First Response is Everything: Public Safety Communications and DAS

June 17, 2016

Consistency in nationwide public safety networks is critical. Distributed antenna systems require attention to prevent near-far interference with in-building wireless — a situation that could otherwise prevent networks from meeting coverage requirements.

By Rick Good

Public safety networks, supported by an information and communications technology infrastructure, are critical to the safety of citizens and first responders everywhere. Implemented across high-rise buildings, campuses, tunnels, shopping malls, airports and parking garages, the public safety network operates as a shared inter-organization, an information technology (IT)-enabled system and a wireless network used by emergency services organizations.

As the United States faces increased terrorist threats and natural disasters, public safety networks are becoming more highly prioritized. Over the past decade, there has been a substantial increase in national, state and local legislation requiring minimum coverage standards for public safety communication systems. And various public safety agencies in the United States have joined forces to collaborate, communicate and share information in the face of major public safety incidents. In fact, many of these agencies are collaborating to design, develop and deploy information and communications technologies to assist first responders and support criminal justice, policing and homeland security endeavors.

In support of these efforts, in February 2012, the Middle Class Tax Relief and Job Creation Act created the First Responder Network Authority (FirstNet), an independent authority within the U.S. Department of Commerce’s National Telecommunications and Information Administration. The FirstNet board of directors is composed of representatives from the public safety community, from local, state and federal government, and from the wireless industry.

Seamless and reliable communications coverage inside buildings is becoming more vital for public safety purposes, to the extent that some municipalities require public safety coverage in buildings before issuing certificates of occupancy. When an emergency occurs in a building, clear, crisp internal and external wireless communications is essential; it allows different rescue teams to communicate with each other when they are inside.

Public safety communication networks include hardened sites that will continue to operate during power outages or water events, and they are designed to continue to operate for as long as possible in the event of a natural or man-made disaster. To that end, in-building wireless solutions for public safety may include repeaters (bidirectional amplifiers) or active distributed antenna system (DAS) infrastructure to satisfy minimum legislative standards and new public safety building codes implemented by International Code Council (ICC) and the National Fire Protection Association (NFPA).

Efficient Response

Public safety DAS guarantees maintainable communication among first responders during a crisis, enabling them to combine efforts and produce a more efficient response to emergencies. A reliable DAS makes a world of difference during an emergency, and organizations such as the NFPA support a more reliable, efficient and life-saving communication system for emergency responders. The NFPA requires 99 percent coverage in designated critical areas and 90 percent coverage in general-use areas. A DAS typically does not provide coverage for areas such as stairwells, except in locations where public safety communication networks are integrated.

According to NFPA, enclosures that meet National Electrical Manufacturers Association (NEMA) Type 4 or Type 4x requirements must be used to house equipment such as radio and power systems to protect against dust and driven rain. All public safety enclosures must be painted red to resemble fire equipment.

Monitoring Alarms

The fire protection association also has requirements for system monitoring alarms. NFPA requires real-time monitoring of the system’s readiness, including alarm requirements for power and battery charger failures, signal booster trouble, antenna malfunctions and battery capacity. The system must generate an alarm when battery capacity falls to 30 percent.

Minimum signal strength is also important to the NFPA, which requires at least −95 dBm within the coverage area, regardless of the radio frequency. The International Fire Code (IFC) has the same requirement.

Battery Backup

To keep the public safety radio system operating when power to the building fails — or when it is deliberately interrupted during an emergency to prevent injury to first responders — the code requires at least 12 hours’ worth of battery backup for equipment supporting the public safety radio system. The NFPA specifies that systems supporting the public safety emergency responder radio coverage must support future frequency requirements. Further, the NFPA stipulates an antenna isolation requirement of 15 dB higher than the gain of the amplifier.

Enhancing the Network

Indoor wireless signal strength, signal degradation and interference can seriously affect public safety DAS performance. Therefore, preparation is key. The near-far performance problem, for example, is inherent in conventional DAS networks. Near-far is a term used to describe performance and capacity degradation when a mobile device is operating within a DAS coverage area but is not serviced by the DAS. When it comes to installing public safety coverage in a building in which a commercial DAS has previously been installed, designers need to ensure that the commercial DAS network does not interfere with the public safety system.

Westell Technologies, a provider of in-building wireless, intelligent site management, cell site optimization and outside plant solutions, offers an in-building wireless system called ClearLink. This system mitigates signal degradation and subsequent performance issues caused by near-far performance reduction.

Public Safety Repeater

In February 2016, Westell engineered and introduced its PS51080 public safety repeater to satisfy the future efforts of FirstNet to deploy and operate a common nationwide public safety broadband network. The repeater meets the NFPA 72 requirement when installed with NFPA-compliant battery backup. Additionally, the repeater has antenna and signal booster failure alarming and a NEMA Type 4 red enclosure.

The Westell repeater lets customers install an in-building repeater that will meet the existing public safety communication regulations and that will also allow them to prepare for future mandates and nationwide network deployments for emergency and disaster preparedness communications. Like the Westell repeater, all new DAS repeater solutions should go beyond simply meeting today’s stringent industry requirements and offer high quality, reassurance and planning. These three aspects are crucial to public safety network success.

Rick Good is senior vice president of in-building wireless at Westell Technologies.

Select NFPA Requirements for Public Safety Coverage

The NFPA requires 99 percent coverage in designated critical areas and 90 percent coverage in general-use areas.
NEMA Type 4 or Type 4x enclosures must house equipment such as radio and power systems to protect against dust and driven rain. Public safety enclosures must be painted red to resemble fire equipment.
System monitoring alarms must provide real-time monitoring of the system’s readiness.
The system must deliver a minimum signal strength of −95 dBm, regardless of the frequency.
The code requires the equipment supporting the public safety radio system to remain operational on a battery backup for no less than 12 hours.
Systems supporting the public safety emergency responder radio coverage need to support future frequency requirements.
The NFPA stipulates an antenna isolation requirement of 15 dB higher than the gain of the amplifier.