| A radio frequency microwave X-band (10 GHz) indoor position tracking system is designed, constructed, and analyzed. The system consists of a transmitter of unknown location, free to move, and four fixed receiver antennas in known locations. The transmitter generates carrier signals on two frequencies. The transmitter is assumed to start at known location, to calibrate for the hardware phase offsets. High speed sampling is performed on the single stage down-converted signals, and estimates of the initial phase offset on each channel of sampled data are made. These estimates are differenced between antennas (single difference) and between frequencies (double difference). The double difference or wide lane measurements are used to provide a rough position solution, from which the narrow lane, or single frequency, carrier phase integer ambiguities are determined. The position solution is then refined with the use of the narrow lane integers and narrow lane measurements. The combination of large signal to noise ratio and a large number of samples results in single frequency phase estimates of very small noise variance. For the combination of frequencies tested, multipath was the dominant error source. The results indicate that if the narrow lane integers are found exactly in the hand-over from the wide lane solution, extremely precise millimeter level positioning is possible even in a multipath-rich environment. |
