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
Someone used to do this. Nextel? There was a way to push to talk to people in your contacts. I’m assuming they are totally capable but they gotta charge you those minutes!
In the early to mid 2000s this was a thing with Nextel, they called it Direct Connect.
Watch this commercial https://youtu.be/5hU1tcQqdX8
you cannot do “similar to their ability to reach cell towers” because cell towers have much stronger transmitters, and much more sensitive receivers. Phones will not be able to “hear” each other at those distances.
you can use Bluetooth and WiFi for direct links, but distances is limited, so you can probably just talk without using devices.
PS In cell phones, Push-to-talk functionality is done via Cell data or WiFi connection. Cell phones are not talking directly to each other.
in theory, sure. but you quickly run into practical issues. how does the caller know to find the callee? what if the callee isn’t in range? what if they are busy? The easiest way to solve this is to centralize the controlling functions, which is basically what the phone network does.
In theory, two cell phones could connect to each other directly. They’d have to be bigger, but they could. The big problem comes when a thousand phones are trying to have one-on-one conversations simultaneously.
Cell phone systems are deliberately designed with very low transmitting power, for two reasons. First, it makes the phone smaller and lower-power, cheaper and with longer battery life. But more importantly, it minimizes the cross-talk between phones. If my phone is powerful enough to talk to another phone, it can also interfere with the transmissions of other nearby phones — even phones too far away to talk to directly can get their data disrupted and garbled. As the number of phones trying to communicate directly with each other gets bigger, the problem gets worse, like [people at a noisy cocktail party](https://en.wikipedia.org/wiki/Cocktail_party_effect) who have to shout to be heard, making the noise of conversation worse for everyone else.
The solution is to have the phones transmit and receive at very low power, and have big, expensive, powerful transmitters and sensitive receivers built into the cell towers. Each phone can only be heard by the nearest cell tower, minimizing the problem of cross-talk. This also lets the system grow to handle more users if it does get overcrowded: just add a new tower, and have everyone transmit even more quietly. Instead of shouting at a loud cocktail party, each person quietly passes a note to a very capable waiter who delivers their message to the recipient.
Some people here have mentioned Nextel’s Direct Connect feature. This was *not* actually a direct connection. Your phone contacted the nearest tower, which sent the message to your friend’s phone via their nearest tower, exactly the same as ordinary cell phone calls. The only difference was you didn’t have to dial.
Basically the reasons everyone else has stated, but…there’s more.
In order to do both (well, all 4 actually) your cell phone would need 4 different antenna, each of which use power all the time (all 4: SMS, cell service, wifi service, and now walloe-talkie radio) and each of which operates at different frequencies with different protocols. We’re already pretty lucky that voice-based cell service is still included (as opposed to VOiP which would operate SMS and Voice signals across an internet-based relay: you can tell when you get these types of calls because they’re always scratchy and dropping pieces). So…there’s hardware requirements, power requirements, firmware requirements AND software requirements that all have to work together and only interfere the way *you* want then to interfere with one another (imagine getting a walkie call whole you’re already on a cell call: which one gets the speaker? Which the mic? Can you control it or is pre-programmed by type of phone). And there’s the fact that even with 8-fold data compression, we’re running out of frequencies available for use. Imagine suddenly increasing the frequency demand by 5 billion users overnight (that’s what adding walkie service would require based on an estimated number of cell phones in active use in the world right now, with that number only likely to go up in the future as cars are added to the cell service mix).
All in all, its just not worth the headache, even if you discount a few of those points as just engineering challenges.
There were actually a couple of apps that allowed you do this using Bluetooth.
A previous app was called Firechat – [https://en.wikipedia.org/wiki/FireChat](https://en.wikipedia.org/wiki/FireChat)
another one was designated for commuters for on the London tube for when there wasn’t Internet connectivity in the tunnels – [https://medium.com/@tubechat_app/introduction-to-tubechat-9e635b121ef6](https://medium.com/@tubechat_app/introduction-to-tubechat-9e635b121ef6)
There is one app that still seems to be available called Bridgefy – [iOS](https://apps.apple.com/us/app/bridgefy-offline-messages/id975776347) [Android](https://play.google.com/store/apps/details?id=me.bridgefy.main&hl=en_NZ&gl=US)
You can “do this” today.
Setup a Wi-fi hotspot
Have your friend connect too it
Call over LAN using any capable Voip app.
The issue is finding the correct hotspot and then your friends local IP. That’s where a provider comes in, except they use a different technology then wifi since the range of wifi isn’t good enough 🙂
I grew up on a sailboat. So using VHF radio was very commong to talk to other boats you could see nearby. But for that to work, we needed and antenna attached to the mast.
The average person isn’t going to be walking about with a 10 meter antenna. ***Mobile radios exist, but there make-up means they are bigger than your typical cellphone.***
It just isn’t practical for most people. Sure it would be a nice feature, but nobody is going to carry around a device 2-3 times bigger than their phone just for this limited feature.
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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