SYNCHRONIZATION PREAMBLE METHOD FOR OFDM WAVEFORMS IN A COMMUNICATIONS SYSTEM

摘要

A highly bandwidth-efficient communications method is disclosed that enables remote stations to synchronize in time and frequency to their serving base station. The invention enables a base station and its remote stations in a cell to synchronize in a noisy environment where signals interfere from other base stations and remote stations in other cells. The base station forms a forward synchronization burst that includes a plurality of tone frequencies arranged in a distinctive orthogonal frequency division multiplexed pattern unique to the base station. The unique pattern enables a remote station to distinguish the base station's bursts from other signals present in a crowded area. The distinctive orthogonal frequency division multiplexed pattern can be a Hadamard code pattern, for example. When the a base station has received a signal on a reverse link from a remote station, having significant interference, the base station selectively forms a request signal requesting the remote station to respond with a reverse synchronization burst that includes a plurality of tone frequencies arranged in the same distinctive orthogonal frequency division multiplexed pattern. The base station then transmits the forward synchronization burst and the request signal at a base station reference instant of time to the remote station. The reverse synchronization signals selectively occupy time slots in the transmission frame from the remote station to the base station, that would otherwise be occupied by channel control or traffic signals. Only when the base station requests the remote station to respond with a reverse synchronization burst, does this burst preempt the time slot from its other uses.