Anis Laouiti

Optimized link state routing protocol for ad hoc networks

In this paper we propose and discuss an optimized link state routing protocol, named OLSR, for mobile wireless networks. The protocol is based on the link state algorithm and it is proactive (or table-driven) in nature. It employs periodic exchange of messages to maintain topology information of the network at each node. OLSR is an optimization over a pure link state protocol as it compacts the size of information sent in the messages, and furthermore, reduces the number of retransmissions to flood these messages in an entire network. For this purpose, the protocol uses the multipoint relaying technique to efficiently and economically flood its control messages. It provides optimal routes in terms of number of hops, which are immediately available when needed. The proposed protocol is best suitable for large and dense ad hoc networks.

Multipoint relaying for flooding broadcast messages in mobile wireless networks

We discuss the mechanism of multipoint relays (MPRs) to efficiently flood broadcast messages in mobile wireless networks. Multipoint relaying is a technique to reduce the number of redundant re-transmissions while diffusing a broadcast message in the network. We discuss the principle and the functioning of MPRs, and propose a heuristic to select these MPRs in a mobile wireless environment. We also analyze the complexity of this heuristic and prove that the computation of a multipoint relay set with minimal size is NP-complete. Finally, we present some simulation results to show the efficiency of multipoint relays.

Performance of Multipoint Relaying in Ad Hoc Mobile Routing Protocols

We analyze the performance of ad hoc pro-active routing protocols. In particular we focuse on the multipoint relay concept introduced in OLSR protocol and which brings a significantimpro vementin broadcast control traffic overhead. We analyze the performance in two radio network model: the random graph model and the unit graph model. The random graph is more suitable for the modelization of indoor networks. The unit graph is more suitable for outdoor networks. We compare the performance of OLSR with the performance of basic link state protocols using full flooding.

OLSR performance measurement in a military mobile ad hoc network

Wireless ad-hoc networks are autonomous, self-configurating and adaptive. Thus, such networks are excellent candidates for military tactical networks, where their ability to be operational rapidly and without any centralized entity is essential. As radio coverage is usually limited, multihop routing is often needed; this is achieved by an ad-hoc routing protocol supporting nodes mobility. We present performance measurements of the OLSR (optimized link state routing) protocol routing, presented at the IETF MANET (mobile ad-hoc network) working group for ad-hoc networks. The measurements are performed at CELAR site on a platform representative of military scenarios in urban areas. It consists of ten routers, eight PDAs and laptops using a IEEE 802.11b radio interface and implementing OLSR v7. Some nodes are mobile within vehicles. The emphasis of the measurements is on the performance of the network (route repair, network convergence speed, user traffic performance) in presence of this mobility.

Cybercar Cooperation for Safe Intersections

The paper addresses the problem of motion autonomy of cybercars across an urban intersection. Cybercars are small electric city vehicles aimed at navigating autonomously. In the context of a crossing, the motion generation together with its safety is critical issues. The proposed approach to the problem lies in the coupling of perception and planning capabilities. A new car to car communication algorithm provides necessary information to a trajectory planner capable of iteratively generate safe trajectories within a dynamic environment in order to drive cybercars safely through the intersection. The main contributions of this work are the development and integration of these modules into one single application, considering explicitly the constraints related to the environment and the system and to provide an original answer to the problem of intelligent crossing

OLSR performance measurement in a military mobile ad-hoc network

Wireless ad-hoc networks are autonomous, self-configurating and adaptive. Thus, such networks are excellent candidates for military tactical networks, where their ability to be operational rapidly and without any centralized entity is essential. As radio coverage is usually limited, multihop routing is often needed; this is achieved by an ad-hoc routing protocol supporting nodes mobility. We present performance measurements of the OLSR (optimized link state routing) protocol routing, presented at the IETF MANET (mobile ad-hoc network) working group for ad-hoc networks. The measurements are performed at CELAR site on a platform representative of military scenarios in urban areas. It consists of ten routers, eight PDAs and laptops using a IEEE 802.11b radio interface and implementing OLSR v7. Some nodes are mobile within vehicles. The emphasis of the measurements is on the performance of the network (route repair, network convergence speed, user traffic performance) in presence of this mobility.

Comparison of Flooding Techniques for Safety Applications in VANETs

In this paper, we study safety applications in Vehicular Ad hoc Networks (VANETs). More specifically we concentrate on emergency situations after a car crash in a platoon of vehicles which have wireless transmission capabilities. In order to avoid multiple collisions, vehicles should exchange emergency information as quickly as possible. To extend the area in which the emergency information is sent, they must relay it. In this article, we study various techniques to disseminate emergency data within a platoon of cars. We examine three different techniques : the pure flooding, the multipoint relay (MPR) diffusion mechanism of OLSR [1] and a geographic aware flooding technique as described in [2]. Different realistic scenarios are considered; we scrutinize various parameters such as vehicle density, and background traffic load.

Multicast overlay spanning trees in ad hoc networks: Capacity bounds, protocol design and performance evaluation

We study the benefits of multicast routing in the performance of wireless ad hoc networks. In particular we show that if a node wishes to communicate with n distinct destinations, multicast can reduce the overall network load by a factor O(n), when used instead of unicast. One of the implications of this scaling property consists in a significant increase of the total capacity of the network for data delivery. Hence, we show that the aggregate multicast capacity of wireless ad hoc networks is O(n) larger than the unicast capacity, when the group size n is small compared to the total number of nodes in the network. We discuss how these information theoretic results can be taken into consideration in the operation of a multicast protocol for wireless mesh networks using Multicast Overlay Spanning Trees (MOST). We perform simulations of the MOST protocol to compare with the theoretical results, and we present a fully working implementation for real network environments.

Quantitative Evaluation of the Cost of Routing Protocol OLSR in a Vehicle Ad Hoc NETwork (VANET)

In this paper we study the channel occupation induced by the OLSR proactive routing protocol used in a linear Vehicular Ad hoc Network (VANET). Unlike previous studies which usually use simulations to evaluate the overhead of routing protocols, we derive a simple analytical model to carry out this evaluation. Moreover, we do not evaluate the total overhead induced by the routing protocol as is usually proposed, but for a given node we compute the channel occupation induced by the routing protocol. This paper provides a quantitative approach to evaluating the cost of a proactive routing protocol in a linear vehicular ad hoc network as a function of several parameters such as the frequency of the control messages, the density of the vehicles, the propagation range of the control messages and the carrier sense area.

Survey of deployment algorithms in wireless sensor networks: coverage and connectivity issues and challenges

Wireless sensor networks (WSNs) have many fields of application, including industrial, environmental and military domains. Monitoring a given zone is one of the main goals of this technology. This consists in deploying sensor nodes in order to detect any event occurring in the zone and report it to the sink. We present a survey that focuses on coverage and connectivity issues in WSNs. We motivate our study by giving different use cases corresponding to different coverage, connectivity, latency and robustness requirements of the applications considered. We present a general and detailed analysis of deployment problems, while highlighting the impacting factors, the common assumptions and models adopted in the literature, as well as performance criteria for evaluation purposes. Different deployment algorithms for area, barrier, and points of interest are studied and classified according to their characteristics and properties. Before concluding, we look at current trends and discuss some open issues.