Receiver integrity monitoring using doppler analysis

A receiver, comprising:

• an antenna operable to receive a plurality of radio signals;
• a memory module operable to store a threshold value in computer readable format;
• and
• a processor in operative communication with the antenna and the memory module and operable to:
• calculate an expected Doppler value of each respective one of the plurality of radio signals;
• determine an actual Doppler value of each respective one of the plurality of radio signals, wherein the actual Doppler value is measured using Doppler bins having widths less than 1 Hz;
• calculate a signal-to-noise ratio (SNR) for each of the plurality of radio signals;
• identify candidate radio signals comprising radio signals received in a common Doppler bin to a predetermined number of radio signals having the largest SNRs of the plurality of radio signals;
• calculate a Doppler error value of each respective one of the candidate radio signals using the expected Doppler value and actual Doppler value of each respective one of the candidate radio signals;
• generate a composite Doppler error value of a combination of the candidate radio signals, the composite Doppler error value being calculated based on the Doppler error values of the combination of the candidate radio signals;
• and
• determine a reliability of the plurality of radio signals using the composite Doppler error value by comparing the composite Doppler error value to a predetermined threshold value, wherein integrity of the plurality of radio signals is confirmed if the composite Doppler error value is less than the predetermined threshold value and integrity of at least one of the plurality of radio signals is not confirmed if the composite Doppler error value is greater than the predetermined threshold value.

A method of integrity analysis of a plurality of radio signals each from a respective one of a plurality of transmitters, comprising:

• calculating a plurality of expected Doppler values regarding a frequency at which each respective one of the plurality of radio signals is anticipated to be received at a receiver based on an assumed location of the receiver and an assumed location of each of the respective ones of the plurality of transmitters, wherein each of the plurality of expected Doppler values corresponds to one of the plurality of radio signals sent from the respective one of the plurality of transmitters;
• receiving the plurality of radio signals at the receiver;
• determining a plurality of actual Doppler values corresponding to each of the plurality of radio signals;
• calculating a signal-to-noise ratio (SNR) for each of the plurality of radio signals;
• identifying candidate radio signals comprising radio signals received in a common Doppler bin to a predetermined number of radio signals having the largest SNRs of the plurality of radio signals, wherein the common Doppler bin has a frequency width of no more than 1 Hz;
• calculating a plurality of individual Doppler error values for each of the candidate radio signals based on respective expected Doppler values and actual Doppler values;
• calculating a first composite Doppler error value of a first subset of a first number of the candidate radio signals calculated based on the plurality of individual Doppler error values of the first subset of the candidate radio signals;
• comparing the first composite Doppler error value to a threshold value;
• if the first composite Doppler error value is less than the threshold value, confirming the integrity of the first subset of the first number of the candidate radio signals;
• and
• if the first composite Doppler error value is greater than the threshold value, calculating a second composite Doppler error value of a second subset of a second number of the candidate radio signals calculated based on the plurality of individual Doppler error values of the second subset of the candidate radio signals, wherein the second number of the candidate radio signals includes one less radio signal than the first number of the plurality of radio signals.