Data Communication through Spread Spectrum Technology on Power Lines

1. ABSTRACT: Data transmission through power lines has received increasing attention in recent years. In fact the electrical energy distribution system is a big back bone that can be use for data communication. The interest for this medium includes automatic reading of energy meter, management of electrical distribution system, automation of buildings, and high speed data rate connection within the home and so on. The main advantages of data transmission on power line communication is the facts that the physical networks is almost already installed, making it a very attractive option. Beside this, physical drawback of the network, it become necessary to install repeaters, if distance matters bridges over distribution transmission, use of technology that reduce the noise level of the power lines, after that we will be able to achieve our goals on power lines. The data flow over power line through high voltage, low voltage, through cooper and other medium has different characteristics. DSSS, OFDM are the main applicable techniques to get QoS over not very good environment for data communication on power lines and this QoS is the point of study of this paper and we will discuss how we can achieve our goal to make our service better at consumer premises. 2. CHANNEL CHARACTERISTICS OF PLC: The power line as a communications channel has specific characteristics that must be considered. This includes the dominant and widely varying noise, impedance changes and multi-path effects. Noise sources are electronics, electro-mechanical and even included by the power lines themselves. Some noise is harmonically related to the 50 or 60Hz. Light dimmers and related products that uses triacs create impulse designed switching supplies, conduct quite a bit of noise onto the power lines. These noises sources have both time domain and frequency domain characteristics. The easiest way to get a first order understanding of signal to Noise ratio SNR on the power line is to look at noise amplitude as a function of frequency, as shown in fig no.1