This research describes the development and application of the Disaggregated Integral Systems Concept Optimization Technology (DISCO-Tech) methodology. DISCO-Tech is a modular space system design tool that focuses on the optimization of disaggregated and non-traditional space systems. It uses a variable-length genetic algorithm to simultaneously optimize orbital parameters, payload parameters, and payload distribution for space systems. The solutions produced by the genetic algorithm are evaluated using cost estimation, coverage analysis, and spacecraft sizing modules. A set of validation cases are presented. DISCO-Tech is then applied to three representative space mission design problems. The first problem is the design of a resilient rideshare-manifested fire detection system. This analysis uses a novel framework for evaluating constellation resilience to threats using mixed integer linear programming. A solution is identified where revisit times of under four hours are achievable for $10.5 million, one quarter of the cost of a system manifested using dedicated launches. The second problem applies the same resilience techniques to the design of an expanded GPS monitor station network. Nine additional monitor stations are identified that allow the network to continuously monitor the GPS satellites even when five of the monitor stations are inoperable. The third problem is the design of a formation of satellites for performing sea surface height detection using interferometric synthetic aperture radar techniques. A solution is chosen that meets the performance requirements of an upcoming monolithic system at 70% of the cost of the monolithic system. / Doctor of Philosophy / Civilians, businesses, and the government all rely on space-based resources for their daily operations. For example, the signal provided by GPS satellites is used by drivers, commercial pilots, soldiers, and more. Communications satellites provide phone and internet to users in remote areas. Weather satellites provide short-term forecasting and measure climate change. Because of the importance of these and other space systems, it is necessary that they are designed in an efficient, reliable, and cost-effective manner. The Disaggregated Integral Systems Concept Optimization Technology (DISCO-Tech) is introduced as a means of designing these space systems. DISCO-Tech optimizes various aspects of the space mission, including the number of satellites needed to complete the mission, the location of the satellites, and the sensors that each satellite needs to accomplish its mission. This dissertation describes how DISCO-Tech works, then applies DISCO-Tech to several example missions. The first mission uses satellites to monitor forest fires in California. In order to reduce the cost of this mission, the satellites share launch vehicles with satellites from other, unrelated missions. Next, DISCO-Tech is used to choose the placement of new ground stations for GPS satellites. Because GPS is an important asset, this study also assesses the performance of the network of ground stations when some of the stations are inoperable. Finally, DISCO-Tech is used to design a group of satellites that measure sea level, since sea level is important for climatology research. A design is presented for a group of satellites that perform these measurements at a lower cost than a planned mission that uses a single satellite.

Constellation reconfi guration consists of transforming an initial constellation of satellites into some final constellation of satellites to maintain system optimality. Constellations with phased deployment, changing mission requirements, or satellite failures would all benefi t from reconfi guration capability. The constellation reconfiguration problem can be broken into two broad sub-problems: constellation design and constellation transfer. Both are complicated and combinatorial in nature and require new, more efficient methods. Having reviewed existing constellation design frameworks, a new framework, the Elliptical Flower Constellations (EFCs), has been developed that offers improved performance over traditional methods. To assist in rapidly analyzing constellation designs, a new method for orbit propagation based on a sequential solution of Kepler's equation is presented. The constellation transfer problem requires an optimal assignment of satellites in the initial orbit to slots in the final orbit based on optimal orbit transfers between them. A new method for approximately solving the optimal two-impulse orbit transfer with fixed end-points, the so-called minimum Delta v Lambert's problem, is developed that requires the solution of a 4th order polynomial, as opposed to the 6th or higher order polynomials or iterative techniques of existing methods. The recently developed Learning Approach to sampling optimization is applied to the particular problem of general orbit transfer between two generic orbits, with several enhancements specifi c to this problem that improve its performance. The constellation transfer problem is then posed as a Linear Assignment Problem and solved using the auction algorithm once the orbit transfers have been computed. Constellations designed for global navigation satellite systems and for global communications demonstrate signifi cant improvements through the use of the EFC framework over existing methods. An end-to-end example of constellation recon figuration for a constellation with changing regional coverage requirements shows the effectiveness of the constellation transfer methods.

Orbital debris is a current and growing threat to reliable space operations and new space vehicle traffic. As space traffic increases, so does the economic impact of orbital debris on the sustainability of systems that increasingly support national security and international commerce. Much of the debris collision risk is concentrated in specific high-density debris clusters in key regions of Low Earth Orbit (LEO). A potential long-term solution is to employ a constellation of observation satellites within these debris clusters to improve monitoring and characterization efforts, and engage in Laser Debris Removal (LDR) as means of collision mitigation. Here we adapted and improved a previous methodology for evaluating such designs. Further, we performed an analysis on the observer constellations' effectiveness over a range of circular, elliptical, and self-maneuvering designs. Our results show that increasingly complex designs result in improved performance of various criteria and that the proposed method of observation could significantly reduce the threat orbital debris poses to space operations and economic growth. / Master of Science / Orbital debris is defined as all non-operational, man-made objects currently in space. US national space regulations require every new satellite to have a de-orbit plan to prevent the creation of new debris, but fails to address the thousands of derelict objects currently hindering space operations. As space traffic increases, so does the economic impact of orbital debris on the sustainability of systems that increasingly support national security and commercial growth. While orbital debris is usually assessed by looking at the full volume of space, most massive debris objects are concentrated in high-density clusters with a higher than normal probability for collision. A potential solution to the growing orbital debris problem is to place a group of observation satellites within these debris clusters to both improve monitoring capabilities and provide a means for preventing potential collisions by engaging with debris via Laser Debris Removal (LDR). This research presents a methodology for comparing and contrasting different observer satellite constellation designs. Our results show that increasingly complex orbit designs improve various performance criteria, but ultimately orbits that more closely match those of the debris objects provide the best coverage. The proposed method of observation and engagement could significantly reduce the threat orbital debris poses to space operations and economic growth.

Lunar constellations providing the capabilities of situational awareness and surveillance for future mission operators are analyzed in this study. The use of specialty orbits, such as sun-synchronous and frozen orbits, are analyzed to determine the applicability of these unique orbits. Additionally, altitude and inclination trades are performed to determine the degree to which mission objectives are achieved through ranges of these orbital parameters. Using the analyzed orbits, constellations of varying patterns are developed and surface coverage figures of merit are used to evaluate them. The research concludes with calculation of the yearly cross-track and in-track stationkeeping costs of a representative constellation. This stationkeeping is necessary for preservation of the designed coverage statistics.

Spacecraft operating on the Martian surface have used relay satellites as a means of improving communication capabilities, mainly in terms of bandwidth and availability. However, the spacecraft used to achieve this have been large spacecraft (1000s of kilograms) and were not designed with relay capability as the design priority. This thesis explores the possibility of using a CubeSat-based constellation as a communications network for spacecraft operating on the Martian surface. Brute-force techniques are employed to explore the design space of possible constellations. An analysis of constellation configurations that provide complete, continuous coverage of the Martian surface is presented. The stability of these constellations are analyzed, and recommendations are made for stable configurations and the orbital maintenance thereof. Link budget analysis is used to determine the communications capability of each constellation, and recommendations are made for sizing each communication element. The results of these three analyses are synthesized to create an architecture generation tool. This tool is used to identify mission architectures that suit a variety of mission requirements, and these architectures are presented. The primary recommended architecture utilizes 18 CubeSats in three orbital planes with six additional larger relay satellites to provide an average of over one terabit/sol downlink and 100 kbps uplink capability.

This thesis focuses on the concept of uniquely factorable constellations (UFCs) in the design of space-time block codes (STBCs) for wireless communication systems using three different approaches. Based on intelligent constellation collaboration, UFCs can provide the systematic design of a full diversity code with improved coding gain. Firstly, motivated by the energy-efficient hexagonal lattice carved from the Eisenstein integer domain, hexagonal UFCs and hexagonal uniquely factorable constellation pairs (UFCPs), of various sizes, are constructed for a noncoherent single-input multiple-output (SIMO) system. It is proved that these designs assure the blind unique identification of channel coefficients and transmitted signals in a noise-free case and full diversity for the noncoherent maximum likelihood (ML) receiver in a noisy case. In addition, an optimal energy scale is found to maximize the coding gain. Secondly, using a matrix similar to the Alamouti matrix and the UFCP concept based on the quadrature amplitude modulation (QAM) constellation, a novel energy-efficient unitary STBC is designed for a noncoherent multiple-input single-output (MISO) system with two transmitter antennas and one receiver antenna by using the QR decomposition. It is shown that the proposed UFCP-STBC design also allows for the blind unique identification of both the transmitted signals and channel coefficients as well as full diversity. In addition, an optimal unitary UFCP-STBC is devised to maximize the coding gain subject to a transmission bit rate constraint. The last approach is to demonstrate how the UFCP concept is applied to the systematic design of a coherent relay network coding system. A class of uniquely factorable Alamouti matrix pairs is proposed for the design of a novel amplify-forward relay network coding scheme, which allows the relay node to transmit its own information. By carefully making use of the Alamouti coding structure and strategically encoding the signals from the two antennas at the relay node, the resulting coding scheme enables the optimal full diversity gain and better coding gain for the ML detector. Comprehensive computer simulations show that the three uniquely factorable designs presented in this thesis have the best error performance compared to the current designs in literature. / Thesis / Candidate in Philosophy

In the recent years, the exponential Internet traffic growth projections place enormous transmission rate demand on the underlying information infrastructure at every level, from the long haul submarine transmission to optical metro networks. In recent years, optical transmission at 100 Gb/s Ethernet date rate has been standardized by ITU-T and IEEE forums and 400Gb/s and 1Tb/s rates per DWDM channel systems has been under intensive investigation which are expected to be standardized within next couple of years.To facilitate the implementation of 400GbE and 1TbE technologies, the new advanced modulation scheme combined with advanced forward error correction code should be proposed. Instead of using traditional QAM, we prefer to use some other modulation techniques, which are more suitable for current coherent optical transmission systems and can also deal with the channel impairments. In this dissertation, we target at improving the channel capacity by designing the new modulation formats. For the first part of the dissertation, we first describe the optimal signal constellation design algorithm (OSCD), which is designed by placing constellation points onto a two dimensional space. Then, we expand the OSCD onto multidimensional space and design its corresponding mapping rule. At last, we also develop the OSCD algorithm for different channel scenario in order to make the constellation more tolerant to different channel impairments. We propose the LLR-OSCD for linear phase noise dominated channel and NL-OSCD for nonlinear phase noise dominated channel including both self-phase modulation (SPM) and cross-phase modulation (XPM) cases. For the second part of the dissertation, we target at probability shaping of the constellation sets (non-uniform signaling). In the conventional data transmission schemes, the probability of each point in a given constellation is transmitted equally likely and the number of constellation sets is set to 2!. If the points with low energy are transmitted with larger probability then the others with large energy, the non- uniform scheme can achieve higher energy efficiency. Meanwhile, this scheme may be more suitable for optical communication because the transmitted points with large probabilities, which have small energy, suffer less nonlinearity. Both the Monte Carlo simulations and experiment demonstration of both OSCD and non-uniform signaling schemes indicate that our proposed signal constellation significantly outperforms QAM, IPQ, and sphere-packing based signal constellations.

The topic of this thesis is signaling design for data transmission through wireless channels between a transmitter and a receiver that can both be equipped with one or more antennas. In particular, the focus is on channels where the propagation coefficients between each transmitter--receiver antenna pair are only partially known or completetly unknown to the receiver and unknown to the transmitter. A standard signal design approach for this scenario is based on separate training for the acquisition of channel knowledge at the receiver and subsequent error-control coding for data detection over channels that are known or at least approximately known at the receiver. If the number of parameters to estimate in the acquisition phase is high as, e.g., in a frequency-selective multiple-input multiple-output channel, the required amount of training symbols can be substantial. It is therefore of interest to study signaling schemes that minimize the overhead of training or avoid a training sequence altogether. Several approaches for the design of such schemes are considered in this thesis. Two different design methods are investigated based on a signal representation in the time domain. In the first approach, the symbol alphabet is preselected, the design problem is formulated as an integer optimization problem and solutions are found using simulated annealing. The second design method is targeted towards general complex-valued signaling and applies a constrained gradient-search algorithm. Both approaches result in signaling schemes with excellent detection performance, albeit at the cost of significant complexity requirements. A third approach is based on a signal representation in the frequency domain. A low-complexity signaling scheme performing differential space--frequency modulation and detection is described, analyzed in detail and evaluated by simulation examples. The mentioned design approaches assumed that the receiver has no knowledge about the value of the channel coefficients. However, we also investigate a scenario where the receiver has access to an estimate of the channel coefficients with known error statistics. In the case of a frequency-flat fading channel, a design criterion allowing for a smooth transition between the corresponding criteria for known and unknown channel is derived and used to design signaling schemes matched to the quality of the channel estimate. In particular, a constellation design is proposed that offers a high level of flexibility to accomodate various levels of channel knowledge at the receiver. / QC 20101014

<p>The topic of this thesis is signaling design for data transmission through wireless channels between a transmitter and a receiver that can both be equipped with one or more antennas. In particular, the focus is on channels where the propagation coefficients between each transmitter--receiver antenna pair are only partially known or completetly unknown to the receiver and unknown to the transmitter.</p><p>A standard signal design approach for this scenario is based on separate training for the acquisition of channel knowledge at the receiver and subsequent error-control coding for data detection over channels that are known or at least approximately known at the receiver. If the number of parameters to estimate in the acquisition phase is high as, e.g., in a frequency-selective multiple-input multiple-output channel, the required amount of training symbols can be substantial. It is therefore of interest to study signaling schemes that minimize the overhead of training or avoid a training sequence altogether.</p><p>Several approaches for the design of such schemes are considered in this thesis. Two different design methods are investigated based on a signal representation in the time domain. In the first approach, the symbol alphabet is preselected, the design problem is formulated as an integer optimization problem and solutions are found using simulated annealing. The second design method is targeted towards general complex-valued signaling and applies a constrained gradient-search algorithm. Both approaches result in signaling schemes with excellent detection performance, albeit at the cost of significant complexity requirements.</p><p>A third approach is based on a signal representation in the frequency domain. A low-complexity signaling scheme performing differential space--frequency modulation and detection is described, analyzed in detail and evaluated by simulation examples.</p><p>The mentioned design approaches assumed that the receiver has no knowledge about the value of the channel coefficients. However, we also investigate a scenario where the receiver has access to an estimate of the channel coefficients with known error statistics. In the case of a frequency-flat fading channel, a design criterion allowing for a smooth transition between the corresponding criteria for known and unknown channel is derived and used to design signaling schemes matched to the quality of the channel estimate. In particular, a constellation design is proposed that offers a high level of flexibility to accomodate various levels of channel knowledge at the receiver.</p>

Made available in DSpace on 2014-12-17T14:55:42Z (GMT). No. of bitstreams: 1 TallesRF_DISSERT.pdf: 1140964 bytes, checksum: 341e86481dc2ae47c2cea90b012c9fc6 (MD5) Previous issue date: 2009-03-12 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / Wavelet coding is an efficient technique to overcome the multipath fading effects, which are characterized by fluctuations in the intensity of the transmitted signals over wireless channels. Since the wavelet symbols are non-equiprobable, modulation schemes play a significant role in the overall performance of wavelet systems. Thus the development of an efficient design method is crucial to obtain modulation schemes suitable for wavelet systems, principally when these systems employ wavelet encoding matrixes of great dimensions. In this work, it is proposed a design methodology to obtain sub-optimum modulation schemes for wavelet systems over Rayleigh fading channels. In this context, novels signal constellations and quantization schemes are obtained via genetic algorithm and mathematical tools. Numerical results obtained from simulations show that the wavelet-coded systems derived here have very good performance characteristics over fading channels / A codifica??o por matrizes wavelets tem se mostrado um m?todo eficiente para combater o desvanecimento, fen?meno que causa flutua??es na intensidade do sinal transmitido em um canal de comunica??o sem fio, devido ? propaga??o por m?ltiplos percursos. Mas como os s?mbolos codificados pelo sistema wavelet s?o n?o-equiprov?veis, os esquemas de modula??o influenciam de maneira fundamental o desempenho desse sistema. Por isso se torna essencial um m?todo eficaz para a obten??o desses esquemas de modula??o de forma a otimizar o desempenho do sistema wavelet, principalmente quando se emprega matrizes wavelets de grandes dimens?es. Esse trabalho aborda o projeto de esquemas de modula??o para um sistema de transmiss?o sem fio baseado na codifica??o por matrizes wavelets em canais com desvanecimento Rayleigh plano. Para o projeto desses esquemas de modula??o s?o criados novas constela??es e esquemas de quantiza??o. O projeto desses esquemas de modula??o ? guiado por um algoritmo gen?tico. Os resultados obtidos atrav?s de simula??es computacionais mostram que os sistemas wavelets empregando esses esquemas obtiveram um bom desempenho em canais caracterizados pelo desvanecimento Rayleigh