Modern mobile devices have built-in hardware to determine their location. However, this hardware must have access to a Global Navigation Satellite System (GNSS) to work, and that’s where Global Positioning System (GPS) comes in. GPS is a US-managed GNSS that mobile devices leverage for location tracking and navigation, disaster management, and environmental needs. However, it is not the only GNSS. One of the major functions of these satellite systems being defense, all the major world powers like to have their own to safeguard their interests. GLONASS, or Global’naya Navigatsionnaya Sputnikovaya Sistema, is a GNSS operated by Russia.
It was developed in the 1970s, when Russia was still part of the Soviet Union, and the first satellite was launched in 1982. It is capable of covering the entire globe with its full constellation of 24 satellites. GLONASS transmits standard precision and high precision signals at L1 and L2 frequencies (with some of its newer satellites also using L3 frequencies), although most consumer devices typically only leverage its standard L1 signal to pinpoint their location. Although it is not particularly better or worse than GPS, its performance in higher latitudes, such as in areas of the Arctic and Siberia, is certainly one of its strengths. That said, using GLONASS alongside GPS in devices allows for better accuracy, especially in urban areas with many buildings that may interfere with GNSS signals.
Although manufacturers initially did not include support for consumer devices, the situation changed when Russia announced a 25% import tax on all devices supporting only GPS and not GLONASS in 2010. Devices supporting both were allowed in duty-free, leading to rapid support for GLONASS, and Apple became one of the first major brands to add this support, starting with the iPhone 4S.
Apple ignores GLONASS in Watch Ultra 4
Since the iPhone 4S, Apple has added GLONASS support to all of its mobile devices, including the various Apple Watch models. However, the Watch Ultra 4, one of the latest additions to the company’s smartwatch lineup, surprisingly does not support GLONASS, although it does support GPS and other GNSS systems like the EU’s Galileo, Japan’s QZSS, and China’s BeiDou. Although Apple hasn’t officially explained anything about why GLONASS support is missing, Woozad speculates that dual GPS frequency support for the Ultra 4 makes using GLONASS less useful. As mentioned, most consumer devices only read the single L1 frequency of the GLONASS signal, but a dual frequency setup requires both frequencies for error correction. This means that the single L1 frequency of GLONASS is not very useful.
Woozad adds that another possible reason is GLONASS’s use of a different signal architecture, which makes it difficult to calculate hardware synchronization delays and can cause positioning errors. Legacy GLONASS satellites rely on a frequency division multiple access (FDMA) signal architecture in which each satellite has a different frequency channel, resulting in different signal propagation delays for each satellite. As a result, hardware manufacturers must calibrate this delay for each satellite, otherwise position errors may occur. Most other GNSS systems use a CDMA architecture with the same frequency for each satellite, with the same delay for each satellite. It’s likely that Apple doesn’t want to deal with all that, and the GLONASS L1 signal isn’t very useful in the Watch Ultra 4’s dual-frequency setup anyway. Plus, since Apple currently doesn’t sell its devices in Russia, it doesn’t have to worry about the country’s GLONASS requirements.
