Predrag Spasojevic - US grants

Two rather different forms of wireless communications, one already established and showing dramatic growth and the other only on the horizon, have the potential to impact dramatically the nature of wireless communications in the home and workplace. One is the increasingly high-speed information link typified by 802.11x/802.15, first applied to broadband internet access but moving toward video and audio entertainment distribution as well, and the other is the sensor network, which can offer security, medical monitoring, and a variety of other important services. Unfortunately these usages are largely incompatible. High-rate applications will generally have adequate power sources for both transmission and processing purposes. Service interruptions have the potential to be annoying, but they are not, in general, threatening to health or safety. Sensor networks, on the other hand, involve messages which are generally short and infrequent, but which may have a high level of importance (consider intrusion or fire alarms, or child
monitors). Moreover, such sensors (and less critical environmental sensors) often require placement that is independent of permanent power sources, and thus require energy efficient operation.

Normally, such disparate requirements would suggest the separation of these applications into different frequency bands, but the emergence of unlicensed bands suggests that designers will not have the option of such comfortable isolation. It is therefore important to consider how such applications may coexist within the same frequency space. In particular, one may speculate that the potential for such coexistence would be enhanced within the private space that we find in homes and businesses - a volume in which radio transmission may be beneficially controlled by a single entity, and in which intra-system interference dominates. It is the premise of this proposal that solutions exist that can allow a wide variety of disparate applications to coexist efficiently within such a constrained, but controlled space. In particular, the researchers believe that coordinated usage characterized by multiple antennas and multiple appliances (MAMA) represents a new type of network, and offers significant opportunities to interwork such disparate systems efficiently.

To accommodate this mixed set of bit-rate and energy requirements, the researchers propose a comprehensive approach that encompasses link layer, MAC layer and cross-layer techniques. At the link layer, the research proposes:
-Flexible bandwidth modulation formats and spatial multiplexing and diversity. With the device transmission rate set by the application, the signaling bandwidth of a device is optimized versus a power level determined either by interference avoidance considerations or by energy constraints. We will argue that this leads to ultra-wideband (UWB) modulation characterized by low-signal-to-noise-ratio (low-SNR).
-Multiple transmit and receive antennas to be utilized in several modes: (1) in multi-input multi-output (MIMO) mode, the channel is harnessed to increase bit-rate; (2) in diversity mode, spatial diversity enhances power efficiency; (3) in beamforming mode, transmitter antennas direct energy away from other devices and networks. Consistent with UWB signaling, our research will focus on the low-SNR regime for MIMO systems.

Since link layer techniques cannot address all the complex requirements of MAMA networks, the researchers propose a cross-layer approach that takes into account the distributed, non-cooperative nature of the networks to achieve a more efficient use of the network power and bandwidth resources. The cross-layer approach consists of two components:
-Game theoretic methods: based on utility functions that depend on transmitted power and throughput, users
adapt their transmitters and receivers to maximize their individual utilities.
-"Thin" MAC layer protocols: for given physical layer transmitters and receivers, incremental redundancy hybrid ARQ provides non-collaborative rate adaptation and spectrum resource sharing.

The proposed space-frequency-cross-layer approach to designing wireless networks is distinctly different from conventional network design where data rate is maximized for a given bandwidth and power, generally ignoring intra- and inter-network interference. The juxtaposition of UWB, MIMO and cross-layer techniques in MAMA networks spans a multidimensional signal space that will create a rich set of research problems and network architectures.

Broader Impact: The work proposed here (if successful) will make possible the coexistence of new high-speed
wireless applications with emerging sensor networks at home and in the workplace. Although the discussion focuses on the home and work environments, it should be understood that the applications are more widespread - to hospitals, factories, and some robotic scenarios. MAMA networks also provide an exciting platform for the educational goals of the academic institutions, including activities for both undergraduates and graduate students.

The research institutions involved in this proposal are Princeton University, the New Jersey Institute of Technology, and Rutgers University, and The Wireless Communications Dept., Bell Labs, Lucent. The work will be done under the auspices of the N.J. Center for Wireless Telecommunications (NJCWT). The NJCWT is an inter-institutional research and educational organization sponsored and funded by the N.J. Commission on Science and Technology.

Proposal Number: 0626740
PI: Dipankar Raychaudhuri
Institution: Rutgers University (collaborative with Kansas U and CMU)

Proposal Number: 0626676
PI: Joe Evans
Institution: Kansas University (collaborative with Kansas U and CMU)

Proposal Number: 0626827
PI: Srini Seshan
Institution: CMU


Title: Collaborative NeTS-FIND: CogNet An Experimental Protocol Stack for Cognitive Radio Networks and Its Integration with the Future Internet

Project Abstract
This project has two major thrusts: the first is to identify broad architecture and protocol design approaches for cognitive radio networks at both local network and the global internetwork level. This architectural study is intended to lead to the design of control/management and data interfaces between cognitive radio nodes in a local network, and also between cognitive radio subnetworks and the global Internet. The second thrust is to apply these architectural and protocol design results to prototype an open-source cognitive radio protocol (the CogNet stack) and use it for experimental evaluations on emerging cognitive radio platforms. A number of architectural issues are examined as we try to identify an efficient and complete solution these include control and management protocols, support for collaborative PHY, dynamic spectrum coordination, flexible MAC layer protocols, ad hoc group formation and cross-layer adaptation.
The experimental component of this project aims to prototype an open-source Linux-based CogNet software protocol stack for use with emerging cognitive radio platforms (such as the GNU/USRP2 radio to be used as the baseline, the KU agile radio or the Lucent/WINLAB network-centric prototype), and make this software available for community research. The prototype software is validated in two steps: first in a wireless local-area radio network scenario with moderate numbers of cognitive radio nodes, and later as part of several end-to-end experiments using a wide-area network testbed such as PlanetLab (and GENI in the future).

This research considers physical layer security in wireless networks. It serves as a counterpoint to traditional methods of security, such as computationally secure crypto-systems, by considering security in the wireless medium itself. An important motivator for this research is the rapid proliferation of wireless communication devices, technologies, and applications, in general. The very nature of wireless networks exposes not only the risks and vulnerabilities that a malicious user can exploit and severely compromise the network but also information confidentiality concerns with respect to the in-network terminals. Although wireless technologies are becoming more and more secure, attackers are becoming smarter, and sole reliance on cryptographic keys in large distributed networks, for example, where terminals can be compromised is unsustainable from the security perspective. A direct consequence of this process is the need to, additionally, tackle security at the very basic physical layer level where the (unconditional) secrecy may be embodied within the information itself, and, also, adapted to the communication medium and network conditions. Furthermore, there is a need for a secure key distribution, a process which can be performed in perfect secrecy only using physical layer techniques, even when, henceforth, relying on conventional cryptographic techniques.
This research studies how, in secure wireless networks, the application delay requirement relative to the communication channel coherence time aspects the selection of signaling strategies and the achievable communication rates at a prescribed security level. In addition, perhaps surprisingly,
successful design of practical secure nested forward error correction codes and secure adaptive incremental error correction strategies applicable to wireless channels is virtually non-existent. Hence, this research focuses on practical coding-scheme designs as essential enabling tools.

There has been a remarkable increase in download of content provided by both traditional commercial suppliers as well those by amateurs. Users have very diverse computer equipment ranging from handheld devices to desktops, and downloaded items range from simple stock quotes to news stories to full movies. Such highly heterogeneous circumstances will be predominant in the networks of the near future. Current schemes for content download are inefficient at addressing the mentioned heterogeneity. The goal of this project is to obtain new and improved schemes that would result in better access to content for the users while improving the network utilization.

The research will focus on three coding techniques to attack the problem: rateless coding at the application layer, network coding at the network layer, and collaborative coding at the physical layer. Quantitative and qualitative limitations of network and rateless coding in heterogeneous environments will be studied to develop new practical coding schemes appropriate in such circumstances. Another research direction is to investigate and analyze mechanism to make networks more uniform using physical layer collaborative transmission schemes. An assessment will be made on how this process affects the performance of the higher layer coding schemes.

Broader Impact: The research, if successful, will improve the efficiency and availability of data in networks. This has the potential to benefit directly and indirectly the population at large. In addition, this collaborative research has the potential to obtain fundamental new insights at the interface of coding and information theory and combinatorial optimization. Several PhD students will be supported and trained in interdisciplinary areas and they would also obtain valuable industrial experience.

This project examines terrorist attacks by individuals who are outside of an organized terrorist group (lone actor attackers) that target public spaces like train stations (soft targets). Such attacks have increased 134 percent in the last 20 years, yet lone actor attack-defend models have not kept up with the trend. The project will develop new models based on game-theory to understand attack and defense strategies combined with immersive simulations that can validate the theoretical models. The project team has expertise in the fields of operations research, industrial and systems engineering, psychology, and electrical and computer engineering. Implementation of this work will contribute to the national priority to reduce risk to critical infrastructures and their users. Furthermore, it will provide advanced training in game-theoretic models for undergraduate and graduate students. This scientific research contribution thus supports NSF's mission to promote the progress of science and to advance our national welfare. In this case, the benefits will be insights to improve man-made emergency management, which can save lives in future events.

This project addresses the gaps in current understanding of lone actor attacks to guide the development of new innovative defense strategies. Specific research objectives are: 1) to develop and analyze game-theoretic models of attack and defense strategies, and protection algorithms, to be used by the defenders against lone actor attackers; 2) to design immersive simulations to provide descriptive agents' behavior and to validate the game-theoretic models using risk metrics such as expected damage, and the fraction of unsuccessful attacks. The intellectual merit of this research is the broadening of the knowledge base of game theory with incomplete information, multi-agent (attacker and defender) learning, and stochastic games of partially observable systems. This is transformational research since it brings a fresh vision into the risk management, immersive simulations, statistical learning and normative behavior studies for infrastructure security. The anticipated results of this research are both analytical and practical for emergency management agencies, transportation safety officers, and the police.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.