Abstract: A method for determining an integrity of a train is provided. The method includes coupling at least one head-of-train device to the train. The head-of-train device includes at least one first radio. The method also includes coupling at least one end-of-train device to the train. The end-of-train device includes at least one second radio. The method also includes communicating between the first and second radios using radio-ranging to determine a length of the train, and determining the integrity of the train based on the length of the train.

Abstract: A differential GPS landing system having at least three GPS receivers at known locations in spatial proximity to each other, wherein each GPS receiver independently receives GPS signals from the plurality of GPS satellites and at least three reference stations, wherein each reference station receives a signal from a different two of the at least three GPS receivers and calculates two separate differential corrections for each satellite, wherein each differential correction is independently calculated using the signals received from a different one of the two GPS receivers. The reference stations preferably average the two calculated differential corrections for each satellite to produce an averaged differential correction for each satellite.