Papers by Muhammad Saleem Awan
VTC Spring 2009 - IEEE 69th Vehicular Technology Conference, 2009
Optical Wireless link provides high bandwidth solution to the last mile access bottleneck. Howeve... more Optical Wireless link provides high bandwidth solution to the last mile access bottleneck. However, an appreciable availability of the link is always a concern. Free Space Optics (FSO) links are highly weather dependent and fog is the major attenuating factor reducing the link availability. However the traffic requirement of a LAN may not require 99.999% availability of FSO at all instants. A hybrid network with intelligent switch over can fulfil the availability and bandwidth requirement. In this paper statistical data of fog and FSO availability in Graz (Austria) has been compared to the traffic data of Technical University Graz (Austria).
2009 IEEE Wireless Communications and Networking Conference, 2009
Wireless optical communication links has the great potential to serve for an increasing demand fo... more Wireless optical communication links has the great potential to serve for an increasing demand for high bandwidth transmission capabilities. However, the widespread deployment of wireless optical communication system has been hampered by reliability or availability issues related to atmospheric variations. Among atmospheric effects on wireless optical link, fog is the most important factor. It is the most deleterious factor for achieving high availability in Free Space Optics (FSO), causing significant attenuation for considerable amount of time. Another technology offering negligible fog attenuation and acceptable data rates is license free ISM band, that can be used as back up link. However, a switch-over mechanism is required for optimal selection of any link depending on weather patterns, link quality, and data rate. A load balancing implementation of switch-over is presented in this paper and behavior of hybrid network is simulated for measured data of more than one year.
2009 Wireless Telecommunications Symposium, 2009
High bandwidth optical wireless communication links are of prime importance, having tremendous po... more High bandwidth optical wireless communication links are of prime importance, having tremendous potential to serve for the future huge data transmission requirements especially for the next generation optical networks. The inherent electromagnetic nature of the transmitted optical signals and the stochastic nature of the earth atmosphere create a number of technical challenges preventing widespread acceptance of technology and its implementation. One of the major concerns for Free Space Optics (FSO) links is fog that causes very high attenuation over non-negligible amounts of time. Another technology offering negligible fog attenuation and acceptable data rates is license free ISM band, which can be used as back up link. However, a switch-over mechanism is required for optimal selection of any link depending on weather condition and link quality maintaining an acceptable data rate. Moreover, synchronization of transceivers is the basic requirement of a communication link. This paper presents an implementation of a self-synchronizing switch-over system and the behaviour of this hybrid network is simulated for measured fog events.
2009 1st International Conference on Wireless Communication, Vehicular Technology, Information Theory and Aerospace & Electronic Systems Technology, 2009
Free Space Optic (FSO) communication systems have the great potential of serving as high bandwidt... more Free Space Optic (FSO) communication systems have the great potential of serving as high bandwidth links. However, their popularity and widespread use is limited by the fact, that this technology is dependent upon an unobstructed line of sight more than any other wireless communication system. Especially weather conditions affecting visibility, such as fog or heavy rain, often cause unacceptable link failures. To increase reliability, a variety of hybrid FSO/RF systems has been introduced, among them a great number of switch-over systems. These systems require an accurate and timely detection of link failure and an appropriate algorithm to react. Generally, the received signal strength is considered as an indicator for link quality. Fluctuations in this indicator prohibit the use of simple threshold comparison techniques. In this paper, a set of switch-over algorithms is introduced and analyzed, using attenuation measurement data of fog events.
This paper illustrates the challenges imposed by the atmospheric channel on the design of a terre... more This paper illustrates the challenges imposed by the atmospheric channel on the design of a terrestrial laser communication link. The power loss due to scattering effect is described using the Kim/Kruse scattering model while the effect and the penalty imposed by atmospheric turbulence is highlighted by considering the bit error rate (BER) of an On-Off Keying modulated link in an optical Poisson channel. The power loss due to thick fog can measure over 100 dB/km while snow and rain result in much lower attenuation. We show that non-uniformity in the atmospheric temperature also contributes to performance deterioration due to scintillation effect. At a BER of 10 -4 , for a channel with a turbulence strength of >0.1, the penalty imposed by turbulence induced fading is over 20 photoelectron counts in order to achieve the same level of performance as a channel with no fading. The work reported here is part of the EU COST actions and EU projects..
Journal of Communications, 2009
Free Space Optics (FSO) is now a well established access technology, better known for its robustn... more Free Space Optics (FSO) is now a well established access technology, better known for its robustness in transmitting large data volumes in an energy efficient manner. However the BER performance of a FSO ground-link is adversely affected by cloud coverage, harsh weather conditions, and atmospheric turbulence. Fog, clouds and dry snow play a detrimental role by attenuating optical energy transmitted in terrestrial free-space and thus decrease the link availability and reliability. We measured the time variation of received optical signal level during continental fog and dry snowfall over a link distance of 80 m. We perform a detailed analysis of the continental fog and dry snow attenuation results and further characterise them by presenting some useful attenuation statistics and also showing their comparison with the corresponding measured density values collected by a particle sensor device. We propose also an empirical relationship between temperature, relative humidity and optical attenuation values for the continental fog case based on standard curve fitting technique.
A technique for modeling the fog droplet size distributions using modified gamma distribution has... more A technique for modeling the fog droplet size distributions using modified gamma distribution has been demonstrated by considering two separate radiation fog events recorded in Graz (Austria) and Prague (Czech Republic). The measurement of liquid water content (LWC) and the optical attenuations at visible wavelength are used to form equations to obtain the three parameters of the modified gamma distribution i.e., the slope (Λ), the intercept (N0 ) and the shape parameter (m). Calculated attenuation or LWC from the retrieved parameters are in excellent agreement with attenuation or LWC obtained from the measurement. Hence this method is useful in the study of fog microphysics and in modeling the fog attenuations for terrestrial FSO links in situations when our measurement data contains values of attenuations only, or liquid water content only or both at a particular location. For the two case studies, Graz and Prague, we obtained the DSD parameters Λ=3.547 ± 1.935, N0 =3.834 ± 2.239,...
Evaluation of fog attenuation results for optical wireless links in free space
2008 IEEE International Workshop on Satellite and Space Communications, 2008
... [5] M. Gebhart, E. Leitgeb, S. Sheikh Muhammad, B. Flecker, C. Chlestil, M. Al Naboulsi, H. S... more ... [5] M. Gebhart, E. Leitgeb, S. Sheikh Muhammad, B. Flecker, C. Chlestil, M. Al Naboulsi, H. Sizun, F. De Fornel: Measurement of light attenuation in dense fog conditions for optical wireless links, SPIE proceedings, Vol. 589, 2005. ...
Linearity in optical attenuations for Free-space optical links in continental fog
Abstract Various measurement campaigns have been carried out at different locations by several in... more Abstract Various measurement campaigns have been carried out at different locations by several institutes to study the weather effects, mainly fog, on Free-space optical (FSO) links. Link distance between the FSO transceiver is different for most of the measurement ...
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Papers by Muhammad Saleem Awan