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Jean-Dominique Decotignie is head of the real-time and networking group at the Swiss Center for Electronics and Microtechnology (CSEM) in Neuchatel, Switzerland.  CSEM SA, the Swiss Center for Electronics and Microtechnology, is a privately held, knowledge-based company carrying out applied research work, product development, prototype and low-volume production.

Dr. Decotignie is also adjunct professor at the Ecole Polytechnique Fédérale (Swiss Federal Institute of Technology) in Lausanne where he teaches real-time systems and real-time networking. He has been very active in the fieldbus domain since its beginning and is IEEE fellow "for contributions to fieldbus technology leading to its adoption and standardization by the industry".

Dr. Decotignie has authored or co-authored more than 100 papers in the field. He has created the first and only international conference series dedicated to industrial communications. His current research interests include industrial and real-time local area networks with a particular emphasis on wireless sensor networks.

Dr. Decotignie received his MS in 1977 and PhD in 1982 both in electrical engineering from the EPFL.

Discussion subject:

Real-Time and wireless sensor networks: is there a possible match?

Abstract:

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Networking at the sensory level is now very common. Fieldbusses have been around for more than 2 decades They can be found in many types of application such as factory automation, process plants, car automation or building automation. Since the first solutions were designed in the early 80s, a number of proposals have flourished and the field is well established both in terms of research and industrial use. Most solutions use wired transmission (twisted pairs, coaxial cables, optical fibers) and provide real-time guarantees at different degrees. Establishing these guarantees has been the subject of a number of papers in previous issues of this workshop.

Using wireless transmission at the sensory level is very attracting. It has been employed for years to link mobile robots or automated guided vehicles to control and supervision computers. At the fieldbus level, a number of solutions have been proposed. The Esprit Project OLCHFA designed in 1992 a full wireless network based on the FIP protocol. LON offers some wireless transceivers that can be used to built a mixed wired / wireless network. The same applies to the first version of the IEC fieldbus. Wireless extensions to Profibus were studied within the R-Fieldbus IST project. Wireless HART is now an established solution in the process control domain.

Wireless sensor networks have emerged at the very beginning of this century as a separate subject leading to a huge quantity of publications with little concern about time. More recently, temporal issues are starting to interest researchers and there are a few proposals claiming real-time support such as IEEE 802.15.4.

It is tempting to reuse in the WSN context the solutions that were developed to construct real-time fieldbusses and the techniques that we employed to analyze the temporal properties. There are however fundamental differences between the propagation properties on cable and in the wireless case. Two of them are the probability that a message is not received correctly and the path losses. Wireless transmission suffers from much higher BER and higher attenuations. While the latter is taken into account in most solutions, the former is mostly ignored when dealing with real-time properties. For instance, papers keep stating that pure TDMA or IEEE 802.15.4 offer real-time guarantees because they avoid collisions. This is true in absence of transmission error, an assumption that does not hold in the wireless domain.

It is easy to show that hard real-time bounds are impossible to guarantee in wireless communications. There is thus a need to find another way to define the real-time properties of wireless sensor networks. The talk will explore some of these ways and also explain why pure TDMA is probably a bad solution to support real-time guarantees.