On Prototyping Multi-Transceiver Free Space Optical Communication Structures

Wireless networking has conventionally been realizedvia radio frequency (RF) based communication technologies. However,the capacity of these networks are limited by the availabilityof the RF spectrum. Free-Space-Optical (FSO) communicationhas the potential to deliver wireless communication links atoptical-level speeds. Although it has the advantage of high speedmodulation, maintenance of line-of-sight (LOS) betweentransceivers during an on-going transmission is an importantissue since FSO transmitters are highly directional. In this paper,we present a prototype implementation of such multi-transceiverelectronically-steered communication structures. Our prototypeuses a simple LOS detection and establishment protocol andassigns logical data streams to appropriate physical links.We showthat by using multiple directional transceivers we can maintainoptical wireless links with minimal disruptions that are caused byrelative mobility of communicating nodes

Transceiver Selection for Multi-Element Free-Space-Optical Communications

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

Prototyping multi-transceiver free-space-optical communication structures

Abstract—Wireless networking has conventionally been realized via radio frequency (RF) based communication technologies. However, the capacity of these networks are limited by the availability of the RF spectrum. Free-Space-Optical (FSO) communication has the potential to deliver wireless communication links at optical-level speeds. Although it has the advantage of highspeed modulation, maintenance of line-of-sight (LOS) between transceivers during an on-going transmission is an important issue since FSO transmitters are highly directional. In this paper, we present a prototype implementation of such multi-transceiver electronically-steered communication structures. Our prototype uses a simple LOS detection and establishment protocol and assigns logical data streams to appropriate physical links. We show that by using multiple directional transceivers we can maintain optical wireless links with minimal disruptions that are caused by relative mobility of communicating nodes. Index Terms—Free-space-optics, FSO-MANET, mobile ad-hoc networks, spherical FSO structures I

2012 IEEE/ACM International Conference on Advances in Social Networks Analysis and Mining Six Degrees of Separation among US Researchers

Abstract—Funding from the government agencies has been the driving force for the research and educational institutions particularly in the United States. The government funds billions of dollars every year to lead research initiatives that will shape the future. In this paper, we analyze the funds distributed by the National Science Foundation (NSF), a major source of research funding in the States, to understand the collaboration patterns among researchers and institutions. Using complex network analysis, we interpret the collaboration patterns at researcher, institution and state levels by constructing the corresponding networks based on the number of grants collaborated. We further analyze the directorates to identify the differences in collaboration trends between disciplines. Keywords-Complex networks; Complex network analysis; Research funding networks; Six degrees of separation; NSF. I

Complex Network Analysis of Research Funding: A Case Study of NSF Grants

Abstract. Funding from the government agencies has been the driving force for the research and educational institutions particularly in the United States. The government funds billions of dollars every year to lead research initiatives that will shape the future. In this paper, we analyze the funds distributed by the United States National Science Foundation (NSF), a major source of academic research funding, to understand the collaboration patterns among researchers and institutions. Using complex network analysis, we interpret the collaboration patterns at researcher, institution, and state levels by constructing the corresponding networks based on the number of grants collaborated at different time frames. Additionally, we analyze these networks for small, medium, and large projects in order to observe collaboration at different funding levels. We further analyze the directorates to identify the differences in collaboration trends between disciplines. Sample networks can be found a