151,682 research outputs found
Electrodynamics of Accelerated-Modulation Space-Time Metamaterials
Space-time varying metamaterials based on uniform-velocity modulation have
spurred considerable interest over the past decade. We present here the first
extensive investigation of accelerated modulation space-time metamaterials.
Using the tools of general relativity, we establish their electrodynamic
principles and describe their fundamental phenomena, in comparison with the
physics of moving-matter media. We show that an electromagnetic beam
propagating in an accelerated modulation metamaterial is bent in its course,
which reveals that such a medium curves space-time for light, similarly to
gravitation. Finally, we illustrate the vast potential diversity of accelerated
modulation metamaterial by demonstrating related Schwarzschild holes
Labelling diversity for media-based space-time block coded spatial modulation
Abstract: Please refer to full text to view abstract
Multidimensional Generalized Quadrature Index Modulation for 5G Wireless Communications
Multidimensional generalized quadrature index modulation scheme is proposed in this paper for conveying extra digital information with the aid of the space, radio frequency (RF) mirrors, and time indices. Explicitly, this proposed scheme cleverly combines another proposed time-indexed generalized quadrature spatial modulation (TI-GQSM) system with media-based modulation (MBM) transmission principle using RF mirrors, and it is referred to as TI-GQSM-MBM scheme. This scheme is attractive because of both the high data rate and the significant performance improvements that can be achieved. The system performance of the proposed schemes in terms of the bit error rate (BER) is evaluated and compared to the performance of the conventional schemes. Simulation results showed that a significant improvement is achieved by the TI-GQSM-MBM scheme as compared to that of TI-GQSM, time-indexed media-based modulation (TI-MBM) and the conventional generalized quadrature spatial modulation (GQSM) schemes for the same rate. It is also demonstrated that the proposed schemes are robust to channel estimation errors (CEEs) as compared to multidimensional generalized spatial modulation (GSM) schemes. Therefore, the proposed schemes can be effectively used as an alternative solution for various 5G and beyond wireless networks
Efficient space-frequency block coded pilot-aided channel estimation method for multiple-input-multiple-output orthogonal frequency division multiplexing systems over mobile frequency-selective fading channels
© 2014 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.An iterative pilot-aided channel estimation technique for space-frequency block coded (SFBC) multiple-input multiple-output orthogonal frequency division multiplexing systems is proposed. Traditionally, when channel estimation techniques are utilised, the SFBC information signals are decoded one block at a time. In the proposed algorithm, multiple blocks of SFBC information signals are decoded simultaneously. The proposed channel estimation method can thus significantly reduce the amount of time required to decode information signals compared to similar channel estimation methods proposed in the literature. The proposed method is based on the maximum likelihood approach that offers linearity and simplicity of implementation. An expression for the pairwise error probability (PEP) is derived based on the estimated channel. The derived PEP is then used to determine the optimal power allocation for the pilot sequence. The performance of the proposed algorithm is demonstrated in high frequency selective channels, for different number of pilot symbols, using different modulation schemes. The algorithm is also tested under different levels of Doppler shift and for different number of transmit and receive antennas. The results show that the proposed scheme minimises the error margin between slow and high speed receivers compared to similar channel estimation methods in the literature.Peer reviewe
Multidimensional Index Modulation in Wireless Communications
In index modulation schemes, information bits are conveyed through indexing
of transmission entities such as antennas, subcarriers, times slots, precoders,
subarrays, and radio frequency (RF) mirrors. Index modulation schemes are
attractive for their advantages such as good performance, high rates, and
hardware simplicity. This paper focuses on index modulation schemes in which
multiple transmission entities, namely, {\em antennas}, {\em time slots}, and
{\em RF mirrors}, are indexed {\em simultaneously}. Recognizing that such
multidimensional index modulation schemes encourage sparsity in their transmit
signal vectors, we propose efficient signal detection schemes that use
compressive sensing based reconstruction algorithms. Results show that, for a
given rate, improved performance is achieved when the number of indexed
transmission entities is increased. We also explore indexing opportunities in
{\em load modulation}, which is a modulation scheme that offers power
efficiency and reduced RF hardware complexity advantages in multiantenna
systems. Results show that indexing space and time in load modulated
multiantenna systems can achieve improved performance
Nonreciprocal Electromagnetic Scattering from a Periodically Space-Time Modulated Slab and Application to a Quasisonic Isolator
Scattering of obliquely incident electromagnetic waves from periodically
space-time modulated slabs is investigated. It is shown that such structures
operate as nonreciprocal harmonic generators and spatial-frequency filters. For
oblique incidences, low-frequency harmonics are filtered out in the form of
surface waves, while high-frequency harmonics are transmitted as space waves.
In the quasisonic regime, where the velocity of the space-time modulation is
close to the velocity of the electromagnetic waves in the background medium,
the incident wave is strongly coupled to space-time harmonics in the forward
direction, while in the backward direction it exhibits low coupling to other
harmonics. This nonreciprocity is leveraged for the realization of an
electromagnetic isolator in the quasisonic regime and is experimentally
demonstrated at microwave frequencies
Space-Time Medium Functions as a Perfect Antenna-Mixer-Amplifier Transceiver
We show that a space-time-varying medium can function as a front-end
transceiver, i.e., an antenna-mixer-amplifier. Such a unique functionality is
endowed by space-time surface waves associated with complex space-time wave
vectors in a subluminal space-time medium. The proposed structure introduces
pure frequency up- and down-conversions and with very weak undesired time
harmonics. In contrast to other recently proposed space-time mixers, a large
frequency up-/down conversion ratio, associated with gain is achievable.
Furthermore, as the structure does not operate based on progressive energy
transition between the space-time modulation and the incident wave, it
possesses a subwavelength thickness (metasurface). Such a multi-functional,
highly efficient and compact medium is expected to find various applications in
modern wireless telecommunication systems
Mixer-Duplexer-Antenna Leaky-Wave System Based on Periodic Space-Time Modulation
We present a mixer-duplexer-antenna leaky-wave system based on periodic
space-time modulation. This system operates as a full transceiver, where the
upconversion and downconversion mixing operations are accomplished via
space-time transitions, the duplexing operation is induced by the nonreciprocal
nature of the structure, and the radiation operation is provided by the
leaky-wave nature of the wave. A rigorous electromagnetic solution is derived
for the dispersion relation and field distributions. The system is implemented
in the form of a spatio-temporally modulated microstrip leaky-wave structure
incorporating an array of sub-wavelengthly spaced varactors modulated by a
harmonic wave. In addition to the overall mixer-duplexer-antenna operation,
frequency beam scanning at fixed input frequency is demonstrated as one of the
interesting features of the system. A prototype is realized and demonstrated by
full-wave and experimental results
Dynamic Modulation Yields One-Way Beam Splitting
This article demonstrates the realization of an extraordinary beam splitter
based on nonreciprocal and synchronized photonic transitions in obliquely
illuminated space-time-modulated (STM) slabs which impart the coherent temporal
frequency and spatial frequency shifts. As a consequence of such unusual
photonic transitions, a one-way beam splitting and amplification is exhibited
by the STM slab. Beam splitting is a vital operation for various optical and
photonic systems, ranging from quantum computation to fluorescence spectroscopy
and microscopy. Despite the beam splitting is conceptually a simple operation,
the performance characteristics of beam splitters significantly influence the
repeatability and accuracy of the entire optical system. As of today, there has
been no approach exhibiting a nonreciprocal beam splitting accompanied with
transmission gain and an arbitrary splitting angle. Here, we show that oblique
illumination of a periodic and semi-coherent dynamically-modulated slab results
in coherent photonic transitions between the incident light beam and its
counterpart space-time harmonic (STH). Such photonic transitions introduce a
unidirectional synchronization and momentum exchange between two STHs with same
temporal frequencies, but opposite spatial frequencies. Such a beam splitting
technique offers high isolation, transmission gain and zero beam tilting, and
is expected to drastically decrease the resource and isolation requirements in
optical and photonic systems. In addition to the analytical solution, we
provide a closed-form solution for the electromagnetic fields in STM
structures, and accordingly, investigate the properties of the wave isolation
and amplification in subluminal, superluminal and luminal ST modulations
- …