Ultrasonic indoor positioning for smart environments: A mobile application

In this paper we present a mobile application and solution for accurate smart indoor positioning. Smart society applications do normally require user location, specifically, in indoor environments high accuracy can enrich augmented or virtual reality, gaming, in-building guidance or support for ambient assisted living. We use encoded ultrasonic signals and TDMA protocol to obtain fine-grained distance measurements. Signals are emitted from a set of low cost ultrasonic local positioning systems, operating around 41kHz. An acquisition module, based on a MEMs microphone and a microcontroller, digitizes at 100kHz the incoming signals and send them over an USB protocol to the mobile device for their processing. We have implemented an Android Application that computes the Time Difference of Arrival (TDOA) to estimate the current position and display it in the mobile screen. Several users can compute their positions autonomously and user privacy is protected. The application can be configured for different encoding techniques and modulation schemes according to the environment requirements. Absolute error less than 5 cm is achieved in a 5×6m complex environment in 85% of the cases for an average position refresh period of 200ms.