Maximum-likelihood decoding and code combining for DS/SSMA slotted ALOHA

TitleMaximum-likelihood decoding and code combining for DS/SSMA slotted ALOHA
Publication TypeJournal Article
Year of Publication1997
AuthorsBigloo, A. M. Y., T. A. Gulliver, and V. K. Bhargava
JournalCommunications, IEEE Transactions on
Pagination1602 -1612
Date Publisheddec.
Keywordsaccess protocols, analytical results, BPSK modulation, code combining, code rate, coherent binary phase-shift keying, delays, direct-sequence spread-spectrum multiple-access, DS/SSMA channels, DS/SSMA slotted ALOHA, FEC, forward error correction, maximum likelihood decoding, maximum-likelihood decoding, multi-access systems, multiaccess interference, multiple packet copies, packet radio networks, packet radio system, packet transmission, performance, phase shift keying, probability, pseudonoise codes, simulation results, spread spectrum communication, stability, successful decoding probability, telecommunication channels, throughput, time delay

This paper considers the combination of multiple copies of a packet to improve the performance of a slotted direct-sequence spread-spectrum multiple-access (DS/SSMA) ALOHA packet radio system with coherent binary phase-shift keying (BPSK) modulation. Both slotted DS/SSMA ALOHA with and without forward error correction (FEC) are considered. For the case with FEC, maximum-likelihood decoding with code combining is used. Code combining allows for the combination of multiple copies of the same packet (which are typically discarded), to obtain a lower code rate for that specific packet, and therefore an improved probability of successful decoding. In both cases, combining multiple copies of the same packet results in a throughput which is an increasing function over a broad range of offered load, so that the system is more reliable from the point of view of stability. In addition, combining provides a higher throughput and a smaller time delay for packet transmission. This is illustrated by means of analytical and simulation results


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