George Lampropoulos

Media-independent handover for seamless service provision in heterogeneous networks

The performance of current Internet applications is based mainly on the capabilities of the underlying network technologies. Modern access systems usually can satisfy delay, loss, or bandwidth requirements; however, design inconsistencies can lead to service degradation as the terminals move across different systems. In this article, the focal point is the satisfaction of service requirements during mobility and more specifically, how the emerging IEEE 802.21 standard enables seamless, inter-technology handover. Based on prior work and a well-known example of seamless mobility, the main seamless mobility principles are identified and used as the basis for further evaluating the potential of the IEEE 802.21 standard to meet the requirements of applications for minimum disruption during an inter-technology handover.

A flexible UMTS/WLAN architecture for improved network performance

Current trends in cellular telecommunications suggest the incorporation of Wireless Local Area Networks (WLANs) as supplementary access technologies into the existing cellular infrastructure. Overlay network architectures are expected to improve both service provision and resource utilization under the condition that sophisticated architectural options are followed. Many proposals suggest that all active connections be handled through the same access network technology. However, this is not believed to be efficient in a heterogeneous environment. Therefore, a mechanism that allows each connection of a terminal to be served by different radio access technology is introduced. Based on a tight coupling architecture for interworking between Universal Mobile Telecommunications System (UMTS) and WLANs, the proposed scheme combines a sophisticated decision mechanism with flexible connection management in a way that ensures seamless service continuity during handover. The performance of the system is evaluated using a detailed simulation model and compared against existing architectures. Simulation results indicate an improvement in parameters such as connection and handover blocking probabilities, which justifies the enhancement in the overall usage of network resources when connections are handled separately.

A Power Consumption Analysis of Tight-Coupled WLAN/UMTS Networks

The proliferation of WLANs and the ubiquitous coverage of cellular networks have resulted in several integration proposals towards 4G networks. Among them, the tight- coupled WLAN/UMTS architectures promise seamless service continuity to users and enhanced network performance. Most of these solutions assume that only one interface is active at a time, while much fewer consider the concurrent use of both WLAN and UMTS interfaces as this is expected to consume more energy. This paper presents a detailed description of power consumption for the two different tight-coupled WLAN/UMTS approaches based on the states of the wireless devices. A simple analytical model is provided for estimating the power consumption in each approach, while a simulation model measures the power needs for more complicated cases. Moreover, the enhancement due to a power-saving mechanism in WLAN is also assumed in the system and useful deductions are provided about the average power consumption per mobile terminal.

A flexible handover mechanism for seamless service continuity in heterogeneous environments

The success of wireless access technologies, such as wireless LANs, has forced mobile operators and manufacturers to consider their integration into 3G infrastructures. Nowadays, several research groups and standardization bodies are working to provide such integrated architectures. One of the main aims of these architectures is to provide seamless service continuity to users that move from one access system to another. Towards this end, new mobility management mechanisms are required to minimize transition time between systems and efficiently handle the scarce radio resources to guarantee specific Quality of Service (QoS). This paper specifies such an architecture, which will enable continuous QoS support in an integrated system of multiple access technologies. More specifically, the paper focuses on the network context information that has to be considered during a transition between these systems and the required handover mechanism for the support of seamless service continuity. This architecture requires slight modifications of existing protocols and supports differentiated treatment for each active service.

A Seamless Service Continuity Scheme for Enhanced Network Performance in UMTS/WLAN Networks

The proliferation of wireless access technologies, mostly wireless LANs, along with the ubiquitous coverage of cellular networks, has spurred many researchers to consider schemes for integrated network provision. In overlaying network environments, flexible resource management and service continuity during handover play a crucial role in the quality-of-service seen by the user. This paper describes an integrated UMTS/WLAN architecture that manages to establish every connection in a mobile terminal through the most appropriate access network, based on both network policies and user preferences. Moreover, connections are handed over independently between UMTS and WLAN, aiming at seamless service continuity. A detailed simulation model is used to measure the performance of the proposed architecture against existing schemes

Dynamic channel assignment with delay and loss considerations for wireless TDMA LANs

The scarce available bandwidth and the unpredictable, variable bit rate traffic in modern packet-switched wireless LANs, require an efficient channel allocation scheme. In this paper we make an overview of traditional call-by-call dynamic channel assignment (DCA) methods and propose a novel DCA method that aims at assigning channels in a more dynamic way, based on the quality-of-service (QoS) required by different connections. Although the method can be applied in different wireless environments, here it is used in a wireless ATM LAN, in conjunction with a TDMA/TDD medium access control protocol. Simulation results at the end of the paper show that this kind of methods can improve significantly the performance of the system.

Radio Access Selection in Integrated UMTS/WLAN Networks

Heterogeneous networks combine different access technologies. An important problem in such networks is the selection of the most suitable radio access network. To perform this task efficiently, a lot of information is required, such as signal strength, QoS, monetary cost, battery consumption, and user preferences. These are well known issues and a considerable effort has been made to tackle them using a number of solutions. These efforts improve the performance of vertical handover but also add considerable complexity. In this paper, we introduce an enhanced algorithm for radio access network selection, which is simple, flexible and applicable to future mobile systems. Its main characteristics are the distribution of the radio access selection process among the mobile terminal and the core network, the evaluation of mobile terminal connections separately and the primary role of user preferences in the final decision. The performance of the algorithm is evaluated through simulation results, which show that the algorithm provides a high rate of user satisfaction. It decreases the messages required for the vertical handovers in the whole network and it alleviates the core network from the processing of unnecessary requests.

Joint application and physical layer adaptation for improved performance in wireless networks

Lately, cross-layer design in wireless networking has met significant interest. Thus, in the recent literature many cross-layer designs for the performance improvement of a variety of wireless communication networks can be found. In this paper, we describe the notion of cross-layer design, note its significance for wireless communication networks and provide a state of the art containing indicative examples of cross-layer designs in major areas of wireless communications. Additionally, as a case study, we describe a cross-layer mechanism that achieves improved performance of real-time applications over IEEE 802.16(e) networks.

A QoS-oriented dynamic channel assignment method for wireless ATM LANs

A centralized approach for dynamic channel assignment (DCA) in wireless systems is presented. The proposed method applies to structured wireless LANs, where base stations act as hubs to offer wireless access to mobile terminals. We focus on wireless ATM LANs, although the method applies also to other packet-based systems, offering quality-of-service (QoS) guarantees. A central scheduler for DCA (CSDCA) is introduced for the dynamic assignment of resources to the requesting base stations. This scheduler takes into account mutual interference constraints of the base stations, current resource usage, and delay constraints of active connections. Simulation results have shown the improved performance attained by the proposed method.

Enhancing performance of IP service in HIPERLAN/2 networks

The demand for multimedia applications nowadays has driven the existing wireless IP technologies towards the direction of more robust and effective solutions. Performance enhancing proxies (PEPs) are featuring as a proper candidate in order to provide with the performance enhancements required The solution evaluated in this paper is a PEP, referred to as wireless adaptation layer (WAL), which aims at offering traffic differentiation and QoS improvements over a wide variety of existing wireless technologies, such as IEEE 802.11b, Bluetooth and HIPERLAN/2. Our focus is on the HIPERLAN/2 wireless infrastructure, which is tested with the presence of the WAL under various traffic conditions. A detailed simulation model shows the improvement in QoS offered by the WAL.