A method and apparatus for detecting signals. According to an embodiment, energy waves are received at a first receiver system and a second receiver system. The first receiver system generates first information using the energy waves received at the first receiver system. The first receiver system receives second information generated using the energy waves received at the second receiver system from the second receiver system. The first receiver system identifies desired information about a repetitive portion of a signal carried in the energy waves received at the first receiver system using the first information and the second information.