Anthony Busson

Point processes for interference modeling in CSMA/CA ad-hoc networks

As interference results from the summation of signals issued by concurrent transmitters, it directly depends on the transmitters location. The point process used to model concurrent transmitters location is thus fundamental in any multi-hop wireless network study. In this paper, we investigate original processes that comply with the CSMA/CA policies. We propose the use of the Simple Sequential Inhibition point process to model CSMA/CA networks where carrier detection depends on the strongest emitter only. We then extend this point process to a family of new point processes modeling a busy medium detection based on the strength of all concurrent signals. We study the impact of these different processes on the interference distribution and show that the results are very different with respect to the different point process. We finally show that the use of a Poisson process is generally inaccurate to model CSMA/CA networks.

Inside VANET: Hybrid Network Dimensioning and Routing Protocol Comparison

In this paper, we are interested in the properties of vehicular ad hoc networks (VANET). We study the mean connection lifetimes to evaluate the feasibility to support non-safety applications. Because connection lifetimes are in the order of a few minutes, an infrastructure network is highly recommended to maintain connectivity between car clusters. Using an hybrid network, we perform comparisons of routing protocols used in the VANET. We show that reactive and geographic routing protocols are very close in terms of performance. However the reactive protocol are more accurate since it does not require neither geolocalization systems nor location services. We propose the use of hybrid networks and we give dimensioning rules to ensure connectivity of the network

An efficient link management algorithm for high mobility mesh networks

Mobility causes frequent link failures in ad-hoc networks. This results in a severe degradation of performance specially in case of high mobility of nodes. This is because the routing protocols for ad-hoc networks are not equipped to handle high mobility. In this paper, we have presented a new link management algorithm to locally manage links. This new mechanism is based on signal strength measurements. We develop the hysteresis mechanism provided by OLSR based on hello packets to include signal strength measurements. The mechanism in OLSR uses Hello packets received/lost to decide to establish link or not. The problem with this approach arises when there is high mobility in which case the time to break the link and use a new path becomes significant. To overcome this, we propose to use signal strength to determine if the link-quality is improving or deteriorating. This combination of the two mechanisms, makes the link management more robust and also helps in anticipating link breakages thereby greatly improving performance.

Usefulness of collision warning inter-vehicular system

This paper studies the contribution and the impact of Inter-Vehicular Communications (IVC) in a vehicles string. We suppose that all, or, a subset of the vehicles are equipped with radio communication devices, enabling communication between them. We evaluate the benefit of the dissemination of warning messages for the reduction of accidents. More precisely, we evaluate and compare the number of vehicles involved in a multi-vehicles crash caused by an accident, with and without the use of IVC. We show that even when a low proportion of vehicles uses IVC, the number of collisions is drastically reduced.

Interference and throughput in spectrum sensing cognitive radio networks using point processes

Spectrum sensing is vital for secondary unlicensed nodes to coexist and avoid interference with the primary licensed users in cognitive wireless networks. In this paper, we develop models for bounding interference levels from secondary network to the primary nodes within a spectrum sensing framework. Instead of classical stochastic approaches where Poisson point processes are used to model transmitters, we consider a more practical model which takes into account the medium access control regulations and where the secondary Poisson process is judiciously thinned in two phases to avoid interference with the secondary as well as the primary nodes. The resulting process will be a modified version of the Matérn point process. For this model, we obtain bounds for the complementary cumulative distribution function of interference and present simulation results which show the developed analytical bounds are quite tight. Moreover, we use these bounds to find the operation regions of the secondary network such that the interference constraint is satisfied on receiving primary nodes. We then obtain theoretical results on the primary and secondary throughputs and find the throughput limits under the interference constraint.

Channel assignment algorithms: a comparison of graph based heuristics

This paper gives the comparison of different channel assignment heuristics proposed in the literature and introduces a new algorithm named MCAIR. Specifically, it compares, static, multi-radio multi-channel algorithms which are graph theory based and where a priori traffic characteristics are unknown. It also proposes new metrics other than overall interference which guide in better evaluating the assignment.

SEAD: A simple and efficient adaptive data dissemination protocol in vehicular ad-hoc networks

Abstract Vehicular ad-hoc network (VANET) is becoming a promising technology for improving the efficiency and the safety of intelligent transportation systems by deploying a wide variety of applications. Smart vehicles are expected to continuously exchange a huge amount of data either through safety or non-safety messages dedicated for road safety or infotainment and passenger comfort applications, respectively. One of the main challenges posed by the study of VANET is the data dissemination design by which messages have to be efficiently disseminated in a high vehicular speed, intermittent connectivity, and highly dynamic topology. In particular, broadcast mechanism should guarantee fast and reliable data delivery within a limited wireless bandwidth in order to fit the real time applications’ requirements. In this work, we propose a simple and efficient adaptive data dissemination protocol called “SEAD”. On the one hand, the originality of this work lies in its simplicity and efficiency regardless the application’s type. Simplicity is achieved through a beaconless strategy adopted to take into account the surrounding vehicles’ density. Thanks to a metric locally measured, each vehicle is able to dynamically define an appropriate probability of rebroadcast to mitigate the broadcast storm problem. Efficiency is manifested by reducing excessive retransmitted messages and hence promoting the network capacity and the transmission delay. The simulation results show that the proposed protocol offers very low packet drop ratio and network load while still maintaining a low end-to-end delay and a high packet delivery. On the other hand, SEAD protocol presents a robust data dissemination mechanism which is suitable either for safety applications or for other kinds of application. This mechanism is able to adapt the protocol performance in terms of packet delivery ratio to the application’s requirements.

Capacity and interference modeling of CSMA/CA networks using SSI point processes

The relative location of simultaneous transmitters, i.e. the set of nodes transmitting a frame at a given time, has a crucial impact on the performance of multi hop wireless networks. Two fundamental aspects of wireless network performances are related to these locations: capacity and interference. Indeed, as interference results from the summation of signals stemmed by concurrent transmitters, it directly depends on the transmitters’ location. On the other hand, the network capacity is proportional to the number of simultaneous transmitters. In this paper, we investigate original point processes that can be used to model the location of transmitters that comply with the CSMA/CA policies, i.e. the Medium Access Control protocol used in 802.15.4 and 802.11 families of wireless technologies. We first propose the use of the Simple Sequential Inhibition point process to model CSMA/CA networks where clear channel assessment depends on the strongest emitter only. We then extend this point process to model a busy medium detection based on the strength of all concurrent signals. We finally compare the network capacity obtained through realistic simulations to a theoretical capacity estimated using the intensity of the SSI point process. It turns out that the proposed model is validated by the simulations.

Anticipation of ETX Metric to Manage Mobility in Ad Hoc Wireless Networks

When a node is moving in a wireless network, the routing metrics associated to its wireless links may reflect link quality degradations and help the routing process to adapt its routes. Unfortunately, an important delay between the metric estimation and its inclusion in the routing process makes this approach inefficient. In this paper, we introduce an algorithm that predicts metric values a few seconds in advance, in order to compensate the delay involved by the link quality measurement and their dissemination by the routing protocol. We consider classical metrics, in particular ETX Expected Transmission Count and ETT Expected Transmission Time, but we combine their computations to our prediction algorithm. Extensive simulations show the route enhancement as the Packet Delivery Ratio PDR is close to 1 in presence of mobility.

Association Optimization in Wi-Fi Networks: Use of an Access-based Fairness

Densification of Wi-Fi networks has led to the possibility for a station to choose between several access points (APs). On the other hand, the densification of APs generates interference, contention and decreases the global throughput as APs have to share a limited number of channels. Optimizing the association step between APs and stations can alleviate this problem and increase the overall throughput and fairness between stations. In this paper, we propose an original solution to this optimization problem based on two contributions. First, we present a mathematical model for the association optimization problem based on a realistic share of the medium between APs and stations and among APs when using the 802.11 DCF (Distributed Coordination Function) mode. Then, we introduce a local search algorithm to solve this problem through a suitable neighborhood structure. This approach has the benefit to be tuned according to the CPU and time constraints of the WLAN controller. Our evaluation, based on simulations, shows that the proposed solution improves the overall throughput and the fairness of the network.