Turbo codes are high-performance forward error correction codes that approach the theoretical Shannon channel capacity limit within a fraction of a decibel. Built from two parallel concatenated recursive systematic convolutional (RSC) encoders linked by a pseudo-random interleaver, turbo decoding utilizes two soft-input soft-output (SISO) decoders that iteratively exchange extrinsic log-likelihood ratios (LLRs), progressively refining bit decisions.