Ken Sandfeld, EVP SOLID, positions three different types of DAS

Ken Sandfeld Solid 150The DAS and Small Cells industry segments can often seem to be at war with each other. Conference, organisations and products have been renamed, sometimes causing more confusion than clarification. So I spoke with Ken Sandfeld, EVP at SOLiD, to gain a better perspective of where the DAS industry is today and where it's headed. He shared his experience of that market, explains the terminology and believes DAS has a growing future opportunity.

What is a DAS system anyway?

Think of DAS (Distributed Antenna System) as a macro network architecture shrunk down and deployed indoors or across a campus. Like the macro, it consists of the signal source, central head end location for distribution, remote amplifiers and antennas to radiate the signals to our smartphones. Transport is also similar to the macro as most traditional DAS use a combination of fibre and copper – typically fibre for longer distances between the central location to remotes amplifiers and then coax cabling between the remote amplifiers and antennae.

With DAS, you can combine signals from multiple operators by installing several microcells at the central location. These systems are transparent to 2G, 3G and LTE. SOLiD was the first to also handle VHF and UHF bands for public safety (first responder) services. These are driven from external rooftop antenna and relay the signals rather than adding capacity.

There are essentially three types of DAS currently being deployed in the marketplace. The oldest and most basic approach – Passive DAS – is simply an RF pipe that uses coax cabling to transmit raw RF signals from a central point around a building or campus and is driven by relatively high power microcells or macrocells.

The most prevalent approach - Hybrid DAS - transmits the raw RF signal over fibre to an amplifier in the closet, then uses coax to the antenna. SOLiD was one of the first DAS manufacturers to incorporate WDM (wave division multiplexing, using different colours) combining multiple RF channels in a single fibre rather than needing multiple strands. This is easier to install and test, and one less source of error.

Lastly, Active DAS connects the fibre all the way through to the end device. Unlike a small cell, the antenna is a simple RF amplifier/convertor and doesn't have any local processing capability. A few DAS vendors have recently launched products like this. Each radio antenna needs both fibre (for data) and copper (for power) cables. These systems are more costly than a hybrid DAS because of the active amplifiers in each antenna, and it remains to be seen if the benefits and higher price will be accepted by the market.

Who buys DAS systems – is it the building owners or the network operators?

In the North America market, there are three main customer segments:

  • Network operators (e.g. Verizon, Sprint, T-Mobile and others)
  • 3rd Party Owners (3POs - e.g. American Tower, Crown Castle, ExteNet and others)
  • Value Added Resellers (VARs - who sell on to Enterprise customers)

Traditionally, network operators have directly funded (or indirectly funded through 3POs) the DAS network. However, we are observing a trend whereby a 3PO, neutral third party (neutral host) or the venue owner will buy and own the DAS infrastructure, and then work with the operators to connect to it. It's a repeatable and effective strategy that enables operators to ensure capacity and coverage in more buildings faster simply by joining the DAS rather than owning it.

In this model, the operators supply and fund their own basestations. And the VAR delivers professional services to the 3PO's and Operators, and manages venue owner relationships.

Is it about coverage or capacity?

DAS solves for both coverage and capacity.

As you know, building materials can make it difficult for RF signals to penetrate through the second and third "walls" (the centre of the building) or underground. Green buildings using LEED construction further exacerbate the problem. These are examples of coverage issues.

The capacity issue is illustrated by the phenomenon of having five-bar coverage but the inability to load a webpage on your smartphone. We see this manifest most frequently at large stadiums but also in dense urban outdoor areas. We observe that as LTE and VoLTE become more prevalent, the problem will become more about capacity than coverage.

Leaving aside the few special cases of large stadiums etc., the majority of DAS installations for offices, hotels and hospital buildings can be served by a single sector microcell from each network operator. Remember that a single LTE sector can handle up to 400 or so concurrent users; 3G microcells can handle over 100. Piping this around the building to multiple antennas provides seamless coverage and more than meets today's demand. Often the biggest capacity constraint on a DAS system is the backhaul connected to the installation – if that's set at (say) 50Mbps, then that's the most traffic the building can carry.

Some DAS designs allow multiple sectors to be switched to different remote antennas, allowing the RF footprint to be reconfigured and make best use of available sector capacity at different times of day.

With Small Cell solutions, you get a full sector of capacity per radio head – say 64 or 128 users. That's a huge total amount of capacity, but I don't believe you need this much to satisfy demand.

Which of these three architectures do you see most future for?

We believe that densifying the network requires both evolutionary and revolutionary technologies and strategies to keep pace with capacity requirements and future 5G networks.

Therefore, we are continuing to evolve traditional DAS products. Today's designs need specialized RF engineers to install and troubleshoot. Single point failures can take out a whole site. We want to make it much easier to deploy, with lesser skilled technicians. We'd like smarter self-diagnosing capabilities, so that you know when an interfering signal shouldn't be there and can filter it out. Where cabling faults occur, the system should disable just the segment involved and flag up the action required.

Long-term, we observe the more revolutionary approach of Active DAS has the potential to deliver a single, intelligent and nearly infinitely scalable infrastructure capable of supporting RF and IP-based services. This architecture enables the fiber infrastructure backbone to stay in place while the end pieces and components get swapped out. It also provides robust analytics and new ROI business models. This is an area we're currently studying to understand how the market reacts to the higher cost.

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