What is the principle of mobile phone automatically receiving short messages in different places?

The frequency of mobile phone signal is very high, generally around 900Mhz, and it propagates through ionospheric reflection, so mobile phones make calls.

The number is transmitted to the nearest base station, that is, the mobile or connected signal tower, and then the base station reduces the frequency of the high-frequency signal.

Communication between base stations, this signal travels in a straight line, and it will be shielded when it meets tall buildings, so those towers are all.

It is very high, transmitted to the base station near the cell phone that answers the phone, and then converted into a high-frequency signal and sent to the cell phone.

The full name of GSM system is digital cellular mobile communication system. Where is the mobile phone? It will automatically call the nearest one.

Base station tracking, so the above communication mode can be realized. Unicom's communication system is theoretically more advanced than mobile, because

Because GSM is the first generation mobile communication system, and CDMA belongs to the second generation, which is the full name of narrowband code division multiple access digital access technology.

However, due to the funds of China Unicom or other technical reasons, the signal in many areas is not as good as mobile.

The principle of SMS- short message service is very simple:

The first is the store-and-forward mechanism. The work of sending data packets by SMS is completed by the short message center in the mobile network instead of the terminal.

If the user is not in the service area, the short message is stored in the short message center, and after the user appears.

Then forward it to him, which is not available in GPRS and other services. The second is the delivery confirmation mechanism. In a circuit-switched data ring

In the environment, the connection is end-to-end, so users can know whether the connection is completed and the data is transmitted.

Say it in a popular way:

The base station has been transmitting signals, a very important part of which is the broadcast message, which is a kind of broadcast message.

This is a paging message (including phone number). Every mobile phone has been listening to paging messages. When it finds the paging message,

If you give it (that is, someone is calling it), it will establish a connection with the base station, through the base station and the caller.

Contact.

If the call is made, the connection is directly established with the base station.

When not talking, there is no connection with the base station, but the base station is still transmitting signals. There is a signal between the base station and the mobile phone.

Transmission does not mean that there is a connection, and the connection needs to complete a series of protocols that both parties abide by.

There are some differences in various network standards, but it is roughly like this: mobile phones register a base in the network.

Under the station (usually the base station with the strongest signal), as people move, they will register with other base stations. while

When a mobile phone initiates a caller, it will tell its registered base station, and the base station will find the registered called phone through a series of channels.

A base station, which will send a paging message, which will be broadcast to all departments or departments registered under the base station.

Divide (sometimes group) mobile phones, and the mobile phones are authenticated again. If so, establish a connection and ring the bell.

So not all mobile phones can receive it, only some mobile phones registered under the base station can receive it, and so on.

Here's the thing.