Estimating DoA From Radio Frequency RSSI Measurements Using Multi-Element Femtocell Configuration

In this paper, a method to estimate the direction of arrival (DoA) of a radio signal using a multi-element antenna based femtocell device is presented. The femtocell estimates the DoA by identifying the peak of received signal strength indicator (RSSI) measurement using multi-element microstrip antenna. This paper is a modified version of a previously reported work titled as estimation of DoA from radio frequency RSSI measurements using an actuator reflector. In long term evaluation, ultradense deployment of the femtocell device is mainly supported by the intelligent beam forming that translates directly to the constraint of DoA estimation. Use of multi-element antenna over omnidirectional antenna in femtocell is mandated by coverage optimization and reduction of cell overshooting. DoA estimation using microstrip antenna alone is a challenging problem, but it is easier with a multiple number of directive antennas covering the whole plane. Other DoA estimation methods, such as phase arrays, are unsuitable for a small device like femtocell due to the complexity and cost limitations. The proposed method to estimate the DoA is simple enough to be applicable for femtocell indoor applications. Both simulation and experimental results are analyzed to evaluate the performance of the method. Results show that the error in estimated DoA has a mean <7 degrees and standard deviation <4 degrees.