Test Innovations Improve In-Building Public Safety Network Validation
By Roger Paje
Tuesday, April 06, 2021 | Comments
Public-safety networks such as FirstNet are being rolled out so first responders have reliable, resilient, optimized broadband communications when carrying out their respective missions. Such networks are designed to deliver instantaneous, uninterrupted communications, as well as to give government agencies the ability to collect and analyze streaming information for better response.

Making this level of communications a reality has a few obstacles. One of the biggest hurdles is in-building transmission. Similar to a commercial cellular distributed antenna system (DAS), an in-building public-safety network is comprised of bidirectional repeaters, and a series of antennas distributed strategically throughout the building to transmit and receive signals from the radio system to individual radios. A typical building environment featuring potential interference sources such as piping and sprinkler systems and signal-weakening construction materials can adversely affect signal transmission.

This is particularly troublesome for public-safety networks. Given their mission-critical nature, there must be 99% floor area radio coverage for buildings to be in compliance. Therefore, contractors, building owners and government agencies must have a coordinated and efficient testing process to ensure operation.

Public Safety Network Design
There is a fundamental difference between in-building public-safety communications networks compared to commercial counterparts.

Among the differences are:
• System exclusivity. Public-safety networks have priority and pre-emption services for first responders, allowing emergency personnel to access the network even when there is high congestion.
• Operating frequencies. U.S. public-safety networks operate at relatively low frequency bands, compared to commercial networks. They range from 30 MHz to 150 MHz, 450 MHz and 800 MHz, helping them achieve excellent propagation and penetration characteristics. This is important to overcome factors such as how deep inside a building the receiver may be, wall composition and energy-saving materials such as “low-e glass.”
• Higher power. LMR handsets typically transmit with 3 to 5 watts of power. This is much more than the typical cellular handset and enough to substantially increase in-building connectivity.

Public-safety communications system hardware and installation also have significant differences from commercial cellular systems. Public-safety radio systems must have hardened equipment with battery backup. Equipment is kept in rooms rated to be able to withstand a fire for a minimum of two hours.

Fire Code Requirements
The National Fire Protection Association (NFPA) and the International Code Council (ICC) continue to develop national level model codes focused on in-building public-safety communications systems. Among the codes issued by these groups are the National Fire Code, National Electrical Code, International Fire Code and International Building Code.

The NFPA and ICC initiatives complement each other. While the exact requirements of the draft codes vary, key specifications have much in common. Another factor is that each jurisdiction can alter the national level model code to meet unique requirements. The specifics of these local ordinances and codes vary, but most include:
• Minimum signal strength limit,
• Established limit over a specified percentage of each floor,
• Specific level of reliability (i.e. power backup, water protection, and cable protection),
• Designated frequency bands for public-safety coverage,
• Testing requirements and procedures, and
• On-going monitoring and maintenance processes

Building owners must comply with local requirements, as well as the national NFPA 72 standard published by the NFPA. Without compliance, a certificate of occupancy, required to lease or sell the building, will not be granted.

GPS Signal Alternatives
For these reasons, simple, time-efficient and economical test solutions are necessary to satisfy in-building network verification. One main obstacle to ensuring in-building performances is a GPS signal within a commercial structure. GPS is the most common method to align position data with test results.

Lack of a GPS signal is particularly evident in NFPA 72 “critical areas,” such as fire command centers, fire pump rooms, exit passageways, elevator lobbies, exit stairs, standpipe cabinets and sprinkler sectional valve locations. In particular, the latter three areas are especially isolated, making GPS signal availability even more sparse.

Multiband Testing Needs
While the current standards require only one system be validated, most modern networks have multiple in-building bands. Even with only one network needing to be tested, each band has an associated cost factor, meaning the expense can be dramatic.

Test systems must be able to conduct accurate and reliable measurements without the GPS while also overcoming the potential time and cost inefficiencies associated with multiband in-building networks. To solve this dilemma, a new generation of test solutions that can validate all bands simultaneously while a technician walks through the building has been developed.

In the absence of GPS, a local “tracker” is used to coordinate the test system’s position with the RF measurements being taken. A true 3D map is created by the tracker, so weak or no-coverage areas can be pinpointed and addressed. The data acquired also helps prepare the required documents to meet legal requirements.

Testing Solutions
To meet all the testing, cost and efficiency goals associated with streamlining in-building verification, an integrated solution is necessary. It leverages hardware and software including:
• Remote Spectrum Monitor. A hardware unit to verify in-building network performance must deliver outstanding sweep speeds, even for smaller resolution (RBW) or video bandwidths (VBW). The latter specifications are important for narrowband public-safety communications standards such as analog FM, Project 25 (P25), TETRA, Digital Mobile Radio (DMR) and digital private mobile radio (dPMR).
• Tracker. Technicians must be able to wear a device that delivers their in-building position to the tracking software as they travel through the facility. A tracker helps to create a 3D replication of the technician’s position that can be stored and used for reference. Stairwells, elevators and other areas previously hard to analyze can now be accurately tested.
• Signal Mapping. Dedicated software collects the RF data from the user-defined frequency bands and coordinates it with the position data to create a detailed and accurate signal map.
• Command Software. Data gathered by the signal mapper is analyzed by command software. This tool also has the capability to prepare 2D/3D coverage mapping images.

Command software also automatically inputs the building’s outline using current location coordinates and a satellite image database. Technicians can take a picture of the floor plan normally found at a main entrance/exit or the elevator doors and fire exits. The photo of the floor plan is overlaid onto the building floor plan and adjusted by the user until there is a fit. This creates the most comprehensive view of the building and in-building network coverage.

Public-safety networks need to be optimized for first responders and emergency personnel to perform mission-critical operations effectively and most safely. A variety of challenges associated with in-building network operation can be overcome using integrated test solutions. With such a testing process, networks can meet the 99% coverage requirements and other parameters set forth in NFPA and ICC standards.

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Roger Paje is a senior product manager at Anritsu Company. He has been in test and measurement for more than eight years. His experience includes working with telecom operators and network equipment manufacturers.

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