The purpose of this study was to evaluate the stability and therefore suitability of available fifth generation (5G) and long-term evolution (LTE) signals for positioning navigation and timing (PNT) purposes with particular focus on answering questions around the time-scale-dependent stability of these sources, which, to our knowledge, has not been addressed in the context of the numerous publications within the PNT community to date. The methodology used directly measured the over-the-air signal phase stability to one or more of the cellular signal sources that were visible from the lab environment simultaneously while using a local atomic clock or differential measurements to isolate the time stability of the observable cellular downlink signals. This approach was taken since it does not require subscription or association with the networks under test. Instead, it exploits a ‘signal of opportunity’ (SoP) approach to signal use for PNT purposes. The somewhat surprising result is that the time domain instability of the sources was highly variable, dependent on the implementation choices of the operator, and that the stability of even the modernized towers was generally best at interrogation intervals of approximately 0.01 s, which indicates that the existing exploitation of these signals within the PNT community has substantial room for improvement through simple changes to the selected update rate used.

Reliable Position, Navigation, and Timing (PNT) is becoming more and more important, considering the proliferation of highly autonomous safety- and liability-critical systems. Due to their vulnerability to various threats such as deliberate Radio Frequency Interference (RFI), including jamming, spoofing, and others, there is significant research into finding backup/fallback solutions that allow safe mission completion or termination. This work compares two such systems: one based on Angle of Arrival (AoA) measurement and one based on cellular (4G and 5G) signals. The results are generated using simulations, which are substantiated by real-world performance measurements. It is shown that both systems have the potential to serve as backup navigation solutions and that the cellular system outperforms the AoA-based solution, albeit at a much higher price and with higher computational requirements.

This paper presents a compact, cost-effective Unmanned Aerial Vehicle (UAV) payload, intended for coastal area remote sensing applications. The payload consists of a compact, in-house–built push-broom imaging spectrometer using Commercial Off-The-Shelf (COTS) components, complemented by navigation sensors for direct georeferencing. The payload furthermore incorporates an upward-facing spectrometer, enabling direct computation of remote sensing reflectance $\boldsymbol {\rho }_{\mathrm {RS}} \left ({{ \lambda }}\right)$ under varying illumination and atmospheric conditions. In contrast to existing micro imaging-spectrometer payloads, the presented Unmanned Aerial Vehicle (UAV) payload offers greater operational versatility and flexibility. While specifically tailored to coastal ocean color mapping, the system can easily be adapted to a wide range of remote sensing applications. Field experiments conducted with the presented payload demonstrate that remote sensing payloads, built with COTS components, allow the retrieval of $\boldsymbol {\rho }_{\mathrm {RS}} \left ({{ \lambda }}\right)$ scientifically usable datacubes. The contribution of this work lies in the proof-of-concept and demonstration that a compact UAV payload based on inexpensive COTS components and which permits onboard processing is able to generate good scientific data.

For reasons of both economic motivation and military conflicts, the intentional interference with critical global navigation satellite systems (GNSS) signals has evolved from nearly unheard of to a daily occurrence over the previous 20 years. As the interference threat is gradually evolving in coherence with the development of new mitigation strategies, it is important to monitor its evolution and keep the GNSS receiver testing capabilities in alignment. This article presents the motivations and outcomes of a 6 year process to first measure, characterise and understand the ecosystem of harmful radio frequency interference (RFI) signals, to development of a comprehensive evaluation framework incorporating software defined radio (SDR) based flexible signal generation. The developed simulation framework allows controlled production of both observed and theorised signal families over the entirety of their measured parameters spaces, and the efficient collection of observation data produced by an array of GNSS receivers to determine if given RFI modulations were stimulating enhanced failure modes in the devices under test. The test results discussed in this paper clearly show that consideration of the parameter space over which the RFI signal types occur must be taken into account when determining expected RFI impacts on GNSS receivers.