-3
\$\begingroup\$

This question already has an answer here:

Every mobile radiates its signal to its nearest tower during phone call.Then is it possible for two mobiles to communicate with out using any tower with in range of 100 meters or more .If it is possible then we call a person who is beside me for free of cost . Thanks in Advance.

\$\endgroup\$

marked as duplicate by tcrosley, PeterJ, jippie, Peter Smith, uint128_t Mar 20 '16 at 18:05

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

  • 3
    \$\begingroup\$ Most likely not possible. The cellphone devices that I am familiar with transmit in one frequency band and receive in a different frequency band. The cell tower transmits and receives in the opposite bands. Thus: no two cellphones can hear each other. They need the cell tower or something that acts like the tower. \$\endgroup\$ – Dwayne Reid Mar 20 '16 at 4:43
  • \$\begingroup\$ For example 98.3 radio frequency and it is transmitting some song .In our mobile if we tune to that frequency we can listen to it.In the same manner if we keep the first mobile to transmit at uplink frequency and if we change the os of second mobile uplink frequency to receive then is it possible to communicate.As we know a circuit which is able transmit to certain frequency also receive at that frequency. Thanks in advance \$\endgroup\$ – pullarao kommineni Mar 20 '16 at 5:12
  • 2
    \$\begingroup\$ "As we know a circuit which is able transmit to certain frequency also receive at that frequency" is wrong, how did you end up with that assumption? Any practical wireless device needs separate circuitry for transmitting and receiving signals. Cellphones commonly include a FM tuner for receiving public broadcasts at e.g. 98.3 MHz, but they generally do not have any transmitter circuitry for that frequency. It is certainly possible to add transmitting circuitry, but it doesn't come for free. \$\endgroup\$ – jms Mar 20 '16 at 6:00
2
\$\begingroup\$

Actually, there are companies promoting this idea already in the 3GPP Standards Process. It is called "LTE Direct". See, for example: https://www.qualcomm.com/invention/research/projects/lte-direct

\$\endgroup\$
5
\$\begingroup\$

No and Yes.


First the no bit. The GSM cellular network is designed around communication between a handset and a base station. The base station does all of the control here. Firstly it decides who can talk when (see multiple access, TDMA, CDMA, etc.) in order to allow many phones to connect. Secondly, it decides how to route a call - you call up a number on your handset, your handset asks the base station to connect the call, and the base station then decides how to proceed - can it ring a phone on the same tower or does it have to route to another tower.

There is nothing designed into the GSM network methodology that allows two handsets to talk directly - they all have to go through the base station. In fact if you think about it, if you are in the middle of nowhere with no base station in range, and you are with your friend, do you get signal from each others phones? No, you don't, because there is no base station within range to tell the phones they are allowed to talk.

@DwayneReid also makes a good point, the Uplink and Downlink GSM frequencies are different meaning that the phones are not listening on a frequency band that phones around them are transmitting on. This is done for a very good reason - if your phone is transmitting at 1W power output, and a phone next to it was listing on the same frequency, the 1W transmission from the phone would completely drown out the ~10nW signal from the base station.


Now the yes bit. It is possible for two devices to communicate with each other directly - take a walkie-talkie for example. However, we are talking about commercial mobile phones here. So can it be done?

Well, we know that GSM is out of the question. But there are also methods for phones to talk nearby. You can get Bluetooth modems with a range of 100m as an example. You can also do VoIP if one phone sets up a Wi-Fi hotspot and the other connects.


TL;DR Yes, it could be possible to get two phones to communicate nearby without going through a base station, but it would not be using GSM or the phones cellular services, it would be with the phones secondary radio services like Wi-Fi and Bluetooth.

\$\endgroup\$
  • \$\begingroup\$ For example 98.3 radio frequency and it is transmitting some song .In our mobile if we tune to that frequency we can listen to it.In the same manner if we keep the first mobile to transmit at uplink frequency and if we change the os of second mobile uplink frequency to receive then is it possible to communicate.As we know a circuit which is able transmit to certain frequency also receive at that frequency. Thanks in advance \$\endgroup\$ – pullarao kommineni Mar 20 '16 at 5:15
0
\$\begingroup\$

There is an app for this - FireChat uses Bluetooth and Wifi over a range of up to 200 feet between handsets using mesh networking, no need for a cell tower or base station. https://appsto.re/gb/OL75Q.i

\$\endgroup\$

Not the answer you're looking for? Browse other questions tagged or ask your own question.