Precoding in multigateway multibeam satellite systems

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

Precoding in multigateway multibeam satellite systems

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

Statistical Properties and Applications of Empirical Mode Decomposition

Signal analysis is key to extracting information buried in noise. The decomposition of signal is a data analysis tool for determining the underlying physical components of a processed data set. However, conventional signal decomposition approaches such as wavelet analysis, Wagner-Ville, and various short-time Fourier spectrograms are inadequate to process real world signals. Moreover, most of the given techniques require \emph{a prior} knowledge of the processed signal, to select the proper decomposition basis, which makes them improper for a wide range of practical applications. Empirical Mode Decomposition (EMD) is a non-parametric and adaptive basis driver that is capable of breaking-down non-linear, non-stationary signals into an intrinsic and finite components called Intrinsic Mode Functions (IMF). In addition, EMD approximates a dyadic filter that isolates high frequency components, e.g. noise, in higher index IMFs. Despite of being widely used in different applications, EMD is an ad hoc solution. The adaptive performance of EMD comes at the expense of formulating a theoretical base. Therefore, numerical analysis is usually adopted in literature to interpret the behavior. This dissertation involves investigating statistical properties of EMD and utilizing the outcome to enhance the performance of signal de-noising and spectrum sensing systems. The novel contributions can be broadly summarized in three categories: a statistical analysis of the probability distributions of the IMFs and a suggestion of Generalized Gaussian distribution (GGD) as a best fit distribution; a de-noising scheme based on a null-hypothesis of IMFs utilizing the unique filter behavior of EMD; and a novel noise estimation approach that is used to shift semi-blind spectrum sensing techniques into fully-blind ones based on the first IMF. These contributions are justified statistically and analytically and include comparison with other state of art techniques

DVB-S based passive polarimetric ISAR – methods and experimental validation

In this work, we focus on passive polarimetric ISAR for ship target imaging using DVB-S signals of opportunity. A first goal of the research is to investigate if, within the challenging passive environment, different scattering mechanisms, belonging to distinct parts of the imaged target, can be separated in the polarimetric domain. Furthermore, a second goal is at verifying if polarimetric diversity could enable the formation of ISAR products with enhanced quality with respect to the single channel case, particularly in terms of better reconstruction of the target shape. To this purpose, a dedicated trial has been conducted along the river Rhine in Germany by means of an experimental DVB-S based system developed at Fraunhofer FHR and considering a ferry as cooperative target. To avoid inaccuracies due to data-driven motion compensation procedures and to fairly interpret the polarimetric results, we processed the data by means of a known-motion back-projection algorithm obtaining ISAR images at each polarimetric channel. Then, different approaches in the polarimetric domain have been introduced. The first one is based on the well-known Pauli Decomposition. The others can be divided in two main groups: (i) techniques aimed at separating the different backscattering mechanisms, and (ii) image domain techniques to fuse the polarimetric information in a single ISAR image with enhanced quality. The different considered techniques have been applied to several data sets with distinct bistatic geometries. The obtained results clearly demonstrate the potentialities of polarimetric diversity that could be fruitfully exploited for classification purposes

Next generation multibeam satellite systems

Satellite communication will play a central role towards fulfilling next generation 5G communication requirements. As a matter of fact, anytime-anywhere connectivity cannot be conceived without the presence of the satellite segment. Indeed, satellite communication industry is not only targeting popular markets but also to high dense populated areas where the satellite will become an essential element to decongest the terrestrial wireless network. In order to deliver broadband interactive data traffic, satellite payloads are currently implementing a multibeam radiation pattern. The use of a multibeam architecture brings several advantages in front of a single global beam transmission. First, as an array fed reflector is employed, the antenna gain to noise ratio can be increased leading to high gain in the achievable throughput. Second, different symbols can be simultaneously sent to geographically separated areas, allowing a spatially multiplexed communication. Last but not least, the available bandwidth can be reused in sufficiently separated beams, increasing the spectrum reuse in the overall coverage area. Whenever the system designers target the terabit satellite system the aforementioned multibeam architecture shall be reconsidered. Indeed, the achievable rates can be extremely increased in case a more aggressive frequency reuse is deployed and interference mitigation techniques are implemented either at the user terminal (multiuser detection) or in the transmitter (precoding). Our study deals with the problem of precoding and linear filtering receiving methods for multibeam satellite systems when full frequency reuse is considered. Concretely, we consider the particular restrictions of satellite communications which, in contrast to terrestrial communication systems, suffer from additional drawbacks. First, the feeder link shall aggregate the overall data traffic leading to a very large rate requirement. This required data rate is even increased whenever linear filtering at the return link and precoding in the forward link are deployed. This is because the feed signals, which are larger than the number of beams, shall be computed on ground. In order to solve this problem, we propose a hybrid architecture where the satellite payload is equipped with a fixed processing. This on-board processing linearly transforms the received and transmitted data in order to keep the feeder link rate requirement low. The on-board processing results to be the same for both return and forward links, leading to a large reduction of the payload complexity, mass and cost. Second, as the data traffic can be generated by different gateways, the precoding method shall be designed accordingly. In contrast to previous works, this work studies the case where the collaboration between different gateways is limited. In addition to the aforementioned contribution, in this work some unexplored aspects of multi-gateway multibeam precoding are also investigated. Finally, we consider an important phenomena that currently needs to be treated in multibeam systems: the fact that a single codeword is embedded the information of multiple users in each beam. This leads to the difficult so-called multigroup multicast model, whose optimization requires computationally complex operations. In order to solve this problem: i) 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, ii) 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, iii) we propose a per beam user grouping mechanism so as its robust version in order to increase the precoding gain. Forth, a method for dealing with the multiple gateway architecture is presented that offers high throughputs with a low inter-gateway communication.La comunicación por satélite desempeñará un papel central en el cumplimiento de los requisitos de comunicación 5G de próxima generación. Como cuestión de hecho, la conectividad cualquier momento y lugar no se puede concebir sin la presencia del segmento satelital. De hecho, la industria de la comunicación por satélite no sólo se dirige a los mercados populares, sino también a la alta densas zonas pobladas donde el satélite se convertirá en un elemento esencial para descongestionar la red inalámbrica terrestre. Para entregar el tráfico de datos interactiva de banda ancha, las cargas útiles de satélites están implementando un diagrama de radiación de haces múltiples. El uso de una arquitectura multihaz aporta varias ventajas frente a un único haz de transmisión global. En primer lugar, como se emplea un reflector alimentado matriz, la ganancia de antena a ruido puede aumentar dando lugar a una alta ganancia en el rendimiento alcanzable. En segundo lugar, diferentes símbolos pueden ser enviados simultáneamente a las áreas separadas geográficamente, lo que permite una comunicación multiplexada espacialmente. Por último, pero no menos importante, el ancho de banda disponible puede ser reutilizado en las vigas suficientemente separadas, el aumento de la reutilización del espectro en el área de cobertura global. Cada vez que los diseñadores de sistemas se dirigen el sistema de satélites terabit se reconsideró la arquitectura multihaz mencionado. De hecho, las tasas alcanzables pueden ser extremadamente aumentaron en caso de reutilización de frecuencias más agresiva está desplegado y las técnicas de reducción de interferencias se implementan ya sea en el terminal de usuario (detección multiusuario) o en el transmisor (precodificación). Nuestros estudio aborda el problema de precodificación y filtrado lineal recibir métodos para sistemas de satélites multihaz cuando se considera la reutilización de frecuencias completa. Concretamente, consideramos las restricciones particulares de comunicaciones por satélite que, en contraste con los sistemas de comunicación terrestres, sufren de desventajas adicionales. En primer lugar, el enlace de conexión deberá agregar el tráfico global de datos que conduce a un requisito tasa muy grande. Esta velocidad de datos requerida es incluso aumentó cada vez filtrado lineal en el enlace de retorno y precodificación en el enlace directo se despliegan. Esto se debe a que las señales de alimentación, que son más grandes que el número de haces, se computarán en el suelo. Con el fin de resolver este problema, se propone una arquitectura híbrida, donde la carga útil del satélite está equipado con un procesamiento fijo. Este procesamiento a bordo transforma linealmente los datos recibidos y transmitidos con el fin de mantener el requisito de baja tasa de enlace de conexión. Los resultados del procesamiento de a bordo para ser el mismo para ambos enlaces directo y de retorno, dando lugar a una gran reducción de la complejidad de carga útil, la masa y el coste. En segundo lugar, como el tráfico de datos puede ser generada por diferentes puertas de enlace, el método de precodificación deberá ser diseñado en consecuencia. A diferencia de los trabajos anteriores, este trabajo estudia el caso en que la colaboración entre las diferentes pasarelas es limitado. Además de la contribución anterior, en este trabajo también se investigan algunos aspectos inexplorados de multi-gateway multihaz precodificación. Finalmente, consideramos un fenómeno importante que necesita actualmente para ser tratados en sistemas multihaz: el hecho de que una sola palabra de código se incrusta la información de múltiples usuarios en cada viga. Esto conduce a la denominada modelo de multidifusión multigrupo difícil, cuya optimización requiere operaciones computacionalmente complejos. En tal escenario, el diseño de precodificación en el enlace directo será dirigido