# State-of-the-Art in Satellite Communication Networks
###### Abstract  
We present a wide range of coverage throughout the globe and play a very important role due to their broadcasting capacity and bandwidth flexibility. They are able to provide broadband services to citizens in rural areas, to passengers aboard vessels, trains, or aircrafts, quick Internet access in emergency scenarios, and backhauling of other access technology. In terrestrial networks, many links and nodes are needed to reach long distances and cover large areas. Satellite networks are very useful in providing wide coverage to villages and places where wired networks are not possible, such as hills and forests. It should be noted that two-thirds of the world still do not have the infrastructure for Internet. This kind of network can be categorized according to their orbits. In particular, geosynchronous satellites, located over the equator, have the same angular speed as the Earth, allowing them to be a fixed point for users. New standards and technologies have been proposed in recent years to exploit the specific characteristics of these platforms, such as scheduling, mobility, routing, QoS, and many others. An important issue is related to the possibility of integrating satellite networks with other platforms to guarantee better services to the more exigent users. New architectures, such as Digital Video Broadcasting, are focusing on multimedia traffic streams with the possibility of using interactive services. This type of traffic requires high bandwidth and high levels of QoS to meet user requirements. Traffic shaping and rate/congestion control, bandwidth allocation, flow control, and video scalability are some of the technical challenges to be considered in managing multimedia traffic over satellite networks. Hence, this Special Issue focuses on applications, platforms, and services where satellites can play an important role in stimulating the continued efforts of studying and analyzing the intrinsic issues of the satellite environment. 19 April  
the utility function, and then an Importance-TOPSIS scheme to choose an LEO satellite if the users choose to access LEO satellites in the first step is proposed. Simulation results showed that the proposed method can reduce the number of handovers, thus improving the overall throughput of the system. [PERSON] et al. [3] proposed a Blockchain-based Authentication Protocol Using Cryptocurrency Technology (BAPC) to address the issue of extended pauses in satellite services caused by user access authentication in situations of frequent switching between satellites and ground users. Three stages of the authentication process are designed introducing the cryptocurrency technology. The satellite cluster is divided into multiple regions to improve the efficiency of block consensus. Their proposal is tested with an NS-2 simulator, verifying that BACP can greatly shorten the response time of switching authentication and significantly reduce the time of block generation and the network throughput. [PERSON] et al. [4] proposed an algorithm able to perform an efficient iterative timing recovery via the steepest descent of low-density parity-check (LDPC) decoding metrics. The complete timing recovery is accomplished where the proposed scheme is combined with a Mueller-Muller (M&M) timing recovery algorithm to perform both the timing capture and the timing track. The simulation results using the proposed method indicate that the LDPC-coded BPSK system suffered from a large timing phase, and frequency offset performs excellently within 0.1 dB of the ideal code performance with rational complexity. Therefore, the proposed iterative technique can be efficiently used in satellites with weak signal timing synchronization. [PERSON] et al. [5] dealt with beam hopping (BH) for satellite systems, which represents a promising technology to provide a high level of flexibility in satellite applications.