Performance analysis of AF cooperative networks with time-varying links: Outage probability

In this paper, we consider an M-relay amplify-and-forward (AF) cooperative system with maximal ratio combining (MRC) at the destination and investigate the effects of both the mobile cooperating-nodes speeds and the receivers´ channel state information (CSI) estimation rates on the system outage performance. By CSI estimation rates we mean how much the receivers´ tracking loops are fast to estimate the channel gains over the individual time slots. The fading links are considered to be frequency-flat time-varying Rayleigh fading and modeled by a first-order autoregressive process (AR1). General closed-form approximate expression is derived for the outage probability, which is further verified through Monte Carlo simulation. The derived expression is valid for time-varying as well as quasi-static fading links for both low and high CSI estimation rates. Furthermore, we analytically show that, due to high speeds of the cooperating-nodes, the outage probability experiences asymptotic floor which could be completely eliminated by well-designed fast tracking loops at the receivers. This outage performance is also investigated under different nodes mobility scenarios.