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What’s the right infrastructure for public-safety DAS?

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When deploying a distributed antenna system (DAS) to provide in-building coverage, some vendors recommend a separate overlay for the public-safety network, while others recommend integrating public-safety coverage and capacity into the cellular wireless network. Which is the right approach?

By John Spindler, TE Connectivity

Venues large and small are interested in (and in some cases required to provide) safety and security, and that means ensuring that first responders can communicate clearly over their radios. Often, this requires deploying distributed antenna systems (DAS) that extend public-safety mobile coverage and capacity to the interiors of buildings. Some vendors recommend a separate overlay for the public-safety network, while others recommend integrating public-safety coverage and capacity into the cellular wireless network. Which is the right approach?

To make a decision on whether or not to integrate public safety and cellular DAS, we need to consider three categories of DAS integration issues: regulatory, technical and economic, and jurisdictional.

Regulatory issues

Individual municipalities typically govern DAS ordinances for public-safety communications. A typical ordinance says that any new building or major renovation with more than three stories or underground facilities has to pass a public-safety communications test. If the building department tests the building, and it fails to provide clear radio communications throughout, the building owners have to fix the problem before they can get an occupancy permit.

National Fire Protection Association (NFPA) and International Fire Code standards apply to public-safety DAS.

The NFPA is a United States trade association that creates and maintains private, copyrighted standards and codes for usage and adoption by local governments. This includes a range of publications that range from model building codes to equipment used by firefighters while engaging in hazardous material (hazmat) response, rescue response, and some firefighting.

The International Fire Code (IFC) is a model code that regulates minimum fire safety requirements for new and existing buildings, facilities, storage and processes. The IFC addresses fire prevention, fire protection, life safety and the safe storage and use of hazardous materials in new and existing buildings, facilities, and processes. The IFC provides a total approach of controlling hazards in all buildings and sites, whether the hazard is indoors or outdoors.

These standards address the issues of high reliability required for life-safety, mission-critical systems. With municipal budgets under stress, cities are increasingly leveraging IFC and NFPA codes in their ordinances rather than developing their own codes. The IFC and NFPA standards are therefore driving new installations of public safety DAS and include requirements such as:

  • Fully waterproof installation using NEMA 4X enclosures;
  • Battery or generator backup;
  • A specific set of monitoring points and alarm notifications to assure system availability; and
  • More extensive coverage for facilities than typically implemented with commercial networks—for instance, the need to provide coverage in stairwells or elevator shafts.

Cellular DAS systems do not need to meet these extensive code requirements, but a converged DAS would have to meet them, and doing so could significantly raise the overall cost of the DAS system.

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