Blockage-Aware Robust Beamforming in RIS-Aided Mobile Millimeter Wave MIMO Systems

Millimeter wave (mmWave) communications are sensitive to blockage over radio propagation paths. The emerging paradigm of reconfigurable intelligent surface (RIS) has the potential to overcome this issue by its ability to arbitrarily reflect the incident signals toward desired directions. This paper proposes a Neyman-Pearson (NP) criterion-based blockage-aware algorithm to improve communication resilience against blockage in mobile mmWave multiple input multiple output (MIMO) systems. By virtue of this pragmatic blockage-aware technique, we further propose an outage-constrained beamforming design for downlink mmWave MIMO transmission to achieve outage probability minimization and achievable rate maximization. To minimize the outage probability, a robust RIS beamformer with variant beamwidth is designed to combat uncertain channel state information (CSI). For the rate maximization problem, an accelerated projected gradient descent (PGD) algorithm is developed to solve the computational challenge of high-dimensional RIS phase-shift matrix (PSM) optimization. Particularly, we leverage a subspace constraint to reduce the scope of the projection operation and formulate a new Nesterov momentum acceleration scheme to speed up the convergence process of PGD. Extensive experiments confirm the effectiveness of the proposed blockage-aware approach, and the proposed accelerated PGD algorithm outperforms a number of representative baseline algorithms in terms of the achievable rate

RIS-Assisted Mobile Millimeter Wave MIMO Communications:A Blockage-Aware Robust Beamforming Approach

Millimeter wave (mmWave) communications are highly affected by blockage, whereas the emerging reconfigurable intelligent surface (RIS) has the potential to overcome this issue. This paper proposes a Neyman Pearson (N-P) criterion-based blockage-aware algorithm to improve resilience to blockage in mobile mmWave multiple input multiple output (MIMO) systems. By virtue of this pragmatic blockage-aware technique, we further propose an outage-constrained beamforming design for RIS-assisted mmWave MIMO transmission to achieve outage probability minimization and achievable rate maximization. Specifically, we propose an accelerated projected gradient descent (PGD) algorithm to solve the computational challenge of high dimensional RIS phase-shift matrix (PSM) optimization. Particularly, we formulate a new Nesterov momentum ac celeration scheme to speed up the convergence rate. Exten sive experiments confirm the effectiveness of the proposed blockage-aware approach and the proposed accelerated PGD algorithm outperforms a number of representative baseline algorithms in terms of the achievable rate performance

Computing Offloading for RIS-Aided Internet of Everything:A Cybertwin Version

Cybertwin technology introduces a novel paradigm employing digital twins to model complex physical systems within a cyber environment, thus enhancing communication, collaboration, and decision-making capabilities. By harnessing advanced technologies, such as reconfigurable intelligent surfaces (RISs) and multi-access edge computing (MEC), seamless interaction between physical and virtual entities is facilitated. In this paper, we propose a cybertwin-driven edge computing framework that leverages RIS technology, complemented by an efficient computing offloading strategy to support largescale Internet of Everything (IoE) applications. Specifically, the proposed strategy focuses on a multi-cell system where numerous randomly distributed end users have the option to offload delay-sensitive and computing-intensive tasks to edge computing nodes. The offloading channels are enhanced by RISs through passive beamforming, while cybertwin technology directs resource cooperation among multi-cells and allocates computing and communication resources. Our main objective is to optimize the system’s utility with respect to task completion latency and energy consumption reduction. To achieve this goal, we conduct the joint optimization of task offloading and resource allocation. Furthermore, we develop a joint task offloading and resource allocation (JTORA) algorithm to derive optimal solutions for passive beamforming design, computing offloading decisions, communication resource scheduling, and computing capacity allocation. The simulation results demonstrate the superiority of the proposed algorithm over benchmark schemes in terms of edge computing efficiency. Furthermore, the system utility can be further enhanced by increasing the number of embedded RIS elements

Cooperative Non-Orthogonal Multiple Access with Index Modulation for Air-Ground Multi-UAV Networks

Unmanned aerial vehicles (UAVs) serve as flexible aerial platforms, enriching air-ground communication networks in various ways. To support massive connectivity within limited time-frequency blocks, non-orthogonal multiple access (NOMA) is proposed to be integrated into UAV networks. However, a common issue associated with almost all NOMA schemes is the susceptibility to inter-user interference (IUI). Therefore, in this paper, we propose a multi-UAV cooperative system aided by NOMA with index modulation, termed MCU-NOMA-IM, to improve the performance of air-ground networks by mitigating IUI and also avoiding the successive interference cancellation (SIC) decoding method that is prone to error floors. With MCUNOMA-IM, the information bits pertaining to multiple UAVs are mapped into multiple dimensions, including the modulated symbols, subcarrier indices, energy allocation patterns. To fully investigate the performance of MCU-NOMA-IM on air-ground networks, we consider scenarios in the presence of three and four UAVs and derive upper-bounds for the bit error rates (BERs). In addition, we propose a multi-clustered-UAV cooperative system aided by NOMA with index modulation (MCCU-NOMA-IM), which groups closely located UAVs into several clusters to reduce the requirement for time resources. Simulation results demonstrate that both MCU-NOMA-IM and MCCU-NOMA-IM greatly outperform cooperative NOMA and non-cooperative NOMA-IM schemes, especially for distant UAVs when the signal-to-noise ratio is sufficiently high, and we also show that the derived BER upper bounds are asymptotically tight

MmWave MIMO-OFDM with Index Modulation: A Pareto-Optimal Trade-off on Spectral-Energy Efficiency

Multiple-input multiple-output orthogonal frequency division multiplexing with index modulation (MIMO-OFDM-IM) has the potential advantage to balance the trade-off between spectral efficiency (SE) and energy efficiency (EE). This paper investigates the application of MIMO-OFDM-IM to millimeter wave (mmWave) communication systems. Taking advantage of the properties of Pareto optimality, we propose a feasible solution to achieve a globally Pareto-optimal trade-off between SE and EE, and the collision constraints of multi-objective optimization problem (MOP) can be solved efficiently. The MOP of SE-EE trade-off can then be converted into a Pareto-optimal set (POS) solution problem. This combinatorial-oriented resource allocation approach on SE-EE relation considers the optimal beam design and power reallocation for downlink multi-user mmWave transmission. We adopt the Poisson point process (PPP) to model the mobile data traffic, and the evolutionary algorithm is applied to speed up the search efficiency of the Pareto front. Compared with benchmarks, the experimental results collected from extensive simulations reveal that the proposed optimization approach is vastly superior to existing algorithms

Millimeter Wave MIMO-OFDM with Index Modulation: A Pareto Paradigm on Spectral- Energy Efficiency Trade-Off

Multiple-input multiple-output orthogonal frequency division multiplexing with index modulation (MIMO-OFDM-IM) has recently received increased attention, due to the potential advantage to balance the trade-off between spectral efficiency (SE) and energy efficiency (EE). In this paper, we investigate the application of MIMO-OFDM-IM to millimeter wave (mmWave) communication systems, where a hybrid analogy-digital (HAD) beamforming architecture is employed. Taking advantage of the Pareto-optimal beam design, we propose a feasible solution to approximately achieve a globally Pareto-optimal trade-off between SE and EE, and the collision constraints of the multi-objective optimization problem (MOP) can be solved efficiently. Correspondingly, the MOP of SE-EE trade-off can be converted into a feasible solution for energy-efficient resource usage, by finding the Pareto-optimal set (POS) towards the Pareto front. This combinatorial-oriented resource allocation approach on the SE-EE relation considers the optimal beam design and power control strategies for downlink multi-user mmWave transmission. To ease the system performance evaluation, we adopt the Poisson point process (PPP) to model the mobile data traffic, and the evolutionary algorithm is applied to speed up the search efficiency of the Pareto front. Compared with benchmarks, the experimental results collected from extensive simulations demonstrate that the proposed optimization approach is vastly superior to existing algorithms

Can becoming a leader change your personality? An investigation with two longitudinal studies from a role-based perspective.

Organizational research has predominantly adopted the classic dispositional perspective to understand the importance of personality traits in shaping work outcomes. However, the burgeoning literature in personality psychology has documented that personality traits, although relatively stable, are able to develop throughout one’s whole adulthood. A crucial force driving adult personality development is transition into novel work roles. In this article, we introduce a dynamic, role-based perspective on the adaptive nature of personality during the transition from the role of employee to that of leader (i.e., leadership emergence). We argue that during such role transitions, individuals will experience increases in job role demands, a crucial manifestation of role expectations, which in turn may foster growth in conscientiousness and emotional stability. We tested these hypotheses in two 3-wave longitudinal studies using a quasi-experimental design. We compared the personality development of 2 groups of individuals (1 group promoted from employees into leadership roles and the other remaining as employees over time), matched via the propensity score matching approach. The convergent results of latent growth curve modeling from the 2 studies support our hypotheses regarding the relationship between becoming a leader and subsequent small, but substantial increases in conscientiousness over time and the mediating role of job role demands. The relationship between becoming a leader and change of emotional stability was not significant. This research showcases the prominence of examining and cultivating personality development for organizational research and practice.</p

Bayesian Beamforming for Mobile Millimeter Wave Channel Tracking in the Presence of DOA Uncertainty

This paper proposes a Bayesian approach for angle-based hybrid beamforming and tracking that is robust to uncertain or erroneous direction-of-arrival (DOA) estimation in millimeter wave (mmWave) multiple input multiple output (MIMO) systems. Because the resolution of the phase shifters is finite and typically adjustable through a digital control, the DOA can be modeled as a discrete random variable with a prior distribution defined over a discrete set of candidate DOAs, and the variance of this distribution can be introduced to describe the level of uncertainty. The estimation problem of DOA is thereby formulated as a weighted sum of previously observed DOA values, where the weights are chosen according to a posteriori probability density function (pdf) of the DOA. To alleviate the computational complexity and cost, we present a motion trajectory-constrained a priori probability approximation method. It suggests that within a specific spatial region, a directional estimate can be close to true DOA with a high probability and sufficient to ensure trustworthiness. We show that the proposed approach has the advantage of robustness to uncertain DOA, and the beam tracking problem can be solved by incorporating the Bayesian approach with an expectation-maximization (EM) algorithm. Simulation results validate the theoretical analysis and demonstrate that the proposed solution outperforms a number of state-of-the-art benchmarks.This work was in part supported by the State Key Laboratory of Rail Traffic Control and Safety (Contract No. RCS2020ZT012), Beijing Jiaotong University and China Railway Corporation (Contract No. N2019G028). This article was presented in part at the 2019 IEEE GLOBECOM’19. The associate editor coordinating the review of this article and approving it for publication was O. Oyman. (Corresponding author: Yan Yang.) Yan Yang is with the State Key Laboratory of Rail Traffic Control and Safety, Beijing Jiaotong University, Beijing 100044, Chin

High-Angular Resolution Dust Polarization Measurements: Shaped B-field Lines in the Massive Star Forming Region Orion BN/KL

We present observational results of the thermal dust continuum emission and its linear polarization in one of the nearest massive star-forming sites Orion BN/KL in Orion Molecular Cloud-1. The observations were carried out with the Submillimeter Array. With an angular resolution of 1" (~2 mpc; 480 AU), we have detected and resolved the densest cores near the BN/KL region. At a wavelength of ~870 micron, the polarized dust emission can be used to trace the structure of the magnetic field in this star-forming core. The dust continuum appears to arise from a V-shaped region, with a cavity nearly coincident with the center of the explosive outflows observed on larger scales. The position angles (P.A.s) of the observed polarization vary significantly by a total of about 90 degree but smoothly, i.e., curl-like, across the dust ridges. Such a polarization pattern can be explained with dust grains being magnetically aligned instead of mechanically with outflows, since the latter mechanism would cause the P.A.s to be parallel to the direction of the outflow, i.e., radial-like. The magnetic field projected in the plane of sky is therefore derived by rotating the P.A.s of the polarization by 90 degree. We find an azimuthally symmetric structure in the overall magnetic field morphology, with the field directions pointing toward 2.5" west to the center of the explosive outflows. We also find a preferred symmetry plane at a P.A. of 36 degree, which is perpendicular to the mean magnetic field direction (120 degree) of the 0.5 pc dust ridge. Two possible interpretations of the origin of the observed magnetic field structure are discussed.Comment: 27 pages, 7 figures; ApJ in pres

Poly (l-lactide acid) improves complete nano-hydroxyapatite bone scaffolds through the microstructure rearrangement

Abstract Cracks often occur when nano-hydroxyapatite bone scaffolds are fabricated with selective laser sintering, which affect the performance of scaffolds. In this study, a small amount of poly (l-lactide acid) (PLLA) was added into nano-hydroxyapatite (nano-HAP) powder by mechanical blending in order to improve the sintering properties. The nano-HAP powder combined with 1wt % PLLA was sintered under different laser power (5W, 7.5W, 10W, 12.5W, 15W and 20W). The fabricated scaffolds were characterized using Scanning Electron Microscope (SEM), X-ray Diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and Micro Hardness Tester. The results showed that nano-HAP particles grew up quickly with the laser power increasing, and there were many strip-like cracks on the surface of sintering zone. The cracks gradually reduced until disappeared when the laser power increased to 15W, together with a great improvement of density. Large pores were observed on the specimen when the laser power further increases, accompanied with the decomposition of HAP into \u3b2-tricalcium phosphate (\u3b2-TCP) and tetracalcium phosphate (TTCP). And the optimum parameters were eventually obtained with laser power of 15W, scanning speed of 1000 mm/min, powder bed temperature of 150\ubaC, laser spot diameter of 2 mm and layer thickness of 0.2 mm. We summarized that the molten PLLA enhanced the particle rearrangement of nano-HAP by capillary force and may absorb thermal stress in laser sintering process, while PLLA would be oxidized gradually until completely excluded from the sintered nano-HAP scaffolds, which was confirmed by FTIR analysis. This study provides a novel method to improve the sintering properties of nano-HAP with no adverse effects which would be used in the application of bone tissue engineering potentially