Relay selection and beamforming with outdated CSI for AF MIMO relay systems

In this paper, we investigate the outage performance of an amplify-and-forward (AF) multiple input multiple output (MIMO) opportunistic relay selection system under time-varying channels. A practical scenario is considered, where both the relay selection and the beamforming transmission are performed with outdated channel state information (CSI), due to channel fluctuations and delays involved in relay selection and CSI feedback. To provide efficient means of evaluating the outage performance, a closed-form expression for the outage probability is given. The effects of parameters, such as the correlation between the outdated and current CSI, the number of antennas are also analyzed. All the analytical results are validated by Monte Carlo simulations.