How does latest-generation HomePlug AV modulate data on the AC power signal, and how does it handle detection, correction, and/or retransmission of errors in that data? How does HomePlug AV compensate for varying noise levels on the power grid, caused by fluorescent lights, motors (vacuum cleaners, hair dryers, heater and air-conditioning fans, etc)? And how do you educate consumers on the potential need to install noise filters on the power inputs of these interference sources, in order to ensure reliable powerline network operation?

HomePlug AV uses a multidimensional approach to the powerline noise problem. Among the techniques it employs are time domain mitigation, frequency domain mitigation, dynamic channel estimation, and a very efficient forward-error-correction method based on Turbo Codes and developed by France Telecom.

In the time domain, transmissions synchronize with the zero-crossing of the AC line cycle. Much of the noise on household AC wiring is time-related. In other words, noise events often repeate at the same locations of the AC cycle. Once recognized, it is a simple matter to time transmissions around the noise.

In the frequency domain, domestic AC wiring noise is not evenly spread across the HomePlug AV frequency spectrum (approximately 2 to 30 MHz). Noise appears at separated frequency points across the band. HomePlug AV employs orthogonal frequency division multiplexing, composed of some 1155 carriers spaced 24 kHz apart (only 917 of which actually find use with HomePlug AV, in consideration of the Amateur Radio community). Each carrier, when modulated, creates analog symbols that contain as many as 10 data bits. For carriers that frequency-cohabitate with noise, adjusted "bit loading" optimizes performance under that challenge.

Dynamic channel estimation is the intelligence behind noise mitigation. This channel-estimation process frequently and repeatedly takes place between every two nodes in the home PLC network, optimizing timing and carrier bit loading for each powerline-network path.

Forward error correction adds bit overhead, but it is essential for robust communications over any medium (wireless or wired). In many cases, FEC eliminates the need to resend a packet or block of packets when data is lost. FEC has the ability to reconstruct the data on the receive end in real time. France Telecom's Turbo Convolution Code technology achieves exceptional performance and realizes greater throughput in the presence of noise, allowing HomePlug AV home networks to operate at a lower SNR. This advanced FEC coding has power efficiencies approaching (within 1 dB of) the theoretical Shannon limit and is well proven, having been widely adopted in harsh communications environments such as cellular telecommunications (CDMA2000 and W-CDMA), satellite (DVB-RCS, CCSD), and broadband wireless (802.16, WiMAX).