Abstract
This paper describes a new approach and implementation methodology for indoor ranging based on the time difference of arrival using code division multiple access with ultrasound signals. A novel implementation based on a field programmable gate array using finite impulse response filters and an optimized correlation demodulator implementation for ultrasound orthogonal signals is developed. Orthogonal codes are modulated onto ultrasound signals using frequency shift keying with carrier frequencies of 24.5 kHz and 26 kHz. This implementation enhances the possibilities for real-time, embedded and low-power tracking of several simultaneous transmitters. Due to the high degree of parallelism offered by field programmable gate arrays, up to four transmitters can be tracked simultaneously. The implementation requires at most 30% of the available logic gates of a Spartan-6 XC6SLX45 device and is evaluated on accuracy and precision through several ranging topologies. In the first topology, the distance between one transmitter and one receiver is evaluated. Afterwards, ranging analyses are applied between two simultaneous transmitters and one receiver. Ultimately, the position of the receiver against four transmitters using trilateration is also demonstrated. Results show enhanced distance measurements with distances ranging from a few centimeters up to 17 m, while keeping a centimeter-level accuracy.
Highlights
Accurate indoor localization opens new perspectives towards location-aware applications.A non-exhaustive list of applications that might take advantage of accurate indoor localization solutions include automation, guidance and assistance of people, virtual reality, etc
We proposed a novel implementation approach for ultrasound orthogonal ranging towards indoor localization using field programmable gate arrays (FPGAs)
A MEMS transducer converts the ultrasound signals into electrical signals. These signals are processed by the FPGA in order to apply range estimation
Summary
Accurate indoor localization opens new perspectives towards location-aware applications. When a pulse is detected, the receiver is triggered, and an estimation of the ranging is performed This technique does not involve expensive computational power to achieve indoor localization. The ultrasound pulse is prone to in-band noise, which may affect the accuracy of the system Another approach proposed in the literature makes use of ultrasound signals, which are modulated using orthogonal sequences [5,6,7,8,9]. The second approach is referred to as frequency hopping spread spectrum (FHSS) and involves several rapidly-switching frequency carriers on which data are modulated [9] Both implementations offer a better reliability against noise, but have the major disadvantage of requiring more computational power.
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