LLR optimization for iterative MIMO BICM receivers

Iterative detection and decoding (IDD) relies on passing useful extrinsic information between the detector and the decoder. Due to the sub-optimality of practical detector and/or decoder, the direct output LLRs from the detector or the decoder may not provide sufficient gains to each other. Proper scaling of the extrinsic LLRs based on certain optimality criteria may improve the performance of the IDD receiver. However, finding optimal scaling function for IDD receiver in general is still an open problem. In this paper, we investigate LLR scaling of the detector and the decoder output based on maximization of generalized mutual information.