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Skip to 0 minutes and 7 seconds Providing wireless services inside buildings is not a new requirement. For years, operators have been dealing with the challenges of wireless coverage in areas where concrete walls and glass windows block radio signals. But in-building wireless service today is more about providing capacity than just ensuring reliable coverage. Why? Foremost, it’s due to smartphones and the easier accessibility to data-intensive applications that people use them for. When close to 80 percent of mobile sessions occur indoors, it’s easy to see why providing more in-building wireless capacity is a concern.

Skip to 0 minutes and 54 seconds Wireless indoor services pose a challenge to operators in three different aspects.

Skip to 1 minute and 0 seconds Coverage: signals from cells located outside buildings do not penetrate easily into all indoor areas. Different construction materials block most of the radio signal, which creates coverage holes inside the buildings.

Skip to 1 minute and 16 seconds Interference: the majority of the base station antennas have side lobes that leak the radio signals also upwards towards the sky. This creates a scenario in which high-rise buildings end up receiving multiple signals from many sources, some near them and some from sites further away. This creates interference in the sense of RF pollution, which has a direct impact on the quality of service that can be offered to the users residing on the higher floors.

Skip to 1 minute and 49 seconds Capacity: the radio network is designed to provide coverage based on macro sites, usually located outdoors and intended to serve users in close vicinity to them. Careful planning has to be done so that these outdoor macro sites will also be able to support indoor traffic. In the previous slide, I mentioned that different construction materials block most of the radio signal, which creates coverage holes inside the buildings. One of these materials is low-emissivity glass. This is coated glass that reflects infrared light, which is heat energy, but also reflects and attenuates radio waves, causing significant in-building coverage issues. Concrete is another material that is widely used in the building industry and greatly attenuates the radio waves trying to penetrate it.

Skip to 2 minutes and 46 seconds Thus, underground basements or garages or buildings with many internal walls will have very poor indoor coverage from external macro sites. The greater the distance of the building from the serving site, the lower signal strength the user will get indoors. All these present more stringent requirements on signal strength and signal quality for supporting indoor users. Different solutions are deployed to provide wireless services indoors.

Skip to 3 minutes and 18 seconds These include: Distributed Antenna Systems (or DAS), Femto cells and small cells, WiFi access points, the likes of which all of us have at home. In this lesson, we will focus on the DAS solutions and how we can optimize them. A Distributed Antenna System is a network of antennas that are installed all across the building interior and are connected to each other by means of coaxial cables or fiber-optic cables. These antennas are usually small in size and are meant to cover the area around them. Distributing these antennas across the inner space of a floor of a building will provide good indoor coverage in that floor. The internal antenna network is connected to a single Radio Base Station.

Skip to 4 minutes and 10 seconds Additional indoor solutions may include also the use of repeaters or signal boosters inside the building. Here, we see the architectural concept of DAS. On the left-hand side, we see a conventional macro site, in which the sector antennas are installed on a tower and connect via cables to the base station. On the right-hand side, we see the DAS setup, in which an antenna system is connected through dedicated DAS equipment to the base station. Each sector has a separate antenna system and they are all connected through a DAS splitter or concentrator to the base station.

Skip to 4 minutes and 53 seconds The DAS splitter or concentrator can be either a passive component, just splitting the RF signal between the sectors, or an active component, which also provides capabilities to boost the signal or process it in other ways, both in the uplink and downlink. DAS has several benefits for the operator in those areas where it is deployed. Providing the required indoor coverage allows the operator to serve more subscribers and thus increase the traffic and the revenue. The DAS is usually technology-agnostic and can support multiple frequency bands. One DAS solution can serve several operators in the same building, by connecting to their separate base stations. Distribution of the signals in the DAS over fiber-optic cables assures minimal signal attenuation in the DAS.

Skip to 5 minutes and 52 seconds Note that DAS solutions can also be deployed in an outdoor setup, for example, in open-air sports arena. Here we see some examples of venues in which DAS has been deployed. These include sports stadiums and arenas, airport terminals and hotels, office buildings and shopping malls, as well as university or college campuses and underground transportation tunnels.

Why DAS?

In this first video, we will explore the concept of Distributed Antenna Systems (DAS), when and why it’s used, and learn some related terminology.

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This video is from the free online course:

Introduction to Radio Network Optimization