The 2G network standard adopted by China Mobile and China Unicom is GSM, while the 2G network standard adopted by China Telecom is CDMA.
The Global System for Mobile Communications, known as GSM, is the most widely used mobile phone standard at present. More than 6,543.8 billion people in more than 200 countries and regions around the world are using GSM mobile phones. The ubiquity of GSM standard makes it common for users to roam internationally after signing a "roaming agreement" between mobile phone operators. The biggest difference between GSM and previous standards is that its signaling and voice channels are digital, so GSM is regarded as the second generation (2G) mobile phone system. This shows that digital communication has been established in the system for a long time. GSM is an open standard currently developed by 3GPP.
CDMA is the abbreviation of CodeDivisionMultipleAccess, which is a new and mature wireless communication technology developed on the spread spectrum communication technology, a branch of digital technology. The principle of CDMA technology is based on spread spectrum technology, that is, the information data to be transmitted with a certain signal bandwidth is modulated by a high-speed pseudo-random code with a bandwidth much larger than the signal bandwidth, so that the bandwidth of the original data signal is expanded and then transmitted by carrier modulation.