Towards a better indoor positioning system: A location estimation process using artificial neural networks based on a semi-interpolated database

Abstract

The Wi-Fi-fingerprinting positioning method is used widely in indoor positioning environments due to its simplicity and wide coverage. However, in the offline phase of the method, the collection process is a fundamental and critical step that requires time and effort. Moreover, the location estimation process, which is executed in the second Wi-Fi-fingerprinting phase (online phase), needs to be accurate enough to guarantee efficient indoor positioning. Hence, in this work, a novel indoor location-estimation process based on a semi-interpolated radio map and artificial neural network (ANN) is presented. A mobile application is built to gather the received signal strength indicator (RSSI) fingerprinting to construct a radio map, which is then expanded with the biharmonic spline interpolation (BSI) method through the estimation of more RSSI values. A feedforward back propagation (FFBP) neural network and generalised regression neural network (GRNN) were built in the online phase for the location-estimation process. They were trained using the expanded dataset by taking the reference point (X, Y) coordinates as their desired output and using two different forms of the data as their inputs. The first inputs are the RSSI values from the 17 access points (APs) – three of the APs have dual-band i.e, support both 2.4 and 5 GHz – and the second input is based on a selected set of APs, which produce a high level of acceptable RSSI and their coordinates. A comparison between these two models was done. The results show that FFBP outperforms GRNNs in terms of structure simplicity, while GRNNs achieved more accurate prediction results with an average distance error of up to 0.48 m. Hence, our proposed methodology leverages building a simple neural network topology that has good location estimation results for indoor positioning in a low-cost localisation process.