CDMA码分多址技术以其良好的性能在3G移动通信的三种标准中都得到应用。CDMA技术通过扩频码使众多用户在同一信道同时传输。CDMA系统的最大缺点是会产生多址干扰以及远近效应。针对这些缺点的众多信号处理技术得到广泛的研究。其中应用最广泛的两大类是：多用户检测技术和MIMO空时处理技术。 多用户检测技术可以从众多的用户信号中检测判决出每个用户的有用信息，有效的抑制了多址干扰，提升了CDMA系统的性能。MIMO空时处理技术主要是利用多输入多输出即用多根接收和发射天线通过分集技术提高系统性能。空时编码技术也可以提高系统的性能，这些技术大大提高了CDMA系统的频谱利用率和系统的容量，但却不用增加系统的带宽以及发射功率。那么将多用户检测技术和MIMO空时处理技术运用于CDMA系统中，是否可以进一步提升系统的性能，使信号能够更加快速和可靠地传输。基于上述构想和目的，本论文展开了各项研究工作。 论文在分析几种经典多用户检测算法优缺点的基础上，重点研究了具有良好性能的恒模算法。首先研究恒模算法的数学模型和基本原理，分析各种恒模算法。研究发现线性约束条件可以降低初始值的影响。在此基础上，再将拟牛顿算法(BFGS)应用于恒模算法，提出了一种BFGS线性约束恒模算法(BFGS-LCCMA)。此外，再将子空间方法应用于线性约束最小二乘恒模算法，提出一种基于子空间的线性约束恒模算法(SUB-LC-LSCMA)。最后将BFGS-LCCMA算法以及SUB-LC-LSCMA 算法应用于MIMO-MC-CDMA下行系统中，比较几种恒模算法在MIMO-MC-CDMA系统中的性能。仿真结果表明，新提出的算法的收敛性能、跟踪性能和误码性能比传统的算法要好，有一定的应用价值。

Nowadays，the 3G communication systems have passed through the standardization epoch and forthcoming commercialization period. At the same time the 4G mobile communication technology is widely investigated. In order to improve bandwidth efficiency and cancel the interference，the multiple access technique is recommended in wireless communication especially the Code Division Multiple Access technology. In Direct-Sequence Code Division Multiple Access(DS-CDMA) system，the channel bandwidth is shared by multiple users who are distinct by different spread code. However, multiple access interference and multi-path distortion degrades the performance of DS-CDMA system. Therefore, many advanced digital signal process techniques are proposed to solve the Problem，which could be classified as Multi-user Detection and Space-Time processing. The Multi-user Detection technology provides a way to restrain the noise and interference at the receiver end. It helps demodulate the information form the CDMA signals reliably. Meanwhile, the MIM0 Space-Time process takes advantages of the diversity gain which is provided by the setting of several transmitting antennae and receiving antennae as well as the encoding gain. It can multiply the utilization rate of the frequency spectrum and increase the channel capacity without additional signal power.The mathematics model and basic principle of Constant Modulus Algorithm (CMA) are shown firstly, then several CMAs proposed recently and its principle and convergence behavior are reviewed systematically. By using the non-orthogonal signature between users, Multi-user detection technology could eliminate the multi-user interference. It takes full advantage of the signal information of all users, which causes the multi-address interference, to detects the signal of individual users, thus reducing. I and the effect of distance while decreasing the precision requirements by the power control system. In this way, the resources of a link spectrum could he effectively utilized, and thereby the capacity of the system significantly enhanced. This thesis combines the Broaden-Fletcher-Goldfarb-Shannon (BFGS) algorithm with constant modulus algorithm, and proposes a BFGS Linearly Constrained Constant Modulus Algorithm (BFGS-LCCMA). This thesis proposes a subspace-based linearly constrained LSCM algorithm (SUB-LC-LSCMA). This thesis also introduced a MIMO (BLAST)-MC-CDMA downlink system and applied the two new proposed algorithms to the system.