## Example of a TDMA system

The GSM digital cellular system is a very good example of a TDMA-based air interface that has been designed to cope with the challenges of the wireless environment. We have already seen that GSM incorporates a reference word within each frame for channel equalization, necessary to overcome the multipath delay problems which FDMA seeks to avoid. The system also involves a technique known as time slot advance where the remote unit measures the time delay for information to be sent on the downlink from base-station to mobile, and then automatically advances the start time of its own uplink transmission in order to compensate for the up-link time delay.

This technique, together with each mobile taking a master timing reference from the base-station, allows the guard-times between TDMA slots to be minimized and also alleviates the need for an accurate and costly timing reference in the cellular handsets.