Determining the physical location of radio nodes is crucial in a wireless sensor network in order to geo-reference the sensor information. This paper presents a localization technique using a mobile radio node attached to a robot. Its position is given by a real time kinematic (RTK) GPS. We propose a new method to obtain the relative bearing between the mobile and the static node using commodity radio hardware. The method exploits the anisotropy of the antenna gain and is not only more precise than the mapping of the RSSI to distance only, it also allows to monitor the integrity of the measurement. Experimental results in an outdoor environment show a standard deviation of 5 • for the angle of arrival. The applicability of the approach for the localization of static radio nodes is demonstated by means of a particle filter. The mean error of the position for experimental data is approximately 13 cm.

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