Algorithms for Communications Systems and their Applications, 2nd Edition

Chapter 8Multicarrier modulation

For channels that exhibit high signal attenuation at frequencies within the passband, a valid alternative to single carrier (SC) is represented by a modulation technique based on filter banks, known as multicarrier (MC) modulation. As the term implies, MC modulation is obtained in principle by modulating several carriers in parallel using blocks of symbols, therefore using a symbol period that is typically much longer than the symbol period of an SC system transmitting at the same bit rate. The resulting narrowband signals around the frequencies of the carriers are then added and transmitted over the channel. The narrowband signals are usually referred to as subchannel (or subcarrier) signals.

An advantage of MC modulation with respect to SC is represented by the lower complexity required for equalization, that under certain conditions can be performed by a single coefficient per subchannel. A long symbol period also yields a greater immunity of an MC system to impulse noise; however the symbol duration, and hence the number of subchannels, is limited for transmissions over time‐variant channels. As we will see in this chapter, another important advantage is the efficient implementation of modulator and demodulator, obtained by sophisticated signal processing algorithms.

8.1 MC systems

In MC systems, blocks of symbols are transmitted in parallel ...