Sparsity-Aided Low-Implementation cost based On-Board beamforming Design for High Throughput Satellite Systems

This paper studies the data rate that a High Throughput Satellite (HTS) system with fully-regenerative payload can achieve when using an intensity modulation/direct detection optical feeder link. A low-order M-ary Pulse Amplitude Modulation (M-PAM) with time-packing is used to modulate the intensity of the laser diode beam, making use of an external Mach-Zehnder modulator. These M-PAM symbols are recovered on-board the satellite with the aid of a photodetector, and are then encapsulated into the 5G radio frame of the access link. The M-PAM modulation order and the overlapping factor of timepacking are jointly selected to tackle the impact of slowly-varying weather conditions. Moreover, the inter-symbol interference that time-packing introduces is mitigated in reception using a Viterbi equalizer. As expected, time-packing enables a finer granularity on the link adaptation capability of the optical feeder link, enabling to adjust its spectral efficiency according to the moderate attenuation that thin cloud layers introduce.

SummaryThis paper introduces architectures for next‐generation high throughput satellite (HTS) systems comprising various satellite payload options, ground terminal advances, and scalable system‐level software control and management techniques. It describes a model to estimate aggregate system capacity as a function of radio band, available spectrum, spot beams, waveforms, and payload capability, including antenna size, power, and digital/analog connectivity across various links and availability objectives. This system model has been used to evaluate aggregate capacity of representative Ka‐Band low earth orbit and geosynchronous orbit systems. A system implementation approach is described for next‐generation HTS systems based on widely used Industry standards. Modulation and coding techniques are based on Digital Video Broadcasting – S2 extensions (DVB‐S2X), which comprises spectrally efficient modulation schemes combined with low‐rate codes. Several implementation technologies are analyzed related to configurable onboard payload and ground‐based, software‐defined resource control and management, key enablers of next‐generation HTS systems. Basic architectural building blocks are introduced for design of end‐to‐end systems across low earth orbit, medium earth orbit, and geosynchronous orbit satellite constellations, with and without onboard processing and inter‐satellite links, and including several efficient scenarios to achieve lossless handovers. Copyright © 2016 John Wiley & Sons, Ltd.

Special Issue: Smart Satellite Systems

Due to recent advances in laser satellite communications technology, free-space optical (FSO) links are presented as an ideal alternative to the conventional radio frequency (RF) feeder links of the geostationary satellite for next generation very high throughput satellite (VHTS) systems. In this paper, we investigate the performance of multibeam VHTS systems that account for nonlinear high power amplifiers at the transparent fixed gain satellite transponder. Specifically, we consider the forward link of such systems, where the RF user link is assumed to follow the shadowed Rician model and the FSO feeder link is modeled by the Gamma-Gamma distribution in the presence of beam wander and pointing errors where it operates under either the intensity modulation with direct detection or the heterodyne detection. Moreover, zero-forcing precoder is employed to mitigate the effect of inter-beam interference caused by the aggressive frequency reuse in the user link. The performance of the system under study is evaluated in terms of the outage probability, the average bit-error rate (BER), and the ergodic capacity that are derived in exact closed-forms in terms of the bivariate Meijer’s G function. Simple asymptotic results for the outage probability and the average BER are also obtained at high signal-to-noise ratio.

Non-terrestrial network (NTN) communication is included in the 3GPP standard because of its excellent features such as resistance to ground physical attacks and wide coverage. Since the available power and storage resources are limited on high throughput satellites (HTSs), optimizing the resource allocation can greatly improve the performance of the HTS based communication system. Notably, weather and other factors make the channel status between the satellite and the terrestrial base stations constantly change. In this paper, we first exploit the model-free feature of reinforcement learning to formulate the aforementioned dynamic and unpredictable channel conditions into the power allocation problem in HTS systems. Due to the complexity of environment state and power allocation, a deep neural network is introduced to replace the Q table, and a deep reinforcement learning framework is built. Furthermore, a power allocation algorithm based on a deep reinforcement learning framework is presented. Finally, the simulation results show that the proposed algorithm is superior to existing algorithms in terms of the long-term system throughput performance, and has better adaptability to dynamic channel environment, thereby improving network performance.

For the past decade Eutelsat has been at the forefront of the development of Ka-band, leading its application to different types of High Throughput Satellites (HTS) Systems in order to pursue the connection and integration of a global and digital society. Eutelsat's most significant investment to date in the Ka-band is KA-SAT, the first and most powerful HTS System in Europe. In commercial service since 2011 it provides over 90 Gbit/s of capacity and offers services that range from consumer broadband access, to newsgathering and domestic broadcasting Relying on this experience Eutelsat is now pursuing its role in the reduction of the digital divide through Kaband High Throughput capability in other parts of the world, including Russia and Latin America. EUTELSAT 3B, launched in May 2014, includes an innovative and flexible Ka-band broadband payload, with five steerable spotbeams enabling mission reconfiguration in orbit. In collaboration with RSCC and to be launched in 2015, the EUTELSAT 36C/AMU1 satellite will embark a Kaband payload which has been designed to offer high-capacity broadband access service over Western Russian. Finally in 2016 EUTELSAT 65 West A will bring a flexible High Throughput payload for broadband access in the Ka-band over Latin America.

Hybrid analog and digital beamforming has emerged as a key enabling technology for millimeter wave (mmWave) massive multiple-input multiple-output (MIMO) communication systems since it can balance the trade-off between system performance and hardware efficiency. Owing to the strong ability of central control, cooperative networks show great potential to enhance the spectral efficiency of mmWave communications. In this paper, we consider cooperative mmWave MIMO systems and propose user association and hybrid beamforming design algorithms for three typical hybrid beamforming architectures. The central processing unit (CPU) of the cooperative networks first matches the service pairs of base stations (BSs) and users. Then, an iterative hybrid beamforming design algorithm is proposed to maximize the weighted achievable sum-rate performance of the mmWave MIMO system with fully connected hybrid beamforming architecture. Moreover, a heuristic analog beamforming design algorithm is introduced for the fixed subarray hybrid beamforming architecture. In an effort to further exploit multiple-antenna diversities, we also consider the dynamic subarray architecture and propose a novel antenna design algorithm for the analog beamforming design. Simulation results illustrate that the proposed hybrid beamforming algorithms achieve a significant performance improvement than other existing approaches and the dynamic subarray architecture has great advantages of improving the energy efficiency (EE) performance.

Optimizing a hybrid beamforming transmitter is a non-convex problem and requires channel state information, leading in most cases to nontrivial feedback overhead. We propose a methodology relying on the principles of deep generative models and unfolding to achieve near-optimal hybrid beamforming with reduced feedback and computational complexity. We first represent the channel as a low-dimensional manifold via a generative adversarial network (GAN) and search the optimum digital and analog precoders in this low-dimensional space. To decrease the search complexity, we find an iteration rule by formulating hybrid beamforming as a bi-level optimization problem and then unfold each iteration as a neural layer. This results in a novel model-based deep neural network that incorporates domain knowledge. Our results show that this method (i) approaches the capacity-achieving spectral efficiency, (ii) provides a superior energy and spectral efficiency tradeoff, (iii) decreases feedback overhead, and (iv) reduces the complexity significantly, by optimizing a single low-dimensional vector per channel coherence time, with the neural network itself trained offline. The achieved spectral efficiency is robust when tested with realistic 3GPP channel models, even if the offline training relies on a simple geometric channel model.

There is an increased interest in the deployment and use of hybrid architectures to benefit the end-user community. Several Low Earth Orbit (LEO) systems are being deployed that provide low latency to end-users. In the GEO world, Very High Throughput Satellite (VHTS) systems are being deployed that maximizes capacity density. In parallel, 3GPP has been actively involved in the development of Non-Terrestrial Transport networks that include satellites. No single technology can provide the best solution in terms of latency, throughput, efficiency, coverage, capacity density and availability for all applications, user terminal types and use cases. A hybrid architecture that uses a combination of LEO, GEO and Terrestrial is desired that optimizes in all dimensions is discussed above. To this end, a user terminal with multiple radio access technologies is desired and a smart logic in user terminals that determine the best path for a session is needed. Various aspects of this Smart Network Edge are described in this paper.

The scarce spectrum and power resources, the inter-beam interference, together with the high traffic demand, pose new major challenges for the next generation of Very High Throughput Satellite (VHTS) systems. Accordingly, future satellites are expected to employ advanced resource/interference management techniques to achieve high system spectrum efficiency and low power consumption while ensuring user demand satisfaction. This paper proposes a novel demand and interference aware adaptive resource management for geostationary (GEO) VHTS systems. For this, we formulate a multi-objective optimization problem to minimize the total transmit power consumption and system bandwidth usage while matching the offered capacity with the demand per beam. In this context, we consider resource management for a system with full-precoding, i.e., all beams are precoded; without precoding, i.e., no precoding is applied to any beam; and with partial precoding, i.e., only some beams are precoded. The nature of the problem is non-convex and we solve it by jointly using the Dinkelbach and Successive Convex Approximation (SCA) methods. The simulation results show that the proposed method outperforms the benchmark schemes. Specifically, we show that the proposed method requires low resource consumption, low computational time, and simultaneously achieves a high demand satisfaction.

High Throughput Satellite (HTS) systems still offer much less bandwidth per user with respect terrestrial broadband networks. In order to reach a very high throughput towards “Tbit/s connectivity”, an important breakthrough is needed in terms of bandwidth availability which can be offered by the use of Extremely High Frequency (EHF) bands (30–300 GHz). In particular, Q-V band (30–50 GHz) and W-band (70–110 GHz) offer very promising perspectives, being not used for commercial systems and offering a large part of the spectrum allocated for satellite services. However, it is well known that EHF band transmission through the atmosphere is subject to absorption and dispersive effects in amplitude and phase that have to be carefully characterized. In this framework, some mitigation techniques have to be analyzed and properly tuned in order to realize an efficient transmission. In this paper, the current experimental activities to support future EHF satellite communication systems are reported, with reference to the Italian Space Agency Q/V-band satellite communication experimental campaign. In particular, a new error model for QPSK modulation scheme has been developed from the experimental data. This error model can be used for the design of optimized channel coding and adaptive transmission schemes for Q/V band satellite channels.

Future High throughput Satellite (HTS) systems, able to support hundreds of gigabit/s or terabit/s connectivity, will require a very large bandwidth availability; this pushes towards the exploitation of the so-called “beyond Ka-band” systems. In particular the use of the Q/V frequency band is foreseen. This paper presents the most important features of the TDP#5 (Technology Demonstration Payload 5) scientific mission that will provide us the opportunity to perform, for the first time, a communication scientific experiment over a Q/V band satellite link.

Future satellite networks could benefit from new paradigms that are currently applied to terrestrial networks, as Software Defined Networking (SDN)and Network Functions Virtualization (NFV); these can improve key system characteristics as flexibility, customization, scalability, etc. This paper presents an analysis on the use of SDN for the optimization of High throughput Satellite (HTS)systems. The latter will use EHF (in particular beyond Ka-band frequencies, such as Q/V and W bands)in the feeder link and in this framework it is mandatory to use spatial diversity to counteract tropospheric fading. One of the most interesting diversity scheme is “smart gateway”; this technique has to be carefully optimized to achieve high system performance. This paper shows that SDN is a good candidate for the intelligent management of this system. In particular, the paper shows an analysis of the use of the SDN paradigm for smart gateway socalled “N+0” and “N+P” diversity schemes. The two schemes allow, in case of heavy fading conditions on one gateway, the redirection of the user traffic towards a redundant gateway (N + P), or the partition of the lost capacity over different active gateways (N + 0), ensuring service continuity.

Low complexity hybrid beamforming for downlink multi-user MIMO OFDM systems

Hybrid beamforming provides a promising solution to achieve high data rate transmission at millimeter waves. Implementing hybrid beamforming at a transceiver based on available channel state information is a common solution. However, many reference methods ignore the complexity of channel estimation for large antenna arrays or subsequent steps, such as the singular value decomposition of a channel matrix. To this end, we present a low-complexity scheme that exploits implicit channel knowledge to facilitate the design of hybrid beamforming for frequency-selective fading channels. The implicit channel knowledge can be interpreted as couplings between all possible pairs of analog beamforming vectors at the transmitter and receiver over the surrounding channel. Instead of calculating mutual information between large antenna arrays, we focus on small-size coupling matrices between beam patterns selected by using appropriate key parameters as performance indicators. This converts the complicated hybrid beamforming problem to a much simpler one: it amounts to collecting different sets of the large-power coupling coefficients to construct multiple alternatives for an effective channel matrix. Then, the set yielding the largest Frobenius norm (or the largest absolute value of the determinant) of the effective channel provides the solution to the hybrid beamforming problem. It turns out that the proposed method does not require information on MIMO channel and can be simply implemented by the received correlated pilot signals that are supposed to be used for channel estimation.