Real-time indoor localization and mapping using digitally coded RF waves with implementation on FPGA

Abstract

One of the most significant topics under extensive research in ubiquitous computing is indoor localization and mapping. The current outdoor techniques using GSM, GPS and Wi-Fi are very expensive and infeasible for indoor mapping. This document presents a unique method of real time indoor localization and mapping using digitally coded electromagnetic waves (ASK and FSK). Localization is acquired with respect to 2-D array (NxM) of transmitter modules in rows and columns (i.e. length and breadth of the indoor region). All the transmitters of row array are tuned at same frequency but each transmitter emits a unique 12 bit digital code. Same is the case with column transmitters. The geometrical wave model of these transmitters renders family of circles, where radius of each circle represents `Received Signal Strength Indicator' (RSSI) value corresponding to a particular transmitter. For locating the object in (NxM) grid, differential mechanism is used i.e. comparing RSSI values of all the adjacent transmitters of row and column respectively at the location of object. Indoor region of particular dimensions can be discretized into NxM grids. Object is installed with customized FPGA core, 2 RF demodulators (for row and column) and two PLL ICs for calculating RSSI values (in 4 bit resolution). For real time response, 2 parallel I2C buses are connected to FPGA core. Wireless control over RF transmitters is used to prevent unwanted RF radiation. Overall, real world is discretized into grids. Also detailed comparison is shown as to how this technique is better than triangulation method.