Interference Mitigation And Measurement Biases Compensation For GNSS Antenna Array Receivers

The Global Navigation Satellite System(GNSS)is playing an increasingly important role in the key areas of military,aviation and safety of life.With the continuous escalation of navigation war and the increasing demand for interference mitigation in high-precision applications,it is necessary to improve the receiver's anti-jamming ability,and on the other hand,to reduce the measurement bias introduced by interference cancellation process.Interference suppression based on antenna array has become the most effective method for GNSS receivers.Based on this background,two key problems of interference suppression and measurement bias compensation in GNSS antenna array receiver are studied in this paper.The main work and innovations include:(1)The traditional power inversion algorithm takes interference suppression as the only goal.It causes attenuation of signal from some directions when steering nulls in the interference directions,which leads to the low availability of the satellite signal.It is found that the selection of reference elements will affect the array gain of the antenna array in the direction of the satellite signal,and then affect the output signal to interference plus noise ratio of the array.In this paper,a power inversion algorithm based on the optimal reference element is proposed.Being different with the traditional method,this method adjusts the reference element in real time by maximizing the acquisition correlation value of satellite signal,and thus improves the array gain in the signal directions.Compared with the traditional method,this method increases N times acquisition unit(N is the number of elements),but it can greatly improve the availability of satellite signals under interference conditions.The experimental results of the four element antenna array show that the method increases the availability of the satellite signal under single jammer from 79%to 98%,and from 74%to 92%under two jammers(3dB loss of the signal-to-noise ratio as the threshold).(2)The second chapter has improved the power inversion algorithm,but the advantage of the array processing,form beams in the signal direction to improve the carrier-to-noise ratio,is still not fully utilized.An array anti-jamming algorithm based on nulling and beamforming is proposed.At the nulling stage,N outputs are formed by selecting each antenna element as the reference element,at the beamforming stage,the relative phase of the N nulling outputs are estimated by using the tracking results,and then the final array output is achieved by weighting and summation of the N nulling outputs.The influence of satellite signal tracking bias on the performance of the algorithm is analyzed.The results show that the array gain loss caused by tracking error can be ignored for the accuracy of the current tracking loop.The performance of the algorithm is evaluated by simulation experiments.The results show that the method has the ability of beamforming to enhance the signal under the interference condition.For the four element antenna array,the tracking ability of the receiver can be improved by nearly 6dB.(3)In order to solve the problem that the traditional array processing method cannot enhance the signal at signal acquisition stage,and thus the receiver has low acquisition sensitivity in harsh interference environments,a combined method based on interference suppression and signal acquisition is proposed.Compared with the traditional methods,which perform interference suppression and signal acquisition in sequence,the proposed method combines these two processes into a single algorithm by maximizing the generalized likelihood ratio of satellite signal detection.At the expense of increasing the computational complexity,it improves the carrier-to-noise ratio by beamforming without prior knowledge,thereby improving the receiver's acquisition sensitivity.The simulation results of the four element antenna array show that the acquisition sensitivity and tracking sensitivity of the receiver can be improved by 5?6dB compared with traditional methods.(4)Adaptive antenna array introduces carrier phase and code phase bias,which cannot meet the requirements of high-precision applications.A distortionless space-time adaptive processor(STAP)is proposed.In this method,the space-time anti-jamming filter is equivalent to a time-domain filter for the satellite signal,and then the array weights are constrained to ensuring linearity of the equivalent filter,thereby eliminating the measurement bias introduced by array processing.In order to evaluate the performance of the algorithm accurately,an evaluation method is designed to eliminate the jitter caused by the thermal noise of the receiver.The evaluation results show that the proposed method does not introduce carrier phase bias,and introduce a fixed code phase bias for all satellite signals determined by the number of taps of space-time filter.The fixed code phase bias could be compensated as zero value without affecting the final positioning result.The research contents of this paper are the expansion and deepening of the array anti-jamming theory in the field of satellite navigation.The main research results have been successfully applied to a variety of GNSS antenna array receivers,and achieved the expected results.