Performance analysis of AF cooperative networks with time-varying links: Error rate and capacity

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 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 expressions are derived for the bit error rate and the system Shannon capacity, which are further verified through Monte Carlo simulations. These expressions are 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 and/or constrained CSI estimation rates, both of the error rate and the capacity suffer from asymptotic limits. These limits could be completely eliminated by a well-designed fast tracking loops at the receivers even though the speeds of the mobile nodes are relatively high.