Decentralized power control for random access with iterative multi-user detection

This paper is concerned with the application of iterative multi-user detection (MUD) in ALOHA-type random access systems. We focus on a random-power transmission scheme, in which the transmission power level of each user is randomly selected according to a certain distribution f. We aim at designing f to maximize the system throughput given an average power constraint for each user. We adopt a suboptimal scheme, in which only type-2 collisions (collisions involving two packets) are resolved. We first prove that, the support (i.e., the smallest closed set whose complement has zero probability) of the optimal f in this case is a discrete set for systems with certain feasible regions (the set of power profiles that can support reliable communications). The related discrete set can be easily obtained according to the boundaries of the feasible region. We then apply this finding to the design of f. Numerical results show that with iterative MUD, the proposed scheme can achieve noticeable performance improvement compared with the conventional ALOHA and offer flexible tradeoff between the system throughput and power consumption.