Study of Various Challenges In IS-OWC – A Review

Abhishek Sharma
2017 International Journal for Research in Applied Science and Engineering Technology  
Inter-satellite optical-wireless communication systems (IsOWC), one of the important applications of FSO/WSO technology, will be deployed in space in the near future. The IsOWC systems provide a high bandwidth, small size, light weight, low power and low cost alternative to present microwave satellite systems. In this paper we have reported the challenges of Is-OWC Key words: Is-OWC (inter-satellite optical wireless communication), LOS (line of sight), I. Satellite optical wireless
more » ... system (Is-OWC) communication usually involves directed line-of-sight LOS and point-topoint laser links from transmitter to receiver through the atmosphere. LOS links require an unobstructed path for reliable communication, whereas diffuse links rely on multiple optical paths from surface reflections. II. ADVANTAGES OF OFDM A. Makes efficient use of the spectrum by allowing overlap. B. By dividing the channel into narrowband flat fading sub channels, OFDM is more resistant to frequency selective fading than single carrier systems are. i.e. robustness to frequency selective fading channels C. Eliminates ISI through use of a cyclic prefix. D. Using adequate channel coding and interleaving one can recover symbols lost due to the frequency selectivity of the channel. E. Channel equalization becomes simpler than by using adaptive equalization techniques with single carrier systems. F. It is possible to use maximum likelihood decoding with reasonable complexity. G. OFDM is computationally efficient by using FFT techniques to implement the modulation and demodulation functions. H. Is less sensitive to sample timing offsets than single carrier systems are. I. Provides good protection against co channel interference and impulsive parasitic noise. III. DISADVANTAGES OF OFDM A. It is more sensitive to ICI (inter carrier interference) which is due to frequency offset. B. Peak to average power ratio (PAPR) is high. C. Bandwidth and power loss can be significant due to guard interval. D. High power transmitter amplifiers need linearization. E. Low noise receiver amplifiers need large dynamic range. IV. BACKGROUND STUDY The application of laser technology to communications, particularly space communications, was envisioned in the very early days of laser development around 1962, described a method for secure communications between a satellite and a submarine. In the 40 years since, government agencies, companies, universities, and individuals in many countries have made tremendous technical progress in optical space communication i.e. inter-satellite optical wireless communication. A comprehensive review of the work in the field of inter-satellite optical wireless communication system reported by various researchers is briefly described. The author studied the error performance of a heterodyne differential phase-shift keying (DPSK) optical wireless (OW) communication system operating under various intensity fluctuation conditions. [8] Specifically, it was assumed that the propagating signal suffers from the combined effects of atmospheric turbulence-induced fading, misalignment fading (i.e., pointing errors) and path-loss. Novel closed-form expressions for the statistics of the random attenuation of the propagation channel were derived and the bit-error rate (BER) performance was investigated for all the above fading effects. Numerical results were provided to evaluate the error performance of OW systems with the presence of atmospheric turbulence and/or misalignment. Moreover, nonlinear optimization was also considered to find the optimum beam width that achieves the minimum BER for a given signal-tonoise ratio value.The author studied the integrated Satellite-High altitude Platform system and presented their work. [9] Their work focused on routing algorithm reliability for evaluation of QOS parameters. The author presented outline on HAP perception growth. IN detail Contrast was also made between HAP, satellite and terrestrial system. [10] Positioning possibilities of using HAP in communication scenarios were explained by collaborating with terrestrial or satellite systems. The author studied the use of laser satellite communication to send Information to one another and also to relay the information to another satellite and then to the ground stations [11] . As the number of satellites orbiting Earth increase year by year, a network between the satellites provides a method for them to communicate with each other. And the laser communication not only eliminates the requirement for the lengthy fibers, but also connects the satellite with the data rates up to several Gbps. The optical wireless communication link performance focusing on data transfer between Low Earth Orbit (LEO) satellites. The system performance, including bit rates, input power, wavelength and distance on an inter-satellite link were analyzed. The author investigated the outage behavior of optical inter-satellite communication links. The main issues addressed in the work wee: (1) source induced Fading, (2) statistically correlated fading, (3) transmitter diversity, (4) selection combining, and (5) equal gain combining. [12] It was shown that the merit of combining was obvious when the correlation coefficient is less than 0.5, the
doi:10.22214/ijraset.2017.8112 fatcat:q4fi6mbq55hpvdx5tqpwp4qlsy