Issue link: https://www.e-digitaleditions.com/i/1255991
52 I ICT TODAY FIGURE 2: Active public safety DAS fed by a repeater attached to the battery backups. Findings from a report by the Marjory Stoneman Douglas High School Public Safety Commission 16 revealed that there was sporadic functioning of the Broward Sheriff Office's radios, and to an unknown extent the school structure itself also hindered the radio functionality. To prevent a similar tragedy, school districts should implement an in-building public safety communication system to ensure that radio signals can penetrate all areas of buildings, including especially difficult areas for radio frequency (RF), such as stairwells, elevators, basements, and thick-walled or shielded areas. Schools are encour- aged to engage with the AHJ early in the process to under- stand the set of requirements for in-building public safety systems since each AHJ interprets each code differ- ently. This helps to prevent delays during installation. Before contacting a systems integrator (SI) or origi- nal equipment manufacturer (OEM), school district offi- cials should make a list of important goals and objectives to address. If cost savings is a concern, a modular DAS can be upgraded easily to stay compliant with code updates. Some OEMs and integrators also provide 24/7 technical support in case an issue arises. Selecting a qualified SI, such as an experienced Regis- tered Communications Distribution Designer (RCDD), should come after understanding the specific school needs and local AHJ requirements. The right SI is trained in selecting the best RF, design, and system based on a building's architectural design. The SI is responsible for site survey/baseline testing, preliminary design, state- ment of work, RF surveying, design revisions and final- izations for ordering equipment, installation, commis- sioning, and system acceptance. They may also perform annual maintenance and health checks after the system is deployed. The system design is based on three considerations: equipment, capacity and coverage. Public safety commu- nication is rarely restricted by capacity when compared to the data-heavy communication of commercial systems. In public safety systems, the propagation characteristics of the low frequencies dictate the use of an active or pas- sive DAS based on the size of the building and its required coverage needs. For buildings of less than 120 thousand square feet (approximately 11,150 m 2 ), a passive public safety DAS consisting of a signal source (typically a repeater) is used to feed a network of passive components through server antennas to provide coverage throughout a building. This is the most common solution for public safety deploy- ments due to the use of lower frequency bands that allow for better propagation and cover- age of large areas with the same RF output power. An active public safety DAS, also known as an optical fiber DAS, is used in venues or schools that are more than 120 thousand square feet (Figure 2). It consists of a sig- nal source repeater that feeds into a fiber DAS headend that converts the RF to optical sig- nal and distributes it over fiber to multiple remote amplifier locations. It is then converted back to RF and distributed to passive networks of compo- nents and antennas.