André-Luc Beylot

Adaptive channel allocation for wireless PCN

In cellular networks, forced call terminations due to handoff call blocking are generally more objectionable than new call blocking. In order to maintain an acceptable call dropping probability rate, we propose, in this paper, two new guard channel schemes: an adaptive one – New Adaptive Channel Reservation (NACR) – and a dynamic one – Predictive Reservation Policy (PRP). In NACR, for a given period of time, a given number of channels is guarded in each cell for handoff traffic. In PRP, the number of reserved channels depends on the actual number of calls in progress in the neighboring cells. An approximate analytical model of NACR is presented. A Tabu search method has been implemented in order to optimize the Grade of Service. Discrete event simulations of PRP and NACR were run. The effectiveness of the proposed methods is emphasized on a complex configuration.

Simulation of vehicular ad-hoc networks: Challenges, review of tools and recommendations

Vehicular communications are considered the next step in increasing transportation safety and comfort. The prohibitive price of operational test beds means that computer simulations are the only viable solution for analysing the performance of different protocols and architectures. However, simulation frameworks used in vehicular ad-hoc networks research are still highly heterogeneous and, as a consequence, many of the proposed ideas can not be compared and validated. In this paper, we focus on the challenges faced when modelling the vehicular environment and the solutions adopted in the main simulation tools. As the research community is concerned with many different problems, from safety related issues to traffic efficiency and from intersection management to Internet access, we consider that every study should chose the appropriate simulator based on its requirements. Consequently, we make some recommendations which take into account the scope of the simulated scenario and the properties of the simulation frameworks.

Resolving the fairness issues in bus-based optical access networks

Packet-based optical access ring is becoming a promising solution in metropolitan networks. Its performance depends mainly on how optical resource sharing takes place among the different competing access nodes. This network architecture has mostly been explored with regard to synchronous transmission, i.e., slotted wavelength-division multiplexing (WDM) ring. However, in this paper, we focus on the performance of asynchronous transmission-based networks with variable packet sizes. Analytical models are presented in an attempt to provide explicit formulas that express the mean access delay of each node of the bus-based optical access network. We prove that in such a network, fairness problems are likely to arise between upstream and downstream nodes sharing a common data channel. Furthermore, we show that sharing the channels available bandwidth fairly but arbitrarily between access nodes, as in slotted WDM rings, does not resolve the fairness problem in asynchronous system. In this regard, we exhibit the inherent limitations of the token bucket access rate-based algorithm once applied to asynchronous transmission bus-based networks. To alleviate the aforementioned problem, we device a new strategy called traffic control architecture using remote descriptors. The proposed solution is based on a preventive mechanism to grant access to the shared resource. As illustrated in this paper, the proposed solution alleviates the performance degradation and the resource underutilization, while achieving fairness among bus nodes.

Resource allocation for real time services using cooperative game theory and a virtual token mechanism in LTE networks

In this paper a two level resource allocation scheme is proposed to enhance the Quality of Service (QoS) for multimedia services in LTE downlink system. It corresponds to a solution that combines cooperative game theory, a virtual token mechanism, and the EXP-RULE algorithm. By using cooperative game theory such as bankruptcy game and Shapley value, the proposed mechanism works by forming coalitions between flow classes to distribute bandwidth fairly. EXP-RULE algorithm has been modified to use a virtual token mechanism to improve its performance. By taking into account constraints such as Shapley value fairness and the virtual token robustness, the proposed mechanism can increase remarkably the performance for real time flows such as video and VoIP in downlink system. The performance evaluation is conducted in terms of system throughput, packet loss ratio (PLR), cell spectral efficiency and fairness index.

Performance Study of Multimedia Services Using Virtual Token Mechanism for Resource Allocation in LTE Networks

The LTE specification provides QoS of multimedia services with fast connectivity, high mobility and security. However, 3GPP specifications have not defined scheduling algorithms to support real time and non-real time application services. In this paper we propose a modified version of M-LWDF and EXP/PF scheduling algorithms based on token mechanism, which provide better performance to real time flows such as video and VoIP in downlink system. By taking the arrival rates of packets to queues into account, the proposed mechanism included in previous scheduling algorithms, can increase remarkably the bit-rate for multimedia services. Simulation results show that the proposed modified algorithms can achieve a throughput gain for real time services specially for video traffic. Performance evaluation is conducted in terms of system throughput and packet loss ratio (PLR).

A Cooperative Low Power Mac Protocol for Wireless Sensor Networks

Over the last decade cooperative communication in wireless sensor networks (WSN) received much attention. A lot of works have been done to propose a MAC layer that supports cooperative communication. However the impact of the association of a cooperative communication technique with a low power listening scheme was not studied in the literature. In this paper we propose CL-MAC, a Cooperative Low power mac protocol for WSNs. CL-MAC implements jointly Low Power Listening and cooperative communication. More precisely, we propose two variants of this protocol: a proactive version CL-MAC(P) and a reactive version CL-MAC(R). In order to evaluate the performances of the two proposed CL-MAC variants, we compare its to those of X-MAC. Simulation results proved that our protocol is able to enhance the use of the channel and to reach promising energy preservation especially in dense networks.

Analysis of interference issues in Integrated Satellite and Terrestrial Mobile Systems

The recent emergence of satellite and terrestrial integrated mobile systems raises new challenges for interference coordination between satellite and terrestrial users. The terrestrial component aims at improving the satellite coverage in highly populated areas where satellite communications often suffer from a high blocking factor caused by the buildings. The term “integrated system” refers to a system composed of a multi-beam Satellite Based Network (SBN) and a Complementary Ground Component (CGC) network that re-uses the same frequency band than the satellites one. This principle is of major interest to improve the spectral efficiency of the overall system and spatially optimize the usage of scarce spectrum resource available at low frequency bands such as L or S-band. Satellite and CGCs are assumed to be controlled by the same resource management entity which allows the coordination of frequency allocation between both components. The understanding of mutual interferences between both components is a key element for the design of such a system taking into account the forecasted balance between the number of terrestrial and satellite users in the system. This paper presents a model of an integrated mobile network composed of a multi-beam satellite, terrestrial base stations and hybrid satellite/terrestrial user terminals. This model is then used for statistical simulations of a continental scale network over Europe in order to analyze interferences between satellite and terrestrial users. The influence of several parameters such as the satellite frequency reuse pattern and the exclusion zone size between terrestrial and satellite cells is then presented.

Properties of the MAC layer in safety vehicular Ad Hoc networks

With intervehicle communications becoming a more and more popular research topic recently, the medium access control layer of the vehicular network has also received a considerable amount of attention. However, this increased interest has not always translated into a careful analysis of the properties exhibited by the MAC protocol when used by vehicular safety applications. This article tries to fill this gap by providing a comprehensive discussion on a number of important characteristics of the link layer in vehicular communications.

Local density estimation for contention window adaptation in vehicular networks

The medium access control protocol of a future vehicular ad-hoc network is expected to cope with highly heterogeneous conditions. An essential parameter for protocols issued from the IEEE 802.11 family is the minimum contention window used by the backoff mechanism. While its impact has been thoroughly studied in the case of wireless local area networks, the importance of the contention window has been somehow neglected in the studies focusing on vehicle-to-vehicle communication. In this paper we show that the adjustment of the minimum contention window depending on the local node density can notably improve the performance of the IEEE 802.11 protocol. Moreover, we compare through simulation in a realistic framework five different methods for estimating the local density in a vehicular environment, presenting the advantages and the shortcomings of each of them.

Resource allocation using Shapley value in LTE networks

The LTE specification provides QoS of multimedia services with fast connectivity, high mobility and security. However, 3GPP specifications have not defined scheduling algorithms to support real time and non-real time application services. In this paper we propose a two level scheduling scheme composed by cooperative game concept and EXP-RULE scheduling algorithm. By using cooperative game theory such as bankruptcy game and Shapley value, the proposed mechanism works by forming coalition between flow classes to distribute the bandwidth fairly. To make a performance judgment, the proposed downlink scheduling scheme has been compared to other well known schedulers such as M-LWDF and PF. Simulation results show that the proposed scheme can improve the performance on the used metrics among services. The performance evaluation is conducted in terms of system throughput, packet loss ratio (PLR), cell spectral efficiency and fairness Index.