Catálogo de publicaciones - libros

We present a dual-hop relayed wireless communication system where the gain of the relay, called combined gain relay (CGR), is produced after combining the channel state information from both hops, depending on the mean hop’s signal-to-noise ratio (SNR). The proposed scheme can be efficiently applied in dual-hop transmissions with unbalanced mean SNRs due to the long-term fading effects produced by the movement of the user in the area served by the wireless network. The overall system performance is studied in Rayleigh fading channels. Closed-form expressions are derived for important system performance metrics, such as average end-to-end SNR, average error probability and outage probability. Furthermore, we investigate the CGR’s average power consumption which in certain cases is lower compared to existed relays. Numerical results and simulations show an improvement in the end-to-end system performance.

The IEEE 802.11 MAC layer is known for its low performances in wireless ad hoc networks. For instance, it has been shown in the literature that two independent emitters nodes can easily monopolize the medium, preventing other nodes to send packets. The protocol we introduce in this article is a simple variation of the original IEEE 802.11 MAC layer which significantly increases the fairness while maintaining a high effective bandwidth. Its principle consists in avoiding systematic successive transmissions by the same emitter through the probabilistic introduction of a waiting time, a virtual NAV, after each emission. The probability to set a NAV is adaptively computed depending on the perceived utility of the previous virtual NAV. This protocol, called PNAV (), is shown to be efficient by simulation and is compared to another IEEE 802.11 adaptation.

Ultra Wide Band (UWB) impulse radio, promises to be suitable for short-range, low-power, low cost and high data rate applications. While most UWB research is concentrating on the physical layer, little research has been published on the link layer. A novel self-organizing link layer protocol (SDD) based on time hopping impulse radio was proposed by the authors. In this paper, the SDD protocol is further developed and specified in detail. The simulations are carried out using the GloMoSim simulation environment.

The use of the wireless sensor networks (WSNs) should be increasing in different fields. However, the sensor’s size is an important limitation in term of energetic autonomy, and thus of lifetime because battery must be very small. This is the reason why, today, research mainly carries on the energy management in the WSNs, taking into account communications, essentially. In this context, we compare different clustering methods used in the WSNs, particularly EECS, with an adaptive routing algorithm that we named LEA2C. This algorithm is based on topological self-organizing maps. We obtain important gains in term of energy and thus of network lifetime.

This paper presents the ALCA (Asymmetric Link Collision Avoidance) protocol. ALCA was designed to deal with a known deficiency of the Basic Scheme Gomez et al., 2001 for power control in 802.11 ad hoc networks, which occurs when links become asymmetrical as a result of power control. The proposed ALCA mechanism conveys transmission duration information to these terminals through a simple modification of the 802.11 MAC protocol. Through extensive simulation, the performance of ALCA is investigated and compared to PCM (a solution that requires major hardware updates). Results indicate that ALCA outperforms PCM while being a considerably less complex solution.

This paper proposes a local power saving algorithm combined with a power-aware routing scheme to provide energy-efficient operation of the network. The power saving algorithm reduces communication energy consumption whereas the power aware routing scheme increases node lifetime. Another objective of the proposed routing strategy is the selection of stable paths in order to achieve robust network operation; to accomplish this scope a new routing metric is presented combining the residual energy level of nodes with an estimation of the stability of links. Simulation studies indicate a reduction in energy consumption and a significant increase in node lifetime whereas the network performance (delivery ratio and routing overhead) is not affected significantly.

Radio interferences and low capacity resources in ad-hoc wireless networks make more complex the quality of service (QoS) support. We propose a solution taking into account radio interferences in mobile ad-hoc networks routing and providing an optimized flooding based on multipoint relays. This solution is based on a modified version of the OLSR routing protocol that considers bandwidth requests and interferences in route selection while providing a very efficient flooding. A comparative performance evaluation based on NS simulations shows that despite the overhead due to QoS support, this solution outperforms classical OLSR in terms of maximum number of acceptable flows, bandwidth amount granted to a flow and route stability. Moreover, the efficiency of the optimized flooding is equal to that provided by the native version of OLSR.

Since the initial draft, the Optimized Link State Routing (OLSR) protocol has been associated with the Multipoint Relay (MPR) protocol to reduce the flooding of OLSR topological messages. Many papers have been written on solutions to improve OLSR by replacing MPR by another topology control protocol, or by modifying MPR heuristic. But few of them have dealt with the particular interactions between MPR and OLSR. In this chapter, we argue that OLSR optimality is bound to the deep cooperation between MPR and OLSR. We also illustrate how OLSR suffers from convergence problems, and finally suggest that solving these convergence issues will open new paths to improve OLSR.

This paper presents the experimental framework currently being developed at INRIA on mobile traffic applications using ad hoc communication. In this paper we propose a set of modifications to the OLSR protocol in order to adapt it to vehicle ad hoc networks. This work is the fruit of a collaboration between two INRIA research teams: HIPERCOM and IMARA. HIPERCOM is working on ad hoc routing protocols and IMARA is working on intelligent vehicles.

A new way to improve the performance of ad hoc networks consists in using cross layer mechanisms. Currently, several protocols have demonstrated some reachable performance gain. Global integration on each level of the protocol stack has to be ensured. We present some efficient methods that may either produce or update cross-layer models. Those models, developed on different levels, allow an efficient organisation of the wireless systems and could take several forms. A cross-layer conceptual model is composed of: cross-layer interaction models and interactions description arrays. In this paper, we propose a method which has been applied to a chosen protocol stack.