There are many applications that allows you to create a device to device communication between mobile phones using wifi and bluetooth with no needs of additional network infrastructure, but the range is too limited.

Mobile devices 3G\4G transmission has a much wider range that could cover a distance useful to replace walkie-talkie in excursions in remote location with total absence of providers infrastructures but unfortunately seems that there aren't Apps that allow something similar.

Are there some technical limits that prevent the hardware in the mobile phone to communicate directly with other device using 3G\4G receiver\transmitter with no provider network or It is just a software limitation that could be addressed by software developers?

  • 3G\4G receiver\transmitter will not help you. This is small antenna, and transmission power is much lower than reception. Why? Because huge base station has resources to make signal stronger. And it is directed, so that it could perceive signal from your phone efficiently. Phone to phone communication will not be efficient. – ar_ Dec 27 '17 at 13:36
  • Unfortunately, questions about hosts and consumer-grade devices are off-topic here. – Ron Maupin Dec 27 '17 at 18:09

There are multiple limitations:

  1. Network Architecture: A communication from a mobile device to another is not direct, it must pass trough a BTS (Base Transceiver Station) and a MSC (Mobile Switching Centre) at least. None of those tasks could be easily put in a mobile app.

  2. Licenses: 3G or 4G works in a range of frequencies that is controlled by a government agency. This agency provide licenses to use the electromagnetic spectrum in that specific frequency to the operators. a license is a leasing, it means, it costs money. Operating unlicensed breaks the law.

  3. Power: A pocket device as your mobile phone transmits its signal with a max power around 30 - 33 dBm ( 1 -2 W). That is usually enough to get to the nearest antenna that usually is located in a high place and with a clear view from a wide area. Your device in your hand, on in your pocket, is surrounded by multiple obstacles that decrease the strength of the received signal, if it is coming from another device in the hands (or pocket) of another person.

  • Thank you for the answer. Could you better explain the first point? I guess the power shouldn't be a too big problem to walkie-talkie like use for excursions, since the BTS antennas are at several kilometers of distance. – AndreaF Dec 27 '17 at 19:33
  • You need a BTS and a MSC because there should be a concentrating / distribution central point to avoid that someone snoops on other communications and to identify terminals. BTS antennas cover several kilomters because they are high and most of the time obstacle-free. In a forest you will be surronded by big rocks, trees, etc that will block the incoming signals. – jcbermu Dec 28 '17 at 8:40

The main unsolvable issue is that 2 differents frequencies are used.

A cellular phone is physically designed to use a specific frequency for TX (Phone to BTS) and RX (BTS to PHONE). This include physical components, such as antennas (yes, there is at least 2 antennas for a cellular phone).

This mean that if you try phone to phone communication (which will be really difficult even to try due to limited access to communication components). You will transmit on a frequency that the other device is not able to receive.

  • Thank you for the answer. Could you give me more info about such frequencies difference? In what range are respectively to be not receivable without BTS ? – AndreaF Dec 27 '17 at 19:25

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