SAFECOM and NCSWIC Publish Infrastructure Obstructions to Radio Propagation

Author: Ted Lawson, Cybersecurity and Infrastructure Security Agency (CISA), Joint SAFECOM-NCSWIC Technology Policy Committee Federal Lead

Wireless communications systems are very complex. Public safety, first responders, and emergency personnel need to use these systems without disruption to operate in a fast-paced, all-hazards environment. However, obstructions or interference to radio signals can cause significant problems for the ability of public safety and emergency responders to communicate during an emergency. According to Chris Maiers, Iowa Statewide Interoperability Coordinator (SWIC), “when it comes to interference with communications systems, it’s easy to default to something like jamming, co-channel, or adjacent channel interference.  However, there are several physical and non-traditional obstructions that can interfere with a radio network that also need to be accounted for and addressed.”

Physical and non-traditional obstruction sources may be fixed structures like bridges and buildings, or non-fixed structures like cranes and event tents. Some obstructions may have moving or alternating components, such as wind turbines, that could periodically interfere with radio frequency (RF) or microwave backhaul. Additionally, human-made impediments that are non-structural may also attenuate signal, as can be the case with high-piling backfill or landfill heaps. These obstructions can cause issues with primary RF sources as well as microwave backhaul and other wireless technologies when new structures are being planned or constructed. Agencies across the United States have used system planning, implementation techniques, administrative policy, and state, city, or municipal code to counteract the impacts of infrastructure obstructions to radio propagation.

The Infrastructure Obstructions to Radio Propagation document points organizations to techniques already in practice to prevent and mitigate these interferences by providing communications system planners and administrators with knowledge to better prepare for changes to existing infrastructure. Specifically, the document describes different forms of obstructions, supplies examples of prevention and mitigation approaches, and highlights best practices already in use by several jurisdictions, including states, territories, or cities that have chosen to pursue more formal guidance to prevent and mitigate signal obstruction.

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