The model of linear frequency modulation continuous wave （LFMCW） applied in underwater detection and the method for the detection of echo signal and the estimation of target parameters were studied. By analyzing the...The model of linear frequency modulation continuous wave （LFMCW） applied in underwater detection and the method for the detection of echo signal and the estimation of target parameters were studied. By analyzing the heterodyne signal, an algorithm with the structure of heterodyne-Practional Fourier Transform （FRFT） was proposed. To reduce the computation of searching targets in a two-dimensional FRFT result, the heterodyne signal would be processed by FRFT at a specific order, after Radon-Ambiguity Transform （RAT） was applied to estimate the sweep rate of the signal. Simulations proved that the algorithm can eliminate the coupling phenomenon of distance and velocity of LFMCW, and estimate targets＇ parameters accurately. The lake trial results showed that the processing gain of LFMCW processed by the algorithm in this paper was 13 dB better than that of the LFM processed by matched filter. The research results indicated that the algorithm applied in LFMCW underwater detection was feasible and effective, and it could estimate targets＇ parameters accurately and obtain a good detection performance.展开更多
Echo cancellation plays an important role in current Internet protocol（IP） based voice interactive systems. Voice state detection is an essential part in echo cancellation. It mainly comprises two parts： double tal...Echo cancellation plays an important role in current Internet protocol（IP） based voice interactive systems. Voice state detection is an essential part in echo cancellation. It mainly comprises two parts： double talk detection（DTD） and voice activity detection（VAD）. DTD is used to detect doubletalk and prevent filter divergence in the presence of near-end speech, and VAD is used to determine the near-end voice activity and output silence indicator when near-end is silent. However, DTD straightforwardly proceeded may mistakenly declare double talk under double silent condition, coefficients update under the far-end silence condition may lead to filter divergence, and current VAD algorithms may misjudge the residual echo from the near end to be far-end voice. Therefore, a voice detection algorithm combining DTD and far-end VAD is proposed. DTD is implemented when VAD declares far-end speech, filtering and coefficients update will be halted when VAD declares far-end silence, and the far-end VAD adopted is multi-feature VAD based on short-time energy and correlation. The new algorithm can improve the accuracy of DTD, prevent filter divergence, and exclude the circumstance that far-end signal only contains residual echo from near end. Actual test results show that the voice state decision of the new algorithm is accurate, and the performance of echo cancellation is improved.展开更多
Laser Doppler velocimetry is a powerful method for precise motion monitoring with the advantages of high precision and noncontact.Among them,self-mixing(SM)laser Doppler velocimetry exhibits high sensitivity for nonco...Laser Doppler velocimetry is a powerful method for precise motion monitoring with the advantages of high precision and noncontact.Among them,self-mixing(SM)laser Doppler velocimetry exhibits high sensitivity for noncooperative targets.The spontaneous amplification of Doppler signals through intracavity interference enables the detection of weak echo signals,meeting practical measurement requirements.However,the frequencydependent gain profile in laser feedback systems exhibits progressive attenuation at higher frequencies due to the inherent gain-frequency constraint,fundamentally limiting their applicability for high-sensitivity velocimetry of high-speed targets.We quantitatively establish for the first time,to our knowledge,that the product of self-mixing interferometry's gain and frequency(GFP)remains constant for higher frequency.In order to improve the bandwidth of SM laser Doppler velocimetry and further enhance the sensitivity of self-mixing interferometry(SMI),a frequency conversion method is implemented to transcend this intrinsic limit.The electro-optical modulator(EOM)and optical injection locking are employed to shift the frequency of the interference signal into the gain region,enabling the extension of gain bandwidth.Theoretically,the measurement bandwidth of Doppler frequency can extend to tens of GHz(the corresponding speed beyond 1 km/s at 1550 nm)due to the large modulation bandwidth of EOM,and the experimental measurement of Doppler frequency exceeds 44 MHz(34.1 m/s at 1550 nm)limited by the target.The system achieves a Doppler frequency measurement precision within 4 Hz.In the meantime,optical injection locking can provide additional optical gain.The seed light of 10μW is amplified to 60 mW,providing a gain of 37 dB.The detection limit of the proposed system is-145.52 dB with 104higher intensity response sensitivity than normal heterodyne interference.Therefore,the system has the advantages of large bandwidth,high sensitivity,and high precision.It is expected to be widely used in the monitoring of noncooperative high-speed moving targets.展开更多
文摘The model of linear frequency modulation continuous wave （LFMCW） applied in underwater detection and the method for the detection of echo signal and the estimation of target parameters were studied. By analyzing the heterodyne signal, an algorithm with the structure of heterodyne-Practional Fourier Transform （FRFT） was proposed. To reduce the computation of searching targets in a two-dimensional FRFT result, the heterodyne signal would be processed by FRFT at a specific order, after Radon-Ambiguity Transform （RAT） was applied to estimate the sweep rate of the signal. Simulations proved that the algorithm can eliminate the coupling phenomenon of distance and velocity of LFMCW, and estimate targets＇ parameters accurately. The lake trial results showed that the processing gain of LFMCW processed by the algorithm in this paper was 13 dB better than that of the LFM processed by matched filter. The research results indicated that the algorithm applied in LFMCW underwater detection was feasible and effective, and it could estimate targets＇ parameters accurately and obtain a good detection performance.
基金supported by the National Youth Science Fund Project(61501052)the National Natural Science Foundation of China(61271182)
文摘Echo cancellation plays an important role in current Internet protocol（IP） based voice interactive systems. Voice state detection is an essential part in echo cancellation. It mainly comprises two parts： double talk detection（DTD） and voice activity detection（VAD）. DTD is used to detect doubletalk and prevent filter divergence in the presence of near-end speech, and VAD is used to determine the near-end voice activity and output silence indicator when near-end is silent. However, DTD straightforwardly proceeded may mistakenly declare double talk under double silent condition, coefficients update under the far-end silence condition may lead to filter divergence, and current VAD algorithms may misjudge the residual echo from the near end to be far-end voice. Therefore, a voice detection algorithm combining DTD and far-end VAD is proposed. DTD is implemented when VAD declares far-end speech, filtering and coefficients update will be halted when VAD declares far-end silence, and the far-end VAD adopted is multi-feature VAD based on short-time energy and correlation. The new algorithm can improve the accuracy of DTD, prevent filter divergence, and exclude the circumstance that far-end signal only contains residual echo from near end. Actual test results show that the voice state decision of the new algorithm is accurate, and the performance of echo cancellation is improved.
基金National Key Research and Development Program of China(2020YFC2200101,2022YFC2204504)China Postdoctoral Science Foundation(2024M761641)Postdoctoral Fellowship Program of CPSF(GZC20240802)。
文摘Laser Doppler velocimetry is a powerful method for precise motion monitoring with the advantages of high precision and noncontact.Among them,self-mixing(SM)laser Doppler velocimetry exhibits high sensitivity for noncooperative targets.The spontaneous amplification of Doppler signals through intracavity interference enables the detection of weak echo signals,meeting practical measurement requirements.However,the frequencydependent gain profile in laser feedback systems exhibits progressive attenuation at higher frequencies due to the inherent gain-frequency constraint,fundamentally limiting their applicability for high-sensitivity velocimetry of high-speed targets.We quantitatively establish for the first time,to our knowledge,that the product of self-mixing interferometry's gain and frequency(GFP)remains constant for higher frequency.In order to improve the bandwidth of SM laser Doppler velocimetry and further enhance the sensitivity of self-mixing interferometry(SMI),a frequency conversion method is implemented to transcend this intrinsic limit.The electro-optical modulator(EOM)and optical injection locking are employed to shift the frequency of the interference signal into the gain region,enabling the extension of gain bandwidth.Theoretically,the measurement bandwidth of Doppler frequency can extend to tens of GHz(the corresponding speed beyond 1 km/s at 1550 nm)due to the large modulation bandwidth of EOM,and the experimental measurement of Doppler frequency exceeds 44 MHz(34.1 m/s at 1550 nm)limited by the target.The system achieves a Doppler frequency measurement precision within 4 Hz.In the meantime,optical injection locking can provide additional optical gain.The seed light of 10μW is amplified to 60 mW,providing a gain of 37 dB.The detection limit of the proposed system is-145.52 dB with 104higher intensity response sensitivity than normal heterodyne interference.Therefore,the system has the advantages of large bandwidth,high sensitivity,and high precision.It is expected to be widely used in the monitoring of noncooperative high-speed moving targets.
