A method of phase correction at a wireless device includes: estimating a phase slope for an OFDM symbol in a data portion of a packet based on an elapsed time from the start of the packet; measuring a residual phase slope from tracking pilots for the OFDM symbol in the data portion of the packet; and adjusting a phase correction based upon the phase slope and the residual phase slope. In an embodiment of the invention, a method for instant conversations in a thread within a discussion forum can be provided. The illumination optical system 300 comprises: a light source 20; a lens array 320; and a superimposing lens system 370.