Public Safety Networks, including the recently awarded FirstNet system, are an increasing consideration for property owners and operators. The FirstNet network will be a single, nationwide, interoperable LTE based broadband network dedicated to public safety communications. Once built, the network will modernize the communications used by law enforcement, fire, and emergency medical personnel, providing them with access to new technologies and increased capacity for their mobile communications and data needs.

Typically, in-building Public Safety Systems use bi-directional amplifier systems (BDA) or a distributed antenna system (DAS). There are several RF related and signal coverage issues to consider when deploying and testing -these in-building solutions.

Interference Management: Systems must operate without causing interference to other parts of the public-safety radio system and technologies must be compatible with the existing public-safety radio system. Many systems employ an over-the-air broadband BDA at the donor antenna. These devices are notorious for causing interference, especially if there is poor isolation between antennas.

Building Areas: are defined as 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, while general building areas must have 90% coverage.

Signal Strength: Minimum inbound and outbound signal strengths of -95 dBm are required. The National Fire Protection Association (NFPA) specifies that each floor be divided into a grid pattern and signal levels measured with a calibrated recording system. The measurement system will take a minimum of 20 readings while walking a pattern within the grid cell. No more than (2) nonadjacent cells can fail the test. Should (2) adjacent cells fail the test; the floor can be divided into additional grids to demonstrate 90% coverage of the general building area. In addition to signal strength, Audio Quality measurements are taken by a qualified technician. Delivered Audio Quality (DAQ) is the most common signal quality measure in Public Safety.

FirstNet will undoubtedly add new testing requirements; however, the key question remains one of compliance. Currently, Public Safety network deployment and compliance varies from state to state and is typically limited to certain types of new construction or buildings. This could change rapidly and building owners may be faced not only with deployment requirements but with ongoing certification and fire code compliance. It is worth noting that FirstNet will be restricted to an outdoor network with little consideration given for provision of service in Buildings. However, that is precisely where the most complex and critical Emergency Responder activities are likely to occur. It is more than likely that similar requirements to the current voice only Public Safety networks will evolve to include data testing as well as audio. That brings a whole new dimension to certification as this adds another level of complexity. Designing, building and maintaining compliance for these LTE networks will require expertise in RF engineering. It is likely that the current approaches of deployment after construction or as an afterthought will need to be reconsidered.

Public Safety-DAS Design Considerations

Designing and building for PS-DAS differs from the cellular case in many ways. First; the signal source is likely to be from an external public safety donor site which is rebroadcast inside the building. Special care must be taken during the building design and construction phases to ensure that the signal source is not compromised. RF reflective window panels, for instance, may prevent operation once construction is complete even if proper initial surveys were performed. Similarly, new construction may block reception of the signal source making the DAS system inoperable.

Correction for compliance after construction can be very costly and delay certification by the Authority Having Jurisdiction (AHJ) which may prevent the issuance of a Certificate of Occupancy, impacting revenue generation for the building owner.

An initial site survey, careful selection, and even pre-construction signal simulation can help prevent these RF problems in advance. Careful design will also take into consideration potential sources of interference and even once built, RF expertise is needed to identify and remove external sources of interference which may again cause compliance tests to fail.

While these problems are manageable today they may become critical if ongoing compliance is mandatory and if applied to existing buildings as a retrofit as well as to new construction.

Integrated Cellular and Public Safety-DAS

Some consideration should be given to the concept of integrated cellular and PS-DAS systems. While it may seem appealing to integrate these two functions, they have very different goals.

PS-DAS is a mission-critical requirement which must always work within well-defined areas and is primarily a coverage, not a capacity solution. There are few revenue-generating opportunities for support of PS-DAS so they are viewed as a compliance issue and the lowest cost to compliance is desirable for the building owner or developer. They are also governed by construction codes which do not apply to cellular. Conversely, Cellular DAS systems, are designed for capacity and performance and need to cover areas that PS-DAS does not. Specifying cellular DAS systems and equipment to the same fire codes required for public safety (e.g. fire resistance) would be cost-prohibitive. While there may be some specific areas for integration on a given system, cellular and PS-DAS systems are typically distinct.

That being said, there is much that can be done during the design phases to ensure that commonalities are exploited and that the two systems coexist without interfering or being interfered with. It should also be evident that while they are different from their use cases, the underlying technologies are similar and RF expertise is needed in order to design, build and maintain these systems in the most cost effective manner.

It should also be evident that as FirstNet grows, the requirement to support its operations in-building and the need for PS-LTE networks will evolve. These networks use LTE based technology with all its inherent complexity which closely tracks cellular systems. While this will probably not change the case for integration with cellular DAS in the short term for the reasons given, it does imply that RF expertise and LTE systems knowledge and experience will be required to achieve and maintain compliance.

The MobileNet Advantage

MobileNet has been testing wireless networks for 15 years and has extensive experience with Public Safety DAS deployments and the macro systems that act as the signal sources. We are also extremely experienced with LTE and its deployment and testing requirements. We believe that MobileNet is an ideal partner for strategy evaluation, design and certification of any current or future evolution of Public Safety Systems particularly as LTE begins to feature in PS-DAS deployment.

For Public Safety Networks, Buildings Owners and Operators need to determine if the building or venue complies with local jurisdiction fire code (in accordance with 2012 IFC Section 510). We perform the following certification tests.

• Grid Testing
• RSSI Testing
• Perimeter Testing

About MobileNet

MobileNet provides a full range of turnkey engineering services for every stage of network deployment, integration, optimization, performance validation and compliance testing to major telecom operators and OEMs across the nation. We have led the deployment of 2G, 3G, and 4G networks for over a decade and have launched over 25,000 UMTS sites and over 5,500 LTE turnkey sites across the U.S, with deep domain expertise that spans GSM through CDMA, to LTE, Wi-Fi, VoLTE, and beyond. We also provide compliance validation services, where our significant experience in E911 enables precise and reliable end to end testing of all major wireless protocols from planning to final execution.

We are a leader in DAS System Verification, Optimization and Design with extensive experience testing over 2500 high profile venues including airports, stadiums, hotels, amusement parks, universities, and business parks. Our long lasting customer relationships attest to our reputation for Quality, Expertise, and Reliability and reflect the integrity we bring to delivering superior services, on-time and on-budget.