ISSN 1210-2512 (Print)

ISSN 1805-9600 (Online)



Proceedings of Czech and Slovak Technical Universities

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Feature articles

ZVÁNOVEC, S., CHVOJKA, P., HAIGH, P. A., GHASSEMLOOY, Z. Visible light communications towards 5G

5G networks should offer an extremely high capacity in the same coverage area. Most promising approaches to achieve this would be to embed large numbers of small cells into the macro-cell coverage area. In such scenarios it is being proposed to adopt optical wireless as an alternative physical layer offering high data rate, mobility and low implementation cost – recent experiments demonstrated up to 1 Tbit/s for optical wireless backhaul links at 1550 nm and up to 5 Gbit/s in access links using visible light communications (VLC). VLC is an emerging technology for future high capacity communication links (it has been accepted to 5GPP) using the visible range of the electromagnetic spectrum (~370 – 780 nm) utilizing white light-emitting diodes (LEDs) to simultaneously provide data transmission and room illumination. Additional VLC can also be used for indoor localization in indoor environment where the existing GPS systems offer very limited if at all services. A major challenge in VLC is the LED modulation bandwidths, which are limited to a few MHz. However, gigabit speed transmission links have already been demonstrated by using high order modulation and equalization schemes. Optical wireless can works with non-line of sight path, is resistant to background noise and adapts the throughput according to the current channel condition. Concurrently, organic LEDs (OLEDs) have been the focus of enormous attention for solid-state lighting applications due to their advantages over conventional LEDs such as ultra-low costs, mechanical flexibility and large photoactive areas. The paper will discuss development of such VLC links to in order to implement broadcasting networks featuring advanced modulation formats such as orthogonal frequency division multiplexing (OFDM) or carrier-less amplitude and phase modulation (CAP) and advanced equalization techniques. The paper will also summarize reached results of joint teams within European project ICT COST IC1101 OPTICWISE (Optical Wireless Communications – An Emerging Technology) dealing VLC and OLED towards 5G networks.

DIMITRIJEVIĆ, B., NIKOLIĆ, B., ALEKSIĆ, S., RAIČEVIĆ, N. Optimization of excitation in FDTD and corresponding source modeling

Source and excitation modeling in FDTD formulation have a significant impact on method performance and required simulation time. Since the instant source introduction yields intensive numerical variations in whole computational domain, a generally accepted solution is to slowly introduce the source, using appropriate shaping functions in time. The main goal of the optimization presented in this paper is to find balance between two opposite demands: minimal required computation time and acceptable degradation of simulation performance. Reducing the time necessary for source activation and deactivation is an important issue, especially in design of microwave structures, when the simulation is intensively repeated in the process of device parameter optimization. Here proposed optimized source models are realized and tested within an own developed FDTD simulation environment.

SILVA, A. Transmission cooperative strategies for MIMO heterogeneous networks

Mobile traffic in cellular networks is increasing exponentially, mainly due to the use of data intensive services like video. One way to cope with these demands is to reduce the cell-size by deploying small-cells along the coverage area of the current macro-cell system. The deployment of small-cells significantly improves indoor coverage. Nevertheless, as additional spectrum licenses are difficult and expensive to acquire it is expected that the macro and small-cells will coexist under the same spectrum. The coexistence of the two systems results in cross-tier interference. In this context, we design several interference alignment based techniques for the downlink of heterogeneous networks, in order to cancel the interference generated from macrocell at small-cell user terminals. More specifically, in this contribution we design interference alignment methods jointly with space-frequency block codes, under different levels of inter-system coordination, and the constraint that the performance of macrocell system is kept close to the case where small-cell system is switched-off. Preliminary numerical results have demonstrated that the proposed methods achieve close to the optimal performance with low overhead.

BIOLEK, D. Some fingerprints of memristive systems

The paper analyzes several fingerprints of the general memristive systems under their periodical excitation. Special attention is given to the behavior of ideal memristors, ideal generic memristors, generic memristors, and other memristive systems which do not fall into the above categories. This approach can be useful for identifying of the type of the system from the signals coming from the experiments with concrete memristive devices.

BOZZI, M., PIERANTONI, L., BELLUCCI, S., Applications of graphene at microwave frequencies

The interest for nanotechnologies has experienced an impressive growth in the last few years. Among the variety of nanostructures, graphene attracts particular attention due to its extraordinary mechanical, electronic and optical properties. Among the novel 2D-materials, graphene exhibits outstanding properties, such as a carrier mobility attaining 200 000 cm2/Vs at room temperature, the question has been posed whether graphene may be exploited for microwave applications in the GHz range. The unique properties of graphene are being exploited in radio-frequency nanoelectronics to realize novel high-speed devices such as field effect transistors, frequency multipliers, transparent solar cells, meta-materials, and graphene plasmonics. Recently, the use of graphene for the implementation of tunable microwave components and antennas has also been proposed. This paper will review the properties of graphene at microwave frequency, it will describe the possible fabrication techniques, and it will present and discuss the most important applications of graphene for the implementation of active and passive microwave components and antennas.

DOBEŠ, J., MÍCHAL, J., POPP, J., GRÁBNER, M., VEJRAŽKA, F. Precise characterization and multiobjective optimization of low-noise amplifiers

Although the contemporary tools for computer-aided design contain various procedures for a noise calculation, their overall ability for a noise optimization is still limited. In the paper, an improved way of computing the noise figure is suggested. Moreover, a novel method for a calculation of noise-figure sensitivities using the sensitivity analysis of noise spectral densities is described. The sensitivities represent a valuable design tool themselves; however, a very important utilization of the noise-figure sensitivities also consists in the derivative-based mono- and multiobjective optimization algorithms. In the paper, an improved procedure for the multiobjective optimization of low-noise amplifiers under several natural constraints is suggested. For accurate characterization of the amplifier, a new method for defining inductors, capacitors, transmission lines, and T-splitters has been suggested, which enables their overall frequency-dispersive description (including Q, ESR, etc.) and precise noise models too. Moreover, a more accurate pHEMT model is also defined (including improved noise pHEMT model), and a reliable way for its characterization is suggested. As a practical utilization of the proposed algorithms, a complete design of an antenna preamplifier for a common GPS/Galileo/GLO­NASS/Compass receiver based on a multiobjective optimization is demonstrated, and a comparison with measured data is described.

HENNIGER, H.; DIEDRICH, E.: Analysis and comparison of new downlink technologies for Earth observation satellites

New generation of earth observation sensors are creating an increasing amount of data which has to be delivered to processing centers. Additionally, many applications require timely availability of this sensor data on ground.

As new link technologies have been made available in the last years and data-rate requirements are still increasing a revise of the traditional direct-downlink technology at X-band frequencies is essential. This work aims in a trade-off of the available technologies.

Generally, there are two approaches to fulfill the requirement of timely delivery of a huge amount of data from space to ground. This is either increasing space-to-ground contact time resulting in a more complex system or increasing carrier frequency whereas link reliability is limited by atmospheric effects.

In this work different approaches like using Ka-band or even optical frequencies or utilizing ground station network with additional locations, as well as GEO-relay concepts are compared against each other whereas physical aspects as well as economic aspects are taken into account. Also possible combinations of different technologies as well as overall system complexity are considered in the analysis.

VRBA, J. Jr. A microwave MTM based sensor for non-invasive blood glucose monitoring

Previous studies have shown that geometries of microwave metamaterial based sensors using zeroth-order mode resonance are easily scalable in order to fit desired sensed area and their dimensions are almost independent on the working frequency. Furthermore, electromagnetic fields irradiated by these sensors have shown in the plane under their aperture very homogeneous irradiated pattern and decays almost as a field of plane EM wave. In this paper, a geometry of such metamaterial based sensor adapted for non-invasive blood glucose monitoring was proposed and tested numerically on two different phantoms representing an earlobe and wrist. The later phantom is based on human anatomical model from Virtual Family, IT’IS Foundation. The phantoms’ dielectric properties are modeled as dependent on glucose concentrations. The sensors’ geometry was optimized in terms of sensitivity on glucose concentration. The final sensor was subsequently manufactured and tested on samples of pig blood-glucose solutions with different glucose concentrations. Furthermore, continuous non-invasive tests were performed on volunteers and the results are discussed.