Global Navigation Satellite Systems (GNSS) have unleashed innovative commercial, scientific, and military applications since the US Global Positioning System (GPS) entered service in the 1980s. Today, GNSS constellations from the US, Europe, China, and Russia circle the planet to provide near-global positioning services. This article will explain how global GNSS constellations will evolve in the coming decades.
America’s Global Positioning System
GPS Modernization’s improvements to the space and control segments, combined with next-generation receivers, will transmit four new signals to make GPS more accurate and resilient while enabling new industries such as autonomous vehicles and urban air mobility.
L2C for dual-frequency accuracy
Civilian dual-frequency receivers will be able to correct for ionospheric effects, acquire signals faster, and operate at greater ranges. L2C’s more powerful signal should also improve reception within buildings and under trees.
Currently transmitting from a number of GPS satellites, L2C is expected to reach final operating capability in the US government’s 2024 fiscal year.
L5 for aviation and other transportation modes
The new L5 signal will enhance FAA’s Wide Area Augmentation System, allowing more efficient routing of civilian aircraft and supporting instrument-only guidance to within 200 feet of the runway.
This signal has been pre-operational since 2014. L5 will reach initial operational capability in FY2024 and final operating capability in FY2028.
L1C for GNSS interoperability
Another signal on the L1 band will make GPS interoperable with Galileo and other GNSS constellations. Multi-constellation receivers will be more accurate under a wider range of conditions.
L1C signals will not be fully available until the late 2020s when Block III designs comprise the entire 24-satellite constellation.
M-Code for restricted users
A new encrypted signal for the American military and other authorized users will eliminate the need to bootstrap from the civilian C/A code. In addition, M-Code signals will be more secure and resistant to adversarial jamming.
M-Code positioning and initial operating capabilities are scheduled for FY2025.
Galileo’s constellation is nearly complete, with twenty-eight of the planned thirty medium Earth orbit (MEO) satellites operational at the end of 2022. This is enough capacity to make three of Europe’s GNSS services operational.
- Open Access Service delivers meter-scale accuracy to the public.
- Public Regulated Service delivers centimeter-scale accuracy to authorized users.
- Search-and-Rescue (SAR) relays distress messages to European ground stations.
Once the constellation is complete, Galileo will offer a High Accuracy Service with sub-meter performance globally. Initial availability is expected in late 2022.  With full service in 2024, receivers in Europe will get better performance and faster convergence times.
Europe’s software-based design approach allows the Galileo constellation to evolve without replacing satellites. For example, an upcoming software update will improve convergence times and compatibility with augmentation services.
Of course, advancing technology will always drive new capabilities. Second-generation Galileo (G2) satellites will enter service in 2024. Electric propulsion and inter-satellite communications will make Galileo operations more efficient. New GNSS technologies will enable more accurate positioning and make Galileo more resistant to jamming and spoofing.
Looking further out, the European Space Agency plans in-orbit testing of LEO satellites to augment Galileo’s MEO constellation.
China’s third-generation positioning system, BeiDou-3, consists of twenty-four MEO satellites providing global coverage plus three satellites each in geostationary orbit (GEO) and inclined geosynchronous orbit (GSO). Civilian signals allow positioning accuracy to within 3 meters globally. Augmentation with signals from GEO and GSO allows 1-meter accuracy in China.
Civilians with BeiDou-enabled devices can send emergency SMS messages similar to the emergency texting service provided by Apple and Globalstar.  China’s military and other authorized users have two-way messaging capabilities.
Future BeiDou-3 developments include GNSS augmentation using ground stations and enhanced two-way messaging.
Fourth-generation plans for BeiDou will include more precise atomic clocks and improved communications technology. Official statements indicate the planned completion of this next phase by 2035.
Russia’s GLONASS constellation consists of eighteen active MEO satellites in high-inclination orbits to serve Russia’s higher-latitude geography. Over the past ten years, Russia began replacing its second-generation GLONASS-M satellites with the more modern GLONASS-K design. By moving from FDMA signals on L1 and L2 frequencies to CDMA signals on L1, L2, and L3, civilian performance will become equivalent to other GNSS constellations.
GLONASS-K and its successor, GLONASS-K2, also reduce Russia’s dependence on western technologies. However, these efforts have not made GLONASS immune to western sanctions following Russia’s annexation of Crimea and the recent invasion of Ukraine. By early 2022, nearly two-thirds of operational GLONASS satellites were beyond their planned service life.  The first GLONASS-K2 prototype has seen repeated delays from its original 2018 launch date. As of early December 2022, Russia had yet to launch GLONASS-K2.
CAST Simulators Support Multiple GNSS Constellations
CAST Navigation has been the leading provider of GPS and GNSS simulator capabilities for more than forty years. CAST simulators have evolved with developments in GNSS constellations, such as the progress from P(Y) Code through SAASM to M-Code AES and MNSA. In this age of multi-constellation positioning, CAST solutions can simultaneously simulate up to four different constellation types on each antenna element.
If your applications demand precise and repeatable GNSS RF signals, then contact CAST Navigation today.