Comparison of Throughput Employing Hybrid ARQ Packet Combining in Forward Link OFCDM Broadband Packet Wireless Access

Nobuhiko MIKI  Hiroyuki ATARASHI  Sadayuki ABETA  Mamoru SAWAHASHI  

IEICE TRANSACTIONS on Communications   Vol.E88-B   No.2   pp.594-603
Publication Date: 2005/02/01
Online ISSN: 
DOI: 10.1093/ietcom/e88-b.2.594
Print ISSN: 0916-8516
Type of Manuscript: Special Section PAPER (Special Section on Multi-carrier Signal Processing Techniques for Next Generation Mobile Communications--Part2)
OFCDM,  hybrid ARQ,  incremental redundancy,  Chase combining,  

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This paper compares the throughput performance employing hybrid automatic repeat request (ARQ) packet combining, i.e., Chase combining, and Incremental redundancy, considering the frequency diversity effect in the broadband forward-link channel for Orthogonal Frequency and Code Division Multiplexing (OFCDM) packet wireless access achieving a peak throughput above 100 Mbps. Simulation results show that the achievable throughput at the average received signal energy per symbol-to-background noise power spectrum density ratio (Es/N0) of 0 and 6 dB employing Incremental redundancy is increased by approximately 35 and 30% compared to that using Chase combining for QPSK and 16QAM data modulation schemes with the coding rate of R = 1/2, respectively, considering a large frequency diversity effect in a 12-path exponential decayed Rayleigh fading channel, since the reduced variations in the received signal level in a broadband channel bring about a larger coding gain in Incremental redundancy. We also show that when adaptive modulation and channel coding (AMC) is applied, Incremental redundancy is superior to Chase combining since the large coding gain is effective in achieving a large time diversity gain for a low number of retransmissions such as M = 1 or 2 for a maximum Doppler frequency up to fD = 400 Hz. It is demonstrated, nevertheless, that the total throughput when employing Incremental redundancy associated with a near optimum MCS set according to the channel conditions becomes almost identical to that using Chase combining when a large number of retransmissions, M, is allowed, such as M = 10, owing to time diversity along with frequency diversity.