oa Adaptive transmission for spectrum-sharing cognitive systems

The concept of cognitive networks has recently emerged as an efficient means for utilizing the scarce spectrum by allowing spectrum sharing between a licensed primary network and a secondary network. Cognitive networks can be divided into three different types; namely, interweave, underlay, and overlay. For the interweave type, the secondary users are only allowed to use the spectrum of the primary network whenever it is idle, which requires continuous sensing of the primary spectrum by the secondary network. For the underlay network, simultaneous transmissions are allowed by letting the secondary network share the spectrum with the primary network, under the condition of maximum interference power level allowed at the primary receiver. Finally, for the overlay type, the secondary network is aware of the signal characteristics of the primary network that are exploited to achieve an enhanced performance for the secondary network by minimizing the interference incurred by the primary transmissions.

In this poster, we present an overview of the three types of cognitive networks. We focus on the underlay cognitive network model, whereby we present the fundamental capacity results of these networks under various power constraints on both the transmit power and the interference power attained at the primary receiver. We then explore practical methods for achieving these capacity results by employing adaptive transmission techniques at the secondary users.