Communication protocol for main and mobile stations where time slots are used for data packet transmission

Claim 1

Method of transmitting data from a plurality of mobile sub-stations to a stationary main station by way of a common channel which is subdivided into time slots the length and synchronization of which being determined by a corresponding time slot distribution of a data transmission signal transmitted by the main station, in which the data packets have a time length essentially equal to the time length t S of the time slots and are transmitted by the sub-station slightly earlier than the beginning of the relevant time slot, the "advancement of time" being selected in such a way that the data packets, when received by the main station, are substantially synchronized with the time slot distribution of the main station, characterized in that a first, request-for-access data packet of a different configuration from that of the actual data packets is transmitted prior to the actual data packets of the message, in that the length t(1) of the first, request-for-access data packet satisfies t(1) < t S - 2t D,max where t S is the time length of the time slots, and t D,max is the maximum time delay that may occur in the coverage area of the main station concerned, and in that during transmission, the beginning of the first, request-for-access data packet substantially coincides with the beginning of a time slot in the sub-station, in that the main station is arranged for measuring the time t B that elapses in this time slot until the beginning of the reception of the first, request-for-access data packet, in that the main station is arranged for sending a code representative of t B to the relevant sub-station, and in that each sub-station is arranged for transmitting in response to the code representative of t B the message data packets with an advancement of time t A equal to tB and a length t(x) substantially equal to t S .