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- A Double Stage Random Access Scheme for Decentralized Single Radio Cognitive NetworksPublication . Oliveira, Rodolfo; Borges, Luís M.; Velez, Fernando J.This work proposes a new scheme to coordinate the medium access of single-radio unlicensed users in a decentralized cognitive radio network. The proposed solution is based on two different stages. Unlicensed users randomly define the medium access sequence during the first stage and part of the second one. Then the nodes simply transmit their packets according to the reserved sequence. The performance of the proposed scheme is theoretically characterized in terms of the throughput achieved by unlicensed users and validated through simulation. Since a random access mechanism is used in the both stages, we also compare the performance of our proposal with a pure Slotted Aloha access scheme and an improved version of it. By comparing their performance, we conclude that the proposed scheme exhibits significant gains in terms of the throughput achieved by unlicensed users, and it can be recommended as a viable solution for future decentralized single radio cognitive networks.
- A two-phase contention window control scheme for decentralized wireless networksPublication . Borges, Luís M.; Velez, Fernando J.; Oliveira, RodolfoMost studies on performance of IEEE 802.11 distributed coordination function (DCF) have proved that the binary exponential backoff (BEB) algorithm suffers from low throughput, long transmission delays and low transmission reliability, for a high traffic load. In this paper, we propose a two-phase contention window (TPCW) access mechanism that enhances the aggregate throughput and transmission reliability while decreasing the medium access delay. In addition, this scheme aims at being computationally simple. This work characterizes the performance of the TPCW mechanism for different parameterization values. An analytical model is proposed for the TPCW access mechanism, which characterizes the frame transmission reliability, the total transmission delay and the aggregate throughput. The validity of our analytical model is verified through extensive simulations. By comparing the performance results, we conclude that the proposed scheme can significantly enhance IEEE 802.11 in terms of frame transmission reliability, total transmission delay and aggregate throughput.