Distributed Antenna Systems: The Architect’s Guide to DAS

Distributed Antenna Systems – The Guide In Brief

  • Reliable cellular communications have become an essential party of everyday life and work
  • External carrier signals and single-source WiFi systems can’t always meet coverage and capacity demands
  • Distributed antenna systems (DAS) meet evolving communication needs, satisfy building codes and future-proof designs
  • Here are six considerations that can help architects evaluate DAS designs to make sure they meet mobile communication user requirements:
    1. System design: Cost-effective, future-proof DAS installations address system needs (coverage vs. capacity), DAS type (active, passive or hybrid), network type (cellular or public), signal source and strategic antenna placement
    2. Product selection: Some products are best suited for active DAS (high capacity), others for passive DAS (expanded coverage)
    3. Partners: Architects and contractors can streamline projects by working closely with DAS integrators who have carrier relationships and are well-versed in federal, state and local regulations
    4. Accurate and timely commissioning and optimization: Signal balancing, antenna tuning and passive intermodulation (PIM) testing help optimize performance and avoid costly delays
    5. Ongoing maintenance: System health monitoring and preventative maintenance keep DAS systems online and cost-efficient
    6. 5G compatibility: By accounting for 5G, DAS systems can be futureproofed and avoid costly retrofits

Reliable cellular communications have become an essential part of everyday life and work – no matter where you are. Today’s office buildings and other structures can “get in the way” of cell phone coverage, creating challenges for everyday communications and emergency response.

General contractors, facility managers and IT leaders are turning to distributed antenna systems, or DAS, to meet evolving communication needs, satisfy building codes and future-proof their building designs. DAS is becoming more important as more people – and things – go online, demanding greater coverage and capacity than single-source WiFi and external carrier signals alone can deliver.

Importantly, DAS helps builders ensure that buildings serve both cellular and public safety needs. Cellular DAS provides phone and data resources for building tenants, business employees and technology infrastructure; while public safety DAS offers separate, code-mandated communication for emergency responders and municipal systems.

The following six considerations can help architects evaluate DAS designs and ensure that antenna systems deliver on coverage, capacity and budget demands.

 

1. Distributed Antenna System Design

Strategic planning is an important step for designing successful DAS deployments. Distributed antenna systems are complex and involve many interrelated, dynamic elements, so the most successful implementations start with the end goal in mind to ensure client needs are met and to avoid potential conflicting priorities (such as increased coverage versus capacity).

DAS needs

A common recommendation is to begin by evaluating system needs based on two key performance metrics.

  • Coverage: Signal saturation throughout the building
  • Capacity: The number of users and amount of data the system can simultaneously support (bandwidth)

For example, a building located far from cell towers or that has thick walls that block cell signals might have coverage issues that could be resolved with a well-designed DAS. Conversely, convention centers and sports venues that host large audiences might have ample coverage, but not enough capacity to serve surging user volume. The solution might be a high-capacity DAS.

By taking full account of current challenges, distributed antenna systems can be designed to serve each client’s unique needs.

DAS type

By taking advantage of the differences between DAS types, solutions can be configured with a range of capabilities to meet client goals within budgetary and time frame constraints.

Active DAS

Active DAS are powered systems that connect directly to carriers such as Verizon, AT&T and T-Mobile. Headends generate new cell signals and distribute them via fiber optic cables to remote nodes strategically positioned throughout a building.

Ideal for buildings that require high capacity (such as sports venues and convention centers), active DAS costs more than passive DAS implementations and can take months to deploy. Part of the process involves carrier agreement negotiations with FCC oversight and approval.

Passive DAS

Passive DAS rebroadcasts existing cell tower signals. A typical installation might involve a rooftop antenna that feeds bidirectional amplifiers strategically placed to maximize building coverage. Components are connected wirelessly or via fiber optic or coax cables.

More affordable than active DAS, passive DAS solutions are best suited to small to mid-sized buildings that need expanded internal coverage. They do not require carrier agreements or FCC approval, and installation can take just a few weeks.

Hybrid DAS

A mix between active and passive DAS, hybrid DAS is often used for multi-building campuses that have varying coverage and capacity needs. They’re also used in unique situations; for example, if there is no nearby cell tower, active DAS might be needed to generate a signal and passive DAS could be used to distribute the signal building-wide.

Passive DAS is often preferred for its affordability, simplicity and short install times, especially for buildings less than 100,000 sq. ft. (though some passive DAS systems can cover up to 500,000 sq. ft.).

Generally speaking, active DAS should only be considered for larger buildings with high-capacity demands, while hybrid systems can reduce costs in unique situations that require active DAS for signal generation but can rely on passive DAS for signal distribution.

Network type

Many buildings need both cellular and public safety networks, which distribute signals from FirstNet (a carrier-provided signal in the public safety range) in addition to city-specific municipal frequencies.

Building codes generally dictate that cellular and public safety systems must be independent. Though they can often use the same pathway support, the transport or “backbone” systems must be separate (though it’s possible the AHJ – Authority Having Jurisdiction – could allow a combined system).

It’s a good idea for architects to familiarize themselves with local codes so they can plan and budget for two independent distributed antenna systems installations if required.

Signal source and antenna placement

Meeting capacity and coverage demands depends on getting a strong signal source and strategically placing directional receivers and antennas throughout a building to maximize coverage. A good first step is to conduct a signal audit.

Software such as iBwave can help audit signal strength throughout a building. The program generates coverage heat maps for each carrier and measures FirstNet and municipal signal strength. It’s a powerful tool that DAS integrators leverage to identify the best antenna placement.

In some cases, existing infrastructure (such as cabling) can be reused to reduce project costs. For new buildings, iBwave can help project antenna and infrastructure placement. Often, the goal is to get the design 95% right up front, before the build, then fine tune adjustments after the building is built.

Future-proofing

Future-proofing can help DAS systems adapt to technology advances and minimize future costs. That means it’s a good idea for architects to understand the carrier landscape.

For example, if a carrier plans to upgrade technologies (such as to 5G), an active DAS design could accommodate both current and upcoming technologies. For passive DAS, carriers can be consulted to confirm that source cell towers will continue to operate for many years.

The best DAS designs account for future contingencies. For example, if a new neighboring building is constructed and blocks the signal between the source tower and roof antenna, DAS configurations can include options for secondary signal sources or alternative antenna placement.

Proper installation also helps futureproof DAS installations. If done wrong, cell tower signals can interfere with DAS systems, overwhelm their capacities or contaminate the signal. This is also a consideration if a new cell tower is erected in the future.

 

2. Product Selection

Product selection has a significant impact on DAS cost and performance. Getting the most bang for the buck often means matching products to system size. If a product solution is too small to provide adequate coverage or capacity, the system won’t perform; too large, and costs get wasted. It’s like ordering an entire pizza for one person or only a slice for a party of ten. Architects, then, can choose the most cost-effective solution based on project scale.

For example, Cel-Fi (Nextivity) and ADRF are two distributed antenna system component manufacturers. Generally speaking, a Cel-Fi chassis is more cost-effective for smaller systems, while an ADRF chassis is better for larger systems (though scope and plan may dictate the need for other systems). Exploring supplier options, capabilities and price points can help match components to project requirements within defined budgets. In addition, using existing infrastructure can make smaller scale systems work at reduced costs.

Costs

Understanding costs upfront can help you navigate the trade-offs for DAS options.

  • DAS equipment and installation: Active DAS costs more than passive DAS, while hybrid DAS systems can use active DAS to generate signals that are passively distributed, which can help reduce total project costs
  • Maintenance: Routine repairs and equipment replacement
  • Fees: Carrier, licensing and remote system monitoring software fees

Cost differences are scale-based and price points are typically based on square footage. Typical installation costs for passive DAS systems run between $0.30 to $1 per sq. ft., while active DAS installations can cost $2 to $4 per sq. ft. for a single carrier.

Monthly payments can help building owners mitigate ongoing costs. This offers cash flow benefits, and some (or all) of the costs can be passed on to building tenants (in the form of increased rent, for example).

 

3. Work with the Right Partners

The right partners can help architects navigate the many moving parts involved in DAS installation projects, from equipment selection and antenna placement to meeting federal, state, local and carrier regulations. Architects should seek experienced DAS integrators who steer projects toward success and away from red tape and costly delays.

Public safety

Building codes require public safety (PS) systems, but it’s not always easy to know what level of PS coverage is needed or how to comply with federal, state and local regulations to pass inspections.

Working with an experienced partner can help architects ensure compliance. For example, a good DAS integrator would know that under the FCC code, Part 90 industrial signal boosters require FCC registration. While Part 20 consumer signal boosters do not require carrier approval, carriers can shut down a system if it is interfering with the cell site or causing capacity issues; the FCC requires that these systems be registered with your wireless provider and have your provider’s consent.

Minnesota has adopted Appendix P, which mandates that all new buildings must have approved emergency responder radio coverage, and that emergency responder radio coverage must be installed in existing buildings when existing wired communication systems are replaced or in a state of disrepair. Other states have their own public safety requirements that must be met before systems can go online.

Cellular

For active DAS, the FCC and carriers have their own regulations and requirements that need to be satisfied before a system can go online. Negotiating terms and waiting for approval can cause costly delays.

One issue is that guidelines and standards are implemented inconsistently. Authorities Having Jurisdiction (AHJs) are often allies for DAS success. But even they can find it challenging to keep up with ever-changing rules and regulations.

A well-informed integrator who has carrier relationships and experience navigating regulations can help architects coordinate with AHJs and ensure DAS systems are compliant and up to code.

 

4. Accurate and Timely Commissioning and Optimization

Whether a building is new or existing, once the DAS system is installed the next phase is commissioning and optimization. In other words, bringing the system online, testing and adjusting it for optimal performance.

  • Signal balancing: Helps ensure optimal coverage and eliminates dead zones while optimizing system performance and efficiency. If the signal isn’t properly balanced, costs can increase due to additional – and unnecessary – antennas
  • Fine tune the antennas: Similarly, antennas must be fine-tuned for optimal performance and to avoid unnecessary costs
  • PIM testing: Passive intermodulation (PIM) testing checks for cable leakage, feedback and unwanted antenna noise. It also ensures the system can adequately handle power loads

Timely optimization and commissioning help avoid costly delays. For example, if a public safety DAS isn’t completed on time or doesn’t meet specs, certificate of occupancy might be denied. That means building owners and property managers won’t be able to have tenants.

In addition, a poorly optimized DAS system will cause frustration when users and employees have poor cell signals, which can also zap productivity and cost businesses money. That, in turn, jeopardizes building occupancy rates.

 

5. Ongoing Maintenance

Planning for ongoing maintenance and evolving system requirements helps optimize performance and cost efficiency – now and in the future. Health monitoring and preventative maintenance increase system uptime, while anticipating changes in requirements and regulations help to future-proof DAS installations.

System health monitoring

System health monitoring is required for public DAS and it is best practice for cellular DAS as well. Monitoring services can automatically alert administrators about issues so they can be resolved quickly and economically. For example, radio frequency (RF) monitoring ensures continuous signal transmission. If an outage is detected, the system can automatically alert technicians who can troubleshoot the problem.

Preventative maintenance

Routine testing helps administrators identify and resolve issues when they begin, and before they snowball into expensive repairs. In addition, ongoing maintenance makes it easy to address tenant-based issues, such as microwave interference or equipment placement, that can’t be accounted for during the planning phase. That makes it easier to plan for system upgrades that address coverage or capacity issues.

Evolving requirements

DAS designs should also account for how evolving signal usage, public safety requirements and carrier requirements might reshape DAS installations. Preventative maintenance, then, extends to anticipating upcoming changes. For example, if a contractor must open a wall to repair a stretch of cable, administrators might take advantage of the opportunity to add a junction that will serve a planned building addition.

 

6. 5G Compatibility

5G compatibility helps futureproof DAS installations, and it’s a critical consideration as 5G coverage extends across the nation.

DAS implementations can include a chassis that’s 5G compatible, which means making the system 5G ready is as easy as adding a card.

That doesn’t mean 5G compatibility isn’t without challenges. Despite its superior speeds, 5G does not easily permeate structural materials such as wood and concrete. DAS implementations can account for this with antenna installations configured to propagate 5G signals building-wide. Doing so not only ensures the system is ready as soon as 5G is available, it also helps property managers reduce the need for future (and expensive) retrofitting for 5G compatibility.

Another consideration is that 5G is still evolving and many changes are on the horizon. Though it’s difficult to anticipate each and every change, DAS planning should avoid overcommitting and rigid designs to help ensure future flexibility.

Distributed antenna systems are robust and reliable solutions to critical connectivity challenges. The considerations listed here can help architects guide efficient and economical DAS installations that successfully meet coverage and capacity demands.