# A Review on Internet of Things for Defense and Public Safety
## 1 Introduction
Defense and Public Safety (PS) organizations play a critical societal role ensuring national security and responding to emergency events and catastrophic disasters. Instead of PS, some authors use the term Public Protection Disaster Relief (PPDR) [15] radio communications, defined in ITU-R Resolution 646 (WRC-12) as a combination of two key areas in emergency response:  
* Public protection (PP) radio communication: communications used by agencies and organizations responsible for dealing with the maintenance of law and order, protection of life and property, and emergency situations. * Disaster relief (DR) radio communication: communications used by agencies and organizations dealing with a serious disruption in the functioning of society, posing a significant, widespread threat to human life, health, property or the environment, whether caused by accident, nature or human activity, and whether they happen suddenly or as a result of complex, long-term processes. Nowadays, the challenge of crisis management is in reducing the impact and injury to individuals and assets. This task demands a set of capabilities previously indicated by European TETRA [16], TCCA [17], and ETSI [18] standardization bodies and American APCO Project-25 [19], which includes resource and supply chain management, access to a wider range of information and secure communications. Military and first responders should be able to exchange information in a timely manner to coordinate the relief efforts and to develop situational awareness. FY 2016 SAFECOM Guidance [20] provides an overview of emergency communications systems and technical standards. Communication capabilities need to be provided in very challenging environments where critical infrastructures are often degraded or destroyed. Furthermore, catastrophes, natural disasters or other emergencies are usually unplanned events, causing panic conditions in the civilian population and affecting existing resources. In large-scale natural disasters, many different PS organizations (military organizations, volunteer groups, non-government organizations and other local and national organizations) may be involved. At the same time, commercial communication infrastructure and resources must also be functional in order to alert and communicate with the civilian population. In addition, specific security requirements including communication and information protection can also exacerbate the lack of interoperability. Sharing various types of data is needed in order to establish and maintain a Common Operational Picture (COP) between agencies and between field and central command staff. Typically, first responders include police officers, firefighters, border guards, coastal guards, emergency medical personnel, non-governmental organizations (NGOs) and other organizations among the first on the scene of a critical situation. These organizations can provide one or more of the functions described above. The relationships between them may depend on the national legislation or the context. Table 1 provides an overview of the main functions and the potential relationships among the agents of the different PS organizations. The rest of this article we will be focus on the military side, since we consider that it covers most of the significant scenarios and functions, and it represents the most challenging cases (in terms of operational and technical requirements) in PS organizations. Over the last years, some research papers focused on evolving PS organizations have been published [21; 22; 23; 24; 25]. Some of these articles have particular interest in the challenges to evolve the LTE