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Ionospheric delay error is one of the most important errors in navigation and positioning.Ignoring the effects of the second and the upper order terms of the ionosphere,dual-frequency/multi-frequency receivers eliminate the effects of ionospheric delay error through ionosphere-free combination model,while single frequency receivers can only weak the ionospheric delay error through the ionospheric model parameters broadcasted by satellite navigation and positioning systems.In the current major satellite navigation systems,GPS uses the Klobuchar ionosphere model,BDS uses the improved Klobuchar ionosphere model,and Galileo uses the NeQuick ionosphere model.