What Is a DAS System?


Distributed Antenna systems (DAS for short), are systems comprised of a series of radio heads strategically placed around a targeted location where there is a need for additional cellular coverage. Each of the radio heads within the DAS system are then routed to a communications hub via fiber-optic cable to allow the cell signal to be processed by a cellular base station.

Like small cell networks, DAS networks are typically implemented in locations such as shopping malls, school campuses, office buildings, or larger venues such as sports stadiums and event arenas. In fact, a new DAS network project is currently underway at Houston’s NRG Stadium, being constructed specifically for Super Bowl 51. This new DAS system, consisting of over 800 antennas, is projected to increase the bandwidth capacity over the previous Super Bowl location by a factor of 4!

To put things into perspective, attendees at Super Bowl 50 consumed approximately 16 terabytes of data during the entire event, and with mobile device popularity showing no signs of slowing down, the installation of such a large DAS network is a telling sign that cellular providers expect Super Bowl 51 data usage to exceed 16 TB by a large margin.

Why Do Cellular Companies Use DAS Antenna Systems?

Distributed antenna systems and the like are the preferred methods for expanding network connectivity in certain locations where space is limited and a traditional cell tower cannot be installed. DAS systems are considerably smaller than traditional macrocell or cell tower counterparts, making them much better options for congested, high-volume locations. In addition to taking up less space than traditional cell towers, DAS networks tend to provide better network coverage as well.

What Is a DAS System?

As the distance between a mobile user and the cellular signal grows, the quality of the cellular signal begins to degrade; however, by strategically placing DAS solutions at targeted locations where providers know their customers will be, the cellular providers can ensure that mobile users are always within close proximity to a strong and fast signal.

A DAS network solution also ensures that users currently receiving cellular signal on traditional macrocell or cell tower networks won’t experience an interruption of service when there is a major event occurring within the same area. These major events (sporting events, concerts, shows, festivals, rallies, etc.) bring thousands of new mobile users into a specific area, sometimes overloading the network and leading to significant signal interruptions. Fortunately, DAS networks are capable of offloading this expanded traffic onto a complimentary network, freeing up bandwidth on existing networks so that they continue to run at optimal levels.

However, although a DAS network may sound similar to a small cell network, there are some key differences between the two competing technologies that anyone looking to deploy targeted bandwidth should be aware of.

DAS & Small Cells: What’s The Difference?

The radio heads of a distributed antenna system are essentially “dummy” radio heads: these access points don’t provide any signal processing like a small cell antenna system would. Instead, DAS radio heads relay the signal to a cellular base station located at a central hub. Once the signal is relayed to the hub, it’s processed at that central location.

Base stations installed at a central hub are essentially macrocells, and by installing additional base station units within the hub, cellular providers can increase their broadband capacity. Since the cell signal is processed at a base station, a single hub can support multiple carriers and multiple bands at the same time, with each carrier installing their own units.

In certain scenarios, like a football stadium used for a Super Bowl, distributed antenna systems can actually be far more efficient that small cells when it comes to supplying multiple band coverage with different operators. Typically, small cells can only support one or two bands with one or two operators at a time, so their total network capacity is significantly more limited than that offered by DAS systems.

Downsides of DAS Technology

1. Cost
When discussing DAS network implementation, there is one significant drawback, and it’s one that always comes up since it’s extremely important to businesses looking to turn a profit. Whenever cellular providers look to expand their network coverage and bandwidth, one of the first things the executives will ask is “How much is this going to cost us?” Unfortunately, DAS systems are not cheap.

In fact, compared to small cell networks, DAS networks are significantly more expensive. The price differential stems from the need to use fiber-optic cables to connect each radio head to a central hub, the development of the hub itself, and the placement of the cellular base stations. As such, the implementation of a DAS network in a large venue, like a football stadium, can cost hundreds of thousands of dollars for all the necessary DAS equipment, along with the tuning and optimization that will be required afterward.

2. Backhaul

Although routing backhaul is a problem for both DAS and small cell networks, DAS is typically more problematic. Because each of the radio heads used to broadcast the cellular signal requires routed fiber-optic cables, the installation process can easily become troublesome. In the case of the Houston Super Bowl Stadium, each of the 800 radio heads will need to be routed by fiber-optic to the central hub in order for the system to work.

This process can potentially create issues with cable management, as keeping the fiber-optic lines out of sight will require that the cables be carefully routed through the walls and other important structures of the facility. If this process is not conducted properly, the routing of these cables can cause serious harm to the structural integrity of the facility, making it unsafe and unfit for visiting patrons.

3. Upgradeability

When it comes to DAS networks, there is also the issue of upgradeability. As new technology becomes available, it is more difficult to upgrade an existing DAS network than it is to upgrade a comparable small cell network. Typically, small cell networks can be upgraded over the air (OTA) without the need for a technician visiting the cell site. DAS network upgrades, however, may require the replacement of the base station and modifications being made to the radio heads themselves, making the upgrade process significantly more difficult.

Advantages of DAS Technology

Although the implementation of a DAS network is more expensive than a small cell network, DAS networks benefit from having a significantly greater cellular capacity. As mentioned above in this post, DAS systems can handle multiple bands for multiple operators at the same time, whereas small cells can only support one or two bands for one or two carriers.

This flexibility allows DAS networks to be far more scalable for large, targeted locations where cellular providers know that demand for additional bandwidth will be high. At large venues where there is a need to supply internet connectivity from multiple cellular providers, a DAS network remains the preferred technology solution.

This capacity to support multiple bands also ensures that a broader range of mobile devices with their own cellular plans can receive a strong internet connection while they’re in close proximity to a DAS radio head, providing a better experience for the cellular consumer.

Choosing Between Small Cells and Das Networks

Cellular providers use the following criteria when determining which network system is right for their planned expansion:

• Coverage Need (voice vs. data)

• Existing Backhaul and Infrastructure

• Exact Location of Required Coverage

There are other factors to take into consideration as well, like building codes and wiring restrictions, but having a firm grasp of these three elements is the best way to determine which solution will work best for any specific deployment.

It is important to note that when designing a DAS network, the network signal being transmitted cannot interfere with an existing macrocell network signal in the area because this interference can cause severe disruptions for mobile users on both signals, as it leads to serious crosstalk, making both networks entirely unusable.

Although DAS technology is currently the preferred method for larger venues, some recent advancements in small cell network technology will allow them to support additional bands and carriers, making them far more competitive with DAS systems. While DAS network installations may make sense with today’s technology, this could be changing in the near future.

For smaller venues, small cells definitely have a cost advantage over a DAS network simply because they require less installation of cables and RF transmitters. Because of the reduced infrastructure requirements, small cell networks can also be deployed at a much faster rate than DAS network solutions. This allows cellular providers more flexibility when attempting to expand their network coverage in order to meet the growing demands of their customers.

The Future of DAS Technology

DAS network solutions will continue to play a role in the effort to expand network connectivity across the United States for the foreseeable future; however, their role in smaller indoor and outdoor venues is likely to be reduced as small cell technology continues to mature.

For larger venues, DAS network solutions will continue to provide scalable network efficiency for multiple bands and carriers. If the cost of a DAS network is not a factor, then it’s likely that cellular providers will continue to choose distributed antenna systems to provide reliable internet connectivity for large groups of people located within a small geographic location.



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