Switching Between Antenna Selection and Spatial Multiplexing in the Amplify-and-Forward MIMO Relay Channel
IEEE Asilomar Conference on Signals, Systems & Computers, pp. 1469 - 1473, October 26th - 29th, 2008. (invited paper)
Multiple-input multiple-output (MIMO) wireless systems can improve performance by adapting between multiplexing and diversity modes of operation based on some instantaneous knowledge of the channel. Previous work has found a sufficient condition for spatial multiplexing to outperform various transmit diversity techniques in the point-to-point MIMO channel. This paper proposes and analyzes the concept of switching between spatial multiplexing assuming no transmit-side channel state information and transmit antenna selection for the narrowband amplify-and-forward MIMO relay channel with direct link. A sufficient condition for multiplexing to outperform antenna selection is derived for fixed-rate transmission. The main result is a new effective condition number of the relay channel that has nice intuitive properties.