Explained: C-Band 5G frequency & why DoT has directed telcos to not install it near airports

On Wednesday, the Department of (DoT) had directed telecommunication service providers not to install any 5G sites in the 3,300-3,670 MHz band — also known as C-Band — within a 2-kilometre radius of runways at all airports in India, as it interferes with aircraft radio altimeters

In doing so, the DoT is looking to avoid a situation similar to one which unfolded in the United States early this year, in which the US Federal Aviation Administration (FAA) too issued a similar directive, resulting in a major standoff between the regulator and wireless carriers. Indian flights were affected too, with Air India cancelled several US-bound flights. 

So, what is C-Band, and how can it affect aircraft altimeters?

C-Band is a 5G frequency band between 3,300 and 3,670 MHz. The highest band offered under 5G is millimetre wave (mmWave), which operates in the 28-39 Giga Hertz (GHz) frequency. The lowest is 700 MHz, which is the most widely deployed frequency band.

C-Band hits the sweet spot in 5G frequencies, offering the widest coverage with the highest speeds possible. As mentioned above, the C-Band operates in the  3.7-3.98GHz frequency, which is close to the 4.2-4.4GHz frequency used by altimeters on airlines. Altimeters are devices that can tell how high above the ground the aircraft is flying. Altimeters are especially useful on a cloudy day or over mountainous terrain where visibility is limited.

Further, a C-Band tower has a coverage radius of a few square kilometres.

In the US, carriers deploying C-Band antennae near airports had sparked off protests from the aviation industry, with airlines claiming  this could interfere with the flights' altimeters. Several airlines have asked "that 5G be implemented everywhere in the country except within the approximate 2 miles (3.2 km) of airport runways" at some key airports.

In a nightmare scenario, flights will not be able to land or take off due to the presence of nearby 5G towers, or even the presence of a significant number of people inside airports using the C-Band 5G network.

So, in a bid to head off this potentially problematic scenario, DoT has issued a preemptive directive to telcos to refrain from installing C-Band towers 2,100 metres from runways.

Prime Minister Narendra Modi had launched 5G services in the country on October 1, with Reliance Jio slowly rolling out its True 5G in a phased manner and an invite-only basis across several cities, and Bharti Airtel launching its 5G Plus service first in eight major cities with an aim to cover most of the country by 2024.