NEAR OPTIMAL QUASI-COHERENT DELAY LOCK LOOP (QCDLL) FOR TRACKING DIRECT SEQUENCE SIGNALS AND CDMA

摘要

A received carrier containing pseudonoise modulation and with additive noise is correlated (15) with a local pseudonoise signal having the same binary sequence but an unknown time delay. A second correlation (16) is performed using a signal derived from the local pseudonoise signal (in a preferred embodiment, its time derivative (Differentiator)). The bandpass filtered (13, 14) outputs of the two correlators are used as inputs to a third correlator, whose low-pass filtered (Fp) output controls the time delay of the local pseudonoise signal to form a delay lock loop in which the delay may be measured and low-freqnency modulation extracted from the signal. This delay lock loop has improved noise rejection as compared to prior art loops, and does not experience the 'cycle slip' effets observed in coherent delay lock loops of conventional design. The invention relates to a new near-optimal method of tracking and demodulating direct sequence and other spread spectrum signals that is superior to those commonly used in signal tracking systems: such as, in navigation satellites signal tracking, and code division multiple access (CDMA) systems for wireless communications.