Search results for "Baseband"
showing 10 items of 10 documents
Narrowband digital filtering with random frequency hopping spread spectrum
2014
International audience; In digital signal filtering, channels with narrow bandwidth need high order digital filter to be selected without introducing modulation errors. If a carrier randomly switches from a channel to another as in military applications, or some civilian communication standards, it is necessary to detect and estimate these jumps before transposing and analyzing signals in the baseband. This paper presents a real time solution to filter narrow band signals with random frequency hopping spread spectrum. The proposed method is based on three steps. Firstly, the detection of Signal Frequency Hopping (SFH) using the Fast Fourier Transform (FFT), an algorithm to estimate the Domi…
Baseband predistorter using direct spline computation
2005
A baseband predistorter is presented. Key features of the predistorter reside in the use of cubic spline interpolation to generate predistorted input data to the power amplifier, without time convergence problems of classical approaches, with the goal of a reduction in the computational effort. Simulated behaviour of the proposed scheme is presented, demonstrating the effectiveness of the approach.
Wireless OFDM-OQAM with a small number of subcarriers
2008
Orthogonal frequency division multiplexing based on offset quadrature amplitude modulation (OFDM-OQAM) is a multicarrier signaling technique which trades off robustness for spectral efficiency when compared to conventional OFDM with a cyclic prefix. In this paper, a novel matrix model for passband OFDM-OQAM signaling with a small number of subcarriers over a multipath frequency selective fading channel is presented. Specifically, in OFDM-OQAM a frequency selective channel is divided into many smaller but still frequency selective overlapping channels, so approximating the frequency response of a subchannel by the channel frequency response sampled at the subcarrier frequency may be inadequa…
Optimum pulse shape for minimum spectral occupancy in FSK signals
1984
The characteristics of a frequency shift keying (FSK) signal giving rise to maximum power within a prescribed frequency band are determined. The baseband pulse shape extends over any integer number of bit periods. An integral equation for the optimum pulse shape is derived and some simple properties of the solution are investigated. The equation has been solved for some values of the product of the prescribed band times the pulse duration and the signal shape is shown. Our results for the particular case of pulses only one bit period long are presented for purpose of comparison with results known in the literature. Plots of out-of-band power for some values of the prescribed band and of pul…
Flat-top ultra-wideband photonic filters based on mutual coherence function synthesis
2008
A novel all-incoherent optical circuit that allows for band-pass microwave-photonic filter design is presented and verified through numerical simulation. In contrast to conventional spectrum-sliced optical architectures that operate on the basis of a finite number of discrete taps, our proposal is based on arbitrary shaping of the spectrum of the broadband optical source in a conventional frequency encoder. This fact dramatically increases the free spectral range of the filter with respect to the conventional discrete-time optical processing. The filter transfer function is given by the mutual coherence function of the filtered source which allows, through an inverse problem, sculpting the …
All-fiber incoherent frequency-to-time mapping method for microwave signal generation with baseband transmission and multicasting support
2008
We present a proof-of-principle experiment for achieving simultaneous distribution of baseband radio-frequency data and up-conversion with broadcasting support over a passive optical network. The technique is based on an incoherent frequency-to-time mapping method for pulse shaping. Specifically, we synthesize the spectral density function of sliced ASE noise from an EDFA with a periodic Mach-Zehnder fiber interferometer optical filter. By using external intensity modulation combined with propagation in an optical fiber, after photodetection, the resultant averaged temporal pulse profile resembles the shape of the incoherent source. The photodetected signal contains both the baseband data a…
Apparent remote synchronization of amplitudes: A demodulation and interference effect
2018
A form of "remote synchronization" was recently described, wherein amplitude fluctuations across a ring of non-identical, non-linear electronic oscillators become entrained into spatially-structured patterns. According to linear models and mutual information, synchronization and causality dip at a certain distance, then recover before eventually fading. Here, the underlying mechanism is finally elucidated through novel experiments and simulations. The system non-linearity is found to have a dual role: it supports chaotic dynamics, and it enables the energy exchange between the lower and higher sidebands of a predominant frequency. This frequency acts as carrier signal in an arrangement rese…
Baseband modulation instability as the origin of rogue waves
2015
International audience; We study the existence and properties of rogue-wave solutions in different nonlinear wave evolution models that are commonly used in optics and hydrodynamics. In particular, we consider the Fokas-Lenells equation, the defocusing vector nonlinear Schrödinger equation, and the long-wave-shortwave resonance equation. We show that rogue-wave solutions in all of these models exist in the subset of parameters where modulation instability is present if and only if the unstable sideband spectrum also contains cw or zero-frequency perturbations as a limiting case (baseband instability). We numerically confirm that rogue waves may only be excited from a weakly perturbed cw whe…
Characterization of Radio Frequency Echo using frequency sweeping and power analysis
2014
International audience; Coupling between repeater's antennas, called Radio Frequency Echo (RFE) deteriorates signal quality and compromises system stability. If the channel insulation is insufficient, the power in the closed-loop raises with time according to the gain margin value. Multiple methods of echo cancellation exists. Generally, these techniques are based on correlation calculation and adaptive filtering. However, their efficiency and algorithm's convergence speed are calling into question under signal's modulation and real-time constraints, specially with narrow band signals having frequency hopping as GSM or TETRA. This paper describes a real time method of RFE detection and esti…
On the Fidelity of IEEE 802.11 commercial cards
2006
The IEEE 802.11 D CF protocol is known to be fair in terms of long-term resource repartition among the contending stations. However, when considering real scenarios, where commercial 802.11 cards interact, very unpredictable as well as sometimes surprising behaviors emerge. Motivation of this paper is to investigate the reasons of the very evident disagreement between the theoretical IEEE 802.11 DCF protocol models and its practical implementations. Inparticular, we try to characterize the card behavior not only in terms of perceived throughput, but also in terms of low-level channel access operations. In fact, the simple throughput analysis does not allow to identify what affecting paramet…