An Off-Grid Makeshift Cell Network

When traveling into the wilderness with a group of people, it’s good to have a method of communications set up both for safety and practicality. In the past people often relied on radios like FRS, CB, or ham bands if they had licenses, but nowadays almost everyone has a built-in communications device in their pocket that’s ready to use. Rather than have all of his friends grab a CB to put in their vehicle for their adventures together, [Keegan] built an off-grid network which allows any Android phone to communicate with text even if a cell network isn’t available.

The communications system is built on the LoRa communications standard for increased range over other methods like WiFi using a SX1278 chip and an ESP8266. The hardware claims a 10 km radius using this method which is more than enough for [Keegan]’s needs. Actually connecting to the network is only half of the solution though; the devices will still need a method of communication. For that, a custom Android app was created which allows up to 8 devices to connect to the network and exchange text messages with each other similar to a group text message.

For off-grid adventures a solution like this is an elegant solution to a communications problem. It uses mostly existing hardware since everyone carries their own phones already, plus the LoRa standard means that even the ESP8266 base station and transmitter are using only a tiny bit of what is likely battery power. If you’re new to this wireless communications method, we recently featured a LoRa tutorial as well.

49 thoughts on “An Off-Grid Makeshift Cell Network

    1. These are essentially 2 WLAN hotspots connected with LORA.

      This is perfectly legal in Germany, when using the right LORA frequency.

      The cellphone only works within few meters of the hotspot.

    2. ISM and SDR bands are, depending on country laws, open in Europe. But both in Germany. On one 860MHz subband you can even dish out 500mW.

      I would stay away from the 433MHz band. Even though it is reserved for low range/power applications, the garage door opener of the neighbours oftentimes turned on the TV which is toggled over a radio switch. I know… shoddy design.

      1. I thought the same. In at least germany, there is only 25mW allowed on LoRaWAN Frequencys.
        Im not sure when or IF we are allowed to use the other frequencys like 865 – 868MHz where 500mW is allowed. I still have to figure that out – but i at least know, the SX1276 is capable of those frequencies.

        https://www.bundesnetzagentur.de/SharedDocs/Downloads/DE/Sachgebiete/Telekommunikation/Unternehmen_Institutionen/Frequenzen/Allgemeinzuteilungen/FunkanlagenGeringerReichweite/2018_05_SRD_pdf.pdf?__blob=publicationFile&v=7

  1. It seems to me that packing a GMRS handheld is still a necessity. At least then if you got lost, searchers might stumble over your frequency. This setup is good in that it keeps all members of the group in contact, but for emergency preparedness it’s not everything, it won’t talk to anyone not on the app.

    1. Well, if you are trully lost, any frequency that can reach as far as needed, illegal to transmit on or otherwise, is a good frequency for that.

      Especially if it pisses off some government agency that might really not like you’re trashing their comms.

      1. Well, no normal “cell”phone can send/receive LoRa Networks.
        So in regards to the actual phones it’s a bunch of WiFi hotspot “cells”.

        But the LoRa part is the important thing here and no cell phone connects to it….
        And calling a WLAN a cell network is at least a stretch.

        1. Americans call it a cell-phone. Anywhere else it’s called a mobile phone.

          Not that it’s “wrong” to call it a cell-phone but it can be misleading.

          “cell networks” have been around for a very long time, much longer than “cell-phones”

          So yes this is “cell network” using “cell phones” even though it is not using what you would more likely describe as a “cell phone network” though technically that is correct to.

          1. Semantics… A “mobile” phone predates “cellular”. This would have a base station on a high perch and a large operating radius with few customers. The subscriber equipment would typically have higher power RF output to deal with the larger operating radius and terrain. Mobile networks provide coverage but not capacity.

            The concept of “cellular” relates to breaking up the large radius base stations into smaller and smaller “cells”, like a honeycomb, to increase capacity. The user equipment gets smaller too, and so does it’s RF output power and thus battery size. All these are “mobile”… but go further that cellular turns into “portable” and pocket sized. Now we also have small cells, pico cells and femto cells which describe an ever smaller coverage area, to increase capacity as an underlay below a larger “macro” cell. This is all to enable more capacity, which from day one is the definition of “cellular”.

            See https://en.wikipedia.org/wiki/History_of_mobile_phones for a good run down and how the cellular concept emerges.

            Of course, language is a collection of sounds that are agreed upon by a population group and understood by all in that group. So call it mobile… cellular… pocket or jazbec phone … as long as the sound is recognized and understood, it gets the job done.

          2. @[RF Dude]

            Your stuck on “phone”

            What was mentioned was “cell networks” and that does not necessarily mean a network for cell phones.

            Cell networks break up channel usage and power so that channels can be reused to increase available bandwidth.

            One cell may use channels 1,4, 7. the next cell may use 2, 5, 8 and another 3, 6, 9 so another cell opposite the first can re-use 1, 4, 7 etc etc

            Technically early UHF TV was a cell network, so to were FM radio. CB radio uses the same principle but was manually controlled – channel too busy so choose another one.

            Our UHF CB radio in this country has repeater channels that work like a cell network.

            It’s just you Americans that use the term “cell phone” anywhere else it’s called a mobile phone even still today with 4GLTE or 5G.

            So it’s not just semantics, cell network does not equal (imply) cell phone.

      2. The fact that they mention LORA and ESP32 in the article, makes me think it’s just a glorified BT or wifi to LORA bridge. You probably connect the phone to it via wifi or BT then use LORA to get the claimed 10km range. So you could in essence have say several camp sites separated by some kms, have one of these at each camp site and everyone at one site could connect to it to communicate with others at other camp sites. In the end just a GMRS/FRS radio would likely be more frustration free with the benefit that you could still communicate to others outside your group in say some kind of emergency where 1st responders might be trying to locate you.

        1. In my country (Australia) many many moons ago we had 27MHz CB radio just like America but our output limit on AM was 4 watts instead of 5 watts (no one cared, most sets were 5W). You could get good range out bush with a Single Side Band (SSB) set and that was the norm for safety.

          Our new “CB” radio is UHF 477MHz and in a vast country like ours were you might need urgent or emergency help when your 6000kM from anywhere, UHF isn’t at all useful. In mountainous and forest terrain it will go about as far as you can through the microphone.

          So anything that may improve safety is a good thing here, even if it takes a bit of preparation so that a group travelling together carries a base.

          I have often thought of an app that can make mobiles useful in disaster events when there is no network by providing services on Wi-Fi. Something that scales and at the same time throttles and prioritises so that one idiot (iPhone user) doesn’t wipe out all bandwidth sending a high res pic via MMS. Something that uses the original phone number as an ID. Provides voice, txt and perhaps MMS, has distributed network address identification (pier to pier), has prioritization for essential services, has a txt broadcast function essential services and a HTTP service to download the app in the absence of the original cell network.

          1. 1) I think you meant 600km
            2) CB @5W will struggle to do 100km in flat terrain
            3) did sat phones cease to exist or something? Relying on CB or UHF radios with ones life seems like a Darwin award waiting to happen…

          2. @AKA Distance reachable depends a lot on atmospheric conditions. I once made a 45 minute long contact from L.A. to Kodiak Alaska on 4 watts AM. Clear as a bell, then just faded away….

            My antenna was Hussler “beer can” load coil mounted on a mirror mount bolted to a piece of galvanized pipe rammed into the ground. Antenna wasn’t more than 8′ off the ground.

          3. @[playaspec]

            I was a avid CB’er in the 70’s and early 80’s.

            I had some very long DX skips off the ionosphere and had QSL cards from several countries.

            But even without skip, SSB can cover a decent range over fairly flat terrain.

            Like any enthusiast of that era I had too many antennas to remember some used the ground as a ground plane lol. Many were made with whatever conductive junk I could find at the time. One very good antenna was just extruded aluminium suspended and supported with thick fishing line.

            I had a long wire directional that was very good for DX skip but obviously only to certain locations.

    1. Agreed, Meshtastic follows the same concept, offers message encryption, GPS coordinate location sharing, has great community support, is well documented and has both Android and iOS apps. It is also easily extendable with python, JavaScript and REST APIs.

  2. So, instead of “have all of his friends grab a CB to put in their vehicle” it’s “have all of his friends grab [this non-standard cobbled-together collection of parts] to put in their vehicle”

    AND require them to carry a d*mned phone too, and some way to keep it charged.

    1. And the assumption that every carries a cell phone…. Really? In the woods hiking/fishing/camping is where we want to get ‘away’ from cell phones/laptops/tvs/air conditioning/etc. and such. Carry a firearm of course, but a cell phone??? Around here, that is our idea of vacationing in the wilderness :) .

      1. Seems like in this case they needs to use WiFi only on the cellphone. So if they are truly trying to get away from the cellphones – they just need to make sure the cellphone radio is off but obviously they are out of the mobile network provider’s range.

        Not sure how much do you hike, but I always found it easier to carry my cellphone with me for taking pictures instead of my DSLR, as my primary objective wasn’t photography. People do like to take a picture or two during their hike, usually.

    2. Well… if you’re in a vehicle you can put the phone beside you, if carrying a phone is too difficult, next to the car charger that you can use to both charge your phone and power the LoRa station, both work on 5V.

      Problem solved!

      Also MUCH less effort and cheaper than installing a CB radio in each vehicle.

  3. Why the need to build a custom android-only app? I think it’s better to make a captive portal web-app that is compatible to any device with a browser. This way there’s no need to install anything on the cellphones and the captive portal automatically displays the text-messaging interface.

    1. Great idea actually. If you’d like to contribute let me know, the whole project is opensource. The reason I wrote a custom app in this case was to get notifications, even when the LoRa app was minimised or removed from the recent apps list. Using a web based app wouldn’t work in this case but I think it would be very cool to support both an app and web-app that way users have more choice.

    2. Great idea, if you’d like you contribute please do so, the project is open source. I created an app because I needed notifications that would show up when the app is minimised or removed from the recent app list. Using a web based app wouldn’t have worked for this requirement but I think being able to support both a web-app and os specific app would be very cool. More options the better.

      1. When you stop to really think about what is the internet, it’s actually not a strange idea at all. We’re just used all of the client devices being “over here” (at home, at the office, etc) and all the servers being “over there” (some big IT business or industrial server farm). The reality is, both can be anywhere on any sized network.

        In this case, it would be having a web server integrated into LoRa node. Rather than making a custom app that you put on every phone to tell it how to speak the necessary protocols to the LoRA node, you put all that special functionality in the LoRa node itself and have the LoRa node just appear as a standard WiFi access point and use a captive portal to automatically direct that device to the web server in the node. That way, any phone, tablet, or laptop with a functioning WiFi radio and web browser can communicate with this system.

  4. CelSol, Ripple, Meshtastic, Gotenna – too many choices for LoRa comms ‘standards’. Hopefully Meshtastic can grow to be the leader since it is opensource, but it would best on a standalone device (like an Aramchat) with no need for the cell phone.

  5. Cool tech, I guess, but FRS is cheaper, universally available without user limit, and has better range. This isn’t a best–in-class solution to anything other than maybe sharing pictures out in the boonies.

    1. You’re not going to be sharing pictures over this thing, least not without massively resizing them. Trying to send a full size picture that a modern phone can take over LORA would probably take all day. LORA isn’t designed for those kinds of bulk data transfers and high bandwidth, it’s designed to send small messages at low power over long distances. Think like SMS when it 1st came about with GSM limited to 140char per msg and no MMS. or getting weather updates from a remote weather station.

  6. today lora now working, i cant buy a device put firmware like linux on my laptop and working
    no lora is still idea not solution, but i need this NOW! because russia, china etc. blocking internet NOW!

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