The Ultimate Guide to Distributed Antenna Systems (DAS)

by | Dec 1, 2021 | Industry News, DAS/5G

Small_Cell

Understanding DAS (Distributed Antenna Systems) can be overwhelming. Between the technical terms and expert explanations, it’s tricky to figure out the best connectivity solution for your building. This is especially true because DAS technology has rapidly evolved in recent years, leading to a range of options with different pros/cons.

 

Though complex, DAS is key to planning your connectivity needs, especially as 5G is rolled out. The solution you choose will impact how much you invest in infrastructure and how you approach cellular carrier contracts, as well as installation requirements and coverage/capacity limitations. To support your company activities now and in the future, it’s important that you make the right architecture choice. 

 

Luckily, our expert team at WBE has 20+ years of experience in Distributed Antenna Systems installation and can take the guesswork out of potential solutions. With that aim, we’ve put together this ultimate guide to DAS and related technologies. Here you’ll get an in-depth look into different types of distributed antenna systems, including the requirements and ideal use of each.  

 

What are Distributed Antenna Systems?

Today, about 80% of daily cell phone data is consumed indoors. As you’ve likely experienced, cellular service indoors can be spotty. That’s because buildings made of concrete and certain metals make it challenging to capture a good signal. Add in large crowds or dead spots and it’s even more difficult. Weak signal, dropped calls, no internet, a quicker draining battery… your mobile experience in these cases may be far from ideal. 

 

DAS (Distributed Antenna Systems) are designed to capture cellular signal and then distribute it within indoor venues or crowded outdoor areas. It’s especially useful for high-traffic zones, such as hotels, shopping malls, schools, hospitals, retail stores, subways, airports, convention centers, stadiums and businesses. High-altitude buildings or remote areas, such as worksites, can benefit from it, too. 

 

That said, DAS is also suitable for a range of businesses that require reliable coverage. It’s considered one of the most comprehensive connectivity solutions available today. 

 

The Basics: How a Distributed Antenna System Works 

Essentially, a DAS captures a signal and then supplies it to a specific space. The exact set-up of DAS depends on 1) the signal source and 2) the distribution system.

 

In one typical scenario, the DAS will pull a cellular signal from a rooftop antenna and then channel that signal through coax cables to an amplifier unit. This unit then boosts the signal and runs it throughout a building through splitters and antennas. 

 

Because there are a variety of signal sources and distribution systems to choose from, DAS set-up may look a little different than this example. To help you wrap your head around the possibilities, we’ll take a closer look at all these types of sources and systems below. 

 

For now, keep in mind that DAS is a dedicated system for capturing and supplying signal to a specific space, so that overall coverage and capacity is improved.

 

DAS Architecture – Signal Sources 

The architecture for DAS starts with the signal source, i.e. where the DAS captures the signal it will relay. There are three possibilities for the signal source: 

 

Off-Air

In this case, a rooftop donor antenna will capture signal from a local cellular tower. This source is the most accessible option, as it requires minimal setup. However, the strength of the DAS will depend on the performance of the antenna and tower.

 

Overview

  • Most affordable
  • Quick installation
  • Carrier agnostic (so you can offer multiple carriers)
  • Performance is dependent on outdoor (macro network) coverage strength and quality

 

Ideal for

Small- or medium-sized buildings with lower budgets, who are interested in providing multiple carrier coverage and don’t require extra capacity.

 

RBS, NodeB, and eNodeB

RBS (Radio Base Station), Node B and eNodeB all work in the same way. This type of device is fed directly from a cellular carrier’s network via fiber optic cables. The device then relays the signal to a DAS. 

 

Overview

  • High performance
  • Adds extra capacity
  • Very expensive, plus high operating costs
  • Longer installation (months to years)
  • Specific to a cellular carrier (as it relies on its network and cabling)

 

Ideal for

Buildings with high budgets who want the best possible performance and are willing to work through each specific carrier.

 

Enterprise Small Cells 

Small cell nodes connect to a carrier’s network through a Femto gateway, which then relays the signal to DAS. 

 

Overview

  • High-quality signal
  • Small coverage area (5,000-15,000 square feet)
  • Supports about 200 users, though it can scale up as a network of small cells
  • More affordable than RBSs
  • Quick installation
  • Relies on backhaul internet connection
  • Not every mobile carrier offers small cells

 

Ideal for

Buildings with hundreds of people who require high-quality signal but want to avoid the high costs and installation time of RBSs.

 

DAS Signal Distribution Technologies 

From one of these sources above, DAS can then distribute and supply signal throughout a building. To do so, a DAS will make use of one of these four distribution technologies. 

 

Passive DAS

Passive DAS is a popular set-up because of its ease of installation. Essentially, a rooftop donor antenna picks up cellular signal, which is channeled through coax cables to an amplifier. From there, the unit strengthens the signal and sends it through a building through splitters. 

 

Pros

  • Very affordable
  • Coverage for all carriers and frequencies
  • Multiple amplifiers can be used in the building
  • Less complicated install
  • Less hassle to get cellular carrier approvals
  • Easier to maintain (as it involves fewer components)

 

Cons

  • Can’t use long cable runs without degrading signal 
  • Not good for very large buildings because long cable runs are needed
  • Doesn’t increase capacity

 

Ideal for

All building sizes except for very large ones, especially with a low budget and multiple carrier needs.

 

Active DAS 

Active DAS is one of the highest performing technologies, as it makes use of optical signal conversion. 

 

In this set-up, the captured signal is sent via coax cables to a digital conversion unit. Here, the signal is converted to optical and then relayed through fiber optic cables to another device called the remote access unit (RAU). 

 

From the RAU, the signal is converted back to analog radio frequency (RF), amplified and then distributed through local antennas. 

 

Pros

  • Ideal for very large spaces (stadiums, airports, campuses, etc.)
  • Uses long cables without any signal loss
  • Can be monitored remotely

 

Cons

  • Very expensive (10 times as much as passive DAS!)
  • Makes use of a single cellular carrier’s frequency
  • More complicated installation, as it relies on signal conversion
  • For multiple carriers, installation is complicated, approvals are lengthy and costs are higher

 

Ideal for

Buildings larger than 100,000 square feet that could take advantage of the high costs and performance levels.

 

Hybrid DAS

As the name suggests, hybrid DAS combines passive and active DAS design. Typically, this involves using both coax and fiber optic cables. The signal is still converted to optical and then back to RF, but the in-building splitters make use of passive amplifiers and coax cables. This ensures a better signal, but doesn’t require as much installation and investment. 

 

Pros

  • Cost-effective option
  • Good for versatile spaces
  • Multiple amplifiers can be used in the building
  • Not limited by cable runs

 

Cons

  • More complicated installation with signal conversion
  • Installation and approvals can still be complicated for multiple carriers

 

Ideal for

Hybrid is considered the best option for the majority of cases. It’s great for buildings of all kinds who want a cost-effective solution. 

 

Digital DAS

​​Finally, digital DAS is a new type of technology that operates within the Common Public Radio Interface (CPRI). At a basic level, it makes use of a Base Band Unit (BBU), which relays the signal through fiber optic or ethernet cable to a master unit. It doesn’t require the signal conversion that other DAS types do. 

 

Due to fewer components, digital DAS is quick and affordable to install. However, it’s still in the early adoption phase and hasn’t yet been widely used.

 

DAS and Small Cells: What’s the Difference?

We’ve already mentioned small cells as a signal source for DAS, which connect to a carrier’s network via a Femto gateway. 

 

However, small cells can also be used as a standalone technology. In this case, instead of supplying a signal to a DAS system, the small cell node is used directly by people. Fun fact: you may have passed by small cells and not noticed! Many small cells today are installed on streetlights and blend into the environment. 

 

Small cells are widely considered an alternative to DAS, though it’s important to remember that their technologies can be combined for optimal results. Of course, there are cases where companies might consider choosing between small cells and DAS. 

 

Small Cells as a Standalone Solution

Small cells are like miniature cellular towers. These small-sized units bring together all required signal technology in one. While they’re not as powerful as towers, they can provide coverage for about 100 users within a 1,000-foot radius. 

 

Pros

  • Cost-effective
  • Easy to install
  • Good for getting high performance for less than a hundred users

 

Cons

  • Relatively small coverage area
  • Made by a single carrier, so multiple small cells needed for multiple carriers
  • Not good for fluctuating capacity demand
  • Potential interference issues 

 

Ideal for

Small cells are ideal for small- or medium-sized buildings, or within a planned network of small cells in a larger area. Ideally, the user demand would be fairly constant. 

 

Choosing Between DAS and Small Cells

To choose between DAS and small cells, it’s important to consider the following areas.

 

Advantages of DAS over Small Cells

There may be some instances where DAS is a preferred solution. Specifically, DAS:

 

  • Provides greater capacity and coverage
  • Is better for multi-carrier and multi-frequency environments

 

Disadvantages of DAS Compared to Small Cells

Some companies may choose small cells over DAS because it:

 

  • May be more expensive
  • Requires lots of fiber optic or coax cables, driving up costs
  • Installation and maintenance can be more complicated
  • Design and planning can be more intensive

 

Side-By-Side DAS and Small Cell Deployment

As we mentioned, DAS and small cell nodes can be used together to maximize their advantages. In this case, small cells would be the signal source for a DAS, which would then distribute coverage across a larger space.

 

Why Do Cellular Companies Use DAS Antenna Systems?

DAS technology is great for expanding network coverage, especially where it isn’t possible to install a cell tower. The strategic placement of DAS can help cellular companies provide a better mobile experience without interruptions. 

 

This is especially true for big events, shows, festivals, etc. that typically overload a network. DAS can handle this high demand and reduce the network load on cellular towers. Overall, cellular carriers have been investing in DAS to get this key in-building coverage and to supplement cell towers in key locations.

 

The Future of DAS Technology: The Key to 5G?

Even though small cells are rapidly being adopted, DAS technology is sure to stick around. Key benefits such as large coverage/capacity, multi-carriers and multi-frequencies make DAS the #1 connectivity solution for many. Specifically, hybrid DAS may become the most popular option, as it brings together the best performance for the lowest installation cost. 

 

In particular, as 5G goes mainstream, DAS may become vital to indoor connectivity. That’s because 5G is often deployed at higher frequencies compared to 3G and 4G. For this reason, indoor coverage will be even more difficult with 5G. Luckily, DAS can better provide signal compared to small cells. 

 

Of course, it’s hard to predict what the future of DAS will look like. For this reason, you should always work closely with a DAS expert like WBE in order to get the best and most up-to-date advice about 5G connectivity solutions.

 

Key Takeaways of DAS Technology 

Now that we’ve described DAS technology in depth, let’s summarize the most important information. In case you missed it, here are the key takeaways of DAS technology:

 

  • The exact set-up of DAS depends on 1) the signal source and 2) the distribution system.
  • DAS gets signal from three potential sources: off-air, RBS or small cells.
  • Distribution systems can be passive, active, hybrid or digital. 
  • Though small cells are considered a DAS alternative, they can be deployed side-by-side.
  • DAS may be vital for indoor 5G connectivity in the future.
  • Our WBE experts can help you create the most effective connectivity plan.

 

Downsides of DAS Technology 

  • Can be cost-prohibitive (depending on set-up, especially active DAS)
  • Installation and maintenance can be complicated
  • Cellular carrier approvals can be involved
  • Design and planning can be intensive

 

Advantages of DAS Technology

  • Provides greater capacity and coverage
  • Coverage for all carriers and frequencies 
  • Multiple amplifiers can be used in the building 
  • The most comprehensive option

 

Choosing the Right DAS Partner 

At the end of the day, distributed antenna systems (DAS) could be the ideal fit for your company’s needs. It’s essential to get in touch with a DAS expert and create a connectivity plan that includes 5G readiness

 

With W. Bradley Electric (WBE), you’ll get full turnkey DAS implementation, tailored for your company’s unique situation. We take an expert approach to your 5G readiness, ensuring that your architecture is enabled for 5G roll-out. 

 

With 20+ years of experience and a five-star reputation, we’re the right partner to advise you on the most cost-effective and comprehensive DAS solution possible. Our experts are ready to future-proof your company’s connectivity, so get in touch today.

 

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