An indoor calibration-free location estimation for dynamic radio frequency environments

One of the most common techniques for the location estimation of mobile users (MU) is the radio frequency (RF) site survey. The main idea of the technique is to build a signal strength model, called a radio map, in the off-line phase and to estimate the location of an MU by finding the best match from the radio map in the on-line phase. However, when signal strength values vary frequently due to the characteristics of environmental dynamics, the radio map will quickly become outdated, and recalibration requires considerable manual effort. A good positioning technique should be able to adapt to a dynamically changing environment. In this paper, we describe the design and implementation of a positioning system which can provide low-cost, but highly adaptable and precise positioning in the context of changeable indoor environments. Instead of constructing a radio map, we use reference points (RP) installed in the localization area to continuously monitor changes in the environment. We then employ the minimum mean square error (MMSE) method to estimate the location of the MU. Experimental results show that the average error distance is under four meters.