Design team members: Akrum Elkhazin
Supervisor: Ed Jernigan
Background
Household electrical wiring, or wiring within a building, can be an effective media to implement a communication network. In the past, communication over power lines has been limited to low speed data rates that could be used to turn on and off electrical appliances. Advancements in digital signal processing technology has made it possible to develop a high speed communication system over powerline. In particular, a PC network based on powerline wiring can provide us with a cheap and easy way to hook up a group of computers in a building. This may be especially attractive to the PC gamer!
Project description
This project prototypes a real-time communication system that connects two computers. The hardware diagram for this system is seen as follows.
The signal processing required for communication will be handed by the PC processors. A sound card on each PC will handle the Digital-to-Analog and Analog-to-Digital conversion. An AM or FM radio transmitter and receiver will be used to modulate the signal up to a carrier frequency. The decouplers are used to isolate the transmitter and receiver from the 120V power signal at 60Hz.
Design methodology
The key to developing an effective communication systems is to choose an appropriate modulation scheme for a particular physical channel. The chosen modulation scheme for the powerline channel was Orthogonal Frequency Division Multiplexing (OFDM). This scheme encodes information on the phase and magnitude of subcarriers. For a given symbol(basic unit in which information is transmitted), the magnitude and phase of each subcarrier represents encoded bit values. The carries are made orthogonal by choosing the symbol time to corresponds to the frequency space between sub carriers. This eliminates inter-carrier interference.
OFDM is an good match for a powerline communication channel. It makes effective use of bandwidth with moderate signal power. In addition, OFDM can work around narrow band interference that may be picket up from the airwaves. Finally, OFDM is relatively immune to noise spikes and low power broad band noise.