A system adjusts a receiving device in response to sensing symbols. An automatic gain control is adjusted in response to receiving a first symbol of a data unit from a first antenna. After adjusting the automatic gain control at least a second and a third symbol of the data unit are received. The automatic gain control in response to receiving a fourth symbol of the data unit from a second antenna is received. After adjusting the automatic gain control at least a fifth and a sixth symbol of the data unit is received. At least one of the first and second antenna is selected based upon a function of a first and second energy, calculated using the second and third symbol, and the fifth and sixth symbol, respectively.