Spreading symbols with sequence before transmission
It is just the control channel that is spread.  It appears that it is spread primarily to make the signal more robust in the face of frequency selective fading, which is probably a major problem at 60 GHz.  It is easy to use spreading to get the robustness because the data rate of the control channel is low.  In other words, the spreading is fulfilling two roles: converting the low control channel data rate to the high OFDM symbol rate, and increasing the control channel's robustness.