Abstract:

Iterative tree search (ITS) is an efficient soft detection scheme in multipleinput multipleoutput (MIMO) systems. However, there often exists in ITS that loglikelihood ratio (LLR) values of some detected bits cannot be evaluated. Although it can be somewhat solved by setting the LLR magnitude for these bits to a constant value, the system performance would be degraded. To overcome this drawback, an improved soft detection scheme is proposed. The scheme ensures that the LLR value of each bit can be calculated and provides highly reliable LLR by appropriately choosing some discarded paths, retaining them and extending them to fulllength paths. The rule of choosing suitable discarded paths is presented and the lowcomplexity approach of extending them to full length is given. Simulations show that the proposed algorithm can obtain better performance than ITS and can achieve good performancecomplexity tradeoff.

Key words: MIMO, soft-MIMO detection, ITS, M-algorithm, bit LLR