中文摘要：

提出一种改进的使用数字相位扫描技术的空时频码,用于多输入多输出正交频分复用系统.该空时频码首先将原多输入多输出信道等效为具有2根发送天线的信道,再与Alamouti正交空时码的构造形式相结合,并在频率维上进行编码.详尽推导了该空时频码的误码性能,表明它可以获得全部的分集增益——空间分集以及频率分集,并且在发送端已知信道的空间相关特性以及时延谱时可以找出优化的子载波交织间距来增大码增益.此外,该空时频码可以达到速率为1的传输,而译码复杂度近似降低为某些空频码的1/8,且仿真结果表明该空时频码比一些空（时）频码具有更好的误码性能.

英文摘要：

A modified space-time-frequency coding scheme using digital phase sweeping for MIMOOFDM（ multiple input multiple output-orthogonal frequency division multiplexing） system is proposed. It transforms the original MIMO channel into an equivalent channel with two transmit-antennas and combines with the structures of Alamouti orthogonal space-time codes while coding across frequency dimension. The error performance of the proposed scheme is derived, which shows that full diversity--frequency and space diversity can be obtained and optimal subcarrier interleaving separation can be searched to obtain larger coding gain if the transmitter has the knowledge of space correlation and delay profile of the channel. Moreover, the rate of the proposed scheme is 1, the decoding complexity is nearly 1/8 of some known codes and simulation results show that it has better error performance than some codes.