Research On Simulation Of Adaptive Algorithm In Demodulation

With the rapid development of wireless communication technology, it is a new subject researched at present how to enhance the demodulation quality in the complicated communication environment. In the field of communication, adaptive algorithm is in general used for adaptive equalization, adaptive frequency tracking .etc. With the deepening of research, a method of demodulation by adaptive algorithm is proposed. It is better in performance than normal demodulation with the interference immunity and strong in trace ability of adaptive filtering, and easy in realization by DSP.Through carrying on research and analysis to various kinds of adaptive algorithms, this paper is focus on the application of the algorithm in demodulation in the digital signal carrier transport. The DPSK signals demodulation basing on adaptive algorithm is improved on and a new method is presented for QDPSK and QAM signals demodulation by adaptive filter. Moreover, the simulation system of modulation and demodulation is built under the environment of dynamic simulation software System View and the simulation experiment of imitating physical environment is made , and it makes analysis of simulation result in performance.Main content of the dissertation include:A brief introduction of System View is given in the matter of its characteristic and main function.Based on the study of many kinds of adaptive algorithm, the dissertation analyzes and compares the performance of these algorithms.The adaptive demodulation method for ASK and FSK signals is discussed, and the method for DPSK signals demodulation by NDLMS adaptive algorithm is given in this paper. In the actual channel, it is proved through simulation that the performance of bit error rate in the new method has improved 2-3dB relative to coherent demodulation by PLL.The methods for QDPSK and QAM signals demodulation by adaptive algorithm are proposed distinguishingly according to the features of quadrature carrier wave.The modules of adaptive algorithms are created in System View such as LMS, NLMS, and NDLMS .etc. Whereupon their performance are analyzed and compared on the premise of demodulation to verify the theory forementioned.The simulation systems of modulation and demodulation for DPSK, QDPSK and QAM signals is created in System View in preparation for analyzing and researching adaptive demodulation.The coherent demodulation and adaptive demodulation are both realized in these forementioned systems in System View, and the corresponding theory is proved by analyzing and comparing in simulation. The method is given to solve the problem in adaptive demodulation that adjudgement will worsen when the SNR is low. By using the error signals to reduce the demodulated signals, the bit error rate will be improved 1~2dB.