This post is about the GSM basics. Let's see together below.
The GSM system is a frequency- and time-division cellular system, each physical channel is characterized by a carrier frequency and a time slot number.
Uplink and downlink signals for one user are assigned different frequencies, this kind of technique is called Frequency Division Duplex (FDD).
Data for different users is conveyed in time intervals called slots, several slots make up a frame. This kind of technique is called Time Division Multiple Access (TDMA). The information carried in one time slot is called a burst.
Every cell has several TRX and every TRX includes 8 timeslots (providing 8 basic physical channels). In the radio subsystem, the physical channel supports the logical channel based on the type of message transmitted. In this way, the physical channels are mapped as different logical channels.
A sequence of eight time slots is called a TDMA frame and has a duration of 4.615 ms. The time slots of a TDMA frame are numbered from 0 to 7. The beginning and end of TDMA frames in uplink and downlink are shifted in time.
