ons in a DS/SS system. Consideration was given to both coherent and non-coherent DLLs or TDLs. Also, since the results were obtained using a simulation model of the receiver, several other different loop configurations were programmed in as design options in addition to allowing such parameters as bandwidth and order of the track- ing looop to be varied at will. For example, the possibility of having the PN tracking loop Doppler-aided from the carrier tracking loop [23] was included. This type of accommodation of channel dynamics involves using the Doppler estimate formed in the carrier tracking loop, e.g., a composite AFC/Costas loop [24], appropriately scaled by the ratio of PN code chip rate to carrier frequency, to rate-aid the PN tracking loop. Another variation included in the simulation was the option of time sharing the single code loop for PN receivers that are required to simultaneously track signals from sev- eral satellites. The objective of the investigation was to identify and evaluate those design configurations out of the above class that would provide robust performance in a frequency-selective scintillation environment. In this regard, the fol- lowing qualitative conclusions were reached: 1. A non-coherent code loop is less susceptible to losing lock than the equivalent coherent one since the former does not depend on carrier phase lock which is difficult to maintain in scintillation conditions. 2. A dedicated (non-time-shared) loop is more robust than a time-shared loop simply because the former samples the code correlator output more frequently and thus does not suffer a loss of effective signal level pro- duced by the reduced measurement rate of a time-shared loop. Last, but by no means least, is the work of Meyr [25]-[27], who applies the theory of renewal (regenerative) Markov processes to the non-linear analysis of correlative tracking systems. The method, which is applicable to systems with periodic non-linearities (such as the PLL) as well as those with non-periodic non-linearities (such