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Working Principle Of Distributed Antenna System
Oct 12, 2018

The problem with wireless devices is that within a facility or campus, each wireless application usually requires its own wired infrastructure access point and other wireless transmitters. The result is a redundant infrastructure. This infrastructure creates a chaotic RF environment, which hampers wireless applications. A shared broadband indoor passive distributed antenna system (DAS) brings a new order to this chaotic environment, thus making high quality wireless services possible. This antenna system can support different kinds of wireless technology provided by different manufacturers in a wide frequency range.

The core of passive antenna is an integrated access device (IAD). Cellular/PCS, bidirectional radio and paging systems are connected to the IAD via a base station or off-air repeater. Various services are grouped together and filtered, and then transmitted using backbone wires or relays (typically 7/8 inch coaxial cables) that connect the floors of the building.

A well-designed antenna array is transmitted from the trunk on each floor to transmit RF energy. The antenna array includes radiation coaxial cable, standard coaxial cable, directional antenna and omnidirectional antenna. Antenna arrays are configured on each floor to provide coverage in a particular area and to keep RF signals within the facility.

Because applications such as wireless local area networks, building automation and security systems usually serve a local area, they are added to passive DAS layer by layer. Local applications connect by using portal devices like IAD. Using portal devices to integrate RF energy from multiple sources, these signals are added to the antenna array. This method requires detailed site investigation and in-depth understanding of building structures and materials.

A passive DAS can handle multiple frequencies used to integrate voice and data, building automation, and security services. Base stations and/or cable repeaters from multiple service providers are centrally located in a main telecommunications room. The access points are centrally located in the middle distribution facility area of each floor.

A stack zone can provide coverage for 500 thousand square feet of space. As needed, fiber optic repeaters provide signals for more areas requiring a larger facility of IAD.

In fact, a passive DAS is a huge, very efficient antenna that distributes RF energy evenly across the building. DAS does not need amplifiers or repeaters. All parts of the system are passive: they are non mechanical and do not require power supply. Therefore, the system does not require monitoring and has high reliability. It is like distribution and HVAC (heating, ventilation and air conditioning) distribution system, is a public system.

DAS follows the IEEE 802.11 standard. They also support standards such as CDMA, GSM, IDEN (integrated digital enhancement network), TDMA, GPRS and UMTS. They can support the continuous broadband frequency range from 400MHz to 2.5GHz. This frequency range covers the vast majority of indoor wireless applications and emerging technologies.

At the same time, a single infrastructure supporting multiple applications will reduce interference and provide reliable wireless coverage within a building.

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