wifi bit rate

[JD]

Any wifi protocol savvy people who can explain this:

iwconfig wlan0
wlan0     IEEE 802.11bgn  ESSID:"Private"
           Mode:Managed  Frequency:2.452 GHz  Access Point: 
00:AA:BB:CC:DD:EE
           Bit Rate=18 Mb/s   Tx-Power=27 dBm
           Retry  long limit:7   RTS thr=2346 B   Fragment thr=2346 B
           Power Management:off
           Link Quality=70/70  Signal level=-36 dBm
           Rx invalid nwid:0  Rx invalid crypt:0  Rx invalid frag:0
           Tx excessive retries:0  Invalid misc:25   Missed beacon:0

The access point is a 54G wifi gateway and router.

My wifi card is the Atheros AR5008 which is an 802.11n card.

How could the bit rate be restricted to 18Mb/s??
Is this a problem with the ath9k driver or the wext driver?
PS: I did not have the issue until installing FC16. This
problem was absent in FC14.