Two-way Ranging using OFDM Waveform with Application to Lunar Surface Navigation

We present a ranging system which measures the distance between two radio nodes by estimating the time of flight (ToF) of a series of short radio frequency bursts modulated using an orthogonal frequency division multiplexing (OFDM) waveform. ToF is estimated by periodically exchanging two precisely timed OFDM frames and measuring the time of reception (ToR) using a cross-correlation-based technique. The two nodes then exchange the estimated ToRs in subsequent OFDM frames and independently compute an estimate of the ToF.OFDM-based waveforms have exploded in popularity for telecommunications applications on Earth due to their resistance to multipath effects and their fast implementation using the FFT algorithm. They are deployed globally as part of wireless LANs using the IEEE 802.11 series of standards and as part of mobile networks using the 4G LTE and 5G NR series of standards. The inherent resistance to multipath effects makes OFDM a promising candidate for operations on the rough lunar surface when compared to the single carrier waveforms traditionally employed in deep space.The main application envisioned for this system is a ground-based local positioning and navigation system serving exploration, science, and commercial activities within a fixed region on the lunar surface. Multiple concepts providing positioning and navigation services on the lunar surface have been proposed, with a lunar global navigation satellite system (LGNSS) being the preferred option. However, in case a full-scale LGNSS constellation is unavailable due to e.g., delays, budgetary issues, or physical constraints, a ground-based local navigation system utilizing a fixed set of transmitting stations could become a viable alternative. In this case, the low-complexity two-way ranging scheme presented in this work can provide the necessary range estimates required for obtaining the positions of astronauts, rovers, and/or other equipment in a region of interest on the lunar surface.In addition to ranging, our system is flexible enough to be easily upgraded to include a low-rate communications signal, thus potentially forming a complete joint positioning and messaging solution for the lunar surface. An initial version of our proposed ranging system was implemented and demonstrated as a software application utilizing devices from National Instruments’ Universal Software Radio Peripheral (USRP) line of software-defined radios, which provides a straightforward path towards porting to space-grade hardware in the future. We provide a detailed exposition of the transceiver architecture as well as results of indoor lab experiments and outdoor test campaigns.