Distributed power allocation for cognitive radio

In this paper, we investigate the idea of using cognitive radio to reuse locally unused spectrum for communications. We consider a multiband/wideband system with two users in which the primary (licensed) user and the secondary (cognitive) user wish to communicate to the base station, subject to mutual interference. We introduce the notion of the virtual noise-threshold which represents a proxy for the primary user to allow cognitive communications. We determine, under the assumption that each user knows only his own channel, the acceptable interference level within a given quality of service. Moreover, we obtain a characterization of the distributed power allocation for each user, as well as the resulting virtual noise threshold. We prove that a cognitive user can vary its transmit power in order to maximize the sum capacity while maintaining a guarantee of service to the primary user.