Digital Communications with Emphasis on Data Modems

8CODING FOR IMPROVED COMMUNICATIONS

8.1 INTRODUCTION

Before delving into the details of error detection and forward error correction (FEC) techniques, it is useful to describe several baseband coding techniques. In the following sections, various forms of baseband pulse code modulation (PCM) are discussed. PCM codes and data compression codes are source coding techniques. Following the description of PCM waveforms, a variety of important coding‐related topics are introduced: gray coding¹ in Section 8.3 and differential coding in Section 8.4; pseudo‐random noise (PRN) sequences in Section 8.5; binary cyclic codes in Section 8.6; cyclic redundancy check (CRC) codes in Section 8.7; data randomizing, or scrambling in Section 8.8; data interleaving in Section 8.9. Following these topics, several forms of FEC channel coding are discussed; Wagner coding and decoding in Section 8.10; convolutional coding and Viterbi decoding in Section 8.11; turbo codes (TCs), parallel concatenated convolutional codes (CCCs) (PCCCs), serially CCCs (SCCCs), double parallel CCCs (DPCCCs), and double serially CCCs (DSCCCs) with reference to the related hybrid CCCs (HCCCs), and self‐concatenated codes (SCCs) in Section 8.12² (the nonturbo codes are collectively referred to as turbo‐like codes); low‐density parity‐check (LDPC) codes, product codes (PCs), and turbo product codes (TPCs) are introduced in Section 8.13; and Bose–Chaudhuri–Hocquenghem (BCH) codes, including M‐ary Reed–Solomon (RS) codes and ...