Abstract: It is well known that the full rate and full diversity complex Space-Time Block Code（STBC） doesn’t exist in four transmit antennas. This paper proposes a simple Quasi-Orthogonal Space-Time-Frequency Block Code（QO-STFBC）scheme with four transmit antennas and [nR] receive antennas, where every two transmit antennas constitute one group and each group transmits signals over different subcarriers. The receiver can separate the received signals from each group via odd/even index FFT operation. After recombining the separated received signals from received antennas, an equivalent half rate orthogonal STFBC（O-STFBC） can be used for decoding. Thus, the full rate and full diversity are achieved at the transmitter and receiver, respectively. Simulation result shows that the proposed QO-STFBC scheme has better performance than the other schemes. The proposed scheme SNR gain is about 4 dB in rate 2 layered Alamouti scheme, about 5 dB in full rate QO-STBC scheme and about 7 dB in half rate O-STBC scheme at 10－3 BER for the transmission of 2 bit/s/Hz.

Key words: Alamouti code, quasi-orthogonal, full diversity, linear decoding, Space-Time-Frequency Block Code（STFBC）

摘要： 众所周知，目前四发射天线上还没有满速率和满分集复杂空时分组码（STBC）。提出了一种四发射天线和[nR]接收天线上的简单准正交空时频分组码（QO-STFBC）的编码方案，其中每两个发射天线为一组，每组通过不同的子载波发射信号。接收方可由奇/偶索引傅里叶运算区分不同的组。在将接收天线上收到的不同信号重组之后，可用等效半速率正交STFBC（O-STFBC）进行解码。因此，在发射端和接收端分别都能获得满速率和满分集特性。仿真结果表明，QO-STFBC编码方案比其他方案具有更好的性能。在传输速率为2 bit/s/Hz，误码率为10－3的情况下，所提出方案的SNR增益分别是：2速分层Alamouti方案大约为4 dB，满速QO-STBC方案约为5 dB，半速O-STBC方案约为7 dB。

关键词: Alamouti码, 准正交, 满分集, 线性解码, 空时频分组码（STFBC）