Overview

We consider a one-way communication system, where the transmission is strictly in the forward direction, from the transmitter to the receiver. In contrast to a two-way system that can use ARQ with error detection and retransmission, the error control strategy for a one-way system must be FEC, which automatically corrects errors detected at the receiver. The class of FEC codes includes block codes, convolutional codes, as well as concatenated codes that are built using block and/or convolutional codes. Turbo codes and LDPC codes are the newest members of the family of FEC codes.

In this chapter, after a brief review of basic ideas behind turbo codes, as well as LDPC codes that are going to be introduced in more detail in Chapter 9, turbo decoding principle will be presented. We will then discuss some of the issues such as the choice of the constituent codes, the interleaving, trellis termination and puncturing. Finally, we give some examples of turbo codes including the one in 3GPP standard.