Problem analysis：
1. Under normal circumstances, Xiaomi phone can completely guarantee the stability of mobile signal, but if the signal is not good after using the protective case, it can be detected whether it is the cause of the protective case.
2. Because now there are some protective shells on the market in order to pursue beauty, using a large area of electroplating process, the metal will play a shielding role on the mobile phone signal, thus affecting the reception and transmission of mobile phone signal.
