Satellites provide seamless coverage and are vital for establishing emergency communications during natural disasters. However, its effectiveness is limited by the allocated spectrum and high deployment costs. To address these challenges, we propose a solution based on the fluid antenna system (FAS), which enables dynamic signal adjustment for enhanced performance. Building on this concept, compact ultra massive antenna array (CUMA) is introduced, which activates multiple ports simultaneously, allowing the in-phase components of signals to be constructively combined. This approach mitigates interference while significantly reducing costs, as each fluid antenna requires only a single RF chain yet achieves substantial improvement in the received signal-to-interference-plus-noise ratio (SINR). In this paper, we consider a satellite CUMA network in which all ground users are assigned to the same satellite for uplink transmission, and the satellite leverages CUMA to mitigate inter-user interference. We derive closed-form expressions for the received CUMA signal power, interference power, and their distributions. Based on these expressions, we present the outage probability in a single integrated form, along with an approximated closed-form expression. The ergodic rate is hence provided. Our findings reveal the conditions under which CUMA outperforms maximum ratio combining in satellite communications scenario under various configurations. Notably, our analysis demonstrates that with a sufficient compact fluid antenna setting, the received CUMA signal becomes deterministic rather than a random variable, indicating that the system performance depends solely on the interference distribution. Moreover, for the compact fluid antenna configuration, increasing the number of ports results in a linear improvement in the beamforming gain. Finally, numerical results are provided to compare orthogonal multiple access CUMA (O-CUMA) and non-orthogonal multiple access CUMA (N-CUMA) in satellite communications, showing that with broad bandwidth,N-CUMA outperforms O-CUMA.

This paper studies the End-to-End (E2E) performance of a High Throughput Satellite (HTS) system that utilizes a transparent (non-regenerative) optical feeder link to transport the DVB-S2 signals associated with the large number of spot-beams in the radio access link. Two main sources of non-linearity are considered to characterize the effect that the satellite forward link has in the DVB-S2 signal, namely the optical Mach-Zehnder Modulator (MZM) in the gateway and the High Power Amplifier (HPA) in the satellite. Digital Pre-Distortion (DPD) and linear equalization are also implemented to mitigate the impact of the non-linear distortion and the inter-symbol interference on the Packet Error Rate (PER) of the received DVB-S2 signal. The performance analysis is carried out using the Total Degradation (TD) as performance indicator. As expected, the Input Back-Off (IBO) of the HPA and the modulation index of the MZM should be jointly optimized according to the DVB-S2 MODCOD that is selected for transmission. Therefore, the stronger is the Forward Error Correction (FEC) code that is used, the lower is the IBO and the higher is the modulation index that can be utilized to minimize the impact of non-linearities in the E2E performance.

This paper deals with the problem of precoding, scheduling, and link adaptation in next generation mobile interactive multibeam satellite systems. In contrast to the fixed satellite services, when the user terminals move across the coverage area, additional challenges appear. Due to the time varying channel, the gateway has only access to a delayed version of the channel state information (CSI), which can eventually limit the overall system performance. However, in contrast to general multiuser multiple-input multiple-output terrestrial systems, the CSI degradation in multibeam mobile applications has a very limited impact for typical fading channel and system assumptions. Under realistic conditions, the numerical results show that precoding can offer an attractive gain in the system throughput compared with the conservative frequency reuse allocations.

To face the challenges of the new era of heterogeneous networks, mobile satellite systems need to provide an increased level of flexibility. As a consequence, a more effective use of the available resources and the exploitation of interference mitigation techniques are considered necessary to tackle the issue. The limits of a traditional configuration are even more noticeable in specific areas of high traffic requests i.e., in hot spots. In this paper, focusing on the forward link of a typical mobile interactive satellite system operating in L-band, where a large imbalance in traffic demand between the multiple beams is common, new configurations that aim at improving the performance of the system are studied. The proposed approach, based on a higher frequency reuse factor and the application of precoding techniques, boosts the system in terms of total capacity and provides higher flexibility, without making any change whatsoever to the space segment. A general analytic formulation of the problem and a pragmatic solution are provided for hot spot scenarios. Simulations are carried out to validate the proposed solution.

There is an urgent need for substantially enhancing random access schemes to be able to support native massive machine-to-machine communications in the next generation wireless systems. Lately, contention resolution diversity slotted ALOHA (CRDSA) and its variants have contributed to a drastic improvement in throughput compared with the traditional slotted ALOHA protocols. In this paper, we further enhance the CRDSA flexibility and performance along different physical layer dimensions. Based on simulation results, we show that there is still room for improvement in terms of throughput and, using heuristic methods, we find an optimized distribution of the packets power that is entering the demodulator for an additive white Gaussian noise channel. Applying this power distribution, which is easy to implement at the terminal in open loop and in a decentralized manner, is shown to achieve significantly enhanced performance. By introducing multi-frequency CRDSA, a drastic reduction in the terminal's peak power requirement is attained. Furthermore, we investigate spread spectrum CRDSA, which improves the robustness of the scheme against irresolvable packet collisions allowing for enhanced energy efficiency. To support the work presented herein, we have developed a computationally efficient yet accurate methodology for estimating CRDSA performance, a novel approximate centrally coordinated CRDSA achievable sum rate analysis accounting for modulation and forward error correction constraints, as well as a more accurate loop probability analysis.

The need for increased data rates has led towards the development of advanced broadband satellite systems able to achieve higher capacity for providing Internet and backbone services in remote areas. Aside of the more conventional geostationary orbit (GEO), Medium Earth Orbit (MEO) satellite constellations are envisaged due to their advantages in terms of shorter link path and low latency; MEO satellite constellations are currently operating at Ka-band and are already showing signs of spectrum saturation in high demand areas in their coverage. In search of additional spectrum, in this paper, we employ the Q-band by investigating the performance of a multi-satellite MEO constellation network in terms of system capacity considering sophisticated propagation and physical layer tools. In particular, within the proposed Q-band solution, a higher throughput can be achieved with respect to a corresponding Ka-band system, by reaching up to 100% gain in terms of system capacity in a clear sky conditions.

In this work, we study the design of a precoder on the user downlink of a multibeam satellite channel. The variations in channel due to phase noise introduced by on-board oscillators and the long round trip delay result in outdated channel information at the transmitter. The phase uncertainty is modelled and a robust design framework is formulated based on availability and power constraints. The optimization problem is cast into the convex paradigm after approximations and the benefits of the resulting precoder are highlighted.

Design of high bandwidth and reliable feeder links are central toward provisioning new services on the user link of a multibeam satellite communication system. Toward this, utilization of the Q/V band and an exploitation of multiple gateways (GWs) as a transmit diversity measure for overcoming severe propagation effects are being considered. In this context, this contribution deals with the design of a feeder link comprising$N+P$GWs ($N$active and$P$redundant GWs). Toward provisioning the desired availability, a novel switching scheme is analyzed and practical aspects such as prediction-based switching and switching rate are discussed. Unlike most relevant works, a dynamic rain attenuation model is used to analytically derive average outage probability in the fundamental$1+1$GW case. Building on this result, an analysis for the$N+P$scenario leading to a quantification of the end-to-end performance is provided. This analysis aids system sizing by illustrating the interplay between the number of active and redundant GWs on the chosen metrics: average outage and average switching rate.

Multibeam satellite systems offer flexibility that aims at efficiently reusing the available spectrum. To fully exploit the flexibility advantages, the payload resources—transmit power and bandwidth—must be efficiently allocated among multiple beams. This paper investigates the resource optimization problem in multibeam satellites. The NP-hardness and inapproximability of the problem are demonstrated motivating the use of metaheuristics. A systematic approach accomplishing the best traffic match is carried out. The additional requirement of minimizing the total power consumption is then considered, giving rise to a multi-objective optimization approach. The solutions to thea prioriaccomplished traffic matching optimization are used to enhance the efficiency of the multi-objective metaheuristic method proposed and, consequently, of the multibeam satellite system. The optimized performance is represented by the Pareto front, which provides trade-off points between total power consumption and rate achieved. This allows the decomposition of the problem into independent color-based sub-problems rendering the proposed two-stage optimization framework suitable for dimensioning the next generation multispot satellite systems.

Exploiting transmit diversity amid a high number of multiple gateways (GW) is a new research challenge in Q/V band satellite communication providing data rates of hundreds of Gbit/s. In this paper, we propose a practical switching strategy in a scenario with N+P GWs (N active and P redundant GWs) towards achieving GW transmit diversity. Differently from other works, the treatment in this paper is analytical and explores two key factors: outage performance and switching rate in detail. Further, the interplay between the number of redundant and active GWs on the availability is illustrated highlighting the contribution of the work towards system sizing.

An increasing number of hybrid mobile systems comprising a satellite and a terrestrial component are becoming standardized and realized. The next generation of these systems will employ higher dimensions adopting multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) techniques. In this work, we build upon recent studies of dual polarization MIMO for each component and propose the use of full-rate full-diversity (FRFD) codes adopting a space-frequency paradigm. We also propose a scheme taking advantage of the separation between the subcarriers to enhance the coding gain. By critically assessing the different options for the 4 transmit, 2 receive hybrid scenario taking into account system and channel particularities, we demonstrate that the proposed scheme is a solution for enhancing the performance of next generation hybrid mobile satellite systems.

Security threats introduced due to the vulnerability of the transmission medium may hinder the proliferation of Ka band multibeam satellite systems for civil and military data applications. This paper sets the analytical framework and then studies physical layer security techniques for fixed legitimate receivers dispersed throughout multiple beams, each possibly surrounded by multiple (passive) eavesdroppers. The design objective is to minimize via transmit beamforming the costly total transmit power on board the satellite, while satisfying individual intended users' secrecy rate constraints. Assuming state-of-the-art satellite channel models, when perfect channel state information (CSI) about the eavesdroppers is available at the satellite, a partial zero-forcing approach is proposed for obtaining a low-complexity sub-optimal solution. For the optimal solution, an iterative algorithm combining semi-definite programming relaxation and the gradient-based method is devised by studying the convexity of the problem. Furthermore, the use of artificial noise as an additional degree-of-freedom for protection against eavesdroppers is explored. When only partial CSI about the eavesdroppers is available, we study the problem of minimizing the eavesdroppers' received signal to interference-plus-noise ratios. Simulation results demonstrate substantial performance improvements over existing approaches.

This paper discusses the performance of Golden codes in a hybrid satellite/terrestrial system framework employing dual polarized MIMO-OFDM transmissions. Although the use of Golden codes in satellite and terrestrial scenarios has been studied independently, a realistic performance assessment must involve both components taking into account the relative delay between their reception. In fact, this work exploits the relative delay to create a multipath scenario and further improve the coding gain of the Golden codes, which is otherwise fixed. This is made possible by utilizing the Golden code in a Space-Frequency coding framework instead of the traditional Space-Time paradigm. The separation between the subcarriers constituting a Golden code is shown to be central to the coding gain enhancement and an algorithm to choose this separation is provided.

This letter studies the potential capacity advantages of introducing a dual polarization per beam paradigm instead of the conventional single polarization per beam in mobile satellite broadcasting systems. This enables the application of MIMO techniques, not yet thoroughly investigated for mobile satellite systems. We engage in a fair system performance comparison between single polarization SISO and dual polarization non-MIMO and MIMO configurations based on the DVB-SH state-of-the-art mobile satellite standard. Along the course, the major advantages and pitfalls of a dual polarization per beam system from an interference, antenna, payload, and capacity perspective are highlighted.

The mobile satellite broadcasting arena is witnessing a constant increase in demand for improved transmission quality and higher number of services in order to remain on par with the corresponding terrestrial counterparts. A promising way forward in this regard is the migration from the conventional single polarization per beam to an advanced dual polarization per beam architecture for effective spectrum exploitation; this also enables the application of advanced multiple antenna (MIMO) techniques. The present paper moves from DVB-SH the current state-of-the-art for mobile satellite services towards a more advanced system architecture doubling the overall system capacity with a minimum power increase. It turns out that a multiplexing gain equal to two comes at a cost of about 6 dB for the conventional single polarization system, whereas for the advanced system the corresponding cost is about 3.5 dB.

The high frequency segment (10-66 GHz) of the IEEE 802.16 standard seems promising for the implementation of wireless backhaul networks carrying large volumes of Internet traffic. In contrast to wireline backbone networks, where channel errors seldom occur, routing decisions in IEEE 802.16 networks are conditioned by wireless channel impairments rather than by congestion, exclusively. This renders a cross-layer routing approach between the routing and the physical layers more appropriate during fading periods. In this paper, an adaptive cross-layer routing scheme is presented based on the selection of the most reliable path in terms of packet error ratio (unipath routing). The paper argues that routing Internet traffic through wireless backhaul networks is modeled more realistically employing evolutionary rather than conventional game theory. The stability of the proposed routing algorithm is proven and the dependence of the speed of convergence on various physical layer parameters is investigated. Is is also shown that convergence may be further accelerated by increasing the amount of information from the physical layer, specifically the physical separation between the alternative paths provided to the routing layer.