To solve the inter carrier interference （ICI） elimination problem of an M-band wavelet multi-carrier modulation system, this paper analyzes the principle of the ICI caused by the Doppler frequency shift and its math...To solve the inter carrier interference （ICI） elimination problem of an M-band wavelet multi-carrier modulation system, this paper analyzes the principle of the ICI caused by the Doppler frequency shift and its mathematical expression based on the M-band wavelet multi-carrier modulation system model. Through the analysis of the mathematical expression and combining with the perfect reconstruction conditions of the filter banks, we propose the design conditions of an M-band filter to reduce and eliminate the ICI. The impulse response model of the filter design conditions and an iterative algorithm is also established. The simulation results show that the proposed ICI reduction and elimination methods can effectively improve the system performance.展开更多
In the present communication, the hydrodynamic model is used to investigate the amplitude modulation as well as demodulation of an electromagnetic wave of high power helicon pump wave into another helicon wave in stra...In the present communication, the hydrodynamic model is used to investigate the amplitude modulation as well as demodulation of an electromagnetic wave of high power helicon pump wave into another helicon wave in strain dependent dielectric material incorporating carrier heating (CH) effects. The consideration of CH in modulation and demodulation is prime importance for the adding of new dimension in analysis of amplification of acoustic helicon wave. By using the dispersion relation, threshold pump electric filed and growth rate of unstable mode from the modulation and demodulation of the high power helicon wave well above from the threshold value will be discussed in the present analysis. The numerical analysis is applied to a strain dependent dielectric material, BaTiO3 at room temperature and irradiated with high power helicon wave of frequency 1.78 × 1014 Hz. This material is very sensitive to the pump intensities, therefore during studies, Gaussian shape of the helicon pump wave is considered during the propagation in stain dependent dielectric material and opto-acoustic wave in the form of Gaussian profile (ω0,κ0) is induced longitudinally along the crystallographic plane of BaTiO3. Its variation is caused by the available magnetic field (ωc), interaction length (z) and pulsed duration of interaction (τ). From the analysis of numerical results, the incorporation of CH effect can effectively modify the magnitude of modulation or demodulation of the amplitude of high power helicon laser wave through diffusion process. Not only the amplitude modulation and demodulation of the wave, the diffusion of the CH effectively modifies the growth rate of unstable mode of frequency in BaTiO3. The propagation of the threshold electric field shows the sinusoidal or complete Gaussian profile, whereas this profile is found to be completely lost in growth of unstable mode. It has also been seen that the growth rate is observed to be of the order of 108 - 1010 s-1 but from diffusion of carrier heating, and that its order is enhanced from 1010 - 1012 s-1 with the variation of the magnetized frequency from 1 to 2.5 × 1014 Hz.展开更多
Non Orthogonal Frequency Division Multiplexing (NOFDM) systems make use of a transmission signal set which is not restricted to orthonormal bases unlike previous OFDM systems. The usage of non-orthogonal bases general...Non Orthogonal Frequency Division Multiplexing (NOFDM) systems make use of a transmission signal set which is not restricted to orthonormal bases unlike previous OFDM systems. The usage of non-orthogonal bases generally results in a trade-off between Bit Error Rate (BER) and receiver complexity. This paper studies the use of Gabor based on designing a Spectrally Efficient Multi-Carrier Modulation Scheme. Using Gabor Transform with a specific Gaussian envelope;we derive the expected BER-SNR performance. The spectral usage of such a NOFDM system when affected by a channel that imparts Additive White Gaussian Noise (AWGN) is estimated. We compare the obtained results with an OFDM system and observe that with comparable BER performance, this system gives a better spectral usage. The effect of window length on spectral usage is also analyzed.展开更多
The average zT determines the conversion efficiency,and the power factor plays an important role in average zT value.However,the inadequate electrical conductivity of SnSe materials seriously limits its application.He...The average zT determines the conversion efficiency,and the power factor plays an important role in average zT value.However,the inadequate electrical conductivity of SnSe materials seriously limits its application.Herein,the TaCl_(5)-doped in polycrystalline SnSe_(0.95) materials synthesized using the melting method and combined with spark plasma sintering technology achieves a zT value of 1.64 at 773 K and a record zTave of 0.62 from 323 K to 773 K.The electrical conductivity increases due to the released electron carrier induced by effective TaCl_(5) doping.According to the DFT calculation,the energy band of TaCl_(5)-doped samples is narrowed,which can enhance the electron transport.Besides,the Seebeck coefficient is maintained at an elevated level as a result of the incorporation of the heavy element Ta.Due to the significantly enhanced electrical conductivity and maintained high Seebeck coefficient,the power factor reaches to 622 mW·m^(-1)·K^(-2) at 773 K for the SnSe_(0.95) t 1.75%(in mass)TaCl_(5) sample,which is almost 21 times higher than that of the pristine sample.Simultaneously,a high average power factor value of 334 mW·m^(-1)·K^(-2) for the SnSe_(0.95) t 1.75%(in mass)TaCl_(5) sample from 323 to 773 K was obtained.It is surprisingly found that the Ta element plays another important role to improve the stability of SnSe_(0.95) by forming Ta2Sn3 and removing the low melting point Sn,which usually existed in n-type SnSe samples,resulting in the decreased lattice thermal conductivity.A low lattice thermal conductivity value of 0.24 W·m^(-1)·K^(-1) was also obtained for the SnSe_(0.95) t 2.0%(in mass)TaCl_(5) sample at 773 K due to the multiscale defects.Consequently,the SnSe_(0.95) t 2.0%(in mass)TaCl_(5) sample obtains a peak zT value of 1.64 at 773 K and a record zTave of 0.62 from 323 to 773 K,and the theoretically calculated conversion efficiency reaches 11.2%,it can be utilized for power generation and/or cooling at a broad temperature range.This strategy of introducing high-valence halides with heavy element can optimize the thermoelectric performance for other material systems.展开更多
A new method suited for hardware implementation is developed to classify 8 different digital modulation types with raised cosine base-band impulse without knowing the carrier frequency and symbol timing. The normalize...A new method suited for hardware implementation is developed to classify 8 different digital modulation types with raised cosine base-band impulse without knowing the carrier frequency and symbol timing. The normalized histogram of stagnation points for instantaneous parameters is used to recognize both ideal rectangular and raised cosine base-band digital signals. Carrier frequency estimation is used to enhance the recognition rate of phase-modulated signals. In the condition of 10 dB signal noise ratio （SNR）, the recognizing rate is over 80% . The new algorithm is suited for hardware implementation.展开更多
Two-dimensional(2D)nonlinear optical mediums with high and tunable light modulation capability can significantly stimulate the development of ultrathin,compact,and integrated optoelectronics devices and photonic eleme...Two-dimensional(2D)nonlinear optical mediums with high and tunable light modulation capability can significantly stimulate the development of ultrathin,compact,and integrated optoelectronics devices and photonic elements.2D carbides and nitrides of transition metals(MXenes)are a new class of 2D materials with excellent intrinsic and strong light-matter interaction characteristics.However,the current understanding of their photo-physical properties and strategies for improving optical performance is insufficient.To address this issue,we rationally designed and in situ synthesized a 2D Nb_(2)C/MoS_(2) heterostructure that outperforms pristine Nb2C in both linear and nonlinear optical performance.Excellent agreement between experimental and theoretical results demonstrated that the Nb_(2)C/MoS_(2) inherited the preponderance of Nb_(2)C and MoS_(2) in absorption at different wavelengths,resulting in the broadband enhanced optical absorption characteristics.In addition to linear optical modulation,we also achieved stronger near infrared nonlinear optical modulation,with a nonlinear absorption coefficient of Nb_(2)C/MoS_(2) being more than two times that of the pristine Nb_(2)C.These results were supported by the band alinement model which was determined by the X-ray photoelectron spectroscopy(XPS)experiment and first-principal theory calculation.The presented facile synthesis approach and robust light modulation strategy pave the way for broadband optoelectronic devices and optical modulators.展开更多
We report on chip-scale optical gates based on the integration of evanescent waveguide unitraveling-carrier photo- diodes （EC-UTC-PDs） and intra-step quantum well electroabsorption modulators （IQW-EAMs） on n-InP s...We report on chip-scale optical gates based on the integration of evanescent waveguide unitraveling-carrier photo- diodes （EC-UTC-PDs） and intra-step quantum well electroabsorption modulators （IQW-EAMs） on n-InP substrates. These devices exhibit simultaneously 2.1 GHz and -16.2 dB RF-gain at 21 GHz with a 450 t2 thin-film resistor and a bypass capacitor integrated on a chip.展开更多
Converters with pulse width modulation are used for connections between the direct current （DC） and alternating current （AC） networks, e.g., in uninterrupted power supply systems, AC electromotor drives, for power...Converters with pulse width modulation are used for connections between the direct current （DC） and alternating current （AC） networks, e.g., in uninterrupted power supply systems, AC electromotor drives, for powering induction furnaces, in audio technique. Spectrum of signals sampled by pulse amplitude modulation and output voltage spectrum of the converter with pulse width modulation have similar properties. Spectrum of signals sampled by pulse amplitude modulation contains a harmonic of frequency equal to the frequency of the modulating signal and the harmonics of frequencies equal to the sum of frequency of the modulating signal and multiples of the sampling frequency. The output voltage spectrum of the converter with bipolar pulse width modulation contains harmonic of frequency equal to the frequency of the modulating signal and harmonics of frequencies equal to sum of the frequency of the modulating signal and multiples of the frequency of the carrier signal. It also contains harmonics of frequencies equal to the sum of the multiples of the frequency of the modulating signal and the multiples of the carrier signal. The comparison analysis was carried out for the harmonics of the output voltage of the converter with bipolar pulse width modulation in time domain. The dependency of the amplitudes and frequency spectrum on the wave forms of the carrier signal and modulating signal was shown. Similarity of the output voltage spectrum of the converter and signal spectrum sampled by the pulse width modulation was also shown. Key words： Output voltage converter with bipolar pulse width modulation, spectral analysis, Fourier series, carrier signal, reference signal.展开更多
基金supported by the National Natural Science Foundation of China (Grant No.60872114)
文摘To solve the inter carrier interference （ICI） elimination problem of an M-band wavelet multi-carrier modulation system, this paper analyzes the principle of the ICI caused by the Doppler frequency shift and its mathematical expression based on the M-band wavelet multi-carrier modulation system model. Through the analysis of the mathematical expression and combining with the perfect reconstruction conditions of the filter banks, we propose the design conditions of an M-band filter to reduce and eliminate the ICI. The impulse response model of the filter design conditions and an iterative algorithm is also established. The simulation results show that the proposed ICI reduction and elimination methods can effectively improve the system performance.
文摘In the present communication, the hydrodynamic model is used to investigate the amplitude modulation as well as demodulation of an electromagnetic wave of high power helicon pump wave into another helicon wave in strain dependent dielectric material incorporating carrier heating (CH) effects. The consideration of CH in modulation and demodulation is prime importance for the adding of new dimension in analysis of amplification of acoustic helicon wave. By using the dispersion relation, threshold pump electric filed and growth rate of unstable mode from the modulation and demodulation of the high power helicon wave well above from the threshold value will be discussed in the present analysis. The numerical analysis is applied to a strain dependent dielectric material, BaTiO3 at room temperature and irradiated with high power helicon wave of frequency 1.78 × 1014 Hz. This material is very sensitive to the pump intensities, therefore during studies, Gaussian shape of the helicon pump wave is considered during the propagation in stain dependent dielectric material and opto-acoustic wave in the form of Gaussian profile (ω0,κ0) is induced longitudinally along the crystallographic plane of BaTiO3. Its variation is caused by the available magnetic field (ωc), interaction length (z) and pulsed duration of interaction (τ). From the analysis of numerical results, the incorporation of CH effect can effectively modify the magnitude of modulation or demodulation of the amplitude of high power helicon laser wave through diffusion process. Not only the amplitude modulation and demodulation of the wave, the diffusion of the CH effectively modifies the growth rate of unstable mode of frequency in BaTiO3. The propagation of the threshold electric field shows the sinusoidal or complete Gaussian profile, whereas this profile is found to be completely lost in growth of unstable mode. It has also been seen that the growth rate is observed to be of the order of 108 - 1010 s-1 but from diffusion of carrier heating, and that its order is enhanced from 1010 - 1012 s-1 with the variation of the magnetized frequency from 1 to 2.5 × 1014 Hz.
文摘Non Orthogonal Frequency Division Multiplexing (NOFDM) systems make use of a transmission signal set which is not restricted to orthonormal bases unlike previous OFDM systems. The usage of non-orthogonal bases generally results in a trade-off between Bit Error Rate (BER) and receiver complexity. This paper studies the use of Gabor based on designing a Spectrally Efficient Multi-Carrier Modulation Scheme. Using Gabor Transform with a specific Gaussian envelope;we derive the expected BER-SNR performance. The spectral usage of such a NOFDM system when affected by a channel that imparts Additive White Gaussian Noise (AWGN) is estimated. We compare the obtained results with an OFDM system and observe that with comparable BER performance, this system gives a better spectral usage. The effect of window length on spectral usage is also analyzed.
基金supported by the Outstanding Youth Fund of Yunnan Province(Grant No.202201AV070005)National Natural Science Foundation of China(Grant No.52162029)National Key R&D Program of China(Grant No.2022YFF0503804).
文摘The average zT determines the conversion efficiency,and the power factor plays an important role in average zT value.However,the inadequate electrical conductivity of SnSe materials seriously limits its application.Herein,the TaCl_(5)-doped in polycrystalline SnSe_(0.95) materials synthesized using the melting method and combined with spark plasma sintering technology achieves a zT value of 1.64 at 773 K and a record zTave of 0.62 from 323 K to 773 K.The electrical conductivity increases due to the released electron carrier induced by effective TaCl_(5) doping.According to the DFT calculation,the energy band of TaCl_(5)-doped samples is narrowed,which can enhance the electron transport.Besides,the Seebeck coefficient is maintained at an elevated level as a result of the incorporation of the heavy element Ta.Due to the significantly enhanced electrical conductivity and maintained high Seebeck coefficient,the power factor reaches to 622 mW·m^(-1)·K^(-2) at 773 K for the SnSe_(0.95) t 1.75%(in mass)TaCl_(5) sample,which is almost 21 times higher than that of the pristine sample.Simultaneously,a high average power factor value of 334 mW·m^(-1)·K^(-2) for the SnSe_(0.95) t 1.75%(in mass)TaCl_(5) sample from 323 to 773 K was obtained.It is surprisingly found that the Ta element plays another important role to improve the stability of SnSe_(0.95) by forming Ta2Sn3 and removing the low melting point Sn,which usually existed in n-type SnSe samples,resulting in the decreased lattice thermal conductivity.A low lattice thermal conductivity value of 0.24 W·m^(-1)·K^(-1) was also obtained for the SnSe_(0.95) t 2.0%(in mass)TaCl_(5) sample at 773 K due to the multiscale defects.Consequently,the SnSe_(0.95) t 2.0%(in mass)TaCl_(5) sample obtains a peak zT value of 1.64 at 773 K and a record zTave of 0.62 from 323 to 773 K,and the theoretically calculated conversion efficiency reaches 11.2%,it can be utilized for power generation and/or cooling at a broad temperature range.This strategy of introducing high-valence halides with heavy element can optimize the thermoelectric performance for other material systems.
文摘A new method suited for hardware implementation is developed to classify 8 different digital modulation types with raised cosine base-band impulse without knowing the carrier frequency and symbol timing. The normalized histogram of stagnation points for instantaneous parameters is used to recognize both ideal rectangular and raised cosine base-band digital signals. Carrier frequency estimation is used to enhance the recognition rate of phase-modulated signals. In the condition of 10 dB signal noise ratio （SNR）, the recognizing rate is over 80% . The new algorithm is suited for hardware implementation.
基金financial support from the National Natural Science Foundation of China(Nos.61874141,11904239)Natural Science Foundation of Hunan Province(Grant Nos.2021JJ40709,2021JJ20080,2022JJ20080)+2 种基金Postgraduate Innovative Project of Central South University(Grant No.2021zzts0056)Open Sharing Found for the Large-scale Instruments and Equipment of Central South Universitysupported in part by the High Performance Computing Center of Central South University。
文摘Two-dimensional(2D)nonlinear optical mediums with high and tunable light modulation capability can significantly stimulate the development of ultrathin,compact,and integrated optoelectronics devices and photonic elements.2D carbides and nitrides of transition metals(MXenes)are a new class of 2D materials with excellent intrinsic and strong light-matter interaction characteristics.However,the current understanding of their photo-physical properties and strategies for improving optical performance is insufficient.To address this issue,we rationally designed and in situ synthesized a 2D Nb_(2)C/MoS_(2) heterostructure that outperforms pristine Nb2C in both linear and nonlinear optical performance.Excellent agreement between experimental and theoretical results demonstrated that the Nb_(2)C/MoS_(2) inherited the preponderance of Nb_(2)C and MoS_(2) in absorption at different wavelengths,resulting in the broadband enhanced optical absorption characteristics.In addition to linear optical modulation,we also achieved stronger near infrared nonlinear optical modulation,with a nonlinear absorption coefficient of Nb_(2)C/MoS_(2) being more than two times that of the pristine Nb_(2)C.These results were supported by the band alinement model which was determined by the X-ray photoelectron spectroscopy(XPS)experiment and first-principal theory calculation.The presented facile synthesis approach and robust light modulation strategy pave the way for broadband optoelectronic devices and optical modulators.
基金supported by the National High Technology Research and Development of China (Grant Nos. 2006AA01Z256,2007AA03Z419 and 2007AA03Z417)the State Key Development Program for Basic Research of China (Grant Nos. 2006CB604901and 2006CB604902)the National Natural Science Foundation of China (Grant Nos. 90401025,60736036,60706009 and 60777021)
文摘We report on chip-scale optical gates based on the integration of evanescent waveguide unitraveling-carrier photo- diodes （EC-UTC-PDs） and intra-step quantum well electroabsorption modulators （IQW-EAMs） on n-InP substrates. These devices exhibit simultaneously 2.1 GHz and -16.2 dB RF-gain at 21 GHz with a 450 t2 thin-film resistor and a bypass capacitor integrated on a chip.
文摘Converters with pulse width modulation are used for connections between the direct current （DC） and alternating current （AC） networks, e.g., in uninterrupted power supply systems, AC electromotor drives, for powering induction furnaces, in audio technique. Spectrum of signals sampled by pulse amplitude modulation and output voltage spectrum of the converter with pulse width modulation have similar properties. Spectrum of signals sampled by pulse amplitude modulation contains a harmonic of frequency equal to the frequency of the modulating signal and the harmonics of frequencies equal to the sum of frequency of the modulating signal and multiples of the sampling frequency. The output voltage spectrum of the converter with bipolar pulse width modulation contains harmonic of frequency equal to the frequency of the modulating signal and harmonics of frequencies equal to sum of the frequency of the modulating signal and multiples of the frequency of the carrier signal. It also contains harmonics of frequencies equal to the sum of the multiples of the frequency of the modulating signal and the multiples of the carrier signal. The comparison analysis was carried out for the harmonics of the output voltage of the converter with bipolar pulse width modulation in time domain. The dependency of the amplitudes and frequency spectrum on the wave forms of the carrier signal and modulating signal was shown. Similarity of the output voltage spectrum of the converter and signal spectrum sampled by the pulse width modulation was also shown. Key words： Output voltage converter with bipolar pulse width modulation, spectral analysis, Fourier series, carrier signal, reference signal.
