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Abstract
周波数選択性フェージング環境下での直接拡散符号分割マルチアクセス(DS-CDMA)の伝送特性を改善する技術として,最小平均二乗誤差(MMSE)規範に基づく1タップ周波数領域等化(FDE)が知られている.しかしながら,等化後の残留チップ間干渉(ICI)がビット誤り率(BER)特性の改善に限界を与える.筆者らはこれまで,周波数領域で等化と逆拡散を同時に行うことで残留ICIを抑圧する周波数領域ジョイント等化・逆拡散を提案してきた.しかし,1タップの周波数領域ジョイント等化・逆拡散では,従来のMMSE-FDEに比べてBER特性の改善効果はわずかである.本論文では,すべての周波数での総合平均二乗誤差を最小とするMMSE等化重みを導出し,マルチタップの周波数領域ジョイント等化・逆拡散を用いた時のDS-CDMAの平均BER特性を計算機シミュレーションにより明らかにしている.また,従来の1タップMMSE-FDEおよびこれまで用いていた1タップ周波数領域ジョイント等化・逆拡散との比較を行っている.
One-tap frequency-domain equalization (FDE) based on the minimum mean square error (MMSE) criterion is a powerful technique to improve the bit error rate (BER) performance of direct sequence code division multiple access (DS-CDMA) signal transmission in a frequency-selective fading channel. However, the presence of the residual inter-chip interference (ICI) limits the improvement of the BER performance of DS-CDMA. In our previous paper, we proposed joint FDE and despreading which can simultaneously perform equalization and despreading in the frequency-domain to reduce the residual ICI. However, one-tap joint FDE and despreading can achieve only slightly better BER performance than the conventional one-tap MMSE-FDE. In this paper, we derive the MMSE weight of joint FDE and despreading for multi-code DS-CDMA by taking into account the totality of equalization errors at all frequency. We evaluate, by the computer simulation, the average BER performance and the BER performance of the multi-tap joint FDE and despreading using a new MMSE weight is compared with that of the conventional one-tap MMSE-FDE and the one-tap joint FDE and despreading.
Journal
- Technical report of IEICE. RCS [List of Volumes]
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Technical report of IEICE. RCS 108(445), 137-142, 2009-02-25 [Table of Contents]
The Institute of Electronics, Information and Communication Engineers
