Efficient OFDM Mobile Radio Packet System Employing LLR Combining Multiuser Detection for ARQ with Adaptive Modulation and Coding Scheme

Riichiro NAGAREDA  Kazuhiko FUKAWA  Hiroshi SUZUKI  

IEICE TRANSACTIONS on Communications   Vol.E90-B    No.6    pp.1444-1453
Publication Date: 2007/06/01
Online ISSN: 1745-1345
DOI: 10.1093/ietcom/e90-b.6.1444
Print ISSN: 0916-8516
Type of Manuscript: PAPER
Category: Wireless Communication Technologies
OFDM,  mobile radio packet,  multiuser detection,  ARQ,  metric combining,  LLR,  adaptive modulation and coding,  

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This paper proposes an OFDM mobile radio packet system that employs a new protocol of automatic repeat request (ARQ) for nonlinear multiuser detection (MUD) with log likelihood ratio combining (LC) on the appropriate bits. The conventional metric combining (MC) MUD separates collided packets by using nonlinear MUD, accumulates the Euclidian distance metrics of the received subcarrier symbols in the packets, and then achieves throughput improvement. However, when MC-MUD detects a packet error, it makes user terminals retransmit the same packets so as to reproduce the collision of the same packets. The proposed LC-MUD scheme simplifies the ARQ protocol and requires no reproduction of the same packet collision. The computer simulations demonstrate the superior throughput of LC-MUD to that of MC-MUD, and further improvement due to adaptive modulation and coding (AMC) optimized for the nonlinear MUD in LC-MUD.