emory of the channel is not limited to a string of three bits, but extends to longer bit series. In this case, equalization is a complex matter requiring elaborated algorithms like mean-squared error (MSE) or signal back-propagation. In contrast, the complexity of OFDM, using serial modulation and frequency domain equalization, scale well as data rates and dispersion increase. The basic concept of OFDM is simple: data are transmitted in parallel on a number of different frequencies. Due to the parallelization of the data flux, the symbol period is much longer than that of a serial system with the same total data rate. Due to the longer symbol period, the channel memory gets shorter, or even disappears completely, since dispersion only affects one symbol. In most OFDM implementations, any residual ISI is removed by using a form of guard interval between adjacent bit intervals called a cyclic prefix. It could seem that this is simply frequency multiplexing, similar to what happens in WDM systems, but there are key differences between standard WDM and OFDM. In standard WDM, the signals transmitted on different wavelengths are completely uncorrelated and guard intervals are used in between adjacent channels in order to reduce crosstalk. WDM multiplexing is performed using an analog optical device, and the same for demultiplexing. OFDM on the other hand, is based on the digital generation of the multiplexed signal by densely packing channels that are generated to be orthogonal from a mathematical point of view. Since the channels can be separated using their orthogonality, there is no need of guard intervals among them. The generation of the multiplexed signal and the demultiplexing is operated via Fast Fourier Transform (FFT) by a dedicated processor; thus it is a computationally effi- cient and fast operation that can incorporate, if needed, equalization in the frequency domain. It is not our scope to review in detail OFDM techniques, but it is quite clear that OFDM could become a useful technique to design very hig