Adaptive modulation for MIMO systems with V-BLAST detection

Adaptive modulation for multiple-input multiple-output (MIMO) systems with zero forcing (ZF) V-BLAST is considered. Motivated by the observation that the detection ordering of the original V-BLAST algorithm, called the forward ordering, is not suitable for adaptive modulation, a new detection ordering for V-BLAST-based adaptive modulation is proposed. This ordering, called the reverse ordering, selects the symbol corresponding to the minimum gain at each iteration, in contrast to the forward ordering which always gives priority to the maximum gain. The advantage of the reverse ordering over the forward ordering is demonstrated through analysis and simulation. It is shown that the reverse ordering can provide about 2 dB gain as compared with the forward ordering and almost comparable to the optimal ordering which is found through an exhaustive search. The V-BLAST based adaptive modulation with reverse ordering performs somewhat worse than the singular value decomposition (SVD) based method [G.G Raleigh et al., March 1998], but the former is shown to be considerably simpler to implement than the latter.