An asymptotic analysis on the performance of coded cooperation systems

User-cooperation or relaying through other nodes is an efficient approach to obtain diversity in wireless networks. In this paper, we consider a coded cooperative system under quasi-static Rayleigh fading and find conditions on the inter-user and user-to-destination channel qualities for cooperation to be beneficial. We define the user cooperation gain (G_f) as the gain in frame error rates due to cooperation when a particular channel code is used. We introduce the cooperation decision parameter (CDP) which is only a function of user-to-destination channel qualities and demonstrate that whether cooperation is useful or not (G_f>1 or G_f<1) depends only on the cooperation decision parameter, not inter-user link quality. We make use of the analytical formulation of the CDP to explore how user cooperation gain behaves in high signal to noise ratios and how relative link qualities of user-to-user and user-to-destination channels affect cooperation benefits in this asymptotic range. Furthermore, we investigate how one can choose a partner from candidate nodes such that the user cooperation gain is larger. All of our theoretical results are supported by simulations.