Performance analysis of joint precoding and MUD techniques in multibeam satellite systems

This paper considers interference mitigation techniques in the forward link of multibeam satellite systems. In contrast to previous works, either devoted to receiver interference mitigation (e.g. multiuser detection) or transmitter interference mitigation (precoding), this work evaluates the achievable rates of the joint combination of both techniques. On the one hand, precoding cannot properly mitigate all the inter- beam interference while maintaining a sufficiently high signal-to-noise ratio. On the other hand, the receiver cost and complexity exponentially increases with the number of signals to be simultaneously detected. This highlights that the receiver cannot deal with all the interferences so that in general only 2 signals are jointly detected. As a result, the use of precoding within a coverage area jointly with multiuser detection can both benefit from each other and extremely increase the achievable rates of the system. This is numerically evaluated in a close-to-real coverage area considering simultaneous non-unique decoding strategies. The results show the benefits of this joint scheme that eventually can increase the current precoding performance a 23%.Peer ReviewedPostprint (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

NOMA and interference limited satellite scenarios

This paper deals with the problem of non-orthogonal multiple access (NOMA) in multibeam satellite systems, where the signals are jointly precoded. It is considered that the number of frames that are simultaneously transmitted is higher than the number of feeds, reducing the precoding interference mitigation capabilities as the system becomes overloaded. In order to solve this problem, we assume that the satellite user terminals are able to perform multi-user detection to mitigate the interference. In the current NOMA approach, it is assumed a successive interference cancellation (SIC) receiver. To increase the spectral efficiency, this paper investigates NOMA with simultaneous non-unique detection (SND). Compared to the case where user terminals perform single user detection (SUD), conventional scheduling heuristic rules do not longer apply in this scenario. Therefore, different scheduling algorithms are proposed considering both SIC and SND strategies. As the numerical evaluations show, SND yields larger average data rates than the SIC receiver. Concerning the scheduling, the best strategy is to pair users with highly correlated channels and the lowest channel gain difference. It is also shown that the sum-rate can be increased in overloaded satellite systems with respect to satellite scenarios, where the number of transmitted frames and feeds is the same.Peer ReviewedPostprint (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

Phase only transmit beamforming for spectrum sharing microwave systems

This paper deals with the problem of phase-only transmit beamforming in spectrum sharing microwave systems. In contrast to sub-6 GHz schemes, general microwave systems require a large number of antennas due to its huge path loss. As a consequence, digital beamforming needs a large number of computational resources compared to analog beamforming, which only needs a single radio-frequency chain, results the less computational demanding solution. Analog schemes are usually composed by a phase shifter network whose elements transmit at a certain fixed power so that the system designer shall compute the phase values for each element given a set of directions. This approach leads to non-convex quadratic problems where the traditional semidefinite relaxation fails to deliver satisfactory outcomes. In order to solve this, we propose a nonsmooth method that behaves well in several scenarios. Numerical evaluations in different spectrum sharing scenarios, which show the performance of our method, are provided.Peer ReviewedPostprint (author's final draft

Agua y Suero Fisiológico para Prevenir la Formación de Paracloroanilina

Indexación: Web of Science; Scielo.ABSTRACT: This study determined if p-chloroaniline (PCA) can be minimized by using distilled water and physiological saline solution following sodium hypochlorite but before chlorhexidine. Hypochlorite 5%, 0.5%, 0.05%, 0.005% and 0.0005% dissolved in 0.9% NaCl and in distilled water were mixed with 2% chlorhexidine for the formation of PCA. The PCA was determined using UV-VISIBLE spectrometry, with spectral curve was determined the wavelength of maximum absorption of PCA. Formed PCA absorbance was measured between 0.025%, 0.02%, 0.015%, 0.01%, 0.005% and 0.0025% hypochlorite and 2% chlorhexidine. 2% chlorhexidine and hypochlorite with physiological saline form a white precipitate which prevents the measurement of PCA. Colored PCA is formed with 0.05%, 0.005% hypochlorite aqueous dilutions and 2% chlorhexidine. The lwavelength of maximum absorption obtained was 470 nm and absorbance of PCA showed a linear decrease. 0.005% NaClO produces the least amount of PCA. The best solvent to prevent the formation of PCA during the interaction of sodium hypochlorite with chlorhexidine is distilled water.Este estudio determinó si la p-cloroanilina (PCA) puede ser minimizada mediante el uso de agua destilada y solución salina fisiológica seguido de la aplicación de hipoclorito de sodio, previo a la aplicación de clorhexidina. Hipoclorito al 5%, 0,5%, 0,05%, 0,005% y 0,0005% fue disuelto en 0,9% de NaCl y en agua destilada se mezcló con 2% de clorhexidina para la formación de PCA. El PCA se determinó mediante espectrometría UV-Visible, y con curva espectral se determinó la longitud de onda máxima del PCA. La absorbancia del PCA formado se midió con 0,025%, 0,02%, 0,015%, 0,01%, 0,005% y 0,0025% de hipoclorito y 2% de clorhexidina. La combinación de 2% de clorhexidina e hipoclorito en solución salina fisiológica forman un precipitado blanco que impide la medición del PCA. El PCA coloreado es formado con 0,05%, 0,005% diluciones acuosas de hipoclorito y 2% de clorhexidina. La longitud de onda máxima obtenida fue de 470 nm y la absorbancia del PCA mostró una disminución lineal. NaClO al 0,005% produce menor cantidad de PCA. El mejor disolvente para evitar la formación de PCA durante la interacción de hipoclorito de sodio con clorhexidina es agua destilada.http://ref.scielo.org/2kpw6