中文摘要：

自Jafarkhani提出非正交空时分组码以来,其构造方法一直是研究热点之一。构造了一种发射天线为4的准正交空时分组码,为了改善该分组码性能,对输入信号进行了旋转预处理,得到旋转后的准正交空时分组码;系统的接收端采用最大似然译码方法。数值仿真显示,没有预处理的准正交空时分组码的误码率与已提出的准正交空时分组码相当。然而,经旋转后的空时分组码的误比特率至少有2dB改善。

英文摘要：

Since Jafarkhani gave the concept on the non-orthogonal space time block code,the constructing methods of it are always one of the hot research topics.This paper proposed a new quasi-orthogonal space-time block code（QOSTBC） for four transmits.Obtained a new rotated QOSTBC when input signal was preprossed by a rotation transformation,to improve the code performance.Adopted maximum likelihood（ML） decoding algorithm at receiver.The numerical simulation results show that the performance of the unpreprocessing QOSTBC is similar to the known QOSTBC.However,BER performance of the rotated QOSTBC is improved 2dB at least.