2011/2

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Effects of Imperfect Reference Signal Recovery on Performance of SC and SSC Receivers over Generalized Fading Channels
(Společnost pro radioelektronické inženýrství, 2011-06) Nikolic, Bojana; Djordjevic, Goran; Milosevic, Nenad
This paper presents the study of the effects of imperfect reference signal recovery on the bit error rate (BER) performance of dual-branch switch-and-stay combining (SSC) and multibranch selection combining (SC) receivers in a generalized - fading channel. The average BER of binary and quaternary phase shift keying (BPSK and QPSK) is derived under the assumption that the reference carrier signal is extracted from the received modulated signal. For SSC receiver the optimal switching threshold (in a minimum BER sense) is numerically evaluated. Hereby we determine and discuss the simultaneous influence of the average signal-to-noise ratio (SNR) per bit, fading severity, product phase-locked loop (PLL) bandwidthbit duration (B_LT_b), switching threshold of SSC and diversity order of SC on BER performance. The influence of B_LT_b in different channel conditions and modulation formats is pointed out. The numerical results are confirmed by computer simulations.
Edge Detection with Sub-pixel Accuracy Based on Approximation of Edge with Erf Function
(Společnost pro radioelektronické inženýrství, 2011-06) Hagara, Miroslav; Kulla, Peter
Edge detection is an often used procedure in digital image processing. For some practical applications is desirable to detect edges with sub-pixel accuracy. In this paper we present edge detection method for 1-D images based on approximation of real image function with Erf function. This method is verified by simulations and experiments for various numbers of samples of simulated and real images. Results of simulations and experiments are also used to compare proposed edge detection scheme with two often used moment-based edge detectors with sub-pixel precision.
Attenuation in Rectangular Waveguides with Finite Conductivity Walls
(Společnost pro radioelektronické inženýrství, 2011-06) Yeap, Kim Ho; Tham, Choy Yoong; Yassin, Ghassan; Yeong, Kee Choon
We present a fundamental and accurate approach to compute the attenuation of electromagnetic waves propagating in rectangular waveguides with finite conductivity walls. The wavenumbers kx and ky in the x and y directions respectively, are obtained as roots of a set of transcendental equations derived by matching the tangential component of the electric field (E) and the magnetic field (H) at the surface of the waveguide walls. The electrical properties of the wall material are determined by the complex permittivity ε, permeability μ, and conductivity σ. We have examined the validity of our model by carrying out measurements on the loss arising from the fundamental TE10 mode near the cutoff frequency. We also found good agreement between our results and those obtained by others including Papadopoulos’ perturbation method across a wide range of frequencies, in particular in the vicinity of cutoff. In the presence of degenerate modes however, our method gives higher losses, which we attribute to the coupling between modes as a result of dispersion.
Design, Fabrication and Properties of Rib Poly(methylmethacrylimide) Optical Waveguides
(Společnost pro radioelektronické inženýrství, 2011-06) Prajzler, Vaclav; Klapuch, Jan; Lyutakov, Oleksiy; Huettel, Ivan; Spirkova, Jarmila; Nekvindova, Pavla; Jerabek, Vitezslav
We report about design, fabrication and properties of the polymer optical waveguides deposited on silica-on-silicon substrate. The design of the waveguides is based on a concept that geometric dimensions of the single mode polymer waveguide are determined by geometrical parameters of the silica layer. The design of the waveguides was schemed for 650 nm, 850 nm, 1310 nm and 1550 nm wavelength. The design of the presented planar waveguides was realized on the bases of modified dispersion equation while the ridge waveguides design was proposed following the Fischbeck concept. Both designs were refined applying RSoft software using beam propagation method. Proposed shapes of the waveguides were etched by standard photolithography process into the silica layers and polymer waveguide layers were subsequently deposited into the treated substrate by spin coating. Poly(methylmethacrylimide) was used as the waveguide core material and polymethylmethacrylate was used as a cover protection layer. Propagation optical loss measurements were done by using the cut-back method and the best samples had optical losses lower than 0.6 dB/cm at 650 nm, 1310 nm and 1550 nm.
Estimation of Outage Capacity for Free Space Optical Links Over I-K and K Turbulent Channels
(Společnost pro radioelektronické inženýrství, 2011-06) Nistazakis, Hector E.; Tsigopoulos, Andreas D.; Hanias, Michalis P.; Psychogios, Christos. D.; Marinos, Dimitris; Aidinis, Costas; Tombras, George S.
The free space optical communication systems are attracting great research and commercial interest due to their capability of transferring data, over short distances, with high rate and security, low cost demands and without licensing fees. However, their performance depends strongly on the atmospheric conditions in the link’s area. In this work, we investigate the influence of the turbulence on the outage capacity of such a system for weak to strong turbulence channels modeled by the I-K and the K-distribution and we derive closed-form expressions for its estimation. Finally, using these expressions we present numerical results for various link cases with different turbulence conditions.

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