DAS


Distributed Antenna System

Utilized to Augment RF Signals for Cellular Networks and Public Safety. Wireless Coverage and Capacity have become the 4th Utility.

 

Going Green has a drawback. Low e glass installed to provide better environmental control by blocking the power of the sun’s rays also blocks physical radio signals. This disrupts first responder radio’s and cell signals. The absence of PS signal and the increasing reliance on cell coverage has resulted in many real estate projects having to scramble for certificate of occupancy and to provide adequate cell phone coverage.

New Construction will not get a CO if the Fire and Police Radios do not pass acceptable testing.

Cellular:

DAS was originally used as a method of getting cellular coverage in to areas where macrocells (transmissions from towers) could not reach because the RF waves were being blocked by high rise buildings.  

Sometimes municipalities would require DAS in lieu of zoning a microcell. As cities became completely built out, carriers moved from using DAS for adding coverage to increasing capacity with it.

DAS systems are used both indoor and outdoor.

Today, you will find outdoor DAS in the downtowns of big cities, on college campuses and major football stadiums. The antennas are being integrated and deployed in bus shelters, street lights, signage, artificial rocks and other aesthetically pleasing concealments.

DAS is also used for coverage indoors (IDAS) in sporting arenas, hospitality venues and in tier-one office buildings. The current challenge is how to cost justify DAS systems in Mid Size office buildings, the Middleprise.

There are three types of IDAS: passive, active and hybrid. A passive IDAS uses coaxial cable to distribute the RF signal to each floor of the building without the help of electronic components. Using couplers, splitters and dividers, a fraction of RF signal is diverted to each level.

 

 

Base Transceiver Station (BTS)

 

 

Image from BICSI Update Conference

DAS or distributed antennas systems consist of a base transceiver station connected to several small antennas mounted at lower levels strategically spread across a certain area.

The cellular signal is then distributed and broadcasted through the antennas instead of being broadcast from atop a tower. The BTS is connected to terrestrial internet connectivity preferably fiber optic data circuits. When DAS is implemented for Capacity vs. Coverage issues connectivity of greater than 100 Mbps is necessary. Sporting Events generate Terrabytes of data in a few hours.

Commscope vision of the future of BTS DAS.

 

 

Image created by DAIS Technologies a leading communications provider of Smart Cities.

In an active IDAS, the RF signal comes in from the donor antenna on a coaxial came to the headend where it is digitized through an optical conversion unit and transported via fiber-optic cable to a remote amplifier unit (RAU) on each floor, which convert the signal back to RF and amplifier the signal and then transmit via coaxial cable to the antenna.

Similar to the active IDAS, a hybrid DAS uses passive elements (couplers splitter and dividers) to attach multiple antennas to the active element (RAU), thus increasing the horizontal DAS reach on each floor.

Funding Models

DAS systems have been traditionally funded by the cellular carriers or by a neutral host providers and were largely only deployed in venues of greater than 250,000 square feet and where a mass of people would be congregating in bursts of activity. Stadiums, Airports, Amusement Parks, but they are not interested in smaller facilities. As most of the major sporting venues have been built out, OEM’s are developing a new business model and low-power DAS technology to penetrate the second and third-tier enterprise market. The key to the business model is less capex and opex for the DAS equipment.

  • - Neutral Host owns the system and rents space on it to cellular carriers
  • - Owner financed
  • - Carrier provided

Other methods of reducing costs of DAS and maximizing usage of deployments include centralized DAS where the DAS base station hotel and the base-band processing is centralized and aggregate for a number of radio nodes. This architecture reduces on-site real estate expenses and allows the shifting of radio system capacity as needs shift during the day. For example, radio capacity could be moved from the football stadium after the game to the bar district.

 

Future Topics:

  • Deployment Best Practices
  • Outdoor DAS and Regulatory concerns
  • PIM Testing

 


 

 



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