Double estimator. A new receiver principle for tracking BOC signals (797924), страница 4
Текст из файла (страница 4)
The effect isreadily reproduced as seen in Figure 12and is revealed by a corresponding offset in the steady state differences, whichis not an integer multiple of TS. Becauseits two estimates are independent thedouble estimator has the potential toestimate this difference by longer termaveraging. This means that one coulddesign an automatic calibration in thesignal processing in order to compensatefor this effect.Another key performance measureof particular interest is that of the multipath.
The simplest method of evaluating the multipath error performance isto consider the effect of a single interfering multipath signal with variousrelative time delays. This provides onlya worst-case analysis of error due to multipath but does provide an adequate performance measure with which we cancompare BOC tracking schemes.Figure 13 shows the multipath errorenvelopes of a conventional BOC receiver and the dual estimator for a BOC(2,1)signal. The dual estimator error envelopeis computed by analyzing the error ofthe corrected SLL delay estimate withmultipath interference.We can see the relative performanceof each scheme by computing the running average error across the dataset,sp ring 2008as shown in Figure 14.
The pattern ofthe dual estimator multipath envelopebroadly follows that of the conventionalreceiver but does show a small improvement (8.2 percent) across the wholedataset.Experimental testSurrey Satellite Technology was responsible for construction and control of thefirst test satellite GIOVE-A (Galileo InOrbit Validation Element) for the Galileo project on behalf of the EuropeanSpace Agency (ESA).
Subsequently, withthe cooperation of ESA, some of the signals were monitored at the University ofSurrey.After testing its feasibility on simulated bench source signals, the GIOVE ABOC(1,1) signal-in-space transmissionwas monitored, with a research-developed single-chip receiver with properties as described in Table 1.The signal was successfully acquiredon June 26, 2006, at 19.57 GMT with anestimated receiver carrier-to-noise density ratio of 45 dBHz. Figure 15 showsthe corresponding I/Q plot taken fromGIOVE-A tracking. We have demonstrated, therefore, that the principle ofdouble estimation works in practice, forone particular BOC modulation.DevelopmentThe relative simplicity of a GNSS receiver architecture based on the double estimating concept provides an attractivechoice for the designer.
In particulara double estimating receiver is comwww.insidegnss.com325SLL error (sub-chips)DLL error (sub-chips)Corrected error-¼ sub-chip10-110Ranging error (m)Timing Error2Dual estimator BOC(2,1)Early-minus-late BOC(2,1)20σNSm| |0σCONVm××-100100200300400-25 -2050000Loop iterationsShowing effect of delay distortion on the sub carrier offset by¼ sub-chip50100FIGURE 12150200 250 300metMultipath delay (m)350 400366.569Multipath error envelope of a conventional and dual estimatingBOC receiver, BOC(2,1), TDC = TDS = TSFIGURE 13Dual estimator BOC(2,1)Early-minus-late BOC(2,1)2020× 10�1.5RunAv(RT)15| |RunAv(RC)××10Estimated carrier to noise density = 45.07 dB=Hz10.50QRunning average error (m)22.959 255-0.50-1.5-10050100150200 250 300metMultipath delay (m)350 400366.569-2-2Running average multipath error of a conventional (blue line)and dual-estimating BOC receiver TDC = TDS = TS for BOC(2,1),FIGURE 14patible with the leading unambiguousBOC search technique named by itsoriginator as “replica code design” (fora further discussion of this technique,see the paper by P.
Ward in AdditionalResources.)Adoption of this search techniquewill deliver a common start value to thesubcarrier delay estimate and the codeestimate within the range ±TC i.e. initially = . A double estimating receiverrequires little more than uncoupling ofthese initial estimates under command,allowing the two independent trackingestimates to emerge as expected in Equation 3, and requiring then a roundedinteger correction according to Equation 4. All other proposed BOC trackingtechniques will require additional hardware resources to become compatiblewith this excellent search technique.www.insidegnss.com FIGURE 15-1.5-10I0.511.52× 10�I/Q plot GIOVE-A in PLL modeBOC (1,1) RF receiverThe hardware required for the dualestimator and the leading BOC tracking techniques is compared in Table 2for correlator designs requiring fullyincoherent operation.The double estimator and the bumpjumping (VE -VL) algorithm both makeefficient use of a receiver’s hardwareresource.
Admittedly we use two additional multipliers and the additionallocal oscillator when compared to thatReceiver type-0.5MultipliersRF Front EndA double super-heterodynereceiver for the GNSS L1/E1bandSampling Frequency16.367 MHzIF4.188MHzCorrelatorFPGAProcessorLeon3 Sparc V8 (FPGA basedSignals ReceivedGalileo L1-B/C — BOC(1,1)TABLE 1.Tested receiver characteristicsIntegratorsLocal oscillatorsLow pass filtersSingle-sideband2×Carrier, 4×Code41×Carrier, 1×Code2Multiple Gate Discriminator(N=4)2×Carrier, 18×Code181×Carrier, 1×Code0Bump Jumping2×Carrier, 10×Code101×Carrier, 1×Code0Dual Estimator2×Carrier, 4×Subcarrier8×Code81×Carrier, 1×Subcarrier,1×Code0TABLE 2.Hardware requirements of BOC tracking techniquessp ring 2008InsideGNSS35double estimatoralgorithm. However, the additionalmultipliers are one-bit, and thereforethe limiting factor in designs will be thenumber of storage elements used (integrators).
A double estimator receiveruses two less integrators per channelthan the VE-VL algorithm. Examplesof hardware resource utilization for aprototype BOC receiver are given in thepaper by P. D. Blunt.grateful to the Research & EnterpriseSupport unit of the University of Surreyfor continuing assistance and professional advice.[7] Hodgart, M. S and P. D. Blunt, “A Dual estimatereceiver of Binary Offset Carrier (BOC) modulatedsignals for global navigation satellite systems”Electronics Letters.
Vol. 43, No. 16, August 2007p 877 (with errata)Manufacturers[8] Kovar, P., and F. Vejrazka, L. Seidl L, and P.Kacmarik, “Galileo Receiver Core Technologies,”Journal of the Global Positioning Systems, Vol. 4,No. 1–2, pp. 176–183The receiver developed using the BOCtracking technique described in thisarticle used the NJ1006A RFIC fromNemeriX, Manno, Switzerland. TheSimulations indicate that, in principle, the receivershould be able to cope with the European BOC(15, 2.5)signal on which difficulties have been reported usingthe bump-jumping technique.
Development has begunto demonstrate this in practice.ConclusionThe double estimator has been demonstrated to work through extensive simulation, with bench tests on a BOC(1,1)signal generated by an SSTL-built Galileo signal generator, and finally with livesignals from the GIOVE-A satellite.Many experimental tests on thesereal BOC signals confirm that convergence of a double-estimator triple-loopreceiver is smooth and stable. Performance in noise and multipath seemssatisfactory. The design is believed tobe inherently tolerant and adaptive togroup delay distortion.Simulations indicate that, in principle, the receiver should be able to copewith the European BOC(15, 2.5) signalon which difficulties have been reported using the bump-jumping technique.Development has begun to demonstratethis in practice.A patent application was initiallyregistered to the University of Surreyin the name of the inventors (Hodgartand Blunt) Reg.
no GB0624516.1. Aninternational patent application wassubsequently filed and has been recentlypublished.AcknowledgementsSome of this research was supportedby the Location and Timing Knowledge Transfer Network, EPSRC, SurreySatellite Technology Limited and Surrey Space Centre. The authors are also36 InsideGNSS test receiver developed using the BOCtracking technique described in thisarticle used the NJ1006A RFIC fromNemeriX, Manno, Switzerland. The correlators were implemented on a Spartan3 FPGA from Xilinx, San Jose, California, USA. The control of the receiver’stracking loops was achieved using theLeon SPARC V8 processor from GaislerResearch, Gotenborg, Sweden.Additional Resources[1] Bello, P. A., and R.L. Fante, “Code Tracking Performance for Novel Unambiguous M-Code TimeDiscriminators,” Proceedings of ION NationalTechnical Meeting 2005, San Diego, California,USA, January 2005[2] Betz, J.
W., “The Offset Carrier Modulation forGPS Modernization,” Proceedings of the ION 1999National Technical Meeting, San Diego, California,USA, January 1999[3] Betz, J. W., “Binary Offset Carrier Modulationsfor Radionavigation,” Navigation: Journal of theInstitute of Navigation, Vol. 48, No. 4, winter2001[4] Blunt, P. D., “Advanced Global NavigationSatellite System Receiver Design,” Ph.D Thesis,University of Surrey, May 2007[5] Blunt P. D, and R. Weiler, M.
S. Hodgart, and M.Unwin, “Demonstration of BOC(15,2.5) Acquisitionand Tracking with a Prototype Hardware Receiver,”European Navigation Conference, Geneva, May2007[9] Simsky A., and J-M. Sleewaegen, M. Hollreiser., and M. Crisci, “Performance Assessment ofGalileo Ranging Signals Transmitted by GSTB-V2Satellites,” Proceedings of ION GNSS 2006, FortWorth, Texas, September 2006[10] Ward, P. W. “A design technique to removecorrelation ambiguity in binary offset carrier(BOC) Spread spectrum signals,” ION 59th AnnualMeeting/CIGTF 22nd Guidance Test Symposium,Albuquerque, New Mexico, USA, June 2003AuthorsDr. M.
![](https://s.studizba.com/z.php?f=/templates/si/i/noavatar.png&w=100&h=100&t=1"){kind=avatar}
