Binary Offset Carrier (BOC) is the agreed modulation for signals of next generation Global Navigation satellite systems (GNSS). Compared to current phase shift keying (PSK) modulation by a code, there is a further modulation by a sub-carrier. There is a known major difficulty with BOC called ‘false lock’ where early/late gates settle on the wrong peak of the multi-peaked correlation function. This invention eliminates the problem by eliminating that correlation. Instead, a two dimensional correlation is tracked independently to realize a dual estimate. An unambiguous lower accuracy estimate derived from the code phase is used to make an integer correction to a higher accuracy but ambiguous independent estimate based on the sub-carrier phase. The actual receiver may adopt a triple loop, instead of the usual double loop, where carrier phase, sub-carrier phase and code phase are tracked independently but interactively.