# Energy Efficient Communications for Reliable IoT Multicast 5G/Satellite Services
## 2 lot over 5G/Satellite  
The massive number of connected sensors/actuators and vehicles in IoT scenarios, often distributed in wide and remote areas, usually require satellite technology. The hardware and energy constrained IoT communications in unlicensed bands below 1 GHz (or on ISM band) and satellite communications at frequencies above 10 GHz favor a hybrid terrestrial/satellite solution, where terrestrial LPWAN networks act together with 5G systems, which could cover the same technology and waveforms of satellite, e.g., in part of C-band, to provide a global connectivity [9; 10].  
Satellite could complement terrestrial networks and the challenges of facing: (1) direct connection of billions of IoT devices in a resource efficient way with the new narrow band satellite communication technologies; (2) the interoperability between satellite systems and a plethora of different RAT technologies and the heterogeneity of sensors/devices; and (3) efficient multicast delivery of the same content stored in 5G small cells data caches to support applications that require very low (sub-1 ms) latency.  
The unprecedented opportunity for the satellite to provide a significant contribution is linked to the definition and implementation of the network slices, which represent one of the pillars introduced in 5G and represent the set of infrastructures and protocols made available to satisfy the requirements of a service, also drawing on different technological domains (multi-tenant) [11]. In addition, to enhance the satellite network device interoperability, and the integration of satellite and terrestrial networks, Software-Defined Networking (SDN) has recently been introduced into this domain due to its expected flexibility, programmability, simplified management, and reduced operating costs [12].  
Satellite systems are historically efficient point-to-multipoint distribution platforms. An interesting overview of the use of satellite in remote IoT environment can be found in [7]. This work highlights the main applications of IoT via satellite such as smart grid, environmental monitoring and emergency management by identifying challenges and issues for an efficient satellite support to M2M/IoT networks. Specifically, they have been pointed out as: (1) specific MAC protocols to assure the access of sensors to the satellite resources; and (2) the support of IPv6 over satellite.  
IoT applications usually rely on a group-based data distribution according to the service requirements or the location of the group; as a consequence, multicast communications schemes are well suited for IoT domain, where many-to-many information passing schemes have been proposed for resource constrained embedded devices [13]. In addition, a recent application trend requires the multicast-based group addressing, which has been introduced and compared with the traditional unicast mode in [14]. To this purpose, in [15], a radio resource management policy is performed on per-group basis to provide multimedia content delivery over 5G/satellite networks, validating its performance for the effects of subgrouping approaches, well-known in terrestrial network, and its robustness to the long propagation delay, a typical constraint in satellite system.