  In this work, we present a switched relaying framework for multiple-input
multiple-output (MIMO) relay systems where a source node may transmit directly
to a destination node or aided by relays. We also investigate relay selection
techniques for the proposed switched relaying framework, whose relays are
equipped with buffers. In particular, we develop a novel relay selection
protocol based on switching and the selection of the best link, denoted as
Switched Max-Link. We then propose the Maximum Minimum Distance (MMD) relay
selection criterion for MIMO systems, which is based on the optimal Maximum
Likelihood (ML) principle and can provide significant performance gains over
other criteria, along with algorithms that are incorporated into the proposed
Switched Max-Link protocol. An analysis of the proposed Switched Max-Link
protocol and the MMD relay selection criterion in terms of computational cost,
pairwise error probability, sum-rate and average delay is carried out.
Simulations show that Switched Max-Link using the MMD criterion outperforms
previous works in terms of sum-rate, pairwise error probability, average delay
and bit error rate.
