近年來，無線通訊系統嚴重受到多重路徑通道干擾。由於正交分頻多工可以對抗頻選性衰弱通道，因此廣泛運用在通訊系統中。但正交分頻多工峰值因素過高，且無法抵抗頻率飄移。 單載波分頻多工傳送端使用單一載波調變，在接收端用頻域等化器，架構類似於正交分頻多工，因此效能也相似。單載波分頻多工為在正交分頻多工前加上離散傅立葉轉換前置編碼的系統。這方法可以降低峰值因素，且有效增加傳送功率效率。因此3GPP LTE 使用單載波分頻多工為上傳架構。 單載波分頻多工可視為單載波頻域均衡的延伸，但可更彈性分配資源。單載波分頻多工通常如正交分頻多工一般使用頻域等化器，但單載波分頻多工容易受到震盪器產生的頻率飄移干擾，造成載波間干擾降低系統效能。在這論文中我們使用資料域等化器與 時域等化器並且比較這些等化器的效能。並提出改進的直接決策方法增進原本直接決策方法的缺陷。此方法會與傳統頻域等化器在不同通道中比較單一與多使用者系統效能。Orthogonal frequency-division multiplexing (OFDM), which is a multicarrier communication technique, has become popularly applicable because of its robustness against frequency selective fading channels. Single-carrier frequency-division multiple access (SC-FDMA) is a technique which can achieve similar performance and essentially the same structure as OFDMA. SC-FDMA pre-codes its information-bearing symbols by discrete Fourier transform (DFT). This pre-coding operation can reduce PAPR and can benefit power efficiency and reduce manufacturing cost. SC-FDMA is adopted as the uplink multiple access technique in the 3GPP LTE specification. SC-FDMA can be considered to be an extension of SC-FDE but it has greater flexibility in resource allocation. SC-FDMA usually uses a frequency-domain equalizer the same as that in an OFDM system because it is simple and convenient. SC-FDMA is however highly sensitive to frequency offset which may be caused by oscillator inaccuracies or Doppler shift. It severely degrades the system performance. In this thesis, we use data-domain equalizers and time-domain equalizers and compare their performances. We also propose a modified decision-directed method to improve decision-directed method. These methods are compared with conventional frequency-domain equalizers over different channels and in multiuser environments.
