Pirmin Pezzei

Analytical expression of FSO link misalignments considering Gaussian beam

In the paper, an optical wireless link for point-to-point communication is analyzed. Its main focus is the analysis of the influence of various misalignments on the received power. Analysis includes influence of the tilt of the transmitter and the receiver as well as their mutual misalignment respecting the Gaussian intensity distribution of the transmitted beam in terms of geometrical optics. As a result of the analysis, expression for influence of the various misalignments on the received power are presented. For the simulation of the link, a MATLAB environment was used. The conclusion contains synthesis of the simulations results. The main contribution is in consideration of the Gaussian beam distribution of the transmitted beam and its analysis for precise prediction of geometrical losses for individual free-space optical links.

Link budget for high-speed short-distance wireless optical link

The paper discusses analyses of high-speed wireless optical link where various effects influence the detected optical power. For purpose of the analyses, Gaussian optical intensity distribution is considered. Further mathematical analysis leads to analytical expressions of attenuation of detected optical power under all common conditions (e.g. misalignment, tilts). All analyses are based on exact mathematical derivation and are modeled using a computer. In conclusion, results of simulations are described and individual influences of various effects are discussed and compared. Emphasis on exact mathematical analysis leads to thorough understanding of a system and allows us to design optical links more effectively with respect to the performance and also the price.

Integration of FSO in local area networks - Combination of Optical Wireless with WLAN and DVB-T for last mile internet connections

Nowadays FSO (Free Space Optics) also called Optical Wireless, is a well-established technology for closing the last mile gap. Optical Wireless is best suited to be directly connected to fibre optics, like the extension of a fibre cable for access networks. But also combinations with RF- and wireless networks are of main interest in current applications. Various technologies have different influences on weather conditions, because of the used wavelengths (frequencies) and the differences in the propagation behaviour and the transmission channel. This contribution will show at first the selection of best suited wavelengths for optical wireless communications (OWC) for the last mile access in relevance to the weather effects and the influences of beam divergence and beam shaping. The second part is showing the usage of FSO in combination with other wireless technologies (as a special scenario with WLAN and DVB-T), available for regions of low Internet coverage. FSO allows a broadband access with high data rate for users not connected so far by fibre cables. It is a well-known fact that peripheral regions lack of reasonable broadband Internet services. WLAN and FSO are license-free transmission technologies and DVB-T has become a geographically widespread technology. This paper will show an alternative Internet access method using WLAN and FSO systems as a data uplink and DVB-T as a downlink channel for broadband data access. The work was carried out within international co-operations in the frame of a special programme of European Union called SEE (South-East-Europe).

Wavelength-selection for high data rate Free Space Optics (FSO) in next generation wireless communications

New results derived from the research in the field or Free Space Optics (FSO) for the qualification of different wavelengths with reference to future communication (including space) are presented. The contribution deals with a thorough discussion of the different optical wavelengths used either for terrestrial as well as for near-Earth and deep space FSO links. Practical results of COST Action IC-0802 are implemented in the modelling of the FSO channel under deteriorating conditions like rain, snow, dust, fog, clouds and other atmospheric effects. It is intended to interconnect well-proved technologies like 850 nm and 1064 nm as well as 1550 nm wavelength with new technologies under development like 10 μm wavelength. Quantum Cascade Lasers (QCLs) are currently experiencing a strong progression. Finally, some recent major performance improvement results obtained by employing some specific modulation and coding schemes are presented.

On the derivation of exact analytical FSO link attenuation model

The development of semiconductor technology has led to an increase of the usable bandwidth of light-emitting diodes LED, which are suitable for indoor high-speed communications or free-space optical FSO communications over a relatively short distance. The high-speed long-distance FSO links, where turbulence effects are considerably high, are a domain of laser sources. Hence, the paper covers the study of an exact analytical model of FSO link attenuation and the benefits of using an elliptically symmetrical Gaussian beam rather than a circularly symmetrical one.

Economic aspects of free space optics as an alternative broadband network connection for the last mile

In order to provide a powerful and fast communications infrastructure to end customers and private households, optical fiber connections are on the increase to close the last mile gap. However, this infrastructure expansion is slow and expensive. In contrast to optical fiber, Free Space Optics (FSO) has nowadays become a well-established technology for the last mile access. This contribution gives an overview of commercial FSO systems and investigates their integration into existing optical fiber networks from an economic point of view. Different optical fiber projects for the last mile, including fiber-to-the-home (FTTH) projects and business park connections, were investigated and compared with FSO systems. The results of the study show, that FSO is a viable and cost-effective alternative to fiber optics. Furthermore, a concept of a point-to-multipoint (P2MP) Optical Wireless (OW) system for a flexible broadband network connection in a settlement area is proposed.

Design of a hardware channel emulator as lab demonstrator for detailed verification of long-distance FSO systems

The field of Free Space Optical (FSO) communications has to deal with several challenges, which have to be considered. One of the most serious amongst them is fog attenuation. In this paper, an effective method for investigation of a long-distant FSO systems performance in the presence of fog is described. The proposed hardware channel emulator for laboratory measurements is based on a controllable optical attenuator, providing uncomplicated experimental environment in terms of fog conditions. An overview of already accomplished fog measurement campaigns is given as well as a rough summary of the self-developed MATLAB channel models. The findings were incorporated into the custom-made voltage driver (attenuator control unit), which controls the optical attenuator and represent sufficient basis for further laboratory long-distance FSO link verifications.

Design and analysis of coupling elements between optical fibres and optical free space

Nowadays optical fibres are significant appliances in telecommunications. They offer advantages, such as a high transmission capacity and minor cable attenuation. Furthermore no crosstalk occurs by using optical fibres. The insensibility to electrical and magnetical interferences is another big benefit for using fibres. Also important to mention is that there is no interference radiation, compared to other systems. Optical fibres do not emit sparks after a possible cable break; therefore they can be installed in explosion-prone environments. One of the major disadvantages of optical fibres is that they are more expensive than normal copper cables. The handling during the transfer is more difficult and after a cable break, the whole optical fibre cable has to be replaced. Another considerable part of using optical cables is the challenge to couple light into it. There are several possible proceedings for coupling, which are introduced in this paper. The main goal of every coupling method is to reduce the losses, which appear at the junctions between every single medium (free space and fibre). These losses can be minored at a specific level. As already proven, the usage of light emitting diodes (LEDs) is not highly recommended. The incoherent light, emitted by LED can be responsible for higher coupling losses. The better way is to use a laser. The usage of optical tapers can increase the numeric aperture - even more light rays are coupled in opposition to a simple fibre cross section. This technique is also demonstrated in this paper. To evaluate different possible coupling methods, software tools can be utilized. Complex test set-ups are not necessary. At the end, some different tools are introduced.

Moment generating function of macrodiversity system with three microdiversity MRC receivers in Gamma shadowed Nakagami-m fading channel

Macrodiversity system with selection combining diversity receiver and three microdiversity maximal ratio combining diversity receivers operating over correlated Gamma shadowed Nakagami-m multipath fading environment is considered. Moment generating function (MGF) of microdiversity MRC receivers output signals are calculated. By using these formulas, closed form expression for MGF function of macrodiversity SC receiver output signal envelope is evaluated. This result can be used for calculation the bit error probability of proposed macrodiversity system with several modulation schemes. Numerical results are presented graphically to show the influence of Nakagami-m severity parameter, Gamma shadowing severity parameter and correlation coefficient of shadowing on MGF.

Implementation of a testbed with a hardware channel emulator for simulating the different atmospheric conditions to verify the transmitter and receiver of Optical Wireless systems

Related to different international activities in the Optical Wireless Communications (OWC) field Graz University of Technology (TUG) has high experience on developing different high data rate transmission systems and is well known for measurements and analysis of the OWC-channel. In this paper, a novel approach for testing Free Space Optical (FSO) systems in a controlled laboratory condition is proposed. Based on fibre optics technology, TUG testbed could effectively emulate the operation of real wireless optical communication systems together with various atmospheric perturbation effects such as fog and clouds. The suggested architecture applies an optical variable attenuator as a main device representing the tropospheric influences over the launched Gaussian beam in the free space channel. In addition, the current scheme involves an attenuator control unit with an external Digital Analog Converter (DAC) controlled by self-developed software. To obtain optimal results in terms of the presented setup, a calibration process including linearization of the non-linear attenuation versus voltage graph is performed. Finally, analytical results of the attenuation based on real measurements with the hardware channel emulator under laboratory conditions are shown. The implementation can be used in further activities to verify OWC-systems, before testing under real conditions.