Single-Station-Based Integrated Communication-Positioning System for Mars UAVs

Among the various methods for Mars exploration, rotary-wing UAVs represent a novel and highly efficient approach. However, the vast distance between Mars and Earth introduces significant communication delays, which fundamentally require these UAVs to operate autonomously. A key challenge lies in achieving accurate positioning of these UAVs under the constraints of limited available resources. Typically, UAVs on Earth utilize Global Navigation Satellite System to obtain their position. However, since there is no GNSS on Mars, relying solely on inertial navigation systems inevitably leads to the issue of error accumulation. One potential solution is visual terrain matching using onboard cameras, as successfully demonstrated by NASA's Ingenuity helicopter. Nevertheless, the sparse and repetitive surface features of Mars can cause visual terrain matching to fail, which is considered one of the possible reasons for the crash during Ingenuity's 72nd flight. To address the positioning challenges for UAVs in the initial phase of Mars exploration, we propose an integrated communication-positioning system utilizing a single base station mounted on a rover or deployer, which combines both functionalities through an antenna multiplexing design. By installing a 4-element antenna array on the UAV, a 2.4 GHz LoRa-based wireless communication link is established between the UAV and the rover. This link is dedicated to transmitting telemetry data for the UAV. Concurrently, the antenna array aids in the UAV's positioning through a fusion algorithm that integrates Pseudo-Doppler Angle of Arrival estimation with Time of Flight ranging. Additionally, the integration with the INS is accomplished through the use of an Extended Kalman Filter, thereby enhancing the positioning ability. The inherent long-range capability and anti-interference characteristics of the LoRa protocol enable adaptation to extended communication distances, while the adoption of radio waves circumvents the image mismatch issue caused by the homogeneous terrain features on the Martian surface. A prototype was developed utilizing an ARM microcontroller with the antenna and signal processing modules integrated through one printed circuit board. Preliminary experiments indicate that the prototype achieves the intended system functionality while maintaining a total mass below 100g.