A Noise Tolerant Spread Spectrum Sound-Based Local Positioning System for Operating a Quadcopter in a Greenhouse. - Zichen Huang; Lok Wai Jacky Tsay; Tomoo Shiigi; Xunyue Zhao; Hiroaki Nakanishi; Tetsuhito Suzuki; Yuichi Ogawa; Naoshi Kondo (Sensors, 2020)