Date Published: July 13, 2017
Publisher: Public Library of Science
Author(s): Rongling Lang, Hong Xiao, Zi Li, Lihong Yu, Yongtang Shi.
In this paper, an anti-jamming method, which turns the single objective optimization problem into a multi-objective optimization problem by utilizing 2-norm, is proposed. The proposed jamming suppression method can reduce the wide nulls and wrong nulls problems, which are generated by the common adaptive nulling methods. Therefore a better signal-noise-ratio (SNR) can be achieved, especially when the jammers are close to satellite signals. It can also improve the robustness of the algorithm. The effectiveness of the proposed method is evaluated by simulation and practical outdoor experiments with the GPS L1 band C/A signals. The experimental results show that with the dedicated method, the nulls targeting at the corresponding jammers become narrower and the wrong nulls can be eliminated.
The Global Navigation Satellite System (GNSS) has been an important component in both military and civilian fields, whereas it is easily interfered due to its own inherent defect. Taking the Global Position System (GPS) as an example, its satellites are up to 20000 kilometers away from the earth. This results in that the power of signal which is received by the ground receiver is very weak (about -160dBW), so GPS signal is susceptible to be jammed. The research on jamming and anti-jamming techniques for (GNSS) has also been widely studied.
Jammer Reduction (JR) and Satellite Availability (SA) are the two crucial indexes when evaluating the performance of jamming suppression. Although PI algorithm is able to form nulls automatically in the interference direction without using the directional information of the GNSS signals and the jammers, the null in the interference direction may be so wide that the GNSS signals fall into the null, especially when jammers and GNSS signals are extremely close to each other. In this case, it is quite difficult for the GNSS receivers to acquire the GNSS signals.
In the experiments, the uniform circular array is adopted, whose radius is R. Assuming that the phase difference from the k-th unit to the reference unit is ϕk, and the difference between the signals received by them can be expressed as:
α(θ, ϕ, φk)=e−i×2π×R×cosϕ×cos(θ−φk)(17)
where θ is an azimuth angle and ϕ is an elevation angle.
A multi-objective optimization jamming mitigation algorithm with 2-norm is proposed in this paper, in order to solve the problem that nulls corresponding to jammers are too wide and the wrong nulls problems in the spatial adaptive jamming suppression algorithms. The direct inverse method and an improved iterative PI algorithm with multi-objective optimization based on 2-norm have been presented. The new MUSIC is also present to avoiding the wrong nulls. Both simulation and practical outdoor experiments are carried out on the basis of GPS signals in band L1 to verify our proposed idea. The corresponding simulation and testing results show that the dedicated algorithms with multi-objective optimization based on 2-norm can make the nulls narrower and the gains in the non-jammed directions more flat. Moreover it raises the entire gains of the arrays, and achieves promotion of GNSS signals’ SNR.