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
  • G01S19/30—Acquisition or tracking or demodulation of signals transmitted by the system code related

Definitions

• Satellite positioning systems implement, for location, several satellites transmitting their positions by radio signals and a receiver placed at the position to locate estimating the so-called pseudo-distances, which separate it from the satellites from the times of propagation of signals from satellites received and performing localization by triangulation.
• the positions of the satellites are determined from a network of tracking ground stations independent of the positioning receivers. They are communicated to the positioning receivers by the satellites themselves by data transmission.
• the pseudo-distances are deduced by the positioning receivers from the apparent delays presented by the signals received with respect to the clocks of the satellites which are all synchronous.
• Current and planned satellite positioning systems in the near future use, for radio signals emitted by their satellites the technique of bandwidth by modulation using sequences pseudo-random binaries, technique known as DSSS (acronym taken from the Anglo-Saxon: "Direct Sequence Spread Spectrum").
• This DSSS modulation consists, after having put the information to be transmitted in the form of a series of binary elements at regular rate, to carry out the product of each information binary element with a pseudo-random binary sequence of significantly faster rate .
• the band spread obtained is proportional to the ratio of the bit rates of the sequence of information bits and of the pseudo-random bit sequence spread.
• each pseudo-random binary sequence used for frequency spreading is made up of binary elements of the same duration taken equal to whole multiples of the periods of the transmission carriers while the different bit rates and frequencies used within the satellites are synchronized and derive from a common clock of high precision.
• the binary information contained in a satellite radio signal from a positioning system is extracted by two demodulations carried out in an entangled fashion, a first demodulation using a carrier generated locally by an oscillator controlled by a loop loop.
• frequency tracking and so-called PLL phase (acronym taken from the Anglo-Saxon: "Phase Loc Loop") allowing the signal received to be transposed into baseband and a second demodulation using locally generated pseudo-random binary sequences by a generator of pseudo-random binary sequences controlled by a tracking loop in time called DLL (acronym drawn from the Anglo-Saxon: Delay Lock Loop) allowing to despread the sequence of binary information present in the received signal.
• the propagation times of the received signals are manifested, on reception, by delays affecting the pseudo-random binary sequences present in the received signals and the carrier modulating the received signal.
• the delays affecting the pseudo-random binary sequences are accessible, modulo the duration of one of their binary elements, at the level of the control signals of the tracking loops in DLL time.
• the delays observed by these loops allow unambiguous or weakly ambiguous measurements, propagation times of the pseudo-random binary sequences because the numbers of entire pseudo-random sequences flowing during the signal paths are relatively small. We are talking about code measures.
• the shortest pseudo-random binary sequence that used for spreading signals from type C / satellites A (acronym from Anglo-Saxon: "Coarse / Acquisition Code or Clear / Aquisition Code), is composed of 1023 binary elements with a bit rate of 1.023 MHz and a duration of one millisecond. Its total duration corresponds to a 300 Kms path for a radio wave and allows modulo distance measurements of 300 Kms. The duration of 1 microsecond of each of its binary elements allows an accuracy of the order of 0.1 microseconds in the measurement of its delay at reception corresponding to a path of 30 meters for a radio wave.
• the ambiguity of the pseudo-distance measurements obtained from the pseudo-random binary sequence of a C / A code due to the fact that we are dealing with modulo measurements 300 Km is easy to lift as soon as the receiver receives more than four satellites because it can then make different points on the same position from different sets of four satellites and only retain the common solution. In the absence of such a possibility, the ambiguity can also be resolved using a very rough prior knowledge of the position. Such measurement ambiguity does not arise with P type satellite signals from the GPS system which use a pseudo-random binary sequence of 266.41 day duration for their spreading, but these signals are not freely available to users.
• FIG. 1 shows the block diagram of a state-of-the-art satellite positioning receiver.
• the receiver comprises a correlator channel 10 attacked by the received signal, coming on the one hand from the positioning satellites visible by the antenna of the receiver, and on the other hand from a disturbing source.
• the correlator channel 10 comprises a correlation channel 12 in phase and in quadrature between the received signal Sr and two respective local carriers F
• NCO p digital control of carrier 14
• the signals I, Q at the output of the carrier correlation channel are then correlated in a code correlation channel 16 with the local, point and delta codes, of the satellite considered, supplied by a digital local code generator 18.
• the correlations of code are then integrated by a respective integrator 20 to supply signals lp, l ⁇ ) Qp, Q ⁇ at the output of the correlator channel 10.
• Satellite radionavigation requires means on the ground (ground segment) in order to control and correct the signals transmitted by the satellites.
• Ground stations in particular use reception means which provide code and carrier measurements. These measurements must be extremely precise as they contribute to the ultimate performance of the system.
• the idea of the invention is based on the use of additional correlation channels in addition to the correlation channel of the signal received from a satellite in order to estimate in real time the inter-correlation errors, in code and in carrier, between the satellite concerned and any other satellite; which is also pursued on other channels and of which we therefore also know the position of the code and phase of the carrier. These estimated errors can thus be corrected very simply in the tracking loops.
• a code correlation channel from the signals I, Q at the output of the carrier correlation channel in phase and in quadrature, with the local codes of the received satellite, supplied by a digital generator of local codes;
• the local codes of the satellite received for the code correlation channel are a point and delta code.
• the code correlation channel in fact comprises two correlation channels: - a point channel (l P , Q P ), - a delta channel (l ⁇ , Q ⁇ ),
• the local codes of the satellite received for the code correlation channel are an advance, point and delta code.
• the code correlation channel actually comprises three correlation channels: - a forward channel (, QA),
• the receiver comprises N reception subsets Si.
• Each correlator channel Cii of received signal is attacked by its reception input Er by the received signal Sr.
• Each of the additional correlator channels of a subset Si receives respectively, on the one hand, at its received signal input Er, a local Slox signal resulting from the modulation of the local carrier F
• FIG. 2 shows a subset of a receiver according to the invention receiving N satellites
• - Figure 3 shows a receiver, according to the invention, for three satellites.
• - Figure 4 shows a correlator channel operating in baseband;
• - Figure 5 shows a subset of the receiver according to the invention operating in baseband
• - Figure 6 shows a baseband receiver, according to the invention, for three satellites
• FIG. 2 shows a subset of a receiver according to the invention receiving N satellites.
• the receiver comprises N reception subsets for the N satellites received.
• Each of these additional correlating channels Cix receives respectively, on the one hand, at its received signal input, a local signal Slox resulting from the modulation of the local carrier F
• the carrier correlation channel 12 in phase and in quadrature between the received signal and two respective local carriers in quadrature
• the code correlation channel 16 on the basis of the signals I, Q at the output of the carrier correlation channel in phase and in quadrature with the local point codes Cpi and delta ⁇ i of the satellite of order i; - an integrator to supply signals lp ix , l ⁇ ix, Qp ⁇ x, Q ⁇ ix at the output of the correlator channel.
• the integrator of the correlator channel Cii of received signal provides signals Ip ⁇ , hii, QPII, Q ⁇ II -
• the subset Si also includes: - an oscillator with digital carrier control OPi (NCO p) to provide local carriers F ⁇ , FQI for the N correlators of the subset Si considered and a digital generator of local codes OCi (NCO c) to provide local codes, punctual Cpi and delta ⁇ i, for the N correlators of the subset Si considered;
• OPi digital carrier control
• NCO c digital generator of local codes
• a multiplier Mi providing, for the other subsets Sx of the receiver, a local signal Sloi, resulting from the modulation of the local carrier F ⁇ by the point code Cpi of the subset Si considered, to effect the correlation of code modulated by the carrier of the satellite considered with the codes modulated by the carrier of the other satellites;
• a correlation corrector CRi supplying from the signals Ipix, I ⁇ I X , QPIX, Q ⁇ I X (X taking, for these signals l Pix , l ⁇ ix , Q Pix , Q ⁇ ix , the values 1 to N) at the output of the N channels correlators of the subset considered Si and of the signals Ip ⁇ , Q Pxx at the output of the channels correlators of the signal received from the other subsets Sx, with x different from i, of the corrected signals l Pi ',
• a carrier discriminator DPi providing, through a carrier loop corrector CBPi, a control signal Vcpi of the numerically controlled carrier oscillator (NCO p) to provide local carriers F ⁇ , FQJ for the N correlators of the subset If considered;
• a code loop discriminator DCi supplying, through a code loop corrector CBCi, a control signal Vcci of the digital local code generator OCi (NCO c) to supply the local, punctual codes Cpi and delta ⁇ i for the N correlators of the subset If considered.
• FIG. 3 shows a receiver for three satellites comprising a first S1, a second S2 and a third S3 reception subsets having three correlating channels each.
• the reception sub-assemblies S1, S2 and S3 comprise the same elements as the detailed sub-assembly of FIG. 2.
• the first S1, second S2, and third S3 subsets of the receiver of FIG. 3 respectively comprise a first C11, a second C22 and a third C33 signal correlator channels attacked at their reception input Er by the signal Sr received by the receiver, each subset further comprising:
• each correlator of each of the subsets Si comprises:
• the code correlation channel 16 on the basis of the signals I, Q at the output of the carrier correlation channel in phase and in quadrature with the local, point codes Cp1, Cp2, Cp3 and delta ⁇ 1, ⁇ 2, ⁇ 3 from the satellites, respectively of order 1, 2, 3, supplied by a digital generator of local codes OC1, OC2 and OC3, respectively for each subset;
• Each subset of three correlators includes:
• a corrector Cr1, Cr2, Cr3 of correlations providing from the signals l Pjx , l ⁇ ix , Q P
• a code loop discriminator DC1, DC2, DC3 providing respectively through a code loop corrector CBC1, CBC2, CBC3 a respective control signal Vcc1, Vcc2, Vcc3 of the digital local code generator OC1, OC2, OC3 (NCO c) to supply the local point and delta codes, Cp1, ⁇ 1 for the three correlators of the first subset S1, Cp2, ⁇ 2 for the three correlators of the second subset S2 and Cp3, ⁇ 3 for the three correlators of the third subset together S3.
• the receiver in Figure 3 is configured to make the following corrections:
• lpi '+ jQpi' lpn + jQpn - Ip22 CP12 + JQP12) - 2 / T— Ip3 3 (Ipi3 + jQp *
• I P ⁇ [l £ A ode (t + r,). Sin ( ⁇ f + ⁇ ) + A 2 .code 2 (t + ⁇ 2) .six ⁇ (cot + ⁇ 2) +
• TI p i [ signai received satemte . (t)] [local code ⁇ . fe 1 (t). local carrier in phase ⁇ . ⁇ (t)] dt
• TQ p [[signal received satemel t)] [local code sateime ⁇ if).
• I PX ' j [A x .code (t + T,). sin ( ⁇ f + ⁇ x )] [code x (t + ⁇ x ). ⁇ x ⁇ (cot + ⁇ )] dt
• I PX ' I P ⁇ A 2 ⁇ [code 2 (t + ⁇ 2 ). sin ( ⁇ t + ⁇ 2 )] [code x (t + ⁇ ). sin (û # + ⁇ x )] dt - o
• Ip3 + jQp3 ' IP33 + JQP33 "(IP11 + jQpil) (lp31 + jQp3l) / - (lp22- jQp22) (' p32 + jQp32) / T l ⁇ 3 '+ JQ ⁇ 3 -' ⁇ 33 + J ⁇ 33 _ (lpi1 + JQPH) (' ⁇ 31 + jQ ⁇ 3 (Ip22 _ JQP22) (' ⁇ 32 + JQ ⁇ 32) / T
• Ipi 'Pu - ⁇ surx different from i (Ipxx - Ipix "Qpxx • Qpix) - 2 / T
• Qpi Qpii - ⁇ surx different from i (Ipxx -Qpix + Qpxx • Ipix) - 2 / T
• the index ii addresses the correlator channel Cii of the subset Si which processes the received signal, different from the other correlator channels Cix of the subset Si which, in turn, process the local signals of the other satellites of respective order x, coming from the correlator channels Cxx of the other subsets Sx.
• the correlator channels are attacked in baseband with signals I and Q.
• FIG. 4 shows a correlator channel 50 operating with a signal received Br in baseband.
• the correlator channel 50 in baseband comprises a correlation channel 52 in phase and in quadrature between the signal received in baseband, in the form of two signals I and Q in quadrature, and two respective local carriers Fi, FQ.
• These local quadrature carriers are generated by a numerically controlled oscillator of carrier 54 (NCO p) of the receiver.
• the signals I, Q at the output of the carrier correlation channel are then correlated in a code correlation channel 56 with the local codes, punctual Cp and delta ⁇ , supplied by a digital local code generator 58.
• the code correlations are then integrated by a respective integrator 60 to supply signals l P , l ⁇ , Q P ⁇ Q ⁇ at the output of the correlator channel 50.
• FIG. 5 shows a subset of rank i of the receiver according to the invention operating in baseband.
• the baseband receiver comprises N reception subsets for N satellites received.
• the subset Si further comprises: - an oscillator with numerically controlled carrier OPi (NCO p) for supplying carriers local Fn, FQI for the N correlators of the subset Si considered and a digital generator of local codes OCi (NCO c) to supply the local codes, punctual Cpi and delta ⁇ i, for the N correlators of the subset Si considered; a first Mli and a second multiplier MQi providing for the other subsets of the receiver a first Slli and a second SIQi local signals resulting from the modulation of the quadrature signals Fn and FQI of the local carrier by the punctual code Cpi of the sub- set considered, for performing the correlation of code modulated by the carrier of the satellite considered with the codes modulated by the carrier of the other satellites;
• NCO p numerically controlled carrier
• NCO c digital generator of local codes
• a corrector CRi of correlation supplying from the signals Ipix, I ⁇ IX, Qpix, Q ⁇ IX at the output of the N correlating channels of the subset considered Si and of the signals lp ⁇ , Qp ⁇ at the output of the correlating channels of the signal received from the other subsets Sx, with x different from i, of the corrected signals l Pi ', l ⁇ i', Qpi ', Q ⁇ i'.
• a carrier discriminator DPi supplying, through a carrier loop corrector CBPi, a control signal Vcpi of the numerically controlled carrier oscillator (NCO p) to supply local carriers Fn, FQI for the N correlators of the subset If considered;
• a code loop discriminator DCi supplying, through a code loop corrector CBCi, a control signal Vcci of the digital local code generator Oci (NCO c) to supply the local, point codes Cpi and delta ⁇ i for the N correlators of the subset If considered.
• FIG. 6 shows a baseband receiver for three satellites Sat1, Sat2 and Sat3 comprising a first S1, a second S2 and a third S3 reception subsets having three correlating channels each.
• the reception subsets S1, S2 and S3 include the same elements as the detailed subset of FIG. 4 operating in baseband.
• the receiver of figure 6 is configured to carry out the same corrections as those of the receiver of figure 3 except that one replaces T / 2 by T in the formulas of correction.
• the receiver according to the invention uses three code correlators:
• the third satellite 3 nothing more is calculated than (Ip, l ⁇ , Qp,
• IPH and Qp in the formulas estimation of the complex amplitude of the signals received respectively from the satellites i, do not take into account the corrections. In order to improve accuracy, we could replace them with IPI 'and Q Pi ' in the formulas. In this case, they become:
• n (Ipii + j Qpii) n ⁇ ⁇ surx different from i (lp ⁇ '+ jQp ⁇ ') n-1.
• (I ⁇ Î '+ j Q ⁇ Î ') n (I ⁇ + j Q ⁇ U) n _ ⁇ surx different from i (lp ⁇ ' + jQp ⁇ ') n-1.
• the iteration indexed by n can be either in time, corresponding each time to new data, or that of a recursive computation converging towards the ideal solution.
• the received signal is filtered (limited spectrum)
• a first satellite is acquired, without correction, by a conventional open-loop search process, well known to those skilled in the art.
• we move on to tracking we deduce the local signal from this first satellite and we correct the inter-correlations on the other channels in the research phase (in open loop). This makes it possible to acquire the weakest satellites (last) by reducing the risk of being wrong because of a correlation with the signal of another more powerful satellite.
• the correlation corrections are calculated and applied to the measurements of all the other satellites already tracked.
• the receiver according to the invention has excellent stability. Indeed, because the inter-correlation coefficients are much less than 1 (-24 dB for C / A codes), the tracking loops are stable and converge towards a state where there is no longer any cross-correlation error.
• the receiver according to the invention allows the estimation of the intercorrelation errors in real time, on the accumulated I and Q punctual samples and deltas, thanks to additional channels, by correlation between the local codes of the tracked satellites and the correction cumulative I and Q samples and deltas before the carrier phase and code discriminators.
• the receiver according to the invention completely eliminates the inter-correlation errors between all the satellites whose signal is continued, in steady state, after a rapid convergence phase. Residual errors, due to thermal noise and loop dragging, depend on the signal-to-noise ratio, dynamics and loop bands. For applications with very low dynamics (ground station) the gain of the method can be very significant, reducing the measurement error from a few meters to a few tens of centimeters, or a factor of 10.

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• 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)

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• 2002
  • 2002-08-13 FR FR0210276A patent/FR2843638B1/fr not_active Expired - Fee Related
• 2003
  • 2003-07-18 US US10/521,107 patent/US7064707B2/en not_active Expired - Fee Related
  • 2003-07-18 EP EP03756500A patent/EP1529221A2/de not_active Withdrawn
  • 2003-07-18 CA CA002494519A patent/CA2494519A1/fr not_active Abandoned
  • 2003-07-18 WO PCT/FR2003/002288 patent/WO2004017089A2/fr not_active Ceased

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