László Csurgai-Horváth

Prediction of drop size distribution parameters for optical wireless communications through moderate continental fog

Wireless optical communication links (OCL), or free space optics links involving optical ground stations are highly influenced by the earth atmosphere due to the interaction of the optical wave with particles of different size and shape. Fog, clouds, rain and snow cause significant signal attenuation, thus limiting the performance of OCL. In this paper, we consider the behavior of OCL in the troposphere under moderate continental fog conditions, which are important for both ground–ground and ground–space OCL. The impact of the droplet size distribution (DSD) of fog is investigated, by processing laser attenuation measurements carried out in Milan (Italy) and Graz (Austria). Significant differences are observed between measured and predicted attenuation when using standard values for the DSD parameters. Hence, new sets of DSD parameters are proposed to model peak, mean and median values of measured attenuation for moderate continental fog. These, in turn, can be useful to make accurate link availability predictions, thus improving the quality of service design for OCL. Copyright

Free-Space Optics and E-Band Radio: Complementary Techniques for Gbit/Sec Wireless

Abstract-Free Space Optics (FSO) and E-band links operating in parallel are investigated. In contrast to previous work in this field equal transmission rate of the two is assumed- 1 Gbit/sec in existing systems with a likely increase in the near future. Propagation characteristics are briefly presented. It is shown that practical difficulties preclude microwave backup to FSO links. Equal transmission rate leads to the possible application of parallel MIMO techniques. Outage capacity based on that is determined regarding for both binary and quaternary modulation and both Direct Detection (DD) and heterodyne techniques in the FSO link. The unexpected conclusion is that it is more the FSO link that serves as backup to the E-band link than the converse.

A Survey of the DVB-T Spectrum: Opportunities for Cognitive Mobile Users

Cognitive radio (CR) systems are designed to utilize the available radio spectrum in an efficient and intelligent manner. Terrestrial Digital Video Broadcasting (DVB-T) frequency bands are one of the future candidates for cognitive radio applications especially because after digital television transition the TV white spaces (TVWS) became available for radio communication. This paper deals with the survey of the DVB-T spectrum; wideband measurements were performed on mobile platform in order to study the variation of the radio signal power in city area aboard a moving vehicle. The measurement environment was a densely built-in region where the proper DVB-T receiving was guaranteed by three TV transmitters, utilizing three central channel frequencies using 610, 746, and 770 MHz. In our paper the methods, the applied antenna, and measurement devices will be presented together with simulated and measured fading statistics. The final result is an estimation of the cognitive DVB-T spectrum utilization opportunity; furthermore a scenario is also proposed for secondary channel usage.

Q-band beacon receiver for Alphasat TDP#5 propagation experiment

In this paper we propose a specific beacon receiver structure for the Alphasat TDP#5 Q/Ka band propagation experiment. The main goal of the experiment is to refine the existing propagation models based on the received data from several different geographical locations over Europe, and also to propose new ground station structures for the experimenters community. The specialty of our receiver that it is composed from the key elements of terrestrial point to point microwave radios, tailored to the requirements of the beacon receiver. In our paper the hardware elements, the real-time data processing capabilities and preliminary received time series will be demonstrated.

From Gigabit to Multi-Gigabit: mm Waves in Mobile Networks' Backhaul

In recent years mm-wave point-to-point radios appeared among wireless equipment. The large available bandwidth - in principle up to 10 GHz - the sparse utilization of the frequency band and efficient spatial filtering make them very advantageous for the backhaul of cellular networks. Present day equipment transmit 1 Gbit/sec over paths of several, about 1 to 3 km-s. The aim of this paper is to briefly present features and applications of these equipments and to discuss development possibilities. Concerning the increase of hop length the already used technique of rate adaptation is analyzed and two diversity techniques are presented. About increase of transmission rate up to 10 Gbit/sec it is shown that simply rescaling the methods used in actual systems is virtually non-viable and more sophisticated methods are needed. Two techniques are proposed and investigated. (i) Spatial demultiplexing of channels is presented; conditions of application are shown. (ii) Possibilities offered by adaptive coding are investigated.

Land Mobile Propagation Fade Duration Modelling by Markov Chains

Fade duration is one of the most important dynamic aspects of path attenuation that corresponds to the time length during which a fixed threshold is exceeded by path attenuation. Precise estimation of the fade duration parameter is essential to be taken into account in wireless communication system design for several reasons like calculating the system outage or unavailability period, sharing the system resource during the events, apply fade mitigation techniques, select the right coding scheme etc. In this paper we are presenting a digital model with N-state partitioned Markov chain for the statistical prediction of the fade duration at different attenuation thresholds. The parameter set of the digital model has been derived from the fade duration statistics of a land mobile satellite link measurement at 1.54 GHz. The parameterizations of this model includes beside the fade events also the interfade periods, therefore leads to a more precise fade duration model and provide the possibility of the implementation of joint fade-interfade duration modelling. The threshold dependence of the Markov chains stochastic matrix elements are determined by an empirical equation

Mobile access of the DVB-T channel and the opportunity for cognitive spectrum utilization

The main goal of the Cognitive Radio (CR) systems is the intelligent and efficient utilization of the radio spectrum. In this paper we introduce our survey in wideband spectrum measurement for studying the Terrestrial Digital Video Broadcasting (DVB-T) frequency bands that are one of the future candidates for cognitive radio applications. The actuality of this subject is that during 2013 Hungary changed the analogue terrestrial broadcasting system to DVB-T, partly freeing up several TV bands, thus opening the opportunity for cognitive systems as well. The regulation of the usage this new band (TV white space, TVWS) is in our country is under development so it is an actual issue. In our paper the methods, the applied antenna and measurement devices will be presented together with fading statistics and predictions about the possibilities of the cognitive spectrum utilization.

FSO-MIMO behavior in variable atmospheric turbulence — An Asymptotic Approach

One of the effects of scintillation caused by atmospheric turbulence is the dependence of spatial correlation on the strength of turbulence itself. This has the effect that the apertures of a multielement array while fully uncorrelated in the case of deep fading become correlated as scintillation becomes milder. In such cases the diversity effect of the MIMO array may disappear. This phenomenon is investigated, maybe the first time. Based on correlation an effective number of apertures is defined. Outage probability vs. turbulence strength (this characterized by Fried parameter) is determined and formulas for average received SNR vs. turbulence strength are given. It is shown that in arrays of large number of apertures probability of outage is highest in the case of shallowest and not of deepest fading.

Attenuation Time Series Synthesis for Land Mobile Satellite Links

This contribution provides a method to synthesize attenuation time series for land mobile satellite links. The time series generator is based on an attenuation threshold dependent fade duration model of the land mobile satellite channel [1, 7]. The fade duration is modeled with partitioned Fritchmans Markov-chain and parameterized on a land mobile satellite measurement performed on the board of a moving vehicle, thus the fading events can be observed in the measurement data are due the multipath propagation. To achieve attenuation time series from the fade duration process the synthesized time series are generated in two steps. At first a two-state Markov model applied to generate the long term behavior of the channel and it models the fading/non fading states. The second step is to simulate the fine structure of the single fading events for the fading periods calculated previously with the two-state fade/non-fade Markov chain. The attenuation threshold dependent Fritchmans model of the fade duration is applicable for the parameterization of the two-state fade/non-fade model and also for the generation of single fading events with any desired duration and fade depth. The combination of the long-term and the short-term synthesized events can be applied to generate time series for long term

Architectural Design of the Q/V Band Site Diversity Experiment Between Austria and Hungary

The architectural design of the Q/V band site diversity experiment between the transmit/receive ground station in Graz/Austria and the receive only ground station in Budapest is described in this paper. The ground station Budapest is connected via Internet to transfer information about the reception quality of the received signals and to request to adjust the modulation and coding. The uplink power is controlled by the station in Graz, based on the local received beacon signal from the satellite. The planed experiments and the expected results are described in the final paragraph of this paper.