Review of GPS-Free Navigation Methods for Unmanned Aerial Vehicles

Purpose. This paper reviews various non-GPS navigation methods for Unmanned Aerial Vehicles (UAVs), with a particular focus on radio frequency (RF) techniques such as Time of Flight (TOF), Received Signal Strength Indicator (RSSI), and Time Difference of Arrival (TDOA). Design / Method / Approach. The study compares time-based and signal strength-based approaches for locating mobile UAVs, emphasizing the accuracy of multilateration and the impact of antenna design. It also explores recent advances in LoRa-based downlink TDOA networks and ensemble averaging to improve location precision. Findings. RF-based navigation methods, particularly those combining TDOA and RSSI, have proven effective for UAV navigation. LoRa-based systems utilizing ensemble averaging have demonstrated accuracy of better than four meters under controlled conditions, making them a viable alternative in scenarios where GPS usage is limited or unavailable. Theoretical Implications. This study contributes to the understanding of RF-based navigation systems and their application in UAVs, highlighting the potential of TOF and TDOA techniques for high-precision location tracking where GPS usage is limited. Practical Implications. Implementing LoRa-based downlink TDOA networks could offer a cost-effective, ground-based alternative to GPS, especially in environments where GPS signals are unreliable or unavailable. Originality / Value. This review addresses the growing need for alternative UAV navigation methods in the absence of GPS, discussing advanced sensor fusion techniques and synchronization methods unique to LoRa technology. Research Limitations / Future Research. While promising, the accuracy of LoRa-based navigation systems requires further validation in real-world UAV applications. Future research could explore optimizing power consumption and reducing infrastructure costs.