LOSS OF LOCK INDUCED BY DOPPLER OR CODE RATE MISMATCH IN CODE TRACKING LOOPS.

The combined effect of both noise (jamming) and Doppler shift on the mean time to loss of lock is analyzed for two types of loops, the delay locked loop (DLL) and tau-dither loop (TDL). The effect of an automatic gain control circuit in front of the DLL is also discussed. An explicit expression for the mean time to loss of lock (MTLL) that includes dependence on the Doppler shift is derived. A graph of the MTLL vs. timing error variance for different values of the Doppler shift and a graph of the SNR vs. Doppler shift at constant MTLL are derived. The effect of the Doppler shift is shown to be important and should not be ignored for high-processing-gain systems.