardWare to a loW poWer, or poWer doWn, state, eXcept
`When the pseudorange and/or other GPS calculations are
`being performed, or When an alternative source of poWer is
`available. HoWever, the receiver portion of the modem is at
`least periodically turned on (to full poWer) to determine if
`the basestation 10 has sent a command to determine the
`remote’s position.
`This above-mentioned Doppler information is very short
`in duration since the required accuracy of such Doppler
`information is not high. For eXample, if 10 HZ accuracy Were
`required and the maXimum Doppler is approximately +7
`kHZ, then an 11 bit Word Would suf?ce for each satellite in
`vieW. If 8 satellites Were in vieW, then 88 bits Would be
`required to specify all such Dopplers. The use of this
`information eliminates the requirement for the remote 20 to
`search for such Doppler, thereby reducing its processing
`time by in eXcess of a factor of 10. The use of the Doppler
`information also alloWs the GPS mobile unit 20 to process
`more quickly a sample of GPS signals and this tends to
`reduce the amount of time for Which the processor 32 must
`receive full poWer in order to compute a position informa
`tion. This alone reduces the poWer consumed by the remote
`unit 20 and contributes to improved sensitivity. Additional
`information may also be sent to the remote 20, including the
`epochs of the data in the GPS message.
`The received data link signal may utiliZe a precision
`carrier frequency. The remote receiver 20 may employ, as
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`shoWn in FIG. 6 Which is described beloW, an automatic
`frequency control (AFC) loop to lock to this carrier and
`thereby further calibrate its oWn reference oscillator. A
`message transmission time of 10 msec, With a received
`signal to noise ratio of 20 dB, Will normally alloW frequency
`measurement via an AFC to an accuracy of 10 HZ or better.
`This Will typically be more than adequate for the require
`ments of the present invention. This feature Will also
`enhance the accuracy of the position calculations Which are
`performed, either conventionally or using the fast convolu
`tion methods of the present invention.
`In one embodiment of the invention, the communication
`link 16 is a commercially available narroW bandWidth radio
`frequency communication medium, such as a tWo-Way pager
`system. This system may be used in embodiments Where the
`amount of data transmitted betWeen the remote 20 and
`basestation 10 is relatively small. The amount of data
`required for the transmission of Doppler and other data (eg
`initialiZation data such as the identities of the satellites in
`vieW) is relatively small and similarly the amount of data
`required for the position information (e.g.. pseudoranges) is
`relatively small. Consequently, narroWband systems are
`adequate for this embodiment. This is unlike those systems
`Which require the transmission of large amounts of data over
`a short period of time; these systems may require a higher
`bandWidth radio frequency communication medium.
`Once the remote 20 receives a command (e.g., from the
`basestation 10) for GPS processing t