Doppler acceleration influence on code tracking in direct sequence spread spectrum systems: threshold calculation and AGC algorithms

A study of AGC (automatic gain control) for a coherent direct-sequence spread spectrum system is given. The influence of presync or postsync AGC on the performance of a coherent second-order delay lock loop (DLL) is analyzed. Two criteria of performance are used: the mean time to lose lock and the worst case steady-state tracking error of the loop. The threshold degradation due to Doppler acceleration is derived. It is shown that proper adaptation of the loop parameters results in performance close to the optimum even under high Doppler acceleration conditions. The algorithm to adapt the loop is quite simple, so digital implementation (digital signal processor, look-up table, etc.) can easily be realized.<
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