SMART Passives Enhance In-Building Public Safety Communications

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The Public Safety Communications Imperative

When emergencies arise inside a high-rise building, time is of the essence. Once first responders arrive on scene, they must be able to communicate reliably and clearly with each other.

“It’s imperative that mission critical radio transmissions for our first responders: fire, police, and emergency medical services get in and out of buildings, covering all common areas and into the emergency exits, areas of refuge, utility, and mechanical spaces,” says Tom McCabe, Manager-Business Development at Wireless Telecom Group. “Safety and lives are on the line.”

Such communications are critical, both for first responders themselves and people inside the building.

The third pillar of the Safer Buildings Coalition’s Three Pillars of Public Safety Communications says, ‘First Responder Communications Must Work’. “The portable radios used by first responders is their most important tool and the message must get through,” McCabe emphasizes.

Dedicated Public Safety Communications Networks 

Because of the critical nature of their use, public safety communications typically use a dedicated wireless network that is separate from commercial cellular services. This arrangement allows first responders to communicate with command centers and among themselves outdoors, in vehicles and inside buildings, without interference from other wireless networks.

In-building PSC networks are unique since they are designed to cover not just general use areas such as lobbies and corridors and limited-use areas such as stairwells, elevators, equipment rooms, and parking garages. These networks operate on the same public safety radio frequencies used outdoors, typically, VHF, UHF, and 700/800 MHz.

An Emergency Radio Communications Enhancement System (ERCES), also known as a bi-directional amplifier (BDA) or passive distributed antenna system (DAS), is a life safety system like a fire alarm system. ‘Passive’ means RF signals are not changed or converted in any manner.

An ERCES consists of:

  • An outdoor donor antenna mounted on the roof or on the side of the building and pointed towards a nearby transmitter site captures downlink radio signals and brings them inside.
  • Coaxial cable feeds the signal into a BDA that then amplifies or boosts the signal to indoor DAS antennas mounted at key points throughout the building.
  • Coaxial cable connects the BDA to DAS antennas using a series of passive RF signal splitters and couplers.
  • Uplink signals from portable radios within the building pass from the DAS antennas to the BDA then into the greater public safety network through the outdoor donor antenna.

Fire Code Specifications

An ERCES design must comply with NFPA72[1], NFPA1221 and IFC510[2] DAS fire codes for Emergency Responders Radio Coverage Systems (ERRCS) for all new and renovated buildings. These codes specify parameters such as minimum signal strength (-95 dBm), wireless coverage (99% in critical areas as designated by the local fire department., 90% in other areas), delivered audio quality (DAQ=3.0) equipment enclosures (NEMA-4), fire-rated cables (2 hours), and standby battery backup (2 hours).

As a matter of practice, always consult with the Authority Having Jurisdiction (AHJ) regarding applicable local specifications or ordinances.

McCabe points out, “More and more jurisdictions throughout the world are adding in-building, public safety radio communications requirements to their building and fire codes. Modern building materials that enable LEEDS/Green Compliance attenuate radio signals due to molecular level metallic coatings and films on walls and windows through the steel floor pans with reinforced poured concrete.”

The Need for DAS Monitoring

The City of San Francisco (CA) Fire Department (SFFD) first developed an addendum for ERCES monitoring to complement NFPA1221 and IFC510. Together these codes standardize the requirements for in-building radio coverage for first responders in new or heavily renovated buildings.

SFFD found that seismic activity, heavy renovation, and building maintenance often cause cable cuts or damage, and disconnect or damage antennas leading to catastrophic radio coverage failures for first responders.

“A building’s risers and plenums are alive with activity in terms of adding and maintaining HVAC, improved lighting, heavy renovation, security systems, high-voltage, IT, and telecommunications structured cabling,” McCabe explains. “That increases the opportunity for ERRCS – public safety DAS cabling to be damaged, cut, and antennas disconnected, only to be found out in the midst of an emergency event.”

Maintaining code compliance for ERCES coverage and signal strength becomes a maintenance challenge if every system must be regularly tested on site for RF communications integrity in critical areas. 

Introducing the SMART Passives System

Microlab, based in Parsippany, NJ, designs and manufactures the SMART Passives System. The heart of the SMART Passives System is an embedded Internet of Things (IoT) chipset that enables RF diagnostics, control, and processing.

The SMART Passives Systems comprises the SMART Gateway that is collocated with BDA. The SMART Gateway communicates with up to 30 SMART Couplers that are installed close to DAS antennas.

Each SMART Coupler has onboard IoT diagnostics capabilities and a unique identifier or media access control (MAC) address.

Proactive Fault Monitoring

To facilitate the monitoring, the SMART Gateway generates a calibrated, continuous wave (CW) tone in the industrial, scientific, and medical (ISM) band at 902-928 MHz. The SMART Couplers use the calibration tone to measure the voltage standing wave ratio (VSWR) at each coupled and through port.

If all is well, there are no dead zones so the system can deliver specified signal strength and DAQ levels.

The reference VSWR is continuously monitored and compared, providing proactive alarming by monitoring for any abnormalities that may indicate a catastrophic failure, such as an open or short circuit caused by cut or damaged coaxial transmission lines or disconnected antennas.

Changes from the calibrated VSWR and power levels are an indication of a fault or change from the properly terminated 50-Ohm load of an antenna. The fault will generate an alarm indicating a short or open circuit within the overall ERCES.

Network Access

If a failure is detected, the detecting SMART Coupler signals the SMART Gateway which in turn sends an alarm notification through SNMP traps via email or SMS with the detecting SMART Coupler’s MAC address.

Each SMART Coupler’s MAC address may be recorded on the ERCES’s as-built drawings, providing an approximate location of the fault within the building to expedite troubleshooting and time to restoration.

The SMART Gateway has a normally-closed dry contact terminal that will generate an alarm output that is tied to the building’s fire alarm system for further failure notification.

Users can connect a computer browser to the SMART Gateway to easily monitor all diagnostics and alarms within a convenient, multi-layered graphical user interface (GUI) that displays all relevant data, such as network information of the SMART Coupler nodes, alarm statuses, along with time- and date-stamped VSWR measurements.

In addition to VSWR, the SMART Passives System also monitors the RSSI RF power of the calibrated, CW test tone to ensure every component is functioning properly.

Handling Power Failures

Up to 30 SMART Couplers are powered by a 24VDC bias from the SMART Gateway over the DAS coaxial cable.

Communications and diagnostics between the network of SMART Couplers and the SMART Gateway take place over the DAS coaxial cabling.

Batteries or a local source of DC power and network connectivity are not required.

In the event of a SMART Gateway power failure, public safety radio traffic will always pass over the DAS. However, the operator will lose monitoring and diagnostics until power is restored.

SMART Gateways that are AC-powered may be connected to the equipment room’s backup power source such as an uninterrupted power supply (UPS) or diesel generator.

DC-powered SMART Gateways may be connected to the head-end’s battery backup unit (BBU) required for the radio equipment.

Monitoring Alternatives

The SMART Passives System is a diagnostic centric, VSWR- and signal strength-based, calibrated test and measurement system. The SMART Couplers are a direct replacement for the required tappers and couplers used in a passive DAS design and may be ordered in 6, 10, 15, and 20 dB coupled port values. The SMART Passives System is agnostic to the RF band or antenna type.

By comparison, radio frequency identification (RFID) tags are used to check the availability or continuity of an antenna but provide no qualitative, diagnostic information to indicate degradation over time that could prompt preemptive repair before a complete failure occurs.

SMART Passives System Deployment Costs

SMART Passives System costs are incremental to the overall costs for the required ERCES devices.

SMART Couplers are a direct replacement for the required tappers and couplers used in a ERCES design and may be ordered in 6, 10, 15, and 20 dB coupled port values.

Studies show that for an 800 MHz ERCES in a 250,000 sq. ft. building, a SMART Passives System may be implemented for $0.18 to $0.20 per sq. ft.

There is no incremental labor charge to install a SMART Coupler since it is merely a replacement for the existing tappers or couplers using common N-type connectors.

The SMART Passive System Advantage

Building owners are responsible for procuring, implementing, and maintaining an ERCES in new or heavily renovated properties where first responder coverage is poor. This step is necessary for the building owners to receive a certificate of occupancy (CO).

The CO is issued after demonstrating proof-of-performance and high-quality first responder radio coverage. The AHJ typically will perform annual walkthroughs to assess RF coverage on a floor-by-floor basis.

So constant monitoring of the system is imperative. An embedded IoT based test and measurement system is continuously sniffing for catastrophic outages, such as, short- or open-circuit conditions, properly terminated antennas, and received signal strength at each SMART Coupler in a riser or plenum.

This way the building owner and its system integrator can proactively alleviate surprise outages, poor coverage, and speed up the annual AHJ inspections.

More importantly, troubleshooting is expedited by having the MAC address of each SMART Coupler recorded on the as-built drawings, enabling field engineers and technicians to know where an outage occurred.

This step alone saves technician on-site maintenance time while assuring ERCES performance. As such, the monitoring service could become part of a system integrator’s service level agreement (SLA) with building owners, thereby driving new monthly recurring revenues (MRR).

About Microlab

Microlab, a Wireless Telecom Group company, based in Parsippany, NJ, designs and manufactures passive components for high-performance RF and microwave applications including signal dividers, directional couplers and filters that exhibit broadband, low loss and low PIM characteristics.

Learn more about Microlab’s SMART Passives System: https://microlabtech.com/lmr-public-safety.

[1] NFPA = National Fire Protection Association

[2] IFC = International Fire Code

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