Early cellular networks, including 1G, operated at a frequency of 850 MHz and 1900 MHz . Then, 2G and 3G networks operated at additional frequency bands and spectrum around 2100 MHz, and 4G LTE technology operated at additional frequency bands and spectrum around 600 MHz, 700 MHz, 1.7/2.1 GHz, 2.3 GHz, and 2.5 GHz.