Decision-directed coherent delay-lock tracking loop for DS-spread-spectrum signals

In this paper we present a non conventional joint data demodulation-pseudo-noise (PN) code tracking scheme for direct sequence (D8) spread-spectrum (88) signals which solves problems of components imbalance and sensitivity with a remarkable hardware simplicity and no performance degradation. An integrate-and-dump Costas loop is employed for carrier recovery and data demodulation of the 88 signal. Both data and carrier are then used to derive the baseband error signal of the code tracking loop. Moreover, a single passband correlator is used to perform the early-late correlation, leading to a hardware complexity equivalent to that of the tau-dither scheme, but without its loss in performance. Results of a thorough theoretical analysis of the system in an AWGN environment are reported. We provide performance curves in terms of steady-state jitter and mean time to first lock loss. A superior jitter performance for low values of Ebl No with respect to a traditional noncoherent DLL is shown, along with the potential gain of Manchester coding upon the more usual NRZ format.