• 2025.04.11: I made a B-Box show in Huawei IRB Ceremony🎉
• 2025.01.19: I am a Special Guest for Popping Competition🎉

[13] Movable Antenna-Enhanced Wireless Communications: General Architectures and Implementation Methods
🧑‍🎓 Boyu Ning, Songjie Yang, Yafei Wu, Peilan Wang, Weidong Mei, Chau Yuen, Emil Björnson

• Abstract:

  Movable antennas (MAs), traditionally explored in antenna design, have recently garnered significant attention in wireless communications due to their ability to dynamically adjust the antenna positions to changes in the propagation environment. However, previous research has primarily focused on characterizing the performance limits of various MA-assisted wireless communication systems with less emphasis on their practical implementation. To address this gap, in this article, we propose several general MA architectures that extend existing designs by varying several key aspects to cater to different application scenarios and tradeoffs between cost and performance. Additionally, we draw from fields such as antenna design and mechanical control to provide an overview of candidate implementation methods for the proposed MA architectures, utilizing either direct mechanical or equivalent electronic control. Simulation results are finally presented to support our discussion.

• IEEE Bibtex：B. Ning, S. Yang, Y. Wu, P. Wang, W. Mei, C. Yuen and E. Björnson, “Movable Antenna-Enhanced Wireless Communications: General Architectures and Implementation Methods,” IEEE Wireless Commun., early access, 2025, doi: 10.1109/MWC.013.2400238.

[12] Phase Hopping Scheme for IRS-Aided MIMO Communications
🧑‍🎓 Boyu Ning, Nianzu Li, Weidong Mei, Songjie Yang, Yuchen Zhang

• Abstract:

  Intelligent reflecting surface (IRS) has been deemed as a promising technology to reconfigure the signal propagation environments cost-effectively. However, due to the lack of radio-frequency (RF) chains at the IRSs, their channel estimation becomes a significant challenge. In this correspondence, we propose a novel phase hopping scheme for IRS-aided multiple-input multiple-output (MIMO) communication systems, which dispenses with the channel state information (CSI) by randomly changing the IRS’s reflections over different time slots within the channel coherence time, thereby creating artificial time diversity to enhance the communication performance. Based on a minor modification on the current cellular protocol, we first design a new and compatible frame structure for the proposed phase hopping scheme. Then, we derive its ergodic capacity and outage probability in closed-form using random matrix theory and gain essential insights into its asymptotic behaviors. Numerical results validate our theoretical analysis and show the superiority of our proposed phase hopping scheme to the benchmark scheme without phase hopping.

• IEEE Bibtex：B. Ning, N. Li, W. Mei, S. Yang and Y. Zhang, “Phase Hopping Scheme for IRS-Aided MIMO Communications,” IEEE Trans. Veh. Technol., vol. 74, no. 2, pp. 3491-3496, Feb. 2025.

[11] Codebook Design and Performance Analysis for Wideband Beamforming in Terahertz Communications
🧑‍🎓 Boyu Ning, Weidong Mei, Lipeng Zhu, Zhi Chen, Rui Zhang

• Abstract:

  The codebook-based analog beamforming is appealing for future terahertz (THz) communications since it can generate high-gain directional beams with low-cost phase shifters via low-complexity beam training. However, conventional beamforming codebook design based on array response vectors for narrowband communications may suffer from severe performance loss in wideband systems due to the “beam squint” effect over frequency. To tackle this issue, we propose in this paper a new codebook design method for analog beamforming in wideband THz systems. In particular, to characterize the analog beamforming performance in wideband systems, we propose a new metric termed wideband beam gain, which is given by the minimum beamforming gain over the entire frequency band given a target angle. Based on this metric, a wideband analog beamforming codebook design problem is formulated for optimally balancing the beamforming gains in both the spatial and frequency domains, and the performance loss of conventional narrowband beamforming in wideband systems is analyzed. To solve the new wideband beamforming codebook design problem, we divide the spatial domain into orthogonal angular zones each associated with one beam, thereby decoupling the codebook design into a zone division sub-problem and a set of beamforming optimization sub-problems each for one zone. For the zone division sub-problem, we propose a bisection method to obtain the optimal boundaries for separating adjacent zones. While for each of the per-zone-based beamforming optimization sub-problems, we further propose an efficient augmented Lagrange method (ALM) to solve it. Numerical results demonstrate the performance superiority of our proposed codebook design for wideband analog beamforming to the narrowband beamforming codebook and also validate our performance analysis.

• IEEE Bibtex：B. Ning, W. Mei, L. Zhu, Z. Chen and R. Zhang, “Codebook Design and Performance Analysis for Wideband Beamforming in Terahertz Communications,” IEEE Trans. Wireless Commun., vol. 23, no. 12, pp. 19618-19633, Dec. 2024.

[10] Beamforming Technologies for Ultra-Massive MIMO in Terahertz Communications 🚀 IEEE Featured Journal Article ❤️‍🔥 IEEE Popular Article
🧑‍🎓 Boyu Ning, Zhongbao Tian, Weidong Mei, Zhi Chen, Chong Han, Shaoqian Li, Jinhong Yuan, Rui Zhang

• Abstract:

  Terahertz (THz) communications with a frequency band 0.1 – 10 THz are envisioned as a promising solution to future high-speed wireless communication. Although with tens of gigahertz available bandwidth, THz signals suffer from severe free-spreading loss and molecular-absorption loss, which limit the wireless transmission distance. To compensate for the propagation loss, the ultra-massive multiple-input-multiple-output (UM-MIMO) can be applied to generate a high-gain directional beam by beamforming technologies. In this paper, a review of beamforming technologies for THz UM-MIMO systems is provided. Specifically, we first present the system model of THz UM-MIMO and identify its channel parameters and architecture types. Then, we illustrate the basic principles of beamforming via UM-MIMO and discuss the far-field and near-field assumptions in THz UM-MIMO. Moreover, an important beamforming strategy in THz band, i.e., beam training, is introduced wherein the beam training protocol and codebook design approaches are summarized. The intelligent-reflecting-surface (IRS)-assisted joint beamforming and multi-user beamforming in THz UM-MIMO systems are studied, respectively. The spatial-wideband effect and frequency-wideband effect in the THz beamforming are analyzed and the corresponding solutions are provided. Further, we present the corresponding fabrication techniques and illuminate the emerging applications benefiting from THz beamforming. Open challenges and future research directions on THz UM-MIMO systems are finally highlighted.

• IEEE Bibtex：B. Ning, Z. Tian, W. Mei, Z. Chen, C. Han, J. Yuan, S. Li and R Zhang, “Beamforming technologies for ultra-massive MIMO in terahertz communications,” IEEE Open J. Commun. Soc., vol. 4, pp. 614–658, 2023.

[9] Wide-Beam Designs for Terahertz Massive MIMO: SCA-ATP and S-SARV
🧑‍🎓 Boyu Ning, Tiantian Wang, Chongwen Huang, Yuchen Zhang, Zhi Chen

• Abstract:

  Terahertz (THz) communication is expected to be one of the core enabling technologies for future systems. Due to the poor scattering and severe reflection loss of THz waves, the line-of-sight (LoS) communication is considered as a leading feature in THz multiple-input–multiple-output (MIMO) systems. To realize LoS communication, beam training is a promising scheme to find the beamforming vectors without leveraging explicit channel state information (CSI). In this context, a crucial issue for THz MIMO is how to design the beam codewords for realizing any expected radiation pattern during the training. In particular, the narrow beams can be realized by array response vectors whereas the wide-beam design is still an open problem. In this article, we propose two high-quality algorithms, namely, successive convex approximation (SCA)-based auxiliary target pursuit (SCA-ATP) and the sum of symmetrical array response vectors (S-SARVs), for offline design and real-time design, respectively. Numerical results show that SCA-ATP yields the best performance in terms of the beam-pattern error (BPE) compared with benchmarks, and S-SARV can achieve a close performance to SCA-ATP with low computational complexity.

• IEEE Bibtex：B. Ning, T. Wang, C. Huang, Y. Zhang, and Z. Chen, “Widebeam designs for terahertz massive MIMO: SCA-ATP and S-SARV,” IEEE Internet Things J., no. 12, pp. 10 857-10 869, June 2023.

[8] Multi-IRS-Aided Multi-User MIMO in mmWave/THz Communications: A Space-Orthogonal Scheme
🧑‍🎓 Boyu Ning, Peilan Wang, Lingxiang Li, Zhi Chen, Jun Fang

• Abstract:
  Multiple-input multiple-output (MIMO) and intelligent reflecting surface (IRS) are two appealing technologies in millimeter-wave (mmWave) and terahertz (THz) communications. The challenge of combining these two technologies lies in joint design for active beamforming (at the base-station (BS)/users) and passive beamforming (at the IRSs). In this paper, we consider a multi-IRS-aided multi-user MIMO scenario and propose a novel space-orthogonal scheme by applying zero-forcing techniques. Specifically, we first propose a multi-IRS-based zero-interference criterion, under which multi-user interference can be eliminated regardless of the IRS’s phase shifts. Based on this criterion, we decompose the precoder/decoder matrix into a product of two matrices, with one of them devised for interference cancellation and the other one of them devised for achievable rate maximization. Next, an approximate space-orthogonal technique referred to as partial zero-forcing (IRS-PZF) is proposed for proposed for devising the former matrix whose objective is to cancel the multi-user interference; while two efficient phase-shift schemes are proposed for the IRS passive beamforming, namely, water-filling segment matching (WSM) and phase iterative evolution (PIE), which balance between performance and complexity. Finally, we calculate the latter matrix of the precoder/decoder by applying the singular value decomposition (SVD) for the effective BS-user channels, so as to maximize the users’ achievable rates. Numerical results demonstrate the effectiveness and superiority of our proposed scheme compared with the benchmarks.
• IEEE Bibtex：B. Ning, P. Wang, L. Li, Z. Chen, and J. Fang “Multi-IRS-Aided Multi-User MIMO in mmWave/THz Communications: A Space-Orthogonal Scheme” IEEE Trans. Commun., vol. 70, no. 12, pp. 8138-8152, Dec. 2022.

[7] A Unified 3D Beam Training and Tracking Procedure for Terahertz Communication ❤️‍🔥 IEEE Popular Article
🧑‍🎓 Boyu Ning, Zhi Chen, Zhongbao Tian, Chong Han, Shaoqian Li

• Abstract:
  Terahertz (THz) communication is considered as an attractive way to overcome the bandwidth bottleneck and satisfy the ever-increasing capacity demand in the future. Due to the high directivity and propagation loss of THz waves, a massive MIMO system using beamforming is envisioned as a promising technology in THz communication to realize high-gain and directional transmission. However, pilots, which are the fundamentals for many beamforming schemes, are challenging to be accurately detected in the THz band owing to the severe propagation loss. In this paper, a unified 3D beam training and tracking procedure is proposed to effectively realize the beamforming in THz communications, by considering the line-of-sight (LoS) propagation. In particular, a novel quadruple-uniform planar array (QUPA) architecture is analyzed to enlarge the signal coverage, increase the beam gain, and reduce the beam squint loss. Then, a new 3D grid-based (GB) beam training is developed with low complexity, including the design of the 3D codebook and training protocol. Finally, a simple yet effective grid-based hybrid (GBH) beam tracking is investigated to support THz beamforming in an efficient manner. The communication framework based on this procedure can dynamically trigger beam training/tracking depending on the real-time quality of service. Numerical results are presented to demonstrate the superiority of our proposed beam training and tracking over the benchmark methods.
• IEEE Bibtex：B. Ning, Z. Chen, Z. Tian, C. Han and S. Li, “A Unified 3D Beam Training and Tracking Procedure for Terahertz Communication,” IEEE Trans. Wireless Commun., vol. 21, no. 4, pp. 2445-2461, Apr. 2022.

[6] Intelligent Reflecting Surface Assisted Terahertz Communications Toward 6G 👬
🧑‍🎓 Boyu Ning, Zhi Chen, Chong Han, Zhongbao Tian, Shaoqian Li

• Abstract:
  Terahertz (THz) communications have emerged as a promising candidate to support the heavy data traffic and exploding network capacity in the future 6G wireless networks. However, THz communications face many challenges for practical implementation, such as propagation loss, signal blockage, and hardware cost. In this article, an emerging paradigm of intelligent reflecting surface (IRS)-assisted THz communications is analyzed to address the above issues by leveraging joint active and passive beamforming to enhance the communication quality and reduce overhead. Aimed at practical implementation, an overview of the currently available approaches of realizing THz active/passive beam steering at the transmitter and IRS is presented. Based on these approaches, a beam training strategy for establishing joint beamforming is then investigated in THz communications. Moreover, various emerging and appealing 6G scenarios that integrate IRS into THz communications are envisioned. Open challenges and future research directions for this new paradigm are finally highlighted.
• IEEE Bibtex：Z. Chen, B. Ning, C. Han, Z. Tian and S. Li, “Intelligent Reflecting Surface Assisted Terahertz Communications Toward 6G,” IEEE Wireless Commun., vol. 28, no. 6, pp. 110-117, Dec. 2021.

[5] Joint Power Allocation and Passive Beamforming Design for IRS-Assisted Physical-Layer Service Integration
🧑‍🎓 Boyu Ning, Zhi Chen, Zhongbao Tian, Xiaomei Wang, Cunhua Pan, Jun Fang

• Abstract:
  Intelligent reflecting surface (IRS) has emerged as an appealing solution to enhance wireless communication performance by reconfiguring the wireless propagation environment. In this paper, we propose to apply IRS to the physical-layer service integration (PHY-SI) system, where a single-antenna access point (AP) integrates two sorts of service messages, i.e., multicast message and confidential message, via superposition coding to serve multiple single-antenna users. Our goal is to optimize the power allocation (for transmitting different messages) at the AP and the passive beamforming at the IRS to maximize the achievable secrecy rate region. To this end, we formulate this problem as a bi-objective optimization problem, which is shown equivalent to a secrecy rate maximization problem subject to the constraints on the quality of multicast service. Due to the non-convexity of this problem, we propose two customized algorithms to obtain its high-quality suboptimal solutions, thereby approximately characterizing the secrecy rate region. The resulting performance gap with the globally optimal solution is analyzed. Furthermore, we provide theoretical analysis to unveil the impact of IRS beamforming on the performance of PHY-SI. Numerical results demonstrate the advantages of leveraging IRS in improving the performance of PHY-SI and also validate our theoretical analysis.
• IEEE Bibtex：B. Ning, Z. Chen, Z. Tian, X. Wang, C. Pan, J. Fang and S. Li, “Joint Power Allocation and Passive Beamforming Design for IRS-Assisted Physical-Layer Service Integration,” IEEE Trans. on Wireless Commun., vol. 20, no. 11, pp. 7286-7301, Nov. 2021.

[4] Terahertz Multi-User Massive MIMO With Intelligent Reflecting Surface: Beam Training and Hybrid Beamforming 🚀 ESI highly Cited Paper ❤️‍🔥 IEEE Popular Article
🧑‍🎓 Boyu Ning, Zhi Chen, Wenrong Chen, Yiming Du, Jun Fang

• Abstract:
  Terahertz (THz) communications open a new frontier for the wireless network thanks to their dramatically wider available bandwidth compared to the current micro-wave and forthcoming millimeter-wave communications. However, due to the short length of THz waves, they also suffer from severe path attenuation and poor diffraction. To compensate for the THz-induced propagation loss, this paper proposes to combine two promising techniques, viz., massive multiple input multiple output (MIMO) and intelligent reflecting surface (IRS), in THz multi-user communications, considering their significant beamforming and aperture gains. Nonetheless, channel estimation and low-cost beamforming turn out to be two main obstacles to realizing this combination, due to the passivity of IRS for sending/receiving pilot signals and the large-scale use of expensive RF chains in massive MIMO. In view of these limitations, this paper first develops a cooperative beam training scheme to facilitate the channel estimation with IRS. In particular, we design two different hierarchical codebooks for the proposed training procedure, which are able to balance between the robustness against noise and searching complexity. Based on the training results, we further propose two cost-efficient hybrid beamforming (HB) designs for both single-user and multi-user scenarios, respectively. Simulation results demonstrate that the proposed joint beam training and HB scheme is able to achieve close performance to the optimal fully digital beamforming which is implemented even under perfect channel state information (CSI).
• IEEE Bibtex：B. Ning, Z. Chen, W. Chen, Y. Du, and J. Fang, “Terahertz Multi-User Massive MIMO with Intelligent Reflecting Surface: Beam Training and Hybrid Beamforming,” IEEE Trans. Veh. Technol., vol. 70, no. 2, pp. 1376-1393, Feb. 2021.

[3] Beamforming Optimization for Intelligent Reflecting Surface Assisted MIMO: A Sum-Path-Gain Maximization Approach ❤️‍🔥 IEEE Popular Article
🧑‍🎓 Boyu Ning, Zhi Chen, Wenjie Chen, Jun Fang

• Abstract:
  Recently, intelligent reflecting surface (IRS) has emerged as an appealing technique that enables wireless communications with low hardware cost and low power consumption. In this letter, we consider an IRS-assisted point-to-point multi-input multi-output (MIMO) system, where a source communicates with its destination with the help of an IRS. Our goal is to maximize the spectral efficiency of this system by jointly optimizing the (active) precoding at the source and the (passive) phase shifters (PSs) at the IRS. However, this turns out to be an intractable mixed-integer non-convex optimization problem. To circumvent the intractability, we propose a new sum-path-gain maximization (SPGM) criterion to obtain a high-quality and efficient suboptimal solution to this problem. Specifically, the PSs are first designed based on a simplified optimization problem, which aims to maximize the sum-gains of the spatial paths between the source and the destination. Then, a low-complexity alternating direction method of multipliers (ADMM) algorithm is utilized to solve this simplified problem. Finally, with the above obtained PSs, the source precoding is derived by performing the singular value decomposition (SVD) on the effective channel between the source and the destination. Numerical results demonstrate that the proposed scheme can achieve near-optimal performance.
• IEEE Bibtex：B. Ning, Z. Chen, W. Chen and J. Fang, “Beamforming Optimization for Intelli- gent Reflecting Surface Assisted MIMO: A Sum-Path-Gain Maximization Approach,” IEEE Wireless Commun. Lett., vol. 9, no. 7, pp. 1105-1109, Jul. 2020.

[2] Low-Complexity Analog Beamforming for mmWave Large-Scale MISOME Wiretap Channel
🧑‍🎓 Boyu Ning, Zhi Chen

• Abstract:
  With the popularization of large-scale antenna arrays in wireless communication, the conventional fully digital beamforming, which requires dedicated radio frequency (RF) chain per antenna element, is not viable for large-scale antenna systems due to its prohibitively high hardware cost. On the contrary, the analog beamforming design only requires one RF chain for all antenna elements, and has been widely investigated in recent years. In this letter, we consider the secure analog beamforming design that maximizes the secrecy rate in the large-scale multi-input single-output multi-eavesdropper (MISOME) wiretap channel. However, the associated secrecy rate maximization (SRM) problem is naturally non-convex due to the constant envelope constraint induced by the analog beamformer. To handle the problem, a low-complexity algorithm that combines the Dinkelbach approach and iterative coordinate ascent (ICA) algorithm is proposed to obtain a high-quality suboptimal solution. Numerical results illustrate that the proposed algorithm achieves both higher secrecy rate performance and lower complexity as compared to the existing schemes.
• IEEE Bibtex：B. Ning and Z. Chen, “Low-Complexity Analog Beamforming for mmWave Large- Scale MISOME Wiretap Channel,” IEEE Commun. Lett., vol. 24, no. 2, pp. 268-271, Feb. 2020.

[1] Codebook-based hybrid beamforming design for MISOME wiretap channel
🧑‍🎓 Boyu Ning, Zhi Chen, Xiaomei Wang, Weidong Mei

• Abstract:
  In this letter, in order to tackle the potential security issues in large-scale multi-antenna systems without exorbitant hardware cost, we focus on the codebook-based hybrid beamforming design in multi-input single-output multi-eavesdropper Gaussian wiretap channel to maximize the secrecy rate. However, the secrecy rate maximization (SRM) problem is non-convex by nature due to the codebook constraint imposed by analog beamforming. To handle it, we first reformulate the SRM problem into a combinatorial inner product maximization problem. Then, a combinatorial matching pursuit algorithm is proposed to solve this problem, in which the analog beamformer is designed independently of the digital beamformer. With the obtained analog beamformer, we show that the optimal digital beamformer admits a closed-form expression. Simulation results reveal that the proposed algorithm, though suffering from the inherent precision loss of the codebook, can achieve the near-optimal performance of the optimal FDB.
• IEEE Bibtex：B. Ning, Z. Chen, X. Wang and W. Mei, “Codebook-Based Hybrid Beamforming Design for MISOME Wiretap Channel,” IEEE Wireless Commun. Lett., vol. 8, no. 1, pp. 57-60, Feb. 2019.

[8] Max-Min Beamformer for THz Wideband Communications
🧑‍🎓 Boyu Ning, Weidong Mei; Lipeng Zhu; Zhi Chen; Rui Zhang

• Abstract:

  Analog beamforming is appealing for future terahertz (THz) communications since it can generate high-gain directional beams with low-cost phase shifters. However, the conventional analog beamforming based on array response vector to steer a narrow beam may suffer from severe performance loss in wideband systems due to the “beam squint” effect over frequency. To tackle this issue, we propose a new max-min beamformer design in this paper for THz wideband communication systems, which aims to maximize the minimum beam gain over the entire frequency band. To solve this challenging problem, an augmented Lagrange method (ALM) is proposed to obtain a high-quality solution with low complexity. Numerical results show that the proposed beam design can yield considerably better performance than the conventional narrowband beamformer, especially in the case of large angle of departure (AoD) from the base station (BS) to the user.

• IEEE Bibtex：B. Ning W. Mei, L. Zhu, Z. Chen and R. Zhang “Max-Min Beamformer for THz Wideband Communications,” IEEE Intl. Conf. Commun. (ICC), Rome, Italy, 2023, pp. 1747-1752.

[7] An Optimization-Based Wide-Beam Design for THz MIMO
🧑‍🎓 Boyu Ning, Zhi Chen

• Abstract:

  Beam training is a promising scheme to realize the terahertz (THz) multiple-input multiple-output (MIMO) communication without leveraging the explicit channel state information (CSI). In this context, a crucial issue for THz MIMO is how to design the beam codewords for realizing any expected radiation pattern during the training. The narrow beams can be realized by array response vectors, whereas the wide-beam design is still an open problem. In this paper, we propose a novel optimization-based method for THz wide-beam design, which is referred to as successive convex approximation (SCA)-based auxiliary target pursuit (SCA-ATP). Specifically, we equivalently formulate the wide-beam design as a problem of pursuing the auxiliary target in Euclidean space. By lifting the optimization vector into a positive semidefinite matrix, we can tackle it with the SCA technique by iteratively solving a sequence of simplified subproblems.

• IEEE Bibtex：B. Ning and Z. Chen, “An Optimization-Based Wide-Beam Design for THz MIMO,” IEEE Global Communications Conference, Rio de Janeiro, Brazil, 2022, pp. 1802-1807

[6] Wideband Terahertz Communications with AoSA: Beam Split Aggregation and Multiplexing
🧑‍🎓 Boyu Ning, Lingxiang Li; Wenrong Chen; Zhi Chen

• Abstract:

  Array-of-subarrays (AoSA) is an appealing architecture in terahertz (THz) communications since the analog beamformers on sub arrays can provide beam gain to combat severe propagation loss, by low-cost phase shifters. However, the traditional beamforming scheme for AoSA, i.e., each subarray serves an exclusive user, cannot cope with the effect of beam split in THz wideband communications. In this paper, we propose a novel concept, i.e., beam split aggregation and multiplexing (BSAM), to support wideband THz communication with AoSA architecture. Specifically, we first characterize the direction of beam split and then derive the maximum bandwidth of a subband that will not cause beam split. Finally, based on the above results, we propose a criterion to plan the subbands and design the analog beamformers for BSAM.

• IEEE Bibtex：B. Ning, L. Li, W. Chen and Z. Chen, “Wideband Terahertz Communications with AoSA: Beam Split Aggregation and Multiplexing,” IEEE Global Communications Conference, Rio de Janeiro, Brazil, 2022, pp. 1709-1714.

[5] Space-orthogonal Scheme for IRSs-aided Multi-user MIMO in mmWave/THz Communications
🧑‍🎓 Boyu Ning, Tiantian Wang, Peilan Wang, Zhi Chen, Jun Fang

• Abstract:

  The sum-rate maximization for intelligent reflecting surfaces (IRS)-aided multi-user MIMO is a recent open problem. The challenge lies in the coefficient designs for reflecting phase shifts (at the IRS) and precoder/decoders (at the BS/users). By imposing two additional constraints, i.e., 1) each IRS only serves one user, 2) no interference exists between users, this paper proposes a novel space-orthogonal scheme for multiple IRSs- aided multi-user MIMO in millimeter wave (mmWave) and terahertz (THz) communications. Based on a new zero-interference criterion, we can successively find high-quality solutions for the IRSs’ phase shifts and precoder/decoders one by one. Specifically, we first propose a null-space singular value decomposition (SVD) approach to determine a part of the precoder/decoders. Then, two solutions are developed for IRSs’ phase shifts, namely, the segment matching (SM) and the phase iterative evolution (PIE) solutions. Finally, the remanent part of the precoder/decoders are calculated by SVD with water-filling under the zero-interference constraint. Numerical results demonstrate the effectiveness and superiority of our proposed scheme.

• IEEE Bibtex：B. Ning, P. Wang, L. Li, Z. Chen and J. Fang, “Space-orthogonal Scheme for IRSs-aided Multi-user MIMO in mmWave/THz Communications,” IEEE Intl. Conf. Com- mun. (ICC), Seoul, South Korea, May 2022, pp. 1-6.

[4] Optimization for IRS-Assisted Systems With Both Multicast and Confidential Messages
🧑‍🎓 Boyu Ning, Zhi Chen, Zhongbao Tian, Shaoqian Li

• Abstract:

  In this paper, we propose to apply intelligent reflecting surface (IRS) to the physical-layer service integration (PHY-SI) system, where a single-antenna access point (AP) integrates two sorts of service messages, i.e., multicast message and confidential message, via superposition coding to serve multiple single-antenna users. Our goal is to optimize the power allocation (for transmitting different messages) at the AP and the passive beamforming at the IRS to maximize the achievable secrecy rate region. To this end, we formulate this problem as a bi-objective optimization problem. To tackle the non-convexity of this problem, we propose a Charnes-Cooper transformation (CCT)-based algorithm to obtain its high-quality suboptimal solutions, thereby approximately characterizing the secrecy rate region. Numerical results demonstrate the advantages of leveraging IRS in improving the performance of PHY-SI.

• IEEE Bibtex：B. Ning, Z. Chen, Z. Tian and S. Li, “Optimization for IRS-Assisted Systems With Both Multicast and Confidential Messages,” IEEE Global Communications Conference, Madrid, Spain, 2021, pp. 1-6.

[3] Channel Estimation and Transmission for Intelligent Reflecting Surface Assisted THz Communications
🧑‍🎓 Boyu Ning, Zhi Chen, Wenrong Chen, Yiming Du

• Abstract:

  Intelligent reflecting surface (IRS) is envisioned as a promising technology to broaden signal coverage and enhance transmission in terahertz (THz) communications. Due to the passivity of IRS, the channel measurement can not be achieved by traditional pilot manner and the subsequent cooperative transmission design remains an open problem. This paper investigates the channel estimation and transmission solutions for massive multiple input multiple output (MIMO) IRS-assisted THz system. The channel estimation is realized by beam training and the quantization error is analyzed for evaluating performance. In addition, a novel hierarchical search codebook design is proposed as a low-complexity basis of beam training. Based on above foundations, we propose a cooperative channel estimation procedure to tactfully acquire the channel knowledge. Finally, by leveraging obtained channel information, the designs of IRS and transceivers are directly provided in closed form without reconstructing the full channel matrix or additional optimization. Simulation and numerical results are presented to illustrate the minimum signal to noise ratio (SNR) required for beam training and the efficacy of the proposed transmission solutions.

• IEEE Bibtex：B. Ning Z. Chen, W. Chen and Y. Du “Channel Estimation and Transmission for Intelligent Reflecting Surface Assisted THz Communications,” IEEE Intl. Conf. Commun. (ICC), Dublin, Ireland, Jun. 2020.

[2] Improving Security of THz Communication with Intelligent Reflecting Surface
🧑‍🎓 Boyu Ning, Zhi Chen, Wenjie Chen, Lingxiang Li

• Abstract:

  Intelligent Reflecting Surface (IRS)-assisted beamforming is an emerging paradigm proposed to enhanced signal coverage and multiplexing in terahertz (THz) communications with low hardware cost and reduced power consumption. This paper investigates the beamformer and IRS design to enhance security of downlink THz communication in multi-input single-output (MISO) wiretap channel, where an Alice-Bob pair wishes to communicate secretly with the assist of IRS, in the presence of Eve. Our goal is to maximize the secrecy rate by designing the active beamformer at the base station (BS) and the passive reflecting phase shifters (PSs) at the IRS, which turns out to be an intractable mixed integer non-convex optimization problem. To tackle it, we respectively propose a low-computational- complexity successive design and a high-secure- performance joint design, which both attain high- quality suboptimal solutions. Specifically, in the successive design, we first design the PSs under an introduced principle, followed by that the beamformer is optimally derived, both in closed form. In the joint design, an alternating manner is proposed to optimize the PSs and the beamformer one by one with each other being fixed in each iteration until both reach the convergence. Numerical results show that the proposed designs achieve better secrecy performance than existing IRS-assisted design and traditional non-IRS- assisted secure design.

• IEEE Bibtex：B. Ning, Z. Chen, W. Chen and L. Li, “Improving Security of THz Communication with Intelligent Reflecting Surface,” IEEE Global Communications Conference, Waikoloa, HI, USA, 2019, pp. 1-6.

[1] Optimal Beam Steering Design for Large-Scale mmWave MIMO Wiretap Channel
🧑‍🎓 Boyu Ning, Zhi Chen, Lingxiang Li, Wenrong Chen

• Abstract:

  This paper investigates the optimal secure beam steering design of millimeter wave (mmWave) communications, where an Alice-Bob pair wishes to communicate in secret in the presence of Eve, with each node equipped with large-scale antenna arrays. Owing to the reduced peak-to-average power ratio and hardware cost, beam steering design emerges as an attractive technique in mmWave communications recently. However, from the physical layer perspective, the beam steering design subject to security requirement has not been investigated yet. In this paper, we consider a secrecy rate maximization problem with respect to beam steering design, i.e., analog beam selection of radio frequency (RF) chains and power allocation over the selected RF chains, which turns out to be an intractable mixed integer nonlinear optimization problem. To tackle it, we first determine a set of optimal analog beam candidates, based on which the considered multi-input multi-output (MIMO) wiretap channel is decoupled into a sequence of parallel single-input single-output (SISO) wiretap channels. Then, it is shown that the optimal power allocation over the parallel wiretap channels can be derived in a semi-closed-form. Numerical results illustrate that the proposed design offer better secrecy performance than traditional beam steering design in the presence of wiretapping as long as the channel has more than two propagation paths.

• IEEE Bibtex：B. Ning, Z. Chen, L. Li and W. Chen, “Optimal Beam Steering Design for Large-Scale mmWave MIMO Wiretap Channel,” IEEE Global Communications Conference, Abu Dhabi, United Arab Emirates, 2018, pp. 1-6. 2018.