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 gain of the latter with the accuracy and packet-level detail afforded by the former. In mixed-mode simulation, foreground flows operate in the packet mode, while the other background flows are approximated into a collection of fluid chunks and simulated in the fluid mode. As these two types of flows influence each other at the point of interaction, e.g. the wireless channel in a WLAN, we derive the model of interaction at the wireless medium. We then implement mixed-mode simulation in ns-2 as well as MATLAB, and conduct a comprehensive simulation study to evaluate its performance with respect to the capability of keeping track of network dynamics (in terms of the TCP behavior), accuracy (in terms of the error discrepancy in throughput), and efficiency (in terms of the speed-up in carrying out simulation).Simulation results indicate that, for IEEE 802.11-operated WLANs, mixed-mode simulation significantly expedites the simulation, and yet provides the same level of packet details and accuracy as packet-level simulation does for flows of interest. Specifically, the error discrepancy incurred in mixed-mode simulation is within 2% of the maximum channel bandwidth, and reduces the execution time, in the best case, by two orders of magnitude.