Mobile phone model: iPhone 12
System version: ios14
There is a signal on the mobile phone card, but there is no network. The reasons are:
1. The external reason is that your location is not an area with strong network signal coverage, such as elevator, subway or parking lot. Communication signals in these places often have no problems, but the coverage and construction of network signals are much worse.
2. The internal reason is mainly caused by the problem of mobile phone wireless and baseband.
The full name of mobile phone is mobile phone or wireless phone, usually called mobile phone. It was originally just a communication tool. In the early days, it was also commonly known as big brother. It is a portable telephone terminal that can be used in a wide range. It was first developed from the field mobile phone manufactured by Bell Laboratories in 1940.
At present, the so-called fourth generation mobile phone (4G) is the most widely used in the world. It is mainly based on fdd-lte system in Europe and America and TD-LTE in China. 4G communication technology is continuously optimized, upgraded and innovated based on 3G communication technology, integrates the advantages of 3G communication technology, and derives a series of inherent characteristics, focusing on WLAN technology.