Knowledge Base
What are uplink power and downlink power in a cellular network? How does a cell signal booster improve my cellular connection?
Uplink and downlink refer to the signals transmitted between a cell tower (base station) and a mobile device like a smartphone or cellular modem (user equipment):
How uplink and downlink power are measured
Cell towers and mobile devices use electrical power to transmit signal (voice and data). Uplink power and downlink power refer to the strength of the signal transmitted between the cell tower and the device. Transmit power is measured in decibel-milliwatts (dBm), with 0 dBm being equal to 1 milliwatt (mW).¹
The gain of the tower or device’s antenna is added to its transmit power to calculate Effective Isotropic Radiated Power (EIRP). The maximum EIRP of cellular devices is regulated by the Federal Communications Commission (FCC). Not all devices transmit at the maximum allowed EIRP, and most devices continually adjust their transmit power to most efficiently make use of the network.
Problems with insufficient uplink power
Uplink power is the strength of the signal transmitted by your phone or modem up to the cell tower.
As the table above shows, a cell tower’s downlink power is 50 to 100 times or more greater than your phone’s uplink power back to the tower. Cell tower antennas are large and use a lot of electrical power,⁹ while cell phones have low-gain integrated antennas and small rechargeable batteries.
If the uplink power from your phone is too low, the signal may not reach the base station properly, leading to a weak connection, dropped calls, or that annoying circumstance when you can hear the person on the other end of the call but they can’t hear you. Even if you are able to make a connection, your phone will have to increase its uplink signal strength, consuming more of its limited battery power.
When the distance to the cell tower is too far for your phone to reach or when there are obstructions between you and the tower—like exterior building walls, terrain, and trees—insufficient uplink power is almost always the problem that’s keeping you from using your phone.
Problems with insufficient downlink power
Downlink power is the strength of the signal transmitted by the cell tower to mobile devices within its coverage area.
Downlink power is managed by the cellular network infrastructure, particularly by the base station. The network continuously monitors the signal strength and quality of the connections with the mobile devices in its coverage area, and a tower will adjust its downlink transmit power to provide an optimal signal level to each device connected to it.
Even with significant amounts of transmit power at its disposal, downlink signal from a tower can have a hard time reaching your phone because of distance, obstructions, and interference from other electronic devices. During periods of high network usage, the tower will adjust its downlink power to accommodate more users, making connections more difficult for distant devices. Even if there’s enough downlink power for you to make low-quality voice calls, there may not be enough for video streaming and data downloads.
Cell signal boosters improve your connection to cell towers
A cell signal booster sends and receives cellular signal to and from cell towers; it amplifies the signal both ways and broadcasts the amplified signal inside a building, vehicle, or boat. A cell signal booster can improve your uplink cellular connection when outside signal is weak or when strong outside signal can’t get inside because it’s being absorbed or reflected by building materials.
A cell signal booster has up to five times the uplink power (EIRP) of a typical cell phone—30 dBm vs. 23 dBm. A cell signal booster also has a donor antenna outside the building or vehicle, giving the booster access to clearer, less-obstructed signal. With more uplink power, a booster will give you a stronger connection to distant towers and bypass exterior walls that are blocking cellular signal.
How to choose the right cell signal booster—gain vs. downlink power
In addition to providing increased uplink power, a cell signal booster has downlink power to broadcast signal inside your home, office, vehicle, or vessel. Because it doesn’t need to broadcast as far as a cell tower—100 feet or less, instead of many miles as a tower does—a booster needs much less downlink power than uplink power.
Generally speaking:
- If your problem is weak outdoor cell signal, then the booster’s gain is the important factor to consider. More gain effectively “turns up the volume” of the signal.
- If your problem is strong outdoor cell signal that can’t get inside because it’s blocked by building materials, you don’t need as much gain because the booster simply has to pass the outside signal through to the inside environment. What you do need to pay attention to is the booster’s downlink power: Too much, and the booster will overload and possibly shut itself off to protect the tower and its cellular network. If that happens, you may need to install an attenuator to reduce the amount of signal reaching the booster.
Call Powerful Signal at 435-634-6800
…or contact us online. Our experienced team can help you fix the poor cell phone signal in your home, your business, your vehicle, or your boat.
Notes
¹ Decible-milliwatts are measured using the decibel
(dB) scale. The decibel is a relative unit of measurement that expresses the ratio of two values of power on a common (base 10) logarithmic scale. A negative dBm value—one less than 0—does not mean that the transmitter is putting out no signal; it means the transmitter’s output is less than 1 milliwatt.
² “5G NR UE Power Classes,” RF Wireless World, accessed . 5G NR Power Class 1 sites are limited to 55 dBm maximum power; 5G NR Power Classes 2–4 are limited to 43 dBm.
³ 47 C.F.R. § 30.202(b). “For mobile stations, the average power of the sum of all antenna elements is limited to a maximum EIRP of +43 dBm.”
⁴ “Human Exposure to Radio Frequency Fields: Guidelines for Cellular Antenna Sites,” Federal Communications Commission, updated .
⁵ “HPUE Technology on FirstNet LTE Band 14 and Beyond,” Nextivity (blog), . FirstNet phones are considered Power Class 1 High Power User Equipment (HPUE).
⁶ “47 C.F.R. § 20.21(e)(8)(i)(D). “Power Limits. A booster’s uplink power must not exceed 1 watt [30 dBm] composite conducted power and equivalent isotropic radiated power (EIRP) for each band of operation. Downlink power shall not exceed 0.05 watt (17 dBm) composite and 10 dBm [0.01 watt] per channel conducted and EIRP for each band of operation.”
⁷ “Power Class 2: What You Need to Know,” Qorvo Design Hub (blog), ; “5G NR UE Power Classes,” Techplayon, . 4G and 5G phones that use higher-frequency bands above 2.5 GHz are considered Power Class 2 High Power User Equipment (HPUE).
⁸ “ETSI Technical Specification 136 101 v15.9.0 3GPP,” European Telecommunications Standards Institute, , p. 160. 4G and 5G phones that use lower-frequency bands below 2.5 GHz are considered Power Class 3 equipment.
⁹ A typical cell site will run on 4 to 6 kilowatts of power, while a typical smartphone battery has a capacity of 10 to 12 watt hours. Kurt Behnke, answer to “What’s the power consumption of the average cell phone tower/site?”, Quora, ; Chance Miller, “iPhone 14 battery capacity: Here’s how the numbers compare to iPhone 13,” 9to5Mac, .
