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Talking To Your Fridge? You Need In-House Broadband Over Powerline: Page 3 of 10

HomePlug makes use of a version of OFDM (Orthogonal Frequency Division Multiplexing) specially tailored for powerline environments. OFDM splits the signal into a stream of data symbols for massively parallel simultaneous transmission over a number of narrowband, low data rate subcarrier frequencies. (Note: OFDM is the transmission technique used in 802.11a (aka Wi-Fi5) and 802.11g, 802.16 and WiMax). HomePlug 1.0 specifies 84 equally spaced subcarriers; within each, several differential modulation techniques are employed. As many as 16 nodes can be supported.

Attenuation, or loss of signal strength, is a fact of life. As an electromagnetic signal travels through a medium (e.g., electrical signals through copper conductors) and across various components (e.g., fuse boxes, splices, surge suppressors and circuit breakers), the signal loses some of its strength. Within the limits of the loss budget, which considers the strength of the transmitter, the sensitivity of the receiver and the various attenuating factors between the two, the system will perform adequately.

HomePlug currently offers a range of as much as 300 meters without repeaters, which is well more than the 100 meters supported by 10/100BaseT -- and without the need for running Cat 5 data-grade cable.

Note: UPSs (Uninterruptible Power Supplies) contain transformers, which stop the data communications signal in its tracks. UPSs also typically condition the electric current by running it through a trickle-charge battery pack to smooth the AC waveform in order to filter out power spikes and dips and to compensate for short power interruptions -- this conditioning also strips out the data communications signal. By the way, extension cords should be avoided -- particularly the skinny ones that you use for things like Christmas tree lights -- as they involve one more set of plugs and add to the overall run length with a cord of uncertain performance characteristics.

Interference issues can be significant. EMI (Electromagnetic Interference) sources include brush motors, switching power supplies, fluorescent lights and halogen lamps, all of which produce impulse noise that can affect communications signal integrity over the shared electrical bus. HomePlug deals with these challenges through a combination of forward error correction (FEC) and automatic repeat request (ARQ).