Synchronization characteristics of dual delay lock loop in the presence of code Doppler

In a spread-spectrum system, the transmission delay is actually a function of time when there is relative motion between the transmitter and the receiver. This function (code Doppler) must be tracked by the code tracking loop. A traditional second-order delay lock loop (DLL) can track such a delay type. However DLL suffers from a steady-state tracking error. This paper presents the new delay lock loop using dual loops. The transient response and the steady-state tracking behavior of the loop are investigated and compared to those of the traditional DLL. Results show the steady-state tracking error of the proposed loop due to code Doppler is sufficiently suppressed.