Estimation of LEO-GPS receiver differential code bias based on inequality constrained least square and multi-layer mapping function

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The differential code bias (DCB) of the global navigation satellite system (GNSS) receiver onboard a low earth orbit (LEO) satellite is one of the crucial hardware error sources in ionospheric estimation. In common practice, LEO DCBs are considered as constant within a single day. However, since such receivers are installed on moving platforms, they are subjected to the ever-changing space environment, and thus, LEO DCBs are prone to more frequent fluctuations than receiver DCBs of ground GNSS stations. We estimate the LEO GPS receiver DCBs and plasmaspheric vertical total electron content by using inequality constrained least square and a multi-layer mapping function (MF) approach to minimize mapping errors. The GPS receiver DCBs onboard constellation observing system for meteorology, ionosphere, and climate satellites (COSMIC) is investigated and analyzed during the January 2008 period. The results show that in most cases the multi-layer MF approach performs better than the commonly used single-layer MF. The mapping error from an inaccurately fixed single-layer height can be considerably reduced. Meanwhile, with the help of a multi-layer MF, the mean deviations of DCBs for five receivers compared with those based on a geometric MF at 1400 km are significantly decreased by 59%, 15%, 26%, 47%, and 22%, respectively.