Performance analysis and enhancement for a cooperative wireless diversity network with spatially random mobile helpers

In many studies on wireless cooperative diversity, it is often assumed that the number of helpers and their locations are deterministic or known a priori. In this paper, we relax such assumptions and investigate a wireless diversity system with distributed cooperation and spatially random helpers subject to random direction (RD) mobility. To enable opportunistic relaying with multiple helpers, we consider an ALOHA-like medium access control (MAC) scheme and a timer-based random backoff scheme for multi-helper coordination. Particularly, we analyze the upper bound of combined signal-to-noise ratio (SNR) and unconditional success probability with multi-helper cooperation. We also provide numerical approximations for the delay of the two MAC schemes. To characterize the tradeoff between the success probability and delay, we further define a success/delay ratio, which can be maximized by adapting the intensity of selected helpers. The numerical and simulation results validated the analysis accuracy and demonstrated insightful observations.