Limited Feedback Techniques in Multiple Antenna Wireless Communication Systems

<p>Multiple antenna systems provide spatial multiplexing and diversity benefits.These systems also offer beamforming and interference mitigation capabilities in single-user (SU) and multi-user (MU) scenarios, respectively. Although diversity can be achieved without channel state information (CSI) at the transmitter using space-time codes, the knowledge of instantaneous CSI at the transmitter is essential to the above mentioned gains. In frequency division duplexing (FDD) systems, limited feedback techniques are employed to obtain CSI at the transmitter from the receiver using a low-rate link. As a consequence, CSI acquired by the transmitter in such manner have errors due to channel estimation and codebook quantization at the receiver, resulting in performance degradation of multi-antenna systems. In this thesis, we examine CSI inaccuracies due to codebook quantization errors and investigate several other aspects of limited feedback in SU, MU and multicell wireless communication systems with various channel models. For SU multiple-input multiple-output (MIMO) systems, we examine the capacity loss using standard codebooks. In particular, we consider single-stream and two-stream MIMO transmissions and derive capacity loss expressions in terms of minimum squared chordal distance for various MIMO receivers. Through simulations, we investigate the impact of codebook quantization errors on the capacity performance in uncorrelated Rayleigh, spatially correlated Rayleigh and standardized MIMO channels. This work motivates the need of effective codebook design to reduce the codebook quantization errors in correlated channels. Subsequently, we explore the improvements in the design of codebooks in temporally and spatially correlated channels for MU multiple-input single-output (MISO) systems, by employing scaling and rotation techniques. These codebooks quantize instantaneous channel direction information (CDI) and are referred as differential codebooks in the thesis. We also propose various adaptive scaling techniques for differential codebooks where packing density of codewords in the differential codebook are altered according to the channel condition, in order to reduce the quantization errors. The proposed differential codebooks improve the spectral efficiency of the system by minimizing the codebook quantization errors in spatially and temporally correlated channels. Later, we broaden the scope to massive MISO systems and propose trellis coded quantization (TCQ) schemes to quantize CDI. Unlike conventional codebook approach, the TCQ scheme does not require exhaustive search to select an appropriate codeword, thus reducing computational complexity and memory requirement at the receiver. The proposed TCQ schemes yield significant performance improvements compared to the existing TCQ based limited feedback schemes in both temporally and spatially correlated channels. Finally, we investigate interference coordination for multicell MU MISO systems using regularized zero-forcing (RZF) precoding. We consider random vector quantization (RVQ) codebooks and uncorrelated Rayleigh channels. We derive expected SINR approximations for perfect CDI and RVQ codebook-based CDI. We also propose an adaptive bit allocation scheme which aims to minimize the network interference and moreover, improves the spectral efficiency compared to equal bit allocation and coordinated zero-forcing (ZF) based adaptive bit allocation schemes.</p>

Limited Feedback Techniques in Multiple Antenna Wireless Communication Systems

<p>Multiple antenna systems provide spatial multiplexing and diversity benefits.These systems also offer beamforming and interference mitigation capabilities in single-user (SU) and multi-user (MU) scenarios, respectively. Although diversity can be achieved without channel state information (CSI) at the transmitter using space-time codes, the knowledge of instantaneous CSI at the transmitter is essential to the above mentioned gains. In frequency division duplexing (FDD) systems, limited feedback techniques are employed to obtain CSI at the transmitter from the receiver using a low-rate link. As a consequence, CSI acquired by the transmitter in such manner have errors due to channel estimation and codebook quantization at the receiver, resulting in performance degradation of multi-antenna systems. In this thesis, we examine CSI inaccuracies due to codebook quantization errors and investigate several other aspects of limited feedback in SU, MU and multicell wireless communication systems with various channel models. For SU multiple-input multiple-output (MIMO) systems, we examine the capacity loss using standard codebooks. In particular, we consider single-stream and two-stream MIMO transmissions and derive capacity loss expressions in terms of minimum squared chordal distance for various MIMO receivers. Through simulations, we investigate the impact of codebook quantization errors on the capacity performance in uncorrelated Rayleigh, spatially correlated Rayleigh and standardized MIMO channels. This work motivates the need of effective codebook design to reduce the codebook quantization errors in correlated channels. Subsequently, we explore the improvements in the design of codebooks in temporally and spatially correlated channels for MU multiple-input single-output (MISO) systems, by employing scaling and rotation techniques. These codebooks quantize instantaneous channel direction information (CDI) and are referred as differential codebooks in the thesis. We also propose various adaptive scaling techniques for differential codebooks where packing density of codewords in the differential codebook are altered according to the channel condition, in order to reduce the quantization errors. The proposed differential codebooks improve the spectral efficiency of the system by minimizing the codebook quantization errors in spatially and temporally correlated channels. Later, we broaden the scope to massive MISO systems and propose trellis coded quantization (TCQ) schemes to quantize CDI. Unlike conventional codebook approach, the TCQ scheme does not require exhaustive search to select an appropriate codeword, thus reducing computational complexity and memory requirement at the receiver. The proposed TCQ schemes yield significant performance improvements compared to the existing TCQ based limited feedback schemes in both temporally and spatially correlated channels. Finally, we investigate interference coordination for multicell MU MISO systems using regularized zero-forcing (RZF) precoding. We consider random vector quantization (RVQ) codebooks and uncorrelated Rayleigh channels. We derive expected SINR approximations for perfect CDI and RVQ codebook-based CDI. We also propose an adaptive bit allocation scheme which aims to minimize the network interference and moreover, improves the spectral efficiency compared to equal bit allocation and coordinated zero-forcing (ZF) based adaptive bit allocation schemes.</p>

The role of instilling moral values in primary schoolchildren

The aim of this study was a comprehensive coverage of the effectiveness of instilling moral values in the education of primary schoolchildren for their further update. The following tools were used for the collection and processing of statistical data: scientific literature review, survey results, questionnaires for parents, generalization of theoretical and empirical data, diagnostic methods (direct and indirect pedagogical observation, unfinished sentence technique, game activity, icon exercises, analysis of moral and ethical situations, independent characteristics), statistical methods of calculation. The online utility Text Analyzer was used to process open responses from parent questionnaires. The introduction of individual, group, as well as training forms of work, discussion, feedback techniques, games and art methods into the educational process of primary school has provided positive changes in instilling moral values in students. The interaction of family and school contributed to the development and improvement of parents’ pedagogical knowledge and skills. The levels of moral values in primary schoolchildren in experimental groups after the completion of the formative stage of the experiment significantly exceed the indicators of control groups.

Teaching Experience and Views of Pronunciation Formative Assessment

The current study aimed at investigating the differences between novice and expert Arab EFL teachers in their views of providing pronunciation corrective feedback to their students. Four teachers were recruited for the study. Two novice teachers and two experienced teachers. Both groups of teachers were interviewed about their views of providing pronunciation corrective feedback. Interview data analysis revealed the existence of six major differences between novice and experienced teachers in their views of pronunciation corrective feedback. These differences included timing, frequency, considering students’ proficiency level, considering the skill being taught, focus on form and/or meaning, and the range of pronunciation corrective feedback techniques used. Further suggestions included incorporating a pronunciation corrective feedback component in teacher development as well as professional training programs.

J-EDA: A workbench for tuning similarity and diversity search parameters in content-based image retrieval

Similarity searches can be modeled by means of distances following the Metric Spaces Theory and constitute a fast and explainable query mechanism behind content-based image retrieval (CBIR) tasks. However, classical distance-based queries, e.g., Range and k-Nearest Neighbors, may be unsuitable for exploring large datasets because the retrieved elements are often similar among themselves. Although similarity searching is enriched with the imposition of rules to foster result diversification, the fine-tuning of the diversity query is still an open issue, which is is usually carried out with and a non-optimal expensive computational inspection. This paper introduces J-EDA, a practical workbench implemented in Java that supports the tuning of similarity and diversity search parameters by enabling the automatic and parallel exploration of multiple search settings regarding a user-posed content-based image retrieval task. J-EDA implements a wide variety of classical and diversity-driven search queries, as well as many CBIR settings such as feature extractors for images, distance functions, and relevance feedback techniques. Accordingly, users can define multiple query settings and inspect their performances for spotting the most suitable parameterization for a content-based image retrieval problem at hand. The workbench reports the experimental performances with several internal and external evaluation metrics such as P × R and Mean Average Precision (mAP), which are calculated towards either incremental or batch procedures performed with or without human interaction.

EFL university teachers’ perspectives in written corrective feedback and their actual applications

<p>This study aimed to investigate the English as a foreign language (EFL) university teachers’ perspective and their actual applications in providing written corrective feedback to the writing errors made by the EFL university students and their correlation. The study was based on 80 responses of a Google-Form survey distributed to EFL university teachers with various teaching experiences from the most parts of Indonesia. Correlational design was used in this research. Descriptive statistics and Pearson’s correlation tests were used to analyze data. The results indicated that the majority of teachers had perspectives that it is valuable to provide and vary the strategies of written corrective feedback. In addition, the teachers mostly applied both direct and indirect feedback in various strategies and they only sometimes provided corrections in all aspects of errors and reformulation. It was also found out that the Indonesian EFL university teachers’ perspectives in the written corrective on students’ writing errors highly correlated with their actual applications. The results of the study provide both theoretical and pedagogical implications. Theoretically, it enriches the body knowledge of feedback and EFL writing. Pedagogically, EFL teachers are also suggested to improve their knowledge on various feedback techniques and apply it in their classroom teaching and learning process.</p><p> </p>

The role and importance of feedback techniques in the formation self-esteem and confidence of young football players

The quality of the communicative process can rightfully be attributed to the factor of realizing the potential capabilities of the subjects of the educational process in the framework of sports activities, namely the coach and the athlete. The coach, using the appropriate means of communication, must transfer his knowledge to the athlete and thus realize his professional and personal capabilities. The athlete, in turn, perceiving instructions and information from the coach, strives for the fullest possible realization of his existing abilities. At the same time, during interpersonal interaction in the process of mastering the corresponding motor skills, the coach, in parallel and inevitably, also influences the formation of the psychological qualities of a young football player. The purpose of the work was to analyze the mechanisms and nature of the influence of the use of feedback techniques in the context of the coach's influence on the level of self-esteem and self-confidence of an athlete. Research results. The paper presents the results of theoretical analysis and generalization of practical experience regarding the possibilities of using feedback techniques. In the course of the research, verbal and non-verbal signals from the side of the coach were considered as a factor influencing the process of forming an adequate level of self-esteem and confidence in an athlete. Demonstrated the mechanism and nature of the influence of the use of feedback techniques by the trainer, depending on their positive or negative orientation. In addition, the result of the work was the substantiation of the fact that the systemic, purposeful and consistent use of feedback techniques as a means of communication in the learning process creates favorable conditions for the formation of the necessary level of confidence and the level of self-esteem of an athlete.

Brain-Computer Interfaces Systems for Upper and Lower Limb Rehabilitation: A Systematic Review

In recent years, various studies have demonstrated the potential of electroencephalographic (EEG) signals for the development of brain-computer interfaces (BCIs) in the rehabilitation of human limbs. This article is a systematic review of the state of the art and opportunities in the development of BCIs for the rehabilitation of upper and lower limbs of the human body. The systematic review was conducted in databases considering using EEG signals, interface proposals to rehabilitate upper/lower limbs using motor intention or movement assistance and utilizing virtual environments in feedback. Studies that did not specify which processing system was used were excluded. Analyses of the design processing or reviews were excluded as well. It was identified that 11 corresponded to applications to rehabilitate upper limbs, six to lower limbs, and one to both. Likewise, six combined visual/auditory feedback, two haptic/visual, and two visual/auditory/haptic. In addition, four had fully immersive virtual reality (VR), three semi-immersive VR, and 11 non-immersive VR. In summary, the studies have demonstrated that using EEG signals, and user feedback offer benefits including cost, effectiveness, better training, user motivation and there is a need to continue developing interfaces that are accessible to users, and that integrate feedback techniques.