Active vs Passive DAS: How They Stack Up for the Middleprise

Sep 26, 2019

Today, indoor cellular service is as important as basic amenities such as electrical, gas, and plumbing for businesses across a variety of industries. The frustration and inconvenience of poor cellular coverage indoors translates into metrics that businesses simply cannot ignore. In fact, last year CommScope reported that 75% of employees in the United Kingdom felt their productivity was hampered as a result of poor connectivity. It’s not hard to imagine what the ramifications are for hotels, college campuses, retail outlets, and other businesses whose bottom lines are directly linked with occupancy rates, recruitment and retention, and sales.

Yet poor coverage or dead zones continue to plague many buildings, despite owners’ best efforts to bring outdoor cellular signals indoors. Factors such as building size and construction material, environmental obstacles, and tower locations are often to blame for signal impediment, but the load – or number of users on a network – can also negatively impact cellular coverage. That’s because networks are dynamic and can grow or shrink depending on inter-cell interference levels. The result is inconsistent coverage depending on the time of day, or day of the week.

A recent and significant shift in the in-building coverage market has resulted in solutions that go beyond the traditional passive distributed antenna systems (DAS) – specifically, active DAS hybrids. A hybrid solution delivers intelligence and active antennas not found in a typical passive DAS, at a price point that supports the often-ignored middleprise (buildings up to 500,000 square feet).

The Best of Both Worlds

An active DAS hybrid solution brings together the strengths of both passive and active DAS architectures. For example, it can tap into a small cell donor or an off-air donor signal to create a typical active DAS deployment, complete with active omni-directional antennas, and use Power over Ethernet (PoE) for easier installation. In some cases a building’s shape may be difficult to support with centrally-located omni-directional antennas, so passive DAS elements can be a benefit. Targeted coverage can be achieved using the variety of antenna types, easily driven from the RF output port on Cel-Fi QUATRA.

Price vs Performance

While a passive DAS powered by a BDA is often considered more cost effective to deploy in a middleprise environment, it’s important to note the performance tradeoff. The existing technologies that power traditional passive systems are often complex and complicated, and as such, can have a negative impact on performance. That said, a BDA-based passive DAS is not necessarily less costly, either. For example, the quality of the donor signal at the site greatly impacts the system’s ability to function optimally. When the signal is poor, more equipment is required resulting in higher capital, installation, and operational costs.

In contrast, as long as there is some signal, an active DAS hybrid solution has enough gain to overcome poor signal conditions. This makes the capital requirements easier to predict. In addition, the simplicity of the active DAS hybrid is often preferred by installers, who no longer have to choose between price and performance.

Optimizing Signal Strength

Solutions and deployment models will vary depending on the specific coverage needs, signal source availability, and layouts unique to each building. The flexibility of an active DAS hybrid provides support for a wide range of configurations to meet the needs of the middleprise. For instance, an active DAS hybrid can provide coverage to a large area within an open setting featuring high ceilings and low (or no) walls. An associated coverage unit can simply be placed in a central location for quick installation, using Cat 5e cable to provide power and signal.

In an area with obstacles and other blockers to interior propagation, installers can easily pinpoint coverage using passive antennas rather than coverage units. The active DAS hybrid can then act as the remote source to power and drive a passive DAS. To distribute coverage, coax cable can connect a coverage unit’s external antenna ports to the antennas themselves.

As a result, each carrier’s signal can be amplified independently to 100dB – in sharp contrast to a traditional passive DAS, which enables only one gain value for all carriers. In addition, each band can reach its maximum downlink power because the internal amplifiers of an active DAS hybrid are individually gain-controlled. A BDA-based passive DAS, however, has difficulty delivering a good coverage footprint and user experience when signal conditions are poor.

Ultimately, providing a good customer experience is the end goal, and must be top of mind when evaluating solutions to fit the environment and budget. Although less expensive than active DAS hybrid coverage units, passive antennas often require additional RF engineering resources because the installation is more complex. It is also not a good idea to cut corners as improper installation can result in poor outcomes.

One Size Does Not Fit All 

Unfortunately, there is no standard solution for solving indoor cellular coverage issues. But technology has evolved to include active DAS hybrids, which can adapt to various configurations, deployment models, and donor source options to provide performance levels that simply cannot be matched by traditional passive DAS solutions.

Integrators now have a competitively priced option for the middleprise that does not compromise on performance, and can be tailored to their specific coverage needs. This levels the playing field for customers in this particular market segment, who are no longer forced to choose between solutions that come with a big-business price tag and less expensive options that are simply not reliable enough to support enterprise needs. An active DAS hybrid provides the best of both worlds.

About Dr. Michiel Lötter 

Dr. Lötter is the CTO and VP Engineering at Nextivity, responsible for the Product Development and Product Management of the award winning Cel-Fi product line. He has overseen the development of four generations of chipsets, launched nearly a dozen Cel-Fi hardware and software product platforms for in-building / mobile, and led the creation of the remote Cel-Fi WAVE management system. These included products ranging from plug and play devices for residential and SMB to automotive and marine to enterprise grade solutions for nearly 200 operators across 100 countries.

Prior to Nextivity, Dr. Lötter developed products for Broadcom, Zyray Wireless (co-founder), and Alcatel Altech Telecoms. He holds a Ph.D. from the University of Pretoria in South Africa. He has authored and co-authored a number of journal and conference papers, two books on wireless communications, and is the named inventor or co-inventor on 26 issued US patents.