Which modulation technique is used in 2G?

The first generation mobile systems are based on analog technology. The first technology uses frequency modulation (FM) and frequency division duplexing (FDD), frequency division multiple access (FDMA). The common signalling channels were used in first generation cellular systems.

Each cell had a base station, which used radio signals and a transceiver for communicating with mobile devices. Bade stations were connected to telephone networks. Frequency modulation techniques were used for voice calls by base stations.28 Eyl 2018

The technology behind the Global System for Mobile communication (GSMTM) uses Gaussian Minimum Shift Keying (GMSK) modulation a variant of Phase Shift Keying (PSK) with Time Division Multiple Access (TDMA) signalling over Frequency Division Duplex (FDD) carriers.