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This paper addresses the problem of “robust” positioning, which is the ability of a positioning system to determine position with continuous accuracy in spite of GPS outages. The paper describes an aided INS (AINS) with inertially aided RTK (IARTK) as one solution to a robust RTK positioning problem. It describes the design of the IARTK‐AINS and discusses the factors that control the maximum outage duration for rapid fixed integer ambiguity recovery and the position accuracy during the outage. The IARTK‐AINS implements tightly coupled inertial/GPS integration with floated ambiguity estimation and fixed integer search in a single Kalman filter. The IARTK‐AINS is able to recover L1 integer ambiguities within seconds of a short‐duration GPS outage while maintaining decimeter‐level accuracy throughout the outage. The paper then describes the performance of the IARTK‐AINS during various tests involving controlled GPS outages and uncontrolled GPS availability during navigation in a demanding urban canyon environment.

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The LQ optimal regulator problem with cheap control is investigated for plants of the form x = Ax + Bu, y = Cx + Du, where D ± 0 makes the plant not strictly proper. It is found that perfect regulation of the output with closed‐loop stability is achieved if and only if the plant is detectable, is minimum phase and there exist independent inputs equal to or greater in number to the number of independent outputs.