High-Precision Ranging Technology Of Anti-Interference Receiver Under Nonideal Channel

Anti-interference and high-precision measurement are two important indicators of a satellite navigation receiver with high performance.The difficulty in current receiver design lies in simultaneously satisfying these two indicators.Existing anti-interference methods maintain an unchanged zero value before and after anti-interference by constraining the anti-interference filter during a linear phase,but the methods described above are based on ideal channel characteristics.With the ranging index increased to the order of subnanoseconds,the group delay and nonideal amplitude-frequency characteristics of the receiver channel have become the main factors that restrict further improvement of the ranging index.In particular,when outside interference changes,the receiver will also fluctuate,which results in a serious deterioration in the ranging performance of the receiver.Therefore,research on the impacts of anti-interference on the zero value in a nonideal channel,and methods to eliminate these effects have important theoretical significance and application value.In this paper,a systematic study is conducted aiming at the effects of interference upon the zero value in a nonideal channel,and the associated elimination technology.The main activities and innovations are as follows:1)In a traditional nonideal channel,the effects of an anti-interference filter on the zero value of the receiver focuse only on the zero value offset caused by the shape distortion of the correlation peak in the tracking.However,if the receiver captures the correlation peak side lobe during the capture phase,the zero value will also jump rapidly,which affects high-precision measurements.The estimation results of the delay in the capture phase should be highly stressed,especially for receiving burst system signals.By combining the conventional tracking zero value with a newly defined acquisition zero value,an impact model for anti-interference on the measurement value of zero in an arbitrary channel is established.The precision of the model is verified through simulation: experimental data shows that the offset of the tracking zero value reaches 2–3 ns owing to anti-interference.During the acquisition,when the detection probability is 0.9 and the carrier-to-noise ratio is less than 34 dBHz,the offset of the capturing zero value will exceed 20 ns.2)In a nonideal channel,the trapping effect of a traditional anti-interference filter will lead to an offset of the tracking zero value.Therefore,it is necessary to improve the anti-interference filter so that the zero value remains unchanged before and after anti-interference.This paper presents a method to compensate for the offset of the tracking zero value by correcting the amplitude and frequency response in the anti-interference filter passband,and an amplitude-frequency compensation algorithm with a compensating frequency search is adopted.For special circumstances in a nonideal,nonsymmetric channel with a single narrowband interference,an amplitude-frequency compensation algorithm with symmetric frequencies is adopted.The simulation results show that the offset of the tracking zero value reaches 2~3 ns without amplitude-frequency compensation.Using the amplitude-frequency compensation algorithm,the offset can be reduced more than 55%.Using symmetric frequencies of the amplitude-frequency compensation algorithm,the amplitude of the offset is reduced more than 92%.3)In a nonideal channel,the main lobe of the correlation function of the received signal and the local PN code may deform before and after the anti-interference,thereby affecting the tracking zero value.In this paper,an algorithm that corrects the tracking zero value is proposed based on cancelling the delay correlation peak.By eliminating a series of delay correlation peak components in the correlation peak after they pass through interference suppression filters,the shape of the correlation peak input into the early-late ring can be made consistent with the shape of the correlation peak before interference suppression.This ensures a constant tracking zero value before and after interference suppression.Simulation results show that,when the carrier-to-noise ratio of the input signal is greater than 35 dBHz,the coherent integration time is 10 ms,and the offset amplitude of the tracking zero value will be reduced by more than 86% after the correction.4)To ensure a constant zero value before and after anti-interference,calibration of the nonideal channel is generally required.Traditional calibration methods include the analog domain and digital domain.The analog domain usually has low calibration precision with unsatisfactory realization flexibility;digital domain calibration usually has high computational complexity.This paper presents the tracking zero value correction algorithm with a complete-matching receiver.The algorithm uses the exchange property of convolution: after moving the traditional calibration network to the local code output port,a waveform quantization method is adopted to equivalently realize a calibration network.By using the digital domain to realize the calibration,high accuracy,good flexibility,and low computational complexity can be achieved.Simulation results show that when the quantization bit number is greater than 3 bits,the offset amplitude of the tracking value of zero after correction is reduced by more than 91%.However,when using the traditional 32-point 8-bit IFFT channel calibration method,its performance is only equivalent to the quantification performance of a 2-bit complete-matching receiver,but its resource consumption is much higher.5)The anti-interference filter will cause an uplift in the side lobe of the correlation function,resulting in a rapid jump of the acquisition zero value.Existing interference suppression filters with side lobe suppression will not only increase the interference loss but also require extra hardware resources.This paper presents a acquisition algorithm based on the splitting amplitude characteristic of the correlation peak.The algorithm uses the symmetric splitting characteristic of the interference suppression filter for the correlation function.By constructing new measurements based on side lobe amplitude cancellation,in accordance with the different distribution characteristic detection of the measurements of the main lobe and side lobe of the correlation function,this method examines whether the main lobe of the correlation function is captured and has no effect upon the interference loss.Meanwhile,the amount of hardware resources required is small.Simulation results show that with the presence of narrowband interference under the same detection probability and carrier-to-noise ratio,compared with the original capturing algorithm,the proposed algorithm reduces the offset of the capturing value of zero by 37%–89%.With respect to the interference suppression filter with a seven-order side lobe suppression,the offset of the capturing value of zero is reduced by 26%–69%.The method proposed in this paper can be used for receivers in satellite payloads and receivers in ground monitoring systems.The expected results were obtained.