Research On Coherent Interference Suppression Technique For GPS Receiver

It is vulnerable to the impact of all kinds of interference for GPS receiver, including unintentional interference and intentional interference, because of the low power of GPS signal and the complex electromagretism environment. Unintentional interference mainly refers to multipath interference, intentional disturbance mainly refers to strong coherent interference, Such as military interference. However, no matter what kinds of interference, it is possible to reduce the measurement accuracy of the code phase and carrier phase, leading to GPS receiver can not work properly or locate failures. For two special interference,this paper will look for interference suppression methods from time and space domains.Firstly through feasibility analysis,the paper finds some effective methods to suppress multipath from the digital signal processing technology. Then it starts to introduce the definition and model of multipath signals,simulation results illustrate that multipath interference has a greater impact on the code tracking loop and carrier tracking loop. On this basis, the paper describes four time-domain multipath rejection technology, they are Respectively narrow-related technologies, Strobe related technologies, estimated multipath delay locked loop (MEDLL) and adaptive filtering techniques, simulation results show the effectiveness of the four methods for multipath suppression. The first two methods are part of separation techniques, it has the higher requirement for the bandwidth, the latter two methods of calculation is very complicated, it needs the higher CPU. So in a real environment, it generally uses one or a combination of several methods.For coherent interference, because it can not be effectively suppressed in the time domain or frequency domain, so this paper uses spatial filtering techniques, namely adaptive array signal processing.For non-coherent interference, traditional adaptive filtering techniques can form the main beam in the direction of useful signal and form adaptive nulling in the direction of interferenc as Capon beamformer. However, the presence of coherent interference will produce the desired signal cancellation phenomena, such methods would all lose their effect. Therefore, this paper proposes a solution coherent approachspatial smoothing algorithm, the entire array is divided into several sub-arrays to decoherent processing, under in the direction of the desired signal accurately known, the algorithm can effectively suppress interference.In practice,with the array element mutual coupling,sensor position error, covariance matrix estimation error and DOA estimation error, spatial smoothing algorithm performance will be severely degraded, leading to the main peak of the useful signal offset and not suppressing coherent interference. In order to solve any type of array response mismatch problem, this paper presents a robust worst performance optimal beamforming algorithm, we propose two improved algorithms on the basis of the algorithm,they not only are steering vector error parameter constrained,but also the covariance matrix estimation error parameters constrained,it is important to choose a good parameter for solving the optimal weight vector,this two algorithm respectively give expression in the form of approximate solutions and closed-form solution, the output of the system performance can be further improved. Finally,the simulation verify the correctness and effectiveness of the two mentioned algorithm.