Propagation of an ultrashort radio pulse in a resonance-absorbing atmosphere

The problem on propagation of an ultrashort radio pulse is analytically solved. The pulse has an envelope of a general shape and a carrier frequency lying within or near the frequency interval of an isolated spectral line of a resonance-absorbing component of a gaseous medium. The solution is used to analyze the character of dispersion distortions of a biexponential quasi-monochromatic pulse and a biexponential chirp pulse that propagate along near-surface and elevated atmospheric paths. The analysis is performed for a single strong line of water vapor in the millimeter wavelength band with a resonance frequency of 183.36 GHz. It is found that the most pronounced feature of distortions of the quasi-monochromatic pulse is gradual transformation of its one-peak envelope into a set of field maxima of various heights. The number of maxima is determined by the optical depth of a path, and, in all of the considered cases, the precursor of a propagating pulse is not formed.     

Propagation of a radio pulse in isotropic plasma

The problem of propagation of a radio pulse in isotropic collisional cold plasma is solved. The solution analytically describes the spatiotemporal evolution of the characteristics of a radio pulse with an envelope of a rather general form. Explicit expressions are obtained for the velocity of radio-pulse propagation in isotropic plasma.     

Propagation of a chirp radio pulse in isotropic plasma

The problem of space-time deformation of a chirp radio pulse propagating in cold isotropic collisional plasma is solved analytically. Pulses with rectangular and biexponential initial envelopes are considered as examples to show that, as the covered distance grows, a chirp pulse is at first compressed and then broadened and, simultaneously, the linear increase of the instantaneous frequency observed within the pulse duration changes into an approximately linear decrease. The distance at which a chirp pulse is compressed to the minimum possible duration is estimated, and the effect of absorption on the current shape of the pulse envelope is analyzed.     

Propagation of ultrawideband chaotic radio pulses through the slits of metal surfaces

The leakage of ultrawideband (UWB) chaotic radio pulses through the defects (holes, slits, cracks, etc.) of metal surfaces-an urgent problem arising from their application as information carriers in wireless sensor networks-is investigated. Experiments with UWB chaotic radio pulses leaking from the slits of metal surfaces are described, and the experimental results are analyzed. The signal attenuation has been estimated when chaotic radio signals propagate through slits of different size.     

Propagation along a two-wire line located at the air-Earthinterface

A simple quasi-static expression for the propagation constant of a two-wire transmission line located at the air-Earth interface is derived. A numerical solution of the mode equation shows that the quasi-static approximation is valid when the wire separation is much less than a free-space wavelength. The quasi-static approximation can be used to determine the complex dielectric constant of the Earth from measurements of either the propagation constant or the characteristic impedance of the transmission line     

跳时超宽带无线电的性能分析

超宽带脉冲无线电是无线通信领域的一种全新技术,有着广阔的应用前景.它是一种基带无载波短脉冲,不同于使用正弦载波的传统通信系统.本文用满足FCC频谱规划的脉冲--高斯脉冲的五阶导数推导了TH-BPSK方式下的跳时超宽带扩频系统的误码与多址性能,并研究了多径对其性能的影响,比较了TH-BPSK 与TH-PPM系统性能,分析结果表明TH-BPSK的性能(未考虑多径)明显优于TH-PPM,但是TH-PPM抗多径性能优于TH-BPSK.     

Compensation of a narrowband interference in an ultrawideband communication system based on chaotic radio pulses

The influence of narrowband signals on incoherent reception of ultrawideband chaotic radio pulses in direct chaotic communication (DCC) system is considered. A method for compensating the influence of narrowband signals on the characteristics of this system after incoherent reception of chaotic radio pulses is proposed. The proposed solution enables one to compensate a narrowband signal, preserving the possibility to determine chaotic radio pulses at corresponding time positions. The dependence of the probability of an error per bit on the spreading ratio of chaotic radio pulses is established.     

Propagation of radio waves past a coast line with a gradual change of surface impedance

The amplitude and phase of a radio ground wave are calculated for an oblique crossing of a flat-lying coast line. The surface impedance is allowed to change in a continuous and gradual manner in the vicinity of the coast line. The earlier results for an abrupt boundary are recovered as the width of the transition zone is reduced to zero. In general, it is found that the presence of the transition region will not produce a significant modification of the transmitted field. On the other hand, the reflected waves and the behavior of the field near the coast line are profoundly influenced by the width of the transition. In particular, certain singular behavior of the field associated with an abrupt boundary is virtually eliminated when the transition zone has a finite width.     

The fundamental electromagnetic wave of a single-wire line in a weakly absorbing medium

An approximate dispersion equation valid over a wide frequency range is obtained from the dispersion equation for the symmetric E ₀₀ wave (the Sommerfeld wave) propagating along a finite-conductance metal wire embedded in a lossy dielectric. The boundaries of this frequency range are determined. A technique is developed for solution of the obtained approximate dispersion equation in the frequency band where the pronounced skin effect is observed. The ratio of the wire radius to the thickness of the skin layer is assumed to be no less than 10. This technique is applied to calculate the longitudinal and transverse propagation constants for 1.0-and 2.5-mm-radii copper wires over the frequency range 0.5 MHz to 1000 GHz.     

The propagation time of a radio pulse

The propagation of the ground-wave pulse between points on the ground is of considerable practical importance, particularly in the application of the Loran-C navigation system to the absolute time synchronization of geographically separated clocks. Thus, the envelope of the pulse is frequently used to remove ambiguities which would otherwise result from the pulse synchronization at the characteristic or carrier frequency of the pulse. The propagation of the ground wave over finitely conducting ground modifies the propagation time of the tagged point-in-time on the envelope by amounts which may be sufficiently large as to cause cycle ambiguitypm piradians at the carrier or characteristic frequency of the pulse. It is therefore the purpose of this paper to investigate the magnitude of this error by ascertaining the true signal velocity as determined by tagging a point-in-time on the leading edge of a groundwave pulse and calculating the time corrections for various ground conductivities and distances. These calculations can then be applied to resolve thepm piradians ambiguity of the precision phase velocity instrumentation for Loran-C especially when the system is used for absolute-time synchronization.     

Calculation of the field distribution of an ultrawideband short electromagnetic pulse in the radiating aperture of an open-ended irregular waveguide

A new approach to the numerical calculation of the field of ultrawideband electromagnetic pulses in the radiating aperture of a horn antenna is studied. The approach is based on application of the concept of virtual electromagnetic waveguide and the method of nonstationary waveguide equations. It is shown that the proposed approach enables the control of the error in the obtained results and ensures a high accuracy of these results.     

Propagation of pulse trains through a random medium

Applying the parabolic approximation, the equations for two-frequency symmetric and antisymmetric mutual intensity functions for waves propagating through a random medium are derived, including the multiple scattering effects. These functions are applied to derive the general formulas for the covariance functions of narrowband pulses. They are used to compute the signal intensities for pulse trains passing through an ionospheric irregularity slab.     

Microwave pulse compression utilising an yttrium-iron-garnet delay line

Experiments on the compression of linear frequency-modulated S band pulses in an axially magnetised yttrium-iron-garnet rod are reported. The specimen was operated at room temperature in the magnetoelastic one-port delay mode. Time compression by a factor of 72 has been achieved with a 1 ?s input pulse frequency-modulated by 125 Mc/s.     

Dispersion distortions of a two-frequency radio pulse in cold plasma

Dispersion distortions of a two-frequency radio pulse in cold isotropic plasma are analyzed in meter- and decameter-wavelength ranges. It is demonstrated that the pulse envelope tends to the limiting two-peak shape that reproduces the shape of the energy spectrum of the emitted pulse when the total electron content (TEC) along the path increases. In this case, TEC can be determined using characteristics of the envelope. Effect of the parameters of emitted pulse on its deformation in the course of propagation is described.     

Numerical characterization and modeling of subject-specific ultrawideband body-centric radio channels and systems for healthcare applications

The paper presents a subject-specific radio propagation study and system modeling in wireless body area networks using a simulation tool based on the parallel finite-difference time-domain technique. This technique is well suited to model the radio propagation around complex, inhomogeneous objects such as the human body. The impact of different digital phantoms in on-body radio channel and system performance was studied. Simulations were performed at the frequency of 3-10 GHz considering a typical hospital environment, and were validated by on-site measurements with reasonably good agreement. The analysis demonstrated that the characteristics of the on-body radio channel and system performance are subject-specific and are associated with human genders, height, and body mass index. Maximum variations of almost 18.51% are observed in path loss exponent due to change of subject, which gives variations of above 50% in system bit error rate performance. Therefore, careful consideration of subject-specific parameters are necessary for achieving energy efficient and reliable radio links and system performance for body-centric wireless network.     

Performance evaluation of non‐Gaussian channel estimation techniques on ultrawideband impulse radio channels

We study the problem of adaptive channel estimation for a multipath channel on an ultrawideband (UWB) impulse radio (IR) system. The purpose of the work is to demonstrate that the statistical characteristics of the UWB‐IR environment are strongly non‐Gaussian and that as a result, non‐Gaussian signal processing techniques are both efficient and powerful in a UWB‐IR environment. The multipath channel estimation problem has been chosen as an illustrative example because UWB‐IR systems often operate in complex multipath environments. We study both blind and training‐based estimation techniques and demonstrate that even simple non‐Gaussian strategies can achieve significant performance improvement when compared to more common second‐order estimation techniques. Copyright © 2006 John Wiley & Sons, Ltd.     

Noise immunity of the wireless communications scheme based on ultrawideband chaotic radio pulses in multipath channels

The problem of determining the noise immunity of wireless data transmission based on ultrawide-band (UWB) chaotic radio pulses in the multipath channel with white noise is substantiated. The results have been calculated via numerical simulation using the multipath channel models describing UWB signal propagation in rooms of different classes at distances as long as several tens of meters. The direct chaotic communications method is shown to have the noise immunity high enough to employ this scheme in practical wireless applications where information is transmitted under severe conditions of multipath propagation. In this case, the ultimate data transfer rates are found to 25 Mb/s.     

Propagation of double-exponential pulse through Debye medium

The saddle point method is applied to the problem of signal propagation through Debye medium. The steepest descent method is used to calculate the propagation of a double-exponential pulse through Debye medium, and the results are compared with those obtained through Hosono's (1980) method and finite-difference time-domain (FDTD) method. It is found that a Gaussian function can be used to approximate the propagated signal for sufficiently long propagation distance and the analytical representations for the amplitude, center, and width of the propagated pulse are obtained based on the first-order asymptotic representation. An analytical approximation of the saddle points valid for late time is also obtained