In recent years, the combination of unmanned aerial vehicles (UAVs) and free-space optical (FSO) has gained researchers’ attention as this combination is viewed as a potential candidate for future high capacity front-haul communication links. However, one of the main impairments affecting ground-to-UAV FSO links is signal outages or fading induced by clouds and rain. This manuscript focuses on the BER performance of ground-to-UAV-based FSO communication links using MODTRAN atmospheric data. The transmittance data gathered from the MODTRAN software for various cloud types, rain rates, and altitude was used to evaluate the BER performance of the FSO system under weak atmospheric turbulence. A comparative BER performance of a 2 Gpbs FSO link was analyzed for three different cloud models (Cumulus, Stratus, and Altostratus), four types of rain rate (no rain, drizzle, moderate and heavy rain) at multiple zenith angles (ranging from 0 to 60°) and for a maximum FSO uplink range of 2 km. The wavelengths of interest used for this study were 850 nm, 1064 nm, and 1550 nm. It is concluded that the inclement weather conditions may severely degrade the FSO link at ranges less than 1 km. Also, the 1550 nm wavelength outperformed the other two wavelengths for every chosen model.
Free Space Optics (FSO) technology was originally envisioned to be a viable solution for the provision of high
bandwidth optical connectivity in the last mile of today's telecommunications infrastructure. Due to atmospheric
limitations inherent to FSO technology, FSO is now widely envisioned as a solution for the provision of high bandwidth,
temporary mobile communications links. The need for FSO communications links will increase as mobility is
introduced to this technology. In this paper, a theoretical solution for adding mobility to FSO communication links is
introduced. Three-dimensional power estimation studies are presented to represent mobile FSO transmission under
various weather conditions. Three wavelengths, 0.85, 1.55 and 10 um, are tested and compared to illustrate the pros and
cons of each source wavelength used for transmission, depending on prevalent weather conditions and atmospheric
turbulence conditions. A simulation analysis of the transmission properties of the source wavelengths used in the study
is shown.
Significant research efforts are underway to investigate the application of Free-Space Optics (FSO) for the provision
of high-bandwidth communications links between mobile platforms. The use of FSO between mobile platforms
introduces several interesting challenges in addition to those found in traditional fixed link FSO systems. In this
paper, some of the major hurdles facing fixed FSO communications that carry over into links between mobile
platforms are analyzed. These topics include: issues with alignment and tracking, an investigation into the weather
and its affect on the link, and a study of the feasibility of having uninterrupted communications links. Other topics
presented unique to mobile applications include: the security risks during link alignment, maintaining the link while
tracking and optical power and beam divergence variations that are introduced into the system. In this paper the
results from simulation work performed on some of these issues along with proposed solutions to the challenges are
presented.
In this paper, a comparison of the physical security aspects of a time division multiplexed (TDM) passive optical
network (PON) and a proposed wavelength hopping passive optical network (WH-PON) is presented. Simulated results
of an eavesdropping attempt in both networks are presented. The introduction of a WH-PON will demonstrate how
physical layer security can be introduced to a PON architecture through the use of a pair of matched tunable lasers in the
optical line terminal (OLT). These matched tunable lasers allow for the creation of a secure point-to-point optical link
between the OLT and the end user, without the need for a unique optical transmitter for each end user. The simulation
results presented will demonstrate the operation of each PON architecture, as well as the physical immunity to
eavesdropping that the WH-PON architecture introduces.
KEYWORDS: Free space optics, Detection and tracking algorithms, Unmanned aerial vehicles, Receivers, Transmitters, Mobile communications, Free space optical communications, Optical simulations, Algorithm development, Global Positioning System
Free-space optical (FSO) communications links are envisioned as a viable option for the provision of temporary high-bandwidth
communication links between moving platforms, especially for deployment in battlefield situations. For
successful deployment in such real-time environments, fast and accurate alignment and tracking of the FSO equipment is
essential. In this paper, a two-wavelength diversity scheme using 1.55 μm and 10 μm is investigated in conjunction with
a previously described tracking algorithm to maintain line-of-sight connectivity battlefield scenarios. An analytical
model of a mobile FSO communications link is described. Following the analytical model, simulation results are
presented for an FSO link between an unmanned aerial surveillance vehicle, the Global Hawk, with a mobile ground
vehicle, an M1 Abrams Main Battle Tank. The scenario is analyzed under varying weather conditions to verify
continuous connectivity is available through the tracking algorithm. Simulation results are generated to describe the
performance of the tracking algorithm with respect to both received optical power levels and variations in beam
divergence. Advances to any proposed tracking algorithm due to these power and divergence variations are described
for future tracking algorithm development.
Free-space optical (FSO) communication links are envisioned as a viable option for the provision of temporary high-bandwidth communication links between moving platforms, such as a ground station and a mobile aerial platform such as an unmanned aerial vehicle. One of the limitations of FSO links is the transmission of laser beams through various weather phenomena. One technique to attempt to overcome the effects of weather, such as fog, is to implement a wavelength diversity scheme between the FSO transmitter and receiver. This paper investigates the minimization of link acquisition times using a wavelength diversity scheme between mobile FSO platforms. The wavelength diversity scheme consists of three different wavelengths, 1.55 μm, 0.85 μm and 10 μm. Each wavelength has different advantages and disadvantages for transmission depending of prevalent weather conditions and atmospheric turbulence conditions. A model of a ground-to-air FSO link is developed in order to predict the beam profile in the receiver plane. A simulation analysis of the transmission properties of the wavelength diversity schemes will be presented. Based on the transmission properties, a method for minimizing link acquisition times through the exploitation of various properties of each wavelength is presented and analyzed.
Atmospheric weather conditions adversely affect the performance of free-space optical communications systems. Fog present in the atmosphere has the largest impact on free-space optical systems. We use simulation techniques to investigate the performance of a slant-path, wavelength-diversified free-space optical link between a ground station and an unmanned aerial vehicle in the presence of radiation fog. The free-space optical link is configured to operate using the simultaneous transmission of three wavelengths, 0.85, 1.55, and 10 µm, connecting a ground station to an unmanned aerial vehicle operating at either a 4- or 8-km altitude. The link is further analyzed by combining the multiple carrier wavelengths into either an equal-gain diversity scheme or a selective diversity scheme. The simulation results are obtained using ALTM and PcModWin simulation software from Ontar Corporation. The results obtained demonstrate that the use of either an equal-gain diversity scheme or a selective diversity scheme enables the deployment of a ground-to-air free-space optical communications link. Furthermore, a selective diversity scheme demonstrates a received power approximately three times greater than an equal-gain diversity scheme.
The use of free-space optical (FSO) communications links are envisioned as a viable option for providing a temporary high-bandwidth communications link between a ground station and an unmanned aerial vehicle (UAV). The presence of atmospheric turbulence causes three different phenomena to occur, namely beam wander, scintillation and beam spread, each of which is a wavelength dependent phenomenon. In this paper, simulation tools are used to investigate the effects of atmospheric turbulence on a wavelength diversified ground-to-UAV FSO communications link. This paper compares the effects of atmospheric turbulence on three different wavelengths, 1.55 μm, 0.85 μm and 10 μm. Each of these wavelengths has different advantages depending on prevalent weather conditions and atmospheric turbulence conditions. Based on the effects of atmospheric turbulence on each wavelength, a wavelength diversity scheme is proposed in order to optimize the performance of the FSO link. The largest problem associated with establishing a ground-to-UAV FSO link is alignment and tracking of the FSO link. For this reason, the wavelength diversity scheme is further analyzed as a method to optimize link acquisition and tracking of the ground-to-UAV link by exploiting various characteristics of each wavelength.
An important consideration when deploying free-space optical (FSO) communication links over ultra long distances is the ability to actively steer the laser beam. FSO links are currently being researched as an attractive option for deep-space communication links or as a link to provide broadband communications to aircraft in-flight. In order to establish ultra long FSO links or to actively track FSO links between moving platforms, an active tracking system based on hybrid technology is essential. These hybrid systems are usually a combination of a mechanical gimbal and some array of active optical components. The presence of active optical components in a beam steering device is necessary to provide a high bandwidth while offsetting vibrations present on the mounting platform. This study compares three active beam steering elements that can be used in FSO transmitters and receivers. Performance characteristics of MEMS-based micro mirror arrays, acousto-optic modulators and steerable mirrors are analyzed and compared. A comparison of aperture size, range of motion, resolution and scanning speed is performed. Simulations in order to show the effects of vibration on various different length FSO links are run. A simulation in order to verify the ability of a fast steering mirror to offset vibration effects in a ground-to-UAV link is performed.
Through the use of recent technological developments, it is now feasible to establish free-space optical (FSO) communication links over ultra-long distances. Recent research has shown that FSO systems could be deployed to establish high-rate data links to deep space. This study analyzes beam steering tolerances, beam divergence, and geometric loss for different distance ranges of interest for FSO communication links based on a mechanical gimbaled beam steering mechanism. The tolerance, divergence and geometric loss calculations are performed to evaluate the feasibility of establishing FSO links between the Earth and satellites, the Earth and aircraft, aircraft and satellites, the Earth and moon, the Earth and Mars, and the Earth and the edge of the solar system. The analysis and calculations performed take into consideration the availability of new technology such as low noise photon-counting detectors and fiber lasers and amplifiers. The beam steering tolerance and divergence calculations provide beneficial information for determining the extent to which future FSO systems could be deployed for both commercial, military and space exploration applications. Recommendations on the suitability of an FSO communication link for various applications are then made based on the beam steering tolerance and divergence calculations.
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