Implementation and Analysis of Multi-user MIMO with Amplify-and-Forward Relaying

A two-hop multi-user multiple-input-multiple-output (MU-MIMO) system with multiple single-antenna amplify-and-forward (AF) relays is demonstrated for the first time in a realistic indoor environment with a commercial software radio platform, using OFDM. Good trend correspondence is observed between the averaged error rate results of experiment and simulation, when zero forcing (ZF) detection is employed and a simple constraint on the average power per relay is used. The challenges of relaying a regenerated digital header and simply amplified spatially multiplexed payload are discussed. It is proven theoretically that the effect of the growth of the number of fixed-gain relays is to bring the destination into the location of the relays. For the case of variable gain, subject to a per-node average power constraint, the destination is also brought asymptotically closer, but not as close as the fixed-gain. However, the gap is approximately closed by allowing relays to deactivate if their gain exceeds a threshold.