A comparison of the mean time to lose lock in coherent/noncoherent DLL's

In this paper we present a closed form expression for the MTLL (Mean Time to Lose Lock) of various code tracking DLL's (Delay Lock Loops). The mutual influence of the channel noise and Doppler shift (due to the platform dynamics) on the loop performance is studied. Our analysis is applied to the non-coherent loop where the IF bandwidth, B/sub IF/, is narrow (this is the case where B/sub IF//spl ap/R/sub b/, the data rate) as well as to the case where B/sub IF//spl Gt/R/sub b/. For comparison, the coherent case is also presented. Using the MTLL, we propose an analytical expression for the threshold. The relationships between the MTLL and the jitter variance at the threshold for all loops are given. These results allows us to perform an analytical calculation of the threshold level for multi-loop receivers like the TDRSS user transponder.