Low-power log-MAP turbo decoding based on reduced metric memory access

Due to their powerful error correcting performance, turbo codes have been adopted in many wireless communication standards. Although several low-power techniques have been proposed, power consumption is still a major issue to be solved in practical implementations. Since turbo decoding is classified as a memory-intensive algorithm, reducing memory accesses is crucial to achieve a low power design. To reduce the number of memory accesses for maximum a posteriori (MAP) decoding, this paper proposes an approximate reverse calculation of backward metrics which can be implemented with simple computational complexity. Simulation results show that the proposed method, applied to the W-CDMA standard, reduces the access rate of the backward metric memory by 90% without degrading error correcting performance. A prototype turbo decoder based on the proposed reverse calculation achieves 30% power reduction compared to the conventional decoder.