FirstNet public safety network testing and pre-emption evaluation. Image: MobileNet Services

FirstNet is expected to finally modernize the Public Safety communications infrastructure with AT&T playing a major role in its deployment. However, prioritized access and pre-emption on the AT&T network for public responders is still evolving and the long term implication for mission critical services worth exploring.

Public Safety accessibility is a hot topic in the telecom industry with the First Responder Network Authority (FirstNet) and AT&T recently releasing their initial plans for the proposed deployment of the Nationwide Public-Safety Broadband Network (NPSBN). Once built, the network will modernize the communications used by law enforcement, fire, and emergency medical personnel. This deployment will provide first responders with access to new technologies and increased capacity for their mobile communications and data needs.

Many state governments have asserted the necessity for improved communication in the public safety sector. Innovation in the NPSBN has been long overdue, which has created a lot of excitement around the deployment of FirstNet’s platform. As with any new technology, there are several deployment options, but states had to decide to either jump on the FirstNet bandwagon, or ‘Opt-Out’ to build their own systems using a new LTE-based Radio Access Network (RAN) by Dec 28^th 2017. At the end of the cut off period all fifty states, the District of Columbia, and two U.S. territories eventually elected to Opt-in, noting that odds were stacked against an opt out based on an economical perspective and viability at a commercial scale. With nationwide opt-ins secured, FirstNet and AT&T now face the challenge of convincing public safety customers to sign up for their service. This is not mandatory and it is possible some states may eventually choose to build their own systems if they believe that control over their public safety network outweighs the cost of deploying their own program.

There has been a lot of recent buzz about the concept of prioritized access which has been a major topic of discussion as highlighted in AT&T newsfeeds and industry-wide chatter. The premise of priority access is dedicating available capacity and bandwidth on a network to public safety users before other commercial users. Interestingly, the more aggressive concept of ‘preemptive access’ has also recently been explored by AT&T. With preemptive access, a public-safety user is automatically given exclusive access to the band requested presumably by bumping existing users to other bands. While the actual mechanism for preemptive access is not yet clear, it implies that public safety users will have exclusive and unfettered access to requested bandwidth resources in times of emergency.

Randal Stevenson, Chairman of AT&T recently said, “A term we use is ‘ruthless preemption’ capability, meaning … if you have [commercial] customers in this spectrum and there is a demand by the first-responder community—whether it’s a national crisis or a local crisis or whatever—you have to ruthlessly preempt whoever is on that network, move him to another spectrum band, and give the first responders full access to that spectrum.” This appears to be applicable not only to the new 700MHz band 14 spectrum but also to other AT&T bands. The implication is that FirstNet public safety subscribers may get preemptive access or “ruthless preemption” to all of AT&T’s commercial networks in an emergency, or zombie apocalypse.

Let’s pause for a moment and take a look the long-term impact of preemption as it applies to existing public safety voice networks and the compliance regulations for in building Public Safety Network testing.

Many jurisdictions already require testing and certification of Emergency Responder Radio Coverage Systems (ERRCS) in critical areas and general building areas.

• Critical areas include emergency command centers, fire pump rooms, exit stairs, exit passageways, elevator lobbies, standpipe cabinets and other areas deemed critical by the Authority Having Jurisdiction (AHJ).
• Critical areas must have 99% coverage,
• General building areas must have 90% coverage.

While LTE already supports voice via Voice over LTE (VoLTE), a key requirement for Public Safety users is Mission Critical Push to Talk. MCPTT is part of 3GPPP LTE Release 13, which was only “frozen” by the 3GPP standards body in 2016 and is unlikely to be operational until sometime after 2018. In the short term, this means existing LMR networks will likely continue be the primary system for emergency voice support. It’s anyone’s guess as to how long it’ll take existing users to wean off of tried and tested 700MHz LMR equipment, but we suspect that network control will be a major factor in that part of the process. However, VoLTE does permit expanding the role of the NPSBN to encompass voice offering a long-term path to a fully integrated FirstNet voice and data network.

Looking to the future, it appears that the ERRCS network may become at least partially based on AT&T’s entire spectrum assets. This implies that FirstNet emergency public safety communications, including voice calls, could be supported by the commercial network deployed in that area.

Supporting in-building coverage is already challenging for commercial networks and DAS (Distributed Antenna Systems) have evolved to combat limitations of outdoor macro networks by placing radio systems and antennas directly inside buildings. The ever evolving and rapid expansion of low-powered small cells, the use of higher frequencies and the use of Low-E reflective glass have all impacted in-building coverage, especially in high rises. If FirstNet exists to provide mission critical data and eventually voice, then it would seem inevitable that DAS systems will need to evolve to support it and be certified similar to existing ERRCS networks.

If the public safety function is being provided even in part by a commercial network, potentially on an existing DAS system deployed inside a building, then what rules should apply? Typically dedicated PS in-building networks are designed with different criteria in mind (coverage in critical areas and not capacity) and the equipment is also subject to different codes and fire resistance rules.

Preemption implies that a PS call could theoretically be served on any of the bands in an area, which may not align with the coverage of an existing in-building system. For example, DAS designs may only support a limited set of frequencies and as a result, the first responder might have connectivity externally but not once inside a building. Several questions come to mind; will preemption, ruthless or otherwise, be practical inside a building where the network was deployed by third party? Who will be responsible for coverage? Building Owners? Neutral Hosts? Will the building be required to be certified on all of the potentially served bands? Will these ‘dual use’ networks also require certification to current fire code standards rather than commercial buildings codes? Additionally, once certified how will jurisdictions handle changes in the external macro networks (which often act as a donor site for the in-building network)?

For existing Public Safety Networks the frequencies are well defined and in general, once deployed the networks typically do not change. The opposite will be true of an in-building ERRCS based on a commercial carrier network. If the donor cell changes or the external Macro frequency plan or coverage is redefined the DAS system will most likely require retuning. That in turn may impact the public safety coverage, potentially requiring recertification.

If VoLTE over FirstNet does become the primary voice service for Public Safety then it seems obvious that in-building certification will be required to similar standards as are currently mandated.

It also raises the key question of whether data testing should be part of any FirstNet certification process; as data is the primary reason for its existence. If it is important to test and certify mission critical voice service in buildings; then surely it is just as important to test mission critical data networks for the same reasons.

Hopefully, many of these questions will be answered when the specifics of preemption are better defined and the impact of potentially using AT&T FirstNet for in-building Public Safety Service is understood. In the short term, existing ERRCS voice services are not going away and certification specifications will remain as they are and will likely slowly evolve to encompass FirstNet’s mission Critical Data network as it is deployed.

However, if Mission Critical Data support for in-building ERRCS does become a code requirement, the DAS equipment OEMs that already provide specialized support are well placed to embrace it. Overall this is a shrewd move on AT&T’s behalf as the long term implication is that all in-building networks will eventually have to support AT&T frequencies for Public Safety. We will watch these developments closely and look forward to sharing our thoughts and analysis as more information becomes available.