Subband System Research Articles

SERs of Different Modulation Systems in 1G-4G

The Digital sub-band system is an indispensable technology for the development of modern society, which has a wide range of applications. This work is particularly concerned with developing applications for modulation techniques used in mobile communication. Based on MATLAB, this paper compared the modulation and demodulation of 2ASK, 2FSK, 2PSK, and QPSK horizontally and analysed the practical and theoretical error rates. With the constellation maps of 16QAM, 32QAM, 64QAM, and 256QAM, the relationship between the error rate and the signal-to-noise ratio was studied. In binary modulation systems, 2PSK has the best noise resistance and requires 6dB less SNR than 2ASK when employing the same demodulation approach. In addition, this paper outlined the technologies and modulation standards employed in the development of 1G-4G. To make the comparison clearer, the advantage, disadvantages, and modulation comparisons among 1G-5G are displayed. The analysis and research of digital sub-band modulation technology is the basis for developing new technology in the future.

Electric field to control light scattering on semiconductor QWW

In this work, the study of an external electric field to control the electron Raman scattering in a semiconductor quantum well wire with a cylindrical symmetry grown in a GaAs/Al0.35Ga0.65As matrix is presented. In our model we considered an transversal electric field to the axis of the system. To illustrate our calculations a single electron in the conduction band, that is parabolic and unfolds in a system of sub-bands due to confinement is considered. This approach assumed the results previously obtained by our group where the behavior of the electron states energy, εr, as a function of the electric field and the confinement radius was demonstrated. The unfolding of the electron states, the selection rules elimination, and the positions of the singularities with the change of the electric field for a fixed confinement radius were visible in the emission spectra. Finally, the quantum efficiency and the characteristics of a secondary radiation source based on electron Raman scattering process in a semiconductor quantum well wire with fixed confinement radius, electric field intensity, and incident photon energy to operate properly with the best efficiency, are established.

Intra-band Raman scattering and gain in a double quantum well wire with asymmetrical barriers

In this paper we present a study on electron states in a double quantum well wire with asymmetrical barriers, also emission spectra are analyzed for a process of electron Raman scattering in this system, for which we calculate the differential cross section. The model we use considers the system to be at a temperature of T=0K and the presence of a single electron in the conduction band. In addition, the conduction band is assumed to be parabolic, which splits into a system of sub-bands due to confinement. On the other hand, in this work we study the net Raman gain of the system, illustrating the results through the transition rate since they are directly proportional. The results obtained in this work are compared to those of previous works and we show that the net Raman gain of the double quantum well wire with asymmetrical barriers is greater than that of the step-quantum well wire, and than that of the core/shell quantum well wire, obtaining the results of these systems as limit cases. We also showed that the system studied here is slightly more efficient than the double quantum well with asymmetrical barriers. These results can be applied in the manufacture of electronic and optoelectronic devices as quantum cascade lasers.

Delayless Block Individual-Weighting-Factors Sign Subband Adaptive Filters With an Improved Band-Dependent Variable Step-Size

Delayless individual-weighting-factors sign subband adaptive filter (IWF-SSAF) algorithms with a band-dependent variable step-size (BDVSS) were recently introduced to achieve a robust convergence performance against the impulsive interference and to avoid an undesirable signal path delay in subband systems. In this paper, we develop a block implementation of the delayless IWF-SSAF algorithm designed for an active impulsive noise control (AINC) system. With the block-processing approach, the proposed delayless block IWF-SSAF algorithm can be implemented more efficiently than the original delayless algorithm regardless of number of subbands, which is verified through the computational analysis. Furthermore, an improved BDVSS version (I-BDVSS) is also proposed by using the multiple auxiliary past gradients, which are given for each band by the block-processing. Finally, the simulation results illustrate that the proposed delayless block IWF-SSAF algorithm with the I-BDVSS, even requiring less computational burden, can achieve a better convergence performance than the original delayless algorithm with the BDVSS under severe impulsive noise control environment.

Electron states and electron Raman scattering in a semiconductor quantum well with step-barriers: Electric field effect

In this work, we present the study of an intra-band electron Raman scattering process for a semiconductor quantum well with step-barriers, developed in a GaAs/AlxGa1−xAs matrix. For the solution of this problem, the existence of an electron in a single conduction band and a system under the effect of an external electric field in the direction of confinement were considered. In addition, we will study the electron states for this system. In this study, we calculate the differential cross-section and the net Raman gain, so that the corresponding emission spectra (which are interpreted and discussed) are obtained. For this, we consider a simple parabolic conduction band, which is unfolded into a sub-band system due to confinement. Moreover, the exact solutions of the electron states considering the approximation of the envelope function are obtained. In like manner, we make a comparison between the quantum well with step-barriers with other systems such as the asymmetric double quantum well and the step-quantum well with the objective of studying the differences between these three systems.

A joint-feature learning-based voice conversion system for dysarthric user based on deep learning technology.

Dysarthria speakers suffer from poor communication, and voice conversion (VC) technology is a potential approach for improving their speech quality. This study presents a joint feature learning approach to improve a sub-band deep neural network-based VC system, termed J_SBDNN. In this study, a listening test of speech intelligibility is used to confirm the benefits of the proposed J_SBDNN VC system, with several well-known VC approaches being used for comparison. The results showed that the J_SBDNN VC system provided a higher speech intelligibility performance than other VC approaches in most test conditions. It implies that the J_SBDNN VC system could potentially be used as one of the electronic assistive technologies to improve the speech quality for a dysarthric speaker.

Theory of electron Raman scattering in a semiconductor core/shell quantum well wire

A study of the electron states of a semiconductor core/shell quantum well wire and the electron Raman scattering are presented. Thus, the system has been modeled considering a GaAs/AlxGa1−xAs/AlAs structure. To carry out this study, the exact mathematical expressions that describe the electron states and the Raman differential cross-section in the aforementioned system were obtained. Our model considers T=0K and that, as a consequence of the presence of the confinement, the electron bands unfold in a subband system. In addition, the expressions that describe the differential cross-section and the selection rules for the emission spectra are shown. On the other hand, the net gain of Raman is studied through the transition rate, since they are directly proportional. It should be point out that our results are compared with the results obtained in previous works, especially with the step-quantum well wire. Finally, it is shown that although the core/shell quantum well wire and the step-quantum well wire are very similar systems, the Raman net gain for the step-quantum well wire is much greater than the one for the core/shell quantum well wire.

Electron states in a semiconductor quantum well wire in presence of an external transversal electric field

In this work, the electron states corresponding to a semiconductor quantum well wire grown on a GaAs/AlGaAs matrix with a cylindrical symmetry, in the presence of an external electric field which is homogenous and perpendicular to the axis of the system, is obtained. This study takes into consideration the partial and total confinement of the charge carriers, and assumes T = 0 K. The model on which this is based considers a system of parabolic bands, which unfolds in a system of sub-bands due to confinement. In addition, the selection rules for intraband and interband optic transitions are studied.

Electron states and electron Raman scattering in an asymmetrical double quantum well: External electric field

In this paper studies an electron Raman scattering process for a semiconductor, coupled and asymmetrical double quantum well. Then, the presence of an electron in a single conduction band is considered. In addition, the system is subjected to an external electric field. To carry out this study, the net Raman gain and the differential cross section are calculated. The emission spectra are interpreted and discussed. For this, we obtain the exact solutions of the electron states considering the envelope function approximation and a single parabolic conduction band, which is split into a sub-bands system due to confinement. Furthermore, the effect of the electric field on the electron states and in the differential cross section is studied. To illustrate our findings, we have considered a system growing in a GaAs/AlxGa1−xAs matrix.

Experimental demonstration of multi-Gbps multi sub-bands FBMC transmission in mm-wave radio over a fiber system.

The filter bank multicarrier (FBMC) modulation format is considered as a potential candidate for future wireless 5G due to its feature of high suppression for out-of-band emissions, which allows combining multiple sub-bands with very narrow band-gaps, and hence increases the overall wireless transmission capacity. In this paper, we experimentally demonstrate the generation of multi sub-bands FBMC signals at millimeter-wave (mm-wave) for radio-over-fiber (RoF) systems. The designed multi sub-bands FBMC system consists of 5 sub-bands of 800 MHz with inter sub-band gaps of 781.25 kHz. The composite 5 sub-bands FBMC signal is generated with no band-gap between dc to the first sub-band to preserve the bandwidth of the system. Each FBMC sub-band consists of 1024 sub-carriers and is modulated with uncorrelated data sequences. The aggregate FBMC signal is carried optically by externally modulating a free running laser and is converted to millimeter waves (mm-waves) by photomixing with another free running laser at a frequency offset of 53 GHz. At the receiver, the received electrical mm-wave signal is down-converted to an intermediate frequency (IF) and then post-processed using digital signal processing (DSP) techniques. With the use of the simple recursive least square (RLS) equalizer in the DSP receiver, the achieved aggregate data rate is 8 Gbps and 12 Gbps for 16 quadrature amplitude modulation (QAM), and 64 QAM, respectively with a total bandwidth of 4.2 GHz. The system performance is evaluated by measuring error vector magnitude (EVM) and bit error rate (BER) calculations.

Optically Switchable Photocatalysis in Ultrathin Black Phosphorus Nanosheets.

Recently low-dimensional materials hold great potential in the field of photocatalysis, whereas the concomitantly promoted many-body effects have long been ignored. Such Coulomb interaction-mediated effects would lead to some intriguing, nontrivial band structures, thus promising versatile photocatalytic performances and optimized strategies. Here, we demonstrate that ultrathin black phosphorus (BP) nanosheets exhibit an exotic, excitation-energy-dependent, optical switching effect in photocatalytic reactive oxygen species (ROS) generation. It is, for the first time, observed that singlet oxygen (1O2) and hydroxyl radical (•OH) are the dominant ROS products under visible- and ultraviolet-light excitations, respectively. Such an effect can be understood as a result of subband structure, where energy-transfer and charge-transfer processes are feasible under excitations in the first and second subband systems, respectively. This work not only establishes an in-depth understanding on the influence of many-body effects on photocatalysis but also paves the way for optimizing catalytic performances via controllable photoexcitation.

Electron states and electron Raman scattering in a semiconductor step-quantum well wire

The differential cross-section for an electron Raman scattering process in a semiconductor GaAs/AlGaAs step-quantum well wire is calculated and expressions for the electron states are presented. The system is modeled by considering T=0K and also by a single parabolic conduction band, which is split into a sub-band system due to confinement. The net Raman gain for an electron Raman scattering process is obtained. Also, the emission spectra for several scattering configurations are discussed, and the interpretation of the singularities found in the spectra is given. The results obtained in this study are compared with those obtained for other structures, and so it has been demonstrated that the wire shows greater efficiency.

Electron states and electron Raman scattering in semiconductor step-quantum well: Electric field effect

In this work we determine and show the expressions of the electron states of a step-quantum well with the presence of an external electric field, developed in a GaAs/AlGaAs matrix. The electron states are obtained using the envelope function approximation. In this work it is only necessary to consider a single conduction band, which due to the confinement is divided into a subband system, with T=0K. Expressions for the electron states and the differential cross-section for an intraband electron Raman scattering process of are presented, the net Raman gain is also calculated. In addition, the interpretation of the singularities found in the emission or excitation spectra is given, since several dispersion configurations are discussed. Furthermore, the effects of an electric field on the electron states and on the differential cross section are studied.

Electron states and electron Raman scattering in semiconductor double cylindrical quantum well wire

The differential cross section for an electron Raman scattering process in a semiconductor GaAs/AlGaAs double quantum well wire is calculated, and expressions for the electronic states are presented. The system is modeled by considering T = 0 K and also with a single parabolic conduction band, which is split into a subband system due to the confinement. The gain and differential cross-section for an electron Raman scattering process are obtained. In addition, the emission spectra for several scattering configurations are discussed, and interpretations of the singularities found in the spectra are given. The electron Raman scattering studied here can be used to provide direct information about the efficiency of the lasers.

Adaptive Feedback Cancellation for Realistic Hearing Aid Applications

Acoustic feedback is a well-known phenomenon in hearing aids. Under certain conditions it causes the so-called howling effect, which is highly annoying for the hearing aid user and limits the maximum amplification of the hearing aid. The standard adaptive feedback cancellation algorithms suffer from a biased adaptation if the input signal is spectrally colored, as it is for speech and music signals. Due to this bias distortion artifacts (entrainment) are generated. In this paper, we present a sub-band feedback cancellation system which combines decorrelation methods with a new realization of a known non-parametric variable step size. To apply this step size in the context of adaptive feedback cancellation, a method to estimate the signal power of the desired input signal, i.e., without feedback, is necessary. A major part of this paper is spent with the theoretical derivation of this estimate. Furthermore, the complete system is evaluated extensively for several speech and music signals as well as for different feedback scenarios in simulations with feedback paths measured in concrete applications as well as for real-time simulations with hearing aid dummies. Both use hearing loss compensation methods as applied in physical hearing aids. The performance is measured in terms of being able to prevent entrainment and to react to feedback path changes. For both simulation setups the system shows a good performance with respect to the two performance measures. Furthermore, the overall feedback cancellation method relies only on few parameters, shows a low computational complexity, and therefore has a strong practical relevance.

Electron Raman scattering in semiconductor quantum well wire of cylindrical ring geometry

We study the electron states and the differential cross section for an electron Raman scattering process in a semiconductor quantum well wire of cylindrical ring geometry. The electron Raman scattering developed here can be used to provide direct information about the electron band structures of these confinement systems. We assume that the system grows in a GaAs/Al0.35Ga0.65As matrix. The system is modeled by considering T = 0 K and also a single parabolic conduction band, which is split into a sub-band system due to the confinement. The emission spectra are discussed for different scattering configurations, and the selection rules for the processes are also studied. Singularities in the spectra are found and interpreted.

Electromagnetically induced transparency in a cascade-type quantum well subband system under intense picosecond excitation

The coherent light–matter interaction in a 4-level cascade-type subband system of an asymmetric GaAs/AlGaAs quantum well structure is studied in pump-probe transmission experiments with picosecond (ps) time resolution. Coupling two excited subbands by an intense mid-infrared laser pulse at low sample temperatures is found to result in a substantially increased transparency of the fundamental e1–e2 transition. We find a reduction of the absorption coefficient by ~80%, which is one of the most pronounced electromagnetically induced transparency in solid state systems observed so far.

Electron Raman scattering in semiconductor step-quantum well

The differential cross section for an electron Raman scattering process in a semiconductor GaAs/AlGaAs step-quantum well is calculated and expressions for the electronic states are presented. The system is modeled considering T=0K and a single parabolic conduction band, which is split into a subbands system due to the confinement. The gain and differential cross-section for an electron Raman scattering process are obtained. Also, the emission spectra for several scattering configurations are discussed. The interpretation of the singularities found in the spectra is given. The electron Raman scattering studied here can be used to provide direct information about the efficiency of the lasers.

Estados electrónicos para un cascarón cuántico semiconductor de geometría cilíndrica

En este trabajo obtenemos los estados electrónicos para un cascarón cuántico semiconductor de geometría cilíndrica obtenido a partir de una matriz de . En este caso hemos asumido que el sistema solo tiene una banda la cual se desdobla en un sistema de sub-bandas debido al confinamiento. Utilizando el formalismo de la masa efectiva determinamos las funciones de onda y las energías de los estados.

Exponential spline perfect reconstruction, decomposition and reconstruction with applications in compression and denoising

B-splines caught interest of many engineering applications due to their merits of being flexible and provide a large degree of differentiability and cost/quality trade-off relationship. However, they have less impact with continuous-time applications as they are constructed from piecewise polynomials. On the other hand, exponential spline polynomials (E-splines) represent the best smooth transition between continuous and discrete domains as they are made of exponential segments. In this paper, we present a complete analysis for an E-spline-based subband coding (wavelet) perfect reconstruction (PR) system. Derivations for the scaling and wavelet functions are presented, along with application of the proposed system in image compression and image denoising. In image compression, a comparison of the proposed technique compared with the B-spline-based PR system as well as the basic wavelet subband system with the SPIHT image codec is presented. In image denoising, we report the enhancement achieved with the proposed E-spline-based denoising approach compared with B-spline-based denoising and another basic denoising technique. In both applications, E-splines show superior performance as will be illustrated.