Some embodiments are directed to a method of determining the time of arrival of an incoming satellite signal at a receiver, including receiving an incoming signal, multiplying of the incoming signal by a first real-valued periodic modifying signal to produce a first modified output, correlating the first modified output to obtain a first correlation output, multiplying the incoming signal by a second real-valued periodic modifying signal to produce a second modified output, correlating the second modified output to produce a second correlation output and comparing the first correlation output with the second correlation output.