Alf Isaksson

Multihop multi-channel scheduling for wireless control in WirelessHART networks

The WirelessHART standard uses TDMA and channel hopping to control access to the network and to coordinate communication between network devices, in order to enhance reliability and to improve the throughput of the network. A problem in utilizing multiple channels is that current devices are usually equipped with a single transceiver. Thus, a node can only transmit or receive on one channel at a time. Moreover, contrary to todays wired control systems, if a single access point is used the communication becomes the bottle neck of the control system. Therefore this paper presents how one may schedule the WirelessHART communication using two access points. Furthermore the paper describes a scheduling algorithm managing a multihop multi-channel networked control system based on the WirelessHART standard. A simulation example of a multihop multi-channel network is also shown, using the fixed packet lost utility of the Matlab/Simulink-based tool TrueTime.

Industrial evaluation of process control using non-periodic sampling

The main purpose of this work was to further develop and evaluate non-periodic sampling schemes, focusing on their needed communication and the effect they have on the control performance. The paper focuses on evaluating the schemes in experiments on some real industrial processes at Iggesund Paperboard. The industrial evaluation was done using fast wired communication into an ABB AC800M controller with a pre-filtering block mimicking non-periodic communication. The tests show communication reductions of 90 to 99 % compared to the current default sampling intervals in the industry, without significant loss of performance. However, the results further indicate that often carefully selected slower periodic sampling may reduce almost as much communication. In the end the choice of method for communication reduction will be determined by the implementation effort of non-periodic sampling versus the commissioning effort of slow periodic sampling.