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.