Algorithms for Communications Systems and their Applications, 2nd Edition

Chapter 11Channel codes

Forward error correction (FEC) is a widely used technique to achieve reliable data transmission. The redundancy introduced by an encoder for the transmission of data in coded form allows the decoder at the receiver to detect and partially correct errors. An alternative transmission technique, known as automatic repeat query or request (ARQ), consists in detecting the errors (usually by a check‐sum transmitted with the data, see page 556) and requesting the retransmission of a data packet whenever it is received with errors.

The FEC technique presents two advantages with respect to the ARQ technique.

1. In systems that make use of the ARQ technique, the data packets do not necessarily have to be retransmitted until they are received without errors; however, for large values of the error probability, the aggregate traffic of the link is higher.
2. In systems that make use of the FEC technique, the receiver does not have to request the retransmission of data packets, thus making possible the use of a simplex link; this feature represents a strong point in many applications like time division multiple access (TDMA) and video satellite links, where a central transmitter broadcasts to receive‐only terminals, which are unable to make a possible retransmission request. The FEC technique is also particularly useful in various satellite communication applications, in which the long round‐trip delay of the link would cause serious traffic problems whenever the ARQ technique ...