中文摘要：

在多载波码分多址（MC-CDMA）系统中,码元级频域均衡器（FDE）的性能优于码片级FDE,但其代价是非常高的复杂度。我们的研究表明,扩频序列具有两个基本作用：区分数据流提供复用增益和扩展频谱提供分集增益。由于扩频序列的这两个作用常常耦合在一起,导致了码元级FDE的高复杂度。本文通过将扩频序列解耦为一个码矩阵和一个扩频矩阵,并对扩频矩阵进行优化,得到低复杂度单抽头码元级FDE和提供最大分集增益的扩频矩阵。理论分析与仿真表明,当采用最优扩频矩阵时,所提出的码元级FDE能够以相同的复杂度获得比码片级FDE更高的性能,并且当扩频因子超过可分辨多径个数时还能达到匹配滤波界。

英文摘要：

In multi-carrier code division access（MC-CDMA） systems,symbol-level frequency domain equalizer（FDE） can achieve better performance than chip-level FDE but suffers from higher complexity.Our studies indicates that the spreading sequences has two basic roles,i.e.,separating parallel data streams to provide multiplexing gain and spreading signal spectrum to provide frequency diversity gain.These two roles are often coupled with each other,which leads to the high complexity of symbol-level FDE.In this paper,by decoupling the spreading sequences into an orthogonal code matrix and a spreading matrix that play different roles and judiciously designing the spreading matrix,a low-complexity symbol-level FDE and an optimal spreading matrix that maximizes diversity gain are proposed.Theoretical analysis and simulation results show that the proposed symbol-level FDE outperforms the existing chiplevel FDE and achieves the matched filter bound when the processing gain exceeds the number of resolvable paths.