I am using wireshark in monitor mode to capture all the frame. I buffered all the QosData in order to calculate the biterate of each station on the network. I calculate the biterate but it is not an accurate value. what i need to know is when the station use the network alone and when it uses it with another station?

i know if two station with different wifi card for exemple ( st1 802.11g 54 Mb/s, st2 802.11n 300 Mb/s) if st1 uses alone the line the biterate used is 28 MB/s and if st2 uses alone the network the bit rate increase to approximately 150Mb/s but if the two station use the network at the same time the st1 lost about 80% of its bit rate because of the st1 wifi card

thx in advance