Patent ID: 7430193

Claim:
In a method for synchronizing downlink signals of a mobile communication system, and searching cells wherein a frame of the downlink signal comprises: a first slot which includes a first preamble having a first symbol with a valid symbol length and a second symbol corresponding to part of the first symbol with a phase rotated by 180°, and a second preamble which has a pattern specific to each cell for cell search; and a plurality of second slots which have a plurality of pilot symbols provided on the time axis and the frequency axis, a method for synchronizing downlink signals and searching cells, comprising: (a) estimating a point at which correlation of a cyclic prefix of the downlink signal and a valid symbol becomes the maximum as a symbol timing, and estimating initial symbol synchronization; (b) using a characteristic that the real number part of the autocorrelation of the estimated initial symbol synchronization and the first and second symbols has a negative sign, and estimating frame synchronization; (c) using the estimated frame synchronization and the first and second preambles, and estimating time and frequency synchronization; and (d) using the second preamble and searching the cells when the time and frequency are synchronized through the synchronization step of (c).