Handover Latency and Interoperability in Future Generation Wireless Mobile Heterogeneous Environment

Vertical handover supporting pervasive computing in future wireless networks

This paper presents solutions for security context transfer for vertical handover between heterogeneous networks. Seamless vertical handover is an important function of Beyond 3G systems. Context transfer can help support seamless vertical handover while maintaining required security level. So as to come to solutions for security context transfer, this paper first analyses trust relationship between different participants of vertical handover and gives a definition of security context. Context transfer schemes for no coupling, loose coupling and tight coupling of networks are then presented.

Future generation wireless networks should provide to mobile users the best connectivity to services anywhere at anytime. The most challenging problem is the seamless intersystem/vertical mobility across heterogeneous wireless networks. In order to answer it, a vertical handover management system is needed. In our paper, we propose an intelligent solution answering user requirements and ensuring service continuity. We focus on a vertical handover decision strategy based on the context-awareness concept. The given strategy chooses the appropriate time and the most suitable access network among those available to perform a handover. It uses advanced decision algorithms (for more efficiency and intelligence) and it is governed by handover policies as decision rules (for more flexibility and optimization). To maintain a seamless service continuity, handover execution is based on mobile IP functionalities. We study our decision system in a case of a 3G/UMTS-WLAN scenario and we discuss all the handover decision issues in our solution.

With financial, business and personal transactions shifting to the mobile domain, Mobile Computing and Wireless Communication technologies are on focus. One of the major challenge is to provide best connectivity across heterogeneous networks, in fast moving vehicles, without knowledge and disturbance to the user. An Intelligent system is required for seamless vertical handover, with less battery consumption and with best connectivity. The Vertical Handover process can be optimized for different criteria like cost, bandwidth, signal strength etc. This paper aims to develop a best solution framework for VHO in vehicular networks where OMNeT++ (Objective Modular Network Testbed in C++) can be used for evaluating and testing along with Veins (Vehicles in Network Simulation) software for the simulation of Inter-Vehicular Communication (IVC) framework, which is composed of an event-based network simulator and a road traffic micro simulation model.

Wireless channels vary drastically over time and mobility adds further difficulties to the engineering problem of providing stable and robust communication performance. Handovers occur regularly in mobile environments and the increasing heterogeneity of present networks leads to the requirement for seamless vertical handovers. An important practical problem is the lack of a generic interface that enables applications, such as a vertical handover decision engine, to retrieve comparable link-layer information independently of the deployed technology or the used software and hardware platform. In this paper we propose the Unified Link-Layer API (ULLA) as a solution to this problem. We describe its architecture, how it can be utilized for vertical handover scenarios and introduce our Linux prototype. The prototype performance proves that ULLA is appropriate for mobility management.

Particle swarm optimization application for multiple attribute decision making in vertical handover in heterogenous wireless networks

Future-generation wireless networks have been envisioned as the integration of various wireless access networks, including both wireless wide area networks and wireless local area networks. In such a heterogeneous network environment, seamless mobility support is the basis of providing uninterrupted wireless services to mobile users roaming between various wireless access networks. Because of transparency to lower-layer characteristics, ease of deployment, and greater scalability, the application-layer-based session initiation protocol has been considered the right candidate for handling mobility in heterogeneous wireless networks. However, SIP entails application-layer transport and processing of messages, which may introduce considerable delay. As a case study of the performance of mobility management protocols in the heterogeneous wireless networks, we analyze the delay associated with vertical handoff using SIP in the WLAN-UMTS internetwork. Analytical results show that WLAN-to-UMTS handoff incurs unacceptable delay for supporting real-time multimedia services, and is mainly due to transmission of SIP signaling messages over erroneous and bandwidth-limited wireless links. On the other hand, UMTS-to-WLAN handoff experiences much less delay, mainly contributed by the processing delay of signaling messages at the WLAN gateways and servers. While the former case requires the deployment of soft handoff techniques to reduce the delay, faster servers and more efficient host configuration mechanisms can do the job in the latter case.

Wireless mesh networks (WMN) are believed to be a highly promising technology and will play an increasingly important role in future generation wireless mobile networks. Routing in WMN is a challenging problem as a result of highly dynamic topology as well as bandwidth and energy constraints. The swarm intelligence paradigm, such as ant colony optimization (ACO), has recently been demonstrated as an active approach for routing in both wired and wireless networks. We designed a novel ACO-based multicasting routing algorithm. In the proposed algorithm, a source-based approach is adapted to build a multicast tree among all the multicast members, and an evolutional scheme for the original multicast tree is designed to find a more optimal multicast tree. In addition the evolutional scheme also acts as a local recovery technique when some intermediate nodes move away. Compared with ODMRP and MAODV, the proposed algorithm performs better in terms of average delay, success ratio and efficiency.

Today, wireless network devices are equipped with multiple access technologies like UMTS andWireless LAN. The handover between the technologies has been widely studied in literature. Several of these research papers build their handover mechanisms on top of existing protocols like Mobile IP. These protocols operate on the network layer and recognize link layer changes only by timeouts. Consequently, if no cross layer approach is implemented, a seamless vertical handover between Wireless LAN and UMTS cannot be provided.In this paper, we introduce a vertical handover protocol based on a tightlycoupled network architecture. With this architecture, it is possible to perform the handover on the link layer and thus, reducing the handover delays. The protocol is implemented in a simulation environment and the results reveal that a seamless vertical handover can be performed with blackout times of only a few milliseconds.

Pervasive computing is a vision involving future generation computing environmentsnin which information and communication technologies are seamlessly integrated tonsupport diverse aspects of users' lifestyles. Pervasive computing environments willnsee sophisticated sensors, actuators, and monitoring devices embedded into livingnenvironments and interconnected with a variety of computing devices and networkingntechnologies. In the last decade, significant technological advances have led to thenproliferation of new devices, such as handheld computers (e.g., PDAs and mobilenphones), wearable computers and intelligent home and office appliances. Advances innnetworking technologies have also seen a shift from wired to wireless networks andnincreasing availability of wireless access in businesses and academic institutions, asnwell as in public hot spots located in libraries, coffee shops, and other public places.nAt the same time, developments in wireless technologies have equipped devices withnshort range connection capabilities, allowing computing devices and smart appliancesnlocated within close range of one another to form micro networks without any centralnnetwork infrastructure. Current cellular mobile technology is also providing lownspeed data connections and laying the foundations for future mobile networks thatnwill provide multimedia streaming capabilities to mobile devices.n n Together, these emerging technologies are enabling the vision of pervasive computingnto take shape, so that users are provided with the control and flexibility to performntheir computing tasks in a manner that suits their lifestyles and requirements. Sincenpervasive computing environments combine heterogeneous networking and devicentechnologies, pervasive systems are required to adapt to changes in the context innwhich computational applications operate. This adaptation can take various forms,nsuch as adaptation of applications, communication streams, or underlyingncommunication protocols. One possible type of communication protocol adaptation isnvertical handover between different networks (i.e., redirection of applications'ncommunication streams from one network to another).n n Vertical handover permits users to move freely between heterogeneous networks ornchange computing devices while maintaining application continuity. However, currentnvertical handover solutions are not context-aware and are restricted to reactions tondisconnections as users move out of network coverage. Since the vertical handovernmechanism relies on reactions to disconnections, disruption of the communicationnstream always occurs during the handover process, and the QoS requirements of thenapplication are likely to be violated. This is often inappropriate, especially fornmultimedia applications, which have stringent QoS requirements. A better solution fornpervasive systems is to perform vertical handovers in response to a wider set ofncontext changes, which may include (i) prediction of users moving in or out ofnnetwork coverage, (ii) changes in the network, leading to QoS that is unacceptable fornapplications, (iii) movement of users between different computing devices whilencontinuing their applications, or (iv) users entering preferred networks. This thesisnpresents an innovative solution for vertical handovers in pervasive systems that cannsupport all of these types of context-triggered handover.n n The thesis makes a number of significant research contributions. Firstly, it presents ancontext model that defines types of context information and context changes that arenrelevant to vertical handover in pervasive computing environments. Secondly, itndevelops a set of context evaluation and decision rules for triggering vertical handovernand performing stream adaptations to address QoS requirements. Thirdly, it defines angeneric vertical handover protocol and architecture for handover between networks orndevices. It also presents refinements to the generic solution that take into accountnfeatures of particular networking technologies. Fourthly, the thesis illustratesnmechanisms that can be incorporated into the vertical handover solution to counternand minimise QoS violations during changes between networks, in order to minimisenapplication disruption and maximise handover transparency for the user. Finally, as anproof of concept, the thesis presents a prototype that demonstrates the ability of thenproposed vertical handover architecture to support seamless computing, and alsonenables performance evaluation for various types of networking technology.n

Wireless communication network is evolving towards more heterogeneous with rapid emergence of new radio technologies. 60GHz radio relying on line-of-sight (LOS) transmission is one of the promising solutions to support in-door high quality multimedia applications. Due to the vulnerable nature of LOS links, vertical handover, by switching the mobile device to the backup WLAN system from 60GHz radio, is critical to support a seamless session. However vertical handover for short LOS blocking events degrade perceived quality of the media due to frequent switching. In this paper, we propose a cognitive approach to solve incertitude during vertical handover. We first present an overview of our proposed cognitive network architecture, and further under this framework we introduce and examine via simulations a decision algorithm based on decision theory. Our algorithm takes into account multiple factors such as user preference, network situation, device capability and effect of environment. We show its ability to effectively make handover decision in uncertain situations. The method and results herein are applicable, in general, to any other situation where such a decision is to be made.

The convergence of wireless systems with multimedia services is the challenge of future generation wireless networks. The large variety of QoS requirements of different media as well as the maintenance of synchronization of the different streams to be presented at receiver, demand from the Data link layer some extra functionalities. In this paper, we present an enhanced approach for the efficient management of multimedia applications in third-generation wireless networks. We advocate the use of multiple connections, one for each traffic component of the application, as the effective solution for the transport of multimedia applications in future-generation wireless networks. The effectiveness of this scheme is guaranteed by providing a new link control technique that works on top of a PRMA-type access protocol which jointly manages different streams of a multimedia application. For this purpose, we propose a two-level priority mechanism (static and dynamic priorities) specified by higher protocol layers for link activation, channel access, and admission control procedures specific to a multimedia application and for optimizing the sharing of radio channel resources and management of the reservation queue at the base station. We expect this priority-based mechanism to perform well, especially during periods in which system traffic load is high, and to react well to the deterioration of multimedia service quality, in terms of both QoS parameters and the synchronization of its traffic components.

Modern network technologies first evolved in wired networks and subsequently entered the wireless network field. Applications may work in pure wired network, pure wireless network or hybrid network. Improving performance in these network infrastructures has been a continuous effort for decades. In this dissertation, we tackle two important challenges: (1) improving handover performance in heterogeneous wireless network, and (2) improving TCP performance in multi-hop wireless network. In heterogeneous network, users expect uninterrupted services moving from one network to another. IEEE proposed Media Independent Handover (MIH) to make it possible to achieve better handover performance. Currently, Mobile IPv4 (MIP) is the dominant mechanism for mobility management and is expected to persist into the future. However, when multiple interfaces of a mobile client are connected to a Foreign Agent (FA), MIP and its existing improvements do not perform well when the active interface fails unexpectedly. In this dissertation, we propose novel mechanism and MIP extension with MIH support. We prove experimentally that the new approach eliminates the FA-HA latency and achieves much faster handover, compared with existing mechanism. Our method also allows FA-bicasting, which can improve transmission reliability by combining traffic from different links, through the same FA. In multi-hop wireless networks, the main network factor that affects TCP performance is the medium-access contention, complicated by other factors like hidden terminal. We analyze the TCP congestion window and provide a more accurate estimate of its optimal value than those reported in the prior work. We also show that the much shorter TCP-ACK packets consume comparable channel capacity as the much longer data packets. We therefore propose two methods to improve TCP throughput, as follows. (1) Segregate the flows of data and ACK using static routing in grid wireless network, (2) Develop an improved variant of delayed TCP ACK by minimizing the number of ACK packets. Our evaluation validates the effectiveness of the proposed method, which can enhance TCP performance significantly. In terms of throughput, it achieves up to 204% improvement over the regular TCP in chain-topology wireless networks, and about 35% improvement in a complex grid wireless network. We also propose a new architecture to achieve higher throughput when multiple TCP connections exist.

A hybrid (N/M)CHO soft/hard vertical handover technique for heterogeneous wireless networks

Nowadays, networks are large heterogeneous systems in which efficient and effective support for multi-access technologies is imperative. The enhanced performance and availability of various technologies like WiFi, WiMax, and UMTS have motivated network users towards increased utilization. In these heterogeneous networks, a seamless connectivity with acceptable level of quality should be maintained during vertical handovers. In recent years, a network based mobility solution, Proxy Mobile IPv6 (PMIPv6) has been considered as one of the effective IP mobility management protocol. Its performance and efficiency during handover can be further increased by combining IEEE 802.21 with it. Few research efforts have been done in this domain to evaluate the performance of IEEE 802.21 with PMIPv6. However, these efforts are focused on the theoretical work and have not been supported with detailed experiments. In this paper, a thorough simulation study is conducted to evaluate the performance of vertical handover with respect to handover latency, packet loss, and average throughput during handover. Our simulation analysis shows that IEEE 802.21 enabled PMIPv6 has better performance than PMIPv6 alone.