Junwei Nie

Impact on Antijamming Performance of Channel Mismatch in GNSS Antenna Arrays Receivers

The performance of antijamming is limited by channel mismatch in global navigation satellite system (GNSS) antenna arrays receivers. Only when the amplitude and phase characteristics of each array channels are the same is the interference likely to be completely suppressed. This paper analyzes the impact on antijamming performance of channel mismatch. We built the model of channel mismatch and derived the impact on transfer function with space-time adaptive processor (STAP) of channel mismatch in theory. The impact factor of channel mismatch is proposed by the fuzzy transfer function, which could directly reflect the antijamming performance under channel mismatch. In addition, every characteristic in the channel mismatch model is analyzed. The analysis results show that the greatest impacts on antijamming performance are the range of amplitude wave and the group delay bias, while the influence of the number of amplitudes is next. As for the effect of group delay fluctuation is the smallest.

Adaptive Time Taps of STAP Under Channel Mismatch for GNSS Antenna Arrays

Although antenna arrays can effectively suppress interference and maintain the navigation signal integrity, interference suppression performance is limited by channel mismatch. However, a space-time adaptive processor (STAP) can reduce channel mismatch by introducing time taps within each element, which will further suppress the interference and improve the performance. However, interference suppression depends significantly on the number of time taps. This paper presents a proportion differentiation (PD) algorithm for the adaptive control of time taps based on the antenna arrays output power is presented. The effectiveness of the proposed algorithm is verified through simulations and measured data. The STAP with adaptive time taps has achieved excellent performance for interference suppression performance without increasing the computational load.

Analysis of Cross-Correlation Peak Distortion Caused by Antenna Array Space-Time Adaptive Processing

Space-time adaptive processing (STAP) combines information available from both spatial and temporal domains, which can effectively enhance the GNSS receivers’ performance of interference suppression. But STAP has the potential to distort cross-correlation peak, which would deteriorate acquisition and tracking performance. In this paper, the cross-correlation peak distortion under space-time power inversion (PI) criterion and minimum variance distortionless response (MVDR) criterion are analyzed by theoretical analysis and simulations. Analysis and simulation show that the spatial correlation coefficient between interference and desired signal, taps number of Tapped Delay Line (TDL) and taps delay can directly affect the cross-correlation peak. The conclusions can be used to optimize the antenna array design and space-time adaptive algorithm for reducing cross-correlation peak distortion caused by STAP.

Channel consistency indexes of satellite navigation antenna arrays receivers

Channel mismatch has become a serious limit to further improve the anti-jamming performance on satellite navigation antenna arrays receivers. Consistency degree of each channel could directly determine the anti-jamming performance. In order to analyze and confirm the channel consistency indexes, this paper analyzes the impact of channel mismatch on interference cancellation ratio (ICR), firstly. According to the anti-jamming processing based on power inversion, a method to analyze the consistency indexes is proposed. Simulation experiments show that the difference between theory and simulation value on ICR is less than 0.1dB, when the antenna arrays are equipped with two elements and the channel mismatch degree is random. When channel mismatch is restrained by the proposed channel consistency indexes, the difference between demand and simulation value on ICR is less than 5dB.

Effect of ADC non-ideal characteristics on GNSS antenna array anti-jamming

The key indicators of analog to digital converter (ADC) are effective number of bits (ENOB) and spurious-free dynamic range (SFDR). ENOB would affect the input signal to noise ratio (SNR), and SFDR indicates the degree of spurious introduced by non-linear. The characteristics of multi ADC in antenna array would not be the same, which make the quantization noise introduced by ENOB and spurious indicated by SFDR have little correlation. The quantization noise and spurious cannot be suppressed by antenna array. This paper analyzes the impact of ENOB and SFDR on antenna array antijamming performance, and gives the relationship of interference cancellation ratio (ICR) with ENOB and SFDR. Under ENOB and SFDR restricted, the method is proposed to enhance antijamming performance. The simulation results show the effectiveness of the analysis and proposed method.

Performance of GNSS receivers with AGC in noise pulse interference

In order to improve anti-jamming performance of GNSS receivers, the Automatic Gain Control (AGC) system is commonly utilized. AGC is able to scale the analog input voltage to an optimal level of the ADC. Few studies have investigated how AGC impacts the signal processing of GNSS receivers in pulsed interference conditions. This paper studies the performance of GNSS receivers with AGC in the presence of noise pulse interference. Analytical model of post-correlation carrier-to-noise ratio (CNR) and bit error rate (BER) is derived when AGC is present and absent. Finally analytical model is verified by simulation results. The results suggest that the AGC can provide the GNSS receivers with satisfactory performance.

A spoofing detection method for motion receiver using single antenna

The direction of arrival (DOA) technique is the most effective mean of spoofing detection, but it is high hardware complexity and cannot be applied to motion vectors. In order to suppress this problem, a method based on carrier phase double-difference detection of single antenna which is used in linear motion vector is introduced. This method uses the difference of distance between GPS satellites and spoofers to the receivers, and makes the detection by carrier phase double-difference which only needs single antenna. The model of carrier phase double-difference of single antenna is established, and the binary hypothesis test of spoofing is given based on the model. In the end, theoretical analysis and simulative results prove the effectiveness of the proposed method. The results indicate that the longer displacement distance of the receiver antenna is, the better spoofing detection performance of the proposed method is; the closer to spoofer from the receiver antenna is, the better spoofing detection performance of the proposed method is; the more vertical between DOA and antenna displacement direction is, the better spoofing detection performance of the proposed method is.

Parameter selection analysis of matched spectrum interference

As efficient broad band interference, the matched spectrum interference is usually adopted in navigation counter measurements and anti-jamming tests. Currently, jamming effect comparisons between the matched spectrum interference and interferences with other modulations are often carried out. However, only its band and frequency are taken into consideration in these comparisons. Other parameters are rarely analyzed. Thus, taking root of spectral separation coefficient derived from effective carrier-to-noise ratio as evaluation index, code sequence, code sequence period, frequency and delay between interference and signal are analyzed. Conclusions are expected to guide interference parameters setting to ensure jamming performance.