A pre-despreading delay-and-multiplication (PDDM) acquisition method was proposed to improve the probability of detection of the delayandmultiplication acquisition method for global positioning system (GPS) signal. The PDDM first searches for the pseudo random code phase to de-spread the signal; then two narrow-band filters are applied before and after the delay-and-multiplication operation to reduce the noise power. The signal to noise ratio and the probability of detection are improved consequently. The Monte Carlo simulation shows that while keeping the advantage of not being affected by the frequency offset, the PDDM improves the probability of detection significantly compared to the delay-and-multiplication acquisition method. The effectiveness and practicality of the PDDM was examined by applying it to a software receiver. The GPS signal was successfully acquired.

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