Patent ID: 7103362

Claim:
A method for a radio receiver to acquire timing information for a radio transmitter which transmits, in a time-slotted arrangement, at least one signal which includes a sequence of information indicating the slot timing and having a length at least equal to a known minimum length and which sequence is repeated in said at least one signal at a known interval, the method comprising the steps of: (i) receiving a number of slots of said at least one signal which is at least sufficient to allow reception of two repetitions of said known minimum length of said sequence; (ii) forming a first group of said received slots at least equal in number to said known minimum length and a counterpart group of the same number of received slots but spaced from said first group by said known interval, each group having a first slot and a last slot; (iii) for each slot in said first group and its corresponding slot in the counterpart group, performing a correlation operation to obtain a correlation value for information in each of these corresponding pairs of slots; (iv) summing said obtained correlation values to obtain a correlation sum and storing said obtained correlation sum; (v) obtaining a next correlation sum by: (a) performing a correlation operation to obtain a correlation value for information in the slot at the first slot of said first group and the corresponding slot in said counterpart group; (b) performing a correlation operation to obtain a correlation value for information in the slot outside the first group adjacent to the last slot of said group and the corresponding slot outside said last slot of said counterpart group; (c) reforming said first group and said counterpart group to exclude the respective slots first slots and to include the respective slots adjacent the last slots; and (d) from the correlation sum last obtained, subtracting the correlation value obtained in (a) and adding the correlation value obtained in (b) to obtain a correlation sum; (vi) storing said correlation sum obtained in (d); (vii) repeating steps (v) and (vi) until at least a number of correlation sums equal to said known minimum length are obtained and stored; (viii) examining said stored obtained correlation sums to select the sum with the greatest magnitude, this selected sum indicative of the presence of said sequence and thereby indicating the slot timing.