Synthesising estimated signal level in correlation receiver - uses spread spectrum transmission system and subjects incoming signal to pseudo-random phase changes before processing

摘要

The modified correlation receiver prevents transient loss of degradation of the incoming signal due to noise from adversely affecting performance. The incoming signal (1) is split into three paths (2,3,19). The first two are mixed (8,9) with the output of a pseudo-random phase sequence generator (4) whose effect on the two paths (2,3) is respectively in antiphase. Each path is filtered (10,11), squared (12,13), and filtered again (14,15) before being fed to a comparator (16) whose output tunes the random generator (4) to give zero difference in the comparator. The third path has signals with no shift between input and random generator. It is similarly processed through filters and squarer (21,24,22). The estimated signal level is formed from the processed output of the three paths. The difference (25) between the first two (2,3) is transformed to an absolute value (26), doubled (27), and applied to one input of a summing amplifier (28). The differences (29,30) between first and third, and second and third paths are added (31) and applied to the second input of the summing amplifier (18). e output of this amplifier (k) is the estimated useful signal level.