Experimental Characterisation and Modelling of Atmospheric Fog and Turbulence in FSO

Free space optical (FSO) communication uses visible or infrared (IR) wavelengths to broadcast high-speed data wirelessly through the atmospheric channel. The performance of FSO communications is mainly dependent on the unpredictable atmospheric channel such as fog, smoke and temperature dependent turbulence. However, as the real outdoor atmosphere (ROA) is time varying and heterogeneous in nature as well as depending on the magnitude and intensity of different weather conditions, carrying out a proper link assessment under specific weather conditions becomes a challenging task. Investigation and modelling the ROA under diverse atmospheric conditions is still a great challenge in FSO communications. Hence a dedicated indoor atmospheric chamber is designed and built to produce controlled atmosphere as necessary to mimic the ROA as closely as possible. The experimental results indicate that the fog attenuation is wavelength dependent for all visibility V ranges, which contradicts the Kim model for V < 0.5 km. The obtained result validates that Kim model needs to be revised for V < 0.5 km in order to correctly predict the wavelength dependent fog attenuation. Also, there are no experimental data and empirical model available for FSO links in diverse smoke conditions, which are common in urban areas. Therefore, a new empirical model is proposed to evaluate the wavelength dependent fog and smoke attenuation by reconsidering the q value as a function of wavelength rather than visibility. The BER performance of an FSO system is theoretically and experimentally evaluated for OOK- NRZ, OOK-RZ and 4-PPM formats for Ethernet line data-rates from light to dense fog conditions. A BER of 10-6 (Q-factor ≈ 4.7) is achieved at dense fog (transmittance, T = 0.33) condition using 4-PPM than OOK-NRZ and OOK-RZ modulation schemes due to its high peak-to-average power ratio albeit at the expense of doubling the bandwidth. The effects of fog on OOK-NRZ, 4-PAM and BPSK are also experimentally investigated. In comparison to 4-PAM and OOK-NRZ signals, the BPSK modulation signalling format is more robust against the effects of fog. Moreover, the effects of using different average transmitted optical communication powers Popton the T and the received Q-factor using the OOK-NRZ modulation scheme are also investigated for light and dense fog conditions. The results show that for an FSO system operating at a Q-factor of 4.7 (for BER = 10-6), the required Q-factor is achieved at T of 48% under the thick fog condition by increasing Popt to 1.07 dBm, whereas the values of T are 55% and ~70% for the transmit power of 0.56 dBm and -0.7 dBm, respectively. The experimental characterisation and investigation of the atmospheric turbulence effect on the Ethernet and Fast-Ethernet FSO link is reported using different modulation schemes. The experiment is carried out in a controlled laboratory environment where turbulence is generated in a dedicated indoor atmospheric chamber. The atmospheric chamber is calibrated to mimic an outdoor turbulence conditions and the measured data are verified against the theoretical predictions. The experiment also demonstrates methods to control the turbulence levels and determine the equivalence between the indoor and outdoor FSO links. The results show that the connectivity of Ethernet and Fast-Ethernet links are highly sensitive to atmospheric turbulence. The results also show that the BPSK and OOK-NRZ modulation signalling formats are more robust against the weak atmospheric turbulence conditions than PAM signal

Importance of Simpson/Shinshu Grading in Meningioma’s Excision, Outcome and Recurrence

Objective:&nbsp;&nbsp;The study was aimed to determine the recurrence rate and recurrence-free survival of meningioma surgery with reference to Simpson grading of excision. Material and Methods:&nbsp;&nbsp;The study was conducted in the Department of Neurosurgery, Punjab Institute of Neurosciences (PINS), Lahore. Total 325 patients both male and female of age (13 – 70 years) with supratentorial grade I meningioma operated. The craniotomy with maximum safe excision of the meningioma was done in all patients under general anesthesia. All patients followed-up to one year clinically and radiologically. MRI brain plain and IV contrast were done at 6 months and then annually. The extent of resection was determined with the help of operative notes and post-op MRI and recurrences were studied with help of follow-up MRI. Results:&nbsp;&nbsp;There were 227 female and 98 male patients in ages 13 – 70 years. The mean age of patients was 53.5 years. 227 (70%) skull base meningioma, 71 (22.0%) convexity meningioma, and 26 (8%) falx or tentorium meningioma were operated. We achieved Simpson grade I excision in 55 (17.45%), grade II in 208 (64%), grade III in 23 (7%), and grade IV in 36 (11%) cases. The median recurrence free survival (RFS) with reference to Simpson grading of excision was 250, 120, 98, 80 months for grades I, II, III, and IV excision; it was statistically significant according to the grading of excision.&nbsp; Conclusion:&nbsp;&nbsp;Excision of meningioma up to grades I and II had an excellent outcome with minimum chances of complications

All optical fog-sensor for determining the fog visibility range in optical wireless communication links

The goal of this research work is to use an all optical based fog sensor to study the atmospheric visibility of fog and its constituents on the optical wireless communication (OWC) links in a controlled laboratory test-bid. The fog sensor measures the transmittance of the Infrared (IR) radiations which is used to determine the link visibility. Experimental results obtained show that using the fog sensor the visibility range from 0.37 – 1 km and above with respect to different fog density can be predicted

A New Weighting Scheme in Weighted Markov Model for Predicting the Probability of Drought Episodes

Drought is a complex stochastic natural hazard caused by prolonged shortage of rainfall. Several environmental factors are involved in determining drought classes at the specific monitoring station. Therefore, efficient sequence processing techniques are required to explore and predict the periodic information about the various episodes of drought classes. In this study, we proposed a new weighting scheme to predict the probability of various drought classes under Weighted Markov Chain (WMC) model. We provide a standardized scheme of weights for ordinal sequences of drought classifications by normalizing squared weighted Cohen Kappa. Illustrations of the proposed scheme are given by including temporal ordinal data on drought classes determined by the standardized precipitation temperature index (SPTI). Experimental results show that the proposed weighting scheme for WMC model is sufficiently flexible to address actual changes in drought classifications by restructuring the transient behavior of a Markov chain. In summary, this paper proposes a new weighting scheme to improve the accuracy of the WMC, specifically in the field of hydrology

Study of the atmospheric turbulence in free space optical communications

Abstract-In this paper the effect of atmospheric turbulence on free space optical (FSO) communications is investigated experimentally by designing a turbulence simulation chamber. The distributions of bits ‘0 ’ and ‘1 ’ levels are measured with and without turbulence. The bit error rate (BER) is then obtained from the distributions. The temperature gradient within the channel is less than 6 °C resulting in turbulence of log irradiance variance of 0.002. The received average signal is measured and used to characterise the simulated turbulence strength. We then evaluated the BER with turbulence and found that from an error free link in the absence of turbulence, the BER increased significantly to about 10-4 due to the turbulence effect. I

Sino-Iranian Strategic Partnership: Prospects and Challenges

China and Iran have developed mutual inter-dependence and bilateral cooperation in several fields. Though China and Iran are closer to sign 25 year strategic partnership, yet the final draft of the deal is being negotiated between the two parties. The expectations are high on Iranian side, however one or anotherway there are multiple factors associated with such developments. For instance; Chinese image in contemporary international system, US factor, international sanctions against Iran, Iranian perception and role in the region, and Chinese ambitious Belt and Road initiative is supposed to determine the depth and sustainability of this strategic partnership. This paper argues that the apprehensions attached to the deal are reflecting western perception whereas China’s interest are more economic/commercial and business oriented, thus limiting their cooperation in other fields. This paper addresses the prospects of these negotiations considering the impact of afore mentioned factors on the background of their relations, thus articulates challenges faced by both the parties for expected enhanced strategic partnership. The paper concludes that Sino-Iranian cooperation is not only confined to economic field rather expands to socio-cultural and technological fields as well, but this must also be viewed as part of China’s over all Middle East policy considering her economic might and investment posture through Belt and Road initiative. &nbsp;&nbsp;&nbsp