Distributed Antenna Systems
- 11.1 DAS Business Model
- 11.2 Life Safety and Emergencies
Cell phones are an important part of the way we live, work, entertain, communicate, and interact. There are almost as many cell-phone subscriptions (6.8 billion) as there are people on this earth (seven billion). In 2013 there were 96 cell-phone service subscriptions for every 100 people in the world (information from the United Nations' telecommunications agency). A subscription doesn't mean that everyone has a cell phone; penetration rates in wealthy countries exceed 100% because some people have multiple phones and cell subscriptions. But even in developing and poor countries, the penetration rate of cell phones is around 90%. Africa has very few fixed-line telephones with a rate of 1.4 subscriptions per 100 people, but has 63.5 cell subscriptions per 100 people.
Several studies have profiled the use, behavior, and bond of a smartphone user and the device. A study of 2,000 smartphone users indicates that the average cell phone user reaches for their phone at 7:31am in the morning, and checks personal emails and Facebook before they get out of bed. Incredibly, 40% of cell phone users admit to feeling lost without their device. Another study indicates that the average smartphone user checks their phone 150 times per day.
With cell phone penetration around 90-100% and studies showing that people spend 80-90% of their time indoors, obviously cell phone coverage in buildings is critical. 80% of voice calls and 90% of data usage is indoors. Some buildings have a poor quality cell phone signal, with the result being dropped calls and spotty coverage. Very large facilities, tall buildings, facilities with a high density of occupants, and buildings with a steel roof or steel/aluminum siding, or brick buildings, as well as concrete and steel joists may affect cell signals. Low-E glass windows, which typically are used to reduce energy consumption by minimizing the amount of ultraviolet and infrared light that can pass through also reflect radio waves and cell signals, creating reception issues with in-building wireless coverage.
Other weak wireless situations may be related to a lack of capacity of cell coverage where demand cannot be met. These facilities may be large public venues such as stadiums, convention centers, corporate offices, multitenant high-rise buildings, university campuses, hospitals, manufacturing facilities, upscale hotels and high-rise condos, casinos and federal and local government facilities, as well as rail and subway systems.
The major issues with cell coverage in buildings are either weak signals from the closest cell tower or lack of capacity. The remedies are different for these two problems. Weak signals are typically addressed by strengthening the existing signal from the nearest cell site or tower, referred to as a repeater-based solution. This entails an outdoor antenna on the building pointed toward the nearest cell tower site. The antenna receives the signal from a cell tower and sends it through a cable to a bidirectional amplifier (BDA) that strengthens or boosts the signal, then relays and amplifies the RF signal traffic between the remote base station and the mobile radios.
Figure 11.1 Distributed antenna systems.
The issue with increasing cell capacity is typically addressed by installing smaller antennas in the building. These are active systems referred to as a distributed antenna systems (DAS). Distributed antenna systems are a network of amplifiers and antennas throughout a facility that are connected with copper or fiber cable to a hub. It provides voice and data wireless service within a geographic area or structure.
The headend of the DAS may allow for multiple wireless providers to connect radios at various radio frequencies. A neutral host DAS allows multiple wireless providers to use the network at the same time. The DAS essentially feeds smaller cell antennas that cover the buildings' zones or floors. A distributed antenna system may be deployed indoors or outdoors. For outdoor DAS, some state Public Utility Commissions have require the utility to allow Distributed Antenna Systems in the utility right of way.