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With the availability of BeiDou Navigation Satellite System (BDS) triple-frequency observations,more strategies can be carried out to improve integer ambiguity resolution (IAR) performance for both short and long baseline RTK.In this paper,we first present the intrinsic natures of IAR for short and long baseline RTK.The double differenced mathematical models for short and long baseline are specified first.From the model perspective,the IAR performances of dual-frequency and triple-frequency are analyzed and compared.To improve the AR performance using triple-frequency observations,the integer least-squares (ILS) success-rate can be increased by first partial fixing the Extra Wide-lane (B2&B3) and then the Wide-lane (B1&B2,B1&B3) integer ambiguities in a geometry-based model because of their relatively long wavelengths.For short baselines,the IAR at each carrier can be resolved conditioned on the resolved WL integer ambiguities.For long baselines,two ionosphere-free combinations (B1&B2,B1&B3) can be formulated,and only the integer ambiguity vector on each carrier needs to be fixed with more redundant observations.It turns out that with triple-frequency observations,the performances of both short and long baseline RTK can be improved.