This paper proposes an efficient architecture of a smart public safety platform that involves public professional operators as well as citizens. The proposed system is compliant with the emerging paradigm of a smart city. Its main features are that of monitoring, forecasting and managing emergency situations, arising from environmental disasters or crimes. The proposed platform performs a smart and functional integration of heterogeneous components as a smart data gathering and analysis system, a novel professional communication system, wireless sensor networks and social networks. Each element acts not only as an information collector but has autonomous capabilities to cooperate with the others in order to increase the system efficiency and to reduce the need of human interactions. Finally, the paper highlights some open research issues that represent critical aspects and require additional investigations in order to further improve the performance of the proposed platform.City management, improving quality of offered services by reducing costs, introducing transparency and citizen participation. It has to give the citizens an appropriate, precise and clear information awareness about the correct use of the resources made available by the community and show the possibilities deriving from a direct involvement in civil life. Education, allowing the use of technology to increase access, improving the quality and experience, and reducing costs.Healthcare, allowing more accurate and rapid diagnosis and responses to emergency. Storage and communication platforms permit data to be stored and shared for diagnosis and research. Transportation, improving services, as traffic management in congested areas, and at the same time reducing costs. The goal is to reduce traffic congestion while encouraging the use of public transportation. Environment, improving the environmental conditions, limiting the sources of pollution, increasing the green areas, providing widespread health services, etc. Economy, promoting innovation, productivity, exportation, etc. Public safety, improving the capability of monitoring critical environments and forecasting disasters due to both natural causes or terrorist attacks. It uses real-time information to respond rapidly to emergencies and threats.Among these smart systems, this paper aims to identify an efficient architecture of a smart public safety platform. Indeed, with the huge increase of cities population density, public safety operators need to respond more quickly to emergency situations. It has made essential the need of effective and smart emergency management solutions. New and advanced systems and platforms have to be identified in order to guarantee the safety and well-being of citizens, properly protect services and critical infrastructures. Smart solutions for public safety involves to accomplish complex tasks related to the following:Monitoring and forecasting-adopting specific monitoring activities and analysis of results arising from the monitoring campaigns to prevent natural...

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We consider a multiple‐input multiple‐output (MIMO) channel in the presence of a reconfigurable intelligent surface (RIS). Specifically, our focus is on analysing the spatial multiplexing gains in line‐of‐sight and low‐scattering MIMO channels in the near field. We prove that the channel capacity is achieved by diagonalising the end‐to‐end transmitter‐RIS‐receiver channel, and applying the water‐filling power allocation to the ordered product of the singular values of the transmitter‐RIS and RIS‐receiver channels. The obtained capacity‐achieving solution requires an RIS with a non‐diagonal matrix of reflection coefficients. Under the assumption of nearly‐passive RIS, that is, no power amplification is needed at the RIS, the water‐filling power allocation is necessary only at the transmitter. We refer to this design of RIS as a linear, nearly‐passive, reconfigurable electromagnetic object (EMO). In addition, we introduce a closed‐form and low‐complexity design for RIS, whose matrix of reflection coefficients is diagonal with unit‐modulus entries. The reflection coefficients are given by the product of two focusing functions: one steering the RIS‐aided signal towards the mid‐point of the MIMO transmitter and one steering the RIS‐aided signal towards the mid‐point of the MIMO receiver. We prove that this solution is exact in line‐of‐sight channels under the paraxial setup. With the aid of extensive numerical simulations in line‐of‐sight (free‐space) channels, we show that the proposed approach offers performance (rate and degrees of freedom) close to that obtained by numerically solving non‐convex optimization problems at a high computational complexity. Also, we show that it provides performance close to that achieved by the EMO (non‐diagonal RIS) in most of the considered case studies.