Chik Yue, Carnegie Mellon University ECS-0636621 Upamanyu Madhow, University of Santa Barbara
Our objective is to develop the system architecture, signal processing algorithms and integrated circuit techniques for a robust, quick set-up, point-to-point wireless link which achieves speeds of 10-40 Gbps over a range of several kilometers, using millimeter (mm) wave spectrum. Since these speeds are comparable to those of optical fiber, the outcome of this project enables a fail-safe hybrid communication backbone infrastructure, which can be deployed or restored rapidly in the events of disaster and emergency. The system employs a novel hierarchical architecture which meshes beamforming (to provide link margins sufficient to overcome the limitations of mm-wave propagation in harsh weather) and spatial multiplexing (to provide large spectral efficiency, of the order of tens of bits per second per Hertz, required to realize optical link speeds using channel bandwidths of only several GHz). Beamforming gains are obtained by electronically steerable monolithic arrays. Each such array is a subarray in a larger array, forming a spatially multiplexed virtual multiple-input, multiple-output (MIMO) system: the transmit subarrays send separate data streams, which are separated out at the receiver using spatial interference suppression techniques. Key elements of this mm-wave MIMO system are CMOS IC design for monolithic steerable sub-arrays, signal processing/hardware co-design to obtain algorithms implementable at such high speeds, and hybrid analog/digital processing to enable low-power operation. Substantial effort will go into establishing a cell-based, reusable design/modeling framework to enable CMOS mm-wave VLSI design. The new findings will be incorporated into undergraduate and graduate classes through small design projects.
Intellectual Merit: This is an inherently interdisciplinary project whose success depends critically on intense interaction between the three PI's on this project, whose combined expertise spans CMOS IC design for communication applications (Yue), millimeter wave device and IC design (Rodwell) and signal processing for communication (Madhow). The proposed system is based on innovations at every level, including system concept, signal processing algorithms, and circuit design and packaging. Millimeter-wave MIMO provides spatial multiplexing in line of sight environments, and is therefore a completely new concept relative to MIMO at lower frequencies, which provides spatial multiplexing only in rich scattering environments. The electronically steerable sub-arrays are based on a unique row-column architecture amenable to monolithic realization. The innovation in the signal processing consists of drastic simplifications, including a hierarchical decomposition co-designed with the hardware. Circuit design at mm-wave frequencies push the limits of mixed signal design in low-cost CMOS processes, and our cell-based design framework has the potential of providing a systematic approach to such design. The baseband processing employs novel hybrid analog/digital processing techniques, in order to minimize the performance requirements on high-speed, high-cost, high-power analog-to-digital converters.
Broader Impact: Millimeter-wave MIMO provides the first feasible approach to bridging the capacity gap between wireless and optical systems, which has applications ranging from homeland security (e.g., disaster recovery) to last mile connectivity for enterprise and residential settings. An additional breakthrough is in terms of the ease of deployment of LOS outdoor links, which becomes a simple operation of roughly pointing the transmitter and receiver at each other, rather than precisely aligning the transmit and receive antennas as done in current practice. In addition, the breakthroughs in mm-wave CMOS circuit design and packaging required by this demanding application have the potential for impact well beyond the specific system considered here, and will open up a host of opportunities for harnessing mm-wave spectrum at reasonable cost. The PIs all have strong records of technology transfer, and intend to leverage their strong contacts with the communications industry to push for technology transfer by widely disseminating the results of this work not only through publications, but also using hardware demonstrations easily accessible to visitors. The proposed research will have a significant impact on the undergraduate and graduate curriculum at the PIs' institutions in terms of driving innovations and updates in a number of courses in circuit design and communication systems. Well-established outreach mechanisms in the nanotech area will be used to involve women and minorities, including high school students, in this effort. Due to the inherently interdisciplinary nature of this project, the students involved will receive a broad education cutting across several areas of Electrical and Computer Engineering.
