In order to get TDMA (Time Division Multiple Access) schemes to work, the time-frames from each mobile must be synchronized when received by a base station. This synchronization is achieved by using the concept of TA (Timing Advance). The degree of synchronization is measured by the base station on the uplink, by checking the position of the TSC (Training Sequence Code). This training sequence is mandatory in all frames transmitted from the mobile. From these measurements, the base station can calculate the TA and send this information to the mobile.