Browsing by Author "Demirhan, U."

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    Asymptotic analysis of contention resolution ALOHA with replica concatenation
    (Institute of Electrical and Electronics Engineers Inc., 2019) Akyıldız, Talha; Demirhan, U.; Duman, Tolga M.
    In this paper, we present an asymptotic performance analysis of contention resolution ALOHA (CRA) on the collision channel for both regular and irregular repetition rates. In addition, we consider an improvement to CRA by merging the clean parts of replicas in partial collisions and extend our analysis to this scenario. Specific designs of repetition distributions based on the new analysis show that the optimized solutions for irregular repetition slotted ALOHA (IRSA) perform well in both CRA and the enhanced scheme.
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    Energy harvesting irregular repetition ALOHA with replica concatenation
    (IEEE, 2021) Akyıldız, Talha; Demirhan, U.; Duman, Tolga M.
    In this paper, we consider an asynchronous random access scheme called irregular repetition ALOHA (IRA) as a generalization of contention resolution ALOHA (CRA) with varying repetitions. We present an asymptotic performance analysis of CRA and IRA on the collision channel for regular and irregular repetition rates. We also propose an improvement by merging the clean parts of packet replicas in partial collisions, and extend our analysis to this scenario as well. Specific designs of repetition distributions based on the new analysis show that the optimized solutions of irregular repetition slotted ALOHA (IRSA) perform well in both IRA and the enhanced scheme, and they considerably outperform the regular repetition distributions. We also introduce energy harvesting (EH) to both schemes as a practical and sustainable adaptation, where users are able to harvest energy and store it in their finite-capacity batteries. We model the battery state by a discrete-time Markov chain and derive an optimal transmission policy to maximize the asymptotic performance of the system. We provide comprehensive numerical results for both practical and asymptotic scenarios to verify the validity of the proposed analyses, and illustrate the benefits of the proposed systems.
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    Energy-harvesting irregular repetition slotted ALOHA with unit-sized battery
    (IEEE, 2018-05) Demirhan, U.; Duman, Tolga M.
    We propose an irregular repetition slotted ALOHA (IRSA) based uncoordinated random access scheme for energy harvesting (EH) nodes. Specifically, we consider the case in which each user has a unit- sized battery that is recharged with energy harvested from the environment in a probabilistic manner. We analyze this scheme by deriving asymptotic throughput expressions, and obtain optimized probability distributions for the number of packet replicas for each user. We demonstrate that for the case of IRSA with EH nodes, these optimized distributions perform considerably better than those of slotted ALOHA (SA), contention resolution diversity slotted ALOHA (CRDSA) and IRSA, which do not take into account the EH process, for both asymptotic and finite frame length scenarios.