In this paper, we study multibeam satellite secure communication through physical (PHY) layer security techniques, i.e., joint power control and beamforming. By first assuming that the channel state information (CSI) is available and the beamforming weights are fixed, a novel secure satellite system design is investigated to minimize the transmit power with individual secrecy rate constraints. An iterative algorithm is proposed to obtain an optimized power allocation strategy. Moreover, suboptimal beamforming weights are obtained by completely eliminating the cochannel interference and nulling the eavesdroppers' signal simultaneously. In order to obtain jointly optimized power allocation and a beamforming strategy in some practical cases, e.g., with certain estimation errors of the CSI, we further evaluate the impact of the eavesdropper's CSI on the secure multibeam satellite system design. The convergence of the iterative algorithm is proven under justifiable assumptions. The performance is evaluated by taking into account the impact of the number of antenna elements, number of beams, individual secrecy rate requirement, and CSI. The proposed novel secure multibeam satellite system design can achieve optimized power allocation to ensure the minimum individual secrecy rate requirement. The results show that the joint beamforming scheme is more favorable than the fixed beamforming scheme, especially in the cases of a larger number of satellite antenna elements and higher secrecy rate requirement. Finally, we compare the results under the current satellite air-interface in DVB-S2 and the results under Gaussian inputs.

In this paper, we investigate two new candidate transmission schemes to replace current ones in satellite communication systems. They operate in different domains (frequency and time-space), and we want to know which domain shows overall best performance. The two new transmission schemes are: Non-Orthogonal Frequency Reuse (NOFR) and Beam-Hoping (BH). We propose a novel formulation of the Signal-to-Interference-plus-Noise Ratio (SINR) and spectral efficiency of these two schemes and prove the theoretical duality between them. Further, we also develop a general methodology to include the technological constraints due to realistic implementation, which is common for the two domains and obtain the main factors that prevent the two technologies be in practice dual of each other (what we have called the technological gap). Moreover, we solve the frequency/time-space resource optimization problem with two different cost functions for an asymmetric traffic distribution. Both Gaussian codes and current state-of-the-art adaptive coding and modulation transmission over time division multiplexing (DVB-S2) are assumed in the simulation. It is shown that the Beam Hopping system turns out to show a less complex design and performs better specially for non-real time services.

A novel multibeam satellite system design is proposed in this paper based on jointly optimizing power and carrier allocation in order to best match the asymmetric traffic requests. This design introduces higher and asymmetric interference levels throughout the coverage. However, both power and bandwidth will be used more efficiently. Even though the problem of power and bandwidth allocation has been addressed in terrestrial wireless communications, it is new in satellite systems and since architecture and channel are different, available results and algorithms are not applicable to satellite payload systems. In this paper we formulate the resource allocation problem as max-min SINR balancing based on the recently introduced axiomatic-based interference model, but in addition, we also optimize the carrier allocation when performing the SINR balancing problem. An analytical solution for the optimal carrier allocation is proposed and we iteratively find the optimal power allocation for each beam. The Shannon (upper bound) and current state-of-the art PHY layer technology: DVB-S2 are proposed to be implemented in order to obtain the gap between them. Simulation results show significant improvements in terms of power gain, spectral efficiency and traffic matching ratio comparing with conventional system, which is designed based on uniform bandwidth and power allocation.

Current multibeam satellite systems perform centralized power and carrier allocation assuming a multi-frequency time division multiple access (MF-TDMA) scheme with fixed regular frequency reuse. This approach is not optimal when individual SINR constraints are to be met. In this paper, we formulate the problem of joint power and carrier allocation allowing non-regular frequency reuse. This setting will increase the interference levels but in turn will allow a more efficient use of the power increasing the spectral efficiency. We focus on a distributed formulation of the problem and compare it with the conventional power balancing solution. Numerical results show that the centralized power balancing approach performs better for high SINR constraints, balancing the co-channel interference among all the users and beams. Conversely, the decentralized approach optimizes the satellite terminals' self-interest deteriorating SINR of high loaded beams resulting in worse performance for highly loaded beams.

This paper aims at providing different cost-efficient solutions for the channel impairments in tropical areas. In order to extend service to isolated areas, we propose hybrid architecture based on DVB-S2/RCS+Wi-Fi networks. In this scenario the satellite channel is affected by deep rain events that do not allow ACM modes to protect data. Moreover, the delay in the ACM reaction to fade changes can affect the quality of the video transmission. In order to avoid the QoS reduction, we focus on different fading mitigation techniques (FMT), designing a multi-layer scheme protection, using LL-FEC and AL-FEC in higher layers, and optimizing the intervention threshold and super-frame length in the physical layer.

Synchronization is a challenging task in ultra wideband (UWB) communications, and becomes more difficult in UWB based wireless sensor networks (WSNs) in the presence of multi-user interference (MUI). For such a system, we develop a synchronization scheme including a novel design of transmitted reference (TR) signal model to avoid MUI and an energy-efficient synchronization algorithm. The synchronization signal of cluster-head is designed to be TR symbols with normal reference pulse and the interfering signal of common neighbour nodes is designed to be TR symbols with alternant anti-polar reference pulse, thus the MUI-free operation is obtained. Furthermore, the synchronization algorithm employs sample mean and energy detection relying on the periodicity in the mean of synchronization signal. Theoretic analysis and simulative results prove that the proposed scheme is both reliable and scalable