Signal acquisition in a satellite telephone system

In a telecommunications system, where the receiver must find a signal arranged in a regular pattern in frame periods (10) and further in slots (11) from among several possible frequencies, there is applied a two-step synchronisation procedure. In the first step (20), the receiver records a sample sequence (30) having the length of two frame periods and a sampling ratio of 1/1, and calculates on the basis of this an estimate sequence (32), where each estimate is a sliding average of N successive samples, and N is the number of symbols contained by one slot. The largest estimates (35, 36, 37, 38) correspond to those bursts of the detected signal that have the highest power; on the basis of them, there is calculated a coarse frame synchronisation at the accuracy of 30 symbols. In the second step (24), in each recorded frame there is detected a given reference sequence (14; 43) by looking for a sequence of successive samples that best correlates with the known form (43) of the reference sequence. If the location of the found reference sequences is equal, in both frames, with sufficient accuracy, the signal is found.