Aiming at the contradiction between full rate and orthogonality in diversity scheme for multi-input multi-output system,based on traditional space-frequency block coding,a unitary matrix based transmit diversity scheme for space-frequency block coding multi-antenna system is proposed. The properties of unitary matrix and the idea of block orthogonal are adopted. The specific implementation strategy of the scheme is presented. A typical fixed unitary matrix is generated by means of Givens change. The full rate performance and quasi orthogonal properties of the scheme are deduced and analyzed. Compared with space-frequency block coding scheme,this scheme can utilize 4 transmitting antennas more fully to increase the space diversity perfor-mance. Simulation in different scenarios further proved the superiority in performance of the proposed diversity scheme.%针对多输入多输出系统发射分集方案中正交性与全速率之间的矛盾，在传统空频编码的基础上，提出了一种基于酉阵的空频块编码多天线系统发射分集方案。利用酉矩阵特性和块正交思想，给出了方案具体实施策略，并借助Giv-ens变化生成典型固定酉阵，推导分析了所提方案全速率性能和准正交特性，证明了与空频块编码方案相比，该方案能更加充分地利用4根发射天线来增大空间分集的性能。最后通过不同场景下的仿真对比，也进一步验证了在不增加复杂度的情况下该分集方案的性能优势。
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