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How to Design an Effective Public Safety Distributed Antenna System for Your Building

When it comes to ensuring public safety and emergency communications within a building, having reliable communications is critical. A Distributed Antenna System (DAS) also known as an Emergency Responder Coverage Enhancement System (ERCES) can extend radio signals from emergency responders like police, fire, and EMS into areas of a building that would otherwise be radio frequency (RF) dead zones. This allows clear communication during emergencies when it matters most.

An ERCES is a network of antennas strategically placed throughout a building to enhance RF coverage for public safety bands. An ERCES comprises several components:

  1. Donor Antenna: The donor antenna receives signals from external public safety network tower, typically located on the building’s rooftop or another suitable external location.
  2. ERCES Headend: The ERCES headend processes and distributes the incoming signals to the various antennas within the building. It includes signal amplifiers, power supplies, and other necessary equipment.
  3. Remote Units (Nodes): Remote units, or nodes, receive signals from the ERCES headend and distribute them to the individual antennas located throughout the building.
  4. Antennas: Antennas are strategically placed throughout the building to ensure comprehensive coverage, including stairwells, elevators, basements, and other areas where radio signals may be weak or obstructed.
  5. Cabling Infrastructure: High-quality cabling infrastructure, such as coaxial or fiber optic cables, connects the various components of the ERCES to ensure efficient signal transmission.


Design Considerations for an ERCES

Designing an effective public safety ERCES requires careful planning and expert insight into RF engineering principles, building codes and fire safety regulations. Get it wrong, and you could face costly rework, delays obtaining a certificate of occupancy, and potential fines for code violations. Here are some key considerations:

  1. Understanding the Need: The first step in designing an ERCES is to clearly understand the unique requirements for every building and jurisdiction. Here are some key questions to consider:
    • Building Type and Size: The size and configuration of the building will significantly impact the ERCES design. High-rise buildings with thick concrete walls tend to pose the biggest challenges for signal penetration.
    • Existing Radio Coverage: A site survey should be conducted to assess existing radio signal strength within the building. This will identify areas with weak coverage that require improvement. This could include stairwells, Elevator shafts, and basement areas.  It also prevents spending additional cost to enhance areas that do not require additional coverage.
    • Public Safety Requirements: Understanding the specific communication needs of the local fire department or Authority Having Jurisdiction (AHJ) is critical.  Each jurisdiction has different requirements that can dramatically affect performance and cost.
    • Budgetary Constraints: Public Safety ERCES solutions can vary in cost depending on complexity. Determining customer budget will help guide the design and equipment selection.
    • Redundancy: Designing with redundancy ensures continued operation in case of equipment failure. This can involve backup power supplies and redundant amplifier units and may be required for certain jurisdictions.
  1. Coverage Requirements: The first step is to analyze the building’s construction materials, floor plan layout, and square footage to identify potential dead zones where the emergency radio signals may be blocked or attenuated. This requires reviewing architectural drawings and often performing radio frequency studies through wall samples. The coverage analysis will determine the minimum signal levels required and number and type of antennas needed to ensure a minimum signal strength of -95 dBm is achieved throughout 90% of the building per fire code. Antenna counts may vary depending on areas with ceiling height, openness of the floor plan, or building materials that cause excessive signal attenuation.
  2. Passive vs Active ERCES: For smaller buildings under 250,000 sq ft, a passive ERCES design utilizing donor antennas, coaxial cabling and Bi-Directional Amplifiers (BDAs) may suffice. Passive systems are typically lower cost but have limits in total square footage and number of antennas they can support. Larger projects will likely require an active ERCES with fiber optic cabling distributing signals to remote amplifiers placed in various areas of the building to overcome cable signal losses and support more antennas over larger areas. Active systems use a main hub unit and distributed remote units, providing greater flexibility and scalability.
  3. Frequency Bands: Public safety bands can include VHF (150-170 MHz), UHF (450-470 MHz), 700 MHz, and 800 MHz frequencies depending on the specific requirements of the local fire/police departments. The ERCES must be designed to support all mandated frequency bands used by emergency personnel in that jurisdiction. In some cases, a non-unified public safety frequency plan requires the use of a Class A signal booster that filters and separates different frequency channels. This allows only authorized radio signals to be amplified.
  4. Antenna Selection and Placement: The type and placement of antennas are crucial for optimal signal distribution. Directional antennas can focus signal towards specific areas, while omni-directional antennas provide more general coverage.
  5. Cable Infrastructure: A reliable cabling system is needed to connect the antennas to the ERCES headend equipment. Fiber optic cables offer the best performance for signal transmission.


Once the number of antennas per floor is calculated, great care must go into the cable network design using properly spaced taps, splitters, and couplers to deliver balanced RF signal levels to all distribution antennas. Attenuation due to cable lengths must be carefully calculated, with the head-end amplifier gain set to compensate for total system losses. Too much gain leads to oscillations, too little means inadequate coverage. The riser layout aims for optimal antenna signal levels. Depending on local AHJ requirements, the cabling may need to be installed in conduit.

  1. Battery Backup: Public safety ERCES must have backup battery runtimes of 12 or 24 hours to maintain communications during power outages as mandated by fire codes. This requires properly specifying battery calculations based on the active equipment current draws. The batteries are contained in NEMA-rated enclosures and ventilation may be required depending on battery chemistry types used. Regular battery cycling and replacement every few years is necessary.
  2. Commissioning & Testing: Commissioning with proper RF test equipment and coordination procedures is required to verify signal strength measurements on a grid throughout all areas of the building. This ensures -95 dBm coverage levels are met and oscillation/interference risks are mitigated before fire inspections. The specific test plan must align with the requirements of the local fire marshal. Commissioning documentation is required to demonstrate compliance with fire codes prior to obtaining a certificate of occupancy.
  3. Annual Inspection & Maintenance: Most jurisdictions mandate annual testing, inspection and certification of public safety ERCES installations to ensure continued compliance with fire codes. Overcrowding in buildings, nearby new construction or modifications to the emergency radio systems can all impact ERCES performance over time. Annual maintenance checks backup batteries, verifies alarm monitoring is functional, measurements are within tolerance, and sweeps the riser/antenna system to identify any new issues before problems arise. This annual recertification process is required to avoid costly violations and safety risks.

Designing an effective public safety ERCES is highly complex, which is why engaging experienced RF professionals like Commdex from the start is essential for any building project. Their expertise ensures a code-compliant system optimized for reliable emergency communications when it counts. Overlooking ERCES requirements can be an extremely costly mistake – get it right by consulting the experts.