Getting 9600 Bd into 12.5 kHz isn't too difficult as long as you're willing to sacrifice weak signal performance, Shannons law tells us that. I would imagine OFDM or even m-ary PSK would be capable of providing the required throughput.
The big advantage that GMSK has for manufacturers is that they can use the same class C output stages as they do for FM. PSK and particularly OFDM require extremely linear amplifiers. If we go over to TDM then we're in the land of GSM or NexEdge re-implementation and why should we do that? I think the development of codec2 should be encouraged as it represents something fun, rather than just plugging in black boxes which seems all too prevalent these days. BTW why is there a push to 6.25 kHz channel spacing, the 2m band is hardly that busy these days. A better argument for that could have been made in the early-80s when the channels were choc-a-bloc but not now. We almost went 12.5 kHz then (remember S20x?) but we didn't. Jonathan G4KLX
