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摘要:
针对正交频分复用技术（OFDM）系统的多音干扰，本文提出先通过增加频域分辨率进行多音干扰识别，再基于迭代运算逐个对多个单音干扰进行参数估计、重构和消除的方案。其中，在多音干扰识别阶段，使用ZoomFFT技术以提高频域分辨率并简化计算复杂度。然而，ZoomFFT后的降采样序列点数不一定满足2的整数次幂，对于单音干扰参数估计，此时可采用经典的基于离散傅里叶变换（DFT）的最大似然参数估计（DFT-MLE），但当采样点数太大时，DFT运算将带来很大的实现复杂度。本文在基于DFT-MLE算法基础上给出一种基于快速傅里叶变换（FFT）的单音参数估计法FFT-MLE，不仅简化了运算复杂度，而且相比DFT-MLE其估计性能有更好的鲁棒性。最后的仿真结果说明了该多音干扰消除方案的有效性。
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关键词:
- 多音干扰识别 /
- 多音干扰消除 /
- 基于FFT-MLE的单音参数估计 /
- ZoomFFT /
- 正交频分复用技术 (OFDM)
Abstract:For multi-tone interference in orthogonal frequency division multiplexing (OFDM) system, one scheme is proposed, which first increases frequency domain resolution of multi-tone interference identification, and then performs parameter estimation, reconstruction and elimination on several single-tone interference one by one based on iterative computation. In multi-tone interference identification stage, ZoomFFT technology is used to improve the frequency domain resolution and simplify the computational complexity. However, down sampling sequence number after ZoomFFT does not meet the n power of 2. For single-tone interference parameters estimation, the classical maximum likelihood parameter estimation based on DFT (DFT-MLE) can be used. But when the number of sampling points is too large, DFT operation will bring great implementation complexity. Based on DFT-MLE, this paper presents an FFT based single-tone parameters estimation FFT-MLE. It not only reduces the computational complexity, but also provides better robustness on estimation performance compared with DFT-MLE. The simulation results show that this multi-tone interference cancellation scheme is effective.
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图 1 增加采样长度前后多音干扰频域示意图
Figure 1. Schematic diagram of multi-tone interference frequency domain before and after sampling length increase
图 2 采用ZoomFFT技术的多音干扰识别示意图
Figure 2. Schematic diagram of multi-tone interference identification using ZoomFFT
图 6 DFT-MLE和FFT-MLE Y1值相对Δ变化示意图
Figure 6. Schematic diagram of value range of Y1 with different Δ based on DFT-MLE and FFT-MLE
图 7 AWGN信道下本文方案与其他2种文献方案性能对比
Figure 7. Performance comparison between proposed scheme and two schemes in reference under AWGN channel
图 8 TU信道下本文方案与其他2种文献方案性能对比
Figure 8. Performance comparison between proposed scheme and two schemes in reference under TU channel
表 1 单音参数估计仿真参数配置
Table 1. Simulation parameter configuration of single-tone parameter estimation
仿真条件 参数配置 采样率/MHz 7.56 采样点数N 595 FFT点数NFFT 3 780 单音参数配置 
信道模型 AWGN信道 
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表 2 多音干扰消除方案仿真参数配置
Table 2. Simulation parameter configuration of multi-tone interference cancellation scheme
仿真条件 参数配置 采样率/MHz 7.56 OFDM符号点数 3 780 CP样点数 595 调制方式 QPSK r′1长度N′ 3 780 r1长度N (3 780+595)×10=43 750 NFFT 8 192 降采样倍数D 10 低通滤波器L 带宽：B=1 MHz
滚降系数：μ=0.5
阶数：256单音参数配置 aq=[a1, a2, a3, a4, a5](对应SIR中各设定值)
fq=[200 400, 201 400, 202 400, 1 199 400, 1 200 400]Hz
SIR SIR1=[10,0,10,0,0] dB
SIR2=[0,-10,0,-10,-10] dB
SIR3=[-10, -20, -10, -20, -20] dB信道模型 AWGN信道TU信道[16]
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