Scalability Of Mobile, Base-Station-Oriented RF Networks

The performance and scalability of mobile, base-station-oriented wireless networks with respect to routing and mobility models is addressed in this paper. Using systems-oriented, large-scale discrete event simulation, both performance scalability and complexity scalability are analyzed. Performance scalability addresses the effect of network size on system performance. Complexity scalability, in this case, consists of communication complexity (i.e., amount of control information exchanged to create and maintain network connectivity). Results confirmed the scalability of base-station-oriented networks using the routing, and mobility models, using over 2,000 fully dynamic hosts and routers.

Reconfigurable Optical Wireless Sensor Networks

Optical wireless networks are emerging as a viable, cost effective technology for rapidly deployable broadband sensor communication (SC) infrastructures. The use of directional, narrow beam, optical wireless links provides great promise for secure, extremely high data rate communication between fixed or mobile nodes, very suitable for sensor networks in civil and military contexts. The main challenge is to maintain the quality of such networks, as changing atmospheric and platform conditions critically affect their performance. Topology control emerges as a technique for achieving survivable optical wireless networking based on dynamic and autonomous topology reconfiguration. Topology control is presented as a multilayer approach to provide improved network performance in adverse conditions. The topology control process involves tracking and acquisition of nodes, assessment of link-state information, collection and distribution of topology data, and the algorithmic solution of an optimal topology. This paper focuses on the analysis and implementation of algorithms and heuristics for selecting the best possible topology in order to optimize a given performance objective while satisfying connectivity constraints. The work done at the physical layer is based on link cost information. A cost measure is defined in terms of bit-error-rate and the heuristics developed seek to form a bi-connected topology which minimizes total network cost. At the network layer the key parameter is the traffic matrix. The heuristics developed try to connect the nodes in order to minimize congestion, flow-rate or end-to-end delay. Results include heuristics performance and scalability measurements.
Keywords: optical wireless communication, dynamic networks, topology control, autonomous reconfiguration, graph connectivity, spanning tree, heuristic.

Studies of Free Space Optical Links through Simulated Boundary Layer and Long-Path Turbulence

There is recent interest from the US Department of Defense in free space optical communication networks involving aircraft flying at various altitudes. The optical links between these aircraft may be as long as 100km, and involve communication between network nodes that are moving at sub-sonic speeds. An unresolved issue for links of this kind between pairs of aircraft is the effect of boundary layer turbulence near each aircraft, as well as along the atmospheric path between them. The deployment of optical wireless links in several different scenarios will be described. These include links near to the ground for which the turbulence parameter Cn2 varies along the path between transmitter (TX) and receiver (RX), high altitude links between aircraft, and ground to aircraft links. The last two of these may involve boundary layer turbulence near the aircraft node where the turbulence is localized either at the TX or at the RX. Some of the theoretical approaches to examining these situations will be described, as well as an ongoing program of research to examine these situations experimentally. Ways to mitigate the effects of node motion, and scintillation at the RX will be discussed, including the use of non-imaging concentrators at the RX.
Key Words: Turbulence variation along a path, optical wireless, atmospheric turbulence

Studies of Pointing, Acquisition, and Tracking of Agile Optical Wireless Transceivers for Free Space Op tical Communication Networks

Free space, dynamic, optical wireless communications will require topology control for optimization of network performance. Such networks may need to be configured for bi- or multiple-connectedness, reliability and quality-of-service. Topology control involves the introduction of new links and/or nodes into the network to achieve such performance objectives through autonomous reconfiguration as well as precise pointing, acquisition, tracking, and steering of laser beams. Reconfiguration may be required because of link degradation resulting from obscuration or node loss. As a result, the optical transceivers may need to be re-directed to new or existing nodes within the network and tracked on moving nodes. The redirection of transceivers may require operation over a whole sphere, so that small-angle beam steering techniques cannot be applied. In this context, we are studying the performance of optical wireless links using lightweight, bi-static transceivers mounted on high-performance stepping motor driven stages. These motors provide an angular resolution of 0.00072 degree at up to 80,000 steps per second. This paper focuses on the performance characteristics of these agile transceivers for pointing, acquisition, and tracking (PAT), including the influence of acceleration/deceleration time, motor angular speed, and angular re-adjustment, on latency and packet loss in small free space optical (FSO) wireless test networks.
Keywords: Pointing, acquisition, and tracking; agile transceivers; optical wireless

Performance and Scalability of Wireless Base-Station-Oriented Networks

This paper focuses on the performance and scalability of mobile, base-station-oriented wireless networks, which have been the subject of research and development projects sponsored by the Defense Advanced Research Projects Agency. The background and rationale for such networks is presented as well as performance and scalability analyses of their routing, mobility, and quality of service models. Using systems-oriented, large-scale discrete event simulation, both performance scalability and complexity scalability are analyzed. Performance scalability addresses the effect of network size on system performance. Complexity scalability, in this case, consists of communication complexity (i.e., amount of control information exchanged to create and maintain network connectivity). Results confirmed that the scalability of base station oriented networks using the routing, and mobility model, and the quality of service models enhanced performance, using over 2,000 fully dynamic hosts and routers.

Flexible Optical High Data Rate Wireless Links And Networks Flexible Optical High Data Rate Wireless Links And Networks

The worldwide demand for broadband communications is being met in many places by installed single-mode fiber networks. However, there is still a significant ¿first-mile¿ problem, which seriously limits the availability of broadband Internet access. Free-space optical wireless communication has emerged as a viable technology for bridging gaps in existing high data rate communication networks, and as a temporary backbone for rapidly deployable mobile wireless communication infrastructure. In this paper we describe research designed to improve the performance of such networks along terrestrial paths including the effects of atmospheric turbulence, obscuration, transmitter and receiver design, and topology control.