OFDMA
Orthogonal Frequency Division Multiplexing (OFDM) is a technique for transmitting large amounts of digital data over a noisy channel, such as the power grid. The technology works by splitting the signal into multiple smaller sub-signals that are then transmitted simultaneously at different (orthogonal) frequencies. Each smaller data stream is then mapped to individual data sub-carrier and modulated using some sorts of PSK (Phase Shift Keying) or QAM (Quadrature Amplitude Modulation) i.e. BPSK, QPSK. Besides its high spectral efficiency, an OFDM system reduces the amount of crosstalk in signal transmissions and can efficiently overcome interference and frequency-selective fading caused by multipath.
While OFDM addresses communications in noisy smart grid environments,it is still insufficient to achieve reliable communications in the very harsh conditions.To further improve reliability the OFDM method can be combined with a multiple access scheme. The approach is called OFDMA.
Orthogonal Frequency-Division Multiple Access (OFDMA) is a multi-user version of the OFDM scheme. Multiple access is achieved in OFDMA by assigning subsets of subcarriers to individual data streams. This allows simultaneous transmission of several individual data streams. OFDMA further improves OFDM robustness to fading and interference, but more importantly the individual data streams can be used either to communicate with multiple nodes (power meters) simultaneously or for redundancy, thus greatly improving the reliability of the system.