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Providing end to end service and enhancing the ability of service adaptation under highly integrated wireless environments put the researchers’ community in front of great challenges. Some of them are linked to seamless mobility across heterogeneous wireless networks, but also to the improvement of end to end Quality of Service (QoS) and much more to an efficient utilization of radio resources.
Future generation networks’ aim is to efficiently manage all these challenges while allowing mobile terminals to be Always Best Connected (ABC) (Fodo & Eriksson, 2003). The ABC principle directly complies with seamless handoff functionalities which focus on improving the overall satisfaction of mobile users making use of some parameters in order to make wiser handoff decisions (e.g., Hassan, Nasser, & Hassenein, 2006).
These parameters include: signal strength, Quality of Service, cost of service, power requirements, and more particularly, geographical information and velocity. In vertical handoff, the mobile terminal’s future predicted location has a large weight and imperative effect on the handoff decision and must therefore be handled with a particular care. Predictions might be used by mobile terminals for anticipated radio resource reservation in that sense that enough bandwidth is reserved in the probable future cells in order to minimize service disruptions, handoff latency and packet loss.
Several mechanisms for the enhancement of vertical handoff performances and resource reservation have been proposed.
Todini et al. (2006) describe a packet scheduling algorithm and three resource allocation algorithms, characterized by various degrees of optimality and by different computational complexities. This contribution mainly focuses on OFDMA/TDD system and does not address other types of access networks.
The contribution presented by Samaan, Benmammar, Krief, and Karmouch (2005) describes a novel approach for an advanced reservation protocol, to provide seamless real-time services to mobile users in wireless integrated services networks. Two contributions are presented; the first is the utilization of knowledge about user preferences, goals, and analyzed spatial conceptual maps to predict the user’s future location and the second is a predictive advanced resources reservation protocol suitable for mobile environments. The main limitation of this work is that it does not take into account load conditions of access networks where the resource reservation must be done.
Huang, Chuang, Guan, Yang, and Chen (2007) present a self-adaptive bandwidth reservation scheme, which adopts a probabilistic mobility prediction model to estimate the bandwidth required in neighboring cells, and to reduce the forced termination probability of multimedia handoffs in 4G mobile WiMAX networks. 4G mobile WiMAX advantages are exploited via cross layer design by using bandwidth reservation for different class traffic. However, the authors only addressed resource reservation for WiMAX networks as part of a 4G environment.
Ghosh and Lott (2007) describe uplink - downlink imbalance in realistic TDD and FDD wireless networks, its potential causes and its impact on traffic and overhead channel performance, soft handoff, adaptive server selection an sector load control scheme. The authors define imbalance metrics and a model of receive antenna imbalance in their simulation studies of system robustness using cdma2000 1xEV-DO as an example. In particular, they discuss the effect of soft-handoff on system robustness, and the robustness of Computed Load control, in the presence of uplink-downlink partially-correlated time-varying shadow fading which models link imbalance in real networks. However, the authors did not quantify and compare the performance degradation across various technologies in the presence of link imbalance neither the physics of the phenomena leading to link imbalance.
Su, Han, Wu, and Liu (2007) propose a network aware and source aware video streaming framework to support interactive multiuser communications within single-cell and multicell IEEE 802.11 networks. This framework integrates cross-layer error protection mechanism and performs dynamic resource allocation across multiple users and explores the diversity of content complexity exhibited by different video sequences and the heterogeneity of uplink and downlink channel conditions experienced by different users. Unfortunately, this paper only addresses the resource reservation issue for WLAN networks.