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A Simplified Maximum Likelihood Detector for OFDMSDM Systems in Wireless LAN
Wenjie JIANG Takeshi ONIZAWA Atsushi OHTA Satoru AIKAWA
Publication
IEICE TRANSACTIONS on Communications
Vol.E88B
No.6
pp.24272437 Publication Date: 2005/06/01
Online ISSN:
DOI: 10.1093/ietcom/e88b.6.2427
Print ISSN: 09168516 Type of Manuscript: Special Section PAPER (Special Section on 2004 International Symposium on Antennas and Propagation) Category: Keyword: OFDMSDM, MLD, ZF, complexity reduction, WLAN,
Full Text: PDF(1.6MB)>>
Summary:
This paper presents a reducedcomplexity maximum likelihood detection (MLD) scheme for orthogonal frequency division multiplexing with space division multiplexing (OFDMSDM) systems. Original MLD is known to be an optimal scheme for detecting the spatially multiplexed signals. However, MLD suffers from an exponentially computational complexity because it involves an exhaustive search for the optimal result. In this paper, we propose a novel detection scheme, which drastically reduce the complexity of MLD while keeping performance losses small. The proposed scheme decouples the spatially multiplexed signals in two stages. In stage one, the estimated symbols obtained from zeroforcing (ZF) are used to limit the candidate symbol vectors. In stage two, to form a final estimate of the transmitted symbol vector, the Euclidean or original defined likelihood metric is examined over all symbol vectors obtained from stage 1. Both the bit error rate (BER) and packet error rate (PER) performances are evaluated over a temporally and spatially uncorrelated frequency selective channel through the computer simulations. For a fourtransmit and fourreceive OFDMSDM system transmitting data at 144 Mbit/s and 216 Mbit/ss i.e., employing 16 Quadrature Amplitude Modulation (16QAM) and 64QAM subcarrier modulation over 16.6 MHz bandwidth channel, the degradation in required SNR from MLD for PER = 1% are about 0.6 dB and 1.5 dB, respectively. However, the complexity of MLD is reduced to 0.51000% and 0.01562%.

