應用於單載波無線網路之頻域等化器

Abstract

本論文提出應用於無線區域網路 IEEE 802.11b/g DSSS/CCK單載波之頻域等化器 (frequency domain equalizer)。此等化器系統之通道估計是使用在頻域上之適應性最小平方法 (least squares) 估計而來。對於受到ISI (intersymbol interference) 干擾的訊號而言，此論文使用了類似於OFDM之頻域等化演算法來補償受到干擾的通道。此論文將會對頻域上之 ZF (Zero-Forcing)與 MMSE (Minimum Mean Square Error) 補償演算法加以分析模擬。 在802.11b/g 單載波傳輸模式下，傳輸封包規格並不具有任何的前置循環字首(cyclic prefixes) 所以本論文將採用重疊與捨去的方法來降低由直接FFT轉換所造成的訊號偵測錯誤。一但 802.11b/g DSSS/CCK 單載波傳輸模式下的等化器實現在頻域上許多的硬體運算單元將可以與802.11g OFDM分享共存以達到簡化的接收機設計。最後我們將探討並且模擬此頻域等化器加上空間分歧(space diversity)後之效能提升。

In this thesis a frequency domain equalizer is proposed for WLAN 802.11b/g single-carrier DSSS/CCK transmission mode. Channel estimation is achieved with modified recursive least square (RLS) algorithm in frequency domain. For ISI (intersymbol interference) distorted channel, OFDM like frequency domain ZF (Zero-Forcing) or MMSE (Minimum Mean Square Error) equalization compensates the channel with FFT units and complex multiplier bank. In 802.11b/g single-carrier mode, transmission packets are not equipped with cyclic prefixes so signal overlapping and discarding are applied to decrease the symbol detection error caused by circularly de-convoluting a linear channel convolution process. With the equalizer of single-carrier mode implemented in frequency domain many of its computation resources can be shared with the 802.11g OFDM equalizer offering a low complexity multimode equalizer solution. By combining diversity techniques with FDE (Frequency Domain Equalization) the results can offer substantial gains in performances to increase the overall received SNR and ability to combat heavy multipath.