WO2001042810A1 - A receiver for a satellite based position location system - Google Patents
A receiver for a satellite based position location system Download PDFInfo
- Publication number
- WO2001042810A1 WO2001042810A1 PCT/GB2000/004702 GB0004702W WO0142810A1 WO 2001042810 A1 WO2001042810 A1 WO 2001042810A1 GB 0004702 W GB0004702 W GB 0004702W WO 0142810 A1 WO0142810 A1 WO 0142810A1
- Authority
- WO
- WIPO (PCT)
- Prior art keywords
- frequency domain
- coefficients
- received signal
- domain coefficients
- transform
- Prior art date
Links
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S19/00—Satellite radio beacon positioning systems; Determining position, velocity or attitude using signals transmitted by such systems
- G01S19/01—Satellite radio beacon positioning systems transmitting time-stamped messages, e.g. GPS [Global Positioning System], GLONASS [Global Orbiting Navigation Satellite System] or GALILEO
- G01S19/13—Receivers
- G01S19/21—Interference related issues ; Issues related to cross-correlation, spoofing or other methods of denial of service
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S19/00—Satellite radio beacon positioning systems; Determining position, velocity or attitude using signals transmitted by such systems
- G01S19/01—Satellite radio beacon positioning systems transmitting time-stamped messages, e.g. GPS [Global Positioning System], GLONASS [Global Orbiting Navigation Satellite System] or GALILEO
- G01S19/13—Receivers
- G01S19/24—Acquisition or tracking or demodulation of signals transmitted by the system
Definitions
- the present invention relates to a satellite based position location system such as the Global Positioning System (GPS), and in particular to a receiver for use in such a system.
- GPS Global Positioning System
- GPS Global positioning system
- PVT position, velocity and time
- Other examples of spaced based satellite navigation system are TIMATION, transit, and GLONASS.
- GPS is typically divided into three segments:
- control segment which monitors and maintains the satellite constellation
- user segment which comprises GPS receivers, equipment, data collection and data processing techniques.
- the GPS constellation typically consists of 24 satellites orbiting the earth every 24 hours. A minimum of four GPS satellites must be in clear view of a GPS receiver in order for the receiver to determine accurately its location.
- each satellite broadcasts signals that the GPS receiver receives and decodes and from these calculates the time taken for the signals to reach the receiver, this is called the time in transit.
- the receiver then multiplies the time in transit by the speed of electromagnetic radiation to determine the range from the satellite to the receiver. From there, in order to work out the receiver's 3 dimensional distance, velocity and time, the receiver applies the triangulation calculation. Triangulation involves calculating the intersection of points between four reference points given by the satellites and the intersection fixes or locates the position in 3-dimensional space.
- range measurement inherently contain errors common to measurements created by the unsynchronised operation of the satellite and the user clocks. This is why GPS uses four satellites to effect ranging.
- the measurements from three GPS satellites allow the GPS receiver to calculate the three unknown parameters representing its three dimensional position, while the fourth GPS satellite allows the GPS receiver to calculate the user clock error and therefore determine a more precise time measurement.
- the signals broadcast by a satellite comprise radio frequency (RF) ranging codes and navigation data messages which are transmitted using spread spectrum techniques.
- the ranging codes enable the GPS receiver to measure the transit times of the signals and thereby determine the range between the satellite and the receiver.
- the navigation data messages are based on predetermined information regarding the orbital path of the satellite and thus provide an indication of the position of the satellite at the time the signals were transmitted.
- the encoded signal generated by a satellite is in the form of a pseudo random noise (PRN) code which represents a sequence of random binary chips, each satellite transmitting a unique PRN sequence that repeats itself at definite intervals.
- PRN pseudo random noise
- P-Code Precision Code
- C/A Code Course Acquisition code
- a chip is 1 or -1.
- the codes are transmitted on two L-band frequencies: Link 1 (L1) at 1575.42 MHz and Link 2 (L2) at 1227.6 MHz.
- the code allocations on L1 are Course Acquisition code (C/A Code) and Precision Code (P-Code), and on L2 is only P-Code.
- the C/A Code consists of a 1023 bit pseudo random (PRN) code, and a different PRN code is assigned to each GPS satellite.
- PRN pseudo random
- a 50 Hz navigation data message is superimposed on the C/A Code, and contains the data noted above.
- the receiver can utilise the signal from a satellite by the particular C/A Code being submitted, to make pseudo-range measurements.
- GPS receivers there is a wide range of GPS receivers available today, and typically the internal architecture of a GPS receiver comprises a front end that initially processes the incoming satellite signals, followed by signal processing stages that apply the algorithms to determine the receivers location, speed and time.
- the front end in basic terms is similar to that of a superheterodyne receiver.
- the signal is detected by a GPS antenna and fed to a low noise amplifier. Following amplification, the signal is down converted to a lower workable frequency. This is achieved by mixing or heterodyning the GPS signal with another constant frequency signal. This mixing signal is produced by a local oscillator. When two signals are mixed, the original, the sum of the two and the difference between the two frequencies is output. The filter in the following stages selects only the difference frequency and rejects the others.
- This difference frequency produced by the down conversion step is known as the intermediate frequency IF and which delivers the baseband signal.
- the signal is next converted from analogue to digital in an AD converter.
- the output level of the AD converter is monitored by a voltage comparator to check levels exceeding or dropping below threshold levels, and an automatic gain control continually adjusts the gain of the IF amplifier to maintain a constant output level.
- the digital signal from the AD converter is used as an input to several stages of signal processing dealing with the ranging process.
- the ranging process aims to calculate the distance from the satellite to the receiver using the incoming PRN codes to time how long it has taken the signals transmitted by the satellite to arrive at the receiver.
- each receiver has the capability to generate an exact pattern of the code that each satellite transmits using a PRN signal generator.
- the incoming signal received from a particular satellite is likely to be out of phase with the internal one since the time it takes to travel from the satellite to the receiver, measured in units of time periods to transmit a chip may not be always known.
- the internally generated expected PRN signal from a particular satellite needs to be suitably delayed or phase shifted so that it matches with the received signal when compared. The strength of match can be measured from correlation between the two signal fragments.
- the internally generated sequence can be delayed by rotating the sequence.
- the amount of shifting or offset that was required to match the two signals provides the receiver with a measurement of the time lag between the signal leaving the satellite and arriving at the receiver. This measurement is then used to derive the range.
- the delay that is identified as being the one that is appropriate is the one that yields the highest correlation output. If sub chip sampling is employed, (say 4 samples per chip which is currently common) then a high value is obtained for about 4 of the m rotations. The rotation that yields the highest correlation from these four contiguous rotations is used to calculate the time the signal has taken to travel from the satellite to the observer. Once the time has been estimated, the changes in this time are monitored using various tracking algorithms.
- the present invention in one aspect provides a method for determining synchronisation of a signal received in a global positioning system receiver and transmitted by a global positioning system satellite, said method comprising: transform coding said received signal so as to transform said received signal from time domain to frequency domain coefficients, selecting from said frequency domain coefficients those frequency domain coefficients contributing substantially zero energy, deriving from the selected coefficients an estimation indication of in-band noise.
- the invention advantageously provides for filtering to be performed in the frequency domain, followed, in preferred arrangements, by correlation to be carried out also in the frequency domain. Accordingly, in-band noise is substantially reduced from the incoming GPS signal thereby enabling the value of the correlation to be identified more definitely, thus providing for improved synchronisation. More specifically, in prior art methods, in order to obtain a GPS fix where the incoming signal is weak, within say a building, it was often necessary to perform long correlations. However, by means of the inventions, correlations may be shortened thereby affording a saving in power.
- the spectrum of the GPS baseband signal is a line spectrum, and by observing the line spectrum it has been noted that only a fraction of the bins are non-zero. From the bins that have zero energy, a measure can be derived of the noise in the received signal.
- the method provides for in-band filtering and accurately estimating in-band characteristics of noise. By removing the estimated noise it is possible to compare the correlation against the background noise at in- band.
- In-band filtering of GPS signals is conventionally performed using narrow- band filters having a pre-determined pass band. Such filters cannot remove noise inside a pass-band.
- the present invention in contrast, removes noise across substantially the entire band by estimating the in-band noise.
- the present invention is concerned with the problem of a receiver attaining synchronisation with an incoming satellite transmitted pseudo random noise (PRN) signal in the context of GPS, and for the purposes of this description are consist in a simulation.
- PRN pseudo random noise
- Unit Step is a mathematical device for isolating a non-zero function at prescribed ranged.
- T is the duration of a chip and M is the number of chips in the spreading code.
- Equation 2 The satellite signal s[t] is represented in Equation 2 as follows:
- Equation 3 The contribution of the received signal from a single satellite to the signal at baseband is proportional to s[t].
- the signal r[t] received at baseband from a single satellite can be expressed in Equation 3:
- S[f] is the spectrum of s[t] and is indicative of the frequency variable Fourier spectrum of S[t]. Equation 4 represents S[f]:
- the spectrum is a line spectrum where the lines are separated by a distance of 1/(M T) apart.
- the g[f] is a filter that is a function of the frequency f.
- g[f_] ((-fOCos[fO ⁇ T]Si ⁇ [f ⁇ l] + fCos[f ⁇ T] Sin[f ⁇ 7rT])
- the received signal is buried in noise and the present invention in its preferred form provides a process to perform in band filtering using a discrete Fourier transform.
- the receiver samples the incoming signal with a sampling period of T/samp where samp is an integer, typically 4.
- Equation 13 the inverse Fourier transform of the spreading code shifted by ⁇ is generated as follows. Initially, it is given by Equation 13:
- the Fourier transform of the code shifted by ⁇ bins can be generated efficiently.
- the expression is the i'term of the inverse Fourier transform of the code cyclically shifted by ⁇ bins. From equation 17 above, the i'bin of the Fourier transform of the code shifted by ⁇ , is the product of the inverse Fourier transform of the code with no shifts and the term.
- FRc is denoted as the Inverse Fourier Transform of the spreading code, and is given by Equation 27:
- SF[i'] may be zero, it is not necessary to perform every multiplication.
- the spectrum is a line spectrum it may only be necessary to carry out a smaller proportion of the multiplications, e.g. as in Equation 31 :
- Nsan samples be represented by ⁇ s[0],s[1],s[2],s[3],s[4],s[5],s[6],s[7], s[8], ...s[Nsamp-1] ⁇
- ⁇ sf[0],sf[1],sf[2],sf[3],sf[4],sf[5],sf[6],sf[7],sf[8], ... sf[Nsamp-1] ⁇ be the discrete Fourier transform of ⁇ s[0],s[1],s[2],s[3],s[4],s[5],s[6],s[7],s[8],
- nf(0) is the Transform coefficient for n.
Abstract
Description
Claims
Priority Applications (3)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
EP00985500A EP1257842A1 (en) | 1999-12-10 | 2000-12-08 | A receiver for a satellite based position location system |
AU21916/01A AU2191601A (en) | 1999-12-10 | 2000-12-08 | A receiver for a satellite based position location system |
JP2001544048A JP2003516546A (en) | 1999-12-10 | 2000-12-08 | Receiver for satellite-based position location system |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
GB9929329.2 | 1999-12-10 | ||
GBGB9929329.2A GB9929329D0 (en) | 1999-12-10 | 1999-12-10 | Data processing |
Publications (1)
Publication Number | Publication Date |
---|---|
WO2001042810A1 true WO2001042810A1 (en) | 2001-06-14 |
Family
ID=10866144
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
PCT/GB2000/004702 WO2001042810A1 (en) | 1999-12-10 | 2000-12-08 | A receiver for a satellite based position location system |
Country Status (5)
Country | Link |
---|---|
EP (1) | EP1257842A1 (en) |
JP (1) | JP2003516546A (en) |
AU (1) | AU2191601A (en) |
GB (1) | GB9929329D0 (en) |
WO (1) | WO2001042810A1 (en) |
Cited By (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
CN102466790A (en) * | 2010-11-09 | 2012-05-23 | 何明浩 | Centrifugal acceleration measurement method for airborne electronic support measures (ESM) system |
Citations (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US5347284A (en) * | 1991-02-28 | 1994-09-13 | Texas Instruments Incorporated | System and method for a digital navigation satellite receiver |
US5781156A (en) * | 1995-10-09 | 1998-07-14 | Snaptrack, Inc. | GPS receiver and method for processing GPS signals |
FR2769442A1 (en) * | 1997-10-02 | 1999-04-09 | Dassault Electronique | Satellite radio navigation receiver |
Family Cites Families (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US5263048A (en) * | 1992-07-24 | 1993-11-16 | Magnavox Electronic Systems Company | Narrow band interference frequency excision method and means |
-
1999
- 1999-12-10 GB GBGB9929329.2A patent/GB9929329D0/en not_active Ceased
-
2000
- 2000-12-08 AU AU21916/01A patent/AU2191601A/en not_active Abandoned
- 2000-12-08 WO PCT/GB2000/004702 patent/WO2001042810A1/en not_active Application Discontinuation
- 2000-12-08 JP JP2001544048A patent/JP2003516546A/en active Pending
- 2000-12-08 EP EP00985500A patent/EP1257842A1/en not_active Withdrawn
Patent Citations (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US5347284A (en) * | 1991-02-28 | 1994-09-13 | Texas Instruments Incorporated | System and method for a digital navigation satellite receiver |
US5781156A (en) * | 1995-10-09 | 1998-07-14 | Snaptrack, Inc. | GPS receiver and method for processing GPS signals |
FR2769442A1 (en) * | 1997-10-02 | 1999-04-09 | Dassault Electronique | Satellite radio navigation receiver |
Cited By (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
CN102466790A (en) * | 2010-11-09 | 2012-05-23 | 何明浩 | Centrifugal acceleration measurement method for airborne electronic support measures (ESM) system |
Also Published As
Publication number | Publication date |
---|---|
AU2191601A (en) | 2001-06-18 |
JP2003516546A (en) | 2003-05-13 |
EP1257842A1 (en) | 2002-11-20 |
GB9929329D0 (en) | 2000-02-02 |
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