Pseudorandom noise ranging receiver which compensates for multipath distortion by dynamically adjusting the time delay spacing between early and late correlators

A receiver for demodulating and decoding a composite radio frequency (RF) signal consisting of a plurality of transmitted pseudorandom noise (PRN) encoded signals comprising:

• an RF downconverter, connected to receive the composite RF signal and to provide a composite intermediate frequency (IF) signal;
• means for generating a local sample clock signal;
• a sampling circuit, connected to receive the composite IF signal and the local sample clock signal, and to provide digital in-phase (I) samples and quadrature (Q) samples of the composite IF signal;
• a plurality of channel circuits, each channel circuit for demodulating and decoding one of the transmitted PRN encoded signals, and connected in parallel with the other channel circuits, such that each channel circuit receives the I samples and Q samples at the same time as the other channel circuits, wherein each channel circuit further comprises:
• means for providing an expected carrier phase signal;
• a synchronizing circuit, connected to receive the sample clock signal, the expected carrier phase signal, and a synchronizing adjustment signal, and connected to provide an accumulated carrier phase signal and a PRN code phase control signal, the accumulated carrier phase signal and code phase signals being synchronous with each other;
• a PRN code signal generator, connected to receive the PRN code phase control signal and to provide a local reference PRN code signal;
• decoding and carrier rotation means, including means for simultaneously demodulating and decoding the I and Q sample signals, connected to receive the I samples, the Q samples, the local reference PRN code signal, and the accumulated carrier phase signal, the demodulating means for phase-rotating the I and Q samples by an amount indicated by the carrier phase signal, and the decoding means for multiplying the I and Q samples by the local reference PRN code signal, and providing decoded I and Q samples;
• and
• correlation means, connected to receive the decoded I and Q samples, for determining the correlation power level at first and second code phase delays, and for providing the synchronizing adjustment signal to the synchronizing circuit by comparing the correlation power levels at the first and second phase delays, wherein
• the first and second phase delays are dynamically narrowed by being set to a predetermined wide correlator delay equal to a PRN code chip time during an initial PRN code lock acquisition period, and by being set thereafter to a predetermined narrow correlator delay equal to a fraction of a PRN code chip time.

A method for demodulating and decoding a composite signal consisting of a plurality of transmitted pseudorandom noise (PRN) encoded signals comprising:

• sampling the composite signal in synchronizm with a local sample clock signal, and thereby providing digital in-phase (I) samples and quadrature (Q) samples of the composite signal;
• feeding the I samples and Q samples to a plurality of channel circuits, each channel circuit connected in parallel with the other channel circuits such that each channel circuit receives the I samples and Q samples at the same time as the other channel circuits;
• within each channel circuit:
• generating a local reference PRN code signal in response to a synchronizing adjustment signal;
• decoding the I and Q samples, by multiplying the I and Q samples by the local reference PRN code signal, and in response thereto, producing decoded I and Q samples;
• determining the correlation power level of the I and Q samples at a first and second code phase delays, and for providing the synchronizing adjustment signal in response thereto, the first and second phase delays being dynamically adjusted from a predetermined wide correlator delay during an initial code lock acquisition period, and thereafter being set to a predetermined narrow correlator delay.