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Abstract

Collision-free CSMAMAC protocols are interesting solutions for considering real-time traffic in a wireless context. The goal of this paper is precisely to make an exhaustive presentation (which, we think to be understandable and pedagogical) of the main collision-free CSMA MAC protocols for one-hop wireless LANs, considering priorities (static, hybrid [4]) associated to the frames. The priorities are represented by either the BlackBurst technique [10], [7] or an adaptation of the CAN bus protocol [2] to the wireless context we call CANlike protocol [11], [9], [5]. The cornerstone of this work is the concept of Ambiguity Time Window that we have defined for characterizing the Physical layer, and which allows to specify the parameters of the considered protocols. In our knowledge, such kind of study has never been done.

Résumé

Les applications temps-réel demandent des garanties en terme de Qualité de Service qu'il est difficile d'obtenir dans les réseaux sans fil. Le protocole MAC (Medium Access Control) qui est responsable de l'ordonnancement des messages de données (venant des applications) a un rôle très important car il résout les problèmes d'accès au medium entre les différents n{\oe}uds. Un champ de recherche important porte sur la conception de protocoles MAC, de type CSMA (Carrier Sense Multiple Access), déterministes et sans collision. Notre travail se situe dans ce cadre et porte sur la spécification d'un protocole inspiré de CAN.

Abstract

The performances of the process control applications, which are implemented through networks, depend greatly on the scheduling of the messages. Furthermore, in the context of the wireless networks, because of the unreliable medium, it is difficult to meet the timing requirements imposed by the applications dynamics. The objective of this paper is, by considering a Wireless Local Area Network (WLAN) and a process control application, to compare the performances of this application by using MAC protocols of the type CSMA (which manage the messages scheduling): two protocols with collision avoidance (CA), provided by manufacturers (IEEE 802.11 - WiFi, IEEE 802.15.4 - ZigBee) which do not prevent the occurrence of collisions; a proposed free-collision protocol which is based on priorities specified by means of BlackBurst messages.

Abstract

The message scheduling is an important mechanism in the context of Networked Control Systems. The message scheduling is, in several networks, mainly based on static priorities associated to the messages (for example the network CAN). This static priority scheme has intrinsic limitations and so here we will consider scheduling strategies based on hybrid priorities. Three hybrid priority schemes, resulting from our previous works are first presented. Then we compare the Quality of Service (QoS) offered by these schemes to a process control application and we evaluate the resulting Quality of Control (QoC).

Abstract

This paper wants to present the first reasoning in order to implement on a network a process control application type which is, in a first time, specified with a continuous model (transfer function in the Laplace domain). The network is a local area network and we only consider the MAC layer (frame scheduling) and the physical layer (serial frame transmission). By first reasoning, we mean that, we study the case of a network which is dedicated to the process control application type, and we want to link the stability and the reactivity that the application can get from the service provided by the network (link between the parameters of the open loop transfer function and the network characteristics (frame transfer, frame format, bit rate)). Three networks are considered: CAN, WiFi, ZigBee. This work is a basic work which wants to emphasize the necessary interplay between Automatic Control theory and Networks mechanisms.

Abstract

The message scheduling is an essential mechanism in the context of Networked Control Systems (NCS). It strongly influences the stability of the closed loop distributed control applications. The goal of this paper is to present a study of different priority schemes which can be used for the message scheduling of a process control application implemented through a network (the network CAN will be considered). Two great schemes will be presented: static priority, hybrid priority including a dynamic part and a static part. The dynamic part is based on the dynamic performance of the controlled application. Considering the hybrid priority scheme, several types will be considered for the dynamic part: dynamic part alone, dynamic part and a static time strategy, dynamically controlled time strategy. The comparison of these schemes is done with respect to the stability of a process control application.

Mots-Clés / Keywords