Performance of slotted ALOHA in OFDM based multichannel system

Abstract

In this work slotted ALOHA protocol, OFDM system and the OFDM channel model for the random access purpose is demonstrated. The advantages of OFDM channel model compared to conventional FDMA/CDMA model are discussed. Channel traffic, packet success rate, bit error rate, throughput and delay are the vital Quality of Service (QoS) parameters used for performance measurement for any network access scheme. In this research analytical formulations of these QoS parameters for the proposed ALOHA scheme are derived. Numerous performance improvement techniques are introduced to optimize QoS parameters. Different network parameters are evaluated in case of single packet transmission per user. Analysis for simultaneous multicopy transmissions per user is carried out also. Different multicopy transmission schemes like fixed multicopy transmission and hybrid single-multicopy transmission scheme are analyzed. The effect of capture in the retransmission environment to improve network performance is investigated. Effect of number of channels is also shown. Effect of Reed Solomon coding on system performance is compared with the performance of uncoded system in different channel bit error rate conditions. The analytical expressions become more complex continually with the incorporation of different performance enhancement techniques. Moreover, the proposed system provides significant performance improvement without requiring any sophisticated control and still preserving the simplicity of ALOHA algorithm. Therefore, OFDM based slotted ALOHA seems to be a strong candidate for the future high-speed communication system.