4.10 COMPOUND CODES
Modern error-control coding has advanced beyond classical block and convolutional codes through the development of compound codes—powerful schemes that combine multiple simple component codes to approach the theoretical limits of communication efficiency. Compound codes generally employ iterative or soft-information-exchange decoding, where multiple soft input soft output (SISO) decoders exchange probabilistic information to refine the likelihood of the transmitted bits.
Three principal families dominate this class:
- Turbo codes, which couple convolutional encoders through interleaving; and
- Low-Density Parity-Check (LDPC) codes, which employ sparse linear block structures with iterative message-passing decoders.
- Polar codes, which achieve channel capacity through channel polarization and successive-cancellation decoding rather than iterative message passing.
These codes achieve near–Shannon-limit performance and define the state of the art in coding theory. They provide the best trade-off between bandwidth efficiency, power efficiency, and implementation complexity for modern satellite, wireless, and deep-space systems.
Back to reading