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Solving the Challenges of FirstNet: How to Ensure Public Safety Wireless Works Indoors

Author: James Martin

Copyright: Copyright 9-1-1 Magazine, Feature Content

Date: 2017-10-16
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Get ready for FirstNet with in-building wireless coverage


Today’s landscape of public safety wireless communications is a jumble of local standards and frequency bands (VHF, UHF, 800 P25) without any nationwide standards – but over the next decade, that’s all going to change.

FirstNet – the first standardized nationwide emergency responder network, which will use LTE technology in the 700MHz frequency band and which will eventually supplant the use of existing public safety frequencies – will soon become available for use. However, there are already challenges that will arise from FirstNet’s deployment.

It will initially be deployed as a macro network, and while signals at this frequency penetrate into buildings better than some higher frequencies, there will be many midsize and large buildings that will not be able to get the usable signal strength needed for indoor penetration and coverage.

But while FirstNet is an attempt to unify the national public safety communications infrastructure, it doesn’t initially address specific in-building needs. Despite the current use of lower frequencies (150MHz to 850MHz) to support public safety radios, many buildings experience insufficient radio coverage. Even at these low frequencies, building construction materials can block outdoor radio signals from penetrating indoors.

Underground areas such as basements or tunnels are impossible to cover from the outside, and energy-efficient, LEED-certified buildings that use low-emissivity windows (which block exterior cell signals) make matters worse. There are currently 2.5 billion square feet of LEED-certified buildings in existence, and approximately 45 percent of non-residential building construction this year will be “green.” 

Many local governments mandate the use of in-building wireless systems for public safety systems in buildings over a certain size, but even existing systems will be in for a revamp as FirstNet comes online.


LTE Convergence: Another Wrench in the Works

While LTE is now the dominant technology in commercial cellular networks, there is a lot of work being done to further leverage LTE’s benefits, impacting FirstNet LTE as well.

For example, mobile operators are always looking for more spectrum to expand bandwidth and provide their users with faster throughput. Once they have gotten all they can out of new cell sites, splitting sectors and carrier aggregation, the next thing to do is look at using unlicensed spectrum to further expand available bandwidth. LTE-U, LAA, and MulteFire are all terms that describe approaches to using unlicensed spectrum that will deliver more from current technology.

  • LTE Unlicensed (LTE-U) is a protocol that enables mobile operators to increase bandwidth in their LTE networks by using the unlicensed frequency bands in the 5GHz range, which are also used by Wi-Fi devices.
  • License Assisted Access (LAA) is the name given to the Third-Generation Partnership (3GPP) effort to standardize the use of LTE in Wi-Fi frequency bands. LTE-U is an implementation of LAA.
  • MulteFire is another license-free implementation of LTE. 

Unlicensed LTE protocols will play a significant role in boosting LTE bandwidth and throughput while being a key component of connecting the Internet of Things (IoT). Ideally, in order to speed deployment and deliver an economical solution, public safety, wireless IoT devices, and cellular services will all operate on a converged network leveraging same or similar standards and same/one time deployments.

FirstNet will leverage the same LTE network, so it’s possible that in some cases, the 700MHz public safety frequency may already be supported by some in-building wireless systems. However, the frequencies used for the FirstNet network are not the same as the 700MHz frequencies in use by cellular carriers today, so this would be true in a limited number of cases.

In many instances, it will be necessary to rip out and replace existing public safety (or even commercial, in some cases) in-building wireless systems to facilitate the support of FirstNet – and that means building owners and managers need to ensure they have a system that works not just now, but well into the future.


DAS: How to Solve FirstNet Challenges

A distributed antenna system (DAS) network is one option for public safety agencies and building owners to ensure they are ready for FirstNet as well as to meet current challenges of indoor coverage.

DAS comprises of cabling, small remote units and antennas that are distributed throughout a building and linked to a central distribution hub. This hub in turn connects to the RF source used by the mobile operators. Through a DAS, the wireless signal is distributed to all parts of the building.

Because the signal used to support a DAS is separate from outdoor cellular towers, capacity is dedicated to the building, and because it’s actually an operator-provided and -supported cellular signal being brought into the building, users receive a guaranteed level of service, as opposed to unguaranteed performance of a voice-over-Wi-Fi, for example. Plus, calls can seamlessly hand off from the inside network to the outside network as users move from inside to outside the building.

When buying or upgrading an in-building wireless system to a DAS, there are a few basic requirements:

It should support 700MHz FirstNet frequencies while still supporting existing cellular and IoT frequencies. In addition to the current lack of a unified standard, public safety wireless systems vary by city and county across the nation. Some systems use 150MHz and 450MHz frequencies (which penetrate buildings well), while others use 800MHz frequencies (which do not).

A building might be using 150MHz, 450MHz or 800MHz today, but when FirstNet arrives, the building will have to transition to 700MHz frequency bands. It is probable that all these frequency bands will be in use until the complete FirstNet transition occurs, which may take several years.

A truly wideband DAS can support any frequency from 150MHz to 2700MHz, so it could support many different frequencies with a single layer of equipment, including 700MHz FirstNet, as well as seamlessly support future services with no additional hardware like cabling or remote antenna units needed. This will simplify both deployment and maintenance, while keeping costs down.

It should use fiber infrastructure. Different fire jurisdictions mandate either coaxial cabling or fiber as the transport layer of a public safety wireless system. While most public safety systems today employ coaxial cable, as commercial networks evolve toward fiber, and as FirstNet LTE can be most efficiently deployed on the same layer as commercial LTE, a public safety transition to more fiber is natural. Fiber ensures high signal quality and strength at each remote unit, and can often leverage existing spare fiber in a building to connect the public safety wireless system.

It should have a simple architecture. Many DAS products have a dizzying array of parts due to their inherently narrowband architecture, making it difficult for IT staff to both deploy and maintain them, and building owners shouldn’t have to become wireless system experts to deploy a public safety wireless system. They should be able to employ standard-level cabling and systems technicians, so the system should be as simple as possible to install and configure.

Building owners and contractors should look for DAS solutions that mirror IT data infrastructure, with a limited number of system elements, so it is familiar and easy to understand.

It must comply with fire, life and safety standards. DAS components should be certified for use in public safety deployments by the National Fire Protection Association and be compliant with various international fire codes, as well as have the appropriate enclosures to protect remote units from dust, smoke and ash.

It should offer low TCO. While a public safety wireless system is typically in the budget for new building construction, existing buildings will have to retrofit these systems to support FirstNet frequencies, and they will have to find the money to pay for them.

Ideally, a DAS should have a very low total cost of ownership to keep spending at a minimum. Combined with the above-mentioned synergies with commercial deployments, it can further reduce the costs of deploying FirstNet.

It must offer symmetrical performance. First responders must have a clear, strong signal wherever they are in a structure, especially in places where signal is not typically critical for commercial users, such as in stairwells and elevator banks. A DAS must provide a uniformly strong signal at every antenna.

It must be future-ready. A DAS should support today’s and tomorrow’s public safety frequencies. Users should not have to install special remote units or modules to support one frequency or another, or upgrade remote units when FirstNet comes.


Ready for FirstNet – and the Future

The move toward FirstNet public safety infrastructure represents both a challenge and an opportunity for building owners. The challenge is that many in-building wireless systems will have to be upgraded or deployed – some existing systems support other frequencies but not the new 700MHz FirstNet, and some buildings lack any kind of indoor coverage solution.

But the good news is that the need to support FirstNet offers the chance to deploy a single, converged in-building wireless system that supports all wireless traffic. FirstNet will take several years to roll out, but building owners and facility operators shouldn’t wait to start thinking about this – because a future-ready, full-spectrum in-building DAS is a must for ensuring clear and consistent radio coverage for building occupants and first responders, both now and years down the line.


James Martin is vice president of operations at Zinwave, a provider of wideband distributed network solutions for in-building cellular and public safety services. Martin can be reached at


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