Difference in the Definitions of Coherence in the Space-time Domain and in the Space-frequency Domain

1992 ◽  
Vol 39 (7) ◽  
pp. 1461-1470 ◽  
Author(s):  
William H. Carter
Keyword(s):  
Frequency Domain ◽  
Time Domain ◽  
Space Time ◽  
Space Frequency

Channel Estimating Based on Space-Time-Frequency Pilot for MIMO-OFDM

2012 ◽  
Vol 429 ◽  
pp. 179-185
Author(s):  
Hui Liu ◽  
Jing Shan Jiao ◽  
Fu Chun Zhang ◽  
Ling Zhou
Keyword(s):  
Frequency Domain ◽  
Time Domain ◽  
Space Time ◽  
Three Dimensions ◽  
Space Domain ◽  
Time Frequency ◽  
Time Space ◽  
Mimo Ofdm ◽  
The Time Domain ◽  
Inverse Operation

The pilots that are transmitted by different transmitting antennas must be orthogonal after being shifted. So the time domain channel estimating solution is deduced through LS based on the MIMO-OFDM channel estimating model. The time domain solution need the inverse operation of matrix, and its operating quantity is large. So the three dimensions pilot based on space domain, time domain and frequency domain is designed. The method need not the inverse operation of matrix for the time domain channel estimating solution and can reduce the complexity of channel estimating and make the channel estimating error minimum. It is shown from the simulation that the channel estimating method of this paper based on space domain, time space and frequency domain pilot has better MSE and BER performances compared with the traditional LS algorithm and the document algorithm.

scholarly journals Design of In-phase and Quadrature Two Paths Space-Time-Modulated Metasurfaces

2021 ◽  
Author(s):  
Mengmeng Li ◽  
Mengmeng Li ◽  
Filiberto Bilotti
Keyword(s):  
Frequency Domain ◽  
Electromagnetic Waves ◽  
Specular Reflection ◽  
Small Dimension ◽  
Space Time ◽  
Start Time ◽  
First Order ◽  
Unit Cells ◽  
Potential Applications ◽  
Space Frequency

<p>Space-time-modulated metasurfaces can manipulate electromagnetic waves in space and frequency domain simultaneously. In this paper, an analytical design of space-time- modulated metasurfaces with modulation elements composed of two paths, In-phase (I) and Quadrature (Q), is proposed. The model is derived analytically, <a>the space/frequency domain</a> manipulations are achieved by designing the dimension and time sequence of I and Q paths.<a> In the specular reflection direction, an objective frequency shift of the reflected first order harmonic can be obtained. While, in other directions, the opposite first order harmonic can be easily controlled by changing the dimension of I/Q paths and the objective first order harmonic remains unchanged.</a> Furthermore, with a small dimension of I/Q paths, the first order harmonic can be used for beam scanning by pre-designing the start time of the modulation element. To realize the space-time-modulated metasurface with the required periodically time-varying responses, 2-bit unit-cells loaded with dynamically switchable pin diodes are employed as I/Q modulation. Both analytical and numerical results demonstrate that space and frequency domain manipulations of the reflected fields by the first order harmonics can be simultaneously obtained. The proposed designs have potential applications in wireless communications, radar camouflaging, and cloaking.</p>

scholarly journals A frequency‐space 2-D scalar wave extrapolator using extended 25-point finite‐difference operator

Geophysics ◽  
1998 ◽  
Vol 63 (1) ◽  
pp. 289-296 ◽  
Author(s):  
Changsoo Shin ◽  
Heejeung Sohn
Keyword(s):  
Finite Difference ◽  
Frequency Domain ◽  
Time Domain ◽  
Difference Operator ◽  
Rapid Development ◽  
Synthetic Seismograms ◽  
Domain Modeling ◽  
Time Migration ◽  
Space Frequency ◽  
Grid Points

Finite‐difference frequency‐domain modeling for the generation of synthetic seismograms and crosshole tomography has been an active field of research since the 1980s. The generation of synthetic seismograms with the time‐domain finite‐difference technique has achieved considerable success for waveform crosshole tomography and for wider applications in seismic reverse‐time migration. This became possible with the rapid development of high performance computers. However, the space‐frequency (x,ω) finite‐difference modeling technique is still beyond the capability of the modern supercomputer in terms of both cost and computer memory. Therefore, finite‐difference time‐domain modeling is much more popular among exploration geophysicists. A limitation of the space‐frequency domain is that the recently developed nine‐point scheme still requires that G, the number of grid points per wavelength, be 5. This value is greater than for most other numerical modeling techniques (for example, the pseudospectral scheme). To overcome this disadvantage inherent in space‐frequency domain modeling, we propose a new weighted average finite‐difference operator by approximating the spatial derivative and the mass acceleration term of the wave equation. We use 25 grid points around the collocation. In this way, we can reduce the number of grid points so that G is now 2.5. This approaches the Nyquist sampling limit in terms of the normalized phase velocity.

SIMULATION OF WAVES IN PORO-VISCOELASTIC ROCKS SATURATED BY IMMISCIBLE FLUIDS: NUMERICAL EVIDENCE OF A SECOND SLOW WAVE

2004 ◽  
Vol 12 (01) ◽  
pp. 1-21 ◽  
Author(s):  
JUAN ENRIQUE SANTOS ◽  
CLAUDIA LEONOR RAVAZZOLI ◽  
PATRICIA MERCEDES GAUZELLINO ◽  
JOSE M. CARCIONE ◽  
FABIO CAVALLINI
Keyword(s):  
Frequency Domain ◽  
Time Domain ◽  
Numerical Models ◽  
Domain Decomposition Method ◽  
Temporal Frequency ◽  
Immiscible Fluids ◽  
Type I ◽  
Type Iii ◽  
Space Frequency ◽  
Propagation Of Waves

We present an iterative algorithm formulated in the space-frequency domain to simulate the propagation of waves in a bounded poro-viscoelastic rock saturated by a two-phase fluid. The Biot-type model takes into account capillary forces and viscous and mass coupling coefficients between the fluid phases under variable saturation and pore fluid pressure conditions. The model predicts the existence of three compressional waves or Type-I, Type-II and Type-III waves and one shear or S-wave. The Type-III mode is a new mode not present in the classical Biot theory for single-phase fluids. Our differential and numerical models are stated in the space-frequency domain instead of the classical integrodifferential formulation in the space-time domain. For each temporal frequency, this formulation leads to a Helmholtz-type boundary value problem which is then solved independently of the other frequency problems, and the time-domain solution is obtained by an approximate inverse Fourier transform. The numerical procedure, which is first-order correct in the spatial discretization, is an iterative nonoverlapping domain decomposition method that employs an absorbing boundary condition in order to minimize spurious reflections from the artificial boundaries. The numerical experiments showing the propagation of waves in a sample of Nivelsteiner sandstone indicate that under certain conditions the Type-III wave can be observed at ultrasonic frequencies.

scholarly journals Design of In-phase and Quadrature Two Paths Space-Time-Modulated Metasurfaces

2022 ◽  
Author(s):  
Mengmeng Li ◽  
Mengmeng Li ◽  
Filiberto Bilotti
Keyword(s):  
Frequency Domain ◽  
Electromagnetic Waves ◽  
Specular Reflection ◽  
Small Dimension ◽  
Space Time ◽  
Start Time ◽  
First Order ◽  
Unit Cells ◽  
Potential Applications ◽  
Space Frequency

<p>Space-time-modulated metasurfaces can manipulate electromagnetic waves in space and frequency domain simultaneously. In this paper, an analytical design of space-time- modulated metasurfaces with modulation elements composed of two paths, In-phase (I) and Quadrature (Q), is proposed. The model is derived analytically, the space/frequency domain manipulations are achieved by designing the dimension and time sequence of I and Q paths. In the specular reflection direction, an objective frequency shift of the reflected first order harmonic can be obtained. While, in other directions, the opposite first order harmonic can be easily controlled by changing the dimension of I/Q paths and the objective first order harmonic remains unchanged. Furthermore, with a small dimension of I/Q paths, the first order harmonic can be used for beam scanning by pre-designing the start time of the modulation element. To realize the space-time-modulated metasurface with the required periodically time-varying responses, 2-bit unit-cells loaded with dynamically switchable pin diodes are employed as I/Q modulation. Both analytical and numerical results demonstrate that space and frequency domain manipulations of the reflected fields by the first order harmonics can be simultaneously obtained. The proposed designs have potential applications in wireless communications, radar camouflaging, and cloaking.<br></p>

scholarly journals Design of In-phase and Quadrature Two Paths Space-Time-Modulated Metasurfaces

2021 ◽  
Author(s):  
Mengmeng Li ◽  
Mengmeng Li ◽  
Filiberto Bilotti
Keyword(s):  
Frequency Domain ◽  
Electromagnetic Waves ◽  
Specular Reflection ◽  
Small Dimension ◽  
Space Time ◽  
Start Time ◽  
First Order ◽  
Unit Cells ◽  
Potential Applications ◽  
Space Frequency

<p>Space-time-modulated metasurfaces can manipulate electromagnetic waves in space and frequency domain simultaneously. In this paper, an analytical design of space-time- modulated metasurfaces with modulation elements composed of two paths, In-phase (I) and Quadrature (Q), is proposed. The model is derived analytically, <a>the space/frequency domain</a> manipulations are achieved by designing the dimension and time sequence of I and Q paths.<a> In the specular reflection direction, an objective frequency shift of the reflected first order harmonic can be obtained. While, in other directions, the opposite first order harmonic can be easily controlled by changing the dimension of I/Q paths and the objective first order harmonic remains unchanged.</a> Furthermore, with a small dimension of I/Q paths, the first order harmonic can be used for beam scanning by pre-designing the start time of the modulation element. To realize the space-time-modulated metasurface with the required periodically time-varying responses, 2-bit unit-cells loaded with dynamically switchable pin diodes are employed as I/Q modulation. Both analytical and numerical results demonstrate that space and frequency domain manipulations of the reflected fields by the first order harmonics can be simultaneously obtained. The proposed designs have potential applications in wireless communications, radar camouflaging, and cloaking.</p>

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