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With the development of China’s BeiDou Navigation Satellite System (BDS) and the operation of the real-time service (RTS) of the International GNSS service, BDS real-time precise point positioning (RTPPP) has become possible. In this contribution, the RTS product CLK93 is employed for BDS RTPPP, and its quality for BDS orbit and clock corrections is first assessed by availability and accuracy over a period of 24 days. Following this, the convergence time and positioning accuracy of BDS-only RTPPP are evaluated by performing a 24-day processing with ten stations from the multi-GNSS experiment (MGEX) network. Finally, a real-time kinematic test is conducted in an urban environment to further investigate the performance of BDS-only RTPPP. Experimental results show that the average availabilities of the CLK93 corrections are approximately 95% for the inclined geosynchronous satellite orbit (IGSO) satellites, 90% for the medium earth orbit (MEO) satellites and 65% for the geostationary earth orbit satellites. The mean accuracy of the real-time corrections, which is represented by the signal-in-space ranging error (SISRE) value, is 10 cm for the IGSO and MEO satellites. Furthermore, the average positioning accuracies in the north, east and up components of the ten MGEX stations are approximately 1.7, 2.2 and 2.6 cm, respectively, for the static mode and 10.3, 15.6 and 29.2 cm, respectively, for the kinematic mode. In addi-tion, the average time required to converge to a 20-cm accuracy in the three-dimensional component is approximately 100 and 136 min for BDS-only RTPPP in the static and kinematic modes, respectively. In addition, the positioning accuracy of BDS-only RTPPP in the real-time kinematic test is 0.86, 0.92 and 1.68 m in the east, north and up components, respectively, for the whole solutions during the test, which is obviously worse than that obtained by GPS-only RTPPP.

Although double-differenced (DD) observations between satellites from different systems can be used in multi-GNSS relative positioning, the inter-system DD ambiguities cannot be fixed to integer because of the existence of the inter-system bias (ISB). Obviously, they can also be fixed as integer along with intra-system DD ambiguities if the associated ISBs are well known. It is critical to fix such inter-system DD ambiguities especially when only a few satellites of each system are observed. In most of the existing approaches, the ISB is derived from the fractional part of the inter-system ambiguities after the intra-system DD ambiguities are successfully fixed. In this case, it usually needs observations over long times depending on the number of observed satellites from each system. We present a new method by means of particle filter to estimate ISBs in real time without any a priori information based on the fact that the accuracy of a given ISB value can be qualified by the related fixing RATIO. In this particle filter-based method, the ISB parameter is represented by a set of samples, i.e., particles, and the weight of each sample is determined by the designed likelihood function related to the corresponding RATIO, so that the true bias value can be estimated successfully. Experimental validations with the IGS multi-GNSS experiment data show that this method can be carried out epoch by epoch to provide precise ISB in real time. Although there are only one, two, or at most three Galileo satellites observed, the successfully fixing rate increases from 75.5% for GPS only to 81.2%. In the experiment with five GPS satellites and one Galileo satellites, the first successfully fixing time is reduced to half of that without fixing the inter-system DD ambiguities.