Anant Sahai - US grants

The next explosive growth in networks will come from connecting together billions of low cost, low power sensors, effectors, and smart devices. These will be communicating primarily through wireless means for reasons of mobility, ease of deployment, aesthetics, and cost. Even if such networks start out as special purpose local networks, people anticipate that they will come together in many ways. They will certainly be interconnected with each other through gateways to the broader wired Internet. The goal in this proposed project is to find the right architecture to enable Internet-like gains in the new context of wireless connectivity.

In order for wireless networks to support a wide range of applications and be suitable for mass deployment, they will need to posses the following characteristics: (1) negligible interference that allows peaceful co-existence with other independent wireless systems operating over the shared spectrum; (2) managing interference between nodes to efficiently and fairly share bandwidth; (3) dynamic and energy efficient routing and packet relaying algorithms that support mobility of network nodes; (4) scalability to support a large number of heterogeneous devices and links; (5) precise positioning capabilities to provide location information for the devices for which this is important; (6) robust and energy efficient network protocols that tolerate failure of some network nodes; (7) extremely low power wireless transceivers to ensure longevity for the energy-limited nodes; and (8) small and low cost wireless transceivers to enable widespread deployment.

This proposal is to study the above in the context of ultra-wideband (UWB) wireless signaling and multi-hop routing. Research is intended to achieve multiple objectives, Develop
(1) Efficient algorithms to determine the fundamental tradeoffs involved in tracking the positions of devices within a network of heterogeneous nodes;
(2) Robust and efficient protocols for routing digital communications within such networks and explore the fundamental capacity limits of such systems;
(3) Distributed signal processing algorithms that are network-energy and position aware to take advantage of correlations at the application layer to reduce resource consumption throughout the network hierarchy;
(4) Extremely low power, highly integrated single-chip CMOS architecture to UWB transceivers, and (5) An integrated test environment by combining an in-house FPGA-based testbed (as the digital back-end) with UWB analog front-end from AetherWire Inc. This will ultimately have approximately 30 UWB nodes from Aether Wire Inc. to test and therefore further discover issues involved with such networks.

Many of the innovative recent wireless devices rely on the unlicensed spectrum, spurred by its openness to new uses and users. At the same time, vast amounts of spectrum are still exclusively licensed to services with sparse demand and to standards that use antiquated technologies. The current way of sharing the
limited unlicensed spectrum that we do have is also far from perfect: devices suffer from very limited range even when there are no interference problems, and severe performance degradation when their local spectrum is shared by users from heterogeneous systems.

We look at spectrum management through the lens of the traditional 3 R's of resource use: Reduce, Reuse and Recycle. While Reduce has received by far the most attention from the engineering community, research in Recycle and Reuse is at a much more primitive state. But it is progress in the latter two areas that will be critical for the open and efficient sharing of the spectrum as a whole. Spectrum Recycling refers to fostering sharing and improving overall spectral efficiency while maintaining backward-compatibility with users of
legacy systems like analog broadcast and cellular standards. Spectrum Reuse refers to the collaborative coexistence of multiple wireless systems, using limited interaction to share the spectrum fairly and
efficiently. The proposed research takes a broad, systematic and inter-disciplinary approach to the fundamentals of these two problem areas, combining ideas from physical layer wireless communications,
multiuser information theory and distributed coding, resource allocation and game theoretic analysis.

Information theory is the strategic theory of communication: providing architectural guidance and fundamental bounds. For communication, there are three core quality of service parameters: probability of error, rate, and end-to-end delay. Shannon's seminal capacity theorems establish bounds on rate as the tolerated probability of error goes to zero while the acceptable end-to-end delay goes to infinity. However, for many applications like telemedicine, remote control (e.g. fly-by-wireless in UAVs), and even video-conferencing, short delays are also critical. Unfortunately, it turns out that the classical block-code oriented approaches to information theory are misleading regarding the tradeoffs involving end-to-end delay, especially when feedback is involved. This research aims to remedy that situation and thereby get a deeper understanding of the nature of information flows and their communication requirements. Having these fundamental architectural results will help guide not only the design of next generation communication systems, but is also critical for the setting of regulatory policy governing wireless spectrum since both interactive and non-interactive applications must coexist efficiently in the wireless context.

This research makes three core contributions: (a) Characterizing the tradeoff between delay and probability of error in communication systems with and without feedback in the context of both soft and hard latency constraints by leveraging our new hallucination bound and uncertainty focusing bound techniques, (b) Understanding how to exploit noisy and limited feedback in the above contexts, (c) Deepening our understanding of information flows in the context of interactive control and distributed estimation by taking a new approach to source-channel separation theorems based on the theoretical CS model of showing problem-level equivalences through explicit reductions of one communication problem to another.

Power consumption is an increasingly important issue across society.
For communication, as the ranges of links in wireless networks
continue to shrink, the power consumed in the encoding and decoding
becomes a decidedly nontrivial factor in the choice of system
architecture. This is particularly important in settings such as
wireless patient monitoring, personal area networks, sensor networks,
etc. Shannon's classical information theory only established the
tradeoff between rate and transmit power as the probability of error
goes to zero and the block-length goes to infinity. This research is
about giving new conceptual tools for reasoning about the power
consumption in encoding and decoding as well. The core idea is that in
the age of billion transistor chips, the proper metric for complexity
is the power consumed by the implementation.

Just as simplified channel models have enabled sophisticated analysis
that has revealed deep insights into error correction and transmit
power, this research develops simplified implementation models that
are amenable to analysis. This reveals the fundamental tradeoffs
underlying the interplay between transmission and processing
powers. Crucially, the models developed are compatible with modern
approaches to iterative and "turbo" decoding by massively parallel
ASICs, while also not being limited to just the currently known
families of sparse-graph codes. By developing a unified mathematical
framework, this research allows us to understand the total power cost
of meeting performance objectives like high rate, low distortion, low
delay and low probability of error. This in turn leads to an
understanding of how to better engineer wireless systems as a whole:
opening up avenues for collaboration between circuit designers,
communication theorists, and networking researchers working at higher
layers.

The objective of this research is to develop the theoretical
foundations for understanding implicit and explicit
communication within cyber-physical systems. The approach is
two-fold: (a) developing new information-theoretic tools to
reveal the essential nature of implicit communication in a
manner analogous to (and compatible with) classical network
information theory; (b) viewing the wireless ecosystem itself
as a cyber-physical system in which spectrum is the physical
substrate that is manipulated by heterogeneous interacting
cyber-systems that must be certified to meet safety and
performance objectives.

The intellectual merit of this project comes from the
transformative technical approaches being developed. The key to
understanding implicit communication is a conceptual
breakthrough in attacking the unsolved 40-year-old Witsenhausen
counterexample by using an approximate-optimality paradigm
combined with new ideas from sphere-packing and cognitive radio
channels. These techniques open up radically new mathematical
avenues to attack distributed-control problems that have long
been considered fundamentally intractable. They guide the
development of nonlinear control strategies that are provably
orders-of-magnitude better than the best linear strategies. The
keys to understanding explicit communication in cyber-physical
systems are new approaches to active learning, detection, and
estimation in distributed environments that combine worst-case
and probabilistic elements.

Beyond the many diverse applications (the Internet, the smart
grid, intelligent transportation, etc.) of heterogeneous
cyber-physical systems themselves, this research reaches out to
wireless policy: allowing the principled formulation of
government regulations for next-generation networks. Graduate
students (including female ones) and postdoctoral scholars will
be trained and research results incorporated into both the
undergraduate and graduate curricula.

This project will develop the key technologies needed for interactive wireless applications operating in shared spectrum. Sharing is the new spectrum paradigm, and interactive applications are the most demanding in terms of the quality-of-service they require. Thus, they are the perfect vehicle to push the frontiers of our understanding of sharing. This project will explore new high-reliability coding techniques to protect interactive applications while meeting tight latency constraints and explore how to coexist with neighboring disparate systems through explicit and implicit signaling. The project will contribute the fundamental understanding required to define the correct regulatory structure for spectrum sharing.

Broadly speaking, the interactive applications that this project will study are the key to the next growth phase in commercial wireless - as machines need to interact with each other to improve the performance of real-world systems. Because industrial control is a critical use case, this project can help invigorate the agile manufacturing sector of the economy. Efficiently shared spectrum is much more economical than exclusive-use spectrum and hence could help innovative high-skill manufacturing where the United States has an advantage over low-wage countries. While developing this technology, the project will train students in a way that encourages cross-fertilization of ideas between wireless communication, circuit implementation, control theory, and coding theory. These ideas will be brought into the classroom, including our new M.Eng. courses aimed at educating innovative technical leaders. The project will also broaden participation in the technical workforce by mentoring students from underrepresented groups.

This project aims to explore the fundamental architectural considerations involved in designing/operating wireless networks for fast Machine to Machine (M2M) communication. Current ideas in the M2M space are fundamentally being driven by ``slow M2M'' applications like electricity-monitoring in the Smart Grid with their intellectual foundations coming from the now maturing field of wireless sensor networks. This project advances the field by addressing the high-performance case of industrial automation with tight real-time operating requirements and the demand for very high reliability. To do this, the project will be leveraging new mathematical and conceptual tools developed to understand decentralized control systems as well as modern approaches to doing multiterminal wireless networking that better exploit the full potential of the wireless medium. The techniques used in this project will span networking, control theory, information theory, wireless modeling, signal processing, and circuit implementation.

Broadly speaking, the kind of "Fast M2M" technology that this project is developing has the potential to help invigorate the agile manufacturing sector of the economy. Easily reconfigurable wireless interconnection in the industrial setting could help high-skill manufacturing where the United States has a potential advantage over low-wage countries. In the course of developing this technology, the project will train students and postdocs in a way that encourages cross-fertilization of ideas between wireless communication, networking, circuit implementation, control theory, and information theory. These ideas will also be incorporated into courses, including new M.Eng. courses aimed at educating technical leaders for industry. This is the kind of non-siloed education that is essential for innovation in the future. The project will also broaden participation in the technical workforce by mentoring female graduate students.

This project will study how to engineer modern spectrum sharing systems. Wireless spectrum is now recognized as a key national resource that has to be managed appropriately to support innovation and economic growth. Traditional wireless rules were written by a combination of lawyers and engineers in legal English, and read/interpreted by lawyers and engineers. The emerging revolution in wireless regulation is that the core rules will be embedded in automated Spectrum Access Systems (SASs) that are implemented in a combination of hardware, software, and interaction protocols. Moreover, the SASs will support diverse wireless systems ranging from legacy federal users to traditional cellular carriers to emerging new innovative wireless systems. The ideas developed in this project will be disseminated to industry as well as brought into the classroom, including our new Masters of Engineering courses aimed at educating innovative technical leaders. The project will also broaden participation in the technical workforce by mentoring students from underrepresented groups.

At its technical core, this project will help create a modern theory of how to make scalable and robust SASs by bringing together a combination of software engineering, mathematical wireless theory, as well as an understanding of the policy tradeoffs that we want to support. The key realization is that making scalable systems is about robustly approximating what we want in a safe manner while supporting flexibility. Ideas from virtualization, software-defined-networking, and cloud computing will play an important role. In addition to getting a handle on what the overall architecture should be of our SAS-enabled wireless future, the project will also take insights and embody them into easy-to-use prototype tools that can be adapted by federal regulators and spectrum managers to explore and navigate the design tradeoffs.

This award is a planning grant for the Spectrum Innovation Initiative: National Center for Wireless Spectrum Research (SII-Center). The focus of a spectrum research SII-Center goes beyond 5G, IoT, and other existing or forthcoming systems and technologies to chart out a trajectory to ensure United States leadership in future wireless technologies, systems, and applications in science and engineering through the efficient use and sharing of the radio spectrum. The radio spectrum should be utilized to the greatest public benefit at national and global scales. Spectrum shortages, both real and perceived, are leading to conflicts between existing users and anticipated new uses ? some of which were not imagined when existing spectrum allocations were made decades ago. Many stakeholders seek to protect and advance their interests, with aspects of these interests overlapping and conflicting with each other. Hence, the public debate over the optimal model for managing spectrum is a complex interplay of technology, economics, law and regulation, policy, and the history of past successes and failures.

This project is aimed at the development of a comprehensive plan for an SII-Center which would help maintain and extend US leadership in future wireless technologies, systems, and applications in science and engineering through the efficient use and sharing of radio spectrum. The project team is led by the University of Notre Dame, with partners from Northwestern University, Clemson University, University of California, Berkeley, University of California, Los Angeles, New York University, and Stanford University. The team has an extensive record of successful research, as well as significant and relevant industry and implementation experience. The project seeks to develop plans for a multi-disciplinary center that emphasizes instrumentation of the radio spectrum; collecting and sharing accurate regulatory, usage, and economic data; and developing data-rich system designs and regulatory policies for more efficient spectrum utilization.

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.