Transceiver Selection for Multi-Element Free-Space-Optical Communications
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The focus on wireless networking technologies has always been on radio frequency (RF). However, the capacity of these networks is limited by the availability of the RF spectrum. On the other hand, recent wireless applications have increased the demand for higher speed connections driving the need for higher capacity on the RF spectrum. It is expected that the demand will always stay hungry for more capacity and power, and RF spectrum is close to its saturation and may not be capable of handling future heavy loads. Hence, there is an urgent need for alternative wireless technologies that can complement legacy RF. Recently, Free-Space-Optical (FSO) communication has gained prominence as a technology complementary to RF since it has the potential to deliver wireless communication links at optical-level speeds. FSO transmitters are directional and have the advantage of high-speed modulation. An omni-directional FSO antenna can be built by using multiple transceivers on a spherical structure that will virtually behave like the traditional RF antennas. However, maintenance of line-of-sight (LOS) between transceivers during an ongoing transmission is an important issue that comes with the cost of directionality. Today, the maintenance of LOS in FSO communications is managed by mechanical steering mechanisms that are not flexible and fast enough to recover the disruptions in a mobile scenario. To remedy this problem first, we propose an electronic steering mechanism and an LOS maintenance algorithm for multi-transceiver FSO structures. The electronic steering mechanism and the LOS algorithm provide an ability to maintain optical wireless links with minimal disruptions caused by relative mobility of communicating nodes. Second, we explore the possibility of using the directionality of FSO communications for solving the 3-D localization problem in ad-hoc networking environments along with simulations and proof-of-concept prototype experiments. Lastly, we explore ways of making the LOS maintenance algorithm more energy efficient. The basic versions of the electronic steering mechanism and the LOS algorithm recover from disruptions caused by mobility; however, they do so by activating all the transceivers. This is not efficient in terms of circuit design and power consumption. We design an efficient algorithm, which will manage LOS alignments by activating a smaller number of transceivers instead of keeping all the transceivers busy. We focus on transceiver selection mechanisms to select an optimal subset of transceivers in spherical modules covered with multiple directional FSO transceivers. We design, evaluate, and simulate two different transceiver selection algorithms: Single Mode Selection and Two Mode Selection. We conclude by providing performance results of NS-2 simulations, conclusions, and future work.