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June 5, 2018

What is Spectrum? A Brief Explainer .

What is Spectrum? A Brief Explainer


Riley Davis

The technologies that make wireless work can be hard to visualize—we’ve even called them magical—so in our blog, we’ve been breaking down the “how” behind the “wow”. We’ve talked about how 5G works, and the small cell infrastructure that will make it happen. Today, we’re here to talk about the lifeblood of wireless networks—spectrum—and the new ways we’ll be harnessing its power for 5G.

What is Spectrum?

Spectrum refers to the invisible radio frequencies that wireless signals travel over. Those signals are what enable us to make calls from our mobile devices, tag our friends on Instagram, call an Uber, pull up directions to a destination, and do everything on our mobile devices.

The frequencies we use for wireless are only a portion of what is called the electromagnetic spectrum.

The entire electromagnetic spectrum encompasses other frequencies we interact with daily, even if we don’t think about them. You may remember ROYGBIV from elementary school. That’s the acronym for the colors that make up the visible part of spectrum—the spectrum we see. Other parts of spectrum carry broadcast radio and television or serve other everyday functions.

Portions of electromagnetic spectrum are grouped in “bands” depending on their wavelengths—the distance over which the wave’s shape repeats. The full electromagnetic spectrum ranges from three Hz (extremely low frequency) to 300 EHz (gamma rays).  The portion used for wireless communication sits within that space and ranges from about 20 KHz to 300 GHz.

Spectrum wavelengths are classified into different bands within the electromagnetic spectrum range.

When we talk about radio spectrum, we are talking about the range of radio frequencies that are used for communicating. Think of your radio dial. As you go up and down the dial, you locate the radio stations operating on particular frequencies. Now just imagine that radio dial expanding much, much further in both directions—that’s where you would encounter frequencies assigned to other uses, whether it’s mobile phones, or satellite TV, or air traffic control, or police radios. Spectrum is the entire range of frequencies.

How Does Spectrum Work?

Because a range of spectrum frequencies can be used for cellular communications, different bands have slightly different characteristics. For the purposes of wireless communication, we can think of spectrum in three categories: low-, mid-, and high-band spectrum.

You might have read that we need more of all three for robust 5G networks. That’s because each band of spectrum is essential for a different kind of communication and use case:

  • Low-band spectrum (under 3 GHz) travels longer distances with minimal signal interruption. Today’s wireless networks are built primarily on low-band spectrum, and the wireless industry has used this spectrum to build high-speed wireless networks that cover 99.7 percent of Americans.
  • High-band spectrum (above 24 GHz) travels much shorter distances—think meters, not miles—compared to low-band spectrum, but offers high capacity and ultra-fast speeds.
  • Mid-band spectrum (between 3 and 24 GHz) blends the characteristics of both low- and high-band spectrum—providing a mix of coverage and capacity.

These spectrum frequencies are transmitted between cell sites and our mobile devices. The most common cell sites in use today are the 150 foot cell towers we are accustomed to seeing along highways or atop tall buildings. But small cells—small scale antennas—are now being rapidly deployed to densify network coverage and provide more frequent connection points for 5G’s mid- and high-band spectrum.

Who Manages Spectrum Use?

The Federal Communications Commission (FCC) oversees commercial spectrum allocation. The FCC works collaboratively with the National Telecommunications and Information Administration (NTIA)—which oversees government use of spectrum—international bodies, and Congress to allocate spectrum bands.

The FCC often allocates spectrum for commercial use through a spectrum auction. These auctions work like any other—tracts of spectrum are available to be purchased by the highest bidders, raising money for the U.S. Treasury.

Spectrum can be licensed—meaning it is bought for exclusive use by specific providers—or unlicensed, meaning anyone can use the frequency. Your Bluetooth device and Wi-Fi connection rely on unlicensed bands, for instance. Both licensed and unlicensed spectrum serve important functions, and the FCC has set aside spectrum for both.

Spectrum is a finite resource, however, and we cannot make more of it. But the good news is that spectrum can be repurposed. The federal government controls roughly 60 percent of spectrum, and regulation and legislation can help identify bands that the government should reallocate for commercial use.

Spectrum is a highly complex concept, but the bottom line is that it’s the core component of wireless communications. All of the amazing benefits 5G promises—smart cities, telemedicine, agricultural advancements, and more—depend on it. And the more effectively we utilize it, the greater the benefits.

Let’s see where wireless takes us next.

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