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.