Telecommunication system and a main station for use in such a system

A telecommunication system comprising:

• a main station and a plurality of substations, in which system communication between the main station and the substations occurs by transmission of data samples via a transmission channel in accordance with a multiple access protocol of respective time slots in successive data frames, which channel is common to the substations, wherein for coarse ranging the substations include ranging transmission means for transmitting in a data frame a ranging sequence of samples of low magnitude with respect to the magnitude of data samples to be transmitted in the time slots of said data frame, and the main station includes correlation means for recovering ranging information by correlating a received ranging sequence (rseq) with a reference sequence which is identical to a transmitted sequence, the main station comprising means for providing the reference sequence;
• and, for coarse ranging, the correlation means principally correlates those samples of a received ranging sequence which fall within a time window reserved for ranging in said data frame.