Research On The Demodulation Of Dual PN Code Spread Spectrum System And Its Implementation In LPLC

Low-voltage power line communication refers to a kind of communication technology that can achieve the transmission of data over low-voltage (220/380 V) power line. It has the advantages of rapid deployment, no additional wiring, and it has a very good prospect for application because it can make use of the existing electricity network. However, due to that the electricity network is set specially for the requirements of power transmission rather than the communication demand, the channel characteristics of communication medium is terrible, and it can not obtain satisfactory control results. Therefore, we need to design a power line carrier communication system which is suitable for the environment of power line in China to achieve reliable communication of power line.Through the research on performance and cost of frequently-used power line communication technologies and the complex channel environment of our grid, the article uses neoteric dual PN code spread spectrum technology to achieve the electric power line carrier communication. The focus of the research include modulation and demodulation of dual PN code spread spectrum technology, improved digital matched filter, dual PN code selection, self-adaptation threshold, optimization and improvement of synchronization algorithm.The paper deeply studies the demodulation of dual PN code spread spectrum technology, and has been come to the conclusion that performance of demodulation of the orthogonal receiver using correlator is superior to the envelope detector when PN code is short; Because of the poor performance of the traditional dual PN code and a limited number of m sequences preferred pair, the transmitter selects the improved dual PN code for spread spectrum modulation. The receiver studies an improved digital matched filter to achieve PN code acquisition. In order to realize the fast PN code acquisition, the article designed a improved matched filter by combining the orthogonal sampling technique and parallel matched filters; In order to adapt to time-varying channel signal attenuation and noise of the dynamic changes and improve the PN code acquisition probability of detection while reducing the probability of false alarm, the system use the signal estimation theory to achieve self-adaptation threshold synchronous detection and improve the despreading performance of the communication system; In order to reduce the computational complexity, we use the iterative algorithm in the hardware implementation process, which makes the synchronous computation optimized, and also reduces the cost of hardware.To verify the feasibility of the dual PN code spread spectrum system, a system simulation which adopts the above key technologies is created in Matlab/Simulink environment and implement the system simulation and performance analysis. The system uses the dsPIC33FJ256GP710 to realize the main algorithm part of transmitter and receiver, and designs power amplification circuit, coupling circuit, resonant circuit, and other peripheral circuit. Finally, the system was tested under different testing conditions, test results show that LPLC dual PN code spread spectrum communication system can realize the reliable communication.