Resilient navigation in Global Navigation Satellite System (GNSS)-degraded and -denied environments is becoming more and more required for many applications. It can typically be based on multi-sensor data fusion that relies on alternative technologies to GNSS. In this work, we studied the potential of a low earth orbit (LEO) satellite communication system for a high-dynamic application, when it is integrated with an inertial measurement unit (IMU) and magnetometers. We derived the influence of the main error sources that affect the LEO space vehicle (SV) Doppler-based navigation on both positioning and attitude estimations. This allowed us to determine the best, intermediate and worst cases of navigation performances. We show that while the positioning error is large due to large orbit errors or high SV clock drifts, it becomes competitive with that of an inertial navigation system (INS) based on a better quality IMU if precise satellite orbits are available. On the other hand, the attitude estimation tolerates large orbit errors and high SV clock drifts. The obtained results suggest that LEO SV signals, used as signals of opportunity for navigation, are an attractive alternative in GNSS-denied environments for high dynamic vehicles.

The large availability of Low Earth Orbit (LEO) satellite systems makes them useful beyond their original purposes, such as in positioning, where their signals can be passively used. In order to determine their potential for this purpose, newly deployed systems need to be investigated. This is the case with the Starlink system, which has a large constellation and is advantageous for positioning. It transmits signals in the 10.7–12.7 GHz band, the same as that of geostationary satellite television. Signals in this band are typically received using a low-noise block down-converter (LNB) and a parabolic antenna reflector. Regarding opportunistic use of these signals in small vehicle navigation, the dimensions of the parabolic reflector and its directional gain are not practical for tracking many satellites simultaneously. In this paper, we investigate the feasibility of tracking Starlink downlink tones for opportunistic positioning in a practical situation, when signals are received without a parabolic reflector. For this purpose, an inexpensive universal LNB is selected, and then signal tracking is performed to determine the signal and frequency measurement quality, as well as the number of satellites that can be tracked simultaneously. Next, the tone measurements are aggregated to handle tracking interruptions and to recover the traditional Doppler shift model. After that, the use of measurements in multi-epoch positioning is defined, and its performance discussed as a function of the relevant measurement rate and the required multi-epoch interval duration. The results showed promising positioning which can be improved by selecting a better-quality LNB.

The study of navigation solutions other than GNSS is becoming increasingly important due to growing concerns about the vulnerability of GNSS to interference. The use of existing LEO satellite signals is a promising option in this respect. This study analyzes the accuracy of Doppler shift measurements for three satellite systems: Iridium-next, Orbcomm, and NOAA, based on actual signal acquisition, and evaluates the potential of their combination in positioning. The study takes advantage of Orbcomm’s dual frequency capability to enhance the precision of Doppler shift measurements and proposes a method for obtaining unambiguous Doppler shifts from NOAA’s FM-AM signal. Moreover, it introduces a smoothing technique to further improve Doppler shift measurement accuracy. The positioning results show that positioning with three constellations is more accurate than positioning with one or two constellations, and that the effectiveness of passively combining several LEO systems for positioning is limited by the disparity between satellite constellations and the measurement quality inherent in each system.

Projectiles are subjected to a high acceleration shock at launch (20,000 g and higher) and can spin very fast. Thus, the components of onboard navigation units must therefore withstand such constraints in addition to being inexpensive. This makes only a few inertial sensors suitable for projectiles navigation. Particularly, rate gyroscopes which are gun-hardened and have an appropriate operating range are not widely available. On the other hand, magneto-resistive sensors are inexpensive and can satisfy both gun-hardening and operating range requirements, making them an alternative for angular estimation in guided projectiles. This paper presents a gyroless navigation algorithm for projectiles. The lack of gyroscope is handled by the usage of attitude kinematics computed over past attitude estimates of the filter, coupled with a measurement model based on magnetometer and GPS observations of the attitude. The observability of the attitude when considering non-calibrated magnetometers and its dependency on the initialization is addressed. Then, to cope with the initialization dependency of the filter, we proposed a multi-hypothesis initialization algorithm. In terms of performance, the algorithm is shown to provide a high-rate navigation solution with an interesting performance.

We propose a technique for extracting the Doppler shift and its rate from OneWeb's Ku-band user downlink signals and demonstrate its suitability for opportunistic positioning. Since the downlink waveform and synchronization sequences are not publicly documented, the method exploits the periodicity inherent in the transmitted frames. By performing cross-correlation in the time domain between two consecutive bursts over several frame periods, we obtain an approximate estimate of the Doppler shift and a better accuracy estimate of the Doppler rate, even when the signal is received using a universal (low noise bloc) LNB without a parabolic reflector. The two estimates are merged in a Kalman filter, resulting in an unambiguous Doppler measurement that can be used in positioning calculations. Field experiments show that, for satellites above 67° elevation, the Doppler rate can be estimated with 13.25 Hz s⁻¹ (0.359 m s⁻²) precision and the Doppler shift with a standard deviation of 86.3 Hz (2.34 m s⁻¹). Frequency tracking is feasible down to 55° elevation, and simultaneous processing of three operational OneWeb frequency channels provides continuous measurement availability, with up to 50 % overlap between adjacent beams that further improves Doppler shift accuracy. Positioning using derived Doppler data resulted in a horizontal error of 384 m based on diffuse orbital data, which can be reduced using accurate satellite orbit and clock models. The algorithm is relatively simple and robust in low signal-to-noise ratio conditions, making it suitable for opportunistic use of OneWeb signals for positioning.

Chirp interference is a major source of disturbance in Global Navigation Satellite System (GNSS) signal processing. Whether the chirp interference signal appears continuous or pulsed to a GNSS receiver depends on its bandwidth relative to the receiver bandwidth. This research proposes a method that reduces chirp interference in GNSS receivers for both continuous and pulsed chirp. It combines chirp estimation and suppression with pulse blanking techniques. Simulation results indicate that L1C/A signal acquisition remains successful with up to 62 dB of jammer-to-noise ratio (J/No) for continuous chirp, and 30.5 dB for pulsed chirp. In terms of tracking performance, L1C/A GPS signals can be successfully tracked with J/No of up to 71 dB for continuous chirp and 55 dB for pulsed chirp. The technique was then subjected to a real-life GPS L1C/A signal summed with the strong signal of a commercial civil chirp jammer (J/No = 34.2 dB). It has shown successful acquisition and tracking of all visible satellites with a C/No degradation less than 1 dB and a positioning error of a few meters, which confirmed the effectiveness of the technique. In addition to its attractive performance, the low complexity of the technique makes it practical for real-time implementation with successful positioning in the event of strong chirp interference.