December 22, 2021 by Dominick Arcuri, Subject Matter Expert
With the explosion of in-building systems occurring nationwide, it’s critical for public safety agencies to institute policies for both building owners and their own operations to make sure the systems provide the desired benefit. This article explores a variety of options available to Authorities Having Jurisdiction (AHJs) for equipment type, system design, configuration, and operations, along with the risks associated with different options.
More and more jurisdictions across the nation are requiring distributed antenna systems (DAS) in new and existing buildings to address dead spots in land mobile radio (LMR) coverage. Public safety systems are known as emergency responder radio communication system (ERRCS) in building codes and among the developer community. States and local jurisdictions are mandating an ERRCS whenever the signal levels inside the building do not reach a sufficient level for adequate communication. These systems can provide lifesaving communications and can dramatically enhance public safety operations, but it’s critical for public safety agencies to institute policies for both building owners and their own operations to ensure the systems provide the desired benefit yet do not degrade their LMR system service. This article explores a variety of options available to Authorities Having Jurisdiction (AHJs), the local government entities that mandate ERRCS solutions via building codes, to mitigate the risks and provide reliable in-building coverage without harming the overall system performance.
AHJs generally rely on codes developed by the International Fire Code (IFC) and the National Fire Protection Association (NFPA) as the baseline code for ERRCS. Chapter 5, Section 510 of IFC 2018, contains the requirements for the emergency responder radio coverage for new and existing buildings, including equipment and component requirements, design, installation, and testing. In some cases, NFPA and IFC requirement are complementary. This is the case for the IFC installation requirements, which specifically refer to the NFPA 1221. Many AHJs use these general requirements, including the battery backup requirements. The model codes from IFC and NFPA typically change every three years, but jurisdictions may not automatically adopt these updates. In addition, different jurisdictions have different needs and priorities and can implement modifications to the code that best meet their individual operational requirements.
Neither IFC nor NFPA has very detailed specifications on the type or features of the DAS equipment, other than FCC or other radio licensing authority certification. Many jurisdictions keep the same flexibility in their codes. However, more and more AHJs, based on feedback from their radio system managers, are being more prescriptive on the technical capabilities of the radio boosters. Some, for example, are requiring Class A amplifiers, otherwise known as channelized bi-directional amplifiers (BDAs). Like the name implies, these Class A amplifiers are specifically tuned to the frequencies for the host LMR system. A Class B booster, on the other hand, boosts the entire band. For example, a Class B amplifier might have a range of 851-862 MHz on the downlink (talk out), which could include other public safety and business operators. Amplifying additional signals may result in power fluctuations or noise problems, as explained below, which can generally be avoided by requiring Class A amplifiers.
There are a number of benefits offered by a Class A booster. Their sharp filters avoid having other in-band operators absorb the booster’s radio frequency (RF) power by dedicating power to only the channels in the AHJs system. This vital interference protection capability is unlike the Class B boosters, which may essentially have no power remaining for the AHJs channels due to other operations. As a result, a Class B booster may result in fluctuating power for the public safety channels depending on the use and strength of other LMR operations in the area. And, if new licensees or channels enter the BDA’s band, this problem becomes exacerbated. In addition, Class A amplifiers offer advantages in a feature referred to as uplink squelch. Essentially, if no activity on the talk-back path (LMR user transmission inside the building) on a particular channel is detected, the noise from the BDA is muted. As we’ll discuss later, this can have substantial benefits on the emergency communications LMR system. And finally, in some situations, when there are multiple users actively talking on multiple talkgroups inside the building, a Class A amplifier can configure each channel to the RF conditions of each user, whereas a Class B amplifier would result in the weaker user’s signal being drowned out by a stronger user.
Class A boosters, however, do have some disadvantages. The channel filters for Class A boosters introduce a signal delay, which, if not sized correctly, can cause interference in areas where the boosted signal and the donor signal overlap, such as near windows. Class A boosters can also lead to operational challenges for networks that require growth or configuration changes. Changes to the licensed frequencies of the LMR network or adding new frequencies require reprogramming the BDA, or worse, may trigger a hardware update. Public safety BDAs come in 8, 16, or 32 configurations and new channels could require an upgrade or a replacement. In addition, Class A boosters are more expensive than Class B boosters; however, for a typical building, the cost of the BDA itself is generally a small fraction of the cost of deploying the entire DAS. In general, public safety frequencies do not change very often, perhaps every 10-15 years when systems are upgraded, if ever. A more common change is to shift bands altogether (e.g., VHF to 800 MHz), which would require a hardware change regardless. As a result, the frequency flexibility that a Class B amplifier offers may not be a necessary feature for many AHJs, and the codes should require that building owners reconfigure their ERRCS in the event of licensed frequency changes regardless of the reasoning. After all, broad mandated band changes, such as the recent 800 MHz rebanding, may occur to enhance overall operation and interoperability and should be considered for the long term, regardless of the Class A / Class B decision.
While the objective for the DAS of the AHJ (Fire Marshal) is to amplify the radio signal strength enough to provide usable voice communications throughout the building, protecting the overall quality of the network is of paramount importance to the radio managers. That’s why more and more AHJs work closely with radio managers to set the minimum design requirements. At a minimum, the DAS operator should be required to demonstrate that the design will not increase the uplink noise and harm the overall performance of the donor network. Some managers may require a review and approval of the link budget and additional design parameters such as filter sizes, while others may choose to set the maximum uplink noise each BDA should add to the network. Reviewing the design and link budget is more resource intensive for radio managers and there is no guarantee that the installed network will stay within the designed link budget provided by the DAS operator. Therefore, to minimize resources required for the review, some AHJs settle on setting the maximum unlink noise and signal level, which can effectively be measured before the DAS is commissioned and may also mandate uplink squelch for noise suppression. At a minimum, the radio managers will review the initial design submission and decide if the host site selected by the DAS operator is appropriate. In some cases, there may already be too many existing DAS systems “connected” to a given host site and adding more DAS will have an adverse effect on the uplink noise. Additionally, AHJs may require a coverage “heat map,” which provides a prediction of the coverage performance of the DAS network to be installed. However, this requires some expertise on behalf of the AHJ to interpret the map and many of the parameters used in the DAS design, such as the building material of the walls, may not be available at the time of the design. As a result, this uncertainty may increase the cost of the DAS unnecessarily, and this cost gets passed onto the building owners. Alternatively, AHJs may choose to rely on the final test results as proof of performance.
AHJs need to keep in mind that as they define requirements, they must also be prepared to ensure compliance, as oversight requires resources that end user agencies may not have. Some jurisdictions choose to provide oversight end to end, from reviewing and approving the design to overseeing the implementation and final acceptance testing. This has the benefit of affording the AHJ the complete understanding of the system installed and guarantees that the DAS operator will not only meet the performance requirements, but also will take all steps necessary to protect the host LMR network. In setting the policy, the AHJ should ensure that the expertise to perform this task is available internally or that it has the financial means to outsource. If the policy is designed to leverage the technical resources from the radio operator agency, their management needs to be consulted to ensure resources will be available. In a large county, dozens of DAS may come online each month, which will be a big burden on the radio personnel who may be both overworked and limited in number.
Coverage and Testing
Ultimately, the definitive test of the DAS network will be that it provides the coverage desired throughout the facility. Both the IFC and NFPA codes specify coverage requirements. While the two codes differ slightly, they both address a minimum requirement for radio communication voice quality in general building areas and a more stringent requirement for “critical” areas such as exit passageways and fire control rooms.
The codes also require testing of the system to confirm operation and performance. An initial test is required after installation and periodic testing is specified at least annually to confirm continued satisfactory performance. In addition to the voice quality testing, further tests are required to also confirm proper alarm operation. Some AHJs may require an uplink noise test to ensure the DAS does not adversely affect the donor site and an isolation test to ensure the DAS will not enter into oscillation. This level and depth of performance testing must be required prior to allowing the DAS to be put into service.
Contact us at firstname.lastname@example.org to find out how we can help you retune your DAS processes to ensure all installed DAS meet the needs of the public safety community, do not adversely affect the LMR network, and the requirements do not overly burden property owners/managers.