OTFS-based Inter-satellite Ranging System

Satellite ranging technology is a key component of spacecraft telemetry, tracking, and control, ensuring the safety and reliability of space missions. With the rapid increase in the number of satellites, the emergence of large constellations, and the growing demand for deep-space exploration, requirements for high-precision ranging have become increasingly stringent. Conventional techniques, such as pseudo-code and carrier-phase ranging, are capable of achieving accurate measurements but often demand additional hardware resources and raise system cost, which poses challenges for resource-constrained missions such as microsatellites. In parallel, Orthogonal Frequency Division Multiplexing (OFDM), the dominant modulation scheme in current terrestrial systems, exhibits severe performance degradation under high-Doppler and doubly selective channels, limiting its applicability to dynamic satellite environments. To address these challenges, this paper investigates Orthogonal Time-Frequency Space (OTFS) modulation as a novel solution for integrated communication and ranging. A hybrid method is proposed, in which pseudo-code sequences are embedded into OTFS-modulated signals. In this approach, pseudo-code ranging provides coarse estimates with large unambiguous range, while OTFS delay-Doppler processing refines accuracy and enables Doppler shift estimation. An OTFS communication system model is established, and its performance is evaluated through simulations under high-mobility conditions, highlighting advantages over OFDM. Furthermore, a low-complexity transceiver is designed and implemented using GNU Radio software-defined radio technology to validate feasibility in practice. Simulation and experimental results demonstrate that the proposed method achieves superior robustness against Doppler effects, maintains stable bit error rate (BER) performance, and significantly improves ranging precision. The proposed OTFS-based integrated system offers a cost-effective and resource-efficient solution for future satellite constellations and microsatellite missions, and provides a promising direction for next-generation space communication and navigation systems.