If you try to do an IR transmission system that goes any appreciable distance and you want reasonable reliability and try to be resistant to stray IR disturbance (especially from florescent lights) then the IR beam should use a carrier frequency that is modulated with the data waveform to be sent. The receiver can then detect the carrier frequency to verify the reception came from a legitimate transmitter. Note that TV remote controls have worked like this for a LONG time. They typically use a carrier frequency of 36 to 48 KHz. This scheme of course does limit your effective data rate to less than 1/2 or 1/3 of the carrier frequency. Comercial IR data links may use carrier frequencies up in the MHz range.

Michael Karas