Experimental investigation of the performance of different modulation techniques under controlled FSO turbulence channel

This paper experimentally investigates and compares the performance of the free space optics system employing three different modulation schemes, on-off keying (OOK) with nonreturn- to-zero (NRZ) and return-to-zero (RZ) and the binary phase shift keying (BPSK) operating under the turbulent atmosphere. The received average signal is measured and used to characterize the strength of the turbulence. The experiment is performed with a temperature gradient of 4 degrees at a wind velocity of 4 m/s. The temperature gradient within the controlled channel results in turbulence of a log irradiance variance of 0.002, which is classified as a very weak turbulence. The received signal eye diagram and power histograms are presented and analyzed for performance evaluation of the selected modulation schemes in the weak turbulence model

COMPARISON OF NON CHIRPED NRZ, CHIRPED NRZ AND ALTERNATE-CHIRPED NRZ MODULATION TECHNIQUES FOR FREE SPACE OPTIC (FSO) SYSTEMS

Free Space Optics (FSO) is the technology where transmission occurs through optical waveform that contains datatransformed at the transmitter from electrical signal. Since the transmission medium of FSO is atmosphere, atmosphericscattering is the major cause for interruption of FSO link. Non return zero (NRZ) modulation is the dominant modulationscheme employed in commercial terrestrial Free Space Optic (FSO) communication systems. This research are requiredto investigate three viable modulation techniques; NRZ pulse formats, non-chirped NRZ, chirped NRZ, and alternatechirpedNRZ at 10 Gb/s and 40 Gb/s data rate. The 1550 nm of continuous wave (CW) laser is modulated with threedifferent modulation formats over 1 km of FSO channel. The signal is propogated at different attenuation value based onMalaysia weather conditions. In this paper we have successfully compared the three modulation techniques in FSOsystem due to the Malaysia weather and the performance is accessed at bit error rate (BER) of 1x10-9. The presentedsimulation of these three modulation shows that alternate-chirped NRZ has slightly better performance compared to thenon-chirped NRZ and chirped NRZ modulation format at clear weather, haze, light rain, medium rain and heavy rain.We believe that, this system is an alternative for the future optical wireless network that has a potential to be installed inthe urban and sub-urban area.Key words: Free Space Optic (FSO) Non Return Zero (NRZ) Chirping Modulatio

Performance analysis of mixed Nakagami- m and Gamma–Gamma dual-hop FSO transmission systems

In this paper, we carry out a unified performance analysis of a dual-hop relay system over the asymmetric links composed of both radio-frequency (RF) and unified free-space optical (FSO) links under the effect of pointing errors. Both fixed and variable gain relay systems are studied. The RF link is modeled by the Nakagami-m fading channel and the FSO link by the Gamma-Gamma fading channel subject to both types of detection techniques (i.e., heterodyne detection and intensity modulation with direct detection). In particular, we derive new unified closed-form expressions for the cumulative distribution function, the probability density function, the moment generating function (MGF), and the moments of the end-to-end signal-to-noise ratio (SNR) of these systems in terms of the Meijer's G function. Based on these formulas, we offer exact closed-form expressions for the outage probability (OP), the higher order amount of fading, and the average bit error rate (BER) of a variety of binary modulations in terms of the Meijer's G function. Furthermore, an exact closed-form expression of the end-to-end ergodic capacity is derived in terms of the bivariate G function. Additionally, by using the asymptotic expansion of the Meijer's G function at the high-SNR regime, we derive new asymptotic results for the OP, the MGF, and the average BER in terms of simple elementary functions

Pointing Error Reduction Using Fiber Bundle-based Receiver Design for 200km Inter-Satellite Optical-Wireless Communication (IsOWC) Link

Free Space Optical links have gained significant importance in future generation space optical communication, particularly to establish a reliable optical inter-satellite optical wireless link between two satellite platforms. But the performance of Optical wireless link is degraded very much due to vibration imposed by various sources like; thermal storms, other heavy particles collisions. To address this problem a fiber bundle-based receiver approach other than conventional array of photodetector is required to mitigate the effects of pointing error. The result shows that the effect of pointing errors is reduced in the fiber bundle-based receiver system in compare to conventional receiver and this newly designed receiver system is able to cope up to 10 urad pointing error to achieve minimum Bit Error Rate (BER) and Q-factor for a data rate of 1 Gbps over a 200 km distance. It is practically implementable in Low Earth Orbit (LEO) satellite optical wireless communication link

Kalman Filter Tracking for an FSO Communication System based on Dynamic Beam Steering and Shaping

We present a theoretical free-space optical (FSO) transmitter that utilizes a dynamically steered and shaped laser beam to communicate with a randomly moving receiver adorned with a retroreflector. The transmitter tracks the receiver's position by repeatedly scanning the field of view (FOV), measuring reflections from the retroreflector, and estimating the receiver's position with a Kalman filter. The transmitter sends data to the receiver in between scans. A Monte Carlo simulation is used to determine the optimal FOV subsection to scan at each time step so that time spent scanning is minimized without compromising link reliability. The feasibility of the communication system is evaluated with a hypothetical implementation based on real hardware