Cooperative Regions for Coded Cooperative Systems

Cooperation of mobiles provides signal diversity in wireless networks. In this paper, we consider a coded cooperative system under Rayleigh fading and path loss. For an arbitrary signal to noise ratio, we find conditions on the user geometry for two-user cooperation to be beneficial. We find that whether cooperation is useful or not is only determined by the cooper- ation decision parameter (CDP). We illustrate regions for which cooperation results in a gain in Frame Error Rate (FER) for individual users and use the analytical formulation of the CDP to investigate how locations of the user and the partner affect the user cooperation gain. Our analytical results also provide insights on how a user can choose among many partners to maximize cooperation gain. All of our theoretical results are verified by numerical simulations of the FER. I. INTRODUCTION Cooperative communication enables nodes to use each other's antennas to obtain an effective form of spatial diversity (e.g., (1)-(6)) in a fading wireless environment. Channel coding for cooperative systems have been proposed in (3)- (5). In (6), cooperative coding was extended to multiple input and multiple output systems, where partnering nodes may have different number of antennas. Most of the research on cooperation assumes the cooperating partner has been chosen and investigates how cooperation improves the system's per- formance in terms of outage probability or FER. However, cooperation among users only benefits the partnering users under certain conditions. In (2), the "utilization regions" for the incremental amplify-and-forward protocol and the fixed decode-and-forward protocol were derived. The regions were based on outage analysis. In (7), we provided an asymptotic analysis (in terms of SNR) on the FER performance of the coded cooperative system (4). We also studied the partner choice problem for high SNR region.