Aladdin Saleh

Signal threshold adaptation for vertical handoff in heterogeneous wireless networks

The convergence of heterogeneous wireless access technologies has been envisioned to characterize the next generation wireless networks. In such converged systems, the seamless and efficient handoff between different access technologies (vertical handoff) is essential and remains a challenging problem. The heterogeneous co-existence of access technologies with largely different characteristics results in handoff asymmetry that differs from the traditional intra-network handoff (horizontal handoff) problem. In the case where one network is preferred, the vertical handoff decision should be carefully executed, based on the wireless channel state, network layer characteristics, as well as application requirements. In this paper, we study the performance of vertical handoff using the integration of 3G cellular and wireless local area networks as an example. In particular, we investigate the effect of an application-based signal strength threshold on an adaptive preferred-network lifetime-based handoff strategy, in terms of the signalling load, available bandwidth, and packet delay for an inter-network roaming mobile. We present an analytical framework to evaluate the converged system performance, which is validated by computer simulation. We show how the proposed analytical model can be used to provide design guidelines for the optimization of vertical handoff in the next generation integrated wireless networks.

A Service-Agent-Based Roaming Architecture for WLAN/Cellular Integrated Networks

In this paper, an agent-based integrated service model for wireless local area network (WLAN)/cellular networks and the relevant authentication and event tracking for billing support schemes are proposed. The service model does not require inefficient peer-to-peer roaming agreements to provide seamless user roaming between the WLAN hotspots and the cellular networks, which are operated by independent wireless network service providers. The proposed authentication and event-tracking schemes take the anonymity and intractability of mobile users into consideration and operate independently so that the integrated billing service can be applied to the cellular network, even if it still uses a traditional authentication scheme. Security analysis and overhead evaluation are given to demonstrate that the proposed service model and the supporting schemes are secure and efficient.

Interworking of 3G cellular networks and wireless LANs

The Third Generation (3G) cellular networks provide ubiquitous connectivity but low data rates, whereas Wireless Local Area Networks (WLANs) can offer much higher data rates but only cover smaller geographic areas. Their complementary characteristics make the integration of the two networks a promising trend for next-generation wireless networks. With combined strengths, the integrated networks will provide both wide-area coverage and high-rate data services in hot spots. There are many aspects involved in their interworking, such as mobility, security and Quality of Service (QoS) provisioning. In this paper, we present a survey of most recent interworking mechanisms proposed in the literature, and outline some important open issues to achieve seamless integration.

Vertical Handoff between 802.11 and 802.16 Wireless Access Networks

In this paper, we consider an interworking architecture of wireless mesh backbone and propose an effective vertical handoff scheme between 802.11 and 802.16 wireless access networks. The proposed vertical handoff scheme aims at reducing handoff signaling overhead on the wireless backbone and providing a lower handoff delay to mobile nodes. The handoff signaling procedure in different scenarios is discussed. Together with call admission control, the vertical handoff scheme directs a new call request in the 802.11 network to the 802.16 network, if the admission of the new call in the 802.11 network can degrade quality-of-service (QoS) of the existing real-time traffic flows. Simulation results demonstrate the performance of the handoff scheme with respect to signaling cost, handoff delay, and QoS support.

Mobility Modeling and Performance Evaluation of Heterogeneous Wireless Networks

The future-generation wireless systems will combine heterogeneous wireless access technologies to provide mobile users with seamless access to a diverse set of applications and services. The heterogeneity in this inter-technology roaming paradigm magnifies the mobility impact on system performance and user perceived service quality, necessitating novel mobility modeling and analysis approaches for performance evaluation. In this paper, we present and compare three mobility models in two-tier integrated heterogeneous wireless systems, the independence model as a naive extension of the traditional cell residence time modeling techniques for homogeneous cellular networks, the basic Coxian model which takes into consideration the correlation between the residence time within different access technologies, and the extended-Coxian model for further improved estimation accuracy. We propose a general stochastic performance analysis framework based on application session models derived from these mobility models, applying it to a 3G-WLAN integrated system as an example. Our numerical and simulation results demonstrate the general superiority of Coxian-based mobility modeling over the independence model. Furthermore, using the proposed modeling and analysis methods, we investigate the impact of different parameters on system performance metrics such as network utilization time, handoff rates, and forced termination probability, for a wide range of user applications.

Call Admission Control for Integrated Voice/Data Services in Cellular/WLAN Interworking

Call admission control plays an important role in quality of service (QoS) provisioning in the interworking between the cellular network and wireless local area network (WLAN). Within the WLAN coverage, a service request can be admitted into the cellular network or the WLAN. Due to the heterogeneous underlying QoS support of the cellular network and WLANs, the admission of traffic in the WLAN coverage has a significant impact on QoS satisfaction and overall resource utilization, especially when multiple services are considered. A popular admission strategy (referred to as WLAN-first scheme) is to admit the incoming service requests into the WLAN whenever it is available so as to take advantage of the low cost and large bandwidth of the WLAN. In this paper, we investigate the performance of the WLAN-first scheme. It is observed that the overall resource utilization can be maximized when the admission regions for voice and data services in a cell and a WLAN are properly configured.

Vector Precoding with MMSE for the Fast Fading and Quasi-Static Multi-User Broadcast Channel

Vector precoding is arguably the best form of precoding for the multi-user multiple input multiple output (MIMO) broadcast channel. However, conventional vector precoding schemes are designed to minimize the transmit energy, which is suboptimal in terms of the received signals mean square error (MSE). This paper proposes modifications to vector precoding to overcome this shortcoming. Improvements of about 2 dB are realizable in a fast fading environment. Also, conventional vector precoding schemes usually result in unbalanced levels of interference, resulting in a poor performance for some users. Noting the above, another improvement is proposed by directly minimizing the bit error rate rather than the MSE. This improvement adds another 1 dB of gain, resulting in an overall gain of 3 dB in a quasi static fading environment. These improvements are also applied to Tomlinson-Harashima precoding with similar results.

Application signal threshold adaptation for vertical handoff in heterogeneous wireless networks

In heterogeneous wireless systems, the seamless and efficient handoff between different access technologies (vertical handoff) is essential and remains a challenging problem. The co-existence of access technologies with largely different characteristics results in handoff asymmetry that differs from the traditional intra-network handoff problem. In the case where one network is preferred, the vertical handoff decision should be carefully executed, based on the wireless channel state, network layer characteristics, as well as application requirements. In this paper, we present an adaptive preferred-network lifetime-based handoff strategy, and investigate the effect of an application-based signal strength threshold on the signalling load, available bandwidth, and packet delay.We propose an analytical framework to evaluate the performance of the converged system.We show how the proposed analytical model can be used to provide guidelines for the optimization of vertical handoff in the next generation integrated wireless networks.

Mobile IP performance and interworking architecture in 802.11 WLAN/cdma2000 networks

IEEE 802.11 WLAN is designed to provide high data speed in a small coverage area. 2.5G/3G networks, on the other hand, are intended to offer ubiquitous connectivity with relatively low data speed over a wide area. Accordingly, these two technologies can be viewed as a complement to each other. However, for complementary service, the two access networks have to be integrated and the service provided by both should be transparent to users. Consequently, one of the main challenges is to provide seamless roaming between them that can meet service requirements. Mobile IP (MoIP) has been considered as the most suitable candidate for achieving seamless roaming. We investigate interworking architecture between 802.11 WLAN and 2.5/3G CDMA cellular networks with emphasis on the performance of MoIP. A test bed system has been used and results are presented.

Air interface switching and performance analysis for fast vertical handoff in cellular network and WLAN interworking

The integration of wireless local area network (WLAN) hotspot and the 3G cellular networks is imminently the future mode of public access networks. One of the key elements for the successful integration is vertical handoff between the two heterogeneous networks. Service disruption may occur during the vertical handoff because of the IP layer handoff activities, such as registration, binding update, routing table update, etc. In this paper, the network interface switching and registration process are proposed for the integrated WLAN/cellular network. Two types of fast vertical handoff protocols based on bicasting and non-bicasting supporting real-time traffic, such as voice over IP, are modeled. The performance of a bicasting based handoff scheme is analyzed and compared with that of fast handoff without bicasting. Numerical results and the simulation are given to show that packet loss rate can be reduced by the bicasting during handoff scheme without increasing bandwidth on both wireless interfaces. Copyright