VLSI implementation issues of TURBO decoder design for wireless applications

Finite precision effects on the performance of TURBO decoders have been analyzed and the optimal word lengths of variables have been determined considering tradeoffs between the performance and the hardware cost. It is shown that the performance degradation from the infinite precision is negligible if 4 bits are used for received bits and 6 bits for the extrinsic information. The state metrics normalization method suitable for TURBO decoders is also discussed. This method requires small amount of hardware and its speed does not depend on the number of states. Furthermore, we propose novel power-down techniques, which can achieve very high power-down efficiency without performance or latency degradation at the expense of negligible hardware overhead.