 responsibility to transmit the regional Japanese augmenta- tion system on their GEO satellite (see the following section on augmentation). Multi-constellation By combining even just the four global systems, GPS, GLONASS, BeiDou, and Galileo, there are over 100 non-geostationary satellites available today, with more being planned. This large number of satellites generally provides the opportunity to deploy multi-constellation and multiband receiv- ers. Users will benefit from the following: Ability to compare data across systems to verify signals against each other Each system aligned with UTC (and many broadcasting offsets from UTC) allows the receivers to increase the accuracy of their recovered time More data points and signal bands to reduce position and timing errors from atmospheric conditions Improved coverage by having more satellites distributed all over the sky Increasing resistance to spoofing Already, receivers, even in mobile phones, are increasingly multi-constellation, and this trend will only increase, especially for specialized timing equipment. Augmentation Systems Enhancing GNSS Although not widely used in timing applications, there are several other systems, for example space-based augmentation systems (SBAS) that enhance or augment existing GNSS systems. This enhancement can help guarantee signal integrity, enhance accuracy, or improve performance to cover special applications, such as guiding aircraft to the runway, docking ships, or precision farm- ing. There are some other local, ground-based augmentation systems, such as differential systems that increase the accuracy for ships navigating around harbors, but they are beyond the scope of this book. These augmentation systems are generally regional in nature and therefore based on a small number of GEO satellites (that appear fixed in the sky) with numerous monitoring stations on the ground to observe the original GNSS signals and upload correction data. Figure 3-15 illustrates how these sys- tems function using GPS as an example. Augmentat