Public Safety and DAS:Considerations for In Building Network Design

Indoor Public Safety Challenges

One of the most critical functionalities of a ubiquitous Public Safety network is the capability of indoor use by any Public Safety entity.

The First Priority for First Responders

Imagine a team of firefighters battling a four-alarm fire blazing across thousands of square ft of warehouse space. With smoke and flames reaching more than 25 ft in the air. Visibility is difficult, at best.

Coordinating efforts between command central and the team deployed throughout the building is critical.

Now imagine each firefighter is equipped with a wearable device capable of keeping them safe while they safeguard the area. This device enables GPS and in-building tracking of the movements of each team member. An in-helmet voice communicator connects them to local and regional fire, rescue, and law enforcement. Live-streaming, bidirectional video helps commanders assess which sections have been cleared and which areas officers should avoid.

Such a device will one day be available. But today, non-standardized requirements, mixed technologies, incompatible platforms, and limited finances have left more than 2.8 million safety officials dealing with the challenges of communicating indoors – where it is most critical.

So in 2012, the First Responder Network Authority (FirstNet) was created to build, manage, and maintain the first Public Safety-grade network with nationwide interoperability. It is charged with ensuring high-speed data for video andvoice applications critical to first responders with coverage for 60,000 agencies in 3,252 counties across 50 states and six commonwealths and/or territories.

We’ve Already Taken the First Step

An independent federal authority within the National Telecommunications and Information Administration (NTIA), FirstNet was funded under the Middle Class Tax Relief and Job Creation Act of 2012. Resources allocated include up to $7.3

billion and exclusive licensing within the 700 MHz radio frequency (RF) bands, including the 10 MHz D Block, creating a dedicated 20 MHz Public Safety network.

To help guide the build-out, the Federal Communications Commission (FCC) assembled an advisory board to develop minimum technical requirements. With input from federal, state, tribal, and local public policy entities, the board recommended a network built according to commercial standards for long-term evolution (LTE) technology.

Other requirements, driven mainly by the National Fire Protection Association (NFPA) fire alarm and signaling code number 72, include but are not limited to:• 99 percent coverage in critical areas as designated by the local fire department, and 90 percent coverage in general- use areas• Support for all local Public Safety frequencies• Cellular support for enhanced 911 services • Commercial-grade voice augmentation of land mobile radio (LMR) • All active and powered components housed in environmentally-hardened enclosures• Cybersecurity, operational redundancy, and backup power for 12 hours at 100 percent operation• Future upgradability and backward compatibility • FCC-licensed system designers and operators• Service providers that can provide two-hour response to system failure

One Goal, Many Challenges

One of the most critical functionalities of a ubiquitous Public Safety network is the capability of indoor use by any Public Safety entity. To date, more than 150 local municipalities mandate Public Safety coverage, and International Code Council (ICC) and NFPA codes mandate in-building coverage for first responders.

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1 IAFF, Briefing on Voice and Data Communications (December 2013), www.iaff.org/Comm/PDFs/Fire_Service_Communications.pdf

NFPA 72, in part, outlines the emergency communication requirements related to fire code regulations. But unlike national electric codes, adoption of NFPA 72 is determined by each jurisdiction. This means they can opt to use NFPA 72 as a template for their individual requirements, choose to implement stricter requirements, or omit Public Safety radio coverage enhancement altogether. The result: NFPA requirements across municipalities are complex, and solutions are difficult to standardize. In addition to diverse local requirements, fewer modern buildings have wired Public Safety stations. Without them, LMR transmissions for Public Safety push-to-talk devices suffer from the same RF structural impediments as commercial devices. But LTE does not support mission-critical voice communication yet. So until voice over LTE (VoLTE) is fully tested and approved by FirstNet, Public Safety officers must continue to use RF-based LMR.1

But the biggest challenge for an indoor Public Safety network is proper design. To enable signal coverage, a distributed antenna system (DAS) is required, and many buildings already deploy DAS for commercial cellular services. So what’s the best way to incorporate Public Safety?

Here are two possible ways:• Using a combined solution for both commercial cellular service and Public Safety• A hardened solution with discreet network elements

The All-in-One Solution

Designing an all-in-one DAS solution that meets the requirements of commercial cellular, Public Safety 700/800 MHz, and Public Safety UHF/VHF lower bands presents many challenges, starting with the headend.

HeadendThe RF source supporting Public Safety is typically a bidirectional amplifier (BDA) located on a rooftop. And, in some cases, systems can be based off trunked radio systems with dedicated channels for Public Safety traffic. However, most operators deploy base transceiver station (BTS) sources in the main distribution frame (MDF) closet using a BTS in a remote hoteling model. This means the RF sources are potentially located in two different areas of the building, requiring extensive infrastructure cabling to connect the headend to the RF source.

Antenna GridUsing the same antenna grid for commercial and Public Safety designs is also complicated. Public Safety only requires -95 dB coverage, unless otherwise specified by the local authority having jurisdiction – versus -85 to -65 dB minimum coverage for commercial. Additionally, Public Safety typically transmits far fewer channels/bandwidth per band. At the extreme this translates into a 30 dB difference or, in terms of an amplifier, a 1 mW Public Safety amplifier would be equivalent to a 1 mW commercial system.

Bands such as 150 and 450 MHz propagate much further into structures than commercial cellular bands – so there is a coverage mismatch between Public Safety bands and commercial cellular bands. And Public Safety requirements may dictate coverage in areas not typically important for cellular coverage, such as emergency staircases, making a combined antenna grid design difficult to optimize for both.

Most antennas and splitters are designed to operate from 700 MHz up to 2.5 GHz. While this range covers the emerging Public Safety 700 MHz bands, it neglects the 136-174 and 450-512 MHz UHF/VHF spectrum. There are a few wideband passives that cover the full 150 to 2.5 GHz, but they are not mass produced and thus expensive.

Overcoming Obstacles

NFPA 72, in part, outlines the emergency communica-tion requirements related to fire code regulations. But unlike national electric codes, adoption of NFPA 72 is determined by each jurisdiction.

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Clear Division

Separate cellular and Public Safety services address perceived liability concerns in cases of system failure. Clear separation means clear understanding of who is responsible for each element of the infrastructure.

And since DAS design is based on the weakest signal, the Public Safety network and antenna grid would need to be designed based on the limiting factor of weaker commercial bands. Integrating cellular and Public Safety mandates a denser grid, resulting in increased cost on the Public Safety side.

Signal Interference The combination of commercial cellular DAS and Public Safety can result in interference from adjacent or in-band uplink (UL) and downlink (DL) in the 700 and 800 MHz bands. For spectrum greater than 700 MHz, there are guards between UL and DL frequencies and filters to manage the band noise from adjacent frequencies. This can be solved with duplexing filters at each remote, but it is expensive and can degrade performance of other bands.

The use of separate UL and DL antennas can help mitigate interference, but commercial cellular DAS does not require them. Isolating the antenna grid by at least 50 ft also works, but this makes grid design less efficient and denser than needed.

Another combined design challenge stems from the inability for the typical DAS to handle “simplex” signals used in the narrowband Public Safety bands. Some Public Safety UL and DL channels are on the same frequency, while commercial cellular bands have uniform UL and DL separation. Additionally, Public Safety UHF/VHF has potentially interleaved frequencies with 3 or 5 MHz spacing, making filtering quite challenging.

Code RequirementsThe International Fire Code (IFC) and NFPA 72 require all components supporting Public Safety networks to be housed in National Electrical Manufacturers Association (NEMA) Type 4-compliant enclosures. As the backbone of an all-in-one, in-building Public Safety system, all active components of the DAS would need to be housed in a NEMA-certified, environmentally hardened enclosure to be compliant.

Lastly, NFPA 72 outlines pathway protection for all Public Safety networks. Pathway survivability requires shielding the coax infrastructure with conduit. Half-inch coax is not only difficult to bend, but when the requirement is to fully protect the infrastructure for Public Safety, pulling conduit for the entire commercial grid and Public Safety antennas can significantly increase the cost of the deployment.

Combining Public Safety and cellular service on a single DAS requires design engineers to serve competing masters, adding exponentially more passive and active hardware. The installation becomes more complex, requiring more power, more space, more time, and more expense.

A Two-Pronged Approach

A smarter answer lies in a hardened solution with discreet network elements designed to best serve cellular and RF respectively. Separate headends and separate remotes, while sharing cabling in the riser and in the ceiling.

With converged cellular and wireless on one remote, you have a solution with modular service from the headend to the antenna. It supports cellular enhancements and other building applications, including multiple operators and mobile services, Wi-Fi, video surveillance, building automation, and more.

Adding in a separate, parallel system for Public Safety communications ensures robust mission-critical voice with extended survivability in case of an adverse event.

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Plan for Growth

The most important consideration in deploying our nation’s first ubiquitous wireless broadband public safety network should be planning for growth, change and innovation.

Keeping the two separate also accommodates the different technology needs of buildings already deploying cellular coverage. Why require building owners to bear the cost of a new system based on an integrated solution – when all they need is added support for local Public Safety frequencies?

Additionally, separate cellular and Public Safety services address perceived liability concerns in cases of system failure. Clear separation means clear understanding of who is responsible for each element of the infrastructure.

(Eventual) Infinite Possibilities

The most important consideration in deploying our nation’s first ubiquitous wireless broadband Public Safety network should be planning for growth, change, and innovation. One day, the ideal first responder communications solution will deliver high-speed voice, video, and data coverage – and much more.

A hardened solution with discreet network elements will help ensure commercial cellular and Public Safety coexist by:

• Addressing 450, 700, and 800 MHz spectrum • Accommodating different sensitivity and mobile power• Satisfying pathway survivability requirements of active components• Fulfilling critical Public Safety code requirements• Enabling core cellular technologies and multiple applications• Differentiating ownership and authority, thus liability, of operation, maintenance, and alarm monitoring and service• Meeting major metro area requirements for indoor coverage in new buildings

This flexible, scalable design strategy enables the delivery of secure, cost-effective, and efficient Public Safety coverage. And peace of mind.

About Corning Incorporated

Corning is one of the world’s leading innovators in materials science. For more than 160 years, Corning has applied its unparalleled expertise in specialty glass, ceramics, and optical physics to develop products that have created new industries and transformed people’s lives. Our distributed antenna systems (DAS) enable a wide variety of technologies and services including, GSM, CELL, PCS, iDEN, AWS, WMTS, Paging, UMTS, DCS, 700 MHz LTE, 4G LTE, and Public Safety.

In the early days of indoor wireless coverage, Corning introduced the now-standard neutral host DAS, pioneering a shared cellular and Public Safety passive infrastructure – and we have hundreds of converged Public Safety and cellular coverage solutions to fit facilities large and small. But with an increasing demand for hardened Public Safety systems, we believe the more cost effective, reliable and technically sound approach is a separate solution overlaid with discrete network elements for commercial and Public Safety.

Corning Optical Communications Wireless, Inc. • 13221 Woodland Park Road, Suite 400 • Herndon, Virginia 20171 USA866-436-9266 • FAX: 703-848-0280 • Tech Support Hotline: 410-553-2086 or 800-787-1266 • www.corning.com/opcommCorning Optical Communications Wireless reserves the right to improve, enhance, and modify the features and specifications of Corning Optical Communications Wireless products without prior notification. A complete listing of the trademarks of Corning Optical Communications Wireless is available at www.corning.com/opcomm/trademarks. All other trademarks are the properties of their respective owners. Corning Optical Communications Wireless is ISO 9001 certified. © 2014 Corning Optical Communications. All rights reserved. Published in the USA. CMA-373-AEN / October 2014