Brian A. Floyd, Jacob J. Adams, and Brian L. Hughes Department of Electrical and Computer Engineering North Carolina State University
Intellectual Merit: Research on multi-input multi-output (MIMO) communications has shown that using multiple antennas at both the transmitter and receiver can dramatically improve the capacity of wireless multipath channels. Since many wireless devices are limited in size, using multiple antennas requires close spacing which leads to strong, frequency-dependent coupling between antennas. Coupling can profoundly reduce received power, diversity and capacity. Prior work suggests that impedance matching at the receiver can reclaim most of the lost system capacity; however, these matching networks can be complex and difficult to implement, and they must adapt to changing channel and antenna conditions. Finally, existing antennas for MIMO systems are designed in an ad hoc manner, with no consideration given to finding methods to fully capture all available degrees of freedom and maximize the capacity of the aperture. The goal of this project is to combine information theory, antenna engineering, and radio-frequency (RF) circuit design to enable new approaches to realize compact broadband multi-antenna receivers. The overall approach is to develop multi-mode antennas, reconfigurable receivers, and communication algorithms that act in concert to maximize capacity of the underlying channel. Specifically, a systematic method will be developed to design MIMO antennas based on information-theoretic metrics, such as capacity, by controlling and shaping mutual coupling of the eigenmodes. Novel MIMO receivers will also be developed that employ reconfigurable baseband impedance matching networks which are frequency translated to RF using passive mixer-first architectures. Finally, communication and signal processing algorithms will be developed that can efficiently sense and adjust the matching networks in response to changing channel conditions. To evaluate these new technologies, a hardware test-bed will be constructed consisting of a two-port adaptive MIMO receiver, two-port compact antenna, and a digital interface for control and signal processing. Ultimately, the scaling of performance and complexity will be explored as the techniques are extended to larger multi-port systems. Broader Impacts: This multi-disciplinary project provides a holistic view of MIMO receiver design and develops new models, antenna design methods, communications algorithms and matching techniques which could significantly increase the capacity and performance of future cellular and wireless local area networks. If successful, this project would enable MIMO techniques to be employed even in physically small receivers with strong antenna mutual coupling, allowing increased data rates, larger range, and/or longer battery lives. The combination of theory and experiment will provide opportunities for student participation at all levels.
