2 research outputs found
Intelligent Reflecting Surface Assisted Secure Wireless Communications with Multiple-Transmit and Multiple-Receive Antennas
In this paper, we propose intelligent reflecting surfaces (IRS) assisted
secure wireless communications with multi-input and multi-output antennas
(IRS-MIMOME). The considered scenario is an access point (AP) equipped with
multiple antennas communicates with a multi-antenna enabled legitimate user in
the downlink at the present of an eavesdropper configured with multiple
antennas. Particularly, the joint optimization of the transmit covariance
matrix at the AP and the reflecting coefficients at the IRS to maximize the
secrecy rate for the IRS-MIMOME system is investigated, with two different
assumptions on the phase shifting capabilities at the IRS, i.e., the IRS has
the continuous reflecting coefficients and the IRS has the discrete reflecting
coefficients. For the former case, due to the non-convexity of the formulated
problem, an alternating optimization (AO)-based algorithm is proposed, i.e.,
for given the reflecting coefficients at the IRS, the successive convex
approximation (SCA)-based algorithm is used to solve the transmit covariance
matrix optimization, while given the transmit covariance matrix at the AP,
alternative optimization is used again in individually optimizing of each
reflecting coefficient at the IRS with other fixed reflecting coefficients. For
the individual reflecting coefficient optimization, the close-form or an
interval of the optimal solution is provided. Then, the proposed algorithm is
extended to the discrete reflecting coefficient model at the IRS. Finally, some
numerical simulations have been done to demonstrate that the proposed algorithm
outperforms other benchmark schemes.Comment: 26 pages, 5 figure
Joint Transmit Precoding and Reflect Beamforming Design for IRS-Assisted MIMO Cognitive Radio Systems
Cognitive radio (CR) is an effective solution to improve the spectral
efficiency (SE) of wireless communications by allowing the secondary users
(SUs) to share spectrum with primary users (PUs). Meanwhile, intelligent
reflecting surface (IRS) has been recently proposed as a promising approach to
enhance SE and energy efficiency (EE) of wireless communication systems through
intelligently reconfiguring the channel environment. In this paper, we consider
an IRS-assisted downlink CR system, in which a secondary access point (SAP)
communicates with multiple SUs without affecting multiple PUs in the primary
network and all nodes are equipped with multiple antennas. Our design objective
is to maximize the achievable weighted sum rate (WSR) of SUs subject to the
total transmit power constraint at the SAP and the interference constraints at
PUs, by jointly optimizing the transmit precoding at the SAP and the reflecting
coefficients at the IRS. To deal with the complex objective function, the
problem is reformulated by employing the well-known weighted minimum
mean-square error (WMMSE) method and an alternating optimization (AO)-based
algorithm is proposed. Furthermore, a special scenario with only one PU is
considered and AO algorithm is adopted again. It is worth mentioning that the
proposed algorithm has a much lower computational complexity than the above
algorithm without the performance loss. Finally, some numerical simulations
have been provided to demonstrate that the proposed algorithm outperforms other
benchmark schemes