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Comparison between GFDM and VOFDM  [PDF]
Maximilian Matthé,Ivan Gaspar,Luciano Mendes,Dan Zhang
Mathematics , 2015,
Abstract: This document provides a comparison of the transmission techniques used in Generalized Frequency Division Multiplexing (GFDM) and Vector-OFDM (VOFDM). Within the document both systems are coarsely described and common and distinct properties are highlighted.
Precoded GFDM System to Combat Inter Carrier Interference : Performance Analysis  [PDF]
Shashank Tiwari,Suvra Sekhar Das,Kalyan Kumar Bandyopadhyay
Mathematics , 2015,
Abstract: The expected operating scenarios of 5G pose a great challenge to orthogonal frequency division multiplexing (OFDM) which has poor out of band (OoB) spectral properties, stringent synchronization requirements, and large symbol duration. Generalized frequency division multiplexing (GFDM) which is the focus of this work, has been suggested in the literature as one of the possible solutions to meet 5G requirements. In this work, the analytical performance evaluation of MMSE receiver for GFDM is presented. We also proposed precoding techniques to enhance the performance of GFDM. A simplified expression of SINR for MMSE receiver of GFDM is derived using special properties related to the modulation matrix of GFDM, which are described in this work. This SINR is used to evaluate the BER performance. Precoding schemes are proposed to reduce complexity of GFDM-MMSE receiver without compromising on the performance. Block Inverse Discrete Fourier Transform (BIDFT) and Discrete Fourier Transform (DFT) based precoding schemes are found to outperform GFDM-MMSE receiver due to frequency diversity gain while having complexity similar to zero-forcing receiver of GFDM. It is shown that both BIDFT and DFT-based precoding schemes reduce peak to average power ratio (PAPR) significantly. Computational complexity of different transmitters and receivers of precoded and uncoded GFDM is also presented.
Reduced Complexity Calculation of LMMSE Filter Coefficients for GFDM  [PDF]
Maximilian Matthé,Ivan Gaspar,Dan Zhang,Gerhard Fettweis
Mathematics , 2015,
Abstract: A low-complexity algorithm for calculation of the LMMSE filter coefficients for GFDM in a block-fading multipath environment is derived in this letter. The simplification is based on the block circularity of the involved matrices. The proposal reduces complexity from cubic to squared order. The proposed approach can be generalized to other waveforms with circular pulse shaping.
Low Complexity Transceiver Design for GFDM  [PDF]
Arman Farhang,Nicola Marchetti,Linda E. Doyle
Mathematics , 2015,
Abstract: Due to its attractive properties, generalized frequency division multiplexing (GFDM) is recently being discussed as a candidate waveform for the fifth generation of wireless communication systems (5G). GFDM is introduced as a generalized form of the widely used orthogonal frequency division multiplexing (OFDM) modulation scheme and since it uses only one cyclic prefix (CP) for a group of symbols rather than a CP per symbol, it is more bandwidth efficient than OFDM. In this paper, we propose novel transceiver structures for GFDM by taking advantage of the particular structure in the modulation matrix. Our proposed transmitter is based on modulation matrix sparsification through application of fast Fourier transform (FFT) to reduce the implementation complexity. A unified receiver structure for matched filter (MF), zero forcing (ZF) and minimum mean square error (MMSE) receivers is also derived. The proposed receiver techniques harness the special block circulant property of the matrices involved in the demodulation stage to reduce the computational cost of the system implementation. We have derived the closed forms for the ZF and MMSE receiver filters. Additionally, our algorithms do not incur any performance loss as they maintain the optimal performance. The computational costs of our proposed techniques are analyzed in detail and are compared with the existing solutions that are known to have the lowest complexity. It is shown that through application of our transceiver structure a substantial amount of computational complexity reduction can be achieved.
GPU Accelerated 2-D Staggered-grid Finite Difference Seismic Modelling  [cached]
Zhangang Wang,Suping Peng,Tao Liu
Journal of Software , 2011, DOI: 10.4304/jsw.6.8.1554-1561
Abstract: The staggered-grid finite difference (FD) method demands significantly computational capability and is inefficient for seismic wave modelling in 2-D viscoelastic media on a single PC. To improve computation speedup, a graphic processing units (GPUs) accelerated method was proposed, for modern GPUs have now become ubiquitous in desktop computers and offer an excellent cost-to-performance-ratio parallelism. The geophysical model is decomposed into subdomains for PML absorbing conditions. The vertex and fragment processing are fully used to solve FD schemes in parallel and the latest updated frames are swapped in Framebuffer Object (FBO) attachments as inputs for the next simulation step. The seismic simulation program running on modern PCs provides significant speedup over a CPU implementation, which makes it possible to simulate realtime complex seismic propagation in high resolution of 2048*2048 gridsizes on low-cost PCs.
New significance test methods for Fourier analysis of geophysical time series
Z. Zhang,J. Moore
Nonlinear Processes in Geophysics (NPG) , 2011,
Abstract: When one applies the discrete Fourier transform to analyze finite-length time series, discontinuities at the data boundaries will distort its Fourier power spectrum. In this paper, based on a rigid statistics framework, we present a new significance test method which can extract the intrinsic feature of a geophysical time series very well. We show the difference in significance level compared with traditional Fourier tests by analyzing the Arctic Oscillation (AO) and the Nino3.4 time series. In the AO, we find significant peaks at about 2.8, 4.3, and 5.7 yr periods and in Nino3.4 at about 12 yr period in tests against red noise. These peaks are not significant in traditional tests.
Finite Difference Method of Modelling Groundwater Flow  [PDF]
Magnus.U. Igboekwe, N. J. Achi
Journal of Water Resource and Protection (JWARP) , 2011, DOI: 10.4236/jwarp.2011.33025
Abstract: In this study, finite difference method is used to solve the equations that govern groundwater flow to obtain flow rates, flow direction and hydraulic heads through an aquifer. The aim therefore is to discuss the principles of Finite Difference Method and its applications in groundwater modelling. To achieve this, a rectangular grid is overlain an aquifer in order to obtain an exact solution. Initial and boundary conditions are then determined. By discretizing the system into grids and cells that are small compared to the entire aquifer, exact solutions are obtained. A flow chart of the computational algorithm for particle tracking is also developed. Results show that under a steady-state flow with no recharge, pathlines coincide with streamlines. It is also found that the accuracy of the numerical solution by Finite Difference Method is largely dependent on initial particle distribution and number of particles assigned to a cell. It is therefore concluded that Finite Difference Method can be used to predict the future direction of flow and particle location within a simulation domain.
Modelling of karst structures by geophysical methods. An example: the doline of S. Pietro dei Monti (Western Liguria)
E. Armadillo,F. Massa,G. Caneva,M. Gambetta
Annals of Geophysics , 1998, DOI: 10.4401/ag-4337
Abstract: Integrated geophysical investigations of karst structures were carried out in Liguria and Piedmont (NW Italy); this paper refers to the S. Pietro dei Monti doline, in the karst area of Mt. Carmo (Savona). The techniques used in the integrated study were magnetics, electromagnetics and seismic refraction. The target was to identify, without drilling, the nature of the doline, for example if it is of dissolution or collapse type. A preliminary susceptibility sampling of the outcrop and topsoil and the diffuse fractures with a probable water seepage suggested magnetics and VLF electromagnetics. Such methods applied in an area with an extremely low cultural noise allowed modelling of the buried structure of the doline.
Integrated geophysical measurements on a test site for detection of buried steel drums  [cached]
Marco Marchetti,Alessandro Settimi
Annals of Geophysics , 2011, DOI: 10.4401/ag-4846
Abstract: Geophysical methods are increasingly used to detect and locate illegal waste disposal and buried toxic steel drums. This study describes the results of a test carried out in clayey-sandy ground where 12 empty steel drums had previously been buried at 4-5 m below ground level. This test was carried out with three geophysical methods for steel-drum detection: a magnetometric survey, electrical resistivity tomography with different arrays, and a multifrequency frequency-domain electromagnetic induction survey. The data show that as partially expected, the magnetometric and electromagnetic induction surveys detected the actual steel drums buried in the subsurface, while the electrical resistivity tomography mainly detected the changes in some of the physical properties of the terrain connected with the digging operations, rather than the actual presence of the steel drums.
Geophysical modelling with Colombeau functions: Microlocal properties and Zygmund regularity  [PDF]
G. Hoermann,M. V. de Hoop
Physics , 2001,
Abstract: In global seismology Earth's properties of fractal nature occur. Zygmund classes appear as the most appropriate and systematic way to measure this local fractality. For the purpose of seismic wave propagation, we model the Earth's properties as Colombeau generalized functions. In one spatial dimension, we have a precise characterization of Zygmund regularity in Colombeau algebras. This is made possible via a relation between mollifiers and wavelets.
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