István Frigyes

All-optical tunable filters built with discontinuity-assisted ring resonators

Numerically simulated performance is presented in a new type of bandstop and bandpass filters, built with discontinuity-assisted ring resonator (DARR)-loaded couplers. The operating characteristic of the bandpass filter is similar to that of a long grating with a centered cavity or a photonic crystal with a defect. The filters are tuned by varying the refractive index or the length of the waveguide forming the ring or the cavity. Selectivity and tuning range are controlled by the coupling coefficient of the couplers, by the order of resonance in the rings, and by the reflection coefficient of the discontinuities. A design procedure and the effect of loss are also presented.

Investigations in satellite MIMO channel modeling: accent on polarization

Due to the much different environment in satellite and terrestrial links, possibilities in and design of MIMO systems are rather different as well. After pointing out these differences and problems arising from them, two MIMO designs are shown rather well adapted to satellite link characteristics. Cooperative diversity seems to be applicable; its concept is briefly presented without a detailed discussion, leaving solving particular satellite problems to later work. On the other hand, a detailed discussion of polarization time-coded diversity (PTC) is given. A physical-statistical model for dual-polarized satellite links is presented together with measuring results validating the model. The concept of 3D polarization is presented as well as briefly describing compact 3D-polarized antennas known from the literature and applicable in satellite links. A synthetic satellite-to-indoor link is constructed and its electromagnetic behavior is simulated via the FDTD (finite-difference time-domain) method. Previous result of the authors states that in 3D-PTC situations, MIMO capacity can be about two times higher than SIMO (single-input multiple-output) capacity while a diversity gain of nearly is further verified via extensive FDTD computer simulation.

Effects of the nonlinearity of a Mach-Zehnder modulator on OFDM radio-over-fiber transmission

Radio-over-Fiber (RoF) techniques enable transmission of microwave and millimeter-wave signals for long distances with small loss. Due to the limited signal handling capabilities of electrical/optical components, proper leveling is necessary in order to achieve the highest dynamic range while maintaining distortion at acceptable level. This paper investigates the nonlinear distortion of Orthogonal Frequency-Division Multiplex (OFDM) signals caused by a Radio-over-Fiber stage in the transmission chain if a Mach-Zehnder electro-optical modulator is employed.

A Detailed Experimental Study of the LEO Satellite to Indoor Channel Characteristics

General investigations and results from ratherextensive measurement campaigns are presented tocharacterize the propagation channel of SatellitePersonal Communication Systems; in the measurements the satellite was simulated by a helicopter andmeasurements at S band and L band were made. A newconceptual partitioning of the full link is introduced;the measrement equipment and the environment aredescribed. The major part of the paper deals withpresentation of the measurement results and theiranalyses. Measured and analyzed are average lossincluding satellite elevation and azimuth positiondependence, first-order statistics, Doppler characteristics, andwide-band characteristics. Finally, some rather generalconclusions are drawn.

Realization of true-time delay lines based on acoustooptics

A true-time optical delay line for short radiofrequency (RF) pulses using path length dispersion is proposed. It is an optical implementation of the linear phase-shift theorem of the Fourier transformation. Acoustooptic signal processing is used for conversion into the optical frequency domain and for spatial Fourier decomposition of the pulse. The processing of the pulse is obtained by differentially phase shifting the particular frequency components, followed by a heterodyne reconversion into the RF domain. The optical system is intended to be used for delaying, but also for shaping and filtering of RF pulses, mainly in phased array radar antennas. Theoretical analysis of the system principle is given together with experimental results, demonstrating 2-/spl mu/s time delay of 0.5-/spl mu/s-long pulses with maximum optical phase shift of 1.2/spl pi/. A detailed theoretical and experimental bandwidth analysis is carried out, pointing to the main technical problems and their solutions.

The WSSUS channel model: comments and a generalisation

The paper outlines the wide sense stationary uncorrelated scattering (WSSUS) channel model to emphasise some problems of its theory and a generalisation is given. In the generalised description the difficulties are avoided and clear definitions can be given for the describing functions. As an example, the satellite-to-ground channel is examined in the case when shadowing and reflecting objects have an influence on wave propagation, that is typical in satellite to indoor and satellite to mobile channels. The differences between terrestrial and satellite mobile media are pointed out.

SAT02-6: Application of the 3D Polarization Concept in Satellite MIMO Systems

In contrast to a plane-wave situation electromagnetic wave polarization is a 3-dimensional phenomenon in multipath scatter environments. Recently there is much research work done in order to utilize this fact in MIMO antennas. E.g. it is shown that with appropriate antenna arrangement increase in capacity can be as much as 4-fold or so in terrestrial rich scattering environments. In this paper satellite systems are investigated from this point of view. It is shown that it is hard to achieve an increase of capacity. However, diversity gain (or order of diversity) can be increased and in principle diversity gain of 6 or more is possible while this gain is at most 4 in the 2D (i.e. plane wave) case.

Soliton propagation of microwave modulated signal through single-mode optical fiber

Sinusoidally modulated optical signal transmission is experimentally investigated over a 30 km standard single-mode fiber using a range of optical input powers. Experiments and computer simulations showed that fiber-induced self-phase modulation generates a chirp on the signal with an effect opposite to that induced by chromatic dispersion. Calculations were performed to investigate the distortions caused by simultaneous dispersion and non-linearity using a range of fiber parameters. Soliton propagation of the microwave/millimeter wave modulated signal is reported at elevated intensities in lossless and loss compensated cases.

Application of the MIMO Concept in Millimeter-Wave Broadband Wireless Access Networks

In the usual application of Multiple-Input, Multiple-Output (MIMO) and space–time coding (STC) the basis of the operation is a rich-scattering fading channel and a high density of links. In this paper a different situation: cellular millimeter-wave systems are investigated. It is shown that the MIMO concept can also have advantages in this case. Rain-induced fading characteristics and the concept of route diversity are briefly introduced. A route diversity system can be regarded as a parallel MIMO channel. Basic characteristics of these channels including capacity for various cases are investigated. Optimal codes are determined for space-time convolutional coding. Conceptual design of a route-time coding (RTC) system is shown. Simulation results on coding gain, based on empirical rain attenuation data are given.

Satellite Channel Impairments

A good understanding of the impairments introduced by the propagation channel is of paramount importance in the design of a satellite-based communications system.