Correlating Mobile Antenna Topologies with Received Signal Strength-based Direction-of-Arrival Estimation Method for Sub-Degree Accuracy within Indoor Environments

Various types of Indoor Positioning Systems (IPS) are developed to address the limitations of Global Positioning Systems (GPS) for indoor wireless positioning applications. To achieve highly accurate IPS, multiple, high directional antennas are required. However, mobile devices and smart tags cannot accommodate such antenna requirements due to limited space. This work presents a method to utilize conventional mobile antennas to achieve sub-degree accuracy of IPS. Key mobile antenna design factors, such as directivity and tilting angle are incorporated with a newly devised Received Signal Strength (RSS)-based DoA method to achieve high-quality positioning performance. Using the Received Signal Strength Difference (RSSD) slope enables the design and support employment of a realistic mobile antenna featuring a small size and limited directivity for accurate IPS characteristics. The exemplified low directivity antennas achieve a DoA accuracy of 0.87° at 6.5 GHz. Compared to the method in [4], this approach reduces the root-mean-square error (RMSE) of the DoA estimation by one-fifth and halves the electrical size. Consequently, this enables the realization of highly compact portable devices for accurate IPS with the devised exemplified antenna design and allows for expansion to different mobile antenna designs.