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Mobile
ad-hoc communication is starting to find real-world applications beyond its
military origins, in areas such as vehicular communications and delay
tolerant networking. As the RF spectrum is getting saturated by recent
advances in wireless communications, enabling optical spectrum in wireless
communications is the needed revolution for ultra-high-speed mobile ad-hoc
networks (MANETs) of the future. This project
explores the potential for free-space-optics (FSO) in the context of
very-high-speed mobile ad-hoc and opportunistic networking.
This
project introduces basic building blocks for MANETs
using FSO and prototypes multi-hop high-capacity FSO building blocks and
protocols operating under high mobility. 3-d spherical structures covered
with inexpensive FSO transceivers (e.g., VCSEL and photo-detector pair) solve
issues relevant to mobility and line-of-sight (LOS) management via
availability of several transceivers per node. Such structures facilitate
electronic LOS tracking (i.e., “electronic steering”) methods instead of
traditional mechanical steering techniques. The project also investigates
reliability protocols as management of logical datastreams
through multi-interface FSO structures pose a major challenge. By abstracting
FSO directionality and LOS characteristics, the project explores issues
relating to routing and localization, and develops layer 3 protocols and
FSO-MANET demonstration in a lab setting. Results of this research can
revolutionize the MANET technologies by enabling optical spectrum. FSO has
been used at high-altitude communications, and this project enables FSO
communications at lower-altitudes and in ad-hoc settings. This research will
provide a new application for solid-state lighting technology due to
potential integration of illumination and communication functions.
- M. Yuksel, J. Akella, S. Kalyanaraman, and P. Dutta,
Free-Space-Optical Mobile Ad-Hoc Networks: Auto-Configurable
Building Blocks, To appear in ACM/Springer Wireless Networks,
2009.
Abstract: Existence of
line of sight (LOS) and alignment between the communicating antennas is
one of the key requirements for free-space-optical (FSO) communication.
To ensure uninterrupted data flow, auto-aligning transmitter and
receiver modules are necessary. We propose a new FSO node design that
uses spherical surfaces covered with transmitter and receiver modules
for maintaining optical links even when nodes are in relative motion.
The spherical FSO node provides angular diversity in 3-dimensions, and
hence provides an LOS at any orientation as long as there are no
obstacles in between the communicating nodes. For proof-of-concept, we
designed and tested an auto-configurable circuit, integrated with light
sources and detectors placed on spherical surfaces. We demonstrated
communication between a stationary and a mobile node using these initial
prototypes of such FSO structures. We also performed the necessary
theoretical analysis to demonstrate scalability of our FSO node designs
to longer distances as well as feasibility of denser packaging of
transceivers on such nodes.
- B. Cheng, M. Yuksel, and S. Kalyanaraman, Orthogonal Rendezvous Routing
Protocol for Wireless Mesh Networks, To appear in IEEE/ACM Transactions on Networking, June 2009.
Abstract: Routing in
multi-hop wireless networks involves the indirection from a persistent
name (or ID) to a locator.
Concepts such as coordinate space embedding help reduce the number and dynamism
complexity of bindings and state needed for this indirection. Routing
protocols which do not use such concepts often tend to flood packets
during route discovery or dissemination, and hence have limited
scalability. In this paper, we introduce Orthogonal Rendezvous Routing
Protocol (ORRP) for meshed wireless networks. ORRP is a
lightweight-but-scalable routing protocol utilizing directional
communications (such as directional antennas or free-space-optical
transceivers) to relax information requirements such as coordinate space
embedding and node localization. The ORRP source and ORRP destination
send route discovery and route dissemination packets respectively in
locally-chosen orthogonal directions. Connectivity happens when these
paths intersect (i.e., rendezvous). We show that ORRP achieves
connectivity with high probability even in sparse networks with voids.
ORRP scales well without imposing DHT-like graph structures (e.g.,
trees, rings, torus etc.). The total state information required is O(N3/2) for N-node networks, and the state
is uniformly distributed. ORRP does not resort to flooding either in
route discovery or dissemination. The price paid by ORRP is suboptimality in terms of path stretch compared to
the shortest path; however we characterize the average penalty and find
that it is not severe.
- B. Cheng, M. Yuksel, and S. Kalyanaraman,
Using Directionality in Mobile Routing, (short paper) To appear in Proceedings
of IEEE International Conference on Mobile Ad-hoc and Sensor Systems
(MASS), Atlanta,
GA, September 2008.
Abstract:
- M. Bilgi and M. Yuksel, Multi-Element
Free-Space-Optical Spherical Structures with Intermittent Connectivity
Patterns, Proceedings of
IEEE INFOCOM Student Workshop, Phoenix, AZ, April 2008.
Abstract: Due to its high
bandwidth spectrum, Free-Space-Optical (FSO) communication has the
potential to bridge the capacity gap between backbone fiber links and
mobile ad-hoc links, especially in the last-mile. Though FSO can solve
the wireless capacity problem, it brings new challenges, like frequent
disruption of physical link (intermittent connectivity) and the line of
sight (LOS) requirements. In this paper, we study a spherical FSO
structure as a basic building block and examine the effects of such FSO
structures to upper layers, especially to TCP behavior for stationary
and mobile nodes.
- B. Cheng, M. Yuksel, and S. Kalyanaraman,
Rendezvous-based
Directional Routing: A Performance Analysis, Proceedings of IEEE International
Conference on Broadband Communications, Networks, and Systems
(BROADNETS), pages 271-279, Raleigh, NC, September 2007. (invited paper) (slides)
Abstract: Routing in wireless ad-hoc networks have had to grapple
with the twin requirements of connectivity and scalability. Recently,
[1] has attempted to mitigate this issue by using directional communication
methods to find intersections between source-rendezvous and
rendezvous-destination paths, providing effective routing in
unstructured, flat networks. [1] showed that by “drawing” two lines
orthogonal to each other at each node, it is possible to provide over
98% connectivity while maintaining only order O(N^(3/2)) states. It is
interesting, however to investigate what happens when additional lines
are “drawn” and how that affects connectivity, path length, state
complexity, control packet overhead, and aggregate throughput. In this
paper, we examine how transmitting along one, two, three, and four lines
affects routing and provide both analytical bounds for connectivity as
well as packetized simulations on how these methods stack up in a more
realistic environment. We show that by sending packets out in more
directions, increased connectivity and smaller average path length
results only up to a point. The trade-off, however, is added state
information maintained at each node. We also show that in mobile
environments, adding additional lines increases the chances for
successful packet delivery only marginally.
- Latest version of our FSO
package for ns-2 is available from here.
This
project is supported by National Science Foundation awards 0721452
and 0721612.
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