Code Combining

It is well-known, that by choosing the data rate below the channel capacity, error-free communications is possible. Furthermore, existing practical error-correction coding techniques can be used to meet reliability constraints. However, a basic design problem for reliable digital communications is the selection of the code rate. The popular rate-1/2 code is a good choice for AWGN channels, but is a poor choice for channels where a large fraction of the transmitted bits are destroyed by interference. Designing a system for the worst-case scenario may require extremely low rate codes to bring the data rate below channel capacity (ref. 1). Code combining is an adaptive technique, which matches the code rate to the prevailing channel conditions.