Resource allocation for multi-antenna multicast in OFDM-based cognitive radio networks with imperfect channel information

In this paper, multi-antenna multicast in OFDM-based cognitive radio networks is studied with imperfect channel information at the cognitive base station. The resource allocation problem is formulated to maximize the total weighted transmission rate of all multicast sessions subject to the maximal outage probability constraint of secondary users (SUs) and the maximal interference overweighing probability constraint of primary users (PUs). To tackle the problem efficiently, the closed-form expressions for these two probability constraints are derived, based on which a two-step resource allocation method is proposed: firstly perform the normalized beamforming vector optimization and the subcarrier assignment, and secondly carry out the power allocation. Meanwhile, to optimize the normalized beamforming vectors, two kinds of methods are presented, with one method suitable for the high interference threshold region and the other for the low interference threshold region. Simulation results show that compared with the traditional method which does not consider the channel estimation error, our proposed method can improve the total successfully received rate of multicast users hugely while guaranteeing SUs´ outage probability constraint and PUs´ interference overweighing probability constraint very well.