20 Sep Public Safety Distributed Antenna Systems
For those who don’t have a ready understanding of the difference between commercial cellular and public safety DAS, I thought a simple chart might help to get us started on the right track. This one is definitely worth the refrigerator magnets:
|QUESTIONS||COMMERCIAL CELLULAR DAS||PUBLIC SAFETY DAS|
|WHO USES IT?||Five billion people||Firefighters, police, paramedics, etc.|
|HOW DO YOU USE IT?||With a cell phone||With a two-way radio (Motorola or other)|
|TO WHAT NETWORK IS IT CONNECTED?||AT&T, Sprint, T-Mobile and/or Verizon. Could be one, some or all.||The local municipality’s government radio repeater system|
|WHAT RADIO FREQUENCIES ARE REBROADCAST||Varies by carrier and slightly varies by market, but generally consistent across the nation.||Varies widely by municipality although generally in the VHF, UHF, 700 MHz and 800 MHz ranges.|
|WHAT RULES GOVERN IT?||Anything the wireless carriers decide.||NFPA 1221, IFC 510, governmental statutes and the local Authority Having Jurisdiction (AHJ)|
|WHAT IF MY BUILDING DOESN’T HAVE IT?||People don’t want to come to your building.||You might not get a Certificate of Occupancy, and the firefighter in your building might not be able to talk to his captain on his radio.|
|WHO OPERATES IT?||Could be the carrier, a neutral host company or an integrator hired by the building owner.||An integrator hired by the building owner.|
|ACTIVE OR PASSIVE?||Commercial DAS are always active, meaning they actively conduct signal processing at multiple remote nodes. Only boosters are passive.||Could be active, if a large facility using fiber-fed remotes, or passive in a larger facility that only has a bi-directional amplifier.|
|WHAT’S COMING DOWN THE ROAD?||4G+ and 5G||FirstNet–nationwide broadband public safety network|
PS DAS ORIGINS AND NATURE:
Put simply, the purpose of a PS DAS is to ensure the communication capabilities of the emergency responder working in a building (with his two-way radio), thereby enhancing the safety of the building occupants by making that firefighter, paramedic and police officer more effective and safe.
The origins of PS DAS, in terms of their design and code requirements, is heartbreaking when you consider the technology was available much earlier than it was used for PS DAS. On September 11, 2001, 412 emergency workers died in the infernos of the two World Trade Center towers. As the instability of the structures became apparent to the emergency management leadership, calls went out over the two-way radios to the firefighters, police officers and paramedics in the building to “Get out!” Tragically, because there was no PS DAS in those buildings, many emergency workers did not hear the message. They remained on duty, attempting to rescue building occupants, and died when the buildings fell.
In 2005, the 9/11 Commission made a number of recommendations. Among them was the proposal that high-rise and larger scale buildings be fitted with radio bi-directional amplification systems, tuned to the government emergency responder radio repeater systems for each local municipality, so as to protect emergency responders from ever facing such a horrible situation again. The key to the proposals, and subsequent codifications in the National Fire Protection Association (section 1221) and International Fire (section 510), is that these systems are intended for wherever the ambient signal strength and quality of the municipalities radio repeater system does not meet minimum standards inside buildings. Successive iterations of the NFPA and IFC have refined the signal strength and quality requirements and addressed critical aspects of the system’s survivability (in the event of a fire).
Thus, the system is only needed if the building structure somehow prevents the ingress of the municipality’s radio system. Which means that the signal strength and quality must be measured (which is somewhat difficult to do for a building that is only in the planning stages). And if it passes, then no PS DAS is needed… for the most part.
Certain municipalities, on the West Coast, in Colorado, Texas and Florida and possibly other locales (it’s hard to keep up with all of them because the landscape changes constantly) now require PS DAS regardless of the strength of the ambient signal strength for new, larger buildings. While that mandate makes it easier for a building owner to budget for a PS DAS, the mandates to increase survivability requirements can significantly increase the cost of the system.
But wait, there’s more! Some municipalities and even states (Florida in 2016, for example) have now mandated that PS DAS be implemented retroactively in existing buildings, where ambient signal strength or quality metrics are not met. So an existing building owner must hire a competent PS DAS integrator, obtain signal strength and quality test readings, and then submit those readings to the AHJ. If the building passes, you’re finished. By the way, never has one of our PS DAS tests successfully passed an entire building. Usually it’s the lower floors that fail, and because of the detailed testing requirements of the NFPA and IFC, if even a small area on one floor fails to meet the requirements, then a PS DAS is needed.
And to top it off, new building construction materials, such as low-e glass, significantly impede RF signal propagation. Put simply, modern, LEED certified buildings kill radio signals. If radio signals cannot get in, then you need a PS DAS. (It’s worth mentioning that you’ll also need a cellular DAS unless you don’t care if consumers come to your building).
WHAT’S INCLUDED IN A PS DAS?
Because the municipality radio repeater system operates in a much simpler fashion than a cellular network, the PS DAS is correspondingly simpler and less expensive than a commercial cellular DAS. Again, a simple diagram might be of some use here:
In almost all cases, the PS DAS connects to the municipality’s radio repeater network through a donor antenna located on a rooftop, which connects by coaxial cable to an in-building repeater. This particular PS DAS is active, in that it is a large building system with multiple fiber remotes that take the amplified signal from the in-building repeater and distribute it throughout the building across antennas.
Relevant to the discussion of investment is that a PS DAS is monitored through the building’s Fire Alarm Control Panel (FACP). Often fire alarm integrators are, therefore, asked to design and implement the PS DAS. But the competency to do so, as well as the usage of very expensive tools and software that are necessary, typically rests in the hands of integrators who have significant radio frequency (RF) experience—either through a background in commercial DAS, or two-way radio systems.
PRICING, AND WHETHER COMMERCIAL AND PS DAS SHOULD BE TWO SEPARATE SYSTEMS OR BE COMBINED INTO ONE SYSTEM:
Yes, it is completely feasible to combine PS DAS and commercial DAS. But, in many, perhaps most cases, the economics of combining the systems are less attractive than providing two separate systems.
The PS DAS requires “hardening” of all active electronics, which means encasement in NEMA 4 enclosures. All of those electronics must have 12 hours or more of electrical power back up, which, if a building generator isn’t acceptable then UPSs are needed for all of them—again, in NEMA 4 enclosures. Trunk cables for PS DAS are required to have a two-hour survivability rating, which can be quite expensive if not inside a rated riser closet. In some municipalities, that two-hour rating also applies to the branch cabling extending to the antennas. Finally, the PS DAS, being simpler, on different frequencies and for powerful five-watt radios, requires fewer remote nodes and antennas.
What these various differences mean is that combined systems have more remote nodes and antennas than is needed by the PS DAS, but all those remote nodes, riser cables (and in some cases branch cables) must have expensive NEMA 4 enclosures or two-hour fire ratings not necessary for commercial cellular DAS. Sometimes it makes sense to purchase a combined system, but we recommend that a conscientious building owner allow for pricing both ways, just to be sure.
For stand-alone PS DAS, we recommend budgeting $.35-$.50/foot. The cost increases as the building size requires an active instead of a passive system, but then scales down in cost as the size of the building grows.
Over fifteen years ago the federal government planned for FirstNet as television broadcast transitioned from analog to digital. Remember those digital convertor boxes you had to get in order to watch shows on your fat tube TV? That conversion freed up bandwidth in the 790 MHz range, which was set aside for a national broadband network.
It’s taken all of that time for FirstNet to go from plan to reality. In March of 2017, the federal government finally awarded to AT&T the contract to build the nation’s common frequency (called Band 14), broadband network for emergency responders. Today, all municipal radio networks are simple duplex. They allow radio communication back and forth (with that annoying “Over” whenever what you’re saying is over), but no kind of high bandwidth, full duplex audio and video communications. Plus, they use all sorts of various frequencies, so there is no uniformity.
FirstNet will change all of that. Firefighters will have video displays on their uniforms that allow them to see footage from a surveillance camera, a map of the building, or reported dangerous locations. FirstNet will help make it possible for first responders to locate persons, whether persons trapped in fire or active shooters or other, through telemetry with their cell phones.
Understanding FirstNet makes sense of why more and more municipalities are going beyond the NFPA/IFC testing requirements and insisting on installing a PS DAS regardless. As FirstNet becomes a reality, and emergency responders’ ability to assist civilians increases, none of that investment will have any value if the Band 14 signals cannot be received inside a building.
HOW TO PLAN AND BUDGET FOR PS DAS:
There are a number of arguments to be made for budgeting and installing PS DAS in a new, large commercial building as a standard. These are:
- Predictability and lowest cost for the PS DAS: if preliminary testing is dispensed with, and the PS DAS planned from the outset, the system should cost less than one developed iteratively in stages. Plus, the codes allow the elimination of firefighter jacks in buildings that have a PS DAS.
- Humanitarian and risk mitigation: the presence of PS DAS means there would be an increased chance that first responders can do their job effectively with reduced legal liability for the building owner in the event of a situation resulting in injury or death.
- Synergies with local, in-house two-way radio systems; most PS DAS systems allow for the re-amplification of the building’s in-house Motorola (or other) radios, used by back-of-house staff.
- Trending requirements; more and more municipalities are requiring systems regardless, even retroactively, so it’s very possible that a PS DAS would have to be provisioned later anyway. Plus, a new building erected next to your own, just a few years later, can effectively kill signals that used to penetrate your building.
Assuming I haven’t persuaded you to forge ahead with a PS DAS every time, (and I wasn’t really trying to twist your arm), what is the best way for a building owner to plan and budget for PS DAS?
- First, identify the state and local requirements. In some cases, you won’t have a choice. As of today, in most cases the municipality will require a PS DAS only if signal tests fail. But they often have significant, detailed requirements. Plus, often they are operating under an earlier code version than the latest one, which argues for careful research ahead of time.
- Second, recognize your dilemma and plan accordingly. You won’t know if you need a PS DAS until your building is nearly finished. At that point, it’s going to be very difficult to have the system installed in time to satisfy your need to obtain a Certificate of Occupancy. But you don’t want to contract and pay for a PS DAS if you don’t need it. So, we recommend you obtain a quote for a PS DAS at the outset.
- Third, obtain a quote for a PS DAS in three parts:
- Preliminary testing for when the building reaches approximately 80-85% completion. Soon enough to measure the RF environment accurately but with enough time to install a system if needed. If it passes, then the money expenditure ends.
- The “core” system, including headend, donor antenna, connection to the FACP, etc. and coverage for the likely deficient areas—typically all underground floors, the first one or two above ground floors, and areas that are deep inside concrete walled interiors. These are likely to be needed regardless.
- A per unit price to expand coverage to additional areas (typically these are in approximately 10,000’2 increments)
- Finally, don’t forget to budget for annual inspections, which require a complete retest of signal strength throughout the building and recertification of the PS DAS components, monitoring effectiveness, etc.
I find that once the information about PS DAS is communicated, it isn’t as difficult to figure out as seemed at first. Confusion with commercial cellular systems, which hopefully we’ve eliminated here, accounts for much of the mystery. Differing local codes create another large portion of misperception, and there’s no simple solution—you must research based upon the building location. After those two, the main issue is figuring out how to plan for a PS DAS when you don’t have a building “built” yet. See section above, in case you missed it.
Final word. It does actually take some sophistication to design, implement and test PS DAS. Software and testing equipment are costly and difficult to use without good training. Check on your integrator and make sure he has real bona fides. After all, this is a life safety system.
[Featured on Network Technologies, Inc.’s website: http://www.nticonsultants.com/2017/09/12/public-safety-distributed-antenna-systems-part-ii-of-the-in-building-wireless-systems-series]
[For more info on DAS, Public Safety DAS, ERRCS, etc. read Eric Fichtner’s article HERE]