Samir Tohme

Resource allocation and connection admission control in satellite networks

This work focuses on resource allocation and connection admission control (CAC) issues in broadband satellite networks. Broadband services can now be provided by satellite systems operating in the Ka band, due to the large bandwidth available at such frequencies. In this context, we propose a resource allocation algorithm which integrates three classes of services at the MAC layer: constant bit rate (CBR), bursty data, and best effort services. The double movable boundary strategy (DMBS) is proposed to establish a resource-sharing policy among these service classes over the satellite uplink channel. The DMBS is a dynamically controlled boundary policy which adapts the allocation decision to the variable network loading conditions. Connection-oriented and connectionless services can be supported by the system. The CAC and slot allocation decisions are taken at the beginning of each control period after monitoring the filling level of traffic request queues. A threshold level for the bursty data request queue is defined to regulate the CAC process. The impact of the queue threshold value on the performance of the DMBS allocation policy is particularly evaluated in this study. A dynamic variation of this value is also proposed to enhance the system response to interactive applications. We present a brief analytical formulation for the DMBS model, together with simulation study details and performance evaluation results. The obtained results indicate a good efficiency, in terms of overall channel throughput and CBR blocking probability, for both fixed and dynamic data queue threshold approaches. The dynamic approach, however, outperforms the fixed one in terms of overall encountered bursty data delay.

Micro mobile MPLS: a new scheme for micro-mobility management in 3G all-IP networks

This article presents the micro mobile MPLS scheme, which is a new proposal for IP local mobility in wireless MPLS access networks. Our proposal is based on multiprotocol label switching (MPLS) and mobile IP and relies on two-level hierarchy architecture. With micro mobile MPLS, mobile nodes (MNs) do not require changes to their IP protocol stack, neither for micro-mobility nor macro-mobility. Nevertheless, it still uses Mobile IP for macro-mobility scenarios. The main features of our scheme are related on scalability, flexibility, fast handoff and the ability to provide quality of service (QoS) by using the underlying MPLS traffic engineered paths. Simulation results are given to justify the benefits of our proposed architecture.

Network-Centric Joint Radio Resource Policy in Heterogeneous WiMAX-UMTS Networks for Streaming and Elastic traffic

The convergence of wireless networks is a key solution to deal with the ever-increasing need for bandwidth. In this compound radio environment, users can use concurrently diverse services through multiple RATs. In this paper, we consider a heterogeneous network where cells include two co-localized Radio Access Technologies (RAT): WiMAX and UMTS. The predominance of these systems in nowadays mobile networks underlines the relevance of our choice. We consider the downlink channel for both RATs and two service classes: streaming and elastic traffic. We propose a Joint Radio Resource Management (JRRM) algorithm responsible of routing every arriving user to one of the two RATs, while taking into account the load of each RAT, the spatial distribution of already accepted users, the location of the newly admitted user, and its influence on global performance. In a study based on the Semi Markov Decision Process (SMDP) theory, we show how to obtain an optimal policy that maximizes a predefined reward function accounting for both the operator and user satisfaction. In fact, the reward function consists of a financial gain component, an aggregate throughput component and a blocking cost.

Individual vs. Global Radio Resource Management in a Hybrid Broadband Network

Nowadays, with the abundance of diverse air interfaces in the same operating area, advanced Radio Resource Management (RRM) is vital to take advantage of the available system resources. In such a scenario, a mobile user will be able to connect concurrently to different wireless access networks. In this paper, we consider the downlink of a hybrid network with two broadband Radio Access Technologies (RAT): WiMAX and WiFi. Two approaches are proposed to load balance the traffic of every user between the two available RATs: an individual approach where mobile users selfishly strive to improve their performance and a global approach where resource allocation is made in a way to satisfy all mobile users. We devise for the individual approach a fully distributed resource management scheme portrayed as a non-cooperative game. We characterize the Nash equilibriums of the proposed RRM game and put forward a decentralized algorithm based on replicator dynamics to achieve those equilibriums. In the global approach, resources are assigned by the system in order to enhance global performances. For the two approaches, we show that after convergence, each user is connected to a single RAT which avoids costly traffic splitting between available RATs.

Mobility management support and performance analysis for wireless MPLS networks

Multi-Protocol Label Switching (MPLS) is deployed in the Internet backbone to support service differentiation and traffic engineering. In recent years, there has been interest in extending the MPLS capability to wireless access networks for mobility management support. In this paper, we present analysis of Micro Mobile MPLS, a new micro-mobility management scheme which integrates the Mobile IP and MPLS protocols by using two-level hierarchy architecture. Our proposal supports two protocol variants. First, the fast handoff process, which anticipates the LSP procedure set-up with neighboring locations where a mobile node (MN) may move to, is provided to reduce service disruption. Second, a new mechanism based on the forwarding chain concept is proposed to track efficiently the host mobility within a domain. This concept can significantly reduce registration update costs and provide low handoff latency. Analytical models are developed and simulations are conducted to justify the benefits of our proposed mechanisms.

Congestion Games for Distributed Radio Access Selection in Broadband Networks

Nowadays networks are characterized by the abundance of diverse Radio Access Interfaces (RAI) in the same operating area. The various wireless interfaces can belong to the same Radio Access Technology or not. In such a scenario, a mobile user will be able to select selfishly one of the available radio interfaces in order to enhance its own performance. Therefore, the radio access selection policy is vital and must be designed astutely to avoid resource wastage. In this paper, the RAI selection process is apprehended as a congestion game which is a class of noncooperative games in which users share a common set of limited resources. The cost sustained by a given user depends upon the congestion impact inflected by other users sharing the same resource. Devising distributed resource sharing schemes that optimize user air interface selection depends crucially on the existence of Nash equilibria for the modelling congestion games. In this paper, we model the downlink access for three main broadband technologies (WiMAX, WiFi and 3.5G HSDPA) and study the existence of pure Nash equilibria for various multi-RAI scenarios involving those technologies.

Performance analysis of multiple access protocols for multimedia satellite networks

In this paper, several TDMA-based packet multiple access protocols are studied and evaluated in the geostationary satellite environment. The distributed queueing random access protocol, DQRAP, originally proposed for HFC networks is adapted to the satellite environment. Another protocol, the announced retransmission random access protocol, ARRA, proposed for wireless networks is also studied. Both protocols are modeled and simulated in a VSAT network context. We then propose a new protocol which combines the advantages of both studied schemes and is more adapted to interactive multimedia applications over satellite uplinks. The generalized retransmission announcement protocol, GRAP, regroups the immediate access by contention at low loads, and the reservation access. At higher loads, to achieve a better channel efficiency. An analytical model is proposed to calculate the channel throughput obtained by GRAP under different loading conditions. Simulation results illustrate an improved throughput/delay characteristics and a higher protocol stability compared to both DQRAP and ARRA. Enhanced versions of the protocol are also proposed and evaluated to further improve its efficiency, with reasonable additional complexity.

Performance of the AAL2 protocol within the UTRAN

The UMTS (Universal Mobile Telecommunication System) is the future network for mobile communication systems. The access network of UMTS is called UTRAN (Universal Terrestrial Radio Access Network). In Release 99 of the 3GPP standard, the AAL2/ATM protocol is chosen as a transport protocol within the UTRAN. In this paper, we studied some performance issues of the AAL2 protocol in the context of the UTRAN: the impact of the Timer-CU on traffic performance, the scheduling mechanism in the AAL2 multiplexer and the AAL2 switching. We show that an optimal value of the Timer-CU may be chosen in the case of a mono-service VC. We present a comparison between different scheduling mechanisms (WRR, EDF, FIFO, Priority) in order to chose the suitable algorithm for the CPS multiplexer and finally we present a comparison between the AAL2 switching and the ATM switching.

Analytical framework for dimensioning hierarchical WiMax-WiFi networks

Providing diverse, ubiquitous and cost-effective broadband services is a foremost challenge for the telecommunication community. Fixed WiMAX or IEEE 802.16d is one of the most promising radio access technologies, providing high performance similar to wired xDSL systems, yet superior to that of current 3G mobile technologies. Numerous deployment concepts are foreseen for WiMAX networks. They are designed to cover isolated areas, thus embodying an appealing solution for cellular networks or wireless backhaul for WiFi access. The latter concept is of interest in this paper that puts forward an analytical model based on the economical aspects to dimension hierarchical WiMax-WiFi networks. The proposed model consists in replacing a finite number of nodes by an equivalent continuum. Its key feature lies in accounting for the effect of interference as well as for the physical layer and channel characteristics in an easy and straightforward manner. On the one hand, the model takes into consideration frequency planning and scheduling aspects; and on the other hand, it provides tractable formulae of the end-user mean capacity and coverage probability in order to properly dimension the hybrid network. Last but not least, the economical facet of network planning is considered to unravel the design trade-offs between maximizing the service provider profit and satisfying the end user requirements in terms of performance.

Performance analysis of AAL2/ATM in UMTS radio access network

The focus of this paper is the performance of ATM/AAL2 as a transport technology for Universal Terrestrial Radio Access Network (UTRAN) in UMTS/IMT-2000 setting. In this work, we propose an analytical model for the transparent multiplexing and transport through UTRAN of several voice channels onto a single AAL2/ATM VC. We investigate the queue building up at the AAL2 multiplexer in order to derive some characteristics of the sojourn time of voice frames within the UTRAN. Our results quantify the performance of AAL2/ATM-based transport of voice in terms of mean queue at the multiplexer, mean sojourn time and delay violation probability within the UTRAN.