Real-time Adaptive Suppression of Broadband Noise in General Sensing Signals
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摘要: 自适应滤波是滤除传感输出中宽带噪声的常用方法。自适应过程跟随传感信号统计特征的变化进行调整,收敛时自适应滤波器输出为传感信号的最优估计,而收敛前的调整过程中输出并非最优,且会产生畸变引入额外噪声。该文根据噪声标准差$\sigma $对传感输出进行实时量化变换,变换结果基本保持平稳,且保留传感信号和噪声信息。以变换结果为待滤波信号,自适应滤波器一旦收敛就始终处于收敛状态。对实际传感输出的处理表明,该方法适用于各类传感输出的宽带噪声实时抑制,输出不会产生畸变引入额外噪声。Abstract:
Objective Broadband noise is inevitable in sensing outputs due to thermal noise from the sensing system and various uncorrelated environmental disturbances. Adaptive filtering is a common method for removing such noise. At convergence, the adaptive filter output provides the optimal estimate of the sensing signal. However, during actual sensing, changes in the sensing signal lead to alterations in the statistical characteristics of the output. Therefore, the adaptive process must be re-adjusted to converge to a new steady state. The filter output during this adjustment is not the optimal estimate and introduces distortion, thereby adding extra noise. Fast-converging adaptive algorithms are typically employed to improve the filter’s response speed to such changes. Despite the speed of convergence and the methods used to update filter coefficients, the adjustment process remains unavoidable, during which the filter output is distorted, and additional noise is introduced. To ensure the filter remains at steady state without being influenced by changes in the sensing signal, a new adaptive filtering method is proposed. This method ensures that the input to the adaptive filter remains stationary, thereby preventing output distortion and the introduction of extra noise. Methods First, a threshold $ R $ and quantization scale $ Q $ are defined in terms of the noise standard deviation, $ \sigma $, where $ R = 3\sqrt 2 \sigma $ and $ Q = 3\sigma $. A quantization transformation is applied to the sensing output $ x(n) $ in real time, with the transformation result $ q(n) $ used as the new sequence to be filtered. When the absolute value of the first-order difference of $ x(n) $ is no less than $ R $, the sensing signal $ s(n) $ is considered to have changed, and $ p(n) $ is set as the quantization value of $ x(n) $ according to $ Q $. When the absolute value of the first-order difference of $ x(n) $ is less than $ R $, $ s(n) $ is considered unchanged, and $ p(n) $ is equal to the previous value, i.e., $ p(n) = p(n - 1) $. Let $ q(n) = x(n) - p(n) $, $ q(n) $ contains both the information of the sensing signal and the noise. Although its variance may change slightly, the mean of $ q(n) $ remains 0, ensuring that $ q(n) $ stays relatively stationary. Next, $ q(n - {n_0}) $ is used as the input to the adaptive filter, with $ q(n) $ serving as the reference for the adaptive filter. Here, $ q(n - {n_0}) $ represents the time delay of $ q(n) $ and $ {n_0} $ denotes the length of the time delay. This method performs adaptive linear prediction of $ q(n) $ and filters out broadband noise. Finally, the output of the adaptive filter, $ y(n) $, is compensated with $ p(n) $ to obtain an estimation of the sensing signal $ s(n) $ by removing noise. Results and Discussions The maximum mean square errors produced by the proposed method and conventional adaptive algorithms are compared using computer-simulated noisy band-limited step signals and noisy one-sided sinusoidal signals. Additionally, Signal-to-Noise Ratio (SNR) improvements obtained during filtering are also evaluated concurrently. For the noisy band-limited step signal ( Table 1 ), the maximum mean square error of the proposed method is only 0.18% of that produced by the Recursive Least Squares (RLS) algorithm and 0.15%-0.19% of those generated by the Least Mean Square (LMS) algorithms. Correspondingly, the SNR improvement is 25.88 dB higher than the RLS algorithm and between 28.65 dB and 32.35 dB greater than the LMS algorithms. In processing a noisy one-sided sinusoidal signal (Table 2 ), the maximum mean square error generated by the proposed method is 0.3% of that generated by the RLS algorithm and 0.06% -0.08% of that generated by the compared LMS algorithms. The SNR improvement is 10.25 dB higher than that of the RLS algorithm and 26.53 dB-29.61 dB higher than that of the compared LMS algorithms.Figures 3 and5 illustrate the quantization transformation outcomes for both the noisy band-limited step signal and noisy sinusoidal signal, demonstrating stability and consistency with theoretical expectations. Real sensing outputs primarily cover static or quasi-static signals (Figures 7 and8 ); step or step-like signals (Figures 9 and10 ), and periodic or quasi-periodic signals (Figures 11 and12 ). Comparative analysis of the proposed method against common adaptive algorithms on varied real sensing outputs consistently shows superior filtering performance by the proposed method, with minimal distortion and no additional noise introduction, regardless of whether the sensing signals undergo changes.Conclusions A new adaptive filtering method is proposed in this paper. The proposed method ensures that the adaptive filter always operates at a steady state, avoiding the introduction of additional noise caused by distortion during the adjustment to the new steady state. The results from computer simulations and actual signal processing demonstrate that the proposed method provides effective filtering for both dynamic and static sensing signals, indicating that it outperforms commonly used adaptive algorithms. -
Key words:
- Broadband noise /
- Noise suppression /
- Quantization /
- Real-time filtering /
- Adaptive algorithm
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表 1 传感信号为带限阶跃信号时不同方法滤波效果对比(dB)
自适应算法 信噪比提升量 最大均方误差 本文 10.591 8 –27.716 5 RLS –15.286 7 –0.330 0 NLMS –20.883 2 –0.467 5 SVSLMS –21.761 1 0.503 4 VSSLMS –18.064 8 –0.429 7 表 2 传感信号为单边正弦信号时不同方法滤波效果对比(dB)
自适应算法 信噪比提升量 最大均方误差 本文 5.660 8 –48.215 0 RLS –4.586 1 –23,253 4 NLMS –20.866 3 –17.253 6 SVSLMS –22.038 0 –16.816 6 VSSLMS –23.950 7 –16.269 8 -
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