Lei Xiong

Link Evaluation for MIMO-OFDM System with ML Detection

Link evaluation is very important to system level simulation. Current algorithms for link evaluation show pretty good accuracy for wireless system with linear detections. However, when it comes to MIMO-OFDM system with ML Detection, problems still exists. This paper proposes an Extended Received Block Information Rate algorithm for link evaluation, which is deduced from the view of information and detecting theory. Accuracy and universality of this algorithm for MIMO-OFDM system with ML detection are highlighted. Simulation results show that, comparing to current algorithms for link evaluation, the proposed ERBIR algorithm obtains better accuracy and universality.

On Resource Management in Vehicular Ad Hoc Networks: A Fuzzy Optimization Scheme

Resource management is a crucial task in vehicular ad hoc networks (VANETs) due to the existence of various resources, such as text, audio and video. However, the highly dynamic network feature and the limited memory of the local server pose challenges to resource management, which not only lead to the failure of resource presentations to users, but the transmission of the invalid fragment data would also result in the significant waste of precious bandwidth and memory. To address the issue, our paper proposes a Fuzzy Logic based Resource Management scheme (FLRM) under fog computing platform in VANETs. In the scheme, we first gather and record the request time and download time for each resource by the designed Vehicle to Infrastructure (V2I) communication mode. Depending on the above information, we define a survival time for each stored resource by the proposed fuzzy logic based popularity evaluation algorithm. Motivated by the defined survival time, the local server can update the resource list in real time. In the end, we conduct simulations to verify the performance of FLRM. Results demonstrate that the proposed scheme performs well in terms of throughput, which increases the user experience with fresh resources.

TD-LTE Downlink Performance Assessment in High Speed Scenarios

Long Term Evolution (LTE) is expected to substitute the Global System for Mobile Communications (GSM) as the radio access technology for railway communications. Recently, especial attention has been devoted to high-speed trains since this particular environment poses challenging problems in terms of performance simulation and measurement. In order to severely decrease the cost and complexity of high-speed measurement campaigns, we have proposed a technique to induce effects caused by highly-time varying channels on Orthogonal Frequency-Division Multiplexing (OFDM) signals while conducting measurements at low speeds. In this work, we employ this technique to evaluate LTE transmissions in a Time-Division Duplex (TDD) fashion, which is more convenient for the railway environment due to a number of reasons (e.g., better flexibility in frequency choice and the importance of the uplink transmissions for railway control communications). We assess the performance obtained in high- speed scenarios up to 500 km/h.

A Novel Method for Smoothing Raw GPS Data with Low Cost and High Reliability

The precise spatio-temporal position data of vehicles is useful for most studies, such as wireless link lifetime and node degree in vehicular ad hoc networks. However, due to the system errors and random errors, the existing Global Positioning System (GPS) only provides the positional accuracy about 10m or even worse. In this paper, to address the issue of positional accuracy, a Clustering and Approximating (C-A) algorithm is proposed. We first divide each road into several small parts which are described by linear functions. Then a linear regression algorithm is utilized to approximate traces under system errors, which is reliable for reducing GPS errors. Particularly, when two roads are very close, GPS points may be mapped on adjacent roads. A clustering algorithm is taken to separate GPS points and their positions are revised by the iterative utilization of the linear regression algorithm. In the end, the method mentioned above smoothes raw GPS data of buses in Taiwan to make it available for further researches. Compared with existing methods, the method described in this paper characterized with low cost and high reliability in different situations. Besides, its simple model will make the process of revising data more convenient.

Work in progress: LTE system performance evaluation in high-speed environment

In the case of high-speed railway environment, the performance of mobile communication system is a key issue, which will affect the reliability and efficiency in the wireless communication. In this paper, a LTE system of MIMO based on hardware-in-the-loop (HIL) technology is built to evaluate the performance of LTE system. It contains a transmitter, a receiver and a radio channel emulator with software defined radio (SDR) technology. This system, including figures of the Error Vector Magnitude (EVM) and the Error Bit Ratio (BER), will be obtained under different speeds (80~400km/h) and different scenarios (WINNER C2, WINNER D2 and WINNER D2a). Then, the analysis of relationship between EVM and BER are detailed. At last, environmental factors are inferred which may affect the high-speed mobile communication quality.

Robust QoS-Aware Multi-Service Transmission with Hierarchical Modulation in High-Speed Railway

Adaptive hierarchical modulation is an effective technique to improve the spectral efficiency for multi-service transmission in high-speed railway (HSR) communication systems. Many efforts have been devoted to studying this technique with the perfect channel state information (CSI) assumption. However, the fast time-varying fading channels and feedback delay lead that the perfect CSI cannot be obtained in HSR scenario. Therefore, the performance of the existing non-robust hierarchical modulation schemes degrades severely. This paper proposes a robust adaptive hierarchical modulation scheme, which can bear multiple services in one symbol with different QoS requirements. The closed form bit error rate (BER) expressions of the robust hierarchical modulation scheme are derived, then the adaptive transmission strategy of the HSR communication system is designed. Finally, the performance of the robust hierarchical modulation scheme is evaluated by extensive simulations. Comparing with the uniform modulation scheme, the overall spectral efficiency increases by 15% when the train is at 500 km/h.

See the near future: A short-term predictive methodology to traffic load in ITS

The Intelligent Transportation System (ITS) targets to a coordinated traffic system by applying the advanced wireless communication technologies for road traffic scheduling. Towards an accurate road traffic control, the short-term traffic forecasting which predicts the road traffic at the particular site in a short period is often useful and important. In existing works, Seasonal Autoregressive Integrated Moving Average (SARIMA) model is a popular approach. The scheme however encounters two challenges: 1) the analysis on related data is insufficient whereas some important features of data may be neglected; and 2) with data presenting different features, it is unlikely to have one predictive model that can fit all situations. To tackle above issues, in this work, we develop a hybrid model to improve accuracy of SARIMA. In specific, we first explore the autocorrelation and distribution features existed in traffic flow to amend structure of the time series model. Based on the Gaussian distribution of traffic flow, a hybrid model with a Bayesian learning algorithm is developed which can effectively expand the application scenarios of SARIMA. We show the efficiency and accuracy of our proposal using both analysis and experimental studies. Using the real-world trace data, we show that the proposed predicting approach can achieve satisfactory performance in practice.

On Traffic Bottleneck in Green ITS Navigation: An Identification Method

Traffic congestion has seriously hindered the healthy and sustainable development of economy and society. Many research have been done to address the issue. Intelligent Transportation System (ITS) is key to improve the performance of urban traffic. As one of the essential components of an ITS, green ITS navigation for people and freight is critical, its research must base on the accurate grasp of real-time traffic conditions and the complex nature of the transport network. In order to provide more accurate traffic state information for ITS navigation, we study the traffic bottleneck which is the source of congestion based on complex network and user equilibrium model in this paper. We identify the bottleneck and evaluate its importance according to the consequences of the road failure from two aspects of the traveling cost and the network effectiveness. Furthermore, we verify the performance of the proposed identification method and evacuation strategy by simulating on VISSIM. The research outcome shows that the proposed algorithm is correct and effective.

Energy-Efficient Power Allocation in Cloud Radio Access Network of High-Speed Railway

To meet the increasing demand of high-data-rate services of high-speed railway (HSR) passengers, cloud radio access network (C-RAN) is a promising technique in mobile communication system of HSR. In this paper, we focus on the energy-efficient power allocation problem for providing the high- data- rate services in HSR scenario. Based on the predicted path loss characteristic of HSR, the power allocation is formulated as a non-linear fractional programming problem. The service pro- cessing delay of baseband unit (BBU) pool and radio transmission delay at radio remote units (RRUs) are considered in the services transmission delay constraint. The formulated problem is a non- convex problem, an equivalent convex problem is reformulated firstly, and then propose an iterative algorithm to obtain the optimal power allocation solution. Furthermore, we analyze the effect of small-scale fading on energy-efficiency (EE) performance of the proposed power allocation scheme. Simulation results confirm that the proposed energy-efficient power allocation policy can meet the QoS of passengers and obtain the optimal EE performance.

A Three-Dimensional Accident Driver Model for Vehicular Ad Hoc Networks

Mobility models play a vital role in Vehicular Ad Hoc Networks (VANETs) simulations. Moreover, mobility models with higher extent of reality to fit into the characteristics of VANETs better make simulations more credible and accurate. However, most of traditional mobility models only devote to planar and ideal scenarios. It is rare for them to reflect more realistic environments, such as ubiquitous 3D scenarios where accidents occur frequently because of the complex vehicle motion and human factors. To address these issues, a Three-dimensional Accident Driver Model (T-ADM) is proposed for VANETs in this paper to reflect the real world more realistically. With characteristics based on the combination of plane and space in VANETs, T-ADM can produce 3D scenarios like viaducts in VANETs. Furthermore, T-ADM can mimic the non-standard driver behavior and generate accident scenarios. Finally, a comparison among T-ADM and other mobility models is generated by Matlab and VanetMobiSim. It demonstrates that T-ADM is able to not only reflect the corresponding realistic characteristics mentioned above but also give an objective description of vehicle density and velocity in VANETs.