Advanced asynchronous random access protocols

Fifth generation wireless systems and beyond require linking an enormous number of simple machine type devices leading to a new wave of interest in massive machine type communications (mMTC). Different from the human-centric communication systems, mMTCs are composed of a large number of devices where each user node generates small data blocks sporadically in an unpredictable manner. In such scenarios, traditional multiple access schemes, e.g., time division multiple access or frequency division multiple access, are not suitable because resource allocation and scheduling based approaches cannot be conveniently adopted due to the required complexity and latency, motivating the use of uncoordinated random access (RA) protocols and making asynchronous ALOHA-like solutions ideal candidates for such applications. In this thesis, we consider the design and analysis of advanced asynchronous RA protocols for different settings. We first study contention resolution ALOHA (CRA) and irregular repetition ALOHA (IRA) protocols with regular and irregular repetition rates on the collision channel where collisions are resolved through successive interference cancellation. We also propose concatenation of packet replicas with some clean parts with IRA, named irregular repetition ALOHA with replica concatenation (IRARC). Secondly, we introduce energy harvesting (EH) into the framework with the motivation of self-sustainability, and study RA protocols with EH nodes. Finally, we propose a generalization of IRA with packet length diversity to improve the system performance further. We present asymptotic analyses of all the proposed RA protocols, and determine the optimal repetition distributions to maximize the system throughput. We also provide a comprehensive set of numerical results for both asymptotic and practical scenarios to further demonstrate the effectiveness of the proposed approaches.