MmWave extra-large-scale MIMO based active user detection and channel estimation for high-speed railway communications

The current High-Speed Railway(HSR)communications increasingly fail to satisfy the massive access services of numerous user equipment brought by the increasing number of people traveling by HSRs.To this end,this paper investigates millimeter-Wave(mmWave)extra-large scale(XL)-MIMO-based massive Internet-of-Things(loT)access in near-field HSR communications,and proposes a block simultaneous orthogonal matching pursuit(B-SOMP)-based Active User Detection(AUD)and Channel Estimation(CE)scheme by exploiting the spatial block sparsity of the XLMIMO-based massive access channels.Specifically,we first model the uplink mmWave XL-MIMO channels,which exhibit the near-field propagation characteristics of electromagnetic signals and the spatial non-stationarity of mmWave XL-MIMO arrays.By exploiting the spatial block sparsity and common frequency-domain sparsity pattern of massive access channels,the joint AUD and CE problem can be then formulated as a Multiple Measurement Vectors Compressive Sensing(MIMV-CS)problem.Based on the designed sensing matrix,a B-SOMP algorithm is proposed to achieve joint AUD and CE.Finally,simulation results show that the proposed solution can obtain a better AUD and CE performance than the conventional CS-based scheme for massive IoT access in near-field HSR communications.

Shipborne Underwater Acoustic Communication System and Sea Trials with Submersible Shenhai Yongshi

The Shipborne acoustic communication system of the submersible Shenhai Yongshi works in vertical, horizontal and slant channels according to the relative positions. For ease of use, an array combined by a vertical-cone directional transducer and a horizontal-toroid one is installed on the mothership. Improved techniques are proposed to combat adverse channel conditions, such as frequency selectivity, non-stationary ship noise, and Doppler effects of the platform’s nonlinear movement. For coherent modulation, a turbo-coded single-carrier scheme is used. In the receiver, the sparse decision-directed Normalized Least-Mean-Square soft equalizer automatically adjusts the tap pattern and weights according to the multipath structure, the two receivers’ asymmetry, the signal’s frequency selectivity and the noise’s spectrum fluctuation. The use of turbo code in turbo equalization significantly suppresses the error floor and decreases the equalizer’s iteration times, which is verified by both the extrinsic information transfer charts and bit-error-rate performance. For noncoherent modulation, a concatenated error correction scheme of nonbinary convolutional code and Hadamard code is adopted to utilize full frequency diversity. Robust and lowcomplexity synchronization techniques in the time and Doppler domains are proposed. Sea trials with the submersible to a maximum depth of over 4500 m show that the shipborne communication system performs robustly during the adverse conditions. From the ten-thousand communication records in the 28 dives in 2017, the failure rate of the coherent frames and that of the noncoherent packets are both below 10%, where both synchronization errors and decoding errors are taken into account.

Omnidirectional Antenna Diversity System for High-Speed Onboard Communication

In this article,an omnidirectional dual-polarized antenna with synergetic electromagnetic and aerodynamic properties is propounded for high-speed diversity systems.The propounded antenna comprises a probe-fed cavity for horizontally polarized radiation and a microstrip-fed slot for vertical polarization.Double-layer metasurfaces are properly designed as artificial magnetic conductor boundaries with direct metal-mountable onboard installation and compact sizes.An attached wedge-shaped block is utilized for windage reduction in hydrodynamics.The propounded antenna is fabricated for design verification,and the experimental results agree well with the simulated ones.For vertical polarization,the operating bandwidth is in the range of 2.37–2.55 GHz,and the realized gain variation in the azimuthal radiation pattern is 3.67 decibels(dB).While an impedance bandwidth in the range of 2.45–2.47 GHz and a gain variation of 3.71 dB are also achieved for horizontal polarization.A port isolation more than 33 dB is obtained in a compact volume of 0.247λ_(0)×0.345λ_(0)×0.074λ_(0),whereλ_(0)represents the wavelength in vacuum at the center frequency,wherein the wedge-shaped block is included.The propounded diversity antenna has electromagnetic and aerodynamic merits,and exhibits an excellent potential for high-speed onboard communication.

MPC-based time synchronizationmethod for V2V (vehicle-tovehicle)communication

Purpose–As the strategy of 5G new infrastructure is deployed and advanced,5G-R becomes the primary technical system for future mobile communication of China’s railway.V2V communication is also an important application scenario of 5G communication systems on high-speed railways,so time synchronization between vehicles is critical for train control systems to be real-time and safe.How to improve the time synchronization performance in V2V communication is crucial to ensure the operational safety and efficiency of high-speed railways.Design/methodology/approach–This paper proposed a time synchronization method based on model predictive control(MPC)for V2V communication.Firstly,a synchronous clock for V2V communication was modeled based on the fifth generation mobile communication-railway(5G-R)system.Secondly,an observation equation was introduced according to the phase and frequency offsets between synchronous clocks of two adjacent vehicles to construct an MPC-based space model of clock states of the adjacent vehicles.Finally,the optimal clock offset was solved through multistep prediction,rolling optimization and other control methods,and time synchronization in different V2V communication scenarios based on the 5G-R system was realized through negative feedback correction.Findings–The results of simulation tests conducted with and without a repeater,respectively,show that the proposed method can realize time synchronization of V2V communication in both scenarios.Compared with other methods,the proposed method has faster convergence speed and higher synchronization precision regardless of whether there is a repeater or not.Originality/value–This paper proposed an MPC-based time synchronization method for V2V communication under 5G-R.Through the construction of MPC controllers for clocks of adjacent vehicles,time synchronization was realized for V2V communication under 5G-R by using control means such as multistep prediction,rolling optimization,and feedback correction.In view of the problems of low synchronization precision and slow convergence speed caused by packet loss with existing synchronization methods,the observer equation was introduced to estimate the clock state of the adjacent vehicles in case of packet loss,which reduces the impact of clock error caused by packet loss in the synchronization process and improves the synchronization precision of V2V communication.The research results provide some theoretical references for V2V synchronous wireless communication under 5G-R technology.

Study on 5G Application Scenarios in Intelligent High-Speed Railway

5G technology is indispensable for developing comprehensive perception and ubiquitous interconnection of intelligent high-speed railways(HSRs),and can be applied to many scenarios in intelligent construction,intelligent equipment,intelligent operation and in other fields.In order to promote the standardized application of 5G technology in intelligent HSRs in a scientific and orderly manner and to avoid redundant construction and wasteful investment,it is imperative to carry out a systematical top-level design of the application scenarios at the initial stage.To this end,after investigating and analyzing the 5G application demands in different aspects of HSRs and the general structure of the railway 5G network,this paper formulates an overall planning of 5G technology application scenarios and proposes solutions to some typical application scenarios in the intelligent HSR system,based on the architecture and requirements of the intelligent HSR system.

High-speed railway channel measurements and characterizations: a review

Wireless communication for high-speed railways （HSRs） that provides reliable and high data rate communi- cation between the train and trackside networks is a challenging task. It is estimated that the wireless communication traffic could be as high as 65 Mbps per high-speed train. The development of such HSR communications systems and standards requires, in turn, accurate models for the HSR propagation channel. This article provides an overview of ex- isting HSR channel measurement campaigns in recent years. Particularly, some important measurement and modeling results in various HSR scenarios, such as viaduct and U-shaped groove （USG）, are briefly described and analyzed. In addition, we review a novel channel sounding method, which can highly improve the measurement efficiency in HSR environment.

Elliptical Cell Based Beamforming Design with an Improved β-Fairness Power Allocation for HSR Communication Systems

In this paper,a beamforming scheme to improve the coverage in high-speed railway communication systems is investigated.A dedicated coverage model,where the coverage cell is an ellipse rather than the traditional circular or linear,is considered.Based on the elliptical coverage cell,an optimization problem for the beamforming design is formulated to maximize the percentage of railway coverage,subject to the constraints on equal expected designed propagation gain(the gain obtained by a combination of designed beam and propagation channel)on the elliptical curve,i.e.,the expectation of designed propagation gain on the elliptical curve are all equal.Considering that the coverage can be improved by increasing the minimum designed propagation gain on the railway,the problem can be recast to maximizing the equal expected designed propagation gain on the elliptical curve.Subsequently,a beamforming design with an improved β-fairness power allocation,where the optimization problem is formulated to maximize the minimum expected received power over time with the constraints on elliptical cell based beamforming and mobile service amount,is proposed to further improve the coverage.An alternating iteration algorithm is developed to find the optimal beamforming vector and the instantaneous transmit power.Through numerical results,it is found that the beamforming designed on the elliptical curve covers longer railway than beamforming designed on the railway directly,and the coverage of elliptical cell based beamforming can be increased with the eccentricity.In addition,beamforming with the improvedβ-fairness power allocation can further improve the railway coverage and mobile service amount simultaneously.Moreover,it is shown that the larger eccentricity of the ellipse with appropriately chosen BS location,the larger coverage distance.

Admission Control Scheme for Handover Service in High-Speed Train Communication System

Admission control in high-speed train communication system is quite different from admission control in traditional cellular networks. Conventional admission control strategies cannot be directly applied to this special communication scenario. In this paper, the problem of admission control for handover service is investigated in high-speed train communication environment. An admission control scheme considering bit error rate(BER)and bandwidth borrowing strategy is proposed. On the basis of admission control decision rule taking BER into account, a part of bandwidth obtained by compressing variable rate service in the networks is provided for handover services. The admission control scheme can admit handover services as more as possible while it guarantees the lowest data rate of different services in the networks. Simulation results show that the proposed admission control scheme has a better performance than existing admission control schemes.

Broadband Communications for High-Speed Trains via NDN Wireless Mesh Network

With the increasing utilization of High-Speed Trains （HSTs）, the need for a reliable and high-bandwidth Internet access under high-speed mobility scenarios has become more demanding. In static, walking, and low mobility environments, TCP/IP （transmission control protocol/Internet protocol） can work well. However, TCP/IP cannot work well in high-speed scenarios because of reliability and handoff delay problems. This is mainly because the mobile node is required to maintain the connection to the corresponding node when it handovers to another access point node. In this paper, we propose a named data networking wireless mesh network architecture for HST wireless communication （NDN-Mesh-T）, which combines the advantages of Wireless Mesh Networks （WMNs） and NDN architectures. We attempt to solve the reliability and handoff delay problems to enable high bandwidth and low latency in Internet access in HST scenarios. To further improve reliability and bandwidth utilization, we propose a Direction-Aware Forwarding （DAF） strategy to forward Interest packet along the direction of the running train. The simulation results show that the proposed scheme can significantly reduce the packet loss rate by up to 51% compared to TCP/IP network architecture. Moreover, the proposed mechanism can reduce the network load, handoff delay, and data redundancy.

Integrated nano-structured silicon waveguides and devices for high-speed optical communications

With progress in fabrication technology, integrated photonics plays an increasingly important role in high-speed optical communications, from monolithic transmitters and receivers for advanced optical modulation formats to on-chip subsystems for optical signal processing. We review our recent work on the highly tailorable physical properties of silicon waveguides for communication and signal processing applications, using slot structures. Controllable chromatic dispersion, nonlinearity, and polarization properties of the waveguides are presented, and the enabled wideband wavelength conversion, optical tunable delay, and signal processing of polarization-multiplexing data channels are discussed.

Value and governance of high-speed railway

This paper considers multiple perspectives to explore the concept of high-speed railway(HSR),rationally abstract its value formation mechanism, and quantitatively measure its actual performance. This paper analyzes the governance potential of major countries in the high-speed railway value chain and studies the feasible ways and development strategies to enhance the highspeed railway governance in China. Findings of this paper are as follows. First, the government, as the early manager of high-speed railway governance, has given way to Siemens and other integrated enterprises. Second, the highspeed railway standard output has become the core competitiveness that embodies high-speed railway. Third,the global high-speed railway market presents a hierarchical high-speed railway governance model and changes to a modular approach to governance.

Research on Multi-System Ultra-High Speed Optical Signal Access System

In view of the small transmission capacity and single signal modulation format of the existing optical transmission system, this paper proposes an ultra-high-speed optical signal access scheme based on NEL0670, which can realize the transmission of 100 G DP-QPSK, 200 G DP-16QAM and 400 G DP-16QAM signals, and realize flexible and intelligent reception of multi-system optical signals.

V2X communications with an image sensor

This paper introduces infrastructure-to-vehicle and vehicle-to-vehicle communications using VLC.A VLC coupled with a high-speed image sensor is introduced(i.e.,image sensor communication).The high-speed image sensors provide eyes for autonomous and connected vehicles.VLC imparts data reception capability to image sensors with necessary functions,which can then be provided to autonomous and connected vehicles.In this paper,some of our research on coupling VLC to high-speed image sensors is introduced,including our key findings:the basics of ISC,a vehicle motion model,and range estimation.

High-Performance Broadcasting Algorithms on Cluster

In many clusters connected by high-speed communication networks, the exact structure of the underlying communication network and the latency difference between different sending and receiving pairs may be ignored when they broadcast, such as in the approach adopted by the broadcasting method in MPICH, a widely used MPI implementation. However, the underlying network cluster topologies are becoming more and more complicated and the performance of traditional broadcasting algorithms, such as MPICHs MPI_Bcast, is far from good. This paper analyzed the impact of communication latencies and the underlying topologies on the performance of broadcasting algorithms for multilevel clusters. A multilevel model was developed for broadcasting in clusters with complicated topologies, which divides the cluster topology into many levels based on the underlying topology. The multilevel model was used to develop a new broadcast algorithm, MLM broadcast-2 (MLMB-2), that adapts to a wide range of clusters. Comparison of the performance of the counterpart MPI operation MPI_Bcast and MLMB-2 shows that MLMB-2 outperforms MPI_Bcast by decreasing the broadcast running time by 60%-90%.

Adaptive Tracking for Beam Alignment Between Ship-Borne Digital Phased-Array Antenna and LEO Satellite

In mobile satellite communication networks employing digital beam forming technology,beam alignment imposes great influence on link quality and network efficiency.Owing to complex coupling motion by low earth orbit(LEO)satellite and ship,direction of arrival(DOA)of target satellite varies rapidly and nonlinearly.It then causes difficulty to accurately track the DOA.In this work,an adaptive tracking algorithm is proposed by exploiting advantages of flexible parameter configuration of digital phased-array antenna.The alignment process basically consists of observation and tracking.In the observation stage,two-dimensional(2-D)multiple signal classification(MUSIC)is applied by the ship-borne digital phased-array antenna to estimate beam direction of satellite;in the tracking stage,an extended Kalman filter(EKF)based adaptive tracking is designed to achieve fast and accurate alignment.The proposed adaptive tracking improves performance by adaptively estimating tracking parameters in EKF firstly.The estimation results are then used as feedback to adaptively adjust digital phased-array antenna parameters to improve estimation accuracy of DOA.Simulation results under sea state 5 show that the proposed tracking algorithm improves tracking accuracy and stability over conventional ones.