A mobile phone is connected to a mobile network tower through mobile signal. However, sometimes mobile signal is inhibited or blocked by trees, hills, construction materials or bad weather. When this happens phone calls are dropped, voice quality is reduced, or a slow data connection is experienced by the mobile phone user.


CEL-FI products improve signal between a mobile phone and a mobile network tower, allowing you to have clear voice conversations and a stable data connection inside buildings. The CEL-FI solution takes the mobile signal that is available, amplifies it and rebroadcasts it in the areas where it is required.

At its most basic, each CEL-FI system consists of a donor antenna, a mobile signal booster and a server antenna. The donor antenna is placed in the area where the strongest native signal can be received from the carrier network (signal levels as low as -120 dBm are acceptable); this is usually outside or close to a window. The donor antenna transmits the native mobile signal to the CEL-FI mobile signal booster unit which amplifies the signal. The server antenna communicates wirelessly with the mobile signal booster and broadcasts the enhanced mobile signal in the interior of the building with significantly enhanced signal levels, thus enabling better quality calls and greater data throughout.

In larger or more complex environments additional antennas can be used to increase the coverage area, and if necessary multiple systems may be combined.


  1. CEL-FI by Nextivity offers the only range of repeater solutions that are compliant with Ofcom’s new licence-exempt requirements (IR2102) and legal to use in the UK. CEL-FI solutions are also licence-exempt under ComReg requirements for Ireland.
  2. CEL-FI Signal Boosters work to strengthen poor mobile signal coverage in the home and office by up to four times, offering a massive 100dB gain (GO X, QUATRA units) which is 1000 x stronger than traditional boosters.
  3. The Specific Absorption Rate (SAR) is comparable to that of a smartphone, making them equally harmless to human health and the environment.
  4. They boost 3G / 4G / 5G signal at the same time, most traditional boosters only cover either 3G or 4G but not both.
  5. CEL-FI solutions enhance mobile signal in indoor areas from as little as 80 m² / 1,000 ft² up to 11,600 m² / 125,000 ft². Multiple units can easily be combined to cover larger areas.
  6. Boosting mobile signal in the way CEL-FI units operate, apart from reduced dropped calls, also means improved voice clarity and streaming as well as faster downloads and improved battery life for the devices benefiting from them!
  7. A strong mobile signal has become a necessity, while the issue is not being resolved over time. Anyone living or working behind thick walls or heavy insulation, in basements or in rural / remote areas will be most likely facing mobile signal issues.

With an ever-increasing demand for legal solutions to mobile phone signal problems, this programme is the ultimate service choice!


CEL-FI by Nextivity offer licence exempt mobile phone signal boosters to boost 3G / 4G / 5G for voice and data for any UK network, including the four main Network Operators (EE, Three, O2 and Vodafone) as well as all hosted Virtual Network Operators like BT Mobile, giffgaff etc. Please see our Networks page for more information.

Find out more on the CEL-FI products and see the full range here.