Carrier-to-noise Ratio Estimation And Cross-correlation Mitigation For Indoor And Outdoor Seamless Navigation Receivers

Global Positioning System is the most successful satellite navigation andpositioning system. As a social infrastructure, GPS has been an indispensable tool.But as the limitations of the system structure, the GPS can’t be used in tunnels orlarge buildings. So the indoor positioning technology has developed gradually. Inaddition, the GPS receiver as an important part of the system directly affects theservice performance of the GPS, the development of high-performance GPSreceiver is the hotspot. In order to overcome the problems encountered in the indoorand outdoor seamless location technology based GPS fingerprint node, the C/N0estimation method and high-performance cross-correlation interference mitigationalgorithm has been studied in this paper.Firstly, the mathematical model of the GPS L1signal has been build and thegeneration of C/A code also has been discussed. As a kind of balanced GOLD code,the C/A code has good autocorrelation properties and cross-correlationcharacteristics. This paper also describes the basic structure of the GPS receiver.The IF signals can be treated as complex number when I/Q down-conversion mixeradopted in the RF front-end. The basic principles of indoor and outdoor seamlesspositioning technology based GPS fingerprint node and fingerprint node structurehave been elaborated. We also give a detailed introduction about thedirect-positioning mode, the positioning mode based on the propagation model andthe positioning mode based on the Radio Map.Then, to estimate the C/N0in the indoor and outdoor seamless positioningtechnology, we investigate the suitability of the Beaulieu’s method(BM), the Signalto Noise Variance method(SNV), the Moment method(MM), the Real SignalComplex Noise method(RSCN) and the Narrowband Wideband Power Ratiomethod(NWPR). The BM and MM has good performance in the five C/N0estimation methods when the residual phase noise exists. The SNV and NWPR havea big error when the noise power is large and the RSCN work worse. But there isanother interference signal in the received signal, the NWPR method have a betterresult although it’s sensitive to the navigation data.Finally, for mitigating the cross-correlation between the GPS fingerprint node, we propose a cross-correlation mitigation method based on subspace projection. Forthis problem the weak signal is the target while the strong signal is the interference.If we have acquired the parameters of all strong signals, we can construct the strongsignal subspace matrix. The projection of the input signals onto the strong signalsubspace is the sum of the strong signals and the projection of the noise. Then wecan use the projection as an estimate of the strong signal. After subtracting theestimate from the input signals, the result consists of weak signals, noises and theresidue error resulted from the projection operation. In comparison with directinterference cancellation technique, only the code phases, carrier frequencies,carrier phase and date-bit modulation of strong signals are required when real signalis used and the method is independent of the carrier phases of the strong signalswhen the complex signal is used. And two different scenarios have been discussed.One is that the strengths of the strong signals are almost the same. Another scenariois that the strengths of the strong signals are largely different. And when the lengthof once mitigation operation has be selected appropriately and the data-bit of strongsignals doesn’t invert, the mitigation method based on subspace projection onlyneed to estimate the code phases and the carrier frequencies of the strong signals.And the test results indicate that the method can suppress the cross-correlationinterference effectively.