Wikipedia's article on CBTC [0] seems to want to limit the term to moving block systems only, not including fixed block – I'm not sure if that is correct or if that is just some agenda some Wikipedia editor has.
But it seems to me that even in a fixed block system, the train could operate (semi-automatically) if it knew its location and the location and current state of signals – and the current signal state could be broadcast to it via radio. Would you call such a system CBTC or not?
Also, it seems to me that fixed block with physical signals and moving block CBTC could coexist on the same line. Moving block CBTC trains are authorised to disregard red signals, and instead get their movement authority via radio; fixed block trains are not. If a fixed block train is in a fixed block, that locks the block out for all trains (both fixed and moving); if a moving block train is in a fixed block, that locks the block out for all fixed block trains; but two moving block trains can coexist in the same fixed block provided their moving blocks are non-overlapping.
[0] https://en.wikipedia.org/wiki/Communications-based_train_con...