多径衰落信道下准正交时分复用的研究

基于时频对偶原理，提出了一种准正交时分复用（QOTDM）系统．该系统利用频域具有升余弦性质的脉冲波形的平移准正交特性，采用自适应信道均衡方法，使发送滤波器、信道和接收滤波器的频域总特性具有升余弦性质，信道等效脉冲响应满足奈奎斯特采样点无失真准则．发送端利用上述信道进行时域波形准正交的离散信息符号序列传输；接收端根据信息符号波形的准正交特性，实现准正交分离．与正交频分复用（OFDM）系统相比，QOTDM系统在略微降低频带利用率的条件下，可以降低峰值平均功率比，并且当信噪比较高时具有更强的抗多径衰落能力．仿真结果表明，在准静态多径衰落信道下，采用正交幅度调制，在误比特率为10^-3时，QOTDM比OFDM的平均比特信噪比值约低3dB．

Study on Quasi-Orthogonal Time Division Multiplexing in Multipath Fading Channels

Based on the principle of time-frequency duality of Fourier transform,the quasi-orthogonal time division multiplexing (QOTDM) was proposed,which employed the shift orthogonal property of the pulse function with raised cosine shape in frequency domain so as to make the whole channel features of transmit filter,channel and receiving filter have raised cosine property,and to make the equivalent pulse response satisfy the criterion of Nyquist sampling points with no distortion by using adaptive channel equalization method.At transmitter the quasi-orthogonal discrete information symbols sequence is transmitted over the channel above,and the orthogonal separation is realized according to the quasi-orthogonal property of information symbols at receiver.QOTDM can decrease the peak-to-average power ratio with lowering bandwidth efficiency a little,and is more robust against multipath fading when the signal-to-noise ratio(SNR) is higher compared to the orthogonal frequency division multiplexing(OFDM).Simulation results indicate that when the bit error rate is 10~(-3) QOTDM is about 3 dB lower than the average bit SNR of OFDM by using orthogonal amplitude modulation in quasi-static multipath fading channels.