A Model of Time Performance of a Hybrid Wired/Wireless System

Abstract

The PHY layer in RFieldbus system, which has hybrid wired and wireless segment, integrates two different traditional Asynchrony + DSSS in wired and wireless segment respectively, but with the unique FDL protocol of token-Passing. In order to evaluate the transmission time-performance in such a hybrid system, the protocol stack has been modeled as a multi- server- single- queue, which its target token-rotation time meets a dynamic boundary. The polling-time on the slaves was transformed into an internal token walking time, and the rest two lower priority queues were transformed into two M/G/1/∞ systems with two different Poisson arrival rates, so that the complexities of the time properties when transmission happens in different segment can be depicted easily by 7 different parameters. Then, a simulator RF-P based on OMNet++ platform is constructed with a 4-layers infrastructure. The top layer is the system-module inclosing 4 compound modules, which was composed by different simple modules on bottom layer. The comparison with the real measuring in 13 typical network infrastructures of RFieldbus show: 1, the error deviation of RF-P model is not more then 25%, and is about 10% when there is no mobile segment or stations in the measuring scenarios. 2, Error bias is smaller when the system load is lower. 3, The accuracy of the simulator is better when there is no TCP/IP traffic in the system.