Abstract: While space-time block code with complex signals can not provide full coding rate when the transmit antennas are more than two, the transmission matrix designed through constellation rotation can obtain maximum coding rate and full diversity gain in the meantime. The improved constellation rotated quasi-orthogonal space-time block code in this paper, whose signals transmitted by every antenna in different time belong to different constellations, improves the performance of the system with reducing inter-symbol interference and being advantageous to decode, when assuring maximum coding rate and full diversity gain.

Key words: Quasi-Orthogonal Space-Time Block Code（QOSTBC）, constellation rotation, Sphere Decoding algorithm（SD）

摘要： 当发射天线数大于2时，复信号空时分组码不能实现满速率编码，可以通过星座旋转来设计发送矩阵，使系统同时获得满分集增益和最大的编码速率。通过对传统的旋转星座准正交空时分组码加以改进，使每根天线在不同时隙发射的信号属于不同星座，在保证满分集和最大的编码速率的同时，减小了码间干扰，更有利于译码器译码，提高了系统性能。

关键词: 准正交空时分组码, 旋转星座, 球形译码算法