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.
