Research On The Modulation Schemes Of Low-Voltage Remote Meter Reading System

Recently, with the high development of our country's economy and electric force,traditional meter reading method can not satisfy modernization of power'smanagement. It's automatic meter reading(AMR), which collects remoteconsumption data from customers' utility meters and then automatically transmittingthese data, that can realize automation, normalization and scientization of powermanagement. There are mainly three communication methods used for meter reading:telephone lines, radio frequency and power line carrier. Each method has its ownstrengths and weaknesses. The telephone system provides an ideal communicationinfrastructure for AMR systems due to simplicity of installation, quality of data, highnoise immunity, and reliability. The disadvantage of this method is that it wouldencounter the unavailability of reading the metering data due to the disconnection ofthe telephone line, and change in customer's telephone number, and the cost ofmonthly bill from telephone companies. Radio frequency is wireless and cable free,so it is easy to install. The disadvantages of this method are the interferences ofsurrounding environment, and high costs such applying license of using frequencybands. Power line cartier communication is becoming more and more popularbecause of its good future, although it has some disadvantages, such as difficultcommunications environment.This article studies on the technique of modulation and demodulation fortransmitting data on power lines. First of all, this article discusses the channel'scharacters of low voltage power line from three aspects: impedance, noise and fading.Then the SFSK(Spread Frequency Shifting Key)system based on spread spectrumtechnique is given, and a new method of modulation and demodulation technique isgiven, which is widely used in Ultra Wide Band. But our innovation is that we usethis pulse position modulation in the low voltage remote meter reading. According totheory analysis and computer simulation, the feasibility of the new method is proved.After comparing the two modulation schemes, the conclusion can be achieved that ifthe data rate is up to 1Kbit/s and the system's bit error rate is controlled to less than10^-3, the PPM scheme system should assure the SNR more than 6dB,but the SFSK scheme system should assure the SNR more than 10 dB. So in theory , the PPMsystem's performance is better than the SFSK system's performance. Alsosynchronization plays an important role in communication system. The performanceof synchronization will affect on the performance of communication systems. So atlast, this article discusses carrier synchronization for SFSK system and timingsynchronization for PPM system.