Design And Achievement Of Power Line Carrier Communication System Based On Spread Spectrum Technology

Power line carrier communication is defined as data transmission and communication using existing low-voltage power lines,no need to re-wire the lines,with advantages of network construction cost saving,easy installation,simple maintenance,which is selected by national electric power sector as the main communication technology for the realization of the electricity users data acquisition.The low voltage power network is built for power supply,rather than communication,so the network environment is complex and difficult to ensure the reliability of communication.This paper,with spread spectrum communication technology,researches a suitable carrier communication method in the power line environment.This article describes the international development status in power line carrier communication technology and analyzes the characteristics of power line channel,and propose the overall system method.According to the characteristics of the power line,the direct sequence spread spectrum technology is adopted to realize the LPLC communication system,and the overall scheme of the system is proposed.System mainly includes two parts of the transmitter and receiver.The transmitter is composed of two parts of the spread spectrum modulation and DPSK modulation.The direct sequence spread spectrum is used to expand the spectrum.Then the DPSK is modulated by PN.The receiver is composed of a pseudo random code synchronization module,a demodulation module and a DPSK demodulation module.Aiming at the problem of large amount of computation and high cost of hardware,the paper designs an improved digital matched filter to realize the synchronization of the system.The improved matched filter adopts the iterative method,reduces the complexity of the algorithm,and compares the output value of the digital matched filter with multiple sampling points,and improves the acquisition speed effectively.The improved digital matched filter is used to keep the original fast acquisition performance.For DPSK signal modulation,this paper uses the DPSK differential detection method,through the transmitter differential signal and its delay after a cycle of signal correlation operation,the output signal is through the low pass filter to carry out the sampling decision to achieve the DPSK signal demodulation,which not only avoids the complex carrier recovery,but also does not need special coherent carrier generator,effectively reduces the hardware design complexity.In this paper,a direct sequence spread spectrum system simulation model is built,which is based on the Matlab/Simulink environment,and then the system is simulated and analyzed.The feasibility of the system is verified.On this basis,the main algorithms of the system are realized by using dsPIC33FJ256GP710 chip.The design of the system is mainly divided into the spread spectrum,modulation and receiving end of the transmission side of the solution,the demodulation of several parts;the external circuit is mainly composed of transmission amplifier.coupled circuit,band-pass filter and receiver signal amplification and other parts of the chip processing.Finally,the system is tested under different test conditions.Test results show that the LPLC direct sequence spread spectrum communication system can achieve reliable communication.