Research And Implementation Of Synchronization Technology In Digital Communication Blind Demodulation System

Timing synchronization and carrier synchronization are the key technologies of digital communication blind demodulation system.The performance of synchronization has a direct influence on the performance of the whole digital communication demodulation system.Solving the synchronization problem in the blind demodulation system of non-cooperative digital communication and improving the performance and stability of synchronization effectively in a noisy and complex environment is of significance to advance the performance of the whole demodulation system.This paper aims to study various modulation signals such as MPSK(Multiple Phase Shift Keying)and MQAM(Multiple Quadrature Amplitude Modulation).Firstly,directing at the problems of long loop capture time and poor loop stability in common carrier extraction algorithms,a modified Costas loop carrier extraction algorithm is proposed based on the traditional Costas ring carrier extraction algorithm.The algorithm replaces the traditional multiplicative phase discriminator with a decision-oriented phase discriminator and augments a loop lock detection module after the loop filter module to reset the loop filter parameters when the loop convergence is detected.The simulation results manifests that when the loop acts on the second-order loop filter and the third-order loop filter,compared with the improved Costas loop carrier extraction algorithm which uses multi-coefficient adjustment to replace a set of coefficients for high-order QAM signals,the advanced algorithm can shorten the loop capture time,and after the loop converges,the frequency tracking output jitter range is small,the loop stability is higher,and modes such as MPSK?MQAM.Secondly,aiming at the problems of the classical bit timing algorithm and many improved algorithms,such as poor self noise performance,high bit error rate,long synchronization time,etc.,by improving the loop structure of interpolation filter module and timing error detection module,a Gardner timing recovery algorithm with improved loop structure is proposed,and the improved algorithm is verified by simulation.The simulation results represent an explaination that when the loop acts on QPSK and 8PSK signals,the synchronization stability is better and symbol synchronization can be achieved in a shorter time.When the SNR is-5dB,the convergence radius of QPSK constellation is about 0.26,which is similar to the improved Gardner of frequency and phase lock loop(FPLL)Compared with the timing recovery algorithm,the improved algorithm reduces the convergence radius by about 0.08,effectively shortens the synchronization establishment time,and the timing error jitter is significantly reduced,and the bit error rate is lower under low SNR.Finally,based on the above research outcomes,the paper employs MATLAB simulation to verify the correctness and feasibility of the synchronization module algorithm.For the two modules of carrier synchronization and symbol synchronization,the paper studies and designs a multi-channel parallel loop structure suitable for various modulation modes by the advanced algorithm.Moreover,a multi-channel parallel real-time synchronous demodulation system is achieved with C/C++ language through the VS2013 software platform.Through the algorithm improvement,simulation analysis and software implementation of the digital communication blind demodulation system,the results indicates that the parallel data processing time is apparently less than the serial data processing time,and the test results are consistent with the theoretical simulation results,which illustrates that the system can realize the demodulation of a variety of modulation signals.