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WO1998039667A1 - Procede et recepteur de navigation par satellite pour determiner un lieu geographique - Google Patents

Procede et recepteur de navigation par satellite pour determiner un lieu geographique Download PDF

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Publication number
WO1998039667A1
WO1998039667A1 PCT/IB1998/000113 IB9800113W WO9839667A1 WO 1998039667 A1 WO1998039667 A1 WO 1998039667A1 IB 9800113 W IB9800113 W IB 9800113W WO 9839667 A1 WO9839667 A1 WO 9839667A1
Authority
WO
WIPO (PCT)
Prior art keywords
satellite
signals
data signals
received
base band
Prior art date
Application number
PCT/IB1998/000113
Other languages
English (en)
Inventor
Kenneth Ronald Whight
Andrew Thomas Yule
Original Assignee
Koninklijke Philips Electronics N.V.
Philips Ab
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by Koninklijke Philips Electronics N.V., Philips Ab filed Critical Koninklijke Philips Electronics N.V.
Publication of WO1998039667A1 publication Critical patent/WO1998039667A1/fr

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
    • 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
    • G01S19/38—Determining a navigation solution using signals transmitted by a satellite radio beacon positioning system
    • G01S19/39—Determining a navigation solution using signals transmitted by a satellite radio beacon positioning system the satellite radio beacon positioning system transmitting time-stamped messages, e.g. GPS [Global Positioning System], GLONASS [Global Orbiting Navigation Satellite System] or GALILEO
    • G01S19/42—Determining position

Definitions

  • the present invention relates to a method of, and satellite navigational receiver for determining a geographical location.
  • NAVSTAR GPS satellite based global positioning system
  • the NAVSTAR GPS is described in NATO Standardisation Agreement STANAG 4294 "NAVSTAR global positioning system GPS system characteristics - preliminary draft" but a brief summary of the system is included here.
  • the NAVSTAR GPS consists of a number of satellite vehicles in approximately 12 hour, inclined orbits of the earth, each satellite transmitting continuous positional information.
  • Two positioning services are provided by NAVSTAR, the precise positioning service (PPS) which is reserved for military use and the standard positioning service (SPS) which is available for general use. The following description is confined to the SPS although some features are common to both systems.
  • a user of the GPS receives the transmissions from those GPS satellite vehicles currently in view and calculates their correct positions. Details of these calculations, using an Earth-Centred, Earth-Fixed (ECEF) reference system are given in the STANAG document.
  • ECEF Earth-Fixed
  • the user's clock is said to be in error (in other words, different from satellite vehicle time) by a clock bias C B .
  • C B clock bias
  • the redundancy can be used to solve for C B and the three accurate propagation times required can be calculated.
  • the ranges of the user from the satellite vehicles are equal to the signal propagation times multiplied by the speed of light c.
  • the apparent ranges of the satellite vehicles Prior to correction for the user's clock bias C B , the apparent ranges of the satellite vehicles are all in error by a fixed amount and are called pseudoranges.
  • Figure 1 of the accompanying drawings shows a radio receiver 16 in a user's vehicle 15 receiving signals from four GPS satellite vehicles 11 , 12, 13 and 14.
  • the four pseudoranges of the satellite signals are denoted R1 , R2, R3 and R4.
  • the positions of the satellite vehicles and the user's vehicle are shown as three-dimensional coordinates whose origin is the centre of the earth.
  • Figure 2 of the accompanying drawings shows the equations used by a GPS receiver to calculate the three dimensional coordinates and the clock bias C B from a knowledge of four satellite vehicle positions and their respective pseudoranges.
  • the data transmitted by each satellite vehicle consists broadly of three sets of information, the ephemeris, the almanac and the clock correction parameters.
  • the ephemeris consists of detailed information about the satellite vehicle's own course over a period of a few hours
  • the almanac consists of less detailed information about the complete satellite vehicle constellation for a longer period
  • the clock correction parameters allow the user to correct for the GPS satellite vehicle's own clock errors.
  • the positions of the satellite vehicles are calculated from the GPS ephemeris data and the Keplerian Orbital Parameters which are used to describe the orbit of each satellite vehicle.
  • the satellite vehicle transmissions consist of a direct sequence spread spectrum (DSSS) signal containing the ephemeris, almanac, and the clock correction information at a rate of 50 bits per second (bps).
  • DSSS direct sequence spread spectrum
  • PRN pseudo random noise
  • the PRN signal is known as a coarse/acquisition (C/A) code since it provides the timing marks required for fast acquisition of GPS signals and coarse navigation.
  • the signals received at a user's receiver have a bandwidth of approximately 2MHz and a signal to noise ratio (S/N) of approximately -20dB.
  • the GPS signals are received with a Doppler frequency offset from the GPS centre frequency.
  • a stationary GPS receiver has to be capable of receiving signals with frequencies of up to +4KHz from the GPS centre frequency, and a mobile receiver (as is usually the case) has to be able to receive signals over an even greater frequency range.
  • the GPS receiver must cancel or allow for the Doppler frequency offset and generate the C/A code relevant to each satellite vehicle. Initially, at least, this can be very time consuming since to despread the DSSS signals, the incoming and locally generated PRN codes must be exactly at synchronism.
  • the receiver To find the PRN code delay the receiver must compare the locally generated code and the incoming code at a number of different positions until the point of synchronism or correlation is found. With a code length of 1023 chips this comparison can be a lengthy procedure. However, once the frequency offset and the PRN code delay for each satellite vehicle are known, tracking them is relatively easy.
  • the receiving apparatus comprises hand held devices as well as vehicle borne apparatus, factors such as unit costs and running costs are assuming a greater importance.
  • Implementing the receiving apparatus as integrated circuits helps reduce both types of cost factors but the currently used method for carrying out the high accuracy geometric calculations for a receiver to determine the positions of the satellite vehicles from the ephemeris data usually involves 64 bit double precision floating point numbers requiring a relatively large processor to do the calculations which is expensive from the points of view of the cost of the device, the time required to do the calculations and the electrical power consumed.
  • An object of the present invention is to expedite the calculation of the positions of the satellite vehicles in a satellite navigation system.
  • a method of determining a user position fix in a satellite navigation system comprising receiving encoded data signals transmitted by a plurality of orbiting navigational satellite vehicles, said data signals including ephemeris information which can be used to determine the relative position of each satellite vehicle whose data signals are being received, decoding the received signals to provide base band signals and determining the user position fix by processing the base band signals using fixed point arithmetic to calculate the relative position of each satellite vehicle from the ephemeris information contained in the received data signals.
  • a satellite navigational receiver comprising signal receiving means for receiving encoded data signals from a plurality of orbiting navigational satellite vehicles, said data signals including ephemeris information which can be used to determine the relative position of each satellite vehicle whose data signals are being received, decoding means for decoding the encoded signals and base band signal processing means, characterised in that the base band signal processing means comprises a fixed point arithmetic processing means to calculate the relative position of each satellite vehicle from the ephemeris information contained in the received data signals.
  • the present invention is based on the realisation that by carrying out each step in the calculation at an appropriate, predefined level of accuracy, the processing time drops by an order of magnitude. Further the calculations can be done using 32 bit integer arithmetic which is far easier to implement on a 16 bit microprocessor than 64 bit double precision floating point arithmetic. Thus not only is the microprocessor cheaper but also the amount of electrical power is reduced, which is of particular importance with portable, battery powered apparatus, because the calculations are carried out quicker.
  • all the distances may be represented by non-standard units, for example 1/64 of a metre, which will enable any value of interest to be stored as a 32 bit integer.
  • Figure 1 is a diagrammatic representation of an electronic navigation system
  • Figure 2 shows the four equations for use in a satellite navigation receiver in calculating three dimensional coordinates and the clock bias C B
  • Figure 3 is a block diagram of the main components of a satellite navigational receiver made in accordance with the present invention.
  • FIG. 4 is a block diagram of the base band processing stage included in the receiver shown in Figure 3.
  • the satellite navigational receiver shown in Figure 3 comprises an antenna 20 generally implemented as a small metal patch which collects respective spread spectrum signals from the orbiting satellite vehicles (not shown).
  • the signals are right-hand circularly polarised on a 1575.42MHz carrier.
  • An rf front end 22 is coupled to the antenna 20.
  • the front end is a comparatively simple analogue section including a local oscillator tuned to a local oscillator frequency which is used to frequency down-convert the received signals to a much lower IF.
  • a base band processing stage 24 is coupled to the rf front end 22 and comprises digital circuitry necessary to decode the respective spread spectrum signals from the satellite vehicles in view and to process the information to calculate the positions of the satellite vehicles and then a user position fix.
  • the base band processing stage 24 is shown in greater detail in Figure 4.
  • the stage 24 comprises custom hardware arranged as a number of parallel channels CH1 to CHn. Each channel is capable of tracking a signal transmitted by a single space vehicle. Outputs of the channels CH1 to CHn are coupled to a processor 26 which is implemented as an embedded microprocessor.
  • the processor 26 controls the channels and performs the position or location calculation.
  • the processor 26 may be implemented as a digital signal processor (DSP).
  • DSP digital signal processor
  • a user interface 28 is coupled to an output of the stage 24 and is implemented in a manner to suit a particular application.
  • the user interface 28 will comprise some form of display and man/machine means, for example a keypad (not shown), whereby a user controls the device.
  • the electronic navigation components 20, 22 and 24 are incorporated into a larger system, such as an automotive navigation system, the user interface 28 will comprise a connection to components in the larger system which has its own display and control devices.
  • the heart of a satellite navigation receiver lies in the baseband processing.
  • the custom digital channel hardware CH1 to CHn ( Figure 4) is used to acquire and track signals from a number of different satellite vehicles 11 to 14 ( Figure 1) (one satellite vehicle per channel).
  • All the satellite vehicles have on-board atomic clocks for synchronising their signals with each other, it is possible for the receiver to determine its relative range to each satellite vehicle by measuring the relative time of arrival of characteristic parts of these signals. Referring to Figure 1 , if, for example, the signal from satellite vehicle 11 arrives at the receiver 16 1ms before the signal from satellite vehicle 12, then satellite vehicle 11 must be 300 km closer to the receiver 16 than the satellite vehicle 12.
  • a receiver is tracking signals from four different satellite vehicles it is possible for it to use this timing information to determine its position in three dimensions, as well as obtaining an accurate (sub microsecond) absolute time. If the position of four satellite vehicles (X,, Y it Z,) and their relative ranges R; (where i has the values 1 to 4) can be determined, it is possible to express the actual range to the satellite vehicles, using an (as yet unknown) offset range
  • the basic concept is to carry out every step of the calculation at the appropriate (pre-defined) level of accuracy.
  • parameters that are measurements of distance or position need a range of +/-30, 000, 000m (defined by the orbital radius of the satellite vehicles and a resolution of a fraction of a meter. Therefore if all distances were represented using units of 1 /64th of a meter, that is about 1.5cm, a 32 bit integer could be used to store distance values (the range of a 32 bit integer is approximately +/-2,000,000,000; 2,000,000,000 times 1/64 is 32,000,000).
  • Another way of considering this matter is that the 32 bit integer is a 32 bit number with a fixed (binary) point after the 26th bit.
  • This concept can be expanded to every type of parameter used in the satellite vehicle position calculation (e.g. angles, times, etc) so that all values can be represented by a 32 bit integer, albeit with different implicit binary point positions.
  • the following table of parameters lists their appropriate accuracy and binary point position.

Landscapes

  • Engineering & Computer Science (AREA)
  • Radar, Positioning & Navigation (AREA)
  • Remote Sensing (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Position Fixing By Use Of Radio Waves (AREA)

Abstract

On décrit un procédé qui permet de déterminer la position d'un utilisateur dans un système de navigation par satellite. Le procédé consiste à recevoir des signaux de données codés transmis par une pluralité de véhicules satellites de navigation en orbite (11, 12, 13, 14) (lesdits signaux de données incluant des données des éphémérides qui peuvent être utilisées pour déterminer la position relative de chaque véhicule satellite dont les signaux de données sont reçus), à décoder les signaux reçus pour fournir des signaux bande de base, puis à déterminer la position de l'utilisateur par traitement des signaux bande de base par arythmétique fixe pour calculer la position relative de chaque véhicule satellite à partir des données des éphémérides contenues dans les signaux de données reçus.
PCT/IB1998/000113 1997-03-05 1998-01-29 Procede et recepteur de navigation par satellite pour determiner un lieu geographique WO1998039667A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB9704497.8 1997-03-05
GBGB9704497.8A GB9704497D0 (en) 1997-03-05 1997-03-05 Method of and satellite navigational receiver for determining a geographical location

Publications (1)

Publication Number Publication Date
WO1998039667A1 true WO1998039667A1 (fr) 1998-09-11

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PCT/IB1998/000113 WO1998039667A1 (fr) 1997-03-05 1998-01-29 Procede et recepteur de navigation par satellite pour determiner un lieu geographique

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WO (1) WO1998039667A1 (fr)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1336866A3 (fr) * 2002-02-19 2004-01-07 eRide, Inc. Stratégie de correction pour des récepteurs GPS

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0166300A2 (fr) * 1984-06-13 1986-01-02 Sony Corporation Récepteur pour un système de navigation par satellite du type GPS et méthode pour déterminer la position d'une station stationnaire utilisant ce récepteur
EP0447978A2 (fr) * 1990-03-20 1991-09-25 Pioneer Electronic Corporation Récepteur GPS
US5430657A (en) * 1992-10-20 1995-07-04 Caterpillar Inc. Method and apparatus for predicting the position of a satellite in a satellite based navigation system

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0166300A2 (fr) * 1984-06-13 1986-01-02 Sony Corporation Récepteur pour un système de navigation par satellite du type GPS et méthode pour déterminer la position d'une station stationnaire utilisant ce récepteur
EP0447978A2 (fr) * 1990-03-20 1991-09-25 Pioneer Electronic Corporation Récepteur GPS
US5430657A (en) * 1992-10-20 1995-07-04 Caterpillar Inc. Method and apparatus for predicting the position of a satellite in a satellite based navigation system

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
DOUGLAS A. MacDONALD et al., "Flexible Software Implementation for a Miniature Integrated GPS/INS Tactical System", ION GPS-96; PROCEEDINGS OF THE 9TH INTERNATIONAL TECHNICAL ..., Sept. 1996, (Kansas City), pages 1001-1008. *

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1336866A3 (fr) * 2002-02-19 2004-01-07 eRide, Inc. Stratégie de correction pour des récepteurs GPS

Also Published As

Publication number Publication date
GB9704497D0 (en) 1997-04-23

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