Zoltán Katona

System capacity optimization in time and frequency for multibeam multi-media satellite systems

Current Ka-band, multi-media satellite systems employ spot beam technology to accommodate a wide range of multi-media type services. These satellites typically employ uniform allocation of RF power and bandwidth to spot beams. Since the traffic distribution tends to be highly asymmetrical and with a high degree of uncertainty, the satellite does not have sufficient flexibility to satisfy the traffic request on a beam per beam basis in an efficient manner. This paper investigates two new candidate multibeam system transmission schemes, namely, the Flexible and Beam-Hoping (BH) scheme, focusing on the forward link. We formulate the system-level optimization and propose an iterative algorithm that always converges given the constraints posed by the payload. The algorithm feeds a detailed system-level simulator which takes into account Ka-band channel and physical layer statistics. Our results show that both candidates outperform the conventional system in terms of both adaptation throughput matching to traffic demands and a more efficient use of available resources. The results were obtained during a project funded by the European Space Agency, with title “Beam Hopping techniques for multibeam satellite systems”.

On Construction of Moderate-Length LDPC Codes over Correlated Erasure Channels

The design of moderate-length erasure correcting low-density parity-check (LDPC) codes over correlated erasure channels is considered. Although the asymptotic LDPC code design remains the same as for a memoryless erasure channel, robustness to the channel correlation shall be guaranteed for the finite length LDPC code. This further requirement is of great importance in several wireless communication scenarios where packet erasure correcting codes represent a simple countermeasure for correlated fade events (e.g., in mobile wireless broadcasting services) and where the channel coherence time is often comparable with the code length. In this paper, the maximum tolerable erasure burst length (MTBL) is adopted as a simple metric for measuring the code robustness to the channel correlation. Correspondingly, a further step in the code construction is suggested, consisting of improving the LDPC code MTBL. Numerical results conducted over a Gilbert erasure channel, under both iterative and maximum likelihood decoding, highlight both the importance of the MTBL improvement in the finite-length code construction and the possibility to tightly approach the performance of maximum distance separable codes.

GEO data relay for low earth orbit satellites

This paper focuses on a novel, conceptual data relay system for relaying data transfer between low earth orbit (LEO) satellites and a gateway through a geostationary earth orbit (GEO) satellite, developed in the framework of the GeReLEO project. Novel channel adaptive transmission schemes are introduced in addition to the access scheme supporting several LEO satellites in parallel. On top of this, a novel multibeam receiving antenna with several electronically controlled beams is developed for high-rate unidirectional links. The multiple access and transmission schemes, moreover the concept of the multibeam antenna shall be verified with lab demonstrations during the course of the project.

Performance, cost analysis, and ground segment design of ultra high throughput multi‐spot beam satellite networks applying different capacity enhancing techniques

There is an ever present demand for increasingly higher data rates in multi-spot beam satellite networks. This can be enabled, by shifting carrier frequencies to higher bands, such as the Q/V-band, where more bandwidth is available. Furthermore, the available bandwidth has to be used as efficiently as possible, which requires efficient capacity enhancing techniques. The present paper identifies and analyzes ground segment capacity enhancing techniques for ultra high throughput multi-spot beam satellite networks operating in Q/V-band in the feeder link and in Ka-band in the user link. The impact of several capacity enhancing techniques on system performance is analyzed using a realistic time step-based system simulator. Their impact on the ground segment costs is also analyzed. The examined capacity enhancing techniques are as follows: (i) reduced carrier spacing with adjacent channel interference cancellation; (ii) full frequency reuse with co-channel interference cancellation and scheduling; (iii) four different smart gateway diversity techniques and; (iv) employing optical feeder links as an alternative to radio frequency feeder links. The paper shows that these techniques are capable of improving system performance at the expense of an increase in cost related to the complexity and maturity of the applied capacity-increasing technique.

On mean visibility time of non-repeating satellite orbits

Depending on the parameters of a fixed ground station and on the orbital parameters of a non-geosynchronous satellite, different visibility times are offered to fixed ground stations. In this paper, the focus is on the mean visibility time of a non-geosynchronous satellite with non-repeating ground track as seen by a fixed ground station with a finite sensor range. A mathematical analysis is provided for the calculation of the mean visibility time. There are several possible application areas of these visibility statistics, like optimizing a gateway’s latitude to maximize the mean visibility time of a satellite, thus maximizing the average amount of data that can be uploaded to or downloaded from a satellite during passes. The calculations show a good match with simulation results at all latitudes and the underlying mathematical approach is foreseen to be useful for analyzing and designing complete satellite constellations.

Design of Circular Orbit Satellite Link for Maximum Data Transfer

The present paper provides an analytical expression for the amount of theoretically transmittable data to/from a LEO or MEO satellite and a fixed ground station, during one pass, averaged over an infinite number of passes. The paper shows that this mean transmittable data amount can have a maximum as a function of the satellite orbit altitude, when the other parameters of the communications system are fixed. The paper identifies a maximization method, with which it is possible to find the altitude, at which the mean transmittable data amount is maximized. The paper also shows that, for fixed satellite orbit altitude, it is possible to find the corresponding transmission bandwidth that maximizes the mean transmittable data amount.

Radio resource management strategies for DVB-S2 systems operated with flexible satellite payloads

The increasing demand for high-rate broadcast and multicast services over satellite networks has pushed for the development of High Throughput Satellite (HTS) characterized by a large number of beams (e.g., more than 100). Moreover, the variable distribution of data traffic across beams and over time has called for the design of a new generation of satellite payloads, able to flexibly allocate bandwidth and power. In this context, this paper explores the technical challenges related to radio resource allocation in the forward link of multibeam satellite networks and proposes a strategy based on a modified version of the simulated annealing algorithm and a newly proposed objective function to meet as close as possible the requested traffic across the beams while taking fairness into account. Performance results confirm the effectiveness of the proposed approach and also shed some light on possible payload design implications.

On mean revisit frequency of non-repeating satellite orbits with finite sensor range

The length and the frequency of the visibility times during which a fixed ground station sees a non-geosynchronous satellite is a function of the parameters of a fixed ground station and a function of the orbital parameters of the satellite. The focus, in this paper, is on the mean revisit frequency of a non-geosynchronous satellite with non-repeating ground track as seen by a fixed ground station with a finite sensor range. A mathematical analysis is provided for the calculation of the mean revisit frequency. There are several possible application areas of such visibility statistics, like optimizing a gateways latitude to maximize the mean revisit frequency of a satellite, thus maximizing the communication possibilities. The analytical solution provides a good match with simulation results at all latitudes and the mathematical background of the analytical solution is foreseen to be useful for the analysis and design of satellite constellations.

Radio Resource Management Optimization of Flexible Satellite Payloads for DVB-S2 Systems

The increasing demand for high-rate broadcast and multicast services over satellite networks has pushed for the development of high throughput satellites characterized by a large number of beams (e.g., more than 100). This, together with the variable distribution of data traffic request across beams and over time, has called for the design of a new generation of satellite payloads, able to flexibly allocate bandwidth and power. In this context, this paper studies the problem of radio resource allocation in the forward link of multibeam satellite networks adopting the digital video broadcasting-satellite-second generation standard. We propose a novel objective function with the aim to meet as close as possible the requested traffic across the beams while taking fairness into account. The resulting non-convex optimization problem is solved using a modified version of the simulated annealing algorithm, for which a detailed complexity analysis is presented. Simulation results obtained under realistic conditions confirm the effectiveness of the proposed approach and shed some light on possible payload design implications.

Channel adaptive output back‐off setting of non‐linear power amplifiers for high throughput multi‐spot beam satellite systems

In order to increase the satellite capacity for high throughput systems, the feeder link frequencies are gradually moved to higher bands, such as the Q/V-bands, where more bandwidth is available. Therefore, more spectrum shall be available for the user links at lower frequencies, such as in Ka-band. However, the rain attenuation on the feeder links becomes a limiting issue because of the higher frequencies. It is thus important to find link adaptation, or in other words channel adaptive techniques that can overcome this issue, such as smart gateway diversity or adaptive coding and modulation. This paper, however, introduces and describes a novel patented technique: channel adaptive output back-off (OBO) setting. This technique can be applied on any terrestrial or satellite link, in which a non-linear power amplifier is operated in multicarrier mode and the transmission channel experiences time varying attenuation. As a consequence, this technique can be applied, for example, both on the feeder uplink and on the feeder downlink of multi-spot beam satellite networks. However, due to several reasons, the present paper analyzes its performance only on the feeder downlink. According to the performed analysis, channel adaptive OBO setting can provide around 4.5 dB signal-to-noise and interference ratio improvement in case of deep rain fading compared with the conventional fixed OBO operation. This improvement reduces the outage by around 17% on the end-to-end return link. As a consequence, the feeder downlink and the total return link become much more robust against deep rain fading. Copyright