A dual correlating sequential estimator for spread spectrum PN code acquisition

The sequential estimation (SE) technique introduced by R. B. Ward (1965) was designed for the acquisition of pseudonoise (PN) signals. It proves to be an effective model in medium SNRs as long as inverted PN sequences are not encountered. Recognizing that negative data bits invert PN sequences in spread spectrum transmissions, J. H. Chiu and L. S. Lee (1988) developed an improved sequential estimator (ISE) that processes both types of sequences. The drawback of the ISE design, however, is that it erroneously despreads the incoming signal by inverting it during negative bit acquisitions. To remedy this, a dual correlating sequential estimator (DCSE) is proposed which detects modulation errors by gathering correlation measurements from resident SE and ISE subsystems and corrects for them with an inverting mechanism. Key performance parameters such as mean timing and the variance of acquisition for the SE and DCSE designs are determined via the generalized signal flow graph technique and verified through simulation