Understanding the Gap between the IEEE 802.11 Protocol Performance and the Theoretical Limits

The ability of the IEEE 802.11 Medium Access Control (MAC) protocol to perform well in multi-hop ad hoc networks has been recently questioned. We observe levels of spatial reuse that are 30% to 50% away from the theoretical limit. The goal of this paper is to answer the following question: what prevents the IEEE 802.11 MAC protocol from operating at the limit determined by its physical layer? We identify three problems in the contention resolution mechanism of the IEEE 802.11 MAC protocol, and we show that they account for most of the gap separating the actual and optimal performances of the protocol. For each of the problems, we propose a solution that, once implemented, allows us to quantify the impact of the problem on the performance of the IEEE 802.11 MAC protocol. The resulting protocol operates 10% to 15% away from the theoretical limit. Finally, we show that reducing the overhead of the protocol to some negligible quantity brings the spatial reuse of the protocol to the theoretical limits. It also makes apparent the powerful organizing capacity of the IEEE 802.11 MAC protocol

Enabling Cyber Physical Systems with Wireless Sensor Networking Technologies

[[abstract]]Over the last few years, we have witnessed a growing interest in Cyber Physical Systems (CPSs) that rely on a strong synergy between computational and physical components. CPSs are expected to have a tremendous impact on many critical sectors (such as energy, manufacturing, healthcare, transportation, aerospace, etc) of the economy. CPSs have the ability to transform the way human-to-human, human-toobject, and object-to-object interactions take place in the physical and virtual worlds. The increasing pervasiveness of Wireless Sensor Networking (WSN) technologies in many applications make them an important component of emerging CPS designs. We present some of the most important design requirements of CPS architectures. We discuss key sensor network characteristics that can be leveraged in CPS designs. In addition, we also review a few well-known CPS application domains that depend on WSNs in their design architectures and implementations. Finally, we present some of the challenges that still need to be addressed to enable seamless integration of WSN with CPS designs.[[incitationindex]]SCI[[booktype]]紙

Étude de la variation au cours d'une période de la constante diélectrique complexe d'une cellule électroluminescente

We have calculated from experimental data on electrical currents, in an electroluminescent cell, the values of the complex dielectric constant. Its variations during a period are connected to brightness and absorbed power variations, permit t-ing one to do an energy balance of the cell.Nous avons calculé, à partir de données expérimentales sur les courants traversant une cellule électroluminescente, les valeurs instantanées de la « constante » diélectrique complexe. Les variations de celle-ci sur une période ont pu être mises en relation avec celles de la luminance et de la puissance absorbée, permettant d'envisager un bilan énergétique de la cellule

Étude de la variation au cours d'une période de la constante diélectrique complexe d'une cellule électroluminescente

Nous avons calculé, à partir de données expérimentales sur les courants traversant une cellule électroluminescente, les valeurs instantanées de la « constante » diélectrique complexe. Les variations de celle-ci sur une période ont pu être mises en relation avec celles de la luminance et de la puissance absorbée, permettant d'envisager un bilan énergétique de la cellule

Nachum Dershowitz and Zohar Manna. Proving termnation with multiset orderings

Numerous approaches have been proposed to manage Quality of Service in the Internet. However, up to now none of them was successfully deployed in a commercial IP backbone, mostly because of their complexity. In this paper, we take advantage of the excess network bandwidth to offer a degraded class of traffic. We identify and analyze the impact of link failures on such a service and show that under certain circumstances they provide the main vector to service differentiation. We simulate our QoS scheme on a real IP backbone network and derive Service Level Agreements for the new degraded service. We find that by adding a degraded class of traffic in the network, we can at least double the link utilization with no impact on the current backbone traffic. I