Communications over fading channels with partial channel information : performance and design criteria

The effects of system parameters upon the performance are quantified under the assumption that some statistical information of the wireless fading channels is available. These results are useful in determining the optimal design of system parameters. Suboptimal receivers are designed for systems that are constrained in terms of implementation complexity. The achievable rates are investigated for a wireless communication system when neither the transmitter nor the receiver has prior knowledge of the channel state information (CSI). Quantitative results are provided for independent and identically distributed (i.i.d.) Gaussian signals. A simple, low-duty-cycle signaling scheme is proposed to improve the information rates for low signal-to-noise ratio (SNR), and the optimal duty cycle is expressed as a function of the fading rate and SNR. It is demonstrated that the resource allocations and duty cycles developed for Gaussian signals can also be applied to systems using other signaling formats. The average SNR and outage probabilities are examined for amplify-and-forward cooperative relaying schemes in Rayleigh fading channels. Simple power allocation strategies are determined by using knowledge of the mean strengths of the channels. Suboptimal algorithms are proposed for cases that optimal receivers are difficult to implement. For systems with multiple transmit antennas, an iterative method is used to avoid the inversion of a data-dependent matrix in decision-directed channel estimation. When CSI is not available, two noncoherent detection algorithms are formulated based on the generalized likelihood ratio test (GLRT). Numerical results are presented to demonstrate the use of GLRT-based detectors in systems with cooperative diversity

Bibliography of Lewis Research Center technical publications announced in 1984

This compilation of abstracts describes and indexes the technical reporting that resulted from the scientific and engineering work performed and managed by the Lewis Research Center in 1984. All the publications were announced in the 1984 issues of STAR (Scientific and Technical Aerospace Reports) and/or IAA (International Aerospace Abstracts). Included are research reports, journal articles, conference presentations, patents and patent applications, and theses

Space Station Systems: a Bibliography with Indexes (Supplement 8)

This bibliography lists 950 reports, articles, and other documents introduced into the NASA scientific and technical information system between July 1, 1989 and December 31, 1989. Its purpose is to provide helpful information to researchers, designers and managers engaged in Space Station technology development and mission design. Coverage includes documents that define major systems and subsystems related to structures and dynamic control, electronics and power supplies, propulsion, and payload integration. In addition, orbital construction methods, servicing and support requirements, procedures and operations, and missions for the current and future Space Station are included

Technology for large space systems: A bibliography with indexes (supplement 20)

This bibliography lists 694 reports, articles, and other documents introduced into the NASA Scientific and Technical Information System between July, 1988 and December, 1988. Its purpose is to provide helpful information to the researcher or manager engaged in the development of technologies related to large space systems. Subject areas include mission and program definition, design techniques, structural and thermal analysis, structural dynamics and control systems, electronics, advanced materials, assembly concepts, and propulsion

Mechanisms of transcriptional regulation by SRF co-factors

Serum response factor (SRF) controls gene activation in response to changes in actin dynamics and mitogen-activated protein kinases. SRF has low intrinsic transcriptional activity and requires the recruitment of one of two families of co-activators: the MRTFs (myocardin-related transcription factors) and the TCFs (ternary complex factors). MRTFs are actin-binding proteins. Disruption of the actin-MRTF interaction is sufficient to induce MRTF nuclear accumulation and transcriptional activation. The TCF family are specifically activated by MAPK signalling. This thesis aims to elucidate how the SRF transcription network is controlled. The work presented encompasses two projects focused on each of the co-activator families. The regulation of MRTF shuttling from the cytoplasm to the nucleus is relatively well understood while its regulation once in the nucleus is still uncharacterized. The work demonstrates that nuclear MRTF activities are influenced by nuclear actin. Nuclear actin interferes with MRTF-DNA binding and target gene activation. In the presence of G-actin, nuclear MRTF can associate with target loci and recruit Pol II that, although traverses the gene body, does not generate stable mRNA. This inhibited state is accompanied by hypo-phosphorylation of the Pol II CTD. Dissociation of MRTF-actin interaction is required to re-establish Pol II phosphorylation and mRNA accumulation. The Erk-TCF signalling pathway was used to investigate how chromatin signatures are established in response to cues. Fibroblasts lacking all three TCFs, or reconstituted with mutant derivatives of the Elk-1 TCF were generated. Following Erk activation, chromatin immunoprecipitation and RNA-sequencing techniques, were employed to study the role of the TCFs in chromatin changes and transcriptional activation. It was possible to show that signal-induced chromatin changes occur in absence of transcription, and the specific chromatin signature requires Elk-1 DNA binding and phosphorylation. In addition analysis of the H3K27me3 mark demonstrated that Elk-1 activation is required to maintain a permissive chromatin landscape

Contribution to the Design and Operation of Advanced Mobile Communlcations Systems

El objetivo de esta tesis es estudiar la capacidad de los sistemas LTE (LongTerm Evolution) y Mobile WiMAX (Mobi/e Worldwide fnteroperab;/ity far Microwave Access), definida ésta como "el número máximo de usuarios simultáneos, con diferentes perfiles de servicios, que puede soportar cada nodo de acceso, para cada configuración del sistema". Para poder calcular ésta y la tasa binaria (throughput) se requiere primero calcular dinámicamente !a cantidad de recursos demandados y disponibles, que, a su vez, dependen de cómo se forma la correspondiente MAU (Mínimum Allocation Unit), tanto en LTE como en WiMAX. Ambas tecnologías, propuestas como respuesta a la iniciativa IMT (lnternational Mobile Telecommunications)-Advanced, tienen en común que el cómputo de estos MAUs es complejo debido a que parte de los recursos (overhead) tiene que utilizarse para labores necesarias de señalización, control o sincronización. Aunque el conjunto de tecnologías 3G (Third Generation) basadas en WCDMA (Wide-bond Code Division Mu/tiple Access) y HSPA (High-Speed Packet Access) constituyen en la actualidad el fundamento de las redes móviles de banda ancha más empleadas, LTE es, sin embargo, la tecnología móvil con el crecimiento más rápido de toda la historia. LTE es capaz de proporcionar velocidades de datos muy elevadas con una latencia extremadamente reducida, especialmente en el enlace descendente, DL (downlink), a expensas de incrementar su complejidad. Éstas son algunas de las características que convierten a LTE en una tecnología de banda ancha móvil con enormes posibilidades, no solo para usuarios domésticos sino también para aplicaciones novedosas en comunicaciones M2M (machine-to-machine), servicios de salud tipo mHea/th, los nuevos servicios asociados a las ciudades inteligentes (smart grids). Hay varias razones que explican este rápido despliegue de las redes LTE. Por un lado, el mercado de dispositivos móviles está creciente a tasas muy elevadas(::: 80%), constituyendo ya los teléfonos inteligentes (smartphones) el 75% de los dispositivos de usuario. Por otro lado, la técnica OFDMA (Orthogonal Frequency Division Mu/tiple Access) en el enlace descendente permite que LTE sea capaz de soportar tasas de datos más elevadas que las de HSPA. Hay incluso nuevos comportamientos de usuarios, sobre todo del segmento de población más joven, que están modificando sus preferencias a la hora de ver TV, desplazándose progresivamente desde el televisor convencional al streaming en sus smartphones. La combinación de todos estos factores está espoleando una demanda fuertemente creciente de servicios novedosos y muy intensivos en Mbps (HDTV, vídeo bajo demanda (VoG), gaming, etc.): el tráfico de datos ha crecido un ::: 65% entre los primeros cuatrimestres de 2015 y 2016. Además de la utilización de OFDM, LTE y Mobile-WiMAX tiene otros aspectos en común, como la posible integración de técnicas AMC (Adaptive Modulation and Cading) y MIMO (Multip/elnput ond Multip/e-Output) para poder proveer conexiones más fiables y rápidas. Sin embargo, y a pesar de estas similitudes, LTE y Mobile-WiMAX constituyen soluciones tecnológicas muy complejas que exhiben numerosas diferencias. En particular, un elemento crucial que aumenta la dificultan inherente a ambas se encuentra se encuentra en su flexibilidad en el sentido de que se dejan abiertos muchos aspectos de configuración para que cada empresa pueda diseñar la opción que considere más adecuada. El rendimiento de estas redes depende pues de la forma en la que se soluciona el problema de optimización entre la adecuación de los recursos disponibles en cada configuración a los recursos consumidos por !os usuarios. En esta Tesis se realiza diferentes trabajos de investigación tendentes a: 1. Modelar de forma exacta la velocidad de datos (throughput) disponible para los usuarios. Esto requiere calcular en paralelo los recursos disponibles -una vez descontado el overhead -y los recursos demandados. 2. Calcular, utilizando la heurística anterior, !a capacidad (o número máximo de usuarios simultáneos, con diferentes perfiles de servicios, que puede soportar cada nodo de acceso, para cada configuración del sistema). La validez de los modelos obtenidos se ha probado de forma exitosa en una gran variedad de configuraciones posibles en ambas tecnologías, publicando !os resultados en varias revistas y congresos internacionales