Andy Lock Yen Low

Energy efficient network selection and seamless handovers in Mixed Networks

Network selection is the decision process for a mobile terminal to handover between homogeneous or heterogeneous networks. This handover decision can be either mobile or network initiated. Todays decision is mainly based on the received signal strength (RSS). In the future as the number of available networks increase the selection process must evaluate additional factors such as monetary cost, offered services, network conditions, required energy to operate in a network, system conditions, user and operators preferences. Upcoming IEEE or 3GPP standards provide facilities such as network maps, handover negotiation messages, network and client event reports and message exchange like handover triggers and handover negotiation. In this paper we investigate the use of a cost function to perform an optimal network selection using information provided by these standards, such as network coverage map or network properties. The cost function provides flexibility to balance different factors in the decision making, and our research is focused on improving both seamlessness and energy efficiency of the device and handovers. We evaluated our approach based on usage scenarios over WiFi, WiMax, and 3G networks using captured signal strength traces. The results of our simulations and early implementation show that our schemes select the optimal networks and handovers were triggered at appropriate times to increase overall network connectivity as compared to traditional triggering schemes, while at the same time optimizing energy consumption of multi-radio devices.

Smart Predictive Trigger for Effective Handover in Wireless Networks

Roaming across heterogeneous wireless networks poses a challenging issue in mobility management such as seamless and efficient handover to reduce end-users service interruption. Efficient techniques for seamless handover between access points (APs) when user roams from one area to another can be categorized into three stages in conventional way, i) initiation, ii) preparation, and iii) execution. However, frequent handover may overload the network with signalling traffic and causes call dropping to increase as well. This paper takes a deeper look at predictive triggers at the link layer. With an appropriate implementation of predictive triggering algorithms, early handover initiation and preparation could be performed. This paper addresses the investigation on predictive and accurate mechanisms to generate a handover trigger.

SIP-based proactive and adaptive mobility management framework for heterogeneous networks

In this paper, we present and evaluate the performance of a mobility management system called the Proactive and Adaptive Handover (PAHO) system. PAHO is an application-level approach that uses SIP to manage client-initiated connection handoff across heterogeneous networks based on the IEEE 802.21 framework with designated user/configuration policy. Unlike conventional systems which make sub-optimal decision when managing connection handoff due to limited awareness of the relevant context for the application/service being delivered, PAHO defines proper interface to interact with the application as to determine when and to where the handoff and/or codec switching should take place in the event of network performance degradation. The results showed that using the PAHO approach on an audio/video conferencing session helps reducing the overall handover delay from 10.766s (on non-PAHO system) down to at least 288ms, and slowing down the degradation of MOS value throughout the entire experiment in the event of signal degradation as well as network congestion. It is also shown that load balancing among the access points (AP) could be achieved with an improved Information Server (IS).

A five-order mode converter for multimode waveguide

A numerical model of five-order mode converter that converts the order of modes in an integrated-optic multimode waveguide is proposed. Such a structure is useful in optical guiding wave devices for mode control and mode shuffling. The dimensions and index profile of the device are well within the capabilities of the state of the art of integrated optics technology. We have successfully optimized the structural design of the device for propagation loss of less than 13.1 dB at an operating wavelength of 1.55 /spl mu/m. A cascaded form of the five-order mode converter is also proposed for selective mode conversion without the need of restructuring the connection within the device.

New strategy for optimizing wavelength converter placement.

This paper proposes a new strategic alternate-path routing to be combined with the particle swarm optimization (PSO) algorithm to better solve the wavelength converters placement problem. The strategic search heuristic is designed to provide network connectivity topologies for the converters to be placed more effectively. The new strategy is applied to the 14-node NSFNET to examine its efficiency in reducing the blocking probability in sparse wavelength conversion network. Computed results show that, when applied to the identical optimization framework, our search method outperforms both the equal-cost multipath routing and traffic-engineering-aware shortest-path routing.

A conservative approach to adaptive call admission control for QoS provisioning in multimedia wireless networks

In this paper, we propose a framework called conservative and adaptive quality of service (CAQoS) to perform the quality of service (QoS) provisioning on both real-time and non real-time traffic in the wireless network. Unlike most conventional schemes which gradually scale-down the bandwidth rates of ongoing connections to accommodate new connection/handoff requests, CAQoS introduces an early scaling-down of bandwidth for new connections based on designated provisioning model. The objectives of CAQoS are to minimize the need for frequent bandwidth reallocation and to achieve lower call blocking and handoff dropping rates, while maximizing the overall bandwidth utilization. The performance of CAQoS system is evaluated through simulations of a realistic wireless cellular-based environment. Simulation results showed that CAQoS met our objectives and outperformed the conventional schemes.

Optimal placement of wavelength converters in WDM networks using particle swarm optimizer

The introduction of wavelength converters in all-optical networks can reduce the blocking probabilities of calls. The main contribution of this paper is that we introduce a novel search algorithm namely particle swarm optimizer in finding the optimum solution to the converter placement problem. Experiments have been conducted to demonstrate the effectiveness and efficiency of the proposed algorithm. The computed results show that it is more cost effective to introduce additional wavelength channel in a single fiber than placing more wavelength converters.

IEEE 802.21 Assisted Seamless and Energy Efficient Handovers in Mixed Networks

Network selection is the decision process for a mobile terminal to handoff between homogeneous or heterogeneous networks. With multiple available networks, the selection process must evaluate factors like network services/conditions, monetary cost, system conditions, user preferences etc. In this paper, we investigate network selection using a cost function and information provided by IEEE 802.21. The cost function provides flexibility to balance different factors in decision making and our research is focused on improving both seamlessness and energy efficiency of handovers. Our solution is evaluated using real WiFi, WiMax, and 3G signal strength traces. The results show that appropriate networks were selected based on selection policies, handovers were triggered at optimal times to increase overall network connectivity as compared to traditional triggering schemes, while at the same time the energy consumption of multi-radio devices for both on-going operations as well as during handovers is optimized.

Wavelength Converters Placement in All Optical Networks Using Particle Swarm Optimization

Placement of wavelength converters in an arbitrary mesh network is known to be a NP-complete problem. So far, this problem has been solved by heuristic strategies or by the application of optimization tools such as genetic algorithms. In this paper, we introduce a novel evolutionary algorithm: particle swarm optimization (PSO) to find the optimal solution to the converters placement problem. The major advantage of this algorithm is that does not need to build up a search tree or to create auxiliary graphs in find the optimal solutions. In addition, the computed results show that only a few particles are needed to search the optimal solutions of the placement of wavelength converters problem in an arbitrary network. Experiments have been conducted to demonstrate the effectiveness and efficiency of the proposed evolutionary algorithm. It was found that the efficiency of PSO can even exceed 90% under certain circumstances. In order to further improve the efficiency in obtaining the optimal solutions, four strategic initialization schemes are investigated and compared with the random initializations of PSO particles.

Compound parabolic tapered fiber for fiber coupling with a highly divergent source

A novel fiber tapering shape, which is based on compound parabolic geometry, is proposed to increase the acceptance angle of a compound parabolic concentrator. The proposed design is described by use of ray optics on a step-index multimode fiber.