Free-space optical communication (FSOC) have directional light beams which makes communication links very sensitive to movement. A major challenge in mobile settings is handling of this fragility of FSOC links due to the highly directional distribution of light intensity within the light beams. Differing from previous studies using mechanical steering of the transceivers to remedy the brittleness of FSOC links, we use a square array of stationary elements for each transceiver for better directionality, optimum combination of elements (transmitter/receiver ratio along with location), and robustness to mobility. Based on previous studies showing the optimum transmit to receive area ratio in a square array layout, we locate the transmitters as a box around the center with extra elements on the four corners of the transceiver plane with the rest of the elements on the array being receivers. We design a hardware prototype using the same optimum transmit/receive ratio and a lOxlO square array layout with size, weight and power, cost, and geometric simplicity appropriate for a low-flying multi-copter drone. A full link margin analysis was completed for the lOxlO array, using commercial off-the-shelf components, with the same optimum transmit and receive combination. The range for the system was found to be rv 150 m operating at 1 Mbps. The outcome of this work will give us insight of how the tiling of transmit/receive elements affects a transceiver system to implement a directional wireless link in the optical spectrum for mobile settings, particularly for emerging use of low-flying drones.
Free-space optical (FSO) communication has gained popularity for wireless applications over legacy radio frequency for advantages such as unlicensed operation, spatial reuse, and security. Even though FSO communication can achieve high bit rates, range limitation due to strong attenuation and weather dependency has always restricted its practical applications to controlled settings such as building-to-building communication. Futuristic mobile and secure ad hoc FSO network applications such as smart cars and air-subsea links need more efficient and autonomous link acquisition capabilities, which can be enabled by in-band full-duplex (IBFD) operation. We proposed an IBFD-FSO transceiver prototype consisting of off-the-shelf components to demonstrate the concept of IBFD operation by the isolation technique. We also developed a laser-based IBFD-FSO link model by incorporating an atmospheric attenuation model and self-interference cancellation model. We found that, for clear weather, the maximum achievable link range using commercially available components can be up to 120 m. We also determined weather-dependent performance of the FSO link in terms of visibility and transmit power.
Free-space optical (FSO) communication has gained popularity for wireless applications over legacy radiofrequency for advantages like unlicensed band, spatial reuse, and security. Even though FSO can achieve high bit-rate, range limitation due to attenuation and weather dependency has always restricted its practical applications. Building-to-building communication, smart cars, and air-subsea links are potential futuristic applications for mobile and secure ad-hoc FSO networks, where in-band full-duplex FSO (IBFD-FSO) transceivers will potentially increase network capacity significantly to improve performance and reliability. In this work, we model an IBFD-FSO transceiver consisting of a VCSEL and a photodiode to determine the range and weather dependent performance of the link.
This paper presents realistic simulation modules to assess characteristics of multi-transceiver free-space-optical (FSO)
mobile ad-hoc networks. We start with a physical propagation model for FSO communications in the context of mobile
ad-hoc networks (MANETs). We specifically focus on the drop in power of the light beam and probability of error in
the decoded signal due to a number of parameters (such as separation between transmitter and receiver and visibility
in the propagation medium), comparing our results with well-known theoretical models. Then, we provide details on
simulating multi-transceiver mobile wireless nodes in Network Simulator 2 (NS-2), realistic obstacles in the medium and
communication between directional optical transceivers. We introduce new structures in the networking protocol stack
at lower layers to deliver such functionality. At the end, we provide our findings resulted from detailed modeling and
simulation of FSO-MANETs regarding effects of such directionality on higher layers in the networking stack.
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