An optimum search algorithm for the coherent acquisition in direct-sequence spread-spectrum (DSSS) receivers is proposed and analyzed in this paper. The system consists of two major parts: a phase region estimator and a phase alignment detector. We use an auxiliary sequence to correlate the incoming signal in the phase region estimator. Since the cross-correlation value between the auxiliary sequence and the incoming PN signal has linear magnitude, and can provide the direction for the phase updating, an optimum search algorithm, try and error method, can be adopted to obtain the phase region information of the incoming signal. The mean acquisition time is derived through the signal flow graph theory. The time is compared with that of the conventional serial search scheme, and the results show that the proposed scheme can achieve coarse acquisition significantly faster than the conventional scheme. An optimum search algorithm for the coherent acquisition in direct-sequence spread-spectrum (DSSS) receivers is proposed and analyzed in this paper. The system consists of two major parts: a phase region estimator and a phase alignment detector. We use an auxiliary sequence Since the cross-correlation value between the auxiliary sequence and the incoming PN signal has linear magnitude, and can provide the direction for the phase updating, an optimum search algorithm, try and error method, The mean acquisition time is derived through the signal flow graph theory. The time is compared with that of the conventional serial search scheme, and the results show that the proposed scheme can achieve coarse acquisition significantly faster than the conventional scheme