OFDM for Underwater Acoustic Communications

Chapter 3Nonbinary LDPC Coded OFDM

Channel coding is an integral part of a digital communication system. Various topics regarding to channel coding have been covered by existing books. In this chapter, we first go over two basic formats of coupling channel coding with OFDM modulation. Then, we will focus on nonbinary low-density-parity-check (LDPC) codes, which are used in the simulation and experimental results contained in this book.

3.1 Channel Coding for OFDM

Figure 3.1 shows a classic diagram of a digital communications system in wireless channels, where information bits pass through source coding and channel coding modules before being modulated for transmission. Channel coding is introduced to protect information bits from errors after transmission through communication channels, and the bit-to-symbol mapping are used to increase the transmission spectral efficiency. Figures 3.2 and 3.3 show typical one-dimensional and two-dimensional constellations widely used in wireless systems, including binary phase-shift keying (BPSK), -ary pulse amplitude modulation (PAM), quadrature phase shift keying (QPSK) and -ary quadrature amplitude modulation (QAM).

Figure 3.1 A schematic ...