| Direct sequence spread spectrum communication system has certain anti-jammingcapability and has practical application and development perspective in military andcivilian communications. However, normal direct sequence spread spectrumcommunication system is delicate on the condition of manual interference. Sointerference suppression technology is necessary for improving the anti-jamming abilityof the system.Under the background of narrow band interference suppression for emergencycommunication system based on the framework of direct sequence spread spectrumcommunication, time domain interference suppression techniques are researched mainly.Anti-jamming performance of direct sequence spread spectrum system is simulated. Anadaptive interference suppression algorithm with variable step size based on hyperbolacosine function is carried out. Comparison with traditional adaptive algorithm, the newalgorithm can improve the speed of converge and reduce steady-state error. The mainworks of the thesis include:1. The principle, system characteristic and performance of direct sequence spreadspectrum communication system are researched and simulation platform is designed.Anti-jamming performance and interference suppression requirement of the system areanalyzed in detail by simulation.2. Mathematic model and features of typical narrow band interference are analyzedand a method for modeling them with variable parameters is designed. Models for toneinterference, AR interference and narrow band gaussian interference are setup andsimulated. The method can combine various interferences and simulate actual channelenvironment.3. Adaptive filtering techniques, especially Least Mean Square adaptive algorithmand improved algorithm with variable step size, are researched. The performance of thealgorithms and the suppression effect for various narrow band interferences are verifiedby simulation.4. Based on the conflict between iterate speed during iteration process andsteady-state error in LMS algorithm, an adaptive LMS algorithm with variable step sizecombined with the characteristic of hyperbola cosine function is provided. Thealgorithm can reduce the error in steady state. At the same time, the convergence speedcan be improved. Simulation results show that anti-jamming performance of directsequence spread spectrum communication system used the new algorithm is better thanthat of traditional adaptive LMS algorithm.For the object of direct sequence spread spectrum communication system, timedomain interference suppression algorithms used in the system are analyzed in detail. The research results are applied to actual emergency communication system andanti-jamming performance of the system is improved efficiently. |
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