9,693 research outputs found
Real Time Implementation of CAP Modulation With âBetter-Than-Nyquistâ Pulse Shaping in Visible Light Communications
In this letter we experimentally verify a real-time implementation of the âbetter-than-Nyquistâ pulse shape in carrier-less amplitude and phase (CAP) modulation in the context of a visible light communications system. We use two National Instruments universal software radio peripherals (USRPs) as a transmitter and receiver working independently. Previously reported experimental work on pulse shaping in CAP is also verified in real time, showing lower error vector magnitudes (EVM) can be obtained at shorter filter lengths using the better-than-Nyquist pulses in place of the conventionally used square-root raised cosine as the basis function of the signal. We show that a real time EVM penalty is an additional 3% EVM in the worst case and is a result of synchronisation offset at the receiver
Improving GFDM Symbol Error Rate Performance using Better than Nyquist Pulse Shaping Filters
Fourth generation (4G) cellular systems have been optimized to provide high data rates and reliable coverage to mobile users. New waveforms at the physical layer are needed. Generalized frequency division multiplexing (GFDM) is a candidate modulation for the fifth generation (5G) standard based on multi-branch multicarrier filter bank approach. A main characteristic of GFDM is its low out of band emission, achieved by means of a flexible time-domain pulse shaping of individual subcarriers. In this paper, the influence of the improved Better than Nyquist pulse shaping filters on symbol error rate (SER) performance of the GFDM system in the case of zero forcing (ZF) receiver is investigated. We considered their use in GFDM to evaluate the impact on SER performance in case of 16-QAM transmission over an additive white Gaussian noise channel. Moreover, we also considered the concept of the wavelet for better time-frequency localization of the pulse shaping filters by using the Meyer auxiliary function. Numerical results are reported to demonstrate the superior SER performance achieved
Bandwidth EfïŹcient Root Nyquist Pulses for Optical Intensity Channels
Indoor diffuse optical intensity channels are bandwidth constrained due to the multiple reflected paths between the transmitter and the receiver which cause considerable inter-symbol interference (ISI). The transmitted signal amplitude is inherently non-negative, being a light intensity signal. All optical intensity root Nyquist pulses are time-limited to a single symbol interval which eliminates the possibility of finding bandlimited root Nyquist pulses. However, potential exists to design bandwidth efficient pulses. This paper investigates the modified hermite polynomial functions and prolate spheroidal wave functions as candidate waveforms for designing spectrally efficient optical pulses. These functions yield orthogonal pulses which have constant pulse duration irrespective of the order of the function, making them ideal for designing an ISI free pulse. Simulation results comparing the two pulses and challenges pertaining to their design and implementation are discussed
Can pigeonpea hybrids negotiate stresses better than inbred cultivars?
Pigeonpea [Cajanus cajan (L.) Millsp.] is an important rainfed pulse crop of tropics and sub-tropics, and
during its long growth cycle of 6â9 months it encounters a number of biotic and abiotic stresses. The recently
developed CMS-based pigeonpea hybrids have demonstrated large gains in yield and stability over the traditional
inbred cultivars. In this review, the authors argue that the heterosis expressed in traits like seed germination,
radicle growth, root biomass production and moisture retention during water stress confers advantages
to hybrid plants in negotiating a few abiotic and biotic stresses in much better way than pure line cultivars
Ultrasensitive 3He magnetometer for measurements of high magnetic fields
We describe a 3He magnetometer capable to measure high magnetic fields (B >
0.1 Tesla) with a relative accuracy of better than 10^-12. Our approach is
based on the measurement of the free induction decay of gaseous, nuclear spin
polarized 3He following a resonant radio frequency pulse excitation. The
measurement sensitivity can be attributed to the long coherent spin precession
time T2* being of order minutes which is achieved for spherical sample cells in
the regime of motional narrowing where the disturbing influence of field
inhomogeneities is strongly suppressed. The 3He gas is spin polarized in-situ
using a new, non-standard variant of the metastability exchange optical
pumping. We show that miniaturization helps to increase T2* further and that
the measurement sensitivity is not significantly affected by temporal field
fluctuations of order 10^-4.Comment: 27 pages, 7 figure
Strictly Bandlimited ISI-Free Transmission Over Intensity-Modulated Channels
In this paper, the design and analysis of a new bandwidth-efficient signalling method over the bandlimited intensity-modulated direct-detection (IM/DD) channel is pro- posed. The channel can be modeled as a bandlimited channel with nonnegative input and additive white Gaussian noise. Due to the nonnegativity constraint, the methods previously proposed for conventional bandlimited channels cannot be applied here. We propose a method to transmit without intersymbol interference in a narrower bandwidth compared to previous works, by combining Nyquist pulses with a constant bias. In fact, we can transmit with a bandwidth equal to that of coherent transmission. A trade-off between the required average optical power and the bandwidth is investigated. At low bandwidths, the most power- efficient transmission is obtained by either the parametric linear pulse or the so-called âbetter than Nyquistâ pulse, depending on the exact bandwidth
Bandlimited Intensity Modulation
In this paper, the design and analysis of a new bandwidth-efficient signaling
method over the bandlimited intensity-modulated direct-detection (IM/DD)
channel is presented. The channel can be modeled as a bandlimited channel with
nonnegative input and additive white Gaussian noise (AWGN). Due to the
nonnegativity constraint, standard methods for coherent bandlimited channels
cannot be applied here. Previously established techniques for the IM/DD channel
require bandwidth twice the required bandwidth over the conventional coherent
channel. We propose a method to transmit without intersymbol interference in a
bandwidth no larger than the bit rate. This is done by combining Nyquist or
root-Nyquist pulses with a constant bias and using higher-order modulation
formats. In fact, we can transmit with a bandwidth equal to that of coherent
transmission. A trade-off between the required average optical power and the
bandwidth is investigated. Depending on the bandwidth required, the most
power-efficient transmission is obtained by the parametric linear pulse, the
so-called "better than Nyquist" pulse, or the root-raised cosine pulse.Comment: 28 pages 10 Figure
Improved Nyquist pulse shaping filters for generalized frequency division multiplexing
Generalized Frequency-Division Multiplexing (GFDM) is one of the multicarrier modulation schemes currently under study for next generation 5G cellular networks. One of the main characteristics of GFDM is the low out of band emission that is achieved by means of a flexible time-domain pulse shaping of individual subcarriers. In the paper, we propose to use improved Nyquist pulse shaping filters which have been originally introduced in the context of single-carrier modulation schemes for reducing the sensitivity to symbol timing error due to their higher eye opening and smaller maximum distortion. Here we consider their use in GFDM and evaluate their symbol error rate (SER) performance in case of 16-QAM transmission over an additive white Gaussian noise channel. Moreover, we also considered the concept of the wavelet for better time-frequency localization of the pulse shaping filters by using the Meyer auxiliary function. Numerical results are reported to demonstrate the superior SER performance achieved by the proposed improved Nyquist pulse shaping filters in comparison to that achieved with conventional Nyquist pulse shaping filters
Spark plasma sintered carbon electrodes for electrical double layer capacitor applications
The spark plasma sintering (SPS) is an emerging process for shaping any type of materials (metals, ceramic, polymers and their composites). The advantage of such a process is to prepare densified ceramic materials in a very short time, while keeping the materials internal porosity. In the present work, we have used the SPS technique to prepare activated carbon-based electrodes for Electrochemical Double Layer Capacitor applications (EDLC). Self-supported 600 and 300”m-thick electrodes were prepared and characterized using of Electrochemical Impedance Spectroscopy and galvanostatic cycling in a non-aqueous 1.5MNEt4BF4 in acetonitrile electrolyte. Electrochemical performance of these sintered electrodes were found to be in the same range â or even slightly better â than the conventional tape-casted activated carbon electrodes. Although organic liquid electrolyte was used to characterize the electrochemical performance of the sintered electrodes, these results demonstrate that the SPS technique could be worth of interest in the ultimate goal of designing solid-state supercapacitors
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