Indoor mobile coverage
Indoor mobile coverage
Today, communication is more and more based on wireless techniques. In Finland, people want to use mobile phones and internet everywhere, even in trains. However, there are some places which cannot be reached by radio frequency signals. In these cases, a so called DAS technique, Distributed Antenna System, comes to help.
Hospitals, parking garages, shopping centers, business centers, new apartment buildings – these are examples of places where indoor mobile coverage may often be weak. Reasons for the weak signal are many, one of them being a wall structure strengthened by metal, another could be energy efficient windows used for better thermal insulation.
Sufficient indoor mobile coverage is important not only to regular mobile phone users. It is crucial to the public authorities who use TETRA network that has to work both on the ground and underground. For example, Finland’s national public service broadcasting company (Yle) has a legal obligation to make sure that the authority releases can be distributed by radio and that they reach people even in the highway tunnels.
The solution is an indoor coverage network
Securing the proper flow of radio signals in places with challenging conditions is basically quite simple: you catch the desired frequencies from several base stations, transmit the signal to a repeater and then distribute it indoors via an antenna network. However, carrying out this in practice requires expensive special components and careful planning, as there are plenty of frequencies and the power needed is massive.
Frequencies must not interfere with each other and the returning signal to the base station must not block the base station. Mistakes in assemblies could cause serious damage, therefore only authorized companies are allowed to perform these installations.
Orbis Oy represents manufacturers that are specialized in the Distributed Antenna System technology. Orbis offers a complete range of components to indoor networks, including also customized, application specific assemblies manufactured in Orbis’s own production.
Browacom Oy, located in Haukipudas, Finland, is one of the leading companies in network design and installation. Their specialist, Tero Lepistö has led demanding RF design projects, one of them being the Highway 1 Tunnels between Turku – Helsinki.
Signal from multiple sources
Each telecom operator, as well as the authorities, have their own base stations in different directions. All buildings must have several donor antennas installed outside for catching signals in order to have proper indoor mobile coverage. Base station antennas are set up to a certain direction, for that the two-way signal quality would be as good as possible. Another way of bringing the signal in to the building is by cabling, which today usually means optic fiber cables.
The indoor antenna network is in many cases broadband, covering for example TETRA, 450MHz network and all telecom operators’ frequencies. Often, the network also covers WiFi.
The antennas are usually omni-directional and they look similar to the indoor fire alarms. In tunnels and corridors antennas are often so called radiating cables, that can be installed behind the ceiling so they are hidden from eyes.
Today, the network components on the market are more advanced and safe to use even in the hospitals, where use of mobile phones was forbidden in the past. A strong mobile network enables phones to operate with less power and thus they radiate less.
Some new buildings have suffered from poor indoor mobile coverage, which has caused astonishment and even worse, some reported near-miss situations. In a new nursing home an elderly resident had an attack of disease at night and called for help by using a wrist alarm device. However, the alarm never reached the nurses, as the mobile signal could not pass the wall structure. Luckily, at the same time one of the nurses was making a routine check on that floor and found the patient on time.
The new building methods for apartment buildings highlight energy saving, which leads to the usage of energy saving windows. These type of windows effectively block radio signals. Another challenging material, from the radio signal point of view, is aluminium based vapor barrier used for saunas and bathrooms. Nobody wants to give up the good thermal insulation, so the building designers are forced to consider the indoor mobile coverage solutions, too.
Also, the legislators set requirements for the mobile coverage and this obliges for example hospitals and shopping centers to make sure they follow up on the requirements. The good thing is that there are functional and cost-efficient solutions available.
- Orbis services for in-building networks >>
- Case Story: Järvenpää Social Service and Health Care Center >>
- Case Story: The Tunnel of Tampere >>
- Tampereen rantatunneli >>
Text by: Pentti Niemi
Tero Lepistö at Browacom Oy has expertise in designing indoor mobile coverage solutions. Photographer: Pentti Niemi.
In Turku-Helsinki highway tunnels the antenna is a tunnel long radiating cable. Photographer: Matti Rautanen.