| Compared with antenna array satellite navigation receivers,those single antenna receivers have advantages in size,structure,power consumption and antenna coupling.The time-domain or frequency-domain algorithm for current receivers has made a great contribution to ensuring the safety of Beidou system operation.However,electronic environment is deteriorating and navigation countermeasure is becoming fierce,which means power enhancement and complexity increase of interference.Changes of interference make anti-jamming for current single antenna receivers degrade.To improve receiver anti-jamming performance in case of interference power enhancement,researches are developed as follows.1)In the presence of strong continuous wave interference(CWI),estimation of carrier-to-noise ratio after correlation for coarse acquisition(C/A)code receivers is obviously higher than the real one.To figure out how the estimation deviation is produced,carrier-to-noise ratio estimation model for C/A code receivers in the presence of CWI is built.Correlation between CWI and C/A code which has discrete spectrum results in produce of direct current(DC).Power of the DC from CWI is wrongly counted as signal power eventually leads to carrier-to-noise estimation deviation.Difference between simulation results and theoretical results are smaller than 1dB,which has verified analysis above.2)In the presence of strong CWI,estimation deviation of carrier-to-noise ratio will lead to inaccurate evaluation of receivers' data demodulation performance.Firstly,we analyze why data demodulation bit error rate(BER)is wrongly evaluated.Then,DC removal of receivers' correlator is proposed to improve accuracy of carrier-to-noise ratio estimation.Simulation results verify that data demodulation BER can be accurately calculated by estimated carrier-to-noise ratio.Difference between real BER and the BER calculated by mean variance ratio(MVR)method is smaller 1%.3)Currently,look up table(LUT)bit selection for receivers' numerically controlled oscillator(NCO)phase truncation often depends on experience and doesn't take frequency domain anti-jamming performance into consideration,which leads to remarkable degradation of anti-jamming performance.Relation between NCO phase truncation and anti-jamming performance is firstly analyzed.Then,propose a LUT bit selection method,which takes effective carrier-to-noise ratio loss as optimization target.The proposed method can reduce carrier-to-noise ratio loss induced by NCO phase truncation to a reasonable level.We take jam-to-noise ratio(JSR)of narrow band interference between 50~80dBc as an example.When upper bound of effective carrier-to-noise ratio loss is set as 0.5dB,lower bound of LUT bit calculated by the proposed method is between 7~12bit.Simulation results show that practical carrier-to-noise ratio loss induced by NCO phase truncation is less than 0.3dB,which verifies the proposed method.4)Navigation signal power enhancement leads to degradation of interference detection performance and frequency domain anti-jamming performance.To solve the problem,a new frequency domain anti-jamming algorithm based on consecutive mean excision based on signal cancellation(SCCME)is proposed.Firstly,uniform signal power spectrum density function is used to construct a model to approximate to power spectrum of mixture of signal,noise and interference.Then,we take minimum mean-square error between the model and the power spectrum mixture as criterion and adaptively estimate parameters of the model through gradient descent method.Finally,signal power spectrum cancellation is used to improve performance of interference detection and frequency domain anti-jamming.The proposed method can bring more carrier-to-noise ratio improvement when JNR is low or interference frequency offset is high,which is verified by simulations.When JNR is 25 dB,with interference frequency offset increasing to 4MHz,carrier-to-noise ratio improvement reaches to 7dB. |
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