1. Field
This disclosure relates to local area networks using power line communications.
2. Description of the Related Art
A variety of communications media and standards is available for use in network communications. In this patent, the term “communications medium” means any medium for conveying or transmitting information-bearing waveforms or signals. Communications media include electrical wires, coaxial cables, optical fibers, and wireless communications using radio-frequency, optical, or acoustic carrier waves. An emerging technology for network communications is power line communications (PLC), which may operate in accordance with standards such as IEEE Std 1901-2010 or the International Telecommunications Union ITU-T G.hn standard. ITU-T G.hn is also a standard for phone line communications and communications over TV cable.
PLC may be used for communications between equipment powered from the same power system. For example, home computer systems and home entertainment systems are typically composed of several hardware units interconnected by numerous data cables, such as USB (universal serial bus) cables, Ethernet cables, HDMI (High-Definition Multimedia Interface) cables, audio cables, and/or video cables. Such systems typically have a power cord connecting each unit to an AC power outlet. PLC offers the potential for such equipment to communicate via their power cords and the AC home wiring, eliminating or greatly reducing the number of data cables. The application of PLC is not limited to home electronics systems or even AC power lines.
PLC functions by superimposing a high frequency data signal on the low frequency (typically 50 or 60 Hz) power line. A data signal placed on the power line by one unit may be present everywhere within the same power distribution circuit. Thus the communications bandwidth of the power distribution circuit must be shared by various units. This sharing may lead to reduced performance or inter-unit interference if many units operate from the same power distribution circuit.
Throughout this description, elements appearing in figures are assigned three-digit reference designators, where the most significant digit is the number of the figure in which the element is introduced. An element that is not described in conjunction with a figure may be presumed to have the same characteristics and function as a previously-described element that has the same reference designator.