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Das

What is a distributed antenna system (DAS)?

A DAS is a network of relatively small antennas installed in an area such as a large building that works a signal repeaters. This means there are no isolated spots with bad network coverage.  The technology has been around for over twenty years and in the last decade undergone great innovation with much more innovation on the way. To move a cell service to expand coverage and capacity inside a large building or outdoor network a provider needs a distributed antenna system.

The antenna’s are connected to a central controller which is attached to the wireless carriers network. The DAS can be either active or passive. An active system works by passing the signal through fibre cables. And the passive system allocates the cell signals from the roof antenna.

Deploying and installing a distributed antenna system is a project that is labor intensive and requires specialist technicians. DAS systems are generally installed in large buildings or areas to have cell signals spread evenly and provide voice and data services. Most high rise buildings will need a DAS for instance.

How A DAS Works

image via wikipedia


A distributed antenna system sends a receives cell signals on a carrier frequency. The DAS network improves voice and data connectivity for users. There are two sources;

 

  1. Signal Source

 

This is the signal that distributes from a fed signal. The signal feeding into the DAS comes from one these typical sources. Off air – an antenna of roof, on site base transceiver station and small cells.

 

  1. Distribution System

 

When the cellular signal is received it needs to be distributed throughout the building or area. The types of distribution systems include active – fibre optic or ethernet cable, passive, digital and hybrid.

 

The main reason for installing a DAS is to provide coverage and capacity needs that could not be met without it. That may be because the area has too many people using the network or building materials interfering with the signal, or even too much land between the user and signal.

 

The company providing and installing the DAS will be able to advise on which technology will get the best coverage and capacity suited to the site.

 

 

DAS Types

 

Off-Air

 

An offer air signal referred to also as a repeater uses a roof antenna to transmit signals from the carrier. This is one of the most utilized systems by businesses. As long as the signal from the roof antenna is strong this is the most cost effective DAS to deploy. This is because it is simply extending the coverage of the network and is quick to install. It will not add any capacity to the cell signal.



Base Transceiver Station (BTS)

 

This refers to the technology located inside the cell tower that generates a cell signal. Using a fibre network connection the DAS can connect to multiple base transceivers. It increases the capacity for voice and data. Ensuring thousands of users can access data simultaneously. This is more expensive to deploy than the off-air DAS and will take longer to deploy. The benefits include providing as  much capacity as needed with high performance.


Small Cells

 

This is a newer technology compared to the above DAS networks. It works by creating a secure source back to the carriers network through an internet connection and generates a wireless signal. The small cells come in categories; femtocells, picocells, nanocells, and metrocells.

 

The coverage area provided by small cell is around 6,000 to 20,000 square feet. It is an expensive DAS network compared to off-air but again it depends on what a DAS is needed for as to what system is best. Used as a signal source for DAS, the small cell will provide excellent coverage and is a lower cost than a BTS network. The DAS small cell must have a reliable backhaul internet connection to be effective. Another bonis for the DAS on small cells is it is very fast to deploy.

 

Passive DAS

 

Moving onto the signal distribution a passive DAS works by using coaxial cables, splitters and couplers to distribute a signal. The signal distribution must be close to the cell antenna as the further it moves away the more network loss will occur. The cost is kept down as there is no analog conversion of digital and less equipment is needed.

Active DAS

 

This works by converting analog frequency transmissions from the signal to digital signal for distribution. The technology converting the signal is called a master unit and it can convert from one signal or multiple signals. The digital signal travels on either fibre optic or ethernet cables. There is no constraint as the cables can be run unlimited and are easily expandable for any expansion needed.


Hybrid DAS

 

A hybrid DAS is passive and active. It uses coaxial and cable for the distribution system. The hybrid system is less cost than a full active DAS and more than a passive as it does require some cabling infrastructure and more time to deploy.

 

Digital DAS

 

This is the newest technology in the DAS space. It is the CPRI (common public radio interface) which allows a base band unit to communicate with the DAS master unit an onto remote units and needs no conversion to analog.



The future of DAS technology is going to be integral to generate better coverage and capacity for voice and data services. Its best to get advice and a deployment plan from leading DAS installers and innovators. That way the best DAS suited to specific needs can be installed and be the most cost effective option.

 

We have sourced the above information from years of production and delivery. We would like to cite the following websites as well:

https://en.wikipedia.org/wiki/Distributed_antenna_system

https://www.aflglobal.com/Services/What-We-Do/DAS.aspx

http://rfisolar.com.au/media/Westfieldcasestudy.pdf