Parallel Implementation of a Soft Output Sphere Decoder

Transmission at rates close to capacity over fading multiple antenna channels can be achieved by concatenating inner space-time block codes and powerful outer codes such as turbo or LDPC codes. However, in such systems, computation of the required soft information, or log-likelihood ratios (LLR), for the bits transmitted over the channel is rather complex and some form of approximations are typically used. Herein, we show how the complexity of computing the max-log approximation of the LLR can be reduced by computing all LLR values simultaneously using a parallel sphere decoder implementation