In a recent post, we discussed the difference between active, passive, hybrid, and digital distributed antenna systems (DAS). Here we want to clear up any confusion about “active” DAS.
Most distributed antenna systems that have components that require a power source — whether that be the rooftop antenna or the small cells that transmit signals from floor to floor— are defined as an active DAS.
All Active DAS have a Master Unit that accepts signals, converting RF into Fiber to enhance cellular coverage throughout your building, facility, or outdoor space (see Indoor vs Outdoor DAS). This Master Unit is your distributed antenna system’s brain, transmitting signals to remote units.
This is where the confusion lies: the remote radio units of your active DAS may contain passive elements.
Remote Radio Units (RRUs) in Active DAS
Traditional active DAS uses high-powered remote radio units (RRUs) to extend coverage further into your building or nearby buildings. But these remote units are often fed into a passive network of radio components.
In some instances, you might refer to this as a hybrid DAS system, but what matters here is that it is the active DAS hardware doing the heavy lifting of distributing signal throughout your building.
Deploying passive DAS elements in a primarily active distributed antenna system has its advantages: it places your system’s active hardware in easy-to-access locations for future maintenance, and allows for you to run stronger coaxial cables in areas where more sensitive radio cables would likely be damaged.
The Pros and Cons of Traditional Active Systems
Pros
- Requires minimal maintenance and easy access to equipment
- Extends cellular coverage further from the location of the primary hardware
- Vertical runs up risers take up less space than passive DAS coaxial cabling
- Active units can be remotely monitored
Cons
- Remote Radio Units (RRUs) take up space
- Active DAS is more expensive than passive DAS
- Fiber needs to be run from your active hardware to RRUs, which adds expense to installation
- Difficult to detect issues in the passive DAS elements of your system
Fully Active DAS
Fully active distributed antenna systems do away completely with all passive radio components. Active antennas with full fiber installation take the place of RRUs with passive elements. Fully active DAS are rare because they are so expensive. When people refer to active DAS, they typically mean one that includes at least some passive components.
That said, fully active DAS enables multipath propagation of radio signals (MIMO), allowing you to send multiple signals over a single channel. Obviously, price plays a decisive role in deciding whether to compliment your active DAS with passive components. Making upgrades can be difficult as fully active DAS often requires completely swapping out hardware that could be patched in a traditional system.
The Pros and Cons of Fully Active Systems
Pros
- Full fiber is less expensive to install than coaxial cable
- Overall project costs may be lower despite the equipment being more expensive
- Fully active DAS enables remote monitoring at all points in the system
Cons
- Each antenna draws power, so failure of units is increased
- Upgrades can be expensive and time-consuming
- Fiber is more fragile than coaxial cable and harder to replace
What Active DAS Should I Choose
The best active distributed antenna system for your building or venue depends on many factors.
MCA has the expertise to guide you in choosing the best system for your cellular enhancement needs.