1. Lin, Q., An, Z., Yang, L.: Robooting ultrasonic positioning systems for ultrasound-incapable smart devices. https://arxiv.org/pdf/1812.02349.pdf
2. Indoor positioning via LoRaWAN, indoornavigation.com. https://www.indoornavigation.com/wiki-en/indoor-positioning-via-lorawan
3. WiFi positioning system, WikiPedia. https://en.wikipedia.org/wiki/Wi-Fi_positioning_system
4. Zafari, F., Gkelias, A., Leung, K.K.: A survey of indoor localization systems and technologies. arXiv: https://arxiv.org/pdf/1709.01015.pdf
5. Wang, Q., Lou, H., Men, A., Zhao, F.: An infrastructure-free indoor localization algorithm on smartphone. Sensors 18(10), 3317: https://www.researchgate.net/publication/328067193_An_Infrastructure-Free_Indoor_Localization_Algorithm_for_Smartphones