Institute of Electrical & Electronic Engineers
In this paper, two novel approaches to Filter-and-Forward BeamForming (FF-BF) in an underlay based relay-assisted cognitive network with frequency-selective channels are proposed. In the authors' scheme, secondary users are allowed to transmit through multiple relays simultaneously with primary users over the same spectrum. Such a network suffers from both Inter-Symbol Interference (ISI) and bidirectional interference between the networks. They design FF-BF coefficients of the relays to mitigate these two types of interference. Simulation results show that the proposed approaches improve system performance considerably in frequency-selective environments in comparison to the conventional amplify-and-forward beamforming strategy.