The IRDA protocol would disagree with you Nigel, as I've stated in several dozen posts over the last couple years. The base discovery protocol works at 9600 baud, 50% duty cycle, directly modulated IR, no carrier frequency, no modulation, no encoding. Pulse shaping is used at higher baud rates, and there are some techniques for much higher data transmission that are outside the scope of the question.
All that is required with transmitting IR data baseband without modulation is using packets with good error detection/correction data. So the software end of things is more important that the transmitter/receiver in such cases.