Coverage Can Change Between Formal Tests

After formal acceptance and certification of an indoor public safety radio coverage system, there are several ways that radio frequency (RF) conditions can be altered. Some of the common causes for changes include tenant improvements; new walls constructed; moving equipment, damaging cables; changing antennas; adjusting amplifiers; and altering the RF environment through either additions or removals of transmitting sources (donors). Most of the factors above are gradual and often do not result in immediately apparent failures at the precise location where coverage is decreasing.

The 2024 International Fire Code model language in Section 510 defines emergency responder communications enhancement systems (ERCES) as “maintained” systems rather than “one-time” installations. ERCES systems must remain operational, and Annual inspection/testing is required, and re-testing is required if structural modifications occur that could significantly affect the results of initial field performance tests. The same model code also requires supervisory monitoring for issues such as loss of power; failure of chargers; failure of signal sources; failure of active RF devices; failure of critical components; communication link failure; and active RF device oscillation. As a model code, local jurisdictions can adopt the IFC with some degree of flexibility.

The key differences between the requirements established by the IFC model code and other forms of testing/monitoring are clearly established. Supervision can alert personnel to defined equipment faults, while distributed RF monitoring allows personnel to monitor the actual signal levels at various antenna locations. Both functions serve similar purposes; however, they are not identical.

Distributed RF Monitoring Provides Signal Levels And Additional Context

A booster alarm indicates a fault exists in an active device. However, it typically does not provide any insight as to how the faulty device affects each individual antenna branch or each occupiable area provided service by the distribution network. A cable failure or connector issue within a portion of the local network, an alteration to a particular antenna branch, or a change due to a modification within a structure can impact a portion of the system while still maintaining active equipment function/power.

TX RX Systems describes their DAS Monitoring System as able to monitor up to 256 separate antenna locations and provide real-time signal level updates, coverage information, alarm histories, and three-dimensional representations of buildings. In addition, the company also stated that the monitoring information can be accessed remotely without accessing the building, and that the monitoring system can be integrated with existing DAS. The previous statements illustrate relevance because they relate the measured RF quantity to an identifiable physical location instead of reducing an entire building’s coverage situation to a singular fault/alarm indicator associated with active equipment.

Therefore, identifying a persistent change in a monitored antenna location will allow personnel to begin investigating areas that need evaluation. Identification of potential problems via monitoring is a vital tool for locating possible concerns.

In addition to meeting regulatory requirements for acceptable performance, part 90 Private Land Mobile Radio Service licensees who deploy signal boosting technology have an obligation under 47 CFR § 90.219 to ensure that their systems operate properly and resolve harmfully interfering signals generated by improper operation. Non-licensees who operate part 90 signal boosting technology must obtain explicit permission from licensed entities whose frequencies they wish to use. Therefore, as specified by federal regulations, part 90 Private Land Mobile Radio Service licensees who utilize signal booster technology bear the burden for resolving interference issues resulting from their booster deployment.

Practical Example – Continuous Das Monitoring Identifies Trends Prior To Failure

A well-designed das monitoring solution can provide an excellent method for identifying trends in system performance prior to reaching a point of total failure. Specifically, if a monitored antenna location exhibits historically consistent behavior in terms of signal levels and suddenly begins to deviate from historical norms, the deviation can be used to schedule a field investigation before a scheduled Annual test occurs or before users experience problems communicating using radios deployed within the building.

Large scale hospital/campus complexes, transportation hubs, hotel properties, warehouse properties and high-rise buildings with multiple floors/access-controlled spaces represent examples of environments where a das network extends over numerous floors/space boundaries. In these types of applications, remote monitoring provides substantial assistance in narrowing down which areas of a building may contain RF-related anomalies and subsequently reduces the time it takes to search a facility for an isolated anomaly.

Monitoring Post-Renovation

Historical monitoring data can assist in evaluating changes in system performance following renovations/modifications to a building. The 2024 IFC model language includes provisions that require retesting when structural changes occur that may adversely affect field performance tests conducted at acceptance/test.

Although historical monitoring data does not constitute replacement for required acceptance testing/retesting mandated by code/compliance requirements; it can assist in determining where conditions have been modified and thus direct investigation efforts toward verifying that new conditions meet compliance requirements.

Monitoring becomes most effective when coupled with a systematic methodology for performing RF-based investigations. Upon identifying changes via monitoring, service teams must then select investigative methods based upon symptoms observed in monitored data. Coverage measurements can confirm whether usable communications were impacted by recent changes. Spectrum analysis can confirm existence of unwanted emissions. Noise analysis can characterize receive environment quality. Visual examination/inspection can reveal deficiencies in passively routed paths (e.g., damaged cables/loose connectors/antennas). Finally, comparison of booster gain/alarm status with acceptance test/data/specifications is performed to validate proper functioning.

Availability of these field services is essential to validating assumptions developed through utilization of the monitoring platform since it can identify where issues existed while field instrumentation/equipment and trained engineers define why issues existed.

From a technical perspective establishing clear distinctions between detection/diagnosis is crucial. This prevents misuse of monitoring platforms as replacements for spectrum analyzers/Annual acceptance testing/interference investigations.

While Annual testing remains mandatory wherever required by adopted codes/jurisdictional authorities having jurisdiction, part 90 federal regulations governing operation of booster technologies, local fire code provisions/regulatory agency requirements, and system-specific acceptance criteria remain unchanged by continued implementation/utilization of Continuous monitoring technology.

However, Continuous monitoring preserves data between field visits enables operators of increasingly complex public safety communications infrastructures to become aware of failures occurring earlier than would be possible relying upon Annual testing alone.