MBOC The new optimized spreading modulation (797940), страница 4
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The minimum double sided precorrelation bandwidth for a BOC(1,1) spreading symbol isapproximately 4 MHz – about twice that required for a C/Acode receiver [BPSK-R(1)]. For maximum multipathmitigation performance, the widest pre-correlation bandwidthprovides the best performance. The BOC(6,1) componentimproves the signal to noise ratio for multipath processing byup to 3.5 dB. For intermediate receiver precorrelationbandwidths, the new signals continue to provide equal orbetter performance than BOC(1,1) signals and near thoseavailable from a BOC(2,2) spreading symbol.
Compared toBOC(1,1), the MBOC options provide almost the sameperformance (within 0.4, 0.6, or 0.9 dB of power, dependingupon spreading time series implementation) to low-endreceivers.The first results of this joint design of TMBOC placement andspreading codes has been completed for L1C. The pattern ofBOC(6,1) spreading symbols is as shown in Fig.3. Thesidelobe levels for crosscorrelations between L1C pilot codes,using the original codes selected for BOC(1,1) spreadingmodulations, and a different set of codes from the same familyselected for TMBOC are shown in Fig. 16.
The results arecalculated using both even and odd crosscorrelations.Compared to the baseline spreading codes, the maximumcrosscorrelation level is reduced by 0.1 dB, and its probabilityof occurrence is reduced by a factor of 40. The sidelobe levelsat somewhat higher probability of occurrence are reduced bymore than 1 dB. Similar improvements are evident in Fig. 17for the autocorrelation sidelobes.Radio Frequency CompatibilitySince MBOC places more power at higher frequencies, it alsoprovides some additional benefits in radio frequencycompatibility. Compared to BOC(1,1), the MBOC(6,1,1/11)spectrum has 0.7 dB less self-interference, and 0.3 dB lessinterference to C/A code and SBAS receivers.Performance of Low-End ReceiversGPS L1C and GALILEO L1 OS signals are being designed tobenefit receivers that will make use of technology advances toattain better performance, while continuing to supportreceivers designed for minimal complexity.
For example,receivers that employ modest bandwidths and only use theBOC(1,1) spreading symbols may offer lower cost and891MITRE’s work was supported by the United States Air Forceunder contract FA8721-04-C-0001 and by the FederalAviation Administration under contract DTFA01-01-C-00001.Work by Thomas Stansell was supported by the United StatesAir Forces under contract number FA8802-04-C-0001 withThe Aerospace Corporation.SUMMARY AND WAY AHEADThis paper has described the optimized MBOC spreadingmodulation recommended for GALILEO L1 OS and GPSL1C. The MBOC design continues the trend in mostmodernized signal designs to provide more power at higherfrequencies (away from the center frequency) in order toimprove code tracking and some aspects of multipathperformance.
MBOC does this by adding a small fraction ofBOC(6,1) spectrum to the BOC(1,1) spectrum.REFERENCES[1] http://pnt.gov//public/docs/2004-US-EC-agreement.pdf[2] http://gps.losangeles.af.mil/engineering/icwg/Docs/EC%20and%20US%20Joint%20Statement%20on%20GALILEO%20and%20GPS%20Signal%20Optimization%20%20%2024%20Mar%2006.pdf[3] http://gps.losangeles.af.mil/engineering/icwg/Docs/WGA%20Signed%20Recommendation%20on%20MBOC%20%2023%20Mar%2006.pdf[4] Betz, J. W., ( 2002), ”Binary Offset Carrier Modulationsfor Radionavigation,” NAVIGATION: Journal of TheInstitute of Navigation Vol. 48, No.
4, Winter 2001/02.[5] Betz J. W. et al. (2002), “Candidate Design for anAdditional Civil Signal in GPS Spectral Bands,”Proceedings of ION NTM 2002 - 28-30 January, 2002 San Diego, CA[6] Pratt, A. R et al. (2003), “Performance of GPS GALILEOReceivers Using m-PSK BOC Signals”, Proceedings ofION 2003 – 9-12 September 2003, Portland, Oregon,USA[7] Hegarty, C. J.
et al. (2004), “Binary Coded SymbolModulations for GNSS,” Proceedings of ION-AM-2004,7-9 June 2004, Dayton, Ohio,USA.[8] Hein, G. W. et al. (2005), “A candidate for the GALILEOL1 OS Optimized Signal”, Proceedings of ION GNSS2005 – 13-16 September 2005, Long Beach, California,USA[9] Avila-Rodriguez, J.A.
et al. (2005), “Revised CombinedGALILEO/GPS Frequency and Signal PerformanceAnalysis”, Proceedings of ION GNSS 2005 – 13-16September 2005, Long Beach, California, USA.[10] Wallner S. et al (2005), “Interference Computationsbetween GPS and GALILEO”, Proceedings of ION GNSS2005 – 13-16 September 2005, Long Beach, California,USA[11] Pratt, A. R. et al. (2006), “Tracking Complex ModulationWaveforms – How to avoid Receiver Bias”, Proceedingsof IEEE/ION PLANS 2006 – 24-27 April 2006, SanDiego, California, USA.Since BOC(1,1) already has more high frequency power thanC/A code’s BPSK-R(1) spreading modulation, it alreadyprovides performance benefits over BPSK-R(1).
MBOCprovides additional benefits over BOC(1,1) including codetracking in noise and multipath (when using early-lateprocessing and advanced multipath mitigation techniques),better spreading code performance than the baseline L1Ccodes, less self-interference, better RF compatibility with C/A,and less susceptibility to narrowband interference at the worstcase frequency. These improvements are obtained through theuse of slightly more power at high frequencies, and receiverswith very narrow front-end bandwidths do not obtain thesebenefits or use this signal power. Also, multipath mitigationtechniques like double-delta processing perform better withBPSK-R(1) than with MBOC or BOC(1,1) for receivers withnarrower bandwidths.
Thus, BPSK-R(1), BOC(1,1), andMBOC provide different opportunities to trade performanceagainst support for simple receiver designs.MBOC maintains compatibility with BOC(1,1) receivers,since more than 90% of the power remains available toBOC(1,1) receivers.
Like BOC(1,1), MBOC provides goodpotential interoperability between GPS and GALILEO, withgreater interoperability and compatibility achieved if the sametime waveforms and spreading code families can be employed.Several different waveform options exist and can produce thesame MBOC(6,1,1/11) power spectral density, and evaluationof these different implementation options is continuing. Thefinal choice between BOC(1,1) and MBOC as the commonspreading modulation for L1 OS and L1C awaits anassessment of programmatic aspects.ACKNOWLEDGMENTSThe work of the European Commission Signal Task Force wassupported by many European national space agenciesincluding Deutsches Zentrum für Luft- und Raumfahrt (DLR,Germany), Centre National d´Etudes Spatiales (France), andDefence Science and Technology Laboratory (UnitedKingdom).
Many other members of the European CommissionGALILEO Signal Task Force have also contributed to thiswork, in particular Lionel Ries, Antoine DeLatour and LaurentLestarquit from CNES. Their support and contribution isacknowledged.892.
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