Cell-free systems can effectively eliminate the inter-cell interference by enabling multiple base stations (BSs) to cooperatively serve users without cell boundaries at the expense of high costs of ...hardware and power sources due to the large-scale deployment of BSs. To tackle this issue, the low-cost reconfigurable intelligent surface (RIS) can serve as a promising technique to improve the energy efficiency of cell-free systems. In this article, we consider an RIS aided cell-free MIMO system where multiple RISs are deployed around BSs and users to create favorable propagation conditions via reconfigurable reflections in a low-cost way, thereby enhancing cell-free MIMO communications. To maximize the energy efficiency, a hybrid beamforming (HBF) scheme consisting of the digital beamforming at BSs and the RIS-based analog beamforming is proposed. The energy efficiency maximization problem is formulated and an iterative algorithm is designed to solve this problem. The impact of the transmit power, the number of RIS, and the RIS size on energy efficiency are investigated. Both theoretical analysis and simulation results reveal that the optimal energy efficiency depends on the numbers of RISs and the RIS size. Numerical evaluations also show that the proposed system can achieve a higher energy efficiency than conventional ones.
Content-centric networking (CCN) adopts a receiver-driven, hop-by-hop transport approach that facilitates in-network caching, which in turn leads to multiple sources and multiple paths for ...transferring content. In such a case, keeping a single round trip time (RTT) estimator for a multi-path flow is insufficient as each path may experience different round trip times. To solve this problem, it has been proposed to use multiple RTT estimators to predict network condition. In this paper, we examine an alternative approach to this problem, CHoPCoP, which utilizes explicit congestion control to cope with the multiple-source, multiple-path situation. In addition, a parallelized version of CHoPCoP, pCHoPCoP, is designed to support bandwidth aggregation on multi-homed hosts. We have implemented CHoPCoP/pCHoPCoP on the ORBIT testbed and conducted experiments under various network and traffic settings. The evaluation shows that CHoPCoP can effectively deal with congestion in the multipath environment, and pCHoPCoP can maximize the network utilization for a multi-homed host.
The Extreme Learning Machine（ELM） and its variants are effective in many machine learning applications such as Imbalanced Learning（IL） or Big Data（BD） learning. However, they are unable to solve both ...imbalanced and large-volume data learning problems. This study addresses the IL problem in BD applications. The Distributed and Weighted ELM（DW-ELM） algorithm is proposed, which is based on the Map Reduce framework. To confirm the feasibility of parallel computation, first, the fact that matrix multiplication operators are decomposable is illustrated.Then, to further improve the computational efficiency, an Improved DW-ELM algorithm（IDW-ELM） is developed using only one Map Reduce job. The successful operations of the proposed DW-ELM and IDW-ELM algorithms are finally validated through experiments.
Content-centric networking (CCN) adopts a receiver-driven, hop-by-hop transport approach that facilitates in-network caching, which in turn leads to multiple sources and multiple paths for ...transferring content. In such a case, keeping a single round trip time (RTT) estimator for a multi-path flow is insufficient as each path may experience different round trip times. To solve this problem, it has been proposed to use multiple RTT estimators to predict network condition. In this paper, we examine an alternative approach to this problem, CHoPCoP, which utilizes explicit congestion control to cope with the multiple-source, multiple-path situation. Protocol design innovations of CHoPCoP include a random early marking (REM) scheme that explicitly signals network congestion, and a per-hop fair share Interest shaping algorithm (FISP) and a receiver Interest control method (RIC) that regulate the Interest rates at routers and the receiver respectively. We have implemented CHoPCoP on the ORBIT testbed and conducted experiments under various network and traffic settings. The evaluation shows that CHoPCoP is a viable approach that can effectively deal with congestion in the multipath environment.
Internet of meta-material things (meta-IoT) is a network of sensors composed of meta-materials with the advantages of low cost, ultra-low power consumption, and robust, showing great potential for ...the coming 6G communications. However, existing meta-IoT systems assume specular reflection on meta-IoT sensors, which limits their applications. For example, in chemical factories with harsh environments, receivers are often deployed on mobile robots. Due to their mobility, when measuring the signals, it is infeasible to ensure that the receivers are located at a certain angle relative to the meta-IoT sensors. Therefore, it is necessary to broaden the angle range of reflected signal coverage. In this paper, we propose a meta-IoT system capable of supporting receivers deployed at arbitrary angles in a broadened angle range. To be specific, we first propose an inhomogeneous structural design for meta-IoT sensors to achieve reflection coverage broadening. Then, we establish the signal transmission model from the transmitter to the receiver, going through the proposed meta-IoT sensor. To maximize the reflection coverage while ensuring accurate sensing results, we formulate a joint meta-IoT structure and sensing function optimization problem and propose efficient algorithms to solve it. Simulation results verify the effectiveness of the design method for the proposed meta-IoT system to achieve reflection coverage broadening.
Sixth-generation (6G) cellular systems will have an inherent vulnerability to physical (PHY)-layer attacks and privacy leakage, due to the large-scale heterogeneous networks with booming ...time-sensitive applications. Important wireless techniques including non-orthogonal multiple access, mobile edge computing, millimeter-wave, massive multiple-input and multiple-output, visible light communication, terahertz, and intelligent reflecting surface can improve the spectrum efficiency and quality-of-service but will raise challenges for the 6G PHY and cross-layer security and privacy protection. Existing optimization based PHY and cross-layer security and privacy protection schemes such as the convex optimization method have to rely on accurate attack patterns and strategies and thus suffer from performance degradation in 6G systems that have shorter communication latency, more devices and higher spectrum efficiency than 5G. Reinforcement learning (RL) algorithms help wireless devices optimize their security policies to enhance the security performance in dynamic networks against smart attacks without depending on the attack model. Therefore, this article provides a comprehensive survey on the RL based 6G PHY cross-layer security and privacy protection. In this article, we investigate the potential attacks in 6G systems and discuss the PHY cross-layer security solutions. A brief overview of reinforcement learning algorithms is provided. Afterward, we review the RL based PHY-layer security and privacy protection and discuss how to apply RL algorithms in 6G security scenarios, especially focusing on the game with jammers, eavesdroppers, spoofers and inference attackers. The RL based security solutions for unmanned aerial vehicles (UAVs) and cross-layer scenarios are also reviewed. The future research directions are identified and the corresponding RL based potential solutions are discussed for 6G.
In this article, we will provide a brief introduction of available opensource backscatter platforms that can be used by researchers and engineers to build interesting applications or investigate ...novel backscatter communication technologies. Instead of diving into the details of each platform, we will focus our discussion on the principles used in designing each platform and the unique feature provided by each platform. At the end of this article, we will discuss several key hardware and software modules that can be used by researchers or engineers to build their own backscatter platforms.
5G claims to support mobility up to 500 km/h according to the 3GPP standard. However, its field performance under high-speed scenes remains in mystery. In this paper, we conduct the first large-scale ...measurement campaign on a high-speed railway route operating at the maximum speed of 350 km/h, with full coverage of LTE and 5G (NSA and SA) along the track. Our study consumed 1788.8 GiB of cellular data in six months, covering the three major carriers in China and the recent standardized QUIC protocol. Based on our dataset, we reveal the key characteristics of 5G and LTE in extreme mobility in terms of throughput, RTT, loss rate, signal quality, and physical resource utilization. We further develop a taxonomy of handovers in both LTE and 5G and carry out the link-layer latency breakdown analysis. Our study pinpoints the deficiencies in the user equipment, radio access network, and core network which hinder seamless connectivity and better utilization of 5G's high bandwidth. Our findings highlight the directions of the next step in the 5G evolution.
High-speed rail (HSR) systems potentially provide a more efficient way of door-to-door transportation than airplane. However, they also pose unprecedented challenges in delivering seamless Internet ...service for on-board passengers. In this paper, we conduct the first large-scale disconnection-centric measurement study of TCP performance over LTE on HSR. Our measurement targets the main HSR route in China operating at 300/350 km/h. We performed extensive data collection obtaining 378.3 GB data collected over 56639 km of trips. Leveraging such a unique dataset, we measure important performance metrics such as TCP goodput, latency and loss rate across different congestion control algorithm, mobile carrier, and different train speed. We further develop the LTE disconnection taxonomy, and conduct a in-depth correlation study between TCP stall and LTE disconnection. Our findings reveal the networking performance on today's HSR environment "in the wild", as well as identify several root causes of performance inefficiencies, which together highlight the need to develop dedicated protocol mechanisms that are friendly to extreme mobility.
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