Effects of antenna polarization on RSSI based location identification

Real-time position localization of moving objects in an indoor environment is an encouraging technology for realizing the vision of creating numerous novel location-aware services and applications in various market segments. Increasing the accuracy of these location tracking systems will increase their usefulness. An off the shelf development platform that uses Radio Signal Strength Indication (RSSI) based location tracking technique is studied. In this paper we investigate the affects of polarization on the accuracy of an indoor location tracking system. The accuracy of the location calculation is mainly dependent on accuracy of the range measurements. We present an approach to increase system accuracy based on this investigation. We established a model for determining range from RSSI and showed that the model fits our own experimental data. The model includes parameters used to account of environmental effects and we use the least squares method of determining the parameter values. Antenna polarization angle will affect RSSI and thus range accuracy. We empirically show that the model is still valid for polarization mismatch but with different environmental parameter values. We then analyze the affects that these parameters and polarization have on our location system. A method based on semi-automated trail and error is proposed as a better method for selecting the environmental parameters. Using experimental data we show that if we adjust the model parameters to account for polarization angle then we can increase location accuracy. Adjusting parameters for polarization is fairly trivial to implement when the polarization angle is known. A practical solution for determining the polarization angle is with an accelerometer. The addition of an accelerometer could also be used to increase the battery life of the node.