In IEEE 802.11a wireless LAN network, link adaptation affects the goodput and energy efficiency performances. Most of the conventional link adaptation schemes are focused on the maximum goodput performance. Moreover, they didn’t consider the contention between multiple users. By considering the MAC layer operation, we investigate the effects of SNR and the number of users on the goodput and energy efficiency performances. Through computer simulation, we compare an enhanced link adaptation scheme with MAC Service Data Unit (MSDU)-based adaptive PHY mode selection scheme. Simulation results show that the link adaptation scheme considering the multiple users outperforms the (MSDU)-based adaptive PHY mode selection scheme.