The WiSe-CAN Project

Overview & Research Statement

Modified: 2007/06/18 20:42 by admin - Categorized as: Introduction
In WiDOM, as in any dominance-based protocol (see our PrioMAC webpage), the MAC protocol elects the computer node with the highest priority (lowest number) and gives it access to the medium. This election procedure can also be used to compute the minimum value of sensor readings distributed on different computer nodes and, remarkably, this computation can be performed with a time-complexity that is independent of the number of computer nodes. This procedure forms an important building block for other useful calculations; for example, it is possible to efficiently extract an interpolation of sensor readings and this can be performed with a time-complexity that is independent of the number of computer nodes. This is a crucial asset for addressing problems in future Large-Scale Dense Sensor Networks for Cyber-Physical Systems (CPS).

In this way, we are addressing important challanges in Cyber-Physical Systems such as: (i) scalable architectures and; (ii) the integration of physical dynamics with computations and communications.

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The CAN bus is an example of a commercial-off-the-shelf (COTS) technology that offers a prioritized MAC protocol based on the binary countdown / dominance protocol. CAN is used in a wide range of applications, ranging from vehicles to factory-automation. Its wide application fostered the development of robust error detection and fault confinement mechanisms, while at the same time maintaining its cost effectiveness. An interesting feature of CAN is that the maximum length of a bus can be traded-off for lower data rates. It is possible to have a CAN bus with a bit rate of 1Mbit/s for a maximum bus length of 30 meters, or a bus 1000 meters long (with no repeaters) using a bit rate of 50 Kbit/s. While the typical number of nodes in a CAN bus is usually smaller than 100, with careful design (selecting appropriate bus-line cross section, drop line length and quality of couplers, wires and transceivers) of the network it is possible to go well above this value (which is often also imposed by the software of the CAN transceivers).

We have been using CAN for efficient distributed computation of aggregated quantities. The use of such a prioritized MAC protocol is proposed to be in a way that priorities are dynamically established during runtime as a function of the sensed values involved in the specific distributed computation.

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