Using an inexpensive SDR (such as the USRP or Per Vices Phi), I want to process two or more communication protocols at the same time (e.g. WiFi and GSM). Is it possible to Tx (or Rx) both at the same time, like FDMA, or would they need to do some fast switching between modulations and frequencies, like TDMA? I'm not sure if the receiver would be able to accept it though since it is not expecting TDMA.
So I think FDMA would be the best approach, but like I said the question is whether or not it's possible to construct a waveform that can transmit both protocols simultaneously. I think it may also depend on frequency separation, combined bandwidths, mutual sample rate, etc.