Demodulating QZSS signals

One or more tangible, non-transitory, computer-readable media storing instructions that, when executed by one or more processors, cause the one or more processors to demodulate an L1S signal from a satellite in the Quasi-Zenith Satellite System, wherein the demodulating includes performing operations comprising:

• tracking another L1 signal transmitted by the satellite, to estimate one or more parameters of the other L1 signal;
• predicting, based on the estimated one or more parameters of the other L1 signal, one or more parameters of the L1S signal transmitted by the satellite;
• demodulating the L1S signal to obtain data bits of a data message modulated on the L1S signal by the satellite,
• wherein the demodulating is based on the one or more predicted parameters;
• and
• calibrating a phase offset, wherein calibrating the phase offset comprises:
• detecting a bit in the other L1 signal;
• wiping off the detected bit from in-phase and quadrature (I/Q) samples of the other L1 signal;
• after wiping off said detected bit, integrating a plurality of the I/Q samples of the other L1 signal;
• obtaining an estimated carrier phase of the other L1 signal based on a result of integrating the plurality of the I/Q samples of the other L1 signal;
• detecting one or more bits in the L1S signal;
• wiping off the detected one or more bits from I/Q samples of the L1S signal;
• after wiping off said detected one or more bits, integrating a plurality of the I/Q samples of the L1S signal;
• obtaining an estimated carrier phase of the L1S signal based on a result of integrating the plurality of the I/Q samples of the L1S signal;
• and
• comparing the estimated carrier phase of the other L1 signal with the estimated carrier phase of the L1S signal to calibrate the phase offset.

A Global Navigation Satellite System (GNSS) receiver configured to demodulate an L1S signal from a satellite in the Quasi-Zenith Satellite System, the GNSS receiver comprising:

• at least one tracking loop configured to track another L1 signal transmitted by the satellite, to estimate one or more parameters of the other L1 signal;
• a prediction subsystem configured to predict, based on the estimated one or more parameters of the other L1 signal, one or more parameters of the L1S signal transmitted by the satellite;
• and
• an L1S bit detector, configured to demodulate the L1S signal to obtain data bits of a data message modulated on the L1S signal by the satellite,
• wherein the L1S bit detector is configured to demodulate the L1S signal based on the one or more predicted parameters,
• the one or more parameters of the other L1 signal comprise a carrier phase of the other L1 signal;
• the one or more parameters of the L1S signal comprise a reference carrier phase of the L1S signal;
• and
• the prediction subsystem comprises an adder or a subtractor, configured to predict the reference carrier phase of the L1S signal by adding or subtracting a phase offset to or from an estimated carrier phase of the other L1 signal,
• wherein the prediction subsystem comprises a comparison unit, configured to compare the estimated carrier phase of the other L1 signal with an estimated carrier phase of the L1S signal, to calibrate the phase offset,
• wherein the GNSS receiver comprises a calibration mode in which it is configured to calibrate the phase offset, and comprises an aiding mode in which it is configured to use the calibrated phase offset to predict the reference carrier phase of the L1S signal.