Cellular Repeaters: What They Are and How They’re Used

It’s pretty common for construction companies to have large metal storage buildings for equipment and shops. If you’ve worked in one, you’ve probably also noticed that it can be hard to get a cellular signal sometimes. The same is true for GPS tracking equipment installed on your vehicles and assets while located in these areas.

GPS equipment trackers and fleet trackers use cellular wireless technology as one of the most advanced tracking technologies today. Wireless technology helps communication and data sharing through devices that do not have cables or wires. Cellular networks to WI-Fi are an example of wireless technology. ( Read more.)

But when circumstances prevent the effective connection from trackers to cellular networks, tracking data can be negatively affected. Such circumstances could include the above-mentioned metal buildings or rural areas with fewer cellular towers. How can businesses overcome environmental obstacles to their cellular data connections? They can implement cellular repeaters.

Let’s discuss what cellular repeaters are and how they can be used to improve your cellular connectivity.

What are cellular repeaters?

A cellular repeater (also known as a booster) is a system that can extend cellular coverage to locations in which existing coverage is negatively affected due to weak signal conditions. The components of a cellular repeater typically include:

• A cell tower-facing antenna
• An amplifier driving an antenna intended to service the target area with weak signal conditions.
• A return path amplifier to boost signals from equipment in the targeted service area sufficiently so that they can be received satisfactorily at the cell tower.

Many variations of this arrangement exist; some use directional antennas on both ends, some use multiple antennas or signal feeds on either end.

Sometimes a cellular network experiences a phenomenon called oscillation. This happens when a device, even if stationary, does not connect to the nearest cell tower and instead switches unpredictably between multiple towers. This can make it difficult for GPS systems to accurately find an asset’s location and other data points. Some cellular repeaters incorporate automatic overload detection and recovery, preventing undesirable conditions like oscillation from happening.

Properly applied, a well-designed and deployed cellular repeater system can enhance connectivity—or even make connectivity possible—for phones and IoT devices in places where operation was previously problematic or impossible.

How do cellular repeaters work?

Let’s take a look at the elements of a generic cellular repeater system:

• Cellular tower. Also known as a base transceiver station (BTS). Cellular towers include an assembly of transmitters, receivers, controllers, antennas, and cabling, all mounted high enough to maximize the line-of-sight distance to users.
• Radiation patterns. Designed to supply optimum coverage in the desired zones (area distant from the tower).
• User equipment (UE). This could be cell phones, or in Tenna’s case, GPS trackers for equipment or vehicles. User equipment also emits radiation patterns to connect to cellular towers.

Within the orange box are the specific elements of the cellular repeater:

• Antennas. Antennas on either side of the repeater pick up radiation patterns from cellular towers and user equipment.
• Diplexers. Each duplexe combines signals going to and from the repeater antennas.
• Amplifiers. The amplifiers supply the boost needed to extend the signal range. PA is a Power Amplifier that has the strength to drive the transmit antenna. LNA is a Low Noise Amplifier, which has the sensitivity to pick up and amplify weak and distant signals while also minimizing noise and distortion. Together they create a two-way amplifier system that can extend the reach of our communications link more efficiently.
• Filters. Filters ensure the sending and receiving channels are well separated so the signals are clear and free from interaction and distortion.

You’ll notice that within the cellular repeater there are two signal pathways:

• Downlink. The path from the cellular tower to the user equipment.
• Uplink. The path from the user equipment to the cellular tower.

Cellular devices are essentially two-way radios that can switch between listening and talking very quickly. The cellular tower automatically assigns channels and manages traffic.

What are the limitations and risks of using a cellular repeater?

Availability of any cellular signal

A cellular repeater system can only extend cellular coverage if there is a reliably usable signal available from a tower. A repeater cannot produce service where none exists.

If the available tower signal is at or near the threshold of usability, the repeater system will not be helpful, and it will likely introduce degradation that will break the link budget (the allowable degree of degradation before communications are lost). In other words, using a cellular repeater where there is not adequate signal to be found from a cellular tower not only will not be effective, but can make the poor cellular signal worse.

Weak signals, noise, and link budgets

How can it make something that barely exists worse? All amplifiers introduce some added noise to the cellular signal. Despite boosting the power of a weak signal, the added noise can break the link budget even with the use of LNAs.

In any radio system, if the signal to noise ratio (SNR) falls below certain limits (meaning having a larger amount of noise than usable signal), all the amplification in the world will not help to carry on a conversation or send data. The signal will simply not be decodable. Making the choice of where and how to apply a repeater is every bit as important as which one to choose. Also consider seasonal effects, such as a tree near the cellular tower that will further reduce available signal strength during spring and summer months.

Installation issues

Another consideration is how the repeater system is installed. Any amplification system will oscillate, or become a source of interference, if improperly applied. Think of a singer on stage who gets too close to the speakers with the microphone, resulting in howling and squealing from the speakers. This effect can similarly happen at the radio frequencies used by the cellular equipment if the repeater’s antennas point at one another or can reflect signals at each other. The result is channels becoming jammed with interference, making them utterly useless. Such a situation is also a flagrant violation of FCC rules and cell carrier policy, so therefore illegal. Any repeater installation must be carefully designed and implemented so that any instability or oscillation conditions are prevented. This is mandated by law, and hefty penalties are common for noncompliance.

Cellular repeaters that are commonly available in the mass-market provide enhanced cell coverage inside buildings, where the uplink antenna is outdoors and the downlink antenna is indoors. In such installations, the system benefits from the path loss, or isolation between the inside and outside antennas, provided by the signal absorption and reflection in the building walls. This isolation reduces the likelihood of system instability. Interestingly, this isolation is the reason a repeater is needed in the first place; rebar, metal, some coated glasses, water, and other materials can be detrimental to wireless transmissions. The radiated energy of the tower signal is insufficient within the premises without the repeater, so the repeater is applied to bring the signal in and supply service to the User Equipment within the building. Similarly, the repeater allows the user equipment to have a path to the outside where it has a chance at being “heard” by the tower.

How do I choose a cellular repeater?

There are many examples of repeaters on the market. Most repeaters are targeted to home users who need to improve in-home cellular coverage, so contractors looking for repeaters to improve cellular dead zones in their shops/yards should carefully evaluate their strength and features

Also consider where repeaters will be installed. While installation outdoors presents unique challenges, it is certainly possible to achieve an outdoor installation that provides adequate coverage provided one can find a high spot with a line of sight to the tower. Mounting a directional high gain donor antenna pointed at the tower and away from the area to be served by the boosted signal is the recommended method for achieving a successful outdoor installation. This donor antenna must be placed sufficiently far away from the area that needs boosted service to avoid feedback from reflected signals in that area. The gain of the amplifier must be selected to provide adequate service in the target area while avoiding feedback from the distribution antenna back to the donor antenna.

Suggested options for cellular repeaters

Disclaimer: Tenna has not evaluated the above systems. It is up to the end user to decide the need for a cellular signal amplification system and to implement such a system per the rules and regulations specified by the FCC and the cellular signal providers.

References:

• JD Teck: Outdoor repeater supplier & contractor Better Cell Service Outdoors | Outdoor Cell Phone Boosters ~ JDTECK
• Typical outdoor antennas: Outdoor Antennas | Cell Phone Booster Antennas | weBoost
• Pre-cellular mobile telephony: Telephone World - Pre-Cellular (MTS & IMTS)
• Cellular Basics: https://en.wikipedia.org/wiki/Cellular_network
• Oscillation & Overload in cell repeaters: https://www.wilsonamplifiers.com/blog/oscillation-and-overload/