The HomePlug AV PHY is designed to operate as close as possible to the channel capacity of the powerline. Due to the restrictions imposed by the powerline regulation, a spectrally efficient PHY is essential to support multimedia streams.

HomePlug AV uses the OFDM modulation technique. Its inherent adaptability in the presence of frequency selective channels, resilience to narrowband interference, and robustness to impulse noise make it attractive. It is used in conjunction with bit loading to provide flexibility with which to adapt to the powerline channel, allowing optimized and stable channel throughput.

Time-domain pulse shaping of the OFDM symbols is employed to provide flexible spectral notching (required to satisfy different regulatory constraints throughout the world). Applying this tapering to the beginning and end of the OFDM symbols causes a smoother time-domain transition from symbol to symbol, resulting in a faster spectral roll-off in the frequency domain. This shaping is possible in the AV PHY due to the use of long OFDM inverse fast Fourier transform (IFFT) intervals and cyclic prefix (CP) durations. AV also employs multiple CP lengths for intersymbol interference (ISI) mitigation, allowing it to use a smaller CP on channels exhibiting shorter delay spreads, minimizing overhead.

HomePlug AV employs 1155 carriers, ranging from 1.80 MHz to 30.00 MHz. Of the 1155 available carriers, spaced about 24.414 kHz apart, 917 are used for modulation in North America (the remaining 238 are turned off or “masked” so as not to interfere with licensed services). Carriers may be coherently modulated with binary phase shift keying (BPSK), quadrature phase shift keying (QPSK), 8-quadrature amplitude modulation (QAM), 16-QAM, 64-QAM, 256-QAM or 1024-QAM depending on the SNR measured at the carrier frequency. HomePlug AV uses a parallel-concatenated turbo convolutional code (TCC), widely known to provide channel throughput near the theoretical limit with manageable complexity.

A block diagram of a HomePlug AV transceiver is shown in Figure 3. On the transmitter side, the PHY layer receives its inputs from the MAC layer. Three separate processing chains are shown because of the different error correction coding for HomePlug 1.0.1 control information, HomePlug AV control information, and HomePlug AV packet body data or payload. The control information carries such information as destination and source addresses and frame length while the payload contains the information to be transported. The outputs of the three FEC encoders lead into an OFDM modulation structure. The output feeds the analog front-end (AFE) module that couples the signal onto the powerline.

At the receiver, an AFE operates with an automatic gain controller (AGC) and a time synchronization module to feed separate control and data information recovery circuits. Assuming the digitized waveform out of the AFE is sampled at 75 MS/s, the frame control is recovered by processing the received sampled stream through a 384-point fast Fourier transform (FFT) (for HomePlug 1.0.1 delimiters) and a 3072-point FFT (for HomePlug AV). The output then passes through separate frame control demodulators and frame control decoders for each mode. The following sampled packet body or payload stream contains only HomePlug AV formatted symbols. These are processed through a 3072-point FFT, a demodulator with SNR estimation, a channel de-interleaver, turbo FEC decoder, and a de-scrambler to recover the transmitted information.

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