Patent ID: 7020074

Claim:
A coarse synchronisation method for a receiver in a frequency division multiplexed (FDM) transmission system, in which a signal transmitted during a synchronisation period comprises predetermined data encoded onto a plurality of carriers of different predetermined frequencies and predetermined relative phase within each of a sequence of synchronisation symbols of predetermined symbol length transmitted at a predetermined symbol frequency, comprising the steps of: receiving said transmitted signal at said receiver; performing a sequence of unsynchronised Fast Fourier Transforms (FFTs) on said signal at intervals spaced by a time interval not equal to a predetermined symbol period; removing said coding corresponding to said predetermined data from said carriers and detecting phases of said carriers; summing said detected phases of said carriers to generate an FFT output sum for each FFT and comparing said output sum with a predetermined threshold; declaring synchronisation of an FFT with a symbol if said output sum exceeds said threshold; and synchronising subsequent FFTs to subsequent symbols after said declaration.