How to improve indoor coverage ?

Today, users expect more and more quality indoor coverage. Whether in transport, shopping centres or other areas, they can no longer tolerate the lack of regular and seamless 4G coverage, at least in large cities such as Paris.

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What is indoor coverage?

Providing indoor coverage, or "inside buildings", means providing coverage of areas (e.g. basement areas, buildings with thick walls, etc.) that are not naturally covered by conventional networks.

Indeed, the propagation of waves emitted by conventional outdoor antennas can be disrupted by obstacles and certain materials. For example, if a home is well insulated, its insulation will reduce mobile indoor reception.

Insufficient natural cover

As mentioned above, within a building itself, the so-called "natural" mobile coverage, which results from the emission of radio waves by external relays, cannot be guaranteed.

Indeed, the attenuation of the signal depends on several factors: distance of the relay from the building in question, topography of the premises, overground, built in dense urban areas and the very nature of the construction. This masking phenomenon has become more pronounced in recent years with the emergence of new environmental standards, limiting the penetration of the signal into buildings.

In addition, even if the level of coverage could be satisfactory due to the immediate proximity of a relay, it is often observed, particularly in dense urban areas where traffic is high (e.g. the Parisian metro), that the performance obtained in buildings is degraded, particularly in terms of data flow rates. These phenomena can be explained by a saturation of the external relays.

For all these reasons, the deployed external relays cannot guarantee a good quality of service for mobile applications within buildings, especially in dense urban areas.

Indoor coverage, what are the stakes?

Why are we now talking about connectivity defects in what could be called "white indoor zones"? This is because today, a third of French people use their smartphones in shopping malls, 40% say they use them in transport, and 60% at work (Omnicom statistics; SFR Group; PHD; Baromobile 2015). In total, 80% of all telephone calls would be made indoors. Differences in connectivity quality across locations can therefore affect users, both business and residential, who are hindered in their activities and productivity.

The increase in the number of smartphones, the increased portability of objects, but also the increasing use of comfort sensors (e.g. temperature, maintenance, etc.) may also explain the highlighting of this issue: most of the technologies that have emerged over the past decade require the implementation of reliable and seamless network coverage in order to exploit their full potential.

Indoor coverage is therefore a new connectivity issue, which requires solutions that do not exclude any territory, any user, in order to support the growth of our country.

What solutions to improve indoor coverage?

Several solutions exist to meet the challenges of indoor coverage, both for voice and data services, and for individuals and businesses.

The Distributed Antenna System (DAS)

The DAS (Distributed Antenna System) is a so-called "all-active" solution, which makes it possible to cover sites with large surfaces and/or buildings with several floors.

This solution consists in creating a mobile network within a building, independently of the external network. The broadcast antennas are therefore active and have a similar appearance to Wi-Fi hotspots. The intermediate equipment between the core network and the antennas operates in a similar way to routers.

Developed very recently to provide mobile phone service coverage for commercial buildings. They are not intended to systematically replace traditional solutions, but rather to meet a need for mid-size structures (e.g. office buildings).

The advantages of the DAS:

  • The DAS guarantees a high level of data and voice service, regardless of the number of users
  • Low maintenance requirements
  • Good management of mobility (handover)
  • Single-operator or multi-operator In the case of a multi-operator choice, a single antenna will be sufficient to support all operators (via shared deployment, coaxial, or optical fiber).


The disadvantages of the DAS:

  • High cost: the DAS requires the installation of many radio equipment that must be connected to an optical or coaxial network
  • Complexity related to connections: each radio element must be connected to the central hub, which requires a sufficiently sophisticated "cable management" system (e.g. integrating cable ducts into the building structure itself)
  • Low scalability: it is difficult to upgrade a DAS, due to the need to change all radio elements, base stations, operators and standards
  • An unattractive business model for operators (unless it allows an operator to gain market share)
  • A strong dependence on one or more operators.


The cellular amplifier

Another solution for indoor coverage can be the cellular amplifier, or repeater. This amplifier makes it possible to reinforce the weak initial reception of the external mobile signal by repeating it inside a building. It therefore consists of a receiving antenna (usually located outside) and a transmitting antenna, both of which are connected by a wifi connection.

However, this type of solution is subject to operator authorization. However, they see in these devices a source of interference to their external relays, especially in dense areas, because the repeater is likely to generate noise on the rising track and thus degrade the performance and proper functioning of the relays.

The advantages of the cellular amplifier:

  • Low installation and maintenance costs
  • Immediate commissioning time
  • Single-operator solution.


The disadvantages of the cellular amplifier:

  • Risk of traffic saturation in case of high density
  • Low level of scalability
  • Dependency on operators on their external coverage and ownership of the solution (e.g. antennas to be installed).



FEMTO, or FEMTOCELL, is a relatively recent product that has been developed to address coverage gaps in small spaces, such as a meeting room, a work platform, or an auditorium.

In concrete terms, it is a box that connects to the fixed Internet network to transmit a low-power signal (100 mW maximum). The building must be eligible for a fixed broadband offer (512 kbit/s or more), but this criterion is already met by 99.7% of fixed lines. If its operation does not require the intervention of professional installers, to benefit from it, it may be necessary to declare in advance, on the operator's Internet space, the different mobiles to be connected to the equipment.


With this technology, telephone calls or web page consultations on the smartphone will be made via the fixed Internet line (ADSL or fibre) and no longer via the mobile network.

The advantages of FEMTO:

  • Adapted to high voice and data needs on targeted areas
  • Low deployment cost
  • Compatible with the future 5G
  • Single-operator solution.

The disadvantages of FEMTO

  • Risk of multi-cellular interference
  • Dependency on an operator (possible but complex multi-operator mode)
  • Frequent outages possible due to lack of assured mobility between this independent network and external relays
  • Solution not very encouraged by operators, except for private individuals.

Wi-Fi and voice over Wi-Fi (VoWi-Fi)

The deployment of a Wi-Fi architecture

Wi-Fi is a set of wireless communication protocols governed by the IEEE 802.11 group of standards (ISO/IEC 8802-11). A Wi-Fi network allows several devices (computer, router, smartphone, Internet modem, etc.) to be connected by radio within the same computer network, in order to allow data transmission between them.

The advantages of Wi-Fi:

  • An easy to set up, inexpensive mobile connection available on all connected media (e.g. TV, tablet, computers, etc.)
  • Sufficient capacity to ensure good coverage in areas of high density and/or consumption, and at the deepest end of buildings
  • Not necessarily dependent on an operator operating for a company.
  • Scalability of the solution and complementarity with the future 5G already proven
  • Independent of the mobile network
  • Possibility to connect most devices in a network
  • Possibility to separate internal and guest Wi-Fi services and to encrypt communications end-to-end.

The disadvantages of Wi-Fi:

  • Limited mobility between Wi-Fi spots;
  • No automatic connection to the cellular network;
  • Possible decrease in throughput in case of heavy traffic
  • Risk of interference in dense areas
  • Impossible to prioritize flows
  • Model not very interesting for operators if companies are the managers

What is VoWi-Fi?

VoWi-Fi, or voice over Wi-Fi, is the use of the Wi-Fi network to benefit from mobile services and thus carry voice and not just data.

More precisely, calls made via a smartphone will therefore be made transparently over the Wi-Fi network and no longer over the mobile network, while allowing call continuity between these two networks. However, voice over Wi-Fi requires a compatible phone because calling/SMS will be processed without additional application on the operators' mobile network core.

This technology has recently benefited from the VoLTE (voice service on the 4G network) feature: customers affected by this update can now make all their phone calls over a recorded Wi-Fi network for better quality, this is the "Wi-Fi Calling" feature. The cut-off rate observed by operators is a maximum of 5%.

While this solution has the advantage of being able to compensate for a lack of mobile coverage in an area already covered by Wi-Fi, it has disadvantages:

  • It is not seamless: you must first register on a Wi-Fi network to enjoy it
  • The quality of voice communication depends on the design of the Wi-Fi network and the number of people connected
  • There is a risk of interference due to free access to the Wi-Fi frequency bands.

Thus, the user experience is not guaranteed, and this solution is more of a one-time palliative than a sustainable approach.

Other complementary solutions

More capacitive terminals

The evolution of the standard has made it possible, over the years, to offer higher speeds and new uses have developed (e.g. the interoperability of Wi-Fi networks).

The objective here is therefore to facilitate mobile Internet access for the general public by offering increasingly high speeds. The latest consumer evolution is the 802.11ac standard, which offers a theoretical throughput of 1,300 Mbit/s using 80 MHz channels in the 5 GHz band.

Unfortunately, this evolution has also been accompanied by an increase:

  • Investment and maintenance costs
  • The size and weight of the bollards.

These disadvantages rather encourage caution when deploying Wi-Fi solutions.

A more predictive design

In order to meet more precise sizing and performance requirements, the actors responsible for implementing Wi-Fi networks are increasingly using:

  • Design studies involving simulations of indoor coverage;
  • Performance reports using trace tools.

These tools make it possible to provide guarantees on the achievement of indoor coverage objectives.

The Internet of Things

One of the promises of the Internet of Things or IoT networks, and in particular narrowband networks (LPWANs), is to make it easier to cover buildings from the relays of the external network.

This is true to a certain extent, because in the case of large buildings, this coverage remains difficult.

To overcome these problems, network operators are occasionally required to deploy micro-relays in buildings. This solution remains inexpensive as the micro-relays are able to provide coverage over very large areas.

Some practical tips to improve indoor coverage


The tremendous adoption of 4G technology now makes it essential to integrate mobile networks into all building construction or redevelopment projects.

It is therefore important to study the implementation of mobile networks as soon as possible when a construction or redevelopment project is initiated. Good anticipation facilitates the integration of network infrastructures.

Listening to needs

It is essential to collect all the needs and expectations regarding wireless networks at the start of a project, and to determine the dimensioning data for each of them (e.g. traffic, surface area, etc.).

Streamline decision-making

Several types of solutions exist and must therefore be considered. Similarly, several types of potential providers exist and must be consulted.

Joint processing of network implementation projects opens up opportunities for synergy, whether it is the sharing of network equipment (e. g. antenna, fibre, etc.) or the sharing of development equipment (e. g. technical room, cable tray, etc.).

It also makes it possible to apprehend as soon as possible any problems of electromagnetic cohabitation (EMC) that could degrade the performance of networks and to propose appropriate precautionary measures.

The lifespan of a real estate project is generally around fifteen years. The implementation and operation of mobile networks must be based on an equivalent period of time. It is therefore necessary to compare solutions based on their cost price over this time horizon, as well as by anticipating developments and the treatment of obsolescence.

External sources

Tactis - Directeur associé - Benjamin Fradelle- Aménagement numérique des territoires

Benjamin Fradelle

Associate Director
Since 2002, Benjamin Fradelle has been developing expertise in digital spatial planning, both in terms of defining the strategy of local authorities and in the technical and economic approaches associated with public initiative networks.

Contact Benjamin Fradelle

A question about Indoor coverage ? Need to remove doubts in view of a future project? Send an email to Benjamin Fradelle, Tactis Associate Director.

Tactis - Directeur associé - Benjamin Fradelle- Aménagement numérique des territoires

Benjamin Fradelle

Associate Director Tactis
Since 2002, Benjamin Fradelle has been developing expertise in digital spatial planning, both in terms of defining the strategy of local authorities and in the technical and economic approaches associated with public initiative networks.
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