70. Research on the BDS Inter-Satellite-Type Carrier Phase Bias Introduced by Different NH Code Sign Conventions

As for D1 NAV message broadcast by BDS MEO/IGSO satellites, a secondary code of Neumann-Hoffman (NH) code with length of 20 bits is modulated on ranging code. However, the secondary coding are not implemented on D2 NAV message from BDS GEO satellites. While different GNSS receivers from different manufactures were used for carrier phase difference applications, a bias of 180° (half a cycle) may be induced between those carrier phases obtained from two different sign conventions A and B. The bias would result in that RTK activities failed. For the issue mentioned in former content, this paper presents an intensive research on the rationale of the BDS inter-satellite-type carrier phase bias introduced by different NH code sign conventions. We select three kinds of most popular GNSS OEM boards for testing and verification. A serial of crossover trails and long-term stability tests are executed to identify the half-cycle carrier phase bias between the BDS signals which two different OEM boards output. In addition, we change the sign convention of NH code in the OEM board K508 of ComNav Technology for further validation. Based on our test results, the paper proposes a recommended solution as all GNSS device manufactures should take Convention B for dealing with NH code between different BDS signals, to avoid the inter-satellite-type carrier phase bias in RTK application.