An Innovative Algorithm for Carrier-Phase Navigation

Ronald R. Hatch, Richard T. Sharpe, Yunchun Yang

Abstract:	An algorithm is described that uses the carrier-phase measurements to propagate the position and clock states forward in time with a minimum of computational burden. The algorithm uses the change in the carrier-phase measurement over the propagation interval in a unique way. Specifically, rather than treat the change in the phase measurements as range difference measurements, they are treated as range error measurements. This allows the same gain values that are computed in the low-rate position and clock computations to be used in the high-speed position and clock updates. The change in the phase measurements is corrected by the change in satellite position and may, if one wishes, also be corrected by the change in satellite clock and the expected change in user position and clock. The technique is highly accurate and can be used in all navigation modes, including stand-alone GPS, DGPS and RTK implementations. NavCom has developed two variations of the technique. In one variation, the “maximum availability” mode, the change in the L1 carrier-phase measurements is used and the elevation angle threshold is lowered to a few degrees. (If available the L2 carrier-phase measurements are used as well, simply to reduce the effect of the measurement noise.) This allows the navigation to be maintained with good accuracy when the navigation might otherwise be aborted due to too few satellites at good elevation angles or due to loss of L1 or L2 carrier-phase measurements from signal blockage. Over short intervals all the slowly changing factors can be ignored in the computation. This includes effects from the ionosphere, troposphere, satellite clock, DGPS or RTK corrections. Thus, the computation is very simple and efficient. In the second variation of the technique, the “maximum accuracy” mode, all of the above effects are included in an attempt to make the position propagation as accurate as possible. The intent is to allow the technique to be used for extended intervals. Such an approach allows the primary full-computation to be run at a lower rate, which reduces the computational load without sacrificing any significant accuracy.
Published in:	Proceedings of the 17th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2004) September 21 - 24, 2004 Long Beach Convention Center Long Beach, CA
Pages:	1431 - 1437
Cite this article:	Hatch, Ronald R., Sharpe, Richard T., Yang, Yunchun, "An Innovative Algorithm for Carrier-Phase Navigation," Proceedings of the 17th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2004), Long Beach, CA, September 2004, pp. 1431-1437.
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