GPS - look into Gold Codes [1] and auto-correlation. GPS arrives on your device at -128dBm, give or take, while thermal noise is -111dBm at the ~2MHz sampling bandwidth used. We use the processing gain from correlating against the ~1Mchip/s gold code to extract the lower bitrate signal, so you're pulling signals from approximately 20dB below the relevant thermal noise floor.
[1] https://en.wikipedia.org/wiki/Gold_code