Optimal power allocation for cognitive radio based on a virtual noise threshold

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 the primary user is oblivious to the presence of the cognitive user the acceptable interference level within a given quality of service. We also give an interesting way in the paper to acquire the primary user's side information. The proposed strategy is proved to be the optimal one that achieves the maximum rate for each of the two users under the constraint that the secondary user maintains a guarantee of service to the primary user when cognitive communication is considered.