Oliver W. W. Yang

Vehicular telematics over heterogeneous wireless networks: A survey

This article presents a survey on vehicular telematics over heterogeneous wireless networks. An advanced heterogeneous vehicular network (AHVN) architecture is outlined which uses multiple access technologies and multiple radios in a collaborative manner. The challenges in designing the essential functional components of AHVN and the corresponding protocols (for radio link control, routing, congestion control, security and privacy, and application development) are discussed and the related work in the literature are reviewed. The open research challenges and several avenues for future research on vehicular telematics over heterogeneous wireless access networks are outlined.

Adaptive multipath source routing in ad hoc networks

In this paper, we propose a new multipath routing protocol for ad hoc wireless networks-multipath source routing (MSR), which is an extension of DSR (dynamic source routing). Based on the measurement of RTT, we propose a scheme to distribute load among multiple paths. The simulation results show that our approach improves the packet delivery ratio and the throughput of TCP and UDP, and reduces the end-to-end delay and the average queue size, while adding little overhead. As a result, MSR decreases the network congestion and increases the path fault tolerance quite well.

Energy-aware multicasting in wireless ad hoc networks: A survey and discussion

WANET (wireless ad hoc network) is expected to be deployed in a wide range of civil and military applications. The communicating nodes in these networks might be distributed randomly and are assumed to have packet-forwarding capability in order to communicate with each other over a shared and limited radio channel. Building such networks usually poses a significant technical challenge because energy supplied by batteries is likely to be a scarce resource, and in some applications energy is entirely non-renewable. There are mainly two fundamental classes of energy-aware broadcast/multicast problem in recent research: the MEB/MEM (minimum energy broadcast/multicast) problem and the MLB/MLM (maximum lifetime broadcast/multicast) problem in wireless ad hoc networks with omni-directional and directional antennas. In order to provide a better understanding of the research challenges of the energy-aware multicast routing, this article presents a systematical investigation of current state-of-the-art algorithms for these two classes of optimization problems. Taxonomy, comparison, and open research issues for each problem are also discussed, with an objective to inspire new research interests in this field.

Traffic prediction using FARIMA models

Previous traffic measurements have found the coexistence of both long-range and short-range dependence in network traffic. Therefore, models are required to predict traffic that has both long-range and short-range dependence. This paper provides a procedure to model and predict traffic using FARIMA (p,d,q) models. Our experiments illustrate that the FARIMA model is a good model and is capable of capturing the property of actual traffic. We provide guidelines to simplify the FARIMA model fitting procedure and thus to reduce the time of traffic modeling and prediction.

Finding protection cycles in DWDM networks

We introduce the problem of mesh optical network protection based on multiple logical ring/cycles. A two-staged problem formulation as well as classical ring finding algorithms are first discussed. A state-of-art protection cycle (p-cycle) finding algorithm is then proposed. This algorithm is scalable and especially suitable for sparse mesh networks. Finally, the performance of the algorithm is gauged by running on some real world network topologies.

Design of Adaptive PI Rate Controller for Best-Effort Traffic in the Internet Based on Phase Margin

In this paper, we propose an adaptive PI (proportional-integral) rate controller for the AQM (active queue management) router that would support best-effort traffic in the Internet. Unlike most window-based controllers, our rate-based controller design is derived from the classical control theory and it would allow the users to achieve good stability robustness of the AQM control system by specifying a proper phase margin. We also make our controller adaptive by selecting a simple heuristic parameter to monitor the network environment real-time so that the controller would self-tune only when a dramatic change of the network traffic has drifted the monitoring parameter outside its specified interval. Located in the router, the adaptive PI rate controller calculates desirable source window sizes (i.e., source sending rates) based on the instantaneous queue length of the buffer and advertises it to the sources. Our simulations demonstrate that our AQM control system can adapt very well to sudden changes in network environment, thus providing the network with good transient behavior. By making the source sending rate relatively smooth, our adaptive PI rate controller becomes quite suitable for streaming media traffic control in the Internet

Wireless Traffic Modeling and Prediction Using Seasonal ARIMA Models

Seasonal ARIMA model is a good traffic model capable of capturing the behavior of a network traffic stream. In this paper, we give a general expression of seasonal ARIMA models with two periodicities and provide procedures to model and to predict traffic using seasonal ARIMA models. The experiments conducted in our feasibility study showed that seasonal ARIMA models can be used to model and predict actual wireless traffic such as GSM traffic in China.

Traffic modeling based on FARIMA models

We provide a procedure to fit a FARIMA(p,d,q) (fractional autoregressive integrated moving average) model to the actual traffic trace, as well as a method to generate a FARIMA process with given parameters. We show how to model the traffic by fitting FARIMA models to four measured traces. Our experiments illustrate that the FARIMA model is a good traffic model and is capable of capturing the property of real traffic with long-range and short-range dependent behavior. Unlike previous work on FARIMA models, we deduce some guidelines to reduce the complexity of fitting the FARIMA model which would allow us to reduce the computational time of fitting.

A Lagrangean relaxation and subgradient framework for the routing and wavelength assignment problem in WDM networks

Unlike traditional heuristics, we provide in this paper an optimization framework for the routing and wavelength assignment (RWA) problems with the objective of minimizing the rejection penalty of the connection demands in an all-optical wavelength-division-multiplexing (WDM) network. Our new link-based formulation takes the fairness issue and the limited wavelength conversion into consideration. The framework employs a decomposition approach to decide on the rejection/selection of the route and wavelength assignment for a semilightpath, by appropriately relaxing some of the constraints in the Lagrangean relaxation (LR) method. At the higher level, we update Lagrange multipliers iteratively with the subgradient method. At the lower level, we propose the modified minimum cost semilightpath (MMCSLP) algorithm to solve all the subproblems. A heuristic algorithm is also proposed to generate a feasible RWA scheme based on the solution to the dual problem. When compared with some latest methodology in the literature, we demonstrate that our framework can achieve better performance in terms of the computation time and the number of connection demands rejected. The much shorter computation time is due to the polynomial time complexity of our framework. In addition to achieving a very good (near-optimal) solution, the influence from the change of the number of converters is studied. Finally, we demonstrate that our framework produces fairer routing decisions by adjusting some design parameters in our framework.

Multicast lifetime maximization for energy-constrained wireless ad-hoc networks with directional antennas

We consider the problem of maximizing the lifetime of a given multicast connection in wireless networks that use directional antennas and have limited energy resources. We first provide a globally optimal solution to this problem for the special case of using omnidirectional antennas. This graph theoretic approach provides insights into the more general case of using directional antennas, and inspires us to produce two heuristic algorithms. Experimental results show that minimum total power consumption does not guarantee maximum lifetime for either broadcasting or multicasting, and our algorithms outperform the group of minimum-energy multicast algorithms significantly.