Design Of PSK-based Low Speed Digital Communication System

Along with the entrance of more kinds of meters into more families, the limitations of the pattern of Manual Meter Reading (MMR) was more and more obvious. MMR not only needs workers to go to the sites to read meters, but also this pattern becomes more burdensome and mistakes which can't be avoided. The former MMR has been outdated. It can't meet the needs of the energy department's real-time supervision while Automatic Meter Reading(AMR) can perfectly solve the problem. So in recent years, how to use the technology of AMR through power line is the problem that power and the relative departments urgently want to solve. AMR not only decreases the costs of labor and money in MMR, but also is more reliable and real-time. The research on Power Line Communication (PLC) has been staggeringly going ahead for many years, as many problems still wait to be solved though many efforts have been made in this aspect.The use of low-voltage power line is quite necessary to unite the technology of meter reading and PLC. If the power channel that connects numerous households can be used for data transmission, large quantities of resources can be spared. AMR is a kind of No New Line technology, which need not erect new communication line and can save the corresponding funds and manpower. AMR only needs to install a data collector in meter box. This collector is used to transmit data through low-voltage power distribution network. A gather meter is also necessary beside the low-voltage of middle-voltage transformer to gather the data transmitted from collectors and then transfer the data to data process center through middle-voltage power line or special communication line. It will increase the costs of meter installation in short term. Butin long term it is well worth investing for the large space of its development in usage.However, the process of application of PLC on low-voltage line is not so smooth. The high request of power and the relative departments seems too haste to set high standards as the channel character of low-voltage PLC in China is not so satisfactory when compared with that in Europe and America. High speed and being highly real-time is contradictory to high reliability. To meet such requirements, European and American relative chips are adopted in many researches in China. Though many experiments have been made in this aspect, few make any success. However, phase achievements have been made in low speed meter reading scheme such as using Ultra Narrow Band (UNB) without the bondage of that rule.So a new remedy is suggested in this paper. Phase Shift Keying (PSK) is used in this paper which constitutes Narrow Band PLC (NB-PLC) from the perspective of using frequency band. Comparing the three basic modulation patterns, PSK is the same as ASK and higher than FSK at frequency band utilization ratio, while PSK has the lowest BER at anti-interference which is even better than Spread Spectrum Carrier (SSC) when it runs at low speed. Meter reading through power line requires strong abilities of anti-interference and high reliability. The adoption of PSK is more suitable for the condition of frequency band shortage, high relative speed and heavy interference outside. And PSK can be easily realized and designed with low cost thus decreases the high costs of present AMR design.This system is designed to meet the requirements of being economic, high reliability of power line transmission, and low real-time. This paper first analyzes the low-voltage power line channel character, and then make a comparison between the BERs of several kinds of modulation technologies and expounds the feasibility, advantages and practicability of using PSK technique for the modulation plan of PLC in details. Subsequently, the design of hardware and software are detailedly discussed. Finally, the system debug and performance analysis are also listed in the paper.