Why can’t cellphones connect to each other directly, acting like walkie talkies, at distances similar to their ability to reach cell towers.
In: 80
They can, and they did! You can still buy an old NEXTEL iDen phone with DirecTalk. It did exactly as you describe, 915mhz ISM band with frequency hopping making it a viable scrambled means of SHTF communication to this day. I have LOTS of them.
Why don’t other carriers do this? They can’t charge users for it, and modern networks are shit compared to iDen for packet data without an internet backbone. That is, they can’t do all of the routing to find eachother. Using LTE to go phone to phone would not be very efficient on the handset itself. The tower provides a heartbeat and the phone is mostly in an RX state. For phone to phone it has to be RX/TX back and forth to ack each other. This takes a lot of battery at the expected data rates. Also there’s no FCC clearance on the higher bands, and the range would be extremely low. iDen was 800mhz and the radio could be changed to the open license 900 ISM easily. The closest band that would be usable without license from a user transmitter would be in the 3Ghz range. This would still go very short distances without the tower.
The lack of elevation would give a typical cellphone to cellphone communication range of only a few thousand feet.
Edit; Realized I need to clarify why LTE would be almost impossible this way… The devices in question would need to all communicate with each other to time schedule their radio packet bursts. The tower does lots of work to deal with how many devices there are. What you’re asking for in a modern context of everyone has at least one cell phone and sometimes two would be a mesh network. This being where you could say, text a particular person who is in range among say hundreds. The would require the radio kicking on and at least transmitting an identifier that all of the other phones would hear but ignore. That’s the simple way, and would work. However, what happens if there’s another convo going on? Someone else sends a text to another person? You need a coordinator to make sure the transmissions don’t cover each other. The mesh system would allow a signal to hop from one device to another, but then you have to make sure that the device at the end even got it, which means the communication has to go both ways RX and TX, and make sure that each time it hops it increments a counter and gets dropped after enough hops, AND each packet would have to be stored in each phone to make sure they don’t just send the same packer around in circles forever.
None of this scales well at all, and it’s very hard to implement.
It could only work on certain bands, on certain phones, and would only have a select few “channels” that everyone else could hear publicly for it to be useful. It would be like a very low range walkie talkie, though perhaps full duplex like a phone call by using separate TX and RX channels like phones do for data.
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