Invited Talk

Cognitive radios offer the potential to provide a paradigm shift to the way in which spectrum will be managed in future generation wireless systems. Wide portions of the available radio spectrum have already been allocated to various services which have resulted in a spectrum crisis for future emerging wireless services. Spectrum occupancy measurements, however, demonstrate that large portions of the spectral bands are unoccupied most of the time indicating inefficiency in spectrum utilization. This has paved the way for CR technology that relies on the ability to sense the environment for availability of spectrum and adjust its transmission parameters. Cognitive users (also known as secondary users) will be allowed to use a licensed spectrum owned by primary users provided cognitive user transmission does not harmfully affect the primary network. This talk will address coexistence of secondary users and primary users through appropriate interference mitigation schemes. In particular the focus will be on convex optimization based beamformer design and resource allocation techniques. Convex optimization techniques naturally fit solving problems which arise in CR networks, as the secondary transmissions have certain objectives such as maximizing capacity or signal to interference plus noise ratio (SINR) with constraints such as primary receiver interference. The talk will start with a brief introduction to convex optimization techniques and will cover our recent works on SINR balancing based beamformer design and integer relaxation based resource allocation techniques for OFDM based secondary network. 

Cognitive Radio essentially allows multiple spectrum users to share available spectrum in a harmonious way to maximize spectrum utilization. The concept can be applicable even when there are no primary or secondary users, and essentially all the users of a shared spectrum are on an equal footing. A case of particular interest is the wireless home network space where multiple wireless flows can co-exist, that share the same spectral space and affect one another’s performance. In particular, WiFi, Bluetooth and Zigbee all share the ISM band and therefore interfere with each other. In this talk, we will present the findings of our detailed experimental studies on the effects of such interference on the user’s experience. We will also present a monitoring and diagnostics framework to mitigate such spectral interference in the home network domain.