Research And Implementation On Pseudo-code Synchronization Of Direct Sequence Spread Spectrum Signal In Dense Multipath Environment

Because of the strong anti-interference ability, anti-multipath ability, resistance to intercept ability and easy to realize multiple access communication, direct sequence spread spectrum communication system has been widely used in the field of civil and military communication. In real system, the receiver and transmitter are placed in different places. Therefore, it is necessary to ensure the synchronization of pseudo-code. Only in that way, can we get a r eliable communication. There are two parts of pseudo-code synchronization, capture and tracking.In the indoor environment, more multipath can be recognized by the receiver when the transmission signal band is wider. Under that condition, the receiver has a higher precision of recognizing multipath. The traditional multipath channel model is no longer applicative at this time. However, the signal of receiver should be analyzed by dense multipath channel model. Therefore, it is necessary to simulate and analyze the algorithm of pseudo-code in dense multipath environment.In this paper, firstly, the basic theory of spread spectrum system and pseudo-code synchronization are briefly introduced, which is theoretical basis for the simulation analysis later. Secondly, the algorithm of pseudo-code synchronization in dense multipath environment is mainly discussed. Under white Gaussian noise channel, the detection probability increases and the false-alarm probability decreases with the increasing of signal-noise-ratio. And the detection probability and the false-alarm probability both increase with the decreasing of threshold. When the signal-noise-ratio is big enough, the detection probability is close to 1 and the false-alarm probability is close to 0. Under the dense multipath channel, the detection probability is lower and the false-alarm probability is higher. The relationship of the property between threshold and signal-noise-ratio is similar to that under white Gaussian noise channel. The property of NLOS(Non Line Of Sight) is worse than that of LOS(Line Of Sight). By using the adaptive threshold based on the maximum likelihood estimation, the property of capture gets better. In this paper, the best parameter of adaptive threshold of LOS and NLOS are given. The multipath will make the curve of adaptive distort. Furthermore, which will lead the tracking error. The curve of adaptive is much more into distortion under dense multipath environment than under two path channels. By using narrow related technology to restrain the influence of multipath, the performance of the curve of adaptive is better under LOS environment and NLOS environment with small tracking error. And the method cannot restrain the influence of multipath under NLOS environment with big tracking error. Finally, based on practical demands and development conditions, the plan of this system are designed, and the implementation of synchronization model in digital baseband system with the FPGA is made. In the same time, in order to verify the performance of the system, a verification platform with serial port connection is designed in this paper. The reliability of synchronization system is tested from two aspects, timing simulation and actual test.