A cell phone is a two-way radio. Instead of one big station covering a whole region, phone companies use many smaller towers, each like a little radio station for its own neighborhood. These four pictures show how it fits together. The next class, Cellular Bands and 5G, goes deeper into the frequencies phones use.

Cells Like a Honeycomb
Cells Like a HoneycombSeven hexagon-shaped cells, each with a tower. A car on a road crosses from one cell to the next while its phone switches towers.CELLS LIKE A HONEYCOMBYour phoneis a two-way radio1234
Read all 4 details
  1. 1Cells. Think of each cell tower as a small radio station that only covers its own neighborhood, called a cell. Cells fit together like a honeycomb, which is where the name "cell phone" comes from.
  2. 2A tower for each cell. Each cell has a tower or radio site that serves the phones inside it. Neighboring towers use different channels, the same way two nearby radio stations use different spots on the dial so they do not talk over each other.
  3. 3The handoff. When you drive out of range of an FM station, the music fades to static and you have to find a new station. Your phone does this for you automatically, switching to the next tower in a split second so your call keeps going. This is called a handoff.
  4. 4A two-way radio. A car radio only listens. A cell phone is a two-way radio: it listens to the nearest tower and also talks back, and the tower connects your call or data to the rest of the network.
Inside a Cell Site
Inside a Cell SiteA cell tower with three antenna panels at the top, a second set of antennas lower down, a microwave dish beaming to another tower, an equipment shelter at the base, and fiber running to the network.INSIDE A CELL SITEFiber to the network50 to 200 feetEquipment shelterTower12345
Read all 5 details
  1. 1Antennas. Antennas near the top usually point three ways. Each one covers a slice about one third of a circle, so together they cover all directions.
  2. 2Height. Like a radio station's tower, cell towers are often 50 to 200 feet tall. Higher antennas see over hills and trees, so the signal reaches farther.
  3. 3Radios and power. At the base, a small building or cabinet holds the radios, batteries, and power equipment that keep the site running, even during an outage.
  4. 4Backhaul. Each site needs a link back to the main network. That link, called backhaul, can be fiber in the ground or a microwave radio beam to another tower.
  5. 5Shared towers. One tower can hold antennas for several phone companies. Sharing towers saves money and means fewer towers on the land.
Spectrum: The Invisible Highway
Spectrum: The Invisible HighwayA tower sends three radio waves. The long low-band wave passes through a house and goes far. The medium mid-band wave goes part way. The short high-band wave stops at a tree.SPECTRUM: THE INVISIBLE HIGHWAYLow band: goes farMid band: balanceHigh band: very fast, shortFCC1234
Read all 4 details
  1. 1Low band. Low frequencies, around 600 to 900 megahertz (MHz, millions of wiggles per second), travel far and pass through walls and trees, the same way a low-frequency AM station can still be heard after an FM station has faded. They are great for wide rural areas, but they carry less data.
  2. 2Mid band. Mid frequencies, like 2.5 and 3.5 gigahertz (GHz, billions of wiggles per second), balance distance and speed. Through FCC Auction 108, Numu helped tribes win 2.5 GHz licenses to serve their own lands.
  3. 3High band. Very high frequencies, called millimeter wave, can be extremely fast, but they only reach a short distance and are blocked by walls, trees, and even rain.
  4. 4The FCC. Radio frequencies are a shared public resource. Just as the Federal Communications Commission (FCC) assigns each radio station its frequency and call sign, it divides phone frequencies into bands, like lanes on a highway, and licenses who may use each lane in each area.
From 2G to 5G
From 2G to 5GA road with four signposts for 2G in the 1990s, 3G in the 2000s, 4G LTE in the 2010s, and 5G in the 2020s, ending at a sign that reads Your own network.FROM 2G TO 5G2G1990sCalls and texts3G2000sMobile web4G LTE2010sVideo and apps5G2020sFaster, more devicesYour ownnetwork12345
Read all 5 details
  1. 12G. The "G" stands for generation. In the 1990s, second-generation (2G) networks made phone calls digital and added text messages. Most U.S. carriers have now turned off their 2G and 3G networks.
  2. 23G. In the 2000s, third-generation (3G) networks brought email and simple web browsing to phones.
  3. 34G LTE. In the 2010s, 4G LTE (fourth generation, Long Term Evolution) made streaming video, video calls, and app stores practical. It is still the main network in many rural areas.
  4. 45G. In the 2020s, fifth-generation (5G) networks add more speed, quicker response, and room for many more devices at once.
  5. 5Your own network. A Mobile Virtual Network Operator (MVNO) sells phone service under its own name using another carrier's towers. It is one way a tribe can offer its own branded mobile service without first building every tower.

Remember

Your phone is a two-way radio

Lower frequencies reach farther

5G

Each new "G" adds speed and room

Try it

1. Why is it called a cell phone?

2. Which signal travels farthest and goes through walls best?

Learn more

References

  1. Federal Communications Commission. (n.d.). Auction 108: 2.5 GHz band. https://www.fcc.gov/auction/108
  2. National Telecommunications and Information Administration. (n.d.). Publications. BroadbandUSA. https://broadbandusa.ntia.gov/resources/publications
  3. Telecommunications Law Professionals. (2020, October 26). FCC grants 2.5 GHz licenses in Rural Tribal Priority Window. https://www.tlp.law/2020/10/26/fcc-grants-2-5-ghz-licenses-in-rural-tribal-priority-window/

Questions about broadband for your community?

Our team is happy to help guide your community's broadband plan.

Contact our team