IRS Aided Communications

I. Intelligent Reflecting Surface Aided Communications

Intelligent reflecting surface (IRS) is a promising solution to enhance the wireless communication capacity both cost-effectively and energy-efficiently, by properly altering the signal propagation via tuning a large number of passive reflecting units.

i. Capacity Characterization

1) IRS-aided single-user MIMO channel

We jointly optimized the transmit covariance and IRS reflection coefficients to maximize the capacity. We derived the optimal solution to each IRS reflection coefficient in closed-form.

S. Zhang and R. Zhang, "Capacity characterization for intelligent reflecting surface aided MIMO communication," IEEE J. Sel. Areas Commun., vol. 38, no. 8, pp. 1823-1838, Aug. 2020. [IEEEXplore] [arXiv] (ESI Hot Paper, ESI Highly Cited Paper)

S. Zhang and R. Zhang, "On the capacity of intelligent reflecting surface aided MIMO communication," in Proc. IEEE Int. Symp. Inf. Theory (ISIT), Jun. 2020. [IEEEXplore] (Top 3 Popular Article on ISIT Proceedings, Oct. 2020)

2) IRS-aided multi-user multiple-access channel (MAC) and broadcast channel (BC)

We proposed both inner bound and outer bound for the capacity region of IRS-aided MAC and BC, by leveraging rate-profile and uplink-downlink duality.

S. Zhang and R. Zhang, "Intelligent reflecting surface aided multi-user communication: Capacity region and deployment strategy," IEEE Trans. Commun., vol. 69, no. 9, pp. 5790-5806, Sep. 2021. [IEEEXplore] [arXiv]

S. Zhang and R. Zhang, "Intelligent reflecting surface aided multiple access: Capacity region and deployment strategy," in Proc. IEEE Int. Wkshps. Signal Process. Adv. Wireless Commun. (SPAWC), May 2020. (Invited Paper) [IEEEXplore]

ii. IRS Deployment

1) Network-level: Centralized or distributed IRSs?

We proposed two strategies for deploying a given number of IRS elements: distributed deployment near each user and centralized deployment near the AP. We analytically proved that for both MAC and BC, centralized deployment achieves a larger capacity region compared to distributed deployment, under symmetric channels.

S. Zhang and R. Zhang, "Intelligent reflecting surface aided multi-user communication: Capacity region and deployment strategy," IEEE Trans. Commun., vol. 69, no. 9, pp. 5790-5806, Sep. 2021. [IEEEXplore] [arXiv]

S. Zhang and R. Zhang, "Intelligent reflecting surface aided multiple access: Capacity region and deployment strategy," in Proc. IEEE Int. Wkshps. Signal Process. Adv. Wireless Commun. (SPAWC), May 2020. (Invited Paper) [IEEEXplore]

2) Link-level: Single IRS or double IRSs?

We proposed a cooperative double-IRS deployment that is able to harvest additional cooperative passive beamforming gain and spatial multiplexing gain compared to the single-IRS deployment.

Y. Han, S. Zhang, L. Duan, and R. Zhang, "Cooperative double-IRS aided communication: Beamforming design and power scaling," IEEE Wireless Commun. Lett., vol. 9, no. 8, pp. 1206-1210, Aug. 2020. [IEEEXplore] [arXiv]

Y. Han, S. Zhang*, L. Duan, and R. Zhang, "Double-IRS aided MIMO communication under LoS channels: Capacity maximization and scaling," IEEE Trans. Commun., under revision. [arXiv]

iii. IRS Reflection Optimization with OFDM / OFDMA

1) Single-user SISO-OFDM

We studied the joint power control and IRS reflection coefficient optimization problem to maximize the achievable rate of a SISO-OFDM system aided by an IRS. We also proposed a efficient channel training method based on IRS element grouping.

Y. Yang, B. Zheng, S. Zhang*, and R. Zhang, "Intelligent reflecting surface meets OFDM: Protocol design and rate maximization," IEEE Trans. Commun., vol. 68, no. 7, pp. 4522-4535, Jul. 2020. [IEEEXplore] [arXiv] (ESI Highly Cited Paper)

Y. Yang, S. Zhang, and R. Zhang, "IRS-enhanced OFDM: Power allocation and passive array optimization," in Proc. IEEE Global Commun. Conf. (Globecom), Dec. 2019. [IEEEXplore]

2) Single-user MIMO-OFDM

We jointly optimized the transmit covariance matrices at different sub-carriers and the common IRS reflection coefficients for all sub-carriers to maximize the achievable rate of a MIMO-OFDM system aided by an IRS.

S. Zhang and R. Zhang, "Capacity characterization for intelligent reflecting surface aided MIMO communication," IEEE J. Sel. Areas Commun., vol. 38, no. 8, pp. 1823-1838, Aug. 2020. [IEEEXplore] [arXiv] (ESI Hot Paper, ESI Highly Cited Paper)

3) Multi-user OFDMA

Due to the lack of frequency selectivity at the IRS, it is generally difficult to design a set of reflection coefficients that is good for all users at all sub-carriers. Motivated by this, we proposed a dynamic passive beamforming scheme to create artificial time-varying channels, such that only a subset of the users needs to be simultaneously served in each time slot.

Y. Yang, S. Zhang*, and R. Zhang, "IRS-enhanced OFDMA: Joint resource allocation and passive beamforming optimization," IEEE Wireless Commun. Lett., vol. 9, no. 6, pp. 760-764, Jun. 2020. [IEEEXplore] [arXiv]

iv. Others

Q. Wu, S. Zhang, B. Zheng, C. You, and R. Zhang, "Intelligent reﬂecting surface aided wireless communications: A tutorial," IEEE Trans. Commun., vol. 69, no. 5, pp. 3313-3351, May 2021. (ESI Hot Paper, Invited Paper) [IEEEXplore] [arXiv]

Q. Tao, S. Zhang, C. Zhong, and R. Zhang, "Intelligent reflecting surface aided multicasting with random passive beamforming," IEEE Wireless Commun. Lett., vol. 10, no. 1, pp. 92-96, Jan. 2021. [IEEEXplore] [arXiv]

R. Wang, L. Liu, S. Zhang, and C. Yu, "A new channel estimation strategy in intelligent reflecting surface assisted networks," in Proc. IEEE Global Commun. Conf. (Globecom), Dec. 2021.

Q. Tao, S. Zhang, C. Zhong, W. Xu, H. Lin, and Z. Zhang, "Intelligent reflecting surface aided multiuser downlink transmission: Analysis and design," IEEE Trans. Wireless Commun., under revision.

Z. Wang, L. Liu, S. Zhang, and S. Cui, "Massive MIMO communication with intelligent reflecting surface," IEEE Trans. Wireless Commun., under revision. [arXiv]

(*: corresponding author)