Satellite-based positioning system improvement
A method, device and system for determining a receiver location using weak signal satellite transmissions. The invention involves a sequence of exchanges between an aiding source and a receiver that serve to provide aiding information to the receiver so that the receiver's location may be determined in the presence of weak satellite transmissions. With the aiding information, the novel receiver detects, acquires and tracks weak satellite signals and computes position solutions from calculated pseudo ranges despite the inability to extract time synchronization date f, 'n the weak satellite signals. The invention includes as features, methods and apparatus for the calibration of a local oscillator, the cancellation of cross correlations, a Doppler location scheme, an ensemble averaging scheme, the calculation of almanac aiding from a table of orbit coefficients, absolute time determination, and a modified search engine.
1. In an SPS system for identifying the location of a receiver in the presence of satellite signal attenuation comprising having a plurality of orbital satellites sending synchronized encoded signals on a carrier frequency wherein said encoded signals have repeated epochs containing synchronization data:
a receiver for detecting, acquiring, and tracking a set of the encoded signals and simultaneously determining the code phases of said set with respect to said epochs; and
an aiding source to transmit information to the SPS system,
wherein said receiver is comprised of a correlator with an integrated canceller,
wherein said canceller is used to reduce the amplitude of strong signals,
wherein a canceling finger is provided for each channel for which canceling is to be performed and
said canceling finger takes one input from the code generator input to a prompt finger of a channel tracking a jamming signal and a second input from a code generator input of the finger for which cancellation is to be performed.
2. The SPS system for identifying the location of a receiver of claim 1 wherein the cancellation is performed at a point where the signal is represented by approximately 10 bits.