Orthogonal Frequency Division Multiplexing (OFDM) is the basic transmission technique used by theHomePlug It is currently used in DSLtechnology, terrestrial wireless distribution of television signals, and has also been adapted for IEEE's high ratewireless LAN Standards (802.11a and 802.11g). The basic idea of OFDM is to divide the available spectrum into several narrow band, low data rate sub-carriers. To obtain high spectral efficiency the frequency response. of the subcarriers are overlapping and orthogonal, hence the name OFDM.

Each narrowband subcarrier can be modulated using various modulation formats. By choosing the subcarrier spacing to be small the channel transfer function reduces to a simple constant within the bandwidth of each sub-carrier. In this way, a frequency selective channel is divided into many flat fading sub-channels, which eliminates the need for sophisticated equalizers.

The OFDM used by HomePlug is specially tailored for powerline environments. It uses 84 equally spaced subcarriers in the frequency band between 4.5MHz and 21MHz. Cyclic prefix and differential modulation techniques (DBPSK, DQPSK) are used to completely eliminate the need for any equalization.
Impulsive noise events are overcome by means of forward error correction and data interleaving. HomePlug payload uses a concatenation of Viterbi and Reed-Solomon FEC. Sensitive frame control data is encoded using turbo product codes.

The powerline channel between any two links has a different amplitude and phase response. Furthermore, noise on the powerline is local to the receiver. HomePlug technology optimizes the data rate on each link by means of an adaptive approach. Channel adaptation is achieved by Tone Allocation, modulation and FEC choice. Tone allocation is the process by which certain heavily impaired carriers are turned off. This significantly reduces the bit error rates and helps in targeting the power of FEC and Modulation choices on the good carriers.

HomePlug allows for choosing from DBPSK 1/2, DQPSK 1/2 and DQPSK 3/4 on all the carriers. The end result of this adaptation is a highly optimised link throughput. Certain types of information, such as broadcast packets, cannot make use of channel adaptation techniques. HomePlug uses an innovative modulation called ROBO, so that information is reliably transmitted.
ROBO modulation uses a DBPSK with heavy error correction with bit repetition in time and frequency to enable highly reliable communication. ROBO frames are also used for channel adaptation.