Parallel concatenated codes with iterative decoding - near Shannon limit!
Structure: Two RSC encoders in parallel, connected by an interleaver. Third output is from interleaved data.
Interleaver: Scrambles bit order before second encoder. Creates statistical independence between parity checks.
Iterative Decoding: Two SISO decoders pass "extrinsic information" back and forth. Each iteration improves estimates!
Near Shannon Limit: At rate 1/3 with large interleaver, can achieve BER=10⁻⁵ at just 0.7 dB from capacity!
Applications: 3G/4G cellular, deep space (Mars missions), satellite, WiMAX.