C-Band
The C-Band is a range of radio frequencies between roughly 3.4 and 4.2 gigahertz. It is considered especially valuable for fast mobile networks because it can carry large amounts of data while still covering long distances.
Radio transmits signals via invisible waves in the air. These waves differ in how quickly they oscillate. The oscillations per second are called frequency, measured in hertz. One gigahertz is a billion oscillations per second. The C-Band refers to all radio waves that oscillate roughly 3.4 to 4.2 billion times per second. This range is used, among other things, for satellite transmission and for fast mobile networks.
Why the C-Band is considered a goldmine for mobile carriers
With radio frequencies there is an unavoidable trade-off. Low frequencies travel far and penetrate walls, but transport little data. High frequencies transport huge amounts of data, but are already stopped by a single house wall. The C-Band sits right in the middle of this trade-off.
That’s why experts speak of the middle band or the mid-band. A single cell tower on the C-Band covers several kilometers while delivering speeds that are more than sufficient for video streaming. With very high frequencies, you would need hundreds of towers to cover the same area. That would be unaffordable.
Radio frequencies are also scarce. Two carriers cannot use the same frequency in the same location, or they will interfere with each other. States therefore auction off usage rights individually. In the US auction for C-Band frequencies in 2021, mobile carriers together paid around 81 billion dollars. Verizon alone spent over 45 billion dollars. Such sums show up in quarterly reports and debt disclosures and move stock prices.
From satellite radio to cellular networks: the reallocation
Originally, the C-Band belonged to satellite operators. Television broadcasters sent their programs via C-Band satellites to cable providers on the ground. This worked because C-Band signals remain stable even in heavy rain. Higher frequencies are absorbed much more strongly by raindrops.
As mobile users' data hunger grew, this frequency range became too attractive for mobile networks to ignore. Regulators required satellite operators to give up part of the band. The operators consolidated their transmissions into a narrower upper section. The freed-up lower portion went to mobile networks. In exchange for the changeover, the satellite companies received billions of dollars in payments from the auction proceeds.
Today there is a guard band between the two uses, an empty strip of frequency. It prevents powerful cell towers from drowning out the sensitive satellite receivers. This exact gap was a point of contention with the aviation industry. Altimeters in aircraft operate just above the C-Band, at around 4.2 to 4.4 gigahertz. In the US, the activation of some towers was consequently delayed by months.
C-Band in mobile networks and in news coverage
Anyone achieving very high data rates on their phone in a city is usually using the C-Band or a neighboring mid-band. In Europe, a large share of fifth-generation mobile service, 5G for short, runs at around 3.6 gigahertz. The phone doesn’t show any of this. It just displays a network icon and switches between available bands in the background.
In the news, the term usually appears in three contexts. First, in auctions, when states sell usage rights. Second, in network rollout figures, when a carrier reports how many people it reaches with C-Band. Third, in conflicts with other users, such as aviation or the military.
A common misconception: that C-Band is a technology. It is only a frequency range, a kind of address in the radio spectrum. Which technology transmits there is open. The same frequencies used to carry television signals and today carry 5G. Home Wi-Fi, by the way, is not far off either, sitting at around 5 gigahertz.