Research On The New GNSS Signal Quality Impacted By Nonlinear Distortion

Global Navigation Satellite System (GNSS) increasingly reflect its irreplaceableimportance in military activities and people’s daily lives. Great success with the GPS,Russia and the European Union as well as China was also increased investment inGNSS system. With the development of the global satellite navigation system andmodern process of the major GNSS system, the BOC signal and various BOC derivativesignals are used widly. Compass II-2will also use various BOC signals in the future.The positioning accuracy is one of the most important evaluation indicators in thenavigation system. While the distortion introduced by navigation payload channel willinevitably deteriorate the precision of the navigation signals, of which the most notabledistortion is the group delay of the RF filter and the distortion introduced by amplifiernonlinearthe.How the distortion of the RF devices of payload effect the precisionperformance for new GNSS system is still limited researched. Thus we establish thesimulation model to analyze how each RF channels contribute to signal qualitydeterioration is of great importance.The main research of this paper to carry out is as follows:1. Research various modulation characteristics of BOC signals, MBOC AltBOC,and so on. Define several acquisiton algotithms and their sphere of application, asBPSKlike algotithm and Sub Carrier Phase Cancellation technique. For the mostintricate and flexible object in Galileo and Beidou candidate signals as AltBOC, using avariety of acquisiton algorithms to acquire it. Besides prove that coherent joint is theoptimal ways to achieve Maximum likelihood estimation.2. Explore various generated mechanism of channel distortion, establish payloadRF channel distortion model, including the group delay of the filter model, distortionmodel of mixer and amplifier nonlinear distortion model. For in-depth analysis how thefilter group delay characteristics contribute to the signal quality, thesis design specialfilter that can fit any group delay characteristics of the interest filter phase response.Research the performance of the GNSS system when amplifier working at saturationpoint and2dB rollback point. 3. Establish GNSS performance evaluation system, mainly on the performance ofthe S-curve bias, outband power loss, relation losses, the IQ orthogonality and themultiple pseudo-code consistency. Measure deterioration of tracking precisionintroduced by channel distortion based on the above performance indicators.The main contribution and conclusions of this paper are as follows:1. Indicates filter amplitude-frequency characteristics contribute to signal qualityMinimal, but the asymmetry of the transition band will cause distortion of thecorrelation function thereby massively deteriorating the T-offset.2. Comprehensive assesses how the RF filter group delay characteristics affect thesignal precision. Clarified how the each signal frequency component affacted by filtergroup delay characterisitics. Reached the conclusion that frequency component of thesignal at the third harmonic is affected by the jitter of the filter group delay mostly. Thisconclusion can help to filter design in payload greatly.3. To the relation loss and S-curve bias of constant envelope signal, amplifierimproves them to some extent. But will leed to the out band power loss.4. Research nonlinear distortion of the payload channel, helps to filter design andreasonable choose of amplifier operating point. Ultimately improve the tracking andpositioning accuracy.