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Cognitive radio (CR) is an effective solution to improve the spectralefficiency (SE) of wireless communications by allowing the secondary users(SUs) to share spectrum with primary users (PUs). Meanwhile, intelligentreflecting surface (IRS) has been recently proposed as a promising approach toenhance SE and energy efficiency (EE) of wireless communication systems throughintelligently reconfiguring the channel environment. In this paper, we consideran IRS-assisted downlink CR system, in which a secondary access point (SAP)communicates with multiple SUs without affecting multiple PUs in the primarynetwork and all nodes are equipped with multiple antennas. Our design objectiveis to maximize the achievable weighted sum rate (WSR) of SUs subject to thetotal transmit power constraint at the SAP and the interference constraints atPUs, by jointly optimizing the transmit precoding at the SAP and the reflectingcoefficients at the IRS. To deal with the complex objective function, theproblem is reformulated by employing the well-known weighted minimummean-square error (WMMSE) method and an alternating optimization (AO)-basedalgorithm is proposed. Furthermore, a special scenario with only one PU isconsidered and AO algorithm is adopted again. It is worth mentioning that theproposed algorithm has a much lower computational complexity than the abovealgorithm without the performance loss. Finally, some numerical simulationshave been provided to demonstrate that the proposed algorithm outperforms otherbenchmark schemes.

Joint Transmit Precoding and Reflect Beamforming Design for IRS-Assisted MIMO Cognitive Radio Systems