R&D Directions for Next Generation Broadband Multimedia Systems: An ESA Perspective

Experiments on mobile satellite communications are being carried out to determine if they are technically feasible for future domestic satellite services in the Experimental Mobile Satellite System project, which uses Engineering Test Satellite-V. Experimental ISDN (integrated services digital network) basic-rate communications services have also been offered for marine vehicles. The authors describe the configuration of an experimental system for maritime ISDN satellite communications, and the characteristics of ISDN basic-rate interface connections for the digital telephones, G4 facsimiles, and color video-phone terminals of terrestrial ISDN services. This experiment provided much information for designing future mobile satellite communications systems. Moreover, it indicates that forward error correction in a mobile satellite link with poor transmission quality is very effective at improving the communication quality of mobile satellite systems. >

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.

This paper considers satellite communication networks where each satellite terminal is equipped with energy harvesting (EH) devices to supply energy continuously, and randomly transmits bursty packets to a geostationary satellite over a shared wireless channel. Packet replicas combined with a successive iteration cancellation scheme can reduce the negative impact of packet collisions but consume more energy. Hence, appropriate energy management policies are required to mitigate the adverse effect of energy outages. Although centralized access schemes can provide better performance on the networks’ throughput, they expend extra signallings to allocate the resources, which leads to non-negligible communication latencies, especially for the satellite communication networks. In order to reduce the communication overhead and delay, a distributed random access (RA) scheme considering the energy constraints is studied. Each EH satellite terminal (EH-ST) decides whether to transmit the packet and how many replicas are transmitted according to its local energy and EH rates to maximize the average long-term network throughput. Owing to the nonconvexity of this problem, we adopted a game theoretic method to approximate the optimal solution. By forcing all the EH-STs to employ the same policy, we characterized and proved the existence and uniqueness of the symmetric Nash equilibrium (NE) of the game. Moreover, an efficient algorithm is proposed to calculate the symmetric NE by combining a policy iteration algorithm and the bisection method. The performance of the proposed RA scheme was investigated via numerous simulations. Simulation results showed that the proposed RA scheme is applicable to the EH devices in the future low-cost interactive satellite communication system.

This study proposes a reinforcement learning-based link selection method for Low Earth Orbit satellite networks, aiming to reduce handover frequency while extending link duration under highly dynamic orbital environments. The proposed approach relies solely on basic satellite positional information, namely latitude, longitude, and altitude, to construct compact state representations without requiring complex sensing or prediction mechanisms. Using relative satellite and terminal geometry, each state is represented as a vector consisting of azimuth, elevation, range, and direction difference. To validate the feasibility of policy learning under realistic conditions, a total of 871,105 orbit based data samples were generated through simulations of 300 LEO satellite orbits. The reinforcement learning environment was implemented using the OpenAI Gym framework, in which an agent selects an optimal communication target from a prefiltered set of candidate satellites at each time step. Three reinforcement learning algorithms, namely SARSA, Q-Learning, and Deep Q-Network, were evaluated under identical experimental conditions. Performance was assessed in terms of smoothed total reward per episode, average handover count, and average link duration. The results show that the Deep Q-Network-based approach achieves approximately 77.4% fewer handovers than SARSA and 49.9% fewer than Q-Learning, while providing the longest average link duration. These findings demonstrate that effective handover control can be achieved using lightweight state information and indicate the potential of deep reinforcement learning for future LEO satellite communication systems.

Over the last few years, various enabling technologies and techniques for future Ka-band satellite communication systems were developed. In this paper, we present objectives and results of several projects on direct conversion transceivers and power amplifier linearization, targeting the cost reduction of terminals and satellite subsystems with the use of advanced, enabling techniques. Performances of these techniques are presented based on either hardware prototype tests or computer simulation. It is shown that low complexity digital signal processing can be used to compensate traditional limitations of direct transceivers as well as to linearize power amplifiers. Although the paper concentrates on terminal technologies, the application and benefit of these techniques to satellite subsystems are readily seen.

The design of a K <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">a</inf> -band coplanar waveguide slot-coupled patch antenna ESA with integrated MEMS phase shifters has been described above. The incorporation of MEMS phase shifters into the ESA design results in a compact, efficient uplink mechanism for a future Army satellite communication system. A control board for biasing the phase shifters and initiating beam steering will be incorporated into the final array. The details of this design and the measured beam steering results of the fully-fabricated demonstrator array will be presented at the 2009 IEEE Antennas and Propagation Society Conference.

Many waveforms for future military satellite communication systems rely on spectrally-confined waveforms to increase the number of users and maintain capacity. These waveforms stress the performance of the transmitting amplifiers. The design and planning stages of communication systems often use memory-less nonlinear models, such as amplitude-to-amplitude modulation and amplitude-to-phase modulation models. These models are based on single-tone measurements and do not accurately predict the amplifier performance for wider bandwidth modulations. This paper presents measured comparisons of single-tone characteristics and spectrally-confined waveform performance in solid-state amplifiers at millimeter-wave frequencies. Measurements are performed over a range of data rates with PSK and QAM modulations, with comparison of devices with and without nonlinear memory.

This paper presents the 128-Channel Multicarrier Demodulator (MCD) developed at Bosch Telecom for use in the future European OBP satellite communications system. The development has been supported by the European Space Agency (ESA). In the uplink of this communication system a Multi-Frequenc y Time Division Multiple Access (MF-TDMA) scheme is used. The MCD presented here is capable of demultiplexing and demodulating of a MF-TDMA carrier group with a total bandwidth of 70 MHz comprising 128 single carriers. The MCD equipment consists of three major units: - the service board containing the power supply, clock generation and TM/TC interface. - the analog input section for down converting the input IF to an intermediate frequency suitable for A/D conversion.

A multibeam digital beamforming (DBF) antenna, developed for a future mobile satellite communications system, is mounted on a vehicle for a receiving experiment in a mobile environment using a satellite signal in the L band. The multibeam is formed by 2-dimensional FFT signal processing. Automatic acquisition and tracking of an arriving signal are achieved by selecting a maximum beam out of the multiple beams in real-time.

Radio beacons on the COMSTAR communication satellites transmit continuously at 19 and 28 GHz to permit the long-term measurement of the properties of earth-space propagation needed in designing future high-capacity satellite communication systems. An extensive receiving facility has been established at Crawford Hill, New Jersey, for measuring attenuation, depolarization, coherence bandwidth and scatter of the beacon signals by atmospheric processes. The facility includes a precision 7-meter antenna and multichannel receiving electronics designed to obtain optimum benefit from the COMSTAR beacons. Other Bell Laboratories receiving facilities in Georgia and Illinois are accumulating statistics on signal attenuation and diversity improvements for other climatic conditions.

An increase in the size of on‐board antenna reflectors is a key technology in providing economical services by miniaturized portable equipment in future mobile satellite communication systems. In practice, a mesh antenna can be used as the on‐board antenna. However, since the reflector surface of this antenna is supported by the cable and the mesh, and its size is larger, the surface is subject to larger thermal deformation in orbit than is the solid antenna reflector. Conventional compensation methods such as passive thermal control or rotation of the antenna reflector cannot maintain the required antenna performances. Various methods have been reported to compensate for the deterioration of antenna performance by thermal deformation.This paper describes a static shape control system for a 10‐m diameter antenna which actively compensates for the deformation by using a shape‐measuring sensor and shape‐compensation actuator. The configuration of the sensor and the experimental results by a functional model are described to confirm the design validity. The shape‐compensation method by the actuator was confirmed to be useful in achieving a required surface accuracy.

[Abstract] This paper proposes dynamic bandwidth/channel access technique using FFT based block signal transmission for future broadband mobile satellite communication systems, which is to supplement next generation terrestrial mobile networks. One of the key issues for next generation mobile satellite communication systems is flexible and scalable access technique in terms of data rate and traffic type, to accommodate various satellite users. OFDMA is a technique to meet the above-mentioned requirements, however it needs large output backoff at HPA. To solve this problem, this paper proposes a new bandwidth/channel access technique using FFT based block signal transmission. The proposed technique uses single carrier modulation suitable for small output backoff operation in HPA, keeping flexibility and scalability as OFDMA has. This paper describes basic principle of the proposed dynamic bandwidth/channel access technique and preliminary performance evaluation results by computer simulation.

A concept for a future advanced mobile satellite communications system using a geostationary satellite is described. In the satellite of this system, a multiple spotbeam antenna, onboard beam interconnection, and millimeter-wave and Ka-band components are required. The configuration of the payloads of Japan's COMETS (Communications and Broadcasting Engineering Test Satellite) for advanced mobile satellite communication experiments is also described. The transponder has an IF filter bank and a SCPC/TDM (signal-carrier-per-channel/time-dimension multiplexing) regenerative modem for beam interconnection. >

Satellite communications (Satcoms) systems have become an integral part of modern society, providing critical infrastructure for a wide range of applications. However, as the reliance on Satcoms has increased, cyberattacks on Satcoms systems have emerged as a severe concern, with the potential to cause significant disruption, economic losses, and even loss of life. We first give a tutorial-style overview of the architecture of a Satcoms system, which typically consists of a space segment, a ground segment (encompassing the terrestrial ground stations and users), and the links segment. Following the taxonomy provided by this segment structure, we provide—to the best of our knowledge—the first comprehensive survey of the state-of-the-art cyberattacks (cyberthreats) on all three segments of Satcoms systems. For each Satcoms system segment, we organize the cyberattacks according to categories of Satcoms-specific cyberattacks, which we relate to the threat classifications in the general STRIDE cyberthreat model. Also, for all three segments of Satcoms systems, we comprehensively survey the general cybersecurity strategies and the specific cybersecurity mechanisms (techniques) that defend Satcoms systems against cyberattacks. We distill the critical learned lessons associated with Satcoms cybersecurity strategies, such as the need to balance security with cost-effectiveness. Finally, we outline the open challenges and future research directions in Satcoms systems cybersecurity.

Future satellite communication systems providing broadband access to Internet require high throughput connectivity in the order of hundreds of Gbps or Tbps. Radical changes in technologies are needed to support these demanding requirements. One of the most important changes is the use of Q/V band frequencies which offer larger bandwidths with respect to the Ka band. However, Q/V band communication suffers from highly variable propagation losses and the use of Propagation Impairment Mitigation Techniques (PIMTs) is mandatory for an efficient use of radio resources such as power and bandwidth. In this paper we describe the first Q/V band satellite communication experiments that have been performed through the Alphasat “Aldo Paraboni” hosted payload. In particular, experimental results on ACM optimization will be presented.