Portable anechoic chamber-type calibration and the effect of phase corrections on the results of indoor positioning

For indoor high-accuracy positioning based on pseudolites (PLs), it is difficult to eliminate the effect of carrier phase advances or delays caused by the antenna through the use of differencing techniques because the line-of-sight between different transmitter–receiver pairs in a small area differs greatly. Therefore, antenna calibration is necessary. We propose a portable anechoic chamber-type calibration method based on the use of a transceiver unit that can calibrate both receiver and transmitter antennas. We also propose a method to monitor the variations in hardware delay that are likely due to the temperature variations. Because our method does not use an expensive anechoic chamber, a multipath error is a serious problem that cannot be ignored. In order to randomize the multipath errors, multiple calibrations can be performed at different sites to improve the accuracy of calibrations. The experiment we conducted showed that the antenna phase pattern accuracy of the proposed calibration method could reach millimeter level. In the indoor positioning experiment, the results, with phase center corrections, showed much better positioning accuracy of 6.9, 4.0 and 10.8 mm in X, Y and Z directions, respectively, compared with 9.1, 6.5 and 23.1 mm in X,Y and Z directions, respectively, without phase center correction.