What parameters are to be changed for the 802.11g WLAN model?

I have downloaded the WLAN files from http://www.mathworks.in/matlabcentral/fileexchange/38073-802-11g-wlan-phy-model and 802.11a from http://www.mathworks.in/matlabcentral/fileexchange/3540. On simulating both the files the outputs are the same in terms of BER,SNR and bitrates. What parameters are to be changed in the 802.11g so that it yeilds a better performance. I am relatively new to Simulink. Kindly also tell how to change these parameters. Thank you.