I've got a use case where I'm transmitting small payloads (approximately 64 bytes(without headers)) once per second from a moving vehicle. The vehicle will be operated in a rural environment, which according to cellmapper.net is covered with one large macro-cell for each MNO. This vehicle is being designed to operate at an event which will see a few hundred spectators (all with mobiles phones of course). From previous events, I've had instances where I have full strength signal, but limited actual connectivity on my phone. I suspect that this was due to congestion of the cell, as you have a lot of people all connecting to the same cell?

I know that not every cell supports LTE-M. The MNOs specifically need to upgrade it to support it, so what is it about LTE-M that is different to non-LPWAN LTE? Do these differences mean that I should have connectivity on LTE-M, even when spectator mobile phones are congesting the rest of the network?