Mobile services have met resistance from established interests throughout their history, as they encroach on spectrum previously reserved for others and raise fears over interference, as well as reduced capacity. 5G is no exception, except that now the spectrum is touching different services, including GPS, weather forecasting and aviation navigation, in addition to broadcasting where there has been contention before.
Past history, though, tells us that most of these conflicts turned out to be storms in a teacup and were resolved without the roof falling in on these services, even if some continue to complain over ceding ground to an inexorably advancing cellular industry. But even that merely reflects changing levels of usage, as the world relies ever more on effective high performing mobile services.
This does not mean that the complaints from these sectors are misplaced, but more that their fears tend to be overstated and the ability to resolve the issues perhaps almost deliberately underplayed. In the case of digital terrestrial broadcasting (DTB), for example, the same techniques for making more efficient use of spectrum and mitigating interference within cellular services also helped increase capacity for over-the-air TV. Now we are starting to see terrestrial TV starting to merge with cellular in any case through the High Tower High Power (HPHT) model.
Broadcasting, of course, is rather a special case but now we are hearing concerns expressed by other sectors, in particular meteorology and aviation. These concerns were amplified by the outcome of WRC-19, the most recent World Radiocommunications Conference to set international spectrum allocations.
The WRC-19 agreements designated radio frequencies over which 5G equipment would be allowed to transmit but some of these might appear to be perilously close to those used by some existing services.
In the case of weather forecasting, it was 5G millimeter wave usage in 24 GHz that caused concern, because the 23.8 GHz band is used to measure water levels in the atmosphere. Since this data feeds big predictive models this could in theory have an impact on accuracy of weather forecasts. The risk is that a weather satellite would misinterpret a 5G signal in that band as presence of water vapor, which produces a weak signal at this frequency that computer models turn into measurements of humidity at different altitudes.
The World Meteorological Organization (WMO) had already accepted that 5G would encroach on that band but is now arguing that interference mitigation measures are inadequate. Like previous radio conferences, WRC19 had to mediate between the advancing cellular communities and several existing users of bands, and for weather satellites it tried to do that by setting out-of-band buffers between the specific frequencies used. The buffers, whose effectiveness is measured in signal-to-noise ratio (SNR) or dB, need to be sufficiently wide to prevent a strong 5G signal from spilling over and corrupting a weak signal emanating from water droplets.
The WRC set a limit of -39 dBW for this weather band, meaning that 5G services would be prohibited from emitting noise up to this level outside of the 24 GHz band. This is less than the -42 dBW the WMO had sought and well below the -52.4 dBW it would have liked in an ideal world – that more stringent level having been identified by NASA and the National Oceanic and Atmospheric Administration as being necessary to guarantee weather satellites full freedom from 5G interference. In fact, the situation is a little worse than that, because WRC-19 also allowed 5G operators to emit higher noise levels of -33 dBW out of the 24 GHz band, during a transition period until 2027.
Aviation is another sector crying foul, mainly over the already contentious plans by US regulator the FCC to repurpose C-band spectrum, which houses various satellite and radar incumbents, for cellular. The FAA (Federal Aviation Administration) is concerned about closeness of 5G to the band used by safety-critical radar-based altimeter. Pilots rely on such altimeters for accurate determination of height, most importantly in conditions of poor visibility close to landing.
Various airline industry bodies, and manufacturers like Airbus, have petitioned the FCC to reconsider this reallocation to 5G, and were joined most recently by Garmin, better known to consumers for its sports watches. Garmin also makes FAA-certified radar, and argues that the reallocation could jeopardize air safety, both during landing and to ensure adequate clearance of mountain ranges.
Its petition argues that such safety-critical systems require a higher degree of protection from possible interference than others, although in weather forecasting the WMO mutters darkly about lives being lost in the event of hurricane prediction being less accurate.
These two disputes are, however, likely to be resolved without planes crashing or hurricane evacuations coming too late, if past experience is any guide. It is worth considering the words of William Webb, former director of Ofcom, the UK’s telecom regulator, who led the country’s Spectrum Framework Review and subsequent development of spectrum usage rights in the mid-2000s. Webb has noted that, in practice, such interference issues are almost always exaggerated and turn out to be quite readily resolved.
In a recent article in Forbes magazine, he likened the interference question to the Y2K Millennium Bug fears, which became a global obsession in 1999. This is an apt analogy because, while the start of 2000 came in with hardly a blip in critical computer systems, fearmongers argued this was only because of the great efforts made to eradicate date-related bugs associated with using only two digits to represent years (which of course would lead to, say, year 2005 being mistaken for 1905). The truth is that mitigation efforts did eliminate bugs but also that the exposure of critical systems to such errors was vastly exaggerated.
Similarly in the case of 5G interference, mitigation measures are required, but the compromises made in determining them have so far rarely led to any serious issues.