Multiple Access Interference-Free Multichannel Slotted Aloha Scheme for Time-Asynchronous OFDMA Systems

Junwoo JUNG  Jaesung LIM  Haengik KANG  Hyungwon PARK  

IEICE TRANSACTIONS on Communications   Vol.E98-B   No.4   pp.686-700
Publication Date: 2015/04/01
Online ISSN: 1745-1345
DOI: 10.1587/transcom.E98.B.686
Type of Manuscript: PAPER
Category: Wireless Communication Technologies
multi-channel,  slotted Aloha,  OFDMA,  MAI,  

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Signals transmitted by multiple stations through different multiple subchannels may arrive at a particular station, such as an access point (AP), with different time delays. If the difference in arrival time delays exceeds the cyclic prefix duration, the orthogonality among the subchannels can be broken, which leads to multiple access interference (MAI) among the stations. In this paper, we propose a multichannel slotted Aloha scheme based on an MAI-free group for a simple orthogonal frequency division multiple access (OFDMA) wireless network. Each MAI-free group consists of stations whose signals arrive at the AP within the cyclic prefix duration. The proposed scheme outperforms a conventional scheme using a fast retrial algorithm in terms of throughput due to smaller cyclic prefix duration, lower collision probability, and lower block probability. While the proposed scheme has higher delay overhead in a low arrival rate region, its delay approaches that of the conventional scheme as the arrival rate increases.