Explaining the Different Types of GPS Signals: L1 C/A & L1C

GPS signals – What is GPS?

GPS – Global Positioning System – is the world’s most utilised Global Navigation Satellite System (GNSS). Owned and operated by the United States government, the system is freely accessible to anyone with a GPS receiver. This receiver can calculate its exact position based on data received from the constellation of GPS satellites orbiting the Earth.

All GPS signals are on the L-band of the frequency spectrum, the first and still most used being L1 C/A. While L1 C/A has been dominant for decades, the system is in the process of being modernised and a new advanced L1 signal, L1C, is beginning to be broadcast by newer satellites. There are now 8 GPS satellites broadcasting the signal for commercial use, with a full constellation of 24 satellites planned by the late 2020s.

L1 C/A: The Original GPS Design

GPS L1 is the pioneering, incepting band for navigation, with the majority of applications still using its 1575.42 MHz frequency across the world. Its importance cannot be overstated and while it’s now becoming to be seen as a legacy signal, it will continue broadcasting well into the future and still play an important role as the technology is modernised.

Services using L1 C/A are of relatively good quality, and because it is the oldest and most well-established signal, the cost of technology utilising it is now very low. However, the frequency is quite slow and not the most successful at traveling through objects. Therefore, the United States have proposed a plan of modernisation to improve GPS quality which includes the use of additional signals.

The L1 band will continue to be used as the backbone of the GPS signal but instead of single band positioning, L1 will be used in conjunction with another band, which is called multi-band positioning.

L1C: International Interoperability

L1C is a new signal in the L1 band. It’s broadcast on the same L1 frequency of 1575.42 MHz as the C/A legacy signal and is another civilian-use signal, so what makes it different? L1C was designed specifically to enable interoperability between GPS and other international satellite navigation systems, specifically the European Union’s Galileo constellation of satellites, and allow greater cooperation of technology worldwide.

Users connected to Galileo or other systems can utilise the US’s GPS network due to an international agreement but L1C truly allows the systems to unite like never before and communicate with each other. The implementation will also provide the C/A code to guarantee backwards compatibility and utilise multi-band positioning, but the new signal is broadcast at a higher power level for enhanced performance and a data-less signal carrier to improve tracking.

L1C is a newer signal and the technological infrastructure has only recently begun being deployed. The signals can be broadcast from GPS III and later satellites, of which only eight are currently operational, the first being launched in December 2018. However, 24 GPS satellites are expected to have L1C capability by the end of the 2020s.

GTT Wireless’s commitment to GPS

GTT Wireless vow to be at the forefront of advancements in GPS technology and stock a range of GPS/GNSS outdoor antenna that can be used for a variety of Internet of Things (IoT) applications. Our antenna’s robust IP67/NEMA6 waterproof and UV-resistant design allow them to perform consistently, even in extreme environments. You can visit our antenna store or build a weatherproof outdoor electronics enclosure for your mission critical project using our enclosure designer.