Zhangdui Zhong

Assessment of LTE-R Using High Speed Railway Channel Model

Long Term Evolution for Railway (LTE-R) is commonly believed to be the next generation wireless communication system for high speed railway. The main objective of this paper is to assess the performance of LTE-R under realistic conditions using a hybrid high speed railway channel model involving WINNER II Channel Model that was refined and validated using measurements made within the WP1 Channel Model work package in Europe, high speed train channel model in 3GPP and large-scaled models based on a group of measurements on Zhengzhou-Xian passenger dedicated line in China. The paper presents a detailed evaluation of the BER and PSD for LTE-R suitably dimensioned for the high speed railway channel. The investigation includes analysis of the Doppler shift caused by the velocity of transmitter and receiver, the multipath interference due to reflections and diffractions from terrains in the radio service coverage area, and other serious impairing factors. The results show that LTE-R has promising potential to be used in a high speed railway environment.

Measurement of Distributed Antenna Systems at 2.4 GHz in a Realistic Subway Tunnel Environment

Accurate characterization of the radio channel in tunnels is of great importance for new signaling and train control communications systems. To model this environment, measurements have been taken at 2.4 GHz in a real environment in Madrid subway. The measurements were carried out with four base station transmitters installed in a 2-km tunnel and using a mobile receiver installed on a standard train. First, with an optimum antenna configuration, all the propagation characteristics of a complex subway environment, including near shadowing, path loss, shadow fading, fast fading, level crossing rate (LCR), and average fade duration (AFD), have been measured and computed. Thereafter, comparisons of propagation characteristics in a double-track tunnel (9.8-m width) and a single-track tunnel (4.8-m width) have been made. Finally, all the measurement results have been shown in a complete table for accurate statistical modeling.

MPBC: A Mobility Prediction-Based Clustering Scheme for Ad Hoc Networks

Creating a hierarchical structure by clustering has been considered an effective method to improve the performance of ad hoc networks, such as scalability and stability. This is particularly important for networks with mobile nodes, where the mobility can cause randomly and dynamically changed network topology. In this paper, we propose a mobility prediction-based clustering (MPBC) scheme for ad hoc networks with high mobility nodes, where a node may change the associated cluster head (CH) several times during the lifetime of its connection. The proposed clustering scheme includes an initial clustering stage and a cluster maintaining stage. The Doppler shifts associated with periodically exchanged Hello packets between neighboring nodes are used to estimate their relative speeds, and the estimation results are utilized as the basic information in MPBC. In the initial clustering stage, the nodes having the smallest relative mobility in their neighborhoods are selected as the CHs. In the cluster maintaining stage, mobility prediction strategies are introduced to handle the various problems caused by node movements, such as possible association losses to current CHs and CH role changes, for extending the connection lifetime and providing more stable clusters. An analytical model is developed to find the upper and lower bounds of the average connection lifetime and to find the average association change rate of MPBC. Numerical results verify the analysis and further show that the proposed clustering scheme outperforms the existing clustering schemes in ad hoc networks with high mobility nodes.

Vehicle-to-Vehicle Propagation Models With Large Vehicle Obstructions

Vehicle-to-vehicle (V2V) communication is an enabler for improved traffic safety and congestion control. As for any wireless system, the ultimate performance limit is determined by the propagation channel. A particular point of interest is the shadowing effect of large vehicles such as trucks and buses, as this might affect the communication range significantly. In this paper we present measurement results and model the propagation channel, in which a bus acts either as a shadowing object or as a relay between two passenger cars. The measurement setup is based on a Wireless Open-Access Research Platform (WARP) Field-Programmable Gate Array (FPGA) software radio as transmitter and a Tektronix RSA5106A real-time complex spectrum analyzer as receiver. We analyze the influence of the bus location and car separation distance on the path loss, shadowing, small-scale fading, delay spread, and cross correlation. The main effect of the bus is that it is acting as an obstruction creating an additional 15- to 20-dB attenuation and an increase in the root-mean-square delay spread by roughly 100 ns. A Nakagami distribution is found to well describe the statistics of the small-scale fading, by using Akaikes Information Criterion and the Kolmogorov-Smirnov test. The distance dependence of the path loss is analyzed and a stochastic model is developed.

Joint Beamforming Design and Time Allocation for Wireless Powered Communication Networks

This paper investigates a multi-input single-output (MISO) wireless powered communication network (WPCN) under the protocol of harvest-then-transmit. The power station (PS) with reliable power supply first replenishes the passive user nodes by radio-frequency wireless power transfer (WPT) in the downlink, then each user node transmits independent information to the sink by a time division multiple access (TDMA) scheme in the uplink. We consider the joint time allocation and beamforming design to maximize the system sum-throughput. With perfect channel station information (CSI) at the PS, a semi-closed form solution is proposed by exploiting the strict concavity of the joint design problem. Then, in the case with Gaussian CSI errors, a robust algorithm is proposed to maximize the system throughput subject to the signal-to-noise ratio (SNR) outage probability constraints. Simulation results demonstrate the efficiency of the proposed fast algorithm and validate the robust algorithm.

Performance Analysis of Device-to-Device Communications with Dynamic Interference Using Stochastic Petri Nets

In this paper, we study the performance of Device-to-Device (D2D) communications with dynamic interference. In specific, we analyze the performance of frequency reuse among D2D links with dynamic data arrival setting. We first consider the arrival and departure processes of packets in a non-saturated buffer, which result in varying interference on a link based on the change of its backlogged state. The packet-level system behavior is then represented by a coupled processor queuing model, where the service rate varies with time due to both the fast fading and the dynamic interference effects. In order to analyze the queuing model, we formulate it as a Discrete Time Markov Chain (DTMC) and compute its steady-state distribution. Since the state space of the DTMC grows exponentially with the number of D2D links, we use the model decomposition and some iteration techniques in Stochastic Petri Nets (SPNs) to derive its approximate steady state solution, which is used to obtain the approximate performance metrics of the D2D communications in terms of average queue length, mean throughput, average packet delay and packet dropping probability of each link. Simulations are performed to verify the analytical results under different traffic loads and interference conditions.

High-Speed Railway Communications: From GSM-R to LTE-R

High-speed railways (HSRs) improve the quality of rail services, yield greater customer satisfaction, and help to create socioeconomically balanced societies [1]. This highly efficient transport mode creates significant challenges in terms of investment, technology, industry, and environment. To handle increasing traffic, ensure passenger safety, and provide real-time multimedia information, a new communication system for HSR is required. In the last decade, public networks have been evolving from voice-centric second-generation systems, e.g., Global System for Mobile Communications (GSM) with limited capabilities, to fourth-generation (4G) broad-band systems that offer higher data rates, e.g., long-term evolution (LTE). It is thus relevant for HSR to replace the current GSM-railway (GSM-R) technology with the next-generation railway-dedicated communication system providing improved capacity and capability.

Propagation Measurements and Modeling of Crossing Bridges on High-Speed Railway at 930 MHz

Bridges that cross a railways right-of-way are one of the most common obstacles for wave propagation along a highspeed railway. They can lead to poor coverage or handover failure but have been rarely investigated before. To describe the influence of this nonnegligible structure on propagation, measurements have been taken at 930 MHz along a real high-speed railway in China. Based on different mechanisms, the entire propagation process is presented by four zones in the case of an independent crossing bridge (ICB) and two zones in the case of groups of crossing bridges. First, all the propagation characteristics, including extra propagation loss, shadow fading, small-scale fading, and fading depth, have been measured and extracted. The results are shown in a complete table for accurate statistical modeling. Then, two empirical models, i.e., ICB and crossing bridges group (CBG), are first established to describe the extra loss owing to the crossing bridges. The proposed models improve on the state-of-the-art models for this problem, achieving a root mean square error (RMSE) of 3.0 and 3.7 dB, respectively.

Finite state Markov modelling for high speed railway wireless communication channel

How to provide reliable, cost-effective wireless services for high-speed railway (HSR) users attracts increasing attention due to the fast deployment of HSRs worldwide. A key issue is to develop reasonably accurate and mathematically tractable models for HSR wireless communication channels. Finite-state Markov chains (FSMCs) have been extensively investigated to describe wireless channels. However, different from traditional wireless communication channels, HSR communication channels have the unique features such as very high speed, deterministic mobility pattern and frequent handoff events, which are not described by the existing FSMC models. In this paper, based on the Winner II physical layer channel model parameters, we propose a novel FSMC channel model for HSR communication systems, considering the path loss, fast fading and shadowing with high mobility. Extensive simulation results are given, which validate the accuracy of the proposed FSMC channel model. The model is not only ready for performance analysis, protocol design and optimization for HSR communication systems, but also provides an effective tool for faster HSR communication network simulation.

Resource control in network assisted device-to-device communications: solutions and challenges

Network assisted Device-to-Device (D2D) communications is envisioned as a promising technology to facilitate the discovery of geographically close cellular devices and reduce the communication cost between these devices. In order to fully take advantages of the freedom in resource management introduced by D2D communications, it is essential to design optimal resource control policies. In this article, we first review and classify the state-of-the-art research based on different considered network scenarios. We then introduce our preliminary studies on delay-aware resource control with bursty traffic, in which we propose an optimization framework and formulate a general queuing model for performance evaluation and optimization. Finally, the challenges and open issues are highlighted to serve as guidelines for future research.