Abstract: NS-3 is an important network simulator,offering a lower level abstraction of wireless functionality than NS-2 and is more close to realistic wireless physical layer.In this work,we read the source code and analyzed simulation mechanisms of 802.11 physical layer,including node states and the condition that packets can be received,the computation of the starting and ending time of channel busy state,packet reception power considering the addition effect of multiple path loss and fading models,the computation of bit error rate and packet error rate,and tracking of multiple interfering packets and the computation of interference based on chunk units.We gave some advices for protocol modification.This paper makes a contribution to understand the wireless simulation principle of NS-3.

Key words: NS-3,802.11,Physical layer,Source code analysis