Public safety agencies include the nation’s first responders (such as firefighters, police officers, and ambulance services), 911 call center staff, and a number of local, state, federal, and regional authorities. Communications, often through wireless land mobile radios, are vital to these agencies’ effectiveness and to the safety of their members and the public. Wireless technology requires radio frequency capacity in order to function, and existing wireless technology is designed to work within specified frequency ranges. Interoperability in the context of public safety communications systems refers to the ability of first responders to communicate with whomever they need to (including personnel from a variety of agencies and jurisdictions), when they need to, and when they are authorized to do so. It is important to note that the goal of being able to communicate when necessary and authorized is not the same as being able to communicate with any other individual at any time—a capability that could overwhelm the communications infrastructure and would likely impede effective communication and response time. Different first responder groups each have different professional practices, public safety missions, emergency response procedures, communication protocols, and radio frequencies. These differences have created a variety of obstacles to effective interoperable communications among first responders. Thus, facilitating interoperable communications has been a policy concern of public safety officials for many years. Land mobile radio systems are the primary means of communications among public safety personnel. These systems typically consist of handheld portable radios, mobile radios, base stations, and repeaters. Handheld portable radios are typically carried by public safety personnel and tend to have a limited transmission range. Mobile radios are often located in vehicles and use the vehicle’s power supply and a larger antenna, providing a greater transmission range than handheld portable radios. Base station radios are located in fixed positions, such as public service access points or dispatch centers, and tend to have the most powerful transmitters. A network is required to connect the different base stations to the same communications system. Repeaters are used to increase the effective communications range of handheld portable radios, mobile radios, and base station radios by retransmitting received radio signals. Figure 1 below illustrates the basic components of a land mobile radio system. The transmissions between the elements of a land mobile radio system consist of electromagnetic waves that propagate along designated frequencies of the radio spectrum. Each communications link uniquely occupies a specific frequency or set of frequencies for as long as information is being transmitted. The radio spectrum is a fixed, limited resource that is shared among government and nongovernment entities for many uses in addition to public safety communications, such as television broadcasting, AM/FM radio, and aeronautical radio navigation. Most public safety agencies use their allocated frequencies for voice communications but are increasingly using their portion of the spectrum to support more advanced technologies, such as data, imagery, and video transmissions. The specific frequency bands allocated to public safety agencies are shown in figure 2. Major frequency ranges that are used for public safety communications include the very high frequency (VHF) range and the ultra high frequency (UHF) range. VHF signals travel farther than UHF signals and thus are useful in suburban and rural areas. However, they generally cannot penetrate building walls very well. In contrast, UHF signals are more appropriate for denser urban areas as they penetrate buildings more easily, and it is less critical that the signals be able to propagate for long distances. The frequencies used by federal agencies are managed by the National Telecommunications and Information Administration, while the Federal Communications Commission manages state and local government frequencies. Radio systems are classified as either conventional or “trunked.” Conventional radio systems have dedicated frequencies—also referred to as channels—assigned to individual groups of users. When a user makes a call, other members of the group cannot use the channel until the call is over. In contrast, trunked systems allocate pools of channels for use by multiple individuals. When a call is made by a user on a trunked system, an available channel is automatically selected from the pool of channels, leaving the remaining channels available for others. While trunked systems are more complex and require more infrastructure than conventional systems, they allow for more efficient use of communication channels, reducing congestion. In order to effectively respond to emergencies such as natural disasters and domestic terrorism, public safety agencies need the ability to communicate with their counterparts in other disciplines and jurisdictions. However, the wireless communications systems used by many police officers, firefighters, emergency medical personnel, and other public safety agencies do not provide such capability. For example, emergency agencies responding to events such as the bombing of the federal building in Oklahoma City and the attacks of September 11, 2001, experienced difficulties in trying to communicate with each other. The 9/11 Commission concluded that communications interoperability problems contributed to the large number of firefighter fatalities that occurred at the World Trade Center. Historically, first responder communications interoperability has been significantly hampered by different and incompatible radio systems. Different technologies and configurations, including proprietary designs, by different manufacturers have limited the interoperability of public safety wireless communications systems. These systems have also operated on different frequencies of the radio spectrum. In particular, public safety agencies have been assigned frequencies in new bands over time as available frequencies became congested, and as new technologies made higher frequencies available for use. Existing radios are unable to transmit and receive in all of the public safety frequencies, often making communications between first responders from different jurisdictions difficult. Additionally, as we have previously reported, there is a need for better frequency planning and coordination. Further, public safety agencies have historically planned and acquired communications systems without concern for interoperability, often resulting in multiple, technically incompatible systems in operation throughout any given local jurisdiction. A variety of technical approaches have been adopted to help improve interoperable communications, including the following: Swapping radios: Agencies maintain a cache of extra radios that they can distribute during an emergency to other first responders whose radios are not interoperable with their own. The advantage of this solution is that it does not require that all existing radios be replaced, an important consideration when funds to buy new equipment are limited. However, this approach requires significant logistical support and careful management to implement successfully. Patching: Two or more incompatible radio systems are connected to a central switchboard-like system that translates a signal sent from one connected system so that it can be received by any of the other connected systems. The principal advantage of this solution is that agencies can continue to use existing systems that would otherwise be incompatible. A major disadvantage is that patching requires twice as much spectrum because a patched transmission occupies separate channels on each connected system. Shared channels or mutual aid channels: Agencies agree to set aside a specific channel or channels for connecting to other incompatible systems. This approach provides direct interoperable communications and only occupies one channel per conversation. However, it can cause congestion since these channels require dedicated frequencies and thus have limited capacity. Shared systems: The use of a single or common radio system—typically a trunked system—to provide service to most agencies within a region. Shared systems are the most robust form of interoperability and do not require dedicated channels. While this approach produces optimal performance, it can be very expensive, because it generally requires purchasing all new radios and transmission equipment. Technologies that can help implement shared systems include the following: Internet Protocol based systems: Using the Voice over Internet Protocol, advanced communications systems can offer the flexibility to transmit voice conversations over a data network such as the Internet or a private network. Software-defined radios: These are intended to allow interoperability among agencies using different frequency bands, different operational modes (digital or analog), proprietary systems from different manufacturers, or different modulations (such as AM or FM). However, software-defined radios are still being developed and are not yet available for use by public safety agencies. However, interoperability cannot be achieved solely by implementing technical solutions. Coordination among different agencies and governmental entities is also critical. Response to an emergency may involve all levels of government and many different disciplines, such as law enforcement organizations, fire departments, emergency medical services, transportation, natural resources, and public utility sectors. Each of these agencies is likely to have its own policies, procedures, and communications protocols when responding to an incident. A simplistic example is the word “fire,” which to a firefighter means that something is burning but to a police officer is a command to shoot a weapon. Resolving such cultural and procedural differences can be challenging. Further, the extent to which interoperable communications are needed among different agencies, disciplines, and levels of government (federal, state, local, and tribal) varies based on the size, significance, and duration of an emergency event. Increasing degrees of interoperability may be needed for (1) routine day-to-day coordination between a few agencies in a local area, (2) extended operations involving agencies from multiple jurisdictions working on a larger problem (such as the 2002 sniper attacks in the Washington, D.C., metropolitan area), and (3) a major, large-scale event that requires response from a range of local, state, and federal agencies and disciplines (such as major wildfires, hurricanes, or the terrorist attacks of September 11, 2001). In 2004, we reported that a fundamental barrier to successfully addressing interoperable communications problems for public safety was the lack of effective, collaborative, interdisciplinary, and intergovernmental planning. We recommended that DHS take a number of actions to address this barrier, such as determining the current status of interoperable communications across the nation and encouraging states to establish comprehensive statewide interoperability plans and certify the alignment of their grant applications with their statewide plans. DHS has taken steps to address these recommendations. For example, it recently completed a national survey of first responders to determine the current status of their interoperability capabilities, and it has required states to develop statewide communications plans by the end of 2007. SAFECOM is a DHS program intended to strengthen interoperable public safety communications at all levels of government.