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This paper investigates a novel closed-form noniterative precoding technique for multicast multibeam satellite systems. Next-generation satellite systems will be benefited from the flexible use of the satellite resources especially its power flexible allocation among beams. Intending to obtain a low-computational complexity design, we revisit the well-known signal-to-leakage-and-noise ratio design for multicast transmission. Two alternatives are introduced considering both the physical meaning of the ratio and certain multicast channel vector mapping. We observe the benefits of these techniques in satellite flexible payloads. The proposed technique shows a substantial gain compared to the benchmark according to the numerical simulations. Intuitive insights on the precoding behaviour are also presented., This work is funded by Ministry of Science, Innovation and Universities, Spain, under project TERESA -TEC2017-90093-C3-1-R (AEI/FEDER, UE) and by Catalan government under the grant 2017-SGR-01479., Peer Reviewed, Postprint (author's final draft)

Non-Orthogonal Multiple Access (NOMA) has the potentials to improve the performance of multi-beam satellite systems. The performance optimization in satellite-NOMA systems can be different from that in terrestrial-NOMA systems, e.g., considering distinctive channel models, performance metrics, power constraints, and limited flexibility in resource management. In this paper, we adopt a metric, Offered Capacity to requested Traffic Ratio (OCTR), to measure the requested-offered data (or rate) mismatch in multi-beam satellite systems. In the considered system, NOMA is applied to mitigate intra-beam interference while precoding is implemented to reduce inter-beam interference. We jointly optimize power, decoding orders, and terminal-timeslot assignment to improve the max-min fairness of OCTR. The problem is inherently difficult due to the presence of combinatorial and non-convex aspects. We first fix the terminal-timeslot assignment and develop an optimal fast-convergence algorithmic framework based on the Perron-Frobenius theory (PF) for the remaining joint power-allocation and decoding-order optimization problem. Under this framework, we propose a heuristic algorithm for the original problem, which iteratively updates the terminal-timeslot assignment and improves the overall OCTR performance. Numerical results verify that max-min OCTR is a suitable metric to address the mismatch issue, and is able to improve the fairness among terminals. On average, the proposed algorithm improves the max-min OCTR by 40.2% over Orthogonal Multiple Access (OMA)., The work has been supported by the FNR CORE projects ROSETTA (11632107) and FlexSAT (C19/IS/13696663), in part by the project TERESA (TEC2017- 90093-C3-1-R)., Peer Reviewed, Postprint (published version)

This paper aims to design joint precoding and onboard beamforming at a multiple gateway multibeam satellite system. Full frequency reuse pattern is considered among the beams and each gateway serves a cluster of adjacent beams such that multiple clusters are served through a set of gateways. However, two issues are required to be addressed. First, the interference in both user and feeder links is the bottleneck of the whole system and employing interference mitigation techniques is essential. Second, as the data demand increases, the ground and space segments should employ extensive bandwidth resources in the feeder link accordingly. This entails embedding an extra number of gateways aiming to support a fair balance between the increasing demand and the corresponding required feeder link resources. To tackle these problems, this paper studies the impact of employing a joint multiple gateway architecture and on-board beamforming scheme. It is shown that by properly designing the on-board beamforming scheme, the number of gateways can be kept affordable even if the data demand increases. The proposed beamforming scheme can partially mitigate the interference in the user link. While the user and feeder link channels vary over time, this paper focuses on designing fixed beamforming which is sufficiently robust to the variations in both channels, leading to keep payload complexity low. Moreover, Zero Forcing precoding technique is employed at the gateways to reject the interference in the feeder links as well as it helps the proposed fixed on-board beamforming by partially equalizing the interference in user link.

This paper aims to design joint on-ground precoding and on-board beamforming of a multiple gateway multibeam satellite system in a hybrid space-ground mode where full frequency reuse pattern is considered among the beams. In such an architecture, each gateway serves a cluster of adjacent beams such that the adjacent clusters are served through a set of gateways that are located at different geographical areas. However, such a system brings in two challenges to overcome. First, the inter-beam interference is the bottleneck of the whole system and applying interference mitigation techniques becomes necessary. Second, as the data demand increases, the ground and space segments should employ extensive bandwidth resources in the feeder link accordingly. This entails embedding an extra number of gateways aiming to support a fair balance between the increasing demand and the corresponding required feeder link resources. To solve these problems, this study investigates the impact of employing a joint multiple gateway architecture and on-board beamforming scheme. It is shown that by properly designing the on-board beamforming scheme, the number of gateways can be kept affordable even if the data demand increases. Moreover, Zero Forcing (ZF) precoding technique is considered to cope with the inter-beam interference where each gateway constructs a part of block ZF precoding matrix. The conceived designs are evaluated with a close-to-real beam pattern and the latest broadband communication standard for satellite communications.

This paper present On-Board Precoding (OBP) for a multiple gateway multibeam satellite system where full frequency reuse pattern is employed at both user and feeder links. By reducing the Channel State Information (CSI) roundtrip delay to half, OBP offers significant benefits in the emerging multiple gateway scenario in terms of lower gateways coordination. However, two critical issues need to be addressed: (a) interference in both user and feeder links is the bottleneck of the whole system and employing interference mitigation techniques is essential, (b) clear push towards non-adaptive (fixed) payload implementation, leading to low computationally complex satellite architectures. In order to fulfill requirements (a) and (b), this paper studies the impact of employing a fixed OBP technique at the payload which is sufficiently robust to the variations in both user and feeder link channels. In addition to (a) and (b), the provided simulation results depict the performance gain obtained by our proposed OBP with respect to the conventional interference mitigation techniques in multiple gateway multibeam systems.

This paper introduces the notion of beam-free satellite systems and it investigates different scheduling algorithms for this architecture. Attending to the current satellite gateway cloudification, this paper assumes that users from different beams can be scheduled over the same frame. Indeed, considering full frequency reuse among beams and on ground precoding, we show that whenever the scheduler is able to freely group users independently of their beam location, large attainable rates are obtained. In addition, we also consider that the gateway is able to select a number of simultaneous transmissions which leads to a substantial sum-rate increase. A scheduling scheme based on spectral clustering is proposed and it shows a higher performance compared to other state-of-the-art alternatives. In addition, our method is able to deal with different user terminal traffic classes. Based on the numerical results obtained considering a close-to-real multibeam satellite pattern, we point out that the current per-beam scheduling process is an inefficient network management for multi-beam satellite systems using precoding., Peer Reviewed, Postprint (published version)

Owing to the rapidly increasing traffic demands on satellite connectivity, the current exclusive frequency allocation is becoming obsolete. Instead, aggressive frequency reuse and interference mitigation techniques are promising ideas that both industry and academia are investigating. This paper proposes an optimization precoding technique for dealing with the multibeam interference due to the aggressive frequency reuse. In contrast to general multiuser multiple input multiple output (MIMO) schemes, multibeam satellite precoding techniques call for frame-by-frame quadratically constrained quadratic optimization of a large number of variables. We focus on the multigroup multicast beamforming optimization problem, and we propose to adopt a consensus-based alternating direction method of multipliers (C-ADMM) approach, in order to mitigate complexity. The proposed C-ADMM approach is shown to exhibit comparable optimization performance at considerably lower complexity relative to the prior state-of-art for the formulation considered., Peer Reviewed, Postprint (published version)

This paper aims at designing an onboard beam generation process for a hybrid onboard on-ground multibeam satellite architecture. The proposed method offers a good tradeoff between total throughput and feeder link bandwidth requirements compared with pure on-ground systems. Full frequency reuse among beams is considered, and the beamforming at the satellite is designed for supporting interference mitigation techniques. In addition, in order to reduce the payload cost and complexity, this onboard beamforming is assumed to be constant and the same for forward and return link transmissions so that the same array-fed reflector can be used for forward and return links, leading to a substantial reduction of the payload mass. To meet all these requirements, a novel robust minimum mean square error optimization is conceived. The benefits of the considered scheme are evaluated with respect to the current approaches both analytically and numerically. Indeed, we show that with the DVB-RCS and DVB-S2 standards, our proposal allows increasing the total throughput within a range between 6% and 15% with respect to other onboard processing techniques in the return and forward link, respectively., Peer Reviewed, Postprint (author's final draft)

This paper deals with the problem of precoding in multibeam satellite systems. In contrast to general multiuser multiple-input-multiple-output cellular schemes, multibeam satellite architectures suffer from different challenges. First, satellite communications standards embed more than one user in each frame in order to increase the channel coding gain. This leads to the different so-called multigroup multicast models, whose optimization requires computationally complex operations. Second, when the data traffic is generated by several Earth stations (gateways), the precoding matrix must be distributively computed and meet additional payload restrictions. Third, since the feedback channel is adverse (large delay and quantization errors), the precoding must be able to deal with such uncertainties. In order to solve the aforementioned problems, we propose a two-stage precoding design in order to both limit the multibeam interference and to enhance the intra-beam minimum user signal power (i.e., the one that dictates the rate allocation per beam). A robust version of the proposed precoder based on a first perturbation model is presented. This mechanism behaves well when the channel state information is corrupted. Furthermore, we propose a per beam user grouping mechanism together with its robust version in order to increase the precoding gain. Finally, a method for dealing with the multiple gateway architecture is presented, which offers high throughputs with a low inter-gateway communication. The conceived designs are evaluated with a close-to-real beam pattern and the latest broadband communication standard for satellite communications., Peer Reviewed, Postprint (updated version)

We study the applicability of soft interference cancelation in the forward link of multibeam satellite systems with focus on mobile terminals. We adopt a standard currently used in commercial satellite systems as a reference. The multibeam satellite antenna radiation diagram has been generated using a physical optics re¿ector model while a widely adopted channel model has been used for the land mobile satellite channel. The interference pattern has been derived using a system simulator developed by the European Space Agency. Starting from the analysis of the interference pattern, we study the application of a low-complexity soft interference cancelation scheme for commercial applications. Our results show that, under realistic conditions, a two-colors frequency reuse scheme can be employed while guaranteeing service availability across the coverage and keeping the complexity at the user terminals relatively low., Peer Reviewed, Postprint (author's final draft)

This paper considers a multigateway multibeam satellite system with multiple feeds per beam. In these systems, each gateway serves a set of beams (cluster) so that the overall data traffic is generated at different geographical areas. Full frequency reuse among beams is considered so that interference mitigation techniques are mandatory. Precisely, this paper aims at designing the precoding scheme which, in contrast to single gateway schemes, entails two main challenges. First, the precoding matrix shall be separated into feed groups assigned to each gateway. Second, complete channel state information (CSI) is required at each gateway, leading to a large communication overhead. In order to solve these problems, a design based on a regularized singular value block decomposition of the channel matrix is presented so that both intercluster (i.e., beams of different clusters) and intracluster (i.e., beams of the same cluster) interference is minimized. In addition, different gateway cooperative schemes are analyzed in order to keep the inter-gateway communication low. Furthermore, the impact of the feeder link interference (i.e., interference between different feeder links) is analyzed and it is shown both numerically and analytically that the system performance is reduced severely whenever this interference occurs even though precoding reverts this additional interference. Finally, multicast transmission is also considered. Numerical simulations are shown considering the latest fixed broadband communication standard DVB-S2X so that the quantized feedback effect is evaluated. The proposed precoding technique results to achieve a performance close to the single gateway operation even when the cooperation among gateways is low., Postprint (author's final draft)

This paper deals with the problem of multibeam satellite precoding design under spectrum sharing constraints. These regulation restrictions allow the coexistence with other wireless services such as terrestrial mm-wave wireless local loop systems. This work focuses on the case where the satellite operator can use a certain frequency band whenever the signal power strength is limited in the coverage area. The precoding design is optimized considering this restriction by means of formulating a robust optimization. Numerical results sh ow the trade-off between the achievable rates of the satellite segment and the regulation violation outage, Peer Reviewed, Postprint (published version)

In current satellite communication systems, energy efficiency is of paramount importance since it strongly affects the satellite size and lifetime. In this paper, the energy efficiency of a multibeam downlink system is investigated in terms of maximizing the ratio of system throughput over consumed power. More specifically, the consumed power comprises both operating power which is needed for running the network equipment and transmit power which is needed for forwarding the information to the end users. Regarding the employed transmission technique, Minimum Mean Square Error (MMSE) beamforming together with power optimization for satellite downlink channel is used while full frequency reuse is assumed. By varying the ratio of operating and transmit power, we study the performance of the forward link in terms of spectral and energy efficiency., QC 20130524

This paper aims to design joint precoding and onboard beamforming of a multiple gateway multibeam satellite system, either in a hybrid space-ground mode, or in a totally on-board one. In such an architecture, with employing high throughput full frequency reuse pattern over both user and feeder links, each gateway serves a cluster of adjacent beams such that the adjacent clusters are served through a set of gateways that are located at different geographical areas. However, such a system brings in two challenges to overcome. First, the interference in both user and feeder links is the bottleneck of the whole system and applying interference mitigation techniques becomes necessary. Second, as the data demand increases, the ground and space segments should employ extensive bandwidth resources in the feeder link accordingly. This entails embedding an extra number of gateways aiming to support a fair balance between the increasing demand and the corresponding required feeder link resources. To solve these problems, this study investigates the impact of employing a joint multiple gateway architecture and on-board beamforming scheme. It is shown that by properly designing the on-board beamforming scheme, the number of gateways can be kept affordable even if the data demand increases. Moreover, Zero Forcing (ZF) precoding techniques are considered to cope with the interference in both user and feeder links which embed in the following premises: (i) each gateway constructs a part of block ZF precoding matrix, (ii) the satellite and gateways perform the precoding scheme, and (iii) a joint design of ZF precoding and on-board beamforming at the payload of the satellite so that no signal processing scheme is conceived at the gateways. The provided simulation results depict the performance gain obtained by our proposed schemes.

This paper aims to design joint precoding and onboard beamforming of a multiple gateway multibeam satellite system, either in a hybrid space-ground mode, or in a totally on-board one. In such an architecture, with employing high throughput full frequency reuse pattern over both user and feeder links, each gateway serves a cluster of adjacent beams such that the adjacent clusters are served through a set of gateways that are located at different geographical areas. However, such a system brings in two challenges to overcome. First, the interference in both user and feeder links is the bottleneck of the whole system and applying interference mitigation techniques becomes necessary. Second, as the data demand increases, the ground and space segments should employ extensive bandwidth resources in the feeder link accordingly. This entails embedding an extra number of gateways aiming to support a fair balance between the increasing demand and the corresponding required feeder link resources. To solve these problems, this study investigates the impact of employing a joint multiple gateway architecture and on-board beamforming scheme. It is shown that by properly designing the on-board beamforming scheme, the number of gateways can be kept affordable even if the data demand increases. Moreover, Zero Forcing (ZF) precoding techniques are considered to cope with the interference in both user and feeder links which embed in the following premises: (i) each gateway constructs a part of block ZF precoding matrix, (ii) the satellite and gateways perform the precoding scheme, and (iii) a joint design of ZF precoding and on-board beamforming at the payload of the satellite so that no signal processing scheme is conceived at the gateways. The provided simulation results depict the performance gain obtained by our proposed schemes.