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Analysis of Different Parameter of FSO Communication System by Using Robust Model Design
High-quality Television. Ultra-broadband connectivity and smart internet expansion require very high data speed to access network devices. Radiofrequency {RF} includes bandwidth depletion, fragmentation, and expensive licensing restrictions. Now days only technology is a ray of hope for the last mile access is free-space optical communication (FSO) or optical wireless communication (OWC). In this proposed system we have investigated the implementation of hybrid modulation (NRZ, DQPSK, and Polsk) over FSO channel (under various atmospheric conditions) by using this technique we simultaneously increase the number of users so that they can be able to access the data at the same time without any reduction in performance of the system. In this system model, Q-factor and BER are analyzed and compared between Hybrid SISO-FSO and Hybrid MIMO-FSO model systems under various atmospheric conditions.
The effect of beat noise and other types of additive noise in time-spreading optical-code-division multiple-access (TS-OCDMA) networks is analyzed in this paper. By defining the coherent ratio kt, the ratio of the chip duration to the coherence time of the light source, TS-OCDMA systems are classified into incoherent, partially coherent, and coherent systems. The noise distributions and the bit-error rates are derived, and system performance is discussed for different cases. The performance of coherent systems is limited by the beat noise. With increasing kt, the effect of beat noise decreases in incoherent systems, and they eventually become free of beat noise. Possible solutions to the beat noise problem in coherent and partially coherent systems are also proposed and discussed.
In recent years, free space optical communication has gained significant importance owing to its unique features: large bandwidth, license-free spectrum, high data rate, easy and quick deployability, less power and low mass requirements. FSO communication uses the optical carrier in the near infrared band to establish either terrestrial links within the Earth's atmosphere or inter-satellite or deep space links or ground-to-satellite or satellite-to-ground links. However, despite the great potential of FSO communication, its performance is limited by the adverse effects viz., absorption, scattering, and turbulence of the atmospheric channel. This paper presents a comprehensive survey on various challenges faced by FSO communication system for ground-to-satellite or satellite-to-ground and inter-satellite links. It also provides details of various performance mitigation techniques in order to have high link availability and reliability. The first part of the paper will focus on various types of impairments that pose a serious challenge to the performance of optical communication system for ground-to-satellite or satellite-to-ground and inter-satellite links. The latter part of the paper will provide the reader with an exhaustive review of various techniques both at physical layer as well as at the other layers i.e., link, network or transport layer to combat the adverse effects of the atmosphere. It also uniquely presents a recently developed technique using orbital angular momentum for utilizing the high capacity advantage of the optical carrier in case of space-based and near-Earth optical communication links. This survey provides the reader with comprehensive details on the use of space-based optical backhaul links in order to provide high-capacity and low-cost backhaul solutions.
An overview of works conducted by NEC in the field of optical submarine cable systems focusing on their key technologies is presented and their technical trends towards the next generation are discussed. NEC has constructed a large number of repeatered and repeaterless systems and is capable of developing and manufacturing submarine cables in-house. The firm has been tackling the technological development of the 10-Gbps WDM system to overcome the concerns of S/N ratio degradation due to the accumulation of ASE noise emitted by the optical amplifiers incorporated in the submarine repeaters. NEC is working to enhance the performance of Er3+ doped optical fiber amplifier (EDFA) to offer excellent gain flatness characteristics below 0.1 dB over a bandwidth of 36 nm or more. Research-stage verification of a transpacific-class 9,000 km transmission system using 40 G signals is also completed and technological developments to enable its commercial implementation is in progress at NEC.
The principal disadvantage of using free space optics (FSO) telecommunication systems is the disturbing role played by the atmosphere on light propagation and thus on the channel capacity, availability, and link reliability. The wavelength choice is currently a subject of disagreement among designers and users of FSO equipments. Generally this equipment operates in the visible and the near IR at 690, 780, 850, and 1550 nm. Several authors affirm that equipment working at 1550 nm presents less atmospheric attenuation in the presence of fog and thus better link availability. Others consider that for dense fogs ( visibility < 5 0 0 m ) , all wavelengths are attenuated in the same way (wavelength independence). Fog attenuation in the visible and IR regions is reviewed from an empirical and theoretical point of view. Laser system performance in the presence of fog (advection and convection) in the 0.4- to 15-μm spectral zone is investigated using FASCOD computation. A transmission gain of 42% for a lasercom system working at 780 nm is observed compared to the same system working at 1550 nm. This gain reaches 48% if the same system works at 690 nm. Finally, we propose a fast transmission relationship based on an exact Mie theory calculation valid in the 0.69- to 1.55-μm spectral bands. It enables us to predict fog attenuation according to visibility without using heavy computer codes. © 2004 Society of Photo-Optical Instrumentation Engineers.
Four wave mixing (FWM) induced power penalty is investigated theoretically for asymmetrical dispersion-managed fibers in wavelength division multiplexing (WDM) systems. The power penalty in these fibers is analyzed for various values of channel spacing, maximum dispersion and number of sections in different channels. Using numerical simulations, it is illustrated that the FWM induced power penalty is minimized for the case of two fiber sections with unequally special lengths and symmetrical dispersion values.
This paper contains a review of technologies, theoretical studies, and experimental field trials for optical communications from and to high-altitude platforms (HAPs). We discuss the pointing, acquisition, and tracking of laser terminals and describe how laser beams with low divergence can be used to transmit data at multi-Gigabits per second. Investigating the influence of the atmosphere, background light, and flight qualification requirements on system design, we explain why the data rates in free-space optical communications are still significantly below those possible in today's terrestrial fiber-based systems. Techniques like forward-error correction, adaptive optics, and diversity reception are discussed. Such measures help to increase the data rate or link distance while keeping the bit error ratio and outage probability of the optical HAP communication system low.
This paper suggests a simulation model of optical code division multiple access communication system using optical orthogonal codes. The simulation model provides the opportunity for asynchronous access to the common optical media of random number of users. The developed simulation schema of optical CDMA system is used for tracking the reaction of communication system for research and analysis of different optical orthogonal codes with various parameters assuming of various in structure and kind noises in the common communication channel.
We develop a model for the probability density function (pdf) of the irradiance fluctuations of an optical wave propagating through a turbulent medium. The model is a two-parameter distribution that is based on a doubly stochastic theory of scintillation that assumes that small-scale irradiance fluctuations are modulated by large-scale irradiance fluctuations of the propagating wave, both governed by independent gamma distributions. The resulting irradiance pdf takes the form of a generalized K distribution that we term the gamma-gamma distribution. The two parameters of the gamma-gamma pdf are determined using a recently published theory of scintillation, using only values of the refractive-index structure parameter C-n(2) (or Rytov variance) and inner scale l(0) provided with the simulation data. This enables us to directly calculate various log-irradiance moments that are necessary in the scaled plots. We make a number of comparisons with published plane wave and spherical wave simulation data over a wide range of turbulence conditions (weak to strong) that includes inner scale effects. The gamma-gamma pdf is found to generally provide a good fit to the simulation data in nearly all cases tested. (C) 2001 society of Photo-Optical Instrumentation Engineers.
We investigate the performance and design of free-space optical (FSO) communication links over slow fading channels from an information theory perspective. A statistical model for the optical intensity fluctuation at the receiver due to the combined effects of atmospheric turbulence and pointing errors is derived. Unlike earlier work, our model considers the effect of beam width, detector size, and jitter variance explicitly. Expressions for the outage probability are derived for a variety of atmospheric conditions. For given weather and misalignment conditions, the beam width is optimized to maximize the channel capacity subject to outage. Large gains in achievable rate are realized versus using a nominal beam width. In light fog, by optimizing the beam width, the achievable rate is increased by 80% over the nominal beam width at an outage probability of 10
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. Well-known error control codes are then applied to the channel and shown to realize much of the achievable gains.
Enhanced security has often been cited as an important benefit of optical code-division multiple-access (O-CDMA) signaling but has seldom been analyzed in detail. This paper presents a theoretical analysis of the degree of confidentiality that can be provided by spectral-phase-encoded O-CDMA. Two eavesdropping detector structures are presented that can theoretically break the confidentiality of spectral-phase-encoded signals by detecting the code words in use by a specific user. One of them, an optical beat detector, is quantitatively analyzed to determine the probability of correctly detecting user code words. The confidentiality of user signals is shown to be vulnerable to such a detector if an eavesdropper can isolate a single user signal with a sufficiently high signal-to-noise ratio (SNR). At lower SNRs, combining multiple bits is shown to dramatically increase the probability of an eavesdropper correctly detecting user code words; even for codes long enough to strain implementation capabilities (e.g., 2048 code elements), the probability of correct detection is shown to rise from negligibly low values to virtually 100% by the combining of less than 100 transmitted bits at the eavesdropper's receiver.
Error-control codes can help to mitigate atmospheric turbulence-induced signal fading in free-space optical communication links using intensity modulation/direct detection (IM/DD). Error performance bound analysis can yield simple analytical upper bounds or approximations to the bit-error probability. We first derive an upper bound on the pairwise codeword-error probability for transmission through channels with correlated turbulence-induced fading, which involves complicated multidimensional integration. To simplify the computations, we derive an approximate upper bound under the assumption of weak turbulence. The accuracy of this approximation under weak turbulence is verified by numerical simulation. Its invalidity when applied to strong turbulence is also shown. This simple approximate upper bound to the pairwise codeword-error probability is then applied to derive an upper bound to the bit-error probability for block codes, convolutional codes, and turbo codes for free-space optical communication through weak atmospheric turbulence channels. We also discuss the choice of interleaver length in block codes and turbo codes based on numerical evaluation of our performance bounds.
In free-space optical communication links, atmospheric turbulence causes fluctuations in both the intensity and the phase of the received light signal, impairing link performance. We describe several communication techniques to mitigate turbulence-induced intensity fluctuations, i.e., signal fading. These techniques are applicable in the regime in which the receiver aperture is smaller than the correlation length of fading and the observation interval is shorter than the correlation time of fading. We assume that the receiver has no knowledge of the instantaneous fading state. When the receiver knows only the marginal statistics of the fading, a symbol-by-symbol ML detector can be used to improve detection performance. If the receiver has knowledge of the joint temporal statistics of the fading, maximum-likelihood sequence detection (MLSD) can be employed, yielding a further performance improvement, but at the cost of very high complexity. Spatial diversity reception with multiple receivers can also be used to overcome turbulence-induced fading. We describe the use of ML detection in spatial diversity reception to reduce the diversity gain penalty caused by correlation between the fading at different receivers.
A review of the development in the field of fiber optic communication systems
- Sharma Prachi
- Prachi Sharma