In Building Wireless Training

In-Building Wireless Coverage Solutions: Understanding DAS and Small Cells

In-Building Wireless Coverage Solutions: Understanding DAS and Small Cells

28 February 2018 | Reading Time: 5 minutes

When we talk about ‘In-Building Wireless’ (IBW), what do we actually mean?

Though ‘IBW” may sound like one set-in-stone solution, in actuality, that single term encompasses an entire class of diverse, specialized solutions and technologies – that enterprise owners, managers and architects must understand in order to implement the right IBW solution for their space, and balance the benefits and costs of each effectively.

Typically, when considering IBW, the technologies being considered will be one of the two more significant classes of IBW solution; either distributed antenna systems (DAS), or small cells.

And while the two do share some physical and configuration similarities, they do operate differently. So what’s the difference between the two and what advantages can they offer?

Understanding DAS and small cells 

As we’ve already explored in previous posts, there are multiple considerations to make when selecting an IBW solution. There’s no such thing as a ‘one size fits all’ solution! The size of the space, energy usage and costs, as well as how many operators you will need to interface with, are just a few factors to address – and will influence whether DAS or small cells are a better option.

DAS: powerful and scalable in-building wireless coverage for large venues

What is DAS? Built from a networked series of remote antennas, or nodes, DAS (distributed antenna systems) is one of the industry’s longest-established wireless coverage and capacity technologies.

DAS is an inherently scalable solution, meaning it can be expanded to cover larger spaces and unusually-shaped areas. For example, when cellular service is added to a subway tunnel, arena or in an area such as a tunnelled mountain road, it’s likely being provided with DAS.

What is DAS a suitable solution for? DAS is an effective means of delivering a uniformly high quality of service (QoS) wireless coverage and robust capacity across:

  • Large indoor areas such as high-rise office buildings, hotels and large hospitals

  • A contiguous outdoor area, such as a stadium or sports arena

  • A combination of indoor and outdoor environments, such as a college campus

Of course, not all DAS solutions are the same. So even if an area suits a DAS solution, it’s important to recognize that indoor spaces should be covered by low-power DAS, and outdoor spaces should be served by high-power DAS. The latest generation of DAS solutions can also integrate both low-and high-power networks into a single, unified platform for mixed environments.

Note that each DAS installation will be unique to the environment it serves – there are no ‘out of the box’ DAS solutions. There are, however, new options that help to simplify the installation process, with intelligence-enabled automatic configuration, and an alternative means of signal transport, such as via an existing IT cabling infrastructure.

As a distributed antenna system, DAS connects to an operator’s network through that operator’s own base station, meaning DAS is able to work with one, many or all available wireless operators.

What does DAS infrastructure require? DAS generally relies on RF cable (coaxial cable) to link antenna remotes, and uses fiber-optic cable to connect floors and other discrete areas. These two types of cable then connect to a central processing point (the headend). Newer, more advanced DAS solutions will, today, operate on IT structured cabling instead of coaxial. This offers a number of benefits, from ease (and reduced cost) of installation, to supporting other networks and functions such as Wi-Fi and security systems.

Small cells: affordable, adaptive coverage solutions for smaller indoor locations

Despite the many benefits that DAS presents (and reductions in cost), for smaller enterprise environments it may not be the most economic solution. Instead, for smaller indoor locations, small cells present a flexible, self-contained and more cost-effective solution.

What are small cells? Essentially small cells are just that; small versions of macro cell sites, including base station, radio and antennas, usually combined into a single physical unit.

What are small cells suitable for? In deployments such as small-to-medium office buildings, where day-to-day demand remains fairly consistent and user distribution and demand doesn’t vary much, small cells offer ideal support.

Essentially, small cells suit small-to-medium spaces with consistent demand.

What infrastructure do small cells require? As a relatively easy to install (and cost-effective) option, small cells are an attractive solution for enterprise environments.

However, there are still a number of considerations that need to be made with small cells:

  • Operator support. Unlike DAS solutions, which connect to an outside base station, owned by a wireless operator, small cells include their own baseband unit that must be integrated with operator networks – a one time process. As a result, most major operators have only integrated a limited number of small cells (some have not integrated any). And while this situation is improving slowly, it’s important to keep in mind that small cell solutions typically only support one operator’s network.
  • Interference prevention. In a small cell solution, each small cell creates a discrete ‘cell’ of coverage; and like macro sites, traditional small cells also create overlap areas where cell boundaries meet. As these cross-over areas can cause a significant decrease in service quality (such as dropped connections, choppy voice, reduced data rates), it’s important that solution design, and cell placement is well considered and optimized – though it’s impossible to eliminate cross-sector interference completely.
  • Coverage and capacity limits. If you’re considering a small cell deployment, but expect to significantly expand your IBW solution in future, bear in mind that small cells have a hard upper limit on capacity and coverage. They can reliably support 16-64 users at a time, which for many small to mid-sized enterprise environments will be more than adequate. You should also consider that conventional small cells cannot dynamically share capacity between access points, meaning that large groups of users in small spaces (such as cafeterias) can create bottlenecks.

Is C-RAN the answer? 

As discussed above, DAS solutions are ideal for larger enterprise environments, with small cells commonly used for smaller indoor spaces. Yet there are clearly some limitations with traditional small cells (interference, bottlenecks etc) that you may want to avoid. So what’s the solution?

A C-RAN small cell (cloud radio access network) is a recent innovation from CommScope that may offer the best of both worlds; removing some of the common challenges in small cell deployments.

How does C-RAN work? In a C-RAN small cell, the base band unit centralizes all processing from the small cell’s various radio points. This creates a virtual “super cell” that combines the whole system into a single coverage area – and ensures quality service by eliminating overlap. C-RAN also operates over conventional Ethernet switches and cabling, making it easier to install and maintain.

Choosing the right IBW solution 

Whether a DAS or small cell deployment is right for you will depend on a number of factors, from the size of the space, to the number of users, to capacity demands – and, of course, budget.

DAS and small cells account for the majority of IBW solutions, covering small, medium and large enterprise environments. Of course, IBW solutions are always evolving and improving; leading to more economic, greater performing IBW and giving owners, managers and architects – as well as installers – a greater array of options over time. For owners, managers and architects this is great – it means more choice when it comes to IBW but also, from an engineers perspective, regular IBW innovations increase the importance of maintaining up to date wireless training certifications.


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