Spread Spectrum Signal Characteristic Estimation Using Exponential Averaging and an AD-HOC Chip rate Estimator
NAVAL POSTGRADUATE SCHOOL MONTEREY CA
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This dissertation investigates two methods of spread spectrum SS signal characteristic estimation for the two principle types of SS systems, frequency-hopped FH and direct sequence SS. The exponential averaging detector is used to detect and estimate the hopped frequencies of a SS-FH signal in the presence of interference signals as well as additive-white-Gaussian-noise AWGN. The detection method provides an estimate of the AWGN plus inference spectrum using exponential averaging and then generates an estimate of the desired signal spectrum by combining the estimated AWGN plus interference spectrum with the composite desired signal plus interference plus AWGN spectrum. Finally, this dissertation evaluates the detectors performance as a function of the exponential coefficient, the combining method, the probability of false alarm, signal-to-AWGN ratio, and signal-to-interference ratio. The second method of SS signal characteristic estimation uses a digital ad-hoc chip rate estimator ACRE. The ACRE is used to estimate the chip rate of a half-sine pulse shaped SS direct-sequence signal. The ACRE is explained in relation to its similarities and contrasts to the chip rate detector. The components and performance of the ACRE are presented for standard-ACRE, ACRE with additional filtering, and ACRE with incrementing. The additional filtering results in a reduced chip rate search range but yields improved estimation performance and incrementing has the potential for parallel processing, resulting in dramatically decreased computational time, without loss of performance.
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- Radiofrequency Wave Propagation