James Franklin Buckwalter - US grants

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).

The objective of this research is to demonstrate energy efficient, mixed-signal silicon transceiver circuitry using time-domain signal modulation for high-speed serial links. The approach is to employ plesiochronous double-edge pulse-width modulation to achieve higher data rates than traditional pulse amplitude modulation over a given interconnect. A 90-nanometer silicon mixed-signal transceiver circuit will be invented and fabricated to verify the channel and source coding approach.

Intellectual Merit: This research investigates optimal signaling subject to interconnect bandwidth and peak power constraints imposed by highly scaled silicon integrated circuit processes. Performance improvements will be achieved by combining both advances in CMOS circuit design and communication theory to address the physical constraints of deep submicron CMOS and the adverse effects of the transmission channel.

Broader Impacts: This project addresses energy savings in server and computer communication. It is estimated that more than one gigaWatt of power is required worldwide to power the high-speed serial links that exchange data between microprocessors and memory and enable the benefits of networking and computing for work, entertainment, and social interaction. The outcomes of this research advance a global technology concern, and coincident educational efforts will teach and train students about the interaction of energy and technology and how circuit design addresses the need for low power computation and communication. The project will train a Ph.D. student and includes outreach activities to middle and high school students through active mentorship.

The objective of this research is to demonstrate a millimeter-wave network analysis system that operates at frequencies between 100 and 300 GHz where existing test and measurement solutions are difficult and costly. The approach is to develop wideband, reconfigurable high-frequency circuits that employ a recently discovered traveling wave circuit technique called constructive wave amplification. By introducing localized shunt feedback networks along a single transmission line, traveling wave propagation may be altered through changes to the shunt feedback network. Waves traveling in either direction may be amplified over a wide range of frequencies.

The intellectual merit of this project includes the invention of reconfigurable, millimeter-wave circuits that advance both the state-of-the-art for millimeter-wave circuit design as well as test capabilities. Constructive wave amplification is a transformative aspect to this research because it relaxes known high-frequency transistor limitations. The research effort includes the theoretical analysis of the proposed approaches as well as experimental verification using silicon integrated circuit processes.

The broader impacts of this project include the development of enabling technologies for new scientific, medical, and industrial applications at millimeter-wave frequencies. The proposed monolithic integration of high-frequency circuitry could lead to substantially reduced cost of network analysis. The integrated educational plan includes incorporation of principles of millimeter-wave circuit design and measurement into undergraduate and graduate level courses. To bring the research outcomes to a broader audience, the principal investigator will create a series of instructional videos available online that introduce students at the high-school, undergraduate, and graduate levels to radio frequency circuit design, test, and measurement.

The objective of this research is to develop a state-of-the-art photonic chip-scale probing solution for integrated Si-photonics testing and to enable new multidisciplinary collaborative projects in nano-photonics and opto-electronics. The approach exploits a universal electronic-photonic probing station that integrates electrical, optical far-field, and optical near-field probes for electrical and optical interfacing to integrated circuits and to individual elements within such circuits, together with a full set of external optical and electronic instrumentation to provide an affordable, zero-capital-investment testing capability for Research and Development by academic, industry and government laboratories.

The intellectual merit of this versatile and user friendly Si-Photonics testing instrument includes basic research to identify new phenomena, inventing new photonic technology and creating new applications, as well as providing tremendous benefit to small businesses, various research institutions and government laboratories in their product development efforts. Moreover, it can serve as a testbed for development and reduction to practice of new approaches for efficiently probing and testing Si-photonic chips, gradually evolving to become industry standards.

The broader impact of the instrument spans multiple fields, including information systems, high speed electronics and photonics, and future computer science and engineering to create wealth for 21st century economy by advancing integration of nanoscale photonic, electronic and biomedical science and technology. It will provide service to industry in Southern California and play a significant role in the education and development of human resources in science and engineering at the graduate and undergraduate levels helping to train future engineers.

Cognitive radio techniques will be developed that enable rapid, wideband spectrum sensing in the presence of strong interference. Cognitive radios must detect available spectrum quickly in real time with high-probability of success, which requires extremely high dynamic range in the presence of powerful interference signals. Furthermore, future cognitive radio will operate over multiple frequency bands spread out over a wide frequency range. This compounds the challenges to the receiver design since all filtering must be capable of tuning over wide frequency ranges. Finally, the radio must agilely hop among frequency bands. The time required to detect the power in any channel is an overhead that limits the network throughput.

Most prior cognitive radio research applies digital baseband algorithms to conventional RF and analog radio circuitry, which is not designed to address the spectrum sensing application. This limits the achievable spectrum sensing bandwidth and agility and results in high power consumption for the RF, analog, and digital signal processing blocks. This work is fundamentally different in that it will customize the entire receive chain from the RF circuitry through the digital signal processing (DSP) to incorporate new techniques specifically targeted to address spectrum sensing. The techniques involve the injection of pseudonoise-modulated RF signals into the receiver to identify the blockers via correlation algorithms in the DSP as well as to calibrate and cancel the nonlinear characteristics of the receiver. We will develop and refine the proposed algorithms and demonstrate their utility in a 28-nm CMOS receiver integrated circuit.

Wireless communication technologies such as cellular and WiFi are indispensable for modern society. However, existing wireless networks are under severe stress due to the explosive demand caused by smart mobile devices capable of creating and consuming large amounts of multimedia content (especially images and video). Meeting these demands is estimated to require 1000-fold increases in wireless network capacity, which cannot be obtained by incremental advances using existing spectrum. A promising approach for delivering the required revolutionary advances in wireless by employ the so-called 'millimeter (mm) wave' band, which has huge amounts of available spectrum (e.g., 7 GHz in the unlicensed 60 GHz band alone). The wavelength in these bands is an order of magnitude smaller than that in today's wireless networks, drastically changing the physical and propagation characteristics: for example, mm waves are easily blocked by obstacles such as human bodies, but steerable antenna arrays with a very large number of elements (up to 1000) can fit in compact form factors, enabling us to potentially steer around obstacles using bounces from reflectors. As a consequence, realizing the potential for mm wave communication requires a comprehensive reexamination of existing wireless design principles, using an interdisciplinary approach that goes all the way from antenna design to network protocols. The goal of this project is to take such an approach for establishing fundamental principles for design of next generation mm wave communication networks, with a research agenda combining cross-layer modeling, design, and performance evaluation, firmly grounded in experiment. A key technical issue is to how to efficiently adapt electronically steerable arrays with a large number of elements, and to integrate them into network protocols.

The research is driven by the following cutting edge system concepts: (a) Cellular 1000X, aimed at relieving the cellular capacity bottleneck via 60 GHz cellular links delivering Gbps data rates to the mobile, together with a seamless extension to indoor networks; (b) 'Wireless fiber' backhaul at 140 GHz for enabling Cellular 1000X, based on easy to deploy outdoor wireless mesh networks with link speeds approaching 40-100 Gbps; (c) 40 Gbps indoor 60 GHz links, aimed at going beyond nascent industry efforts such as NG60 that aim to upgrade link speeds in the recently developed IEEE 802.11ad wireless local area network standard. The goal of this project is to design a system that will achieve the stated objectives, and prototype an advanced proof-of-concept that will help pave the way for eventual technology transfer leveraging the close ties of the project team to industry. A 60 GHz experimental platform developed to support the research will be made available to the research community, to stimulate a broader academic effort in this area.

Due to the small carrier wavelengths, beamforming at both ends is critical to make the link budget work, but it is essential to make the beams electronically steerable to steer around obstacles (which ``look bigger at smaller wavelengths''), and to allow automatic network configuration. Cross-layer frameworks for resilient pencil beam networking for both Cellular 1000X and indoor WLANs will be developed and demonstrated. These will incorporate compressive array adaptation techniques, a core innovation to be demonstrated in this project. Compressive adaptation enables 3D beamforming for robust link budgets, steering around blockage, and spatial reuse, and enables scaling of both the number of antenna elements and the nodes in the network, unlike existing scan-based IEEE 802.11ad medium access control (MAC) techniques. System concepts to be designed and tested include (a) `Picocloud' network architectures that employ tight coordination between base stations and APs (for outdoor and indoor environments, respectively) to provide seamless connectivity in the face of blockage; (b) Integration of beamforming with spatial multiplexing in LoS or near-LoS environments, demonstrating the scaling of available degrees of freedom with carrier frequency through prototypes at 60 GHz and 140 GHz.

A reconfigurable phased array at 60 GHz will be developed and integrated with the NSF/CRI-funded WiMi software defined radio platform, in order to enable the preceding system-level explorations (while beamsteering ICs developed by industry have been incorporated into products, external control of the beamsteering coefficients is not available). In addition, a hardware testbed for LoS spatial multiplexing at 140 GHz will be developed to demonstrate the potential for 'wireless fiber' backhaul links beyond 100 GHz.

The millimeter wave (mmWave) frequencies and other bands above 6 GHz are a new and promising frontier for cellular wireless communications and the focus of the fifth-generation (5G) standardization efforts. Due to the massive available bandwidths, the mmWave frequencies offer the possibility of orders of magnitude greater capacity than current cellular systems in the highly congested bands below 3 GHz. However, a key challenge in realizing mmWave mobile cellular networks is energy consumption. Mobile devices and small-cell access points must operate under highly-constrained power budgets, and developing mmWave systems within these power limits is a formidable task. This project will investigate energy consumption from a system's perspective to address the issues in an integrated and coherent manner. The project will develop mathematical models for understanding energy and performance tradeoffs. New technologies for the radio frequency (RF) circuits, antenna array system, signal processing, and network protocols will be jointly developed to optimize performance and deliver energy-efficient mmWave devices.

The research work will pursue four key thrusts: Thrust 1 will seek to understand the fundamental relation between throughput, processing power, and spectral emission constraints, and optimizes this tradeoff by dynamically controlling key energy drivers including bandwidth, quantization resolution, antenna architecture, and waveform selection. This is combined with novel energy-aware scheduling policies and signal processing techniques. Thrust 2 will focus on idle mode power savings and associated problems of energy-efficient directional channel estimation and delay in dynamic environments. Thrust 3 will develop fundamental circuits technologies that enable Thrusts 1 and 2, in particular the novel techniques for both high-efficiency power amplifiers and low-power fully digital RF transceivers. Thrust 4 will obtain the necessary channel models and build circuit prototypes to validate the concepts in Thrusts 1 to 3.

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.

Advances in low-cost low-power silicon radio frequency (RF) integrated circuits (ICs) in the last two decades have opened up the commercial applications for millimeter wave (mmWave) frequencies which are an order of magnitude beyond those used in WiFi and cellular today. Large-scale deployment of mmWave communication networks, such as NextG cellular infrastructure outdoors and NextG WiFi infrastructure indoors, implies that these resources can be leveraged for RF imaging at scales that are not otherwise possible. The project develops foundational algorithms, architectures and protocols for such Joint Communication and Imaging (JCAI) systems. Each sensor in such a system provides 4D measurements (range, Doppler, azimuth angle and elevation angle) whose resolution improves by going to higher frequencies. The project establishes US leadership in a critical technology by developing large-scale RF imaging using frequencies beyond 100 GHz. Outdoor applications include pedestrian and vehicular tracking for global situational awareness supporting vehicular autonomy, and addressing security challenges such as timely detection of illegal drones or unauthorized personnel. In indoor settings, the technology enables fine-grained inference/prediction of human actions for eldercare and smart home applications. RF imaging technologies are especially useful in low-light or high-smoke/fog conditions when visible light or infrared technologies are not effective.<br/><br/>The project develops and demonstrates a framework for JCAI at mmWave frequencies. A core aspect of the technical plan is to drastically improve resolution by synthesizing large apertures (Thrust 1). This employs a combination of novel approaches to single sensor design which utilize large antenna arrays developed for communication, and networked collaboration between multiple sensors. A complementary aspect (Thrust 2) is the strategic utilization of unmanned vehicles to image difficult-to-reach areas, utilizing the fixed infrastructure to reduce the robot payload. In Thrust 3, hardware at 140 GHz previously developed by the PIs for communication will be adapted to support demonstration of networked RF imaging at 100+ GHz. Thrust 4 develops a control plane for networked imaging, including a resource management framework based on imaging demand and imaging capacity, and protocols supporting collaborative imaging. The concepts and methods to be developed have potential impact in a vast array of applications, including vehicular autonomy and road safety, manufacturing automation, indoor and outdoor security, eldercare, and healthcare. The PIs will work closely with industry partners, building on their strong track record in transitioning mmWave research, and plan to incorporate this research into the undergraduate curriculum through courses, capstone projects, and REU projects.<br/><br/>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.