A study on reduced MLD utilizing the QR decomposition for MIMO communication systems

Reduced maximum likelihood detection (R-MLD) has been proposed as an MIMO decoder. It was reported that the R-MLD showed equivalent performance with a full MLD under the symbol level detection for 2 × 2 MIMO systems with reduced computational complexity. However, the computational load becomes extremely large when we apply the idea directly to MIMO systems with three transmission antennas or more. In this paper, we study to apply the idea of the R-MLD to MIMO systems with three transmission antennas or more, and show an example of 4 × 4 MIMO system. We apply the QR decomposition to a 4 × 4 MIMO channel matrix, and divide the upper triangle matrix into four 2 × 2 matrices including one zero matrix so that we can apply the R-MLD scheme hierarchically. Numerical simulations show that allowable packet error rate are achieved with less computational complexity.