Low-power simplex ultrasound communication for indoor localization

We propose an ultrasound communication system designed for time difference of arrival (TDOA) based indoor localization. The concept involves an infrastructure of stationary and independent senders tracking mobile receivers. The main goal is pure line-of-sight (LOS) communication for correct localization. When ignoring the reception energy of multipaths the transmission range is reduced to 20 meters and we need more devices to cover the same area (0.03 devices/m²). Thus, for cost-effectiveness and easy installation, we focus in the sender design on low power consumption for long battery or even energy independent operation. Moreover, we use the energy efficient π=4-DQPSK modulation technique to send 8 data bits in 3.5 ms. An identifier in each message along with the reception time can be used for TDOA localization. The frame synchronization error for a distance of 20m at 3 dB SNR is 11.2 ns. Thus, for speed of sound the distance measurement error is 3.7 μm.