Efficient detection algorithm for 2Nx2N MIMO systems using Alamouti code and QR decomposition

We propose an efficient 2Nx2N MIMO detection algorithm where the transmit signals are grouped in pairs and separately coded using the standard Alamouti space-time code. At the receiver, one or more QR decompositions are performed and the upper triangular property of the R matrices so obtained is exploited in order to successively decode the transmitted symbols starting with those interference-free symbols corresponding to the last two rows and columns of R. Bit-error-rate simulation results, for a 4 x 4 MIMO system and a bandwidth efficiency of 8 bits/s/Hz, show that the proposed technique, while less complex than ordered MMSE V-BLAST, outperforms the latter by 2-6 dB at a BER of 10(-4).