A Global Navigation Satellite System (GNSS) receiver that includes a satellite signal generator generating signal data for a signal that is not being tracked by the receiver. The receiver includes a satellite signal generator running an algorithm to process first and second received signals to produce a software-synthesized satellite signal, and the generated signal data is used to correct bias or is communicated to a spaced-apart GNSS receiver or used for onboard positioning calculations. The satellite constellation may be the Galileo constellation, with the first and second signals being E5A and E5B signals tracked by the receiver and the generated third signal being an E5AltBOC signal. With a half-a-cycle bias resolution technique, the satellite signal generator generates synthetic E5AltBOC data of high quality. For a receiver, which physically tracks E5AltBOC, synthetic E5AltBOC may be used to monitor polarity of a physically tracked E5AltBOC and correct it if error is detected.