Log-likelihood ratio based detection ordering in the V-BLAST combined with space-time block codes

Abstract

We consider a Vertical Bell Laboratories Layered Space-Time (V-BLAST) system combined with space-time block codes which is a multiple antenna system when combined array processing with space-time block coding is used. In this system, transmit antennas are partitioned into several groups and signals in the same group are then encoded with orthogonal space-time block code. Next, each group may go through the same detection process, i.e. nulling, cancelling and detection ordering, as each substream does in the V-BLAST system. In this thesis, we present a new detection ordering for the V-BLAST system which is combined with space-time block coding. The idea is to detect and cancel groups in order of the magnitude of a certain ordering measure which is a function of log-likelihood ratio (LLR) of each group, i.e. the group with the ordering measure which minimizes the error probability is detected first. The motivation is that the error probability can be expressed as a function of group LLR and the reliability of data decision also has a relationship with the group LLR. As a result, the error propagation associated with a wrong decision and the resulting error probability for the remaining groups can be reduced. It is also shown that the proposed LLR-based ordering significantly outperforms the conventional SNR-based ordering. Simplified LLR-based ordering and envelope-based ordering that require a much less computation, but provide a performance virtually identical to the LLR-based ordering, are also proposed.