Electronic – Can a smartphone send directly a message to another smartphone 20 miles away?


According to this website,

a typical cellphone has enough power to reach a cell tower up to 45
miles away

So, can a smartphone send directly a message to another smartphone 20 miles away?

Best Answer

No, it is not possible for one cell phone to communicate directly with another. Not for any physical reason of signal strength, but because the protocol design relies on cell towers playing an active role.

The cell towers orchestrate the communication between themselves and the individual phones. The detail varies between the different protocols, but the towers broadcast timing information and tell the handsets when they are allowed to respond to the tower.

The tower doesn't need to be a big tower, small micro-cells are possible but the network is designed to work for connectivity through the strucure of the network, rather than peer-to-peer.

One key point is that at the handset, transmit and receive are at different frequencies, so a handset and only transmit to a base station, and not to another handset. This allows the base station to transmit and receive at the same time (if very selective filters are used).

Finally, 20 miles range for handset to handset would be surprising. Handset to directional (sectored) antenna in an open environment is plausible but not something to rely on.

See Timing Advance for a tiny fragment of the detail of one specific cell-phone protocol.