Modified Discrete Fourier Transform Research Articles

Papr reduction of FBMC-OQAM signals using Phase Search-PTS and modified discrete fourier transform spreading

In this research, a novel peak-to-average power ratio (PAPR) reduction technique for filter bank multicarrier (FBMC) modulation systems is presented. With multicarrier systems like FBMC, the strategy focuses on the survival of the fittest principle to suit the value of PAPR. The Filter Bank Multicarrier with Offset Quadrature Amplitude Modulation (FBMC-OQAM) has recently captured the attention of numerous academics due to its minimal adjacent channel leakage ratio (CLR). Unfortunately, the issue of increased PAPR measurement has a negative impact on the effectiveness of the FBMC system's energy measurement. In this study, the Phase search-based Partial Transmit Sequence (PS-PTS) approach and Modified Discrete Fourier Transform Spreading (MDFT) are developed for the PAPR reduction of the FBMC-OQAM signals. The increased PAPR measurement is reduced using the PTS and MDFT with osprey optimization method, which may result in a PAPR reduction of roughly 5.1 dB as comparable to the conventional approach.

Joint fast time-varying channel estimation with noise elimination and ICI cancellation for LTE-V2X systems

Vehicle-to-everything (V2X) communication is essential for intelligent transportation systems (ITS) and critical technology to ensure traffic safety. Aiming at the problems of noise interference, time-varying, and inter-carrier interference (ICI) in the LTE-V2X channel, a joint fast time-varying channel estimation with noise elimination and ICI cancellation is proposed in this paper. Firstly, using the autocorrelation characteristics of the Zadoff Chu (ZC) pilot sequence, a modified discrete Fourier transform (M-DFT) channel estimation algorithm is proposed to eliminate the noise in cyclic prefix (CP). Secondly, a joint iterative direct decision (IDD) and time-varying channel fitting (CF), called IDD-CF channel estimation algorithm, is proposed to track the rapid changes of channels on different symbols and eliminate ICI. The system simulation results show that the proposed joint fast time-varying channel estimation algorithm can effectively eliminate the noise and ICI, improve the performance of channel estimation, and have better robustness under different Doppler frequency shifts than the representative channel estimation algorithm.

Quantum dots decorated polyaniline plastic nanocomposites as a novel amperometric sensor for formaldehyde: Experimental and theoretical approach

A fast, reliable, and reproducible sensor is required for the qualitative and quantitative detection of environmental pollutants. Quantum dots and conducting polymer can increase the sensitivity and efficiency of a sensor because of their unique properties. Novel CuO quantum dots decorated polyaniline (PANI) plastic nanocomposites-based amperometric sensor was specially designed and developed for the detection of formaldehyde as an environmental pollutant. The CV, polarization, impedance spectroscopy, chrono-amperometry, linear sweep voltammetry, and differential pulse voltammetry techniques were used for quick and accurate determination of pollutants. The nanocomposite was used in a specially designed working electrode used in the amperometric sensor. The theoretical parameters (Becke's parameter, Lee-Yang-Par correlation functional, and Fukui functions) were determined by DFT, Forcite, COMPASS, and DMol3 modules. A linear current-concentration response was observed with the square of the correlation coefficient, 0.997. A characteristic anodic peak at 0.051 V, EMID = −0.130 V, ΔEp = 0.310 V, cathodic peak (Epc) = −0.2 V, Ecθ = 0.330 V and a OCP of −370 mV confirms the presence of formaldehyde. The performance, storage, and reusability of the sensor were monitored for 720 h. The main advantage of the sensor is the immobilization of antibodies, DNA, or enzyme are not required. The developed sensor was proved to be fast, reliable, and non-specific for quantitative and qualitative determination of environmental pollutants.

A Digital Filter Bank Based Method for Data Reduction in Spaceborne SAR Electronics

On-board data reduction is a major concern in designing of a spaceborne synthetic aperture radar (SAR) system since the volume of acquired SAR data is generally much higher than the downlink capability to the ground-station. The dechirp-on-receive (DoR) method is considered the state-of-the-art SAR data reduction technique. If there is deramping hardware in the SAR instrument, DoR is an effective method to reduce the volume of images for high resolution modes. In this paper, we use a digital signal processing method which applies a modified discrete Fourier transform (MDFT) filter bank for SAR data reduction. We call this method MDFT band selection filter (MDFT-BSF). This paper presents a quantitative analysis of the MDFT-BSF on data reduction performance. In addition, we provide a relationship between the data reduction performance and the number of sub-bands (M), and show that there is an optimal value of M that minimizes the volume of on-board SAR data. An evaluation of MDFT-BSF including a comparison with the DoR method presents that MDFT-BSF has an advantage for SAR data reduction. We show that MDFT-BSF can be implemented and operated on commercial space-grade FPGAs by the development of a spaceborne SAR digital receiver.

Kinetic study of microwave enhanced mercury desorption for the regeneration of spent activated carbon supported mercuric chloride catalysts

A novel microwave enhanced mercury desorption process was proposed for the regeneration of the spent activated carbon supported mercuric chloride catalysts. The mercury species desorption kinetics were investigated in detail by TG experiments, the overall apparent activation energy of 128.4 kJ/mol, the main reaction activation energy of 95.84 kJ/mol and the adsorption energy of 32.56 kJ/mol were confirmed with the combination of the model-free method and the DMol3 DFT module of Materials Studio package. The thermal desorption of HgCl2 and Hg2Cl2 were mainly between 473 K and 670 K, and the dominant mechanism for the desorption process was determined as second-order-model by the model-fitting method and the Z(α) master-plot method. Furthermore, the microwave enhancement degree of 26.36% was proved by the microwave heating experiment for the mercury desorption within 1500 s at 673 K, and the mercury content was significantly reduced from 19500 mg/kg to 149 mg/kg, which met the requirement of US land disposal restrictions (<260 mg/kg). Moreover, the preliminary activation of the spent activated carbon after microwave heating was demonstrated from the results of XRD, SEM and nitrogen adsorption analysis. Meanwhile, the HgCl2 solution with the concentration of 40–50 g/L could be effectively prepared by the water leaching of the condensate of mercury species, which could be used to regenerate the catalyst by soaking adsorption with activated carbon after microwave heating. Finally, a novel microwave enhanced mercury desorption process was proposed, which can synchronous realize the harmless and recovery of the spent activated carbon supported mercuric chloride catalysts.

Auxiliary Prony‐based algorithm for performance improvement of DFT phasor estimator against transient of CCVT

The measured fault voltage signal through coupling capacitor voltage transformer (CCVT) contains transient components which highly affect the estimated fundamental frequency phasor. This paper presents a new hybrid method which aims to calculate and remove the unwanted effect of CCVT transient on the fundamental phasor estimation. The main novelty of the proposed method is that proposed method is independent from the CCVT parameters involved in the transient response. In other words, unlike previously published papers, this method calculates the CCVT characteristics involved in the transient response. To such aim, by utilizing frequency modulation, fault voltage signal is shifted. Utilizing simple but comprehensive formulations based on integration and Prony-complex theory, the CCVT characteristics are calculated in the first cycle after fault inception. After that, by utilizing modified discrete Fourier transform (MDFT), the fundamental phasor component is calculated in one cycle. Several simulated test signals are applied to the proposed method. The simulation results illustrate that the proposed method removes the unwanted effects of CCVT. Also, it is fast and has a good precision in estimating the fundamental phasor component of fault voltage signal under different simulation scenarios.

The Modified Discrete Fourier Transform Algorithm by Improving the Convergence Rate Based Numerical Experiment of a C80 Fullerene Cage with D5h Symmetry

The Modified Discrete Fourier Transform Algorithm by Improving the Convergence Rate Based Numerical Experiment of a<i> C</i>₈₀ Fullerene Cage with <i>D</i>₅<i>_h</i> Symmetry

The DFT Calculations of Structures and EPR Parameters for the Dinuclear Paddle-Wheel Copper(II) Complex {Cu2(μ2-O2CCH3)4}(OCNH2CH3) as Powder or Single Crystal

Abstract Density functional theory (DFT) calculations of the structures and the Cu2+ g factors (g x , g y and g z ) and hyperfine coupling tensor A (A x , A y and A z ) were performed for the paddle-wheel (PW)-type binuclear copper(II) complex {Cu2(μ2-O2CCH3)4}(OCNH2CH3) powder and single crystal. Calculations were carried out with the ORCA software using the functionals BHandHlyp, B3P86 and B3LYP with five different basis sets: 6-311g, 6-311g(d,p), VTZ, def-2 and def2-TZVP. Results were tested by the MPAD analysis to find the most suitable functional and basis sets. The electronic structure and covalency between copper and oxygen were investigated by the electron localisation function and the localised orbital locator as well as the Mayer bond order for the [CuO5] group. The optical spectra were theoretically calculated by the time-dependent DFT module and plotted by the Multiwfn program for the [CuO5] group and reasonably associated with the local structure in the vicinity of the central ion copper. In addition, the interactions between the OCNH2CH3, NH3 and H2O molecules and the uncoordinated PW copper(II) complex were studied, and the corresponding adsorption energies, the frequency shifts with respect to the free molecules and the changes of the Cu–Cu distances were calculated and compared with the relevant systems.

Design of FRM-based MDFT filter banks in the canonic signed digit space using modified meta-heuristic algorithms

An optimal totally multiplier-less sharp transition width Modified Discrete Fourier Transform (MDFT) filter bank is proposed in this work. Since, here, the aim is to design a low complexity sharp transition width MDFT filter bank, the filters of the filter bank are designed using Frequency Response Masking technique to reduce the number of multipliers and hence the complexity. To replace multipliers with adders and shifters, the filter coefficients are converted into the Canonic Signed Digit space. In order to reduce the number of adders and shifters in the multiplier-less implementation, restricted number of non-zero bits is used in the conversion. This may degrade the performances of the MDFT filter bank. The performances are improved using modified meta-heuristic algorithms. A new hybrid algorithm which combines the qualities of Harmony Search Algorithm and Gravitational Search Algorithm is proposed in this work to optimise the performance of the MDFT filter bank.

Design of low complexity sharp MDFT filter banks with perfect reconstruction using hybrid harmony-gravitational search algorithm

The design of low complexity sharp transition width Modified Discrete Fourier Transform (MDFT) filter bank with perfect reconstruction (PR) is proposed in this work. The current trends in technology require high data rates and speedy processing along with reduced power consumption, implementation complexity and chip area. Filters with sharp transition width are required for various applications in wireless communication. Frequency response masking (FRM) technique is used to reduce the implementation complexity of sharp MDFT filter banks with PR. Further, to reduce the implementation complexity, the continuous coefficients of the filters in the MDFT filter banks are represented in discrete space using canonic signed digit (CSD). The multipliers in the filters are replaced by shifters and adders. The number of non-zero bits is reduced in the conversion process to minimize the number of adders and shifters required for the filter implementation. Hence the performances of the MDFT filter bank with PR may degrade. In this work, the performances of the MDFT filter banks with PR are improved using a hybrid Harmony-Gravitational search algorithm.

Design of Multiplier-Less MDFT Filter Banks with Perfect Reconstruction using ABC Algorithm

In this paper the design of a totally multiplier-less M-Channel Modified Discrete Fourier Transform (MDFT) Filter bank with Perfect reconstruction has been proposed. Canonic Sign Digit (CSD) based Finite Impulse Response (FIR) prototype filter with low implementation complexity is designed. The performance of the MDFT filter bank designed with this filter is optimized using Artificial Bee Colony (ABC) algorithm. This design leads to very low implementation complexity and hence low power dissipation and low chip area, which are desirable in upcoming applications such as software defined radio, wireless communication and portable computing systems.

Performance Comparison of MDFT Filter Bank with OFDM in Multi-Carrier Systems

Based on the filter bank, the theory of multi-carrier modulation using Orthogonal Frequency Division Multiplexing (OFDM) and Modified Discrete Fourier Transform (MDFT) filter bank has been discussed and the detailed derivation process has been given. Following these discussions, the actual implementation of MDFT filter bank in multi-carrier modulation systems has been discussed, and then the comparison of their prototype functions, Peak to Average Power Ratio (PAPR) and Symbol Error Rate (SER) are drawn. Experimental results demonstrate that compared with the OFDM system, prototype functions of MDFT have obvious advantage in spectrum leakage. In terms of PAPR, they have similar performance. Whether using QPSK or 16QAM modulation, MDFT is superior to OFDM in symbol error rate as a whole and with increasing of filter length L, the advantage becomes more and more apparent.

Design of Multiplier-less Sharp Transition Width MDFT Filter Banks using Modified Metaheuristic Algorithms

The significant advantage of modified discrete Fourier transform (MDFT) filter banks over the conventional discrete Fourier transform (DFT) filter banks is the structure inherent alias cancellation in the former. When the number of channels is increased, the filters in the filter bank need to be of sharp transition width. This increases the complexity of the filters and hence that of the filter bank. Frequency Response Masking (FRM) approach is known to reduce the complexity of sharp transition width filters. This paper proposes a method to realize MDFT filter banks using FRM with much lesser complexity. To further reduce the complexity, the filter banks are made totally multiplier-less. This is done by converting the coefficients to the canonic signed digit (CSD) representation. Metaheuristic algorithms are used to improve the performance of the CSD represented filter banks. Modified integer coded genetic algorithm, differential evolution, artificial bee colony, harmony search and gravitational search algorithms are proposed to be used for the optimization of the proposed multiplier-less MDFT filter banks. This design method reduces the complexity, power consumption and chip area for the implementation of the uniform filter banks.

Optimization and Implementation for the Modified DFT Filter Bank Multicarrier Modulation System

The modified Discrete Fourier Transform (MDFT) filter bank is a Nearly Perfect Reconstruction (NPR) system based on pseudo-QMF filter bank. In this paper, we introduce an optimized algorithm to implement the MDFT filter bank based multicarrier modulation system. The system based on this optimization algorithm has the low error rate and system delay. To verify the designed system we have compared the MDFT multicarrier modulation system with the OFDM modulation system. The results show that at high speed communication the data error rate in the MDFT filter bank multicarrier modulation system is clear improved in comparison with OFDM systems.  Index Terms—MDFT filter bank, NPR, Error rate, Optimization algorithm

Zero-padding or cyclic prefix for MDFT-based filter bank multicarrier communications

In this paper, the problem of channel equalization in modified discrete Fourier transform (MDFT)-based filter-bank multicarrier system (FBMC) is addressed. Two different system models based on padding zeros or using cyclic prefix in each transmitted block are presented. The proposed systems utilize IFFT/FFT blocks embedded in an MDFT-FBMC system. In the first one, an equalization block similar to single-carrier systems is included as the first stage in the receiver. The second system basically consists of an OFDM embedded in the MDFT-based transmultiplexer (TMUX). For both systems, the channel equalization is performed at the receiver in the frequency-domain by using a one-tap per subcarrier equalizer. Finally, several simulation results obtained in different scenarios are presented to assess the performance of the proposed systems compared to the standardized DFT-based systems (OFDM).

An Area Efficient Real-Time PFFT Architecture Using Parallel Distributed Arithmetic

In this letter, an area-efficient architecture for the hardware implementation of the real-time prime factor Fourier transform (PFFT) is presented. In the proposed architecture, a prime length DFT module with the one-point-per-cycle (OPPC) property is implemented by the parallel distributed arithmetic (DA), and a cyclic convolution feature is exploited to simplify the structure of the DA cells. Based on the proposed architecture, a real-time 65-point PFFT processor is designed, and the synthesis results show that it saves over 8% gates compared to the existing real-time 64-point DFT designs.

Efficient iterative design of modified DFT filter banks

An iterative algorithm based on the Lagrange multiplier method is presented for designing modified discrete Fourier transform (MDFT) filter banks with perfect reconstruction (PR). The dominant work at each iteration is to solve a system of linear equations involving a symmetric block matrix. By exploiting its special structure, the block matrix is factored into the product of lower and upper triangular matrices, thus leading to improved efficiency. The main benefit of the proposed scheme is that it allows the efficient design of PR MDFT filter banks with a large number of channels and/or long prototype filters.

Computational Nanoscience with NWChem

The NWChem software as been used to examine many nanoscale systems and their properties over the years. In this paper, an overiew of the general capabilities of NWChem is given as well as more specific details on the planewave and Gaussian based density functional codes usually used for nanoscale investigations. Examples are given of the scientific literature using NWChem, as well as two case studies: 1) Band gaps in oxides using exact-exchange based exchange-correlation functionals with the planewave DFT module, 2) Optical properties of chromophores using the Gaussian based DFT module.

Tone interference suppression in DS-SS systems with modified DFT

The performance of traditional interference excision methods based on the discrete Fourier transform (DFT) in direct sequence spread spectrum (DS-SS) systems varies significantly with the frequency of the interference because the DFT of the interference becomes more dispersive with the increase of grid biases in the DFT operation. This paper presents a new excision method using modified DFT (MDFT) with an estimated grid bias. Minimum dispersion of the interference is achieved in the MDFT domain. Both theoretical analysis and experimental simulation are presented to show that the interference can be excised with a minimum distortion of the desired signal in a large range of interference-to-signal ratio.

Design of low-delay nonuniform oversampled filterbanks

Low-delay nonuniform oversampled filterbanks have a good applicability in real-time audio applications. An appealing trade-off between complexity and frequency division is obtained by using filterbanks having uniform sections generated by generalized DFT modulation, with transition filters between the uniform sections. We propose two methods for designing such filterbanks, with no restrictions on the widths of transition filters. The first method is iterative and each iteration consists of convex optimization problems. In the second, faster method, the transition filters are designed using a frequency sampling technique. We present an example of design showing the good results of the proposed methods.