DS-CDMA HARQ with Overlap FDE

Hiromichi TOMEBA
Kazuaki TAKEDA
Fumiyuki ADACHI

IEICE TRANSACTIONS on Communications   Vol.E90-B    No.11    pp.3189-3196
Publication Date: 2007/11/01
Online ISSN: 1745-1345
DOI: 10.1093/ietcom/e90-b.11.3189
Print ISSN: 0916-8516
Type of Manuscript: PAPER
Category: Wireless Communication Technologies
DS-CDMA,  HARQ,  overlap FDE,  

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Turbo coded hybrid ARQ (HARQ) is known as one of the promising error control techniques for high speed wireless packet access. However, in a severe frequency-selective fading channel, the HARQ throughput performance significantly degrades for direct sequence code division multiple access (DS-CDMA) system using rake combining. This problem can be overcome by replacing the rake combining by the frequency-domain equalization (FDE) based on minimum mean square error (MMSE) criterion. In a system with the conventional FDE, the guard interval (GI) is inserted to avoid the inter-block interference (IBI). The insertion of GI reduces the throughput. Recently, overlap FDE that requires no GI insertion was proposed. In this paper, we apply overlap FDE to HARQ and derive the MMSE-FDE weight for packet combining. Then, we evaluate the throughput performance of DS-CDMA HARQ with overlap FDE. We show that overlap FDE provides better throughput performance than both the rake combining and conventional FDE regardless of the degree of the channel frequency-selectivity.