What is the principle of sending signals and messages by mobile phones?

The frequency of mobile phone signal is very high, generally around 900Mhz, and it propagates through ionospheric reflection. The signal of the calling mobile phone is transmitted to the nearest base station, that is, the mobile or connected signal tower, and then the frequency of the high-frequency signal is reduced by the base station, and the base station communicates with the base station. This kind of signal travels in a straight line, and it will be blocked when it meets tall buildings, so those towers are erected very high and transmitted to the base station near the mobile phone that answers the phone, and then converted into high-frequency signals and sent to the mobile phone.

The full name of GSM system is digital cellular mobile communication system. In which area, the mobile phone will automatically track the nearest base station, so the above communication mode can be realized. Unicom's communication system is more advanced than mobile in theory, 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 Unicom funds or other technical reasons, signals in many areas are not as good as mobile. The landlord can refer to the relevant modern communication principles and technologies.