Comparative Study of Open-Loop Transmit Diversity Schemes with Four Antennas in DFT-Precoded OFDMA Using Turbo FDE and Iterative Channel Estimation

摘要

This paper presents comprehensive comparisons on the block error rate (BLER) performance of open-loop (OL) transmit diversity schemes with four antennas for discrete Fourier transform (DFT)-precoded Orthogonal Frequency Division Multiple Access (OFDMA). One candidate scheme employs a quasi-orthogonal (QO) - space-time block code (STBC) in which four-branch minimum mean-square error combining (MMSEC) is achieved at the cost of residual inter-code interference (ICI). Another candidate employs a combination of the STBC and selection diversity called time switched transmit diversity (TSTD) or frequency switched transmit diversity (FSTD), We apply a turbo frequency domain equalizer (FDE) associated with iterative decision-feedback channel estimation (DFCE) using soft-symbol estimation to reduce channel estimation (CE) error. The turbo FDE includes an ICI canceller to reduce the influences of the residual ICI for QO-STBC. Based on extensive link-level simulation results, we show that a combination of the STBC and TSTD (FSTD) is suitable as a four-antenna OL transmit diversity scheme for DFT-precoded OFDMA using turbo FDE and iterative DFCE.%本稿では，Discrete Fourier transform (DFT)-precoded Orthogonal Frequency Division Multiple Access (OFDMA)を用いるシングノレ キャリアFDMAにおける4アンテナの開ループ(OL: Open-loop)送信ダイバーシチの平均ブロック誤り率(BLER: Block Error Rate)を比較評価する.第1の候補は，4アンテナの疑似直交(QO:Quasi-Orthogonal)-空間.時間プロック符号(STBC: Space-Time Block Code)である.第2の候補は，STBCと時間スィツチ送信ダイバーシチ(TSTD: Time Switched Transmit Diversity),あるいは周波数スイツチ送信ダイバーシチ(FSTD: Frequency Switched Transmit Diversity)を組み合わせる送信ダイ バーシチである.評価では，ターボ周波数領域等化(FDE: Frequency Domain Equalizer)を用い，さらに，チャネル推定精度を 向上し残留コード間干渉を低減するために，繰り返し判定帰還チャネル推定(DFCE: Decision-Feedback Channel Estimation)を 適用する.計算機シミュレーシヨン評価より,STBCとTSTDを組み合わせる方法が，QO-STBCに比較して目標BLERを 満たす所要平均受信SNRを低減でき，4アンテナのOL送信ダイバーシチ法として適していることを示す.