Date of Award


Degree Name

MS in Electrical Engineering


Electrical Engineering


College of Engineering


Vladimir Prodanov

Advisor Department

Electrical Engineering

Advisor College

College of Engineering


This paper proposes a method of short-range indoor localization using differential phase measurements of synchronized two-tone ultrasonic signals in an Orthogonal Frequency Multiple Access (OFDMA) scheme. This indoor positioning system (IPS) operates at an ultrasonic frequency of approximately 40kHz and synchronizes using an infrared signal. The OFDMA scheme allows for a receiver to process the signals from multiple transmitters continuously without the signals interfering with each other. The phases of the signals are measured using Goertzel Filters, allowing for low-complexity frequency content analysis. A MATLAB simulation using the proposed localization method is performed using four transmitter nodes in the corners of a 2.5m x 2.5m room and a receiver node within. The designs for the synchronizing transmitter node and the receiver node are then implemented in hardware and tested at 22cm and 28cm. The work described in this paper found that the proposed IPS functions correctly in simulation, and the hardware implementation of the receiver and transmitter provides accurate distance measurements with variance as low as 0.05cm. This variance is on the same order of magnitude as the wavelength of the ultrasonic signals used. The hardware used in the implementation of this design is low-power, low-cost, and easy to implement, but it carries with it design tradeoffs. The main difficulty introduced by the hardware is the generation of imperfectly orthogonal signals due to a time-discretization error imposed by the clock of the transmitter's general purpose microcontroller. This error is theoretically and experimentally analyzed yielding closely matching values.