基于NCLMS的QPSK-PCMA系统仿真分析

Simulation and Analysis of NCLMS-based QPSK-PCMA System

载波成对多址接入(Paired Carrier Multiple Access,PCMA)允许卫星通信上下行链路在时域和频域完全重叠,从而大幅提升卫星频谱利用效率,在卫星通信中具有非常重要的研究价值和意义。考虑到QPSK(Quadrature Phase Shift Keying)调制方式在卫星通信中的广泛应用,将归一化复数最小均方滤波器(Normalized Complex Least Mean Square,NCLMS)用于PCMA自干扰抵消,将划分频率槽技术以及超前、即时、滞后精确时延估计技术分别用于频率和时延的粗捕和精捕阶段,重点研究了NCLMS学习步长和NCLMS环路有限抽头响应滤波器FIR(Finite Impulse Response)抽头阶数对自干扰抵消结果的影响,并进行了Matlab仿真验证。仿真结果表明:NCLMS自适应学习步长对自干扰抵消结果影响较大,学习步长取2-12与学习步长取2-16相比,信噪比恶化约1.5 d B;5阶抽头NCLMS环路FIR滤波器即可达到很好的自干扰抵消性能,继续增加FIR滤波器抽头阶数意义不大。

PCMA （Paired Carrier Multiple Access） allows up and down links to use the same spectrum at the same time,which can greatly improve the spectrum efficiency and has important significance in satellite communications. As QPSK is commonly used in satellite communications, a self-interference cancellation method based on NCLMS （Normalized Complex Least Mean Square） is proposed. The dividing frequency slot technique and the Early-Prompt-Late technique for accurate time delay estimation are used respectively in the coarse and precise estimation stages of the frequency and time delay. The effect of NCLMS learning step and NCLMS loop FIR （ Finite Impulse Response） taps number on self-interference cancellation is mainly investigated and simulated with Matlab. The simulation results show that the step length for NCLMS self-adaptive learning will impress the results of self-interference cancellation ,comparing with 216 the step length of 212 having made SNR deteriorated about 1.4 dB, and that PCMA performance is good enough for self-interference can- cellation with five NCLMS loop FIR filter taps, thus there is no need to increase filter taps number.