FDMA involves separating users by frequencies—each user gets his own frequency
set: one frequency for the uplink, and a corresponding frequency for the downlink.
TDMA together with FDMA, used by GSM, involves separating users by time slots, as well as frequencies. Each
user gets assigned a frequency and then a time slot when they are allowed to transmit.
GSM places eight time alots on each 200-kHz frequency channel of GSM.