Mixed-mode simulation for IEEE 802.11-operated WLANs

In this paper, we address the issue of integrating packet level simulation with fluid model based simulation for IEEE 802.11-operated wireless LANs (WLANs), so as to combine the performance gains of the latter with the accuracy and packet level details afforded by the former. In mixed mode simulation, foreground flow is simulated at the packet level, while the other background flows are approximated into a collection of fluid chunks and simulated in the fluid mode. Note that these two types of flows influence each other at the point of interaction, e.g. the wireless channel in a WLAN. In order to realize mixed mode simulation, we develop the model of interaction at the wireless channel between the foreground flow and the other background flows, in view of their achievable throughput. We then implement mixed mode simulation in ns-2 [2], and conduct a comprehensive simulation study to evaluate mixed mode simulation with respect to accuracy (in terms of error discrepancy) and efficiency (in terms of speed-up in conducting simulation). Simulation results indicate that for IEEE 802.11-operated WLANs, it is feasible to blend fluid model based simulation into packet level simulation, and the performance improvement is quite significant while the accuracy and the packet level details desired are not compromised. Specifically, mixed mode simulation incurs only approximately 2 % of the error discrepancy, and reduces the execution time by two orders of magnitude. This, coupled with the fact that mixed mode simulation is able to retain packet level details for the connection of interest, makes it an excellent candidate for carrying out large-scale simulation for IEEE 802.11-operated WLANs.