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The First Responders Network Authority (FirstNet) is an independent entity within the Department of Commerce’s National Telecommunications and Information Administration (NTIA). FirstNet is responsible for deploying the Nationwide Public Safety Broadband (NPSBN) of emergency communications. Small and large-scale incidents are handled through this network, which provides emergency service personnel with reliable, redundant, and secure broadband LTE connections.

To accomplish this, a dedicated spectrum resource for public safety was established – 20 MHz in the 700 MHz band (LTE Band 14). To provide state-of-the-art technology, existing and future advancements from LTE Release 8 to 14 are utilized. Ensuring the availability of high-quality LTE FDD14 devices with proper public safety-related requires special attention to developing core specifications, test requirements, and equipment.

 

Background

The Department of Commerce and FirstNet awarded wireless carrier AT&T the contract to build a dedicated network for first responders. As part of the 25-year agreement, AT&T receives 20 MHz of 700 MHz spectrum and “success-based” reimbursements (totaling $6.5 billion over the next five years) to support constructing an IP-based, high-speed mobile network that gives priority access to first responders.

Today, many first responders have devices from commercial network operators to do the latest high-quality voice, video, data, and location determination applications. In addition, most also have an old analog and/or P25 radio as a dedicated public safety voice-centric device. This has several disadvantages:

  1. Commercial networks lack dedicated spectrum available for public safety, and aren’t required to prioritize traffic from public safety devices. During a crisis, networks can be flooded with activity, leading to denial of services and complete network unavailability, blocking critical emergency communications. Older analog and/or P25 radios leave the emergency responder without high-quality voice, video, high-speed data, and/or location determination capabilities.
  2. Analog and/or P25 digital radios are costlier than today’s best LTE mobile devices, mostly due to the vast difference in economies of scale. Taking advantage of the scale economies that exist in the commercial mobile phone ecosystem is the best way to build high-quality, advanced-technology electronics at the lowest possible price.
  3. Commercial LTE mobile devices (like smartphones) have technologies that surpassed currently existing analog and P25 public safety devices. Voice-over-LTE and Video-over-LTE can only be found in the latest smartphones.

FirstNet’s aims to eliminate these disadvantages by using a dedicated LTE network, allowing first responders to communicate across agencies at local, state, and federal levels. FirstNet will cover all U.S. states and territories, with each having a specifically-designed plan tailored to address its needs and questions. Each state or territory governor will decide about participating in FirstNet. Any who opt out must design its own interoperable Radio Access Network (RAN) with the rest of FirstNet. AT&T will build out this network and although the spectrum will be shared, public safety devices should always get top priority.

 

Challenges

An estimated 30,000 to 50,000 cell sites will be required for creating a system that allows first responders to communicate nationally. Spectrum sharing between FirstNet and AT&T needs further evaluation, as questions remain about how quickly the dedicated Band 14 spectrum could overload during a massive emergency. Public safety devices would operate on Band 14, but could use portions of the commercial network (if necessary). Commercial devices can use Band 14 spectrum when free of public safety devices, which can complicate spectrum sharing, especially during a crisis. The shared LTE network must operate under the strict condition of public safety always having the top priority. This preemption feature is still largely unproven, especially on an important scale like a nationwide public safety network.

Public safety devices have unique requirements that should go beyond normal commercial technologies. High-performance call reliability (even in rural areas), battery life, audio and video quality, along with location determination aren’t just conveniences when considering emergency services that are relied upon for public safety. In addition, there are recently standardized LTE features made specifically for public safety. However, most still need to be developed on real devices and have their performance verified before being deployed on a live network.

One of these features is the LTE release 11 feature High Power User Equipment (HPUE) for Band 14. A normal device (Power Class 3) without HPUE can only transmit at a maximum output power of +23 dBm (max 200 mW). An HPUE device (Power Class One) can transmit at a maximum output power of +31 dBm (max 1.25 W). This increase has a direct effect on transmission range and ultimately increases cell range from ~4 to ~8 km, providing an essential boost in coverage for rural areas. This can increase reliability of coverage in rural areas and/or decrease the number of cell sites needed, resulting in massive cost savings for the operator.

Another set of features specifically for public safety were developed in LTE release 13 and 14. Major changes were made to mission critical push-to-talk (MC-PTT) to support:

  • Isolated operations – enables local services in case backhaul connection to centralized macro core is lost.
  • Device-to-device communications – allows devices to discover and communicate with each other directly.
  • Group communication over LTE – push-to-talk over eMBMS.
  • Several enhancements to priority and preemption – fundamentally important for ensuring network access when sharing spectrum with commercial users.

LTE Release 14 also added MC-Video for video calls, and MC-Data for sharing large amounts of data like HD images, videos, blueprints, and more.

Other features not specifically developed but critical for public safety relate to improvements in location determination performance while indoors. Relying mainly on satellite signals (like GPS) for determining location isn’t reliable because the signals are too low-power, and often attenuated to the point of being obsolete when in a building. In addition, determining vertical position isn’t possible, which can be problematic in multi-floor buildings.

Updates in LTE release 13 and 14 bring enhancements to network-based positioning (OTDOA & eCID), adding the ability for using WLAN, Bluetooth, and Metropolitan Beacon Systems (MBS) in determining device location. MBS a particularly promising new technology that could bring accurate vertical position determination to our public safety community.

 

Testing of LTE Public Safety Devices

It’s important to ensure a device’s proper performance being used for public safety purposes. PTCRB certification in Band 14 is required for devices operating on FirstNet, meaning they’ll run through RF, RRM, Protocol, Location-Based Services, UICC, and the other conformance tests required by PTCRB.

Conformance tests are good for ensuring device performance, but may not be completely exhaustive. Conformance tests are generic by nature but become required once there’s at least two devices supporting a feature, and can validate a case running on test equipment. With new features like HPUE (past) and MC-PTT (future), there’s often a delay before enough devices are available to validate all conformance tests. It could make sense to require test cases before they’re officially validated, however some areas go beyond conformance including:

  • LTE receiver performance in the presence of interference created by high-power TV transmitters.
  • GPS receiver performance in the presence of interference created by FDD14 HPUE device transmissions.
  • VoLTE audio quality in the presence of the extreme background noise one could encounter during an emergency.
  • ViLTE Video quality in marginal light conditions.

Test & measurement manufacturers are at the forefront of enabling critical wireless technologies for the FirstNet LTE network. Manufacturers like Rohde & Schwarz for example, provide test equipment used in conformance and high-performance test systems. Their CMW500 network emulator can simulate the entire FirstNet network for testing of FDD14 LTE mobile devices.

As FirstNet wireless devices and mobile networks are developed, test and measurement providers will be called for solutions across the entire public safety ecosystem; from chipsets and devices, to conformance/acceptance testing, network performance & optimization, along with service and repair.

 

Future Applications

Future innovations in the public safety arena could include software to locate individuals along with first responders in residential and commercial buildings containing multiple floors, using vertical detection. Telemetry data gathered from UAVs and transmitted over the public safety network could be leveraged for better situational awareness in the event of a public safety incident.

Obtaining live feed of a situation from first responders (perhaps through wearable devices such as bodycams), could provide more information on a situation than currently available. Wearables and handheld devices to lessen weight amounts of gear needed by first responders is important. Improvements in graphical user interfaces, applications, and security software is also imperative. It may be possible to use artificial intelligence (AI) on personal and public safety apps to distinguish what events require first responders.

However, the public safety marketplace’s size keeps traditional suppliers in handheld radio and bodycam markets from adding new technology. It’s also worth noting how difficult it can be to break manufacturers in the public safety arena, considering how new technology deployment for first responders is both time consuming and expensive. 5G technologies promise to ultimately bring extreme data rates, ultra-low latency, and reliable capabilities. With future 5G networks, it may be possible (for example) to provide fire fighters with building blueprints using a real-time augmented reality HD display.

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