What is Distributed Antenna System (DAS)?
A Distributed Antenna System (DAS) is a network of antennas across your buildings and facilities that enhance your ability to transmit radio and cellular signals within outdoor and indoor environments. These systems are often used to amplify in-building wireless coverage, though there are numerous outdoor applications.
Signals travel from exterior antennas along various cable types to specialized equipment like bi-directional amplifiers (BDA), remote radio units (RRU), head-end units (HEU), baseband units (BBU), backup batteries, and ceiling or wall-mounted antennas. The quantity and types of cables and equipment utilized in your DAS will vary based on the system you select to suit your facility’s needs and your organization’s budgetary requirements.
Public Safety vs. Cellular DAS Solutions
Public Safety DAS
Unlike Cellular DAS options, having a properly configured Public Safety DAS (PSR/PSC) installed inside your buildings is a legal requirement in most jurisdictions. These systems boost radio and cellular frequencies in the 700 to 800MHz range. The 700 to 800Mhz range is used exclusively by first responder agencies (EMS, Police, Fire). Building codes refer to the DAS solutions that boost them as emergency responder radio coverage systems (ERRCS).
Cellular DAS
While Public Safety DAS are built to enhance signal coverage for a singular specific frequency range, Cellular DAS can be configured and designed to boost coverage for multiple frequency bands, like those used by major cellular carriers and those used in private cellular networking (like CBRS). The greater the frequencies your system supports, the more complex it will be to design and install.
How Are DAS Designed?
The first step in designing a DAS system is to conduct an RF Benchmarking Test. During this phase, the tester will walk the entire building layout and use devices that measure the signal strength at set intervals (every ten feet, for example). Once they’re done, a report will be generated that clearly shows where there are weak spots in the building. It’s important to note that benchmark testing should be conducted before a building’s construction is completed, as it will be easier for wires and equipment to be placed.
Once the report has been reviewed, a certified technician will design a DAS system that directs wireless coverage to areas with weak or no signal. Some areas most likely to need additional coverage are stairwells, elevators, subterranean locations, and storage closets.
The technician – or integrator – will also work with the Authority Having Jurisdiction (AHJ) to ensure the system meets local, state, or federal compliance requirements.
DAS Architecture – Signal Sources
When designing a DAS, the point where it captures the signal (ie: the signal source) that it will ultimately relay is what kicks off the entire architecture.
The signal source has three possible options:
- Off-Air
- RBS, NodeB, and eNodeB
- Enterprise Small Cells
Off-air signal source is often the most accessible option and requires minimal setup. With an off-air signal source, rooftop donor antennas capture the signal from a local cellular tower. However, the strength of the DAS will depend on the performance of the antenna and tower.
Key Features
- Best option for cost-conscious organizations
- Relatively quick installation
- Can support multiple carriers
- Signal quality is dependent on the macro network
Off-air signal source is ideal for cost-conscious organizations interested in providing multiple carrier coverage and have relatively small buildings.
The RBS (Radio Base Station), Node B, and eNodeB operate similarly. They are directly connected to a cellular carrier’s network through fiber optic cables and relay the signal to a DAS.
Key Features
- Excellent performance
- Adds increased capacity
- High installation and operation costs
- Installation time can range from months to years
- Must be tied to a specific carrier network
These types of signal sources are ideal for organizations with large budgets that want to achieve the best possible performance while working with a single, specific carrier.
By connecting to a cellular network through a Femto gateway, Enterprise Small Cells can then relay the signal to a DAS.
Key Features
- Excellent signal quality (although not available for all carriers)
- Coverage area of less than 15,00 square feet
- Required to support hundreds of users, with the option to scale up as a network
- Less expensive than RBSs and offers a relatively quick installation timeline
Enterprise Small Cells are ideal for buildings occupied by large numbers of people and requiring excellent signal quality, but are seeking to avoid the high expense and long installation time of RBSs.
Can You Upgrade A Public Safety DAS To Be A Cellular DAS?
Yes. But doing so can be cost-prohibitive. Part of installing a DAS system is evaluating your coverage needs and designing a system that meets or exceeds them. Designing a Public Safety DAS is considerably less complex than designing a Cellular DAS system. For starters, Cellular DAS require antenna patterns to be tighter to provide ubiquitous coverage for those additional frequencies. It makes the system more expensive because there is more to it – more antennas, cabling, tappers, splitters, connectors, and additional associated labor.
But the real additional expense comes from planning for an upgrade ahead of time. If you see a future need to upgrade your Public Safety DAS to a Cellular DAS, it can make the process more affordable if you include this goal in the initial planning and design phases. Doing so allows your systems integrator to perform an RF benchmark survey at site to help determine the system you need today (and the one you need tomorrow). This lets them properly map out your installation so that it leaves room for future upgrades. Otherwise, your site will need to be surveyed again, and your system will be redesigned to accommodate the system’s expansion. It’s always best to plan ahead.
Expandable Public Safety DAS Solutions
As mentioned earlier, if your organization determines that there will be a future need for Cellular DAS, it generally makes installing your Public Safety DAS more expensive. This is especially true for buildings and facilities that do not utilize drop ceilings. Suppose your facility has ceilings made of drywall or another solid material. In that case, it’s impractical to cut into those materials later to install all the components necessary to add the additional antennas.
Those extra components we mentioned before — cables, tappers, splitters, connectors — all need to be in place to optimize their placement in anticipation of the later upgrade. At the same time, this minimizes the future expense of upgrading because everything is optimized and where it needs to be, allowing for a much faster installation process.
Future-Proof DAS Installations
Typical Cellular DAS installations include frequency ranges up to near 2200 MHz. To include a greater range of frequencies in preparation for a 5G future requires an even more complex installation with even greater costs. While many may shy away from extending their budget even further, it’s important to note once again that planning for the future is always the better investment.
Major carriers’ 3G networks are already going offline, and while 4G has no anticipated sunset date, it will certainly move towards obsolesce in time. Planning for 5G sets your buildings up to have a reliable communications infrastructure for the next 20 years or more.
Antenna Density by DAS Solution
Lower frequencies travel farther than higher frequencies, as such Public Safety DAS installations require the fewest number of antennas. A standard Cellular DAS installation requires more antennas configured to higher 4G LTE frequencies. While a “future-proof” Cellular DAS requires even more antennas to cover PLTE, CBRS, and 5G frequencies.
To loosely illustrate the concept, we’ve provided three drawings below.*
Is there a difference between an indoor and outdoor DAS?
Yes and no. Indoor DAS (iDAS) and Outdoor DAS (oDAS) systems generally use the same components. The major difference is in the design of the system and its installation. Outdoor systems environments have additional considerations – specifically things like the environment. The antennas and other components used in an oDAS must be hardened against weather extremes like heat, cold, and rain. DAS are generally shielded from such extremes as they are located within your facility.
What types of DAS systems do you offer?
As mentioned, we can install Public Safety or Cellular DAS for indoor and outdoor environments, but those designations only specify the frequencies the system is meant to enhance. Four types of DAS systems have varying equipment requirements and associated costs — Passive DAS, Active DAS, Hybrid DAS, and Digital DAS. Of those four, we currently offer our clients the first three as options.
Active DAS
Active Distributed Antenna Systems (DAS) can be expensive, with long installation times, but are the ideal solution for extremely large buildings (500,000 square feet or more) such as airports, convention centers, or stadiums. Since they are able to accommodate signals from multiple carriers, a separate antenna per service is required, which adds to the installation cost and time. However, they are the best option to ensure that diverse groups of individuals have adequate signals on their devices, regardless of the service provider.
Passive DAS
Passive DAS solutions are typically the most affordable. They have the lowest maintenance needs and are relatively easy to install. However, they are not the strongest or most effective. Passive generally means that the system isn’t powered and utilizes primarily coaxial cables to function, which can produce weaker connections as signal strength is lost over significant distances. Passive systems are best for Public Safety DAS installations at small to medium sized buildings and facilities.
Hybrid DAS
A Hybrid DAS mixes Passive and Active DAS. With a Hybrid DAS, some components are separated from the primary antenna, which allows for a blend of fiber optic and coaxial cables and powered and unpowered equipment. This system type is more powerful than a Passive DAS but less powerful than an Active DAS – as such is more middle-of-the-road cost-wise. But only a site survey can determine if a Hybrid DAS will meet your needs and budgetary requirements.
Digital DAS
Operating within the Common Public Radio Interface (CPRI), digital DAS is a relatively new technology in its early adoption phase. A Base Band Unit (BBU) is used to relay the signal through fiber optic or ethernet cables to a master unit. Unlike other DAS options, it does not require signal conversion. As mentioned earlier, MCA does not currently provide Digital DAS to our customers.
How Can MCA Help With Cellular Coverage Enhancement Needs?
Mobile Communications America is a Tier 1 National Integrator of Carrier-Grade DAS Solutions. We provide services every step of the way — including consultation, site surveys, iBwave design, solution engineering, system testing, and on-site installation. And with our equipment service agreements, you can hire us to perform ongoing system monitoring and maintenance to ensure your signal levels stay consistent and strong.
About MCA
Mobile Communications America (MCA) is one of the largest and most trusted integrators in the United States, offering world-class voice, data, and security solutions that enhance the quality, safety, and productivity of customers, operations, and lives.
More than 65,000 customers trust MCA to provide carefully researched solutions for a safe, secure, and more efficient workplace. As your trusted advisor, we reduce the time and effort needed to research, install, and maintain the right solutions to improve your workplace.
Our team of certified professionals across the United States delivers a full suite of reliable technologies with a service-first approach. The MCA advantage is our extensive service portfolio to support the solution lifecycle from start to finish.