CA1254637A - Enhanced global positioning system delta-range processing - Google Patents
Enhanced global positioning system delta-range processingInfo
- Publication number
- CA1254637A CA1254637A CA000494119A CA494119A CA1254637A CA 1254637 A CA1254637 A CA 1254637A CA 000494119 A CA000494119 A CA 000494119A CA 494119 A CA494119 A CA 494119A CA 1254637 A CA1254637 A CA 1254637A
- Authority
- CA
- Canada
- Prior art keywords
- delta
- range
- signals
- satellites
- information
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Abstract
ENHANCED GLOBAL POSITIONING
SYSTEM DELTA RANGE PROCESSING
By Alison Brown Abstract of the Invention A circuit is shown which utilizes signals trans-mitted from global positioning system satellites to create change in phase signals. The change in phase signals are measured over a predetermined time interval, one second, and stored. The stored signals are applied to a Kalman filter and back to the storage unit so that each one second time interval includes the information from all previous time intervals. This accumulated information is referred to as accumulted Delta-Range information which permits a more rapid determination of position by the circuit.
SYSTEM DELTA RANGE PROCESSING
By Alison Brown Abstract of the Invention A circuit is shown which utilizes signals trans-mitted from global positioning system satellites to create change in phase signals. The change in phase signals are measured over a predetermined time interval, one second, and stored. The stored signals are applied to a Kalman filter and back to the storage unit so that each one second time interval includes the information from all previous time intervals. This accumulated information is referred to as accumulted Delta-Range information which permits a more rapid determination of position by the circuit.
Description
3 ~ Y~
ENHANCED GLOBAL POSITIONING
SYSTEM DELTA RA~G~ PROCESSING
By ~1 i son Brown Field of the Invention The present inventicn relates to an apparatus and method for improving the accuracy obtained from a global positioning system which comprises a plurality of satellites each broadcasting two or more navigational signals.
Background of the Invention The NAVSTAR Global Positioning System (GPS) is a satellite-based radio-navigation system intended to provide highly accurate three-dimensional position and precise time on a continuous global basis. When the system becomes fully operational in late 1988, it will consist of l~ satellites in six orbital planes, and three active spares.
Each satellite will continuously transmit navigation signals at two carrier frequencies, Ll =
1575.42 MHz and L2 = 1227.6 MHz consisting of the P-code ranging signal (a 10.23 MBPS pseudonoise code), the C/A-code ranging signal (a 1.023 MBPS pseudonoise code), and 50 BPS data providing satellite ephemeris and clock bias information. Unbalanced Quadri-Phase Shift Keying (UQPSK) modulation is utilized with the clata bits added to the ranging codes, the C/~-cocle signal lagging the P-code signal by 90; and the C/A-code signal power nominally exceeding the P-code signal power by 3dB.
Navigation using GPS is accomplished by passive triangulation. The GPS user equipment measures the Pseudo-Range to four satellites, computes the position of the four satellites using the received ephemeris data;
and processes the Pseudo-Range measurements and satellite positions to estimate three-dimensional user position and --1-- ~r, q~
3 ~' precise time.
GPS receiver signal processing can be partitioned into three parts: RF signal processing, estimation of In-phase (I) and Quadrature-phase (Q) signals, and subsequent processing of these I and Q signals to implement code and carrier tracking, data demodulation, SNR estimation, sequential detection, and lock detection functions. Traditionally, all three parts are implemented using analog signal processing techniques.
10A paper briefly reviewing analog RF signal processing implementation which describes three digital signal processing (DSP) techniques for implementing the I/Q generation function, and describes DSP algorithms for implementing the subsequent processing functions may be 15found in the NTC '83 lEEE_1983 National Teles~stems Conference papers, entitled "Digital Signal Processing Techniques For GPS Receivers," by Mark A. Sturza, November 1983.
A Delta-Range (DR) measurement is derived from the difference in carrier phase over a fixed time interval.
Position can be estimated using Delta-Ranges through the change in the satellite position over the observation interval. In the prior art, it would generally take approximately 24 hours of processing Delta-Range measurements to obtain a reasonable accuracy for the location of the receiver utilizing a global positioning system.
Accordingly, it is an object of the present invention to reduce the amount of time required to obtain an accurate location of the receiver utilizing a global positioning sytem.
~5~37 Summary of the Invention The present invention replaces the measurement of the Delta-Range over a plurality of predetermined time intervals with an improved configuration. Under tne improved configuration, the Delta-Range measurement, generally measured over a one-second period, is accumulated for the first second. Therea~ter, tne Delta-Range is accumulated for the first and second second;
followed by accumulation of the Delta-Range for the first, second and third second; and so on. The heart of the invention is the realization that such accumulation of all Delta-Range measurements for each new time interval and all old time intervals eliminates many of the errors created when measuring a Delta-Range for an individual time period. By adding information from previous Delta-Range measurements to the newest Delta-Range measurement, it is possible to determine the position of the receiver utilizing a global positioning system in a much faster time time frame.
For example, an accurate position can be determined utilizing the global positioning system and the present invention in less than eight hours. This is an improvement of better than 3:1.
Thus, in accordance with a broad aspect oE the invention, there is provided a method for enhancing the information received from a global positioning system which includes a plurality of satellites each transmitting at least two carrier frequency signals, comprising the steps of:
a) identifying a plurality of selected satellites;
b) setting information storage units for accumulated Delta-Range information for each selected satellite -to zero;
~S~S63~
c) tracking the selected satellites;
d) receiving said carrier frequency signals from said selected satellites;
e) measuring the phase of said carrier frequency signals from said selected satellites;
f) storing changes in phase of said carrier frequency signals over a predetermined time interval in said storage units to create a Delta-Range measurement for each selected satellite;
g) accumulating the Delta-Range measurement by adding the above-mentioned accumulated Delta-Range information for each sat-ellite to the Delta-Range measurement from step f for each satellite;
h) processing the accumulated Delta-Range information from each selected satellite through a filter which receives said input information and produces said information into output information, said output information being position information; and i) repeating steps f, g and h until said position informa-tion is refined to the accuracy desired.
In accordance with another broad aspect of the invention there is provided apparatus for enhancing the infor-mation received from a global positioning system which includes a plurality oE satellites each transmitting at least two carrier fxequency signals, comprising:
a) means for selecting a plurality of satellites whose transmitted signals are to be received;
b) means for storing;
~L~54~637 c) means for setting each means for storing to zero;
d) means for receiving said carrier frequency signals from said selected satellites;
e) means ~Gr measuring the pha~e of said carrier frequency signals received from said selected satellites;
f) means for measuring changes in phase of said carrier frequency signals over a predetermined time interval;
g) means ~or placing said measured changes in phase in said means for storing over said time interval to create a Delta-Range measurement for each selected satellite;
h) means for accumulating said Delta-Range measurement by adding the above mentioned accumulated Delta-Range information for each satellite to said Delta-Range measurement;
i) filter means for processing said accumulated Delta-Range information from each selected satellite for producing an output representing position information.
In accordance with another broad aspect of the invention there is provided an apparatus for improving the accuracy of measurement informati.on obtained from a plurality of satellites of a global positioning system, said apparatus comprising:
a satellite selectable global positioning system receiver, said receiver being capable of receiving A-t least two carrier frequencies from each selected satellite and tracking the differ-ence between their phase measurements, to produce Delta-Range signals ~-hich are derived from said phase measurements;
sai.d global positioning system receiver being operatively associated with a resettable data storage and accumulation means, -3b-Pr 5 ~r~37 said receiver providing said data`storage and accumulation means with said Delta-Range signals;
said resettable data storage and accumulation means storing and accumulating said Delta-Range signals over a ~irst time interval;
said resettable storage means processing said Delta-Range signals to develop a first set of Accumulated Delta-Range signals, said first set of signals being a function of the accumulation of Delta-Range signals at said storage means during said first time interval;
said storage means operatively connected to a filter means, said storage means transmitting said Accumulated Delta-Range singals to said filter and simultaneously feeding back said slgnals to the storage means, so that said Accumulated Delta-Range signals may be stored in said storage means during a sec-ond time interval and processed together with a second set of Delta-Range signals, for deriving a second set of Accumulated Delta-Range signals at the end of said second time interval, at which time said second set of Accumulated Delta-Range signals are transmitted to said filter means;
said filter means further processing said :Eirst and said second sets of Accumulated Delta-Range signals from each selected satellite to develop an output signal representative of enhanced position information.
In accordance with another broad aspect of the inven-tion, there is provided a method for improving the accuracy ~L~S~รง~37 of position measurement information obtained from a global positioning system having a plurality of satellites, eac~ of said satellites transmitting at least two carrier frequency signals, comprising the steps of:
a) receiving the transmitted satellite carrier frequency signals;
b) processing said satellite signal through a receiver means capable of identifying and tracking each of the satellites according to their transmitted carrier frequency sig-nals;
c) deriving an output signal from said receiver means which is characteristic of Delta-Range information for each of said satellites;
d) processing said output signal through a data accumulation and storage means, deriving an Accumulated Delta-Range information signal, by storing said signal for a pre-determined time interval, creating an Accumulated Delta-Range information signal corresponding to each satellite;
e) repeating said step (d) to further refine the signal so processed, whereby an Accumulated Delta-Range signal is derived which corresponds to an accurate position :Eo:r each satellite to the degree desired.
Description of the Drawings A better understanding of the benefits and advantages of the present invention will be available after a careful review of the following specification and drawing, wherein:
-3d-~5~1~37 Figure 1 is a block diagram showing the enhanced glo~al positioning system Delta-Range positioning of the present invention.
Description of the Preferred Embodiment . _ A GPS receiver makes a measurement of Pseudo-Range (PR), the difference between the time of reception and time of transmission of the GPS signal, from tracking the -3e-58-23lF
Pseudo Random Noise (PRN) codes modulated on the GPS
carrier. The Delta-Range ~DR) measurement is derived from the difference in carrier phase over a fixed time interval, generally one second, measured using a Phase LocXed ~oop ~PL~). The Pseudo-Ranges and Delta-~anges are related to user position error, Ru, velocity error, Vu, and user clock and frequency offsets, Bu and ~u through equations l.l - 1.5.
~ ~c~ 1.1 ~ k k (~ k ) Bk 1.2 DRi ~ PRk _ p~ l 1.3 P~i PRi ~ PR~ ku + Bk 1.4 DRi ~ DRl - DRi C (~ U + ~ + ~ku 1.5 11 L~S from user to ith satellite at time tk.
R Position of user.
~.S~3 ~
Velocity of user.
~ ~ Position of ith satellite.
PR~ Pseudo Range to ith satellite at time tk.
DRk Delta-Range to ith satellite at time tk.
~u Users clock offset from GPS time.
bB~ Chan~e in user's c~oc~ offset over one sec.
LOS is an abbreviation for Line Of Sight Vector which incorporates the elevation angle and azimuth angle of ~ satelliteO
For static point positioning the user's velocity is known to be zero and so equation 1A5 simplifies to D-Rk ~ (~ 1 )- R + ~Bk 1.6 The LOS vector to a GPS satellite does not change significantly over a one second interval, so to improve the geometry of the navigation solution it is advan-tageous to accumuiate Delta-Ranges even longer time intervals to form a new measurement variable, Accumulated Delta-Ranges (ADR).
Since the Delta-Ranges are formed from the L~37 difference between two phase measurements from the carrier tracking phase-locked loops, it is important to note that Accumulating Delta-Ranges to form a new measurement do not increase the measurement error.
DRk , ~ (nk + ~2~ ~ n 2~ ) 1.7 ADR ~ ~ DR ~(n 2~ 2 ~=1 + nk-l + ~k 1 nk-2 ~ 2 . . , . ~ nl + ~2 ~ n c ) ADRk y ~(n~ + 2~ ~ n ~ 2~ ) 1.8 Note, that the term n represents an integer number of cycles whereas the term 0k represents the number of radians in each part cycle of the phase shift. The term nk l, represents the number of integer cycles one second before, whereas the term 0k l represents the number of radians within the partial cycle from the sample the second before. These Delta-Range differences are added together wherein the final Accumulated Delta-Range includes all of the information from the initial start through to the final measurement at n time period.
$~
Defining the phase measurement errors to be:
E[02] = u~ E~0k0j] = O j~k E[0~ = o Then i 15DRk O ~ Var ~DR~ - 2a~ 7 DRkDRk 1 _ at 1. 9 ADR ~0 Var ~ADR~ - a~ 1.10 i Since adjacent Delta-Range measurements share a common phase measurement, the phase errors associated with these common measurements cancel out in the Accumulated Delta-Range measurement. The Delta-Ranges have zero mean error but are correlated between adjacent time intervals. Alternatively, the Accumulated Delta-Ranges share a common bias error, the initial carrier phase error, but apart from this bias all samples are uncorrelated.
The measurement equation for the Accumulated Delta Range measurement becomes A~k ADR~ ADRk , (~ 1) ~ k ~0 1.11 As time increases, the satellite geometry for estimating position error improves. Because of the independence between each measurement, it is possible to process an Accumulated Delta-Range every second from each satellite tracked. This allows position to be determined to far greater accuracy than by processing Pseudo-Range Measurements as in the prior art.
As shown in equation 1.10 the Accumulated Delta-Range measurements, generated every second, are independent of each other and each have the same measurement noise as the one second Delta Range Measurements. Four Accumulated Delta Ranges from four satellites being tracked are generated every second and can be processed optimally using a Kalman filter to estimate user position and satellite errors.
As is well-known, a Kalman filter is a device which receives inputs from two or more variables and processes those variables to produce an output which is a function of the input variables. For example, if pressure and temperature were known inputs, it would be possible to feed this information into a Kalman filter to produce an output representing altitude. A similar process is used 3~
here. Wherein the Accumulated Delta-Range Measurements from the four satellites are applied to a Kalman filter which produces an output representing the position of the receiving station.
The most significant error sources are the 0 satellite ephemeris errors and the satellite clock error.
These errors can be modeled by including four additional states per satellite in addition to the four user position and clock frequency offset states, as shown in Table 1. The observation equation now becomes ADRk y tlk ~ li) ~ (Ru ~ R~) + Bk _ Bu _~k + a~ 1.12 The clock errors are all lumped together in one clock offset term per satellite which estimates the change in the relative user and satellite clock error over the accumulation time interval.
~B~ Y (~k _ B0) _ (~k _ B0) i 1 TABLE 1 - KAL~N FILTER STATES
_ __ _ ._ State Description nitial State No. . ariance Noise - ---- _ _ 1 Xu ~ Position Error lOOCm
ENHANCED GLOBAL POSITIONING
SYSTEM DELTA RA~G~ PROCESSING
By ~1 i son Brown Field of the Invention The present inventicn relates to an apparatus and method for improving the accuracy obtained from a global positioning system which comprises a plurality of satellites each broadcasting two or more navigational signals.
Background of the Invention The NAVSTAR Global Positioning System (GPS) is a satellite-based radio-navigation system intended to provide highly accurate three-dimensional position and precise time on a continuous global basis. When the system becomes fully operational in late 1988, it will consist of l~ satellites in six orbital planes, and three active spares.
Each satellite will continuously transmit navigation signals at two carrier frequencies, Ll =
1575.42 MHz and L2 = 1227.6 MHz consisting of the P-code ranging signal (a 10.23 MBPS pseudonoise code), the C/A-code ranging signal (a 1.023 MBPS pseudonoise code), and 50 BPS data providing satellite ephemeris and clock bias information. Unbalanced Quadri-Phase Shift Keying (UQPSK) modulation is utilized with the clata bits added to the ranging codes, the C/~-cocle signal lagging the P-code signal by 90; and the C/A-code signal power nominally exceeding the P-code signal power by 3dB.
Navigation using GPS is accomplished by passive triangulation. The GPS user equipment measures the Pseudo-Range to four satellites, computes the position of the four satellites using the received ephemeris data;
and processes the Pseudo-Range measurements and satellite positions to estimate three-dimensional user position and --1-- ~r, q~
3 ~' precise time.
GPS receiver signal processing can be partitioned into three parts: RF signal processing, estimation of In-phase (I) and Quadrature-phase (Q) signals, and subsequent processing of these I and Q signals to implement code and carrier tracking, data demodulation, SNR estimation, sequential detection, and lock detection functions. Traditionally, all three parts are implemented using analog signal processing techniques.
10A paper briefly reviewing analog RF signal processing implementation which describes three digital signal processing (DSP) techniques for implementing the I/Q generation function, and describes DSP algorithms for implementing the subsequent processing functions may be 15found in the NTC '83 lEEE_1983 National Teles~stems Conference papers, entitled "Digital Signal Processing Techniques For GPS Receivers," by Mark A. Sturza, November 1983.
A Delta-Range (DR) measurement is derived from the difference in carrier phase over a fixed time interval.
Position can be estimated using Delta-Ranges through the change in the satellite position over the observation interval. In the prior art, it would generally take approximately 24 hours of processing Delta-Range measurements to obtain a reasonable accuracy for the location of the receiver utilizing a global positioning system.
Accordingly, it is an object of the present invention to reduce the amount of time required to obtain an accurate location of the receiver utilizing a global positioning sytem.
~5~37 Summary of the Invention The present invention replaces the measurement of the Delta-Range over a plurality of predetermined time intervals with an improved configuration. Under tne improved configuration, the Delta-Range measurement, generally measured over a one-second period, is accumulated for the first second. Therea~ter, tne Delta-Range is accumulated for the first and second second;
followed by accumulation of the Delta-Range for the first, second and third second; and so on. The heart of the invention is the realization that such accumulation of all Delta-Range measurements for each new time interval and all old time intervals eliminates many of the errors created when measuring a Delta-Range for an individual time period. By adding information from previous Delta-Range measurements to the newest Delta-Range measurement, it is possible to determine the position of the receiver utilizing a global positioning system in a much faster time time frame.
For example, an accurate position can be determined utilizing the global positioning system and the present invention in less than eight hours. This is an improvement of better than 3:1.
Thus, in accordance with a broad aspect oE the invention, there is provided a method for enhancing the information received from a global positioning system which includes a plurality of satellites each transmitting at least two carrier frequency signals, comprising the steps of:
a) identifying a plurality of selected satellites;
b) setting information storage units for accumulated Delta-Range information for each selected satellite -to zero;
~S~S63~
c) tracking the selected satellites;
d) receiving said carrier frequency signals from said selected satellites;
e) measuring the phase of said carrier frequency signals from said selected satellites;
f) storing changes in phase of said carrier frequency signals over a predetermined time interval in said storage units to create a Delta-Range measurement for each selected satellite;
g) accumulating the Delta-Range measurement by adding the above-mentioned accumulated Delta-Range information for each sat-ellite to the Delta-Range measurement from step f for each satellite;
h) processing the accumulated Delta-Range information from each selected satellite through a filter which receives said input information and produces said information into output information, said output information being position information; and i) repeating steps f, g and h until said position informa-tion is refined to the accuracy desired.
In accordance with another broad aspect of the invention there is provided apparatus for enhancing the infor-mation received from a global positioning system which includes a plurality oE satellites each transmitting at least two carrier fxequency signals, comprising:
a) means for selecting a plurality of satellites whose transmitted signals are to be received;
b) means for storing;
~L~54~637 c) means for setting each means for storing to zero;
d) means for receiving said carrier frequency signals from said selected satellites;
e) means ~Gr measuring the pha~e of said carrier frequency signals received from said selected satellites;
f) means for measuring changes in phase of said carrier frequency signals over a predetermined time interval;
g) means ~or placing said measured changes in phase in said means for storing over said time interval to create a Delta-Range measurement for each selected satellite;
h) means for accumulating said Delta-Range measurement by adding the above mentioned accumulated Delta-Range information for each satellite to said Delta-Range measurement;
i) filter means for processing said accumulated Delta-Range information from each selected satellite for producing an output representing position information.
In accordance with another broad aspect of the invention there is provided an apparatus for improving the accuracy of measurement informati.on obtained from a plurality of satellites of a global positioning system, said apparatus comprising:
a satellite selectable global positioning system receiver, said receiver being capable of receiving A-t least two carrier frequencies from each selected satellite and tracking the differ-ence between their phase measurements, to produce Delta-Range signals ~-hich are derived from said phase measurements;
sai.d global positioning system receiver being operatively associated with a resettable data storage and accumulation means, -3b-Pr 5 ~r~37 said receiver providing said data`storage and accumulation means with said Delta-Range signals;
said resettable data storage and accumulation means storing and accumulating said Delta-Range signals over a ~irst time interval;
said resettable storage means processing said Delta-Range signals to develop a first set of Accumulated Delta-Range signals, said first set of signals being a function of the accumulation of Delta-Range signals at said storage means during said first time interval;
said storage means operatively connected to a filter means, said storage means transmitting said Accumulated Delta-Range singals to said filter and simultaneously feeding back said slgnals to the storage means, so that said Accumulated Delta-Range signals may be stored in said storage means during a sec-ond time interval and processed together with a second set of Delta-Range signals, for deriving a second set of Accumulated Delta-Range signals at the end of said second time interval, at which time said second set of Accumulated Delta-Range signals are transmitted to said filter means;
said filter means further processing said :Eirst and said second sets of Accumulated Delta-Range signals from each selected satellite to develop an output signal representative of enhanced position information.
In accordance with another broad aspect of the inven-tion, there is provided a method for improving the accuracy ~L~S~รง~37 of position measurement information obtained from a global positioning system having a plurality of satellites, eac~ of said satellites transmitting at least two carrier frequency signals, comprising the steps of:
a) receiving the transmitted satellite carrier frequency signals;
b) processing said satellite signal through a receiver means capable of identifying and tracking each of the satellites according to their transmitted carrier frequency sig-nals;
c) deriving an output signal from said receiver means which is characteristic of Delta-Range information for each of said satellites;
d) processing said output signal through a data accumulation and storage means, deriving an Accumulated Delta-Range information signal, by storing said signal for a pre-determined time interval, creating an Accumulated Delta-Range information signal corresponding to each satellite;
e) repeating said step (d) to further refine the signal so processed, whereby an Accumulated Delta-Range signal is derived which corresponds to an accurate position :Eo:r each satellite to the degree desired.
Description of the Drawings A better understanding of the benefits and advantages of the present invention will be available after a careful review of the following specification and drawing, wherein:
-3d-~5~1~37 Figure 1 is a block diagram showing the enhanced glo~al positioning system Delta-Range positioning of the present invention.
Description of the Preferred Embodiment . _ A GPS receiver makes a measurement of Pseudo-Range (PR), the difference between the time of reception and time of transmission of the GPS signal, from tracking the -3e-58-23lF
Pseudo Random Noise (PRN) codes modulated on the GPS
carrier. The Delta-Range ~DR) measurement is derived from the difference in carrier phase over a fixed time interval, generally one second, measured using a Phase LocXed ~oop ~PL~). The Pseudo-Ranges and Delta-~anges are related to user position error, Ru, velocity error, Vu, and user clock and frequency offsets, Bu and ~u through equations l.l - 1.5.
~ ~c~ 1.1 ~ k k (~ k ) Bk 1.2 DRi ~ PRk _ p~ l 1.3 P~i PRi ~ PR~ ku + Bk 1.4 DRi ~ DRl - DRi C (~ U + ~ + ~ku 1.5 11 L~S from user to ith satellite at time tk.
R Position of user.
~.S~3 ~
Velocity of user.
~ ~ Position of ith satellite.
PR~ Pseudo Range to ith satellite at time tk.
DRk Delta-Range to ith satellite at time tk.
~u Users clock offset from GPS time.
bB~ Chan~e in user's c~oc~ offset over one sec.
LOS is an abbreviation for Line Of Sight Vector which incorporates the elevation angle and azimuth angle of ~ satelliteO
For static point positioning the user's velocity is known to be zero and so equation 1A5 simplifies to D-Rk ~ (~ 1 )- R + ~Bk 1.6 The LOS vector to a GPS satellite does not change significantly over a one second interval, so to improve the geometry of the navigation solution it is advan-tageous to accumuiate Delta-Ranges even longer time intervals to form a new measurement variable, Accumulated Delta-Ranges (ADR).
Since the Delta-Ranges are formed from the L~37 difference between two phase measurements from the carrier tracking phase-locked loops, it is important to note that Accumulating Delta-Ranges to form a new measurement do not increase the measurement error.
DRk , ~ (nk + ~2~ ~ n 2~ ) 1.7 ADR ~ ~ DR ~(n 2~ 2 ~=1 + nk-l + ~k 1 nk-2 ~ 2 . . , . ~ nl + ~2 ~ n c ) ADRk y ~(n~ + 2~ ~ n ~ 2~ ) 1.8 Note, that the term n represents an integer number of cycles whereas the term 0k represents the number of radians in each part cycle of the phase shift. The term nk l, represents the number of integer cycles one second before, whereas the term 0k l represents the number of radians within the partial cycle from the sample the second before. These Delta-Range differences are added together wherein the final Accumulated Delta-Range includes all of the information from the initial start through to the final measurement at n time period.
$~
Defining the phase measurement errors to be:
E[02] = u~ E~0k0j] = O j~k E[0~ = o Then i 15DRk O ~ Var ~DR~ - 2a~ 7 DRkDRk 1 _ at 1. 9 ADR ~0 Var ~ADR~ - a~ 1.10 i Since adjacent Delta-Range measurements share a common phase measurement, the phase errors associated with these common measurements cancel out in the Accumulated Delta-Range measurement. The Delta-Ranges have zero mean error but are correlated between adjacent time intervals. Alternatively, the Accumulated Delta-Ranges share a common bias error, the initial carrier phase error, but apart from this bias all samples are uncorrelated.
The measurement equation for the Accumulated Delta Range measurement becomes A~k ADR~ ADRk , (~ 1) ~ k ~0 1.11 As time increases, the satellite geometry for estimating position error improves. Because of the independence between each measurement, it is possible to process an Accumulated Delta-Range every second from each satellite tracked. This allows position to be determined to far greater accuracy than by processing Pseudo-Range Measurements as in the prior art.
As shown in equation 1.10 the Accumulated Delta-Range measurements, generated every second, are independent of each other and each have the same measurement noise as the one second Delta Range Measurements. Four Accumulated Delta Ranges from four satellites being tracked are generated every second and can be processed optimally using a Kalman filter to estimate user position and satellite errors.
As is well-known, a Kalman filter is a device which receives inputs from two or more variables and processes those variables to produce an output which is a function of the input variables. For example, if pressure and temperature were known inputs, it would be possible to feed this information into a Kalman filter to produce an output representing altitude. A similar process is used 3~
here. Wherein the Accumulated Delta-Range Measurements from the four satellites are applied to a Kalman filter which produces an output representing the position of the receiving station.
The most significant error sources are the 0 satellite ephemeris errors and the satellite clock error.
These errors can be modeled by including four additional states per satellite in addition to the four user position and clock frequency offset states, as shown in Table 1. The observation equation now becomes ADRk y tlk ~ li) ~ (Ru ~ R~) + Bk _ Bu _~k + a~ 1.12 The clock errors are all lumped together in one clock offset term per satellite which estimates the change in the relative user and satellite clock error over the accumulation time interval.
~B~ Y (~k _ B0) _ (~k _ B0) i 1 TABLE 1 - KAL~N FILTER STATES
_ __ _ ._ State Description nitial State No. . ariance Noise - ---- _ _ 1 Xu ~ Position Error lOOCm
2 Yu - Position Error lOOOm
3 Zu - Position Error lOOOm
4 ~Bu - Clock Frequency lOOOm 0.67mm ~a - - - - -- -
5,9,13,17 aB Change in Clock Offset 0 2mm over accumulation inverva
6,10,14,1a Alon~ Trac~ Satellite 0.8
7,11,15,19 Radial Satellite Error 6.3
8,12,16,20 Cross Track Satellite 3.0 15 ___ . Error . _ This term can also be used to include noise terms to model the range errors introduced by atmospheric effects. The relative clock offset, B, is propagated using the estimate of the users clock frequency offset every second.
State Propagation ~Bi 1 ~ ~Bi + ~Bu 1.1 #~
The measurement equation can be written in vector format, as shown for ~he second sa~e71ite tracked.
2 ~lN , oT ~ T , QT ' T]- 1 15 Q1N is the delta LOS vector from the satellite to the u~er, ( 1 - 1), expressed in local level coordinates.
~ 1~ is the same ~ector but expressed in orbital frame coordinates for the second GPS satellite selected, that is with XO in the Along Track Direction, YO in the Radial direction and ZO in the Cross Track direction.
Processing the Accumulated Delta-Ranges using this Kalman filter gives position to significantly greate~
accuracy ~han that normally achievable by GPS, even for P-code users. After tracking for two hours at lower latitudes the Root Sum Square (RSS) position error drops to around 1.0 m RSS and continues to improve gradually, reaching about 0.3 m RSS after about seven hours. At higher latitudes the position accuracy degrades slightly due to the different satellite geometry, but approxi-mately 1 m RSS is achievable in around five hours.
Referring now to the drawing, Fig. 1 shows a receiver 10 which receives transmitted navigational signals froM the satellites that comprise the global positioning system via an antenna 12. The transmitted signals are applied to a satellite select circuit 14 which selects the most desirable satellites to be tracRed by the global positioning system receiver 16. Once each satellite has been selected, the storage units 18 for each selected satellite are set to zero or cleared of any stored information contained therein. The global 63'7 positi~ning receiver then tracks the particular satellites selected and receives the carrier frequency signals from each. After measuring the phase of each of the received carrier signals, the change of phase in the carrier signals is stored within the information storage units 18. In the preferred embodiment, this information is stored over a one second time interval. The Delta-Range measurements are accumulated within the storage units 18 so that the first Delta-Range dstermined by the first one second interval is accumulated with the Delta-Range information from the second time interval and so on. The outputs of the storage units 18 are applied to a Kalman filter 20 and back to the input of storage units 18 to create Accumulated Delta-Range information.
At each time interval, the step of reapplying the output of the storage unit 18 to its input is repeated so there is an accumulation of the Delta-Range information. These steps are repeated as often as necessary until the position information at the output 22 of the Kalman filter represents the accuracy desired.
It will be understood that the present invention may be practiced through the utilization of software or hardware; hardware being represented by the block diagram of Fig. 1.
3~
State Propagation ~Bi 1 ~ ~Bi + ~Bu 1.1 #~
The measurement equation can be written in vector format, as shown for ~he second sa~e71ite tracked.
2 ~lN , oT ~ T , QT ' T]- 1 15 Q1N is the delta LOS vector from the satellite to the u~er, ( 1 - 1), expressed in local level coordinates.
~ 1~ is the same ~ector but expressed in orbital frame coordinates for the second GPS satellite selected, that is with XO in the Along Track Direction, YO in the Radial direction and ZO in the Cross Track direction.
Processing the Accumulated Delta-Ranges using this Kalman filter gives position to significantly greate~
accuracy ~han that normally achievable by GPS, even for P-code users. After tracking for two hours at lower latitudes the Root Sum Square (RSS) position error drops to around 1.0 m RSS and continues to improve gradually, reaching about 0.3 m RSS after about seven hours. At higher latitudes the position accuracy degrades slightly due to the different satellite geometry, but approxi-mately 1 m RSS is achievable in around five hours.
Referring now to the drawing, Fig. 1 shows a receiver 10 which receives transmitted navigational signals froM the satellites that comprise the global positioning system via an antenna 12. The transmitted signals are applied to a satellite select circuit 14 which selects the most desirable satellites to be tracRed by the global positioning system receiver 16. Once each satellite has been selected, the storage units 18 for each selected satellite are set to zero or cleared of any stored information contained therein. The global 63'7 positi~ning receiver then tracks the particular satellites selected and receives the carrier frequency signals from each. After measuring the phase of each of the received carrier signals, the change of phase in the carrier signals is stored within the information storage units 18. In the preferred embodiment, this information is stored over a one second time interval. The Delta-Range measurements are accumulated within the storage units 18 so that the first Delta-Range dstermined by the first one second interval is accumulated with the Delta-Range information from the second time interval and so on. The outputs of the storage units 18 are applied to a Kalman filter 20 and back to the input of storage units 18 to create Accumulated Delta-Range information.
At each time interval, the step of reapplying the output of the storage unit 18 to its input is repeated so there is an accumulation of the Delta-Range information. These steps are repeated as often as necessary until the position information at the output 22 of the Kalman filter represents the accuracy desired.
It will be understood that the present invention may be practiced through the utilization of software or hardware; hardware being represented by the block diagram of Fig. 1.
3~
Claims (13)
1. A method for enhancing the information received from a global positioning system which includes a plurality of satellites each transmitting at least two carrier frequency signals, comprising the steps of:
a) identifying a plurality of selected satellites;
b) setting information storage units for accumulated Delta-Range information for each selected satellite to zero:
c) tracking the selected satellites;
d) receiving said carrier frequency signals from said selected satellites;
e) measuring the phase of said carrier frequency signals from said selected satellites;
f) storing changes in phase of said carrier frequency signals over a predetermined time interval in said storage units to create a Delta-Range measurement for each selected satellite;
g) accumulating the Delta-Range measurement by adding the above-mentioned accumulated Delta-Range information for each satellite to the Delta-Range measurement from step f for each satellite;
h) processing the accumulated Delta-Range infor-mation from each selected satellite through a filter which receives said input information and produces said information into output information, said output informa-tion being position information, and i) repeating steps f, g and h until said position information is refined to the accuracy desired.
a) identifying a plurality of selected satellites;
b) setting information storage units for accumulated Delta-Range information for each selected satellite to zero:
c) tracking the selected satellites;
d) receiving said carrier frequency signals from said selected satellites;
e) measuring the phase of said carrier frequency signals from said selected satellites;
f) storing changes in phase of said carrier frequency signals over a predetermined time interval in said storage units to create a Delta-Range measurement for each selected satellite;
g) accumulating the Delta-Range measurement by adding the above-mentioned accumulated Delta-Range information for each satellite to the Delta-Range measurement from step f for each satellite;
h) processing the accumulated Delta-Range infor-mation from each selected satellite through a filter which receives said input information and produces said information into output information, said output informa-tion being position information, and i) repeating steps f, g and h until said position information is refined to the accuracy desired.
2. A method, as claimed in claim 1, wherein:
step a includes the selection of four satellites.
step a includes the selection of four satellites.
3. A method, as claimed in claim 1, wherein:
step f includes a one second time interval.
step f includes a one second time interval.
4. A method, as claimed in claim 1, wherein:
step h includes the use of a Kalman filter.
step h includes the use of a Kalman filter.
5. Apparatus for enhancing the information received from a global positioning system which includes a plurality of satellites each transmitting at least two carrier frequency signals, comprising:
a) means for selecting a plurality of satellites whose transmitted signals are to be received;
b) means for storing;
c) means for setting each means for storing to zero;
d) means for receiving said carrier frequency signals from said selected satellites;
e) means for measuring the phase of said carrier frequency signals received from said selected satellites;
f) means for measuring changes in phase of said carrier frequency signals over a predetermined time interval;
g) means for placing said measured changes in phase in said means for storing over said time interval to create a Delta-Range measurement for each selected satellite;
h) means for accumulating said Delta-Range measurement by adding the above mentioned accumulated Delta-Range information for each satellite to said Delta-Range measurement;
i) filter means for processing said accumulated Delta-Range information from each selected satellite for producing an output representing position information.
a) means for selecting a plurality of satellites whose transmitted signals are to be received;
b) means for storing;
c) means for setting each means for storing to zero;
d) means for receiving said carrier frequency signals from said selected satellites;
e) means for measuring the phase of said carrier frequency signals received from said selected satellites;
f) means for measuring changes in phase of said carrier frequency signals over a predetermined time interval;
g) means for placing said measured changes in phase in said means for storing over said time interval to create a Delta-Range measurement for each selected satellite;
h) means for accumulating said Delta-Range measurement by adding the above mentioned accumulated Delta-Range information for each satellite to said Delta-Range measurement;
i) filter means for processing said accumulated Delta-Range information from each selected satellite for producing an output representing position information.
6. Apparatus, as claimed in claim 5, wherein:
said plurality of satellites includes four satellites.
said plurality of satellites includes four satellites.
7. Apparatus, as claimed in claim 5, wherein:
said time interval includes a one second time interval.
said time interval includes a one second time interval.
8. Apparatus, as claimed in claim 5, wherein:
said filter means includes a Kalman filter.
said filter means includes a Kalman filter.
9. An apparatus for improving the accuracy of measurement information obtained from a plurality of satellites of a global positioning system, said apparatus comprising:
a satellite selectable global positioning system receiver, said receiver being capable of receiving at least two carrier frequencies from each selected satellite and tracking the difference between their phase measurements, to produce Delta-Range signals which are derived from said phase measurements;
said global positioning system receiver being operatively associated with a resettable data storage and accumulation means, said receiver providing said data storage and accumulation means with said Delta-Range signals;
said resettable data storage and accumulation means storing and accumulating said Delta-Range signals over a first time interval;
said resettable storage means processing said Delta-Range signals to develop a first set of Accumulated Delta-Range signals, said first set of signals being a function of the accumulation of Delta-Range signals at said storage means during said first time interval;
said storage means operatively connected to a filter means, said storage means transmitting said Accumulated Delta-Range signals to said filter and simultaneously feeding back said signals to the storage means, so that said Accumulated Delta-Range signals may be stored in said storage means during a second time interval and processed together with a second set of Delta-Range signals, for deriving a second set of Accumulated Delta-Range signals at the end of said second time interval, at which time said second set of Accumulated Delta-Range signals are transmitted to said filter means;
said filter means further processing said first and said second sets of Accumulated Delta-Range signals from each selected satellite to develop an output signal representative of enhanced position information.
a satellite selectable global positioning system receiver, said receiver being capable of receiving at least two carrier frequencies from each selected satellite and tracking the difference between their phase measurements, to produce Delta-Range signals which are derived from said phase measurements;
said global positioning system receiver being operatively associated with a resettable data storage and accumulation means, said receiver providing said data storage and accumulation means with said Delta-Range signals;
said resettable data storage and accumulation means storing and accumulating said Delta-Range signals over a first time interval;
said resettable storage means processing said Delta-Range signals to develop a first set of Accumulated Delta-Range signals, said first set of signals being a function of the accumulation of Delta-Range signals at said storage means during said first time interval;
said storage means operatively connected to a filter means, said storage means transmitting said Accumulated Delta-Range signals to said filter and simultaneously feeding back said signals to the storage means, so that said Accumulated Delta-Range signals may be stored in said storage means during a second time interval and processed together with a second set of Delta-Range signals, for deriving a second set of Accumulated Delta-Range signals at the end of said second time interval, at which time said second set of Accumulated Delta-Range signals are transmitted to said filter means;
said filter means further processing said first and said second sets of Accumulated Delta-Range signals from each selected satellite to develop an output signal representative of enhanced position information.
10. The apparatus of Claim 9 wherein the Accumulated Delta-Range signals are continuously processed and updated by said storage means over a subsequent series of time intervals, said filter means processing a subsequently derived series of Accumulated Delta-Range signals, whereby the position information so derived is continually updated and made more accurate at the end of each of said subsequent time intervals.
11. The apparatus of Claim 9 wherein the filter is a Kalman Filter.
12. A method for improving the accuracy of position measurement information obtained from a global positioning system having a plurality of satellites, each of said satellites transmitting at least two carrier frequency signals, comprising the steps of:
a) receiving the transmitted satellite carrier frequency signals;
b) processing said satellite signal through a receiver means capable of identifying and tracking each of the satellites according to their transmitted carrier frequency signals;
c) deriving an output signal from said receiver means which is characteristic of Delta-Range information for each of said satellites;
d) processing said output signal through a data accumulation and storage means, deriving an Accumulated Delta-Range information signal, by storing said signal for a pre-determined time interval, creating an Accumulated Delta-Range information signal corresponding to each satellite;
e) repeating said step (d) to further refine the signal so processed, whereby an Accumulated Delta-Range signal is derived which corresponds to an accurate position for each satellite to the degree desired.
a) receiving the transmitted satellite carrier frequency signals;
b) processing said satellite signal through a receiver means capable of identifying and tracking each of the satellites according to their transmitted carrier frequency signals;
c) deriving an output signal from said receiver means which is characteristic of Delta-Range information for each of said satellites;
d) processing said output signal through a data accumulation and storage means, deriving an Accumulated Delta-Range information signal, by storing said signal for a pre-determined time interval, creating an Accumulated Delta-Range information signal corresponding to each satellite;
e) repeating said step (d) to further refine the signal so processed, whereby an Accumulated Delta-Range signal is derived which corresponds to an accurate position for each satellite to the degree desired.
13. The method of Claim 12, wherein the Accumulated Delta-Range signal derived as a result of steps (d) and (e) is further repeatedly processed through a Kalman Filter to correlate said accumulated signals and correct the information derived, so information obtained from signal processing is further refined and more accurately presented.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000494119A CA1254637A (en) | 1985-10-29 | 1985-10-29 | Enhanced global positioning system delta-range processing |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000494119A CA1254637A (en) | 1985-10-29 | 1985-10-29 | Enhanced global positioning system delta-range processing |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1254637A true CA1254637A (en) | 1989-05-23 |
Family
ID=4131740
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000494119A Expired CA1254637A (en) | 1985-10-29 | 1985-10-29 | Enhanced global positioning system delta-range processing |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1254637A (en) |
-
1985
- 1985-10-29 CA CA000494119A patent/CA1254637A/en not_active Expired
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| US4646096A (en) | Enhanced global positioning system Delta-Range processing | |
| US5467282A (en) | GPS and satellite navigation system | |
| AU637747B2 (en) | P-code-aided global positioning system receiver | |
| US4912475A (en) | Techniques for determining orbital data | |
| CA2298213C (en) | Receiver calibration technique for global orbiting navigation satellite system (glonass) | |
| AU622688B2 (en) | Global positioning system receiver with improved radio frequency and digital processing | |
| CA2188667C (en) | Global positioning system (gps) receiver for recovery and tracking of signals modulated with p-code | |
| US6441777B1 (en) | Signal structure and processing technique for providing highly precise position, velocity, time and attitude information with particular application to navigation satellite systems including GPS | |
| JP3012857B2 (en) | Demodulation circuit for wide area positioning system receiver | |
| EP1728094A2 (en) | Methods and apparatuses of estimating the position of a mobile user in a system of satellite differential navigation | |
| AU608491B2 (en) | Digital system for codeless phase measurement | |
| US4647935A (en) | Apparatus for determining the magnitude of phase discontinuities introduced into a received signal at known instants | |
| CA1309478C (en) | Techniques for determining orbital data | |
| CA1254637A (en) | Enhanced global positioning system delta-range processing | |
| WO1984001832A1 (en) | Method and apparatus for deriving pseudo range from earth-orbiting satellites | |
| Langley | GPS Receivers and the Observables | |
| Sada | Global positioning system | |
| US6172639B1 (en) | Signal structure and processing technique for providing highly precise position, velocity, time and attitude information with particular application to navigation satellite systems including GPS | |
| Stone et al. | Carrier phase integer ambiguity resolution using dual frequency pseudolites | |
| Abidin | 8 Fundamentals of GPS Signals and Data | |
| Jovancevic et al. | Open Architecture GPS Receiver | |
| Hui | On satellite signal processing techniques applicable to GPS geodetic equipment | |
| Brown et al. | Static point positioning with an L1, C/A code GPS receiver | |
| Greenberg | An Automatic Omega Navigation System for Submarines | |
| Langley | Satellite navigation |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |