Blind opportunistic interference alignment in cognitive radio systems

In this paper a new Opportunistic Interference Alignment (OIA) technique is presented that can be applied in a blind manner to Cognitive Radio systems. The proposed technique aims at relaxing the strong assumptions made in existing approaches where it is assumed that the Secondary User (SU) has knowledge of Channel State Information (CSI) concerning the Primary User´s (PU) transmissions, although this may not be possible, in general. First, the OIA technique of [1] is extended so that the required CSI can be blindly estimated from the second order statistics of the received symbols. More specifically, the Secondary Receiver post-coding matrix is re-designed in order to null-out completely the interference generated by the PU´s transmissions, in contrast to the original work where an interference reduction approach was adopted. Then, a novel estimation mechanism is proposed that enables the SU to apply the new OIA technique in a blind manner. The performance of the proposed technique is evaluated both theoretically as well as via simulations, under perfect and imperfect CSI.