基于多输入多输出(MIMO)技术的空时编码技术将信道编码和天线分集技术相结合，能在不增大发射功率和不扩展频带的前提下提高无线衰落信道的通信系统容量和通信质量，满足未来无线移动通信对高速数据传输的要求。与传统空时编码不同，差分空时编码不需要任何信道状态信息，在通信终端处于高速移动环境下的快速衰落信道中仍能保持较好的性能。 本文首先分析了无线MIMO通信系统模型，讨论了各类空时编码技术的设计准则和编译码方案，对空时编码的性能特点进行总结比较。然后分析了不需要信道状态信息的差分酉空时编码调制技术，讨论了不同信噪比情况下的星座构造准则，研究了基于最优分集乘积准则的群结构、矩阵旋转和正交设计差分酉空时码的星座特点，对三种星座的性能进行了仿真，比较了各自的优缺点。 传统的差分酉空时编码仅仅考虑了单电平发射功率，限制了高信噪比时性能的提高。本文重点研究了基于多电平的差分酉空时编码技术，通过在单电平星座码字内引入电平相位变化因子，提出了一种改进的多电平差分酉空时编码星座构造方案，在相同的星座尺寸下，多电平星座扩大了星座点之间的最小距离，提高了星座集的分集乘积；推导了多电平差分酉空时编码的最大似然译码方案，分析了译码算法的复杂度，并对改进的多电平星座性能进行了实验仿真。仿真结果证明多电平的差分酉空时编码的性能比传统的差分酉空时编码有着明显的优势。

Space-time code（STC）,which based on multi-antenna at the transmitter and receiver, is the combination of channel coding and antenna diversity techniques. It can increase system capacity and data rates without spreading the system bandwidth and increasing the transmit power in wireless fading channel, satisfy the desire of the future wireless communication systems. Different with the conventional STC, differential Space-time code can keep good performance when neither the transmitter nor the receiver knows the channel state information in Rayleigh flat fading channels. This thesis first discussed the design criterion, en/decoding scheme and the characteristic of each kind of space-time coding techniques, analysed and compared the performance. Then we studied the optimal diversity product constellation structure criterion of differential unitary space-time coding（DUSTC）in high signal to noise ratio situation, analysed the constellation structure and en/decoding algorithm of three DUSTC which based on the group structure, the orthogonal design and the matrix rotation in detailed, simulated and compared the performances. The traditional DUSTC with only one level of amplitude are considered and this may degrade the performance of code. This dissertation proposed a new code which named Multi-Level DUSTC through relax the constraint of amplitude to allow the information symbols to have multiple level and keep the fast maximum likelihood (ML) decoding algorithm. The minimal distance between constellations can be enlarged and the constellation diversity product is enhanced. Simulation results demonstrate the improved new DUSTC outperforms the original differential unitary space-time code, and the Multi-Level DUSTC is preferable choice for the future wireless communication system.