Xuming Fang

A CoMP soft handover scheme for LTE systems in high speed railway

With the development of high-speed railway and public growing demand on data traffic, people pay much more attention to provide high data rate and high reliable services under high mobility circumstance. Due to the higher data rate and lower system latency, long-term evolution (LTE) has been chosen as the next generations evolution of railway mobile communication system by the International Union of Railways. However, there are still many problems to be solved in the high mobility applications of LTE, especially the higher handover failure probability, which seriously degrades the reliability of railway communication. This article proposes an optimized handover scheme, in which the coordinated multiple point transmission technology and dual vehicle station coordination mechanism are applied to improve the traditional hard handover performance of LTE. The scheme enables the high speed train to receive signals from both adjacent base stations and obtain diversity gain when it moves through the overlapping areas, so it improves the quality of the received signal and provides reliable communication between train and ground eNodeBs. Numerical analysis and simulation results show that the proposed scheme can decrease the outage probability remarkably during handover and guarantee the reliability of train to ground communication.

An On-Vehicle Dual-Antenna Handover Scheme for High-Speed Railway Distributed Antenna System

Distributed antenna technology, as one of the important next-generation wireless communication technologies, has aroused extensive attention. The technology has been applied in high-speed movement environment. Due to the high density coverage of distributed antennas, almost anywhere in the area has line-of-sight (LOS) to reach at least one fixed antenna. However it may correspondingly result in smaller overlap between adjacent cells and higher probability of handover failure in high-speed movement scenario. In order to solve these problems, this paper proposes a novel handover scheme based on on-vehicle dual-antenna for high-speed railway distributed antenna system (DAS). On-vehicle antennas which collaborate each other, are mounted on the top of high-speed train (the one is in the front-end and the other is in the rear-end). The proposed scheme utilizes distributed transceivers and centralized processing technology. The numerical analysis results show that the novel scheme can pre-trigger handover appropriately, guarantee the higher handover success rate, and increase the system throughput by around 50%. In addition, the scheme is feasible and easy to be implemented.

Handover Scheme for 5G C/U Plane Split Heterogeneous Network in High-Speed Railway

Being a promising technology for fifth-generation (5G) communication systems, a novel railway communication system based on control/user (C/U) plane split heterogeneous networks can provide a high-quality broadband wireless service for passengers in high-speed railways with higher system capacity, better transmission reliability, and less cochannel interference. However, due to its special architecture where the C-plane and the U-plane must be split and supported by a macro Evolved Node B (eNB) and a phantom eNB, respectively, it would suffer more serious handover problem, particularly in intermacrocell handover, which directly degrades its applicability and availability in high-speed railways. Moreover, no technical specification has been released about this network architecture. Therefore, this paper focuses on redesigning and analyzing technical details and handover procedures based on Long-Term Evolution (LTE) specifications to guarantee the proposed systems practicability and generality and its analytical tractability. To resolve the handover problem, this paper proposes a handover trigger decision scheme based on GM(1, n) model of the grey system theory. By this scheme, the received signal quality from the (N + 1)th measurement report can be predicted from the Nth measurement period, and the predicted values can be then utilized to make the handover trigger decision. The simulation results show that our proposed scheme is capable of triggering handover in advance effectively and of enhancing handover success probability remarkably.

Efficient Multiple-Group Multiple-Antenna (MGMA) Scheme for High-Speed Railway Viaducts

The capacity of a multiple-input-multiple-output (MIMO) channel with N transmit and receive antennas for highspeed railways (HSRs) is analyzed based on the 3-D modeling of the line of sight (LOS). The MIMO system utilizes a uniform linear antenna array. Instead of increasing the number of antennas or simply changing the parameters of the antenna array, such as separation and geometry, the capacity gain can be obtained by adjusting the weights of multiantenna array groups, because there are few scatterers in strong LOS environments. On the other hand, it is hard to obtain the array gain of MIMO beamforming for HSRs because of drastic changes in the receiving angle when the train travels across E-UTRAN Node B. Without changing the antenna design of Long-Term Evolution systems, this paper proposes a multiple-group multiple-antenna (MGMA) scheme that makes the columns of such a MIMO channel orthogonal by adjusting the weights among MGMA arrays, and the stable capacity gain can be obtained. The value of weights depends on the practical network topologies of the railway wireless communication system. However, the reasonable scope of group number N is less than 6. In selecting N, one important consideration is the tradeoff between practical benefit and cost of implementation.

Admission Control Based on Available Bandwidth Estimation for Wireless Mesh Networks

Admission control plays a very important role in guaranteeing the quality-of-service (QoS) in wireless mesh networks (WMNs). In this paper, based on the channel and hidden terminal information, we first estimate the available bandwidth in the operation of medium access control (MAC). We then design an admission control algorithm (ACA) at the MAC layer to address the QoS issue for real-time and nonreal-time traffic. For real-time traffic, all nodes on a route make an admission control decision based on the estimated available bandwidth. For the nonreal-time traffic, a rate adaptation algorithm is proposed to adjust the sending rates of sources to prevent the network from entering the congestion state. Finally, through extensive simulations, we demonstrate the effectiveness of our algorithm.

Beamforming and positioning-assisted handover scheme for long-term evolution system in high-speed railway

As the railway industry expands and trains speed-up, the reliability and efficiency of wireless communication systems in high-speed railway have to face the severe challenges. The high-speed brings about more severe Doppler effect, the postponement of handover triggering location and more frequent handover. Therefore the influence caused by the high-speed decreases the reliability of wireless communication network. In this study, considering the decision of `global system for mobile communication for railway` evolution to long-term evolution for railway (LTE-R) by International Union of Railways, a scheme based on the beamforming and positioning information is proposed to improve the system handover performance for the LTE system which is being applied to the high-speed railway. In the overlapping region, both the current serving eNodeB and the target eNodeB start to use beamforming with different gain factors to improve handover success probability. The results have shown that the proposed scheme increases the handover success probability effectively.

An efficient handoff algorithm based on received signal strength and wireless transmission loss in hierarchical cell networks

Compared with the macrocell systems, the femtocell systems allow users to obtain broadband service with high data rate by using lower costs of transmit power, operation and capital expenditure. Traditional handoff algorithms used in macrocells cannot well satisfy the mobility of users efficiently in hierarchical macro/femto cell networks. In this paper based on the received signal strength (RSS) and wireless transmission loss, a new handoff algorithm in hierarchical cell networks called RWTL-HO is proposed, which considers the discrepancy in transmit power between macrocell and femtocell base stations. The simulation results show that compared with the conventional algorithm, the proposed algorithm improves the utilization of femtocells by doubling the number of handoffs; and in comparison with the handoff algorithm based on combining the RSSs from both macro and femto cell base stations, reduces half the number of redundant handoffs.

Control and data signaling decoupled architecture for railway wireless networks

Current implementations of narrowband Global System for Mobile Communications for railway systems are facing significant challenges in meeting the emerging massive capacity demands of passenger services. To extend the capacity, this article presents a control and data signaling decoupled architecture, namely, C/U-plane decoupled architecture for railway wireless networks, in which the relatively important C-plane of passenger services is kept on high-quality lower frequency bands to handle mobility, while the corresponding U-plane is moved to higher frequency bands to gain broader spectra. In this railway wireless network with C/U-plane decoupled architecture, the U-plane and C-plane handovers are also physically decoupled. To achieve the seamless and soft U-plane handover, we introduce a handover scheme based on coordinated multi-point transmission and reception and bi-casting. In addition, channel mappings and physical layer frames are redesigned to facilitate the design. Our study has demonstrated that by decoupling the C/U planes, the network performance is greatly enhanced, leading to a more effective way to provide high speed communications for railway systems.

A Short-Term Forecasting Algorithm for Network Traffic Based on Chaos Theory and SVM

Recently, the forecasting technologies for network traffic have played a significant role in network management, congestion control and network security. Forecasting algorithms have also been investigated for decades along with the development of Time Series Analysis (TSA). Chaotic Time Series Analysis (CTSA) may be used to model and forecast the time series by Chaos Theory. As one of the prevailing intelligent forecasting algorithms, it is worthwhile to integrate CTSA and Support Vector Machine (SVM). In this paper, after the vulnerabilities of Local Support Vector Machine (LSVM) in forecasting modeling are analyzed, the Dynamic Time Wrapping (DTW) and the “Dynamic K” strategy are introduced, as well as a short-term network traffic forecasting algorithm LSVM-DTW-K based on Chaos Theory and SVM is presented. Finally, two sets of network traffic datasets collected from wired and wireless campus networks, respectively, are studied for our experiments.

Greedy-based dynamic channel assignment strategy for cellular mobile networks

This letter proposes a greedy-based dynamic channel assignment (GDCA) strategy in cellular mobile communication networks. Its main feature is that it dynamically allocates the channels based on the greedy method. Instead of the regular hexagon cell shape considered by previous strategies such as BCO, BDCL, various CP-DCA, the new strategy can be applied to any irregular cell shape. In addition, it reuses channels in terms of C/I ratio criteria. By system simulation, the proposed strategy outperforms the still used FCA on call blocking probability, and even has better performance compared to BDCL and CPDCA, etc.