I/Q imbalance mitigation for space-time block coded communication systems

Multiple-input multiple-output (MIMO) space-time block coded (STBC) wireless communication systems provide reliable data transmissions by exploiting the spatial diversity in fading channels. However, due to component imperfections, the in-phase/quadrature (I/Q) imbalance caused by the non-ideal matching between the relative amplitudes and phases of the I and Q branches always exists in the practical implementation of MIMO STBC communication systems. Such distortion results in a complex conjugate term of the intended signal in the time domain, hence a mirror-image term in the frequency domain, in the data structure. Consequently, I/Q imbalance increases the symbol error rate (SER) drastically in MIMO STBC or STBC MIMO orthogonal frequency division multiplexing (OFDM) communication systems, where both the signal and its complex conjugate are utilized for the information transmission, hence should be mitigated effectively. In this dissertation, the impact of I/Q imbalance in MIMO STBC systems over flat fading channels, the impact of I/Q imbalance in STBC MIMO-OFDM systems and in time- reversal STBC (TR-STBC) systems over frequency-selective fading channels are studied systematically. With regard to the MIMO STBC and the STBC MIMO-OFDM systems with I/Q imbalance, orthogonal space-time block codes (OSTBCs), quasi-orthogonal STBCs (QOSTBCs) and rotated QOSTBCs (RQOSTBCs) are studied, respectively. By exploiting the special structure of the received signal, low-complexity solutions are provided to mitigate the distortion induced by I/Q imbalance successfully. In addition, to mitigate I/Q imbalance while at the same time to exploit the multipath diversity for STBC OFDM systems over frequency-selective fading channels, a new encoding/decoing scheme for the grouped linear constellation precoded (GLCP) OFDM systems with I/Q imbalance is studied. In Chapter 1, the objectives of the research are elaborated. In Chapter 2, the various I/Q imbalance models are introduced, and the model used in this dissertation is established. In Chapter 3, the performance degradation caused by I/Q imbalance of the transceivers in MIMO STBC wireless communication systems over flat fading channels and the solutions are studied. A 2 Tx Alamouti system, a 4 Tx quasi-orthogonal STBC (QOSTBC) system, and a 4 Tx rotated QOSTBC (RQOSTBC) system with I/Q imbalance are studied in detail. By exploiting the special structure of the received signal, low-complexity solutions are proposed to mitigate I/Q imbalance successfully. Since STBCs are developed for frequency-flat fading channels, to achieve the spatial diversity in frequency-selective fading channels, MIMO-OFDM arrangements have been suggested, where STBCs are used across different antennas in conjunction with OFDM. In Chapter 4, the performance degradation caused by I/Q imbalance in STBC MIMO-OFDM wireless systems over frequency-selective fading channels and the solutions are studied. Similarly, a 2 Tx Alamouti system, a 4 Tx quasi-orthogonal STBC (QOSTBC) system, and a 4 Tx rotated QOSTBC (RQOSTBC) system with I/Q imbalance are studied in detail, and low-complexity solutions are proposed to mitigate the distortion effectively. However, OFDM systems suffer from the loss of the multipath diversity by converting frequency-selective fading channels into parallel frequency-flat fading subchannels. To exploit the multipath diversity and reduce the decoding complexity, GLCP OFDM systems with I/Q imbalance are studied. By judiciously assigning the mirror-subcarrier pair into one group, a new encoding/decoding scheme with a low-complexity is proposed to mitigate I/Q imbalance for GLCP OFDM systems in Chapter 5. Since OFDM communication systems have high peak-to-average power ratio (PAPR) problem and are sensitive to carrier frequency offset (CFO), to achieve both the spatial and multipath diversity, time-reversal STBC (TR-STBC) communication systems are introduced. In Chapter 6, the I/Q imbalance mitigating solutions in TR-STBC systems, both in the time domain and in the frequency domain, are studied

An adaptive algorithm for direct conversion receivers: Architecture and performance analysis

Master'sMASTER OF ENGINEERIN

Personalized Recommendation for Balancing Content Generation and Usage on Two-Sided Entertainment Platforms

Online entertainment platforms such as Youtube host a vast amount of user-generated content (UGC). The unique feature of two-sided UGC entertainment platforms is that creators’ content generation and users’ content usage can influence each other. However, traditional recommender systems often emphasize content usage but ignore content generation, leading to a misalignment between these two goals. To address the challenge, this paper proposes a prescriptive uplift framework to balance content generation and usage through personalized recommendations. Specifically, we first predict the heterogeneous treatment effects (HTEs) of recommended contents on creators’ content generation and users’ content usage, then consider these two predicted HTEs simultaneously in an optimization model to determine the recommended contents for each user. Using a large-scale real-world dataset, we demonstrate that the proposed recommendation method better balances content generation and usage and brings a 42% increase in participants’ activity compared to existing benchmark methods

Detector induced anisotropies on the angular distribution of gravitational wave sources and opportunities of constraining horizon scale anisotropies

The cosmological principle has been verified using electromagnetic (EM) observations. However its verification with high accuracy is challenging due to various foregrounds and selection effects, and possible violation of the cosmological principle has been reported in the literature. In contrast, gravitational wave (GW) observations are free of these foregrounds and related selection biases. This may enable future GW experiments to test the cosmological principle robustly with full sky distribution of millions of standard bright/dark sirens. However, the sensitivities of GW detectors are highly anisotropic, resulting in significant instrument induced anisotropies in the observed GW catalog. We investigate these instrumental effects for 3rd generation detector networks in term of multipoles $a_{\ell m}$ of the observed GW source distribution, using Monte Carlo simulations. (1) We find that the instrument induced anisotropy primarily exists at the $m=0$ modes on large scales ($\ell \lesssim 10$), with amplitude $\langle |a_{\ell 0}|^2 \rangle \sim 10^{-3}$ for two detectors (ET-CE) and $\sim 10^{-4}$ for three detectors (ET-2CE). This anisotropy is correlated with the sky distribution of signal-to-noise ratio (SNR) and localization accuracy. Such anisotropy sets a lower limit on the detectable cosmological $a_{\ell 0}$. (2) However, we find that the instrument induced anisotropy is efficiently canceled by rotation of the Earth in $m\neq 0$ components of $a_{\ell m}$. Therefore $a_{\ell m}$ ($m\neq 0$) are clean windows to detect cosmological anisotropies. (3) We investigate the capability of 3rd generation GW experiments to measure the cosmic dipole. Through Monte Carlo simulations, we find that cosmic dipole with an amplitude of $\sim 10^{-2}$ reported in the literature can be detected/ruled out by ET-CE and ET-2CE robustly, through the measurement of $a_{11}$.Comment: 7 pages, 6 figures, submitted to MNRA

Proposing a novel comprehensive evaluation model for the coal burst liability in underground coal mines considering uncertainty factors

Coal burst is a severe hazard that can result in fatalities and damage of facilities in underground coal mines. To address this issue, a robust unascertained combination model is proposed to study the coal burst hazard based on an updated database. Four assessment indexes are used in the model, which are the dynamic failure duration (DT), elastic energy index (WET), impact energy index (KE) and uniaxial compressive strength (RC). Four membership functions, including linear (L), parabolic (P), S and Weibull (W) functions, are proposed to measure the uncertainty level of individual index. The corresponding weights are determined through information entropy (EN), analysis hierarchy process (AHP) and synthetic weights (CW). Simultaneously, the classification criteria, including unascertained cluster (UC) and credible identification principle (CIP), are analyzed. The combination algorithm, consisting of P function, CW and CIP (P-CW-CIP), is selected as the optimal classification model in function of theory analysis and to train the samples. Ultimately, the established ensemble model is further validated through test samples with 100% accuracy. The results reveal that the hybrid model has a great potential in the coal burst hazard evaluation in underground coal mines. © 202

A Decision Tree Approach for Assessing and Mitigating Background and Identity Disclosure Risks

The Facebook/Cambridge Analytica data scandal shows a type of privacy threat where an adversary attacks on a massive number of people without prior knowledge about their background information. Existing studies typically assume that the adversary knew the background information of the target individuals. This study examines the disclosure risk issue in privacy breaches without such an assumption. We define the background disclosure risk and re-identification risk based on the notion of prior and conditional probabilities respectively, and integrate the two risk measures into a composite measure using the Minimum Description Length principle. We then develop a decision-tree pruning algorithm to find an appropriate group size considering the tradeoff between disclosure risk and data utility. Furthermore, we propose a novel tiered generalization method for anonymizing data at the group level. An experimental study has been conducted to demonstrate the effectiveness of our approach

Population policy and urban housing in China

Thesis (M.Arch.)--Massachusetts Institute of Technology, Dept. of Architecture, 1999.Includes bibliographical references (leaf 52).This thesis will focus on how urban housing design reflects the new one-child family population policy in the traditional urban context in Beijing, China. The population policy has changed the size and structure of traditional family, and further affected children's growing up environment. Children, used to grow up in a joint family of three generations in a traditional courtyard house, now have isolated by apartment box. The traditional social and spatial relationships among children, families, and neighbors have been extremely weakened. My intention is to restore the lost relationships for lonely children in a high density residential complex. This complex, transformed from the traditional single story courtyard house, becomes one big house, where all neighbors live under one roof as one big family. As a consequence, children in a one child family still have the same feeling of multi generations living together as their old generations had before.by Mingzheng Gao.M.Arch

3-D mapping of tellurium inclusions in CdZnTe crystals by means of improved optical microscopy

CdZnTe crystals are employed for the preparation of room temperature operating X-ray detectors. High resistivity is usually reached by contemporarily doping with group III or group VII elements and using tellurium deviated charge. This latter condition is responsible for the presence in crystals of a large number of tellurium inclusions. These can be incorporated at the growing interface or can form during cooling as a result of the retrograde behavior of the liquidus curve. Unfortunately, inclusions severely limit the performances of CdZnTe-based detectors, in particular in the case of imaging devices. This is why, monitoring tellurium inclusion density has become very important: i) for assessing the material quality ii) for studying the formation mechanisms of inclusions during growth iii) for checking the effectiveness of post-growth thermal treatments to reduce inclusion concentration. Tellurium inclusions are typically revealed by transmission optical microscopy in the near infrared. However, determination of the concentration of inclusions is complicated by the fact that at high magnification, the depth of field is much less then the sample thickness, so that in a single photograph only few inclusions appear really sharp. In order to overcome this problem, it is possible to take a set of photographs at different focal planes and, by means of specific software, reconstruct all inclusions on a single focal plane. This technique, also provided with some commercial microscopes, suffers two main problems: i) if one inclusion is present beneath a second one, only one is detected ii) any information about the depth in the sample of each inclusion is lost. For this reason, we have developed an instrument for the 3D mapping of the inclusions. The system is mounted on a standard optical microscope with automatic vertical movement. Pictures are taken at different focal planes. Images are then elaborated by dedicated software that ascribes each inclusion to the proper focal plane. As a result, all the inclusions are counted and precisely localized in 3D. By using the different objective lenses of the microscope is possible to tune the desired compromise between resolution and width of the monitored area. However, at high magnification it is possible to map inclusions down to 1 micron diameter. The system can be practically installed on any optical microscope that can operate in transmission mode