During a call connection, a burst can easily be lost when the mobile station happens to be located in a fading dip for that particular frequency, or if it is subjected to interference. There is a high probability for the next burst to be received if it is sent on a different frequency. This can be done by using frequency hopping. The coding and interleaving scheme in GSM is constructed so that loss of a single burst have minimal influence on the speech quality. In frequency hopping, a predefined set of frequencies is used in each cell. The mobile station changes frequencies once every TDMA frame, i.e. 217 times per second.
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