Technical options for providing indoor mobile coverage

Options for the deployment of indoor mobile coverage include using a small cell repeater or installing a network of antennas, known as a Distributed Antenna System (DAS).

For a small cell deployment, the cells connect to an existing carrier (MNO/MVNO) to repeat their service either via an external aerial or more commonly via a fixed internet connection, such as broadband. Connecting via fixed internet can provide a reliable service.

As the name suggests, small cells are ideal where only a comparatively small area requires coverage. Depending on the installation small cells can also typically only provide one service provider network, however.

As of March 2025 some progress has been made on the development of small cell solutions which provide connectivity to multiple networks, and it is expected that more of these solutions will become commercially available in the near future. If it is a requirement of your indoor mobile solution to deploy multiple network providers, then we advise you contact suppliers to understand their capabilities to provide this through a single small cell.

A variety of small cells are available, with three most common types being:

• Femtocells that typically support up to 16 device connections
• Picocells for up to 64 device connections
• Microcells for up to 200 device connections

Although the technology differs between types of small cell, they all provide similar solutions, with just the range and number of device connections required that need consideration.

If the use case for small cells is primarily for voice, and as Wi-Fi calling (see section below) becomes more popular and easier to use, these smaller devices may slowly fall out of use and may become obsolete.

A DAS is a network of spatially separated cellular antennas used to blanket buildings with reliable mobile connectivity signals. The distributed signal is generated from a signal source. Depending on the type of DAS setup, the signal source can be over the air (such as an antenna), an on-site base transceiver station (BTS), or a  small cell. Overall performance will vary depending on the equipment used.

To deploy DAS, antennas are mounted throughout the area to be covered and linked back to a central management unit. This internal system is then connected to an outside network via either:

• an external antenna installed on the top or side of the building that connects to the outside cell network 
• a dedicated fibre connection back to the carrier
• a small cell

A DAS solution can be set up to provide signals from multiple providers within a building using the same infrastructure and equipment.

How this signal is then fed to the internal antenna system depends on the DAS solution. There are various options, including active, passive and hybrid. 

An Active DAS system can distribute a signal from an external source, whether an antenna or small cell, via fibre or ethernet cabling. This signal is transmitted to nodes, or active antennas which convert external digital signals to analogue and broadcast the signal in the area around them.

As the solution is powered the signal does not degrade when travelling longer distances, so can be suitable for large deployments.

A Passive DAS or mobile booster takes an outside cell signal and delivers it throughout a building using passive components. With a passive system the signal is passed to the antennas via coaxial cable. As signal power degrades the further it has to travel on these coaxial cables the antennas at the end of long cable runs may have a weaker signal.

Amplifiers can be added to boost the signal, but this requires a more complex installation and careful consideration. 

In a hybrid DAS service, components of both passive and active systems can be mixed on the same solution to balance cost, signal strength and complexity of deployment to meet user needs.