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[IEEE 2018 International Conference on Current Trends towards Converging Technologies (ICCTCT) - Coimbatore, India (2018.3.1-2018.3.3)] 2018 International Conference on Current Trends towards Converging Technologies (ICCTCT) - Impact of Modulation Techniques for Hybrid-WDM Based FSO
摘要： Free space optical communication (FSO) provides high data rate by allowing light passed through the atmosphere. It is very effective and efficient technology for wireless communication. This emerging field basically uses invisible beams of light such as ultraviolet, infrared, etc. This work exclusively deals with the designing of hybrid WDM based FSO system using the simulation software Opti-System 7.0 with Minimum-Shift Keying and Differential-phase-shift keying. Further their study has been made as to which modulation techniques provides better means of communication. The normal rain weakening from rain power information which are gathered for a period for six months. The concert of the future system is evaluated in terms of Bit Error Rate, Q-factor, and Receiver Sensitivity are examined with respect to link distance for using rain attenuation 20.5dBm. The transmission wavelength and data rate is 1550nm and 2.5Gbps considered for investigation.
关键词： Receiver Sensitivity,Hybrid WDM,BER,Free space optical communication,DPSK,MSK
更新于2025-09-23 15:23:52
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Modeling of Short-Range Ultraviolet Communication Channel Based on Spherical Coordinate System
摘要： The study on short-range ultraviolet (UV) communication (UVC) channel modeling is often based on prolate-spheroidal coordinate system in previous studies. In this letter, we propose a single scattering coplanar model based on spherical coordinate system, where the transmitter beam and receiver field of view (FOV) can point arbitrarily under the limitation that the sum of transceiver elevation angles and half of their own FOV is less than 180°, and the transmitter beam and receiver FOV are above ground. We utilize the number of intersections between a special ray on the transmitter cone and the receiver conical surface to distinguish the UVC scenarios, which makes the analysis of UVC channel modeling comprehensible. Meanwhile, we validate the proposed model in comparison with the single scattering model and the Monte Carlo simulation model through numerical calculations. The results show that the proposed model agrees well with the both models. This work presents a new method to estimate the path loss of short-range UVC and provides guidelines for the experimental system design.
关键词： ultraviolet communications,Atmospheric propagation,free-space optical communication
更新于2025-09-23 15:22:29
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Transmission characteristics of 24.5??Gb/s atmospheric laser communication based on optical frequency comb
摘要： Through cascading Mach–Zehnder intensity modulator (MZIM) and phase modulator (PM), an optical frequency comb (OFC) with 7 flat comb teeth is produced. The frequency interval of the OFC is 25 GHz and the flatness is less than 1.5 dB. The 7 channels of the OFC are used as the carrier source of the one-to-many free-space optical (FSO) communication system, and the atmospheric turbulence simulation pool is used to simulate the turbulence intensity in the real atmosphere to verify its feasibility for FSO communication. In the experiment, the bit error rate (BER) and eye diagram are measured under the back-to-back (BTB) conditions, and the temperature difference of atmospheric turbulence simulation pool are 80 ?C, 150 ?C and 220 ?C. Each channel of the system can stably transmit the on–off keying (OOK) signal of 3.5 Gb/s, and the 7 channels can stably transmit the OOK signal of 24.5 Gb/s. Thereby, the OFC can be used in place of multiple lasers or laser arrays as a carrier source for a one-to-many FSO communication system.
关键词： Wavelength division multiplexing,Optical frequency comb,Atmospheric turbulence,Free-space optical communication
更新于2025-09-23 15:19:57
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Parallelized and adaptive square-root unscented Kalman filter for carrier recovery in satellite-to-ground coherent optical communications
摘要： An adaptive square-root unscented Kalman filter with a parallelized architecture for carrier recovery is proposed in QPSK based satellite-to-ground coherent optical communication systems. A new observation model is raised in the proposed scheme to make the state estimation more accurate. The process noise covariance (Q) and the measurement noise covariance (R) are adaptively estimated to make them consistent with their theoretical covariance. For verification of the feasibility of the proposed scheme, corresponding simulations of carrier recovery in satellite-to-ground laser links are carried out and compared with the scheme that is based on linear Kalman filter (LKF). The simulation results demonstrate that, compared with parallelized LKF, the proposed scheme has a wider range of block size and laser linewidth options, and it can relax the required transmit power by up to 0.5-3 dB under different zenith angle at the same BER. Moreover, the proposed scheme can achieve high estimation accuracy and fast tracking capability simultaneously in the case of dynamic frequency offset with better tolerance against the initial errors in Q and R.
关键词： Atmospheric propagation,Adaptive Kalman filter,Free space optical communication,Coherent communications,Carrier recovery
更新于2025-09-23 15:19:57
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Asymptotic Performance of Generalized Transmit Laser Selection Over Lognormal Turbulence Channels
摘要： In free space optical communication systems, transmit laser selection (TLS) has been proposed as an efficient fading-mitigation technique over turbulence channels. In TLS, the transmitter is equipped with a number of laser sources and the best laser source is selected for transmission. In practice, feedback error or outdated selection due to temporal changes in the channel may result in selecting another source rather than the best one. In this paper, we consider a FSOC system with generalized TLS (GTLS) where the nth best laser is selected among the available N lasers. Under the assumption of lognormal turbulence channels in addition to pointing errors, we derive a closed-form expression for asymptotic bit error rate. We use our derived closed-form expression to determine the diversity gains. We finally present simulation results to corroborate our analytical findings.
关键词： Free space optical communication,diversity order,lognormal fading,generalized transmit laser selection
更新于2025-09-23 15:19:57
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Performance of Free Space Optical Communication Base on Orbital Angular Momentum with Pointing Errors
摘要： Due to the misalignment of the receiver, the spiral spectrum appears to be extended when the Laguerre-Gaussian beam is applied to atmospheric laser communication. This paper investigates the spiral spectrum spread of the Laguerre-Gaussian beam in the case of receiver misalignment. The analytical expression of Laguerre-Gaussian spiral spectrum under the influence of alignment error is studied by mathematical derivation and simulation. The results show that the detection probability of the original orbital angular momentum (OAM) state varies with the lateral displacement distance and the inclination angle. The bit error rate and channel capacity of each channel were studied to verify the effects of misalignment in multiple OAM communication systems.
关键词： Orbital Angular Momentum,Laguerre-Gaussian beam,Pointing Errors,Free Space Optical Communication,Spiral Spectrum
更新于2025-09-23 15:19:57
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A New Modulation Technique to Improve Received Power Under Turbulence Effects For Free Space Optical Communication
摘要： This paper focus on new modulation technique to improve the performance of the conventional modulation that uses intensity modulation/direct detection (IM/DD) for On-Off Keying (OOK) modulation. This new modulation technique that is Dual Diffuser Modulation (DDM) can create superior modulation with able to reduce scintillation index, enhance power received and threshold signal level. The analysis result shows that the free space optical (FSO) can have good performance of power received under strong turbulence. The DDM are better performance as compare with conventional IM/DD-OOK and IM/DD-OOK with diffuser. This can help FSO system to combat with severe turbulence effect for optimum operation.
关键词： Turbulence Effects,Received Power,Free Space Optical Communication,Modulation Technique
更新于2025-09-23 15:19:57
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Evaluation of Atmospheric Detrimental Effects on Free Space Optical Communication System for Delhi Weather
摘要： Free Space Optical (FSO) communication systems are gaining popularity due to its tremendous speed, advanced capacity, cost effectiveness, secure and easy to deploy wireless networks. This technology has proven an effective choice for last mile applications and hard to reach areas where deployment of optical fibre links is not feasible. But FSO link is highly weather dependent and as signal passes through the atmospheric channel, the main impairments are the atmospheric turbulence, which induce fading and deteriorate the system performance. Delhi has a great potential for FSO communication because of its clear skies. Since there is no analysis for weather condition found in Delhi, this work provides analysis of typical Delhi weather condition ranging from heavy to light rain, fog and clear sky. The performance of FSO link is analysed in terms of attenuation and link length margin under different weather condition. The results are concluded to identify which atmospheric condition influences more on FSO link performance.
关键词： rain attenuation,atmospheric attenuation,free space optical communication,absorption,scattering,visibility,rainfall rate,Delhi weather condition,fog attenuation,link margin
更新于2025-09-23 15:19:57
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Joint FSO Fronthaul and Millimeter-Wave Access Link Optimization in Cloud Small Cell Networks: A Statistical-QoS Aware Approach
摘要： We investigate resource optimization for downlink cloud small cell network where the baseband unit pool communicates with the buffer-aided small remote radio heads (SRRHs) through free space optical fronthaul, and SRRHs transmit to the user equipments (UEs) by using time division multiplexing based millimeter wave access links. Our objective is to maximize the supportable aggregate data arrival rate in the network by exploiting inter-dependence of fronthaul and access links. Towards this objective, we consider maximum acceptable end-to-end queue-length bound violation probability constraints, load-balancing constraints in the access link, fronthaul link selection constraints, and transmit power budget constraints of fronthaul and access links. Since the joint fronthaul and access link optimization is a non-convex and combinatorial problem, we develop iterative solution by decomposing the original optimization problem into two sub-problems. The first sub-problem optimally obtains fronthaul and access link power allocation and fronthaul link selection by using Lagrangian dual decomposition and canonical one-to-one matching techniques. By employing Lagrangian dual decomposition and alternating optimization techniques, the second sub-problem obtains near optimal data arrival rate for each UE, UE-SRRH associations, fronthaul rate allocation among the transmitted data for the UEs, and transmission duration scheduling in millimeter wave access link. An algorithm of polynomial complexity is developed in order to determine the supportable aggregate data arrival rate by considering statistical quality-of-service requirements, and its convergence is proved. Simulation results depict that the proposed scheme significantly improves the aggregate data arrival rate over several benchmark schemes.
关键词： statistical-QoS,fronthaul,millimeter wave,optimization,Free space optical communication
更新于2025-09-19 17:15:36
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Capacity analysis of free space optical communication system under atmospheric turbulence
摘要： In this paper, the analytical channel capacity of the free space optical (FSO) system under weak, moderate and strong turbulence is derived. The FSO channel statistics follows the log-normal distribution under weak turbulence and follows the Gamma–Gamma distribution under moderate and strong turbulence. The three generally used adaptive transmission schemes in FSO communication system are as follows (1) optimal simultaneous power and rate adaptation, (2) optimal rate adaptation with constant transmit power, and (3) truncated channel inversion with a fixed rate. The closed-form approximations for the average ergodic channel capacity for these adaptive transmission schemes under different atmospheric turbulence without any pointing error are derived. Simulation results depict the excellent agreement of the proposed analytical models with the Monte Carlo simulation.
关键词： Channel capacity,Free space optical communication,Signal to noise ratio,Adaptive transmission,Atmospheric turbulence
更新于2025-09-19 17:13:59