Cognitive radio enables efficient use of the scarce radio spectrum by sensing available bands and communicating in an opportunistic manner. Although significant work has been reported in the literature that enables dynamic use of these under-utilized spectrum resources, the underlying assumption in cognitive radio is the availability of a flexible and efficient wideband receiver. Designing such a receiver, however, is challenging. The specific problems are the inter-modulation and harmonic distortion caused by the wide passband of the receiver, the need for a wide tuning range frequency synthesizer to span the frequency band of interest, and the use of power-hungry high-speed ADCs to reduce sensing time. In the proposed research, the harmonic mixing process in wideband receivers is viewed as a multi-user access system in communications. This perspective allows leveraging on existing work on multi-user detection theory to develop techniques to overcome many of the implementation challenges. To fully realize the benefits of the proposed approach, several research tasks will be pursued, including developing a scalable receiver architecture, exploring analog combining methods of multi-phase/multi-frequency clocks to maximize performance after digital equalization, and devising a robust and high-performance digital equalizer that exploits the structure of the mixing process. Furthermore, this research will demonstrate the feasibility and the advantages of the proposed approach to wideband receiver design by realizing it on silicon. A complete design framework will be developed based on a clear understanding of various design options and the corresponding tradeoffs in performance and implementation complexity.
Broader Impact:
The proposed research should help realize a high-performance cognitive radio, which has emerged as a promising approach to efficiently exploit the scarce radio electromagnetic spectrum. In addition, the concepts developed in this research are broadly applicable to many existing and emerging wideband systems such as in multi-standard/multi-band radios and software defined radios. The principles can also be applied to non-communication applications in radar systems and sensor networks. The above research plan is coupled with an education plan that describes how the proposed research will help train both graduate and undergraduate students. The multi-disciplinary nature of the proposed research will broaden the students technical understanding, which the PI believes is essential for next generation of engineers. The proposal also includes plans to improve the participation of undergraduate students and members of under-represented groups.
