Overview

A power line communications (PLC) system modulates voice, data, and video signals and sends them over the existing A/C power lines to the h ome. Power lines offer the best existing infrastructure and the lowest cost broadband communications and home networking presently available. The signals are simply A/C coupled to the power line through a transformer or balun. The frequencies are low enough to minimize radiation as the signal travels down the power lines to the receiver. The range is adequate to service nearly all of the outlets. Even with connections on different phases, communications is possible though coupling between the phases (phase jumping). Communications through the power lines are classified as current carrier devices and provide an excellent way to establish networks and communications in an already existing infrastructure.

As is the case with all systems, noise and jamming signals are also present on the power lines. Also, multipath and impedance mismatches occur, which can cause some of the band to be unusable. Because a power line is hard wired and does not rely on electromagnetic waves through the air, signal blockage is irrelevant. However, power lines have to contend with appliances and other devices plugged into the outlets which can cause attenuation, mismatches and noise.

PLC devices that are presently in use have operated with minimal dropouts and have been very reliable in spite of the potential problems that exist on the power lines. Most of the newer systems today utilize spread spectrum, parallel channels,...