The one I'd consider is BPSK. That's really just Manchester code, and could be treated pretty much like OOK (On-Off-Keying) and if the bandwidth demand is high enough, it could be easily enhanced with the use of the UART and a small PAL. Some MCU's (no 805x types I know of, but some ARMs) support Manchester encoding and simply gating an oscillator with a '1' would do much of the work. Simple filtering will do the rest. If one wanted to be really precise, one could use a classic PLL (14046 maybe) which would allow the transmitter and receiver to remain in sync would help too, and active filtering of the received stream would then produce an active signal for, say, a one, while none was produced for a zero. There's no end to what one could do. It's just a matter of how much effort/hardware is to be involved.

QPSK, for example, is a bit of a problem because there are inherent decoding ambiguities. FSK is very reliable for fixed stations, which is what this represents, and OOK is nearly as much so, offering a bit more bandwidth with what amounts to the same effort and investment.

RE