The Double Difference Effect of Ionospheric Correction Latency on Instantaneous Ambiguity Resolution in Long-Range RTK

The primary goal of this paper is to estimate the influence of the double-difference (DD) ionospheric corrections latency on the instantaneous (one-epoch) ambiguity resolution (AR) in long-range RTK under typical ionospheric conditions. The key to the success in integer AR lies mainly in mitigation of the atmospheric errors, which comprises ionospheric and tropospheric delays. Between these two, the former has the greatest influence on the AR since both ambiguities and ionospheric delay are frequency dependent. Instantaneous RTK is one of the most challenging topics in contemporary precise geodetic applications; hence, a multiple reference station approach is currently being implemented and tested in the MPGPSTM (Multi Purpose GPS Processing Software) software. Atmospheric corrections are used in order to obtain a high quality RTK position over long distances. DD ionospheric delay correction prediction derived from the previous correctly resolved epoch was applied. Yet, at the beginning of the session, a short initialization period is still required in order to produce the initial prediction. This method assures a high success rate of the instantaneous AR for long baselines (~100 km). Since the previous-epoch ionospheric delay is used, and instantaneous mode is applied in the algorithm, the proposed method is robust against cycle slips and gaps and still capable of producing centimeter-level RTK positions. Different DD ionospheric delay correction latencies were simulated in 10 s increments, and sent to the rover in order to test the AR. The AR results were compared and analyzed, and the performance of the RTK positioning was tested. Several hours of GPS data, collected at the State of Israel permanent network, was processed. The analyses show that about 90 s latency may exist while the instantaneous ambiguities could still be resolved correctly. The numerical tests presented in this study show centimeter-level positioning results for the mobile receiver.