July 13, 2017 —
In March, the First Responder Network Authority (FirstNet) awarded AT&T a contract to build the first nationwide public safety broadband network for emergency first responders. The network will use Long Term Evolution (LTE) high-speed wireless data technology on frequencies in the 700-MHz band. Eventually, the network will supplant the use of existing public safety frequencies. As the FirstNet network evolves, public agencies and building owners will have to assume the burden of bringing network coverage indoors at venues so first-responder radios will work in all locations. In many instances, jurisdictions will require in-building coverage. The following information explains the convergence of public safety frequencies in connection with the new FirstNet standard and the requirements for systems that support the network’s wireless coverage inside buildings.
Despite the current use of lower frequencies in the range of 150 MHz to 900 MHz to support public safety radios, the in-building coverage challenge remains unsolved. Even at these low frequencies, building construction materials can block outdoor radio signals from penetrating indoors. Underground areas, such as basements, are impossible to cover from the outside; outdoor radios dominate the airwaves; and energy-efficient, Leadership in Energy and Environmental Design (LEED)-certified buildings make matters worse. In the United States, LEED-certified buildings enclose 2.5 billion square feet, and this year, approximately 45 percent of nonresidential building construction will be green (environmentally friendly).
As a result, in-building wireless systems are a must for ensuring clear and consistent radio coverage for building occupants and first responders. Many local governments mandate the use of in-building wireless systems for public safety systems in buildings larger than a certain size, but even existing systems will be in for a revamp as the FirstNet network comes online.
Existing public safety networks and radios operate in several public safety radio communications frequency bands, including the 150-MHz, 450-MHz and 800/900-MHz bands. In effect, the United States is a patchwork quilt of public safety communication networks. With the advent of the FirstNet public safety broadband network, these will all begin to converge around 700-MHz LTE. LTE is now the dominant technology used in commercial cellular networks, but a lot of work is being done to further make use of LTE’s benefits. The results also will affect FirstNet LTE.
For example, mobile operators are always looking for more radio-frequency spectrum to expand bandwidth and provide their users with faster throughput. Once they have derived all the capacity they can with new cell sites, sector-splitting and carrier aggregation, the next thing is to consider using unlicensed spectrum to further expand available bandwidth. LTE in unlicensed spectrum (LTE-U), licensed-assisted access (LAA), and MulteFire computer software and firmware offer ways to use unlicensed spectrum that will deliver bandwidth more from current technology.
LTE-U protocol enables mobile operators to increase bandwidth in their LTE networks by using the unlicensed frequency bands in the 5-Hz range — bands that Wi-Fi devices also use. Licensed-assisted access is the name given to the Third-Generation Partnership Project (3GPP) effort to standardize the use of LTE in Wi-Fi frequency bands. LTE-U is an implementation of LAA. The MulteFire LTE technology developed by Qualcomm operates solely in unlicensed spectrum and uses self-organizing functionality; LAA aggregates unlicensed spectrum with an anchor in licensed spectrum.
Unlicensed LTE protocols will play a significant role in boosting LTE bandwidth and throughput while serving as a key component for connecting the internet of things (IoT). Ideally, in order to speed deployment and deliver an economical solution, public safety, wireless IoT devices, and cellular services will all operate on a converged network (see Figure 1).
FirstNet’s public safety broadband network will make use of the same LTE network, so it’s possible that, in some cases, the 700-MHz public safety frequency may already be supported by some in-building wireless systems (although the frequencies used for the FirstNet network are not the same as the 700-MHz frequencies in use by cellular carriers today, so this would be true in a limited number of cases). In many instances, however, it will be necessary to rip and replace existing in-building wireless systems to facilitate the support of the FirstNet network.
What does this all mean for those considering buying or upgrading an in-building wireless system? There are three basic requirements:
1. Support 700-MHz FirstNet frequencies while still supporting existing cellular and IoT frequencies. Ideally, the solution should support public safety, cellular and IoT frequencies in a single system. This will simplify both deployment and maintenance, while keeping costs down. A truly wideband distributed antenna system (DAS) can support any frequency from 150 MHz to 2700 MHz, so it could support many different frequencies with a single layer of equipment, including 700-MHz FirstNet communications. And, this solution could seamlessly support future services.
2. Use fiber infrastructure. Many current DAS solutions use coaxial cabling or a hybrid architecture that combines fiber and coax cabling. An all-fiber infrastructure is easier and less costly to deploy, and often it can make use of fiber-optic cable already in place in the building.
3. Have a simple architecture. Many DAS products have a dizzying array of parts because of their inherently narrowband architecture, making it difficult for information technology (IT) staff to both deploy and maintain them. Building owners and contractors should look for DAS solutions that mirror IT data infrastructure with a limited number of system elements so it is familiar and easy to understand.
Meeting the FirstNet Challenge
The move toward FirstNet public safety infrastructure represents both a challenge and an opportunity for building owners. The challenge is that many in-building wireless systems will have to be upgraded or deployed because some existing systems support other frequencies, but not the 700-MHz frequencies the new FirstNet network will use, and some buildings lack any kind of indoor coverage solution. But the good news is that the need to support the new public safety broadband network offers the chance to deploy a single, converged in-building wireless system that supports all wireless traffic. The FirstNet network will take several years to roll out. It is not too early now to begin planning how to support it.
James Martin is vice president of operations at Zinwave. Prior to joining Zinwave, Martin was senior manager at TE Connectivity (formerly ADC/LGC Wireless) for more than 16 years. His leadership helped TE Connectivity emerge as a top-tier DAS manufacturer in the wireless space. Early in his career, he was employed at Hughes Network Systems and was responsible for the design, deployment and optimization of more than 500 macro cell sites across the southeastern United States. During this time, he was also instrumental in defining the first small cell systems designed and deployed by Hughes Network Systems. Contact James Martin at firstname.lastname@example.org