A Navigation System Without GPS: Signals of Opportunity as an Alternative
GPS is the world's most widely used navigation system – but it has weaknesses. In urban canyons, tunnels or densely built-up city centres, signal dropouts occur repeatedly. US researchers have now developed an alternative that works entirely without GPS satellites.
GPS: Accuracy and Limitations
Most navigation systems rely on GPS (Global Positioning System). Signal travel times from multiple satellite orbits are evaluated to calculate a position. Under optimal conditions, GPS achieves an accuracy of up to 2 metres. However, in urban canyons, near high-rise buildings or in deeply incised terrain, signal reflections and obstructions regularly cause outages and inaccuracies.
SOP – Signals of Opportunity
Researcher Zak Kassas and his team at the University of California, Riverside set out to find a robust alternative – and focused on signals that are already ubiquitous: mobile networks, radio, Wi-Fi and TV frequencies. These form invisible networks of electromagnetic signals that are receivable almost everywhere.
The concept is called SOP – Signals of Opportunity. It uses a broad range of frequencies and directions to enable precise positioning even when GPS signals are unavailable or unreliable.
How the System Works
The Kassas team demonstrated the SOP system using an autonomous vehicle equipped with a dedicated SOP receiver. During the start-up phase, the system draws on GPS data and the vehicle's accelerometers to establish its initial position. On this basis, the SOP system then derives the relevant access data from surrounding mobile masts and uses these for continuous positioning – independently of GPS.
Outlook
SOP navigation offers a particularly promising failsafe for drones and autonomous vehicles: where GPS fails, existing radio signals take over positioning. The technology could in future be deployed as a complement or backup to existing GPS systems, significantly improving navigational reliability in challenging environments.