CNRG research is focused on the design and analysis of architectures and protocols for communication networks including wireless, satellite and optical networks. Our primary goal is the design of network architectures that are cost effective, scalable, and meet emerging needs for high data-rate and reliable communications. An important aspect of CNRG research is the development of architectures and algorithms that are optimized across multiple layers of the protocol stack. To that end, CNRG research crosses disciplinary boundaries by combining techniques from network optimization, machine learning, queueing theory, graph theory, network protocols and algorithms, hardware design and physical layer communications.
Increasingly we have come to depend on wireless networks for internet access. Unfortunately, existing wireless networks are almost exclusively confined to single hop access, as provided by cellular telephony or wireless LANs. Multi-hop wireless networks can be deployed; however, current protocols typically result in extremely poor performance for even moderate sized networks. Our research in the area of wireless networks attempts to bridge the gap between wireless networks and the wired internet, by addressing issues in the control and management of wireless networks, including mobile ad hoc networks, sensor networks, and wireless mesh networks. Our goal is to develop develop architectures, protocols, and control algorithms for providing efficient and reliable wireless networking. Our projects include fundamental aspects of network control, robust wireless network design, as well as the design of practical practical network control algorithms for routing, scheduling and flow control.
Effective Control of Wireless Networks
Wireless Mesh Networks (WMNs) have emerged as a solution for providing last-mile Internet access. By exploiting advanced communication technologies such as adaptive modulation and coding, MIMO, OFDM, and Software Radio, WMNs can achieve access rates that are comparable to those achieved by wired access technologies. However, hindering their success is our relative lack of understanding of how to effectively control wireless networks; especially in the context of advanced physical layer technologies, realistic models for channel interference, and distributed operation. The goal of this project is to develop effective and practical network control algorithms that make efficient use of wireless resources through joint topology adaptation, network layer routing, MAC layer scheduling, and physical layer power, channel, and rate control.
A Migration Approach to Optimal Network Control
Our new NSF project introduces a novel architectural paradigm for wireless network control, whereby control algorithms are designed to operate in networks with both new and legacy nodes. This new paradigm allows optimal control algorithms to be incrementally deployed alongside existing schemes, thus providing a migration path for new control algorithms, and the promise of dramatic improvement in network performance. -more-
Toward Reducing Control Overhead in Wireless Networks
Network control mechanisms, such as scheduling, routing, and flow control, ensure effective data transport in a communication network, but also require the exchange of network state information, such as channel conditions and queue-length information, which amounts to “control overhead”. The project investigates the tradeoffs between the rate of sending such control information, and the ability to effectively control the network in terms of performance metrics such as throughput, stability, delay and network utility. The project takes a two-pronged approach: First, a rate-distortion framework is being developed for understanding the impact of degraded network state information on network performance. Second, mechanisms are being developed for reducing the amount of control overhead and the impact of these mechanisms on network performance is being investigated. The project develops a fundamental understanding of the requirements for protocol overhead, which will lead to more efficient network control policies, with reduced overheads.-more-
Protection and restoration in wireless mesh networks
Most previous work on routing in ad hoc networks has focused almost entirely on the problem of route discovery. Little, if any, attention has been paid to the problem of reliable communications in a mobile network. In a network this is often accomplished by providing "backup" routes. However, recovery using backup routes in ad hoc networks is very different from a static fiber networks due to the high degree of mobility that results in rapid topology changes. This project will develop efficient recovery mechanisms in a mobile ad hoc environment. -more-
Enhancing Access to Radio Spectrum for Real-Time Monitoring and Control
Future trends toward intelligent infrastructure systems, such as the smart grid, intelligent transportation systems, unmanned aircraft systems, and environmental monitoring systems, give rise to the need for reliable communications for real-time monitoring and control operations. Wireless networking is a promising technology for meeting these requirements; however, existing spectrum allocations are not likely to suffice. This project explores the use of shared spectrum for meeting the communication requirements of future intelligent infrastructure systems. A key challenge in this context is how to meet the reliability, latency and bandwidth requirements of monitoring and control operations using intermittently available shared spectrum. This project addresses these challenges by drawing upon a variety of disciplines including wireless networking, cyber-physical systems, optimization and economics. Specific questions being addressed include how to model the service requirements of emerging monitoring and control applications, how to pool various bands of spectrum to enable the design of robust monitoring and control networks, and how to structure spectrum markets to enable these applications to acquire the needed bandwidth.-more-
Over the past decade the growth in the use and capabilities of communication networks has transformed the way we live and work. As we progress further into the information age, the reliance on networking will increase. With the expected explosive growth in data traffic, networks will be strained in terms of both transport and processing requirements. Wavelength Division Multiplexing (WDM) is emerging as a dominant technology for use in backbone and access networks. With WDM, the capacity of a fiber is significantly increased by allowing simultaneous transmission on multiple wavelengths (channels), each operating at the maximum electronic rate. Systems with between 40 and 80 wavelengths are presently being deployed for point-to-point transmission. With tens of wavelengths per fiber and transmission rates of up to 10 Gbps per wavelength, capacities that approach a Tera-bit per second can be achieved. Our research in the area of optical networks include survivable network design, access network architecture, and mechanisms for optical bypass of the electronic layers.
Mechanisms for optical bypass
While WDM systems are likely to meet future transport demands, electronically processing all of the traffic at network nodes will present a significant bottleneck. Fortunately, it is not necessary to electronically process all traffic entering and leaving each node. For example, much of the traffic passing through a node is neither sourced at that node nor destined to that node. To reduce the amount of traffic that must be electronically processed at intermediate nodes, future WDM systems will employ WDM Add/Drop multiplexers (WADMs) and cross-connects, that allow each wavelength to either be dropped and electronically processed at the node or to optically bypass the node's electronics. Our research in this area is focused on developing mechanisms for providing optical bypass to the electronic layer thereby reducing the size and cost of electronic switches and routers in the network. These mechanisms include traffic grooming of low rate streams, logical topology reconfiguration, and optical flow switching.
Modern communication networks are constructed using a layered approach, with one or more electronic layers (e.g., IP, ATM, SONET) built on top of an optical fiber network. This multitude of layers is used in order to simplify network design and operations and to enable efficient sharing of network resources. However, this layering also gives rise to certain inefficiencies and interoperability issues. Networks often rely on the electronic layers to provide most protection and restoration services. However, in a layered network, the protection mechanisms provided at the electronic layer may not be robust in the face of failures in the underlying optical layer. For example, SONET networks typically provide protection against single link failures using a ring network architecture, and protection in general “mesh” networks (e.g., ATM, WDM) is typically provided using disjoint paths. However, even electronic topologies that are designed to be tolerant of single link failures, once they are embedded on the physical (e.g., fiber) topology, may no longer be survivable to single physical (fiber) link failures. This is because the failure of a single fiber link can lead to the failure of multiple links in the electronic topology, which may subsequently leave the electronic topology disconnected. Thus, network survivability mechanisms often cannot provide their claimed level of protection and restoration, when embedded on a physical topology. The goal of this project is to develop a fundamental theory for understanding cross-layer survivability, and mechanisms for providing survivability in layered networks. -more-
While the field of communications and networks is rapidly advancing due to the increased popularity of the Internet, space communication systems are at a much more immature state of development. Certain attributes of the satellite channels make techniques previously developed for terrestrial networks inefficient or entirely unsuitable. For example, satellite systems often have longer propagation delays and higher bit error rates than their terrestrial counterparts; and the open air interface for satellite channels lends itself to the concept of dynamic sharing of resources. This gives rise to a range of problems including: Resource allocation (such as power and bandwidth), media access control, system management, dynamic routing in the presence of changing topologies and fluctuating loads, and interconnection with terrestrial and wireless networks. Of particular interest is the design of architectures and protocols for heterogeneous networks that include both space and terrestrial segments, which gives rise to a range of issues including: Space/ground network architectures, the design of efficient end-to-end protocols, quality of service assurance and the design of efficient interfaces between the ground and space portions of the network.