The PHY Data rate is the number of bits that are processed per unit of time. This rate is different for control and data packets.
802.11b supports 4 data rates – 1Mbps, 2 Mbps, 5.5 Mbps and 11 Mbps
1 Mbps always used for control packets
Other rates used for data packets
The Phy rate also depends on rate adaptation algorithm if this is selected (Minstrel or Generic)
In NetSim, the PHY rate is set in the function fn_NetSim_IEEE802_11_SetDataRate(NETSIM_ID nDeviceId, NETSIM_ID nInterfaceId, NETSIM_ID nReceiverId,NetSim_PACKET* packet,double time) present in IEEE802_11_Phy.c file inside IEEE802_11 project.