Massive MIMO 시스템을 위한 채널 추정 및 피드백 기법

학위논문 (박사)-- 서울대학교 대학원 : 전기·컴퓨터공학부, 2017. 2. 이정우.To meet the demand of high throughput in next generation wireless systems, various directions for physical layer evolution are being explored. Massive multiple-input multiple-output (MIMO) systems, characterized by a large number of antennas at the transmitter, are expected to become a key enabler for spectral efficiency improvement. In massive MIMO systems, thanks to the orthogonality between different users' channels, high spectral and energy efficiency can be achieved through simple signal processing techniques. However, to get such advantages, accurate channel state information (CSI) needs to be available, and acquiring CSI in massive MIMO systems is challenging due to the increased channel dimension. In frequency division duplexing (FDD) systems, where CSI at the transmitter is achieved through downlink training and uplink feedback, the overhead for the training and feedback increases proportionally to the number of antennas, and the resource for data transmission becomes scarce in massive MIMO systems. In time division duplexing (TDD) systems, where the channel reciprocity holds and the downlink CSI can be obtained through uplink training, pilot contamination due to correlated pilots becomes a performance bottleneck when the number of antennas increases. In this dissertation, I propose efficient CSI acquisition techniques for various massive MIMO systems. First, I develop a downlink training technique for FDD massive MIMO systems, which estimates the downlink channel with small overhead. To this end, compressed sensing tools are utilized, and the training overhead can be highly reduced by exploiting the previous channel information. Next, a limited feedback scheme is developed for FDD massive MIMO systems. The proposed scheme reduces the feedback overhead using a dimension reduction technique that exploits spatial and temporal correlation of the channel. Lastly, I analyze the effect of pilot contamination, which has been regarded as a performance bottleneck in multi-cell massive MIMO systems, and propose two uplink training strategies. An iterative pilot design scheme is developed for small networks, and a scalable training framework is also proposed for networks with many cells.1 Introduction 1 1.1 Massive MIMO 1 1.2 CSI Acquisition in Massive MIMO Systems 3 1.3 Contributions and Organization 6 1.4 Notations 7 2 Compressed Sensing-Aided Downlink Training 9 2.1 Introduction 10 2.2 System Model 13 2.2.1 Channel Model 13 2.2.2 Downlink Channel Estimation 16 2.3 CS-Aided Channel Training 19 2.3.1 Training Sequence Design 20 2.3.2 Channel Estimation 21 2.3.3 Estimation Error 23 2.4 Discussions 26 2.4.1 Design of Measurement Matrix 26 2.4.2 Extension to MIMO Systems 27 2.4.3 Comparison to CS with Partial Support Information 28 2.5 Simulation Results 29 2.6 Conclusion 37 3 Projection-Based Differential Feedback 39 3.1 Introduction 40 3.2 System Model 44 3.2.1 Multi-User Beamforming with Limited Feedback 45 3.2.2 Massive MIMO Channel 47 3.3 Projection-Based Differential Feedback 48 3.3.1 Projection-Based Differential Feedback Framework 48 3.3.2 Projection for PBDF Framework 51 3.3.3 Efficient Algorithm 57 3.4 Discussions 58 3.4.1 Projection with Imperfect CSIR 58 3.4.2 Acquisition of Channel Statistics 61 3.5 Simulation Results 62 3.6 Conclusion 69 4 Mitigating Pilot Contamination via Pilot Design 71 4.1 Introduction 72 4.2 System Model 73 4.2.1 Multi-cell Massive MIMO Systems 74 4.2.2 Uplink Channel Training 75 4.2.3 Data Transmission 77 4.3 Iterative Pilot Design Algorithm 78 4.3.1 Algorithm 79 4.3.2 Proof of Convergence 81 4.4 Generalized Pilot Reuse 81 4.4.1 Concept of Pilot Reuse Schemes 81 4.4.2 Pilot Design based on Grassmannian Subspace Packing 82 4.5 Simulation Results 85 4.5.1 Iterative Pilot Design 85 4.5.2 Generalized Pilot Reuse 87 4.6 Conclusion 89 5 Conclusion 91 5.1 Summary 91 5.2 Future Directions 93 Bibliography 96 Abstract (In Korean) 109Docto

메탄자화균 DH-1의 SoxR 전사 조절 네트워크 규명

학위논문 (석사)-- 서울대학교 대학원 : 공과대학 협동과정 바이오엔지니어링전공, 2018. 8. 서상우.Methanotrophs are bacteria that use methane as a sole carbon source and energy source. Since methane takes up almost 90% of natural gas and shale gas and causes global warming, methanotrophs that consume methane are considered as promising industrial strains. Methylomonas sp. DH-1, a novel methanotroph, has a lot of merits such as fast growth, high methanol resistance, innate carotenoid pathway, and so on. However, lack of physiology and genetics about this strain and absence of proper metabolic engineering tools are the bottleneck in industrial application of Methylomonas sp. DH-1. Thus, it is required to understand its genetic and physiologic characteristics and engineering tools tailored to this strain, so that it can be used in diverse industries. We focused on understanding regulatory networks in Methylomonas sp. DH-1 particularly in response to oxidative stress. SoxR, a known transcriptional regulator that governs transcription against oxidative stress, has different mechanism in enterobacteria and non-enterobacteria. When superoxide, nitric oxide, or redox active compounds exist in enterics, SoxR is activated and genes coding proteins that defend cells against oxidative stress are transcribed. SoxR in non-enterics in known not to regulate superoxide dismutase or else. Understanding SoxR transcriptional regulatory network in methanotroph lets this strain be used in various ways. In this study, genome-wide SoxR transcriptional regulatory network in Methylomonas sp. DH-1 was elucidated. SoxR of Methylomonas sp. DH-1 was firstly selected from four candidate proteins. Recombination and epitope tagging strategy, and sequencing library protocols were constructed specific to Methylomonas sp. DH-1. Based on RNA-seq of wild-type and SoxR knock-out mutant under both methane and methanol conditions, SoxR-dependent genes were selected. The number of differentially expressed genes in each condition was 522 and 260, respectively. Genome-wide binding sites of SoxR were also identified by Chromatin Immunoprecipitation sequencing (ChIP-seq) under both conditions. By combining transcriptome with genome-wide binding sites, YgiT-type zinc finger protein (AYM39_RS22995) was identified as SoxR regulon.Abstract.................................................................................... iv List of Tables...................................................................... viii List of Figures...................................................................... ix Chapter 1. Introduction............................................. 1 1.1 Need for making use of methanotrophs in industry..................... 1 1.2 Methylomonas sp. DH-1 as a promising industrial strain......... 3 1.3 SoxR transcriptional regulator in bacteria........................................ 4 1.4 The scope of this study......................................................................... 6 Chapter 2. Materials and methods.......................... 8 2.1 Bacterial strains, media, and culture conditions............................. 8 2.2 Design and construction of linker-8X myc-KanR cassette......... 8 2.3 Preparation of DNA fragments for recombination to construct SoxR knockout mutant......................................................................... 11 2.4 Preparation of DNA fragments for recombination to construct SoxR-myc mutant.................................................................................. 12 2.5 Electroporation-based recombination of DNA fragments in Methylomonas sp. DH-1.................................................................... 12 2.6 RNA-seq.................................................................................................... 15 2.7 ChIP-seq.................................................................................................... 16 Chapter 3. Results and discussion........................ 18 3.1 Selection of SoxR from candidate genes...................................... 18 3.2 Comparison of transcriptional levels between wildtype and SoxR knockout mutant in methane condition.............................. 18 3.3 Comparison of transcriptional levels between wildtype and SoxR knockout mutant in methanol condition............................. 25 3.4 Epitope tagging strategy on Methylomonas sp. DH-1............ 27 3.5 Genome-scale binding profiles of SoxR........................................ 30 Chapter 4. Conclusion..................................................................................... 37 References............................................................................................................. 39 Supplements......................................................................................................... 44 국문 초록................................................................................................................ 61Maste

Ein Vergleich der Dichtung von Gottfried Benn und Hyeongdo Gi

학위논문(석사) --서울대학교 대학원 :외국어교육과(독어전공),2010.2.Maste

Development of the Wheel Loader Front Linkage Retaining High Breakout force and Small Angle Change of an attachment

학위논문 (석사)-- 서울대학교 대학원 : 기계항공공학부, 2012. 8. 김종원.휠로더의 대표적인 프런트 링키지 구조에는 지-바 타입(Z-bar type)과 패럴렐 타입(Parallel type) 두 가지 구조가 있다. 지-바 타입은 굴삭력이 매우 좋으나 작업 구간에서 작업부의 각도 변화가 심하다. 반면 패럴렐 타입의 경우 작업부의 각도 변화가 작지만, 실린더의 수축에 의하여 굴삭 작업이 이루어지기 때문에 매우 비효율적이고 굴삭력이 작다. 따라서 두 가지 타입 휠로더의 장점을 동시에 확보할 수 있는 독창적인 프런트 링키지의 개발이 필요하다. 본 논문에서는 지-바 휠로더의 굴삭력을 유지하면서 작업 전 구간에서 작업부의 각도변화가 작은 새로운 휠로더 프런트 링키지 메커니즘을 고안하였다. 또한 새로운 링키지에 대한 기구학 해석을 통해 작업구간에서 작업부의 각도변화를 도출하고, 정역학 해석을 통해 굴삭력을, 동역학 해석을 통하여 작업 구간에서 실린더에 부가되는 반력을 도출한다. 또한 이를 토대로 설계 변수인 핀 포인트의 위치를 가지치기 방식의 완결탐색방법을 통해 최적화 하여, 지-바 수준의 굴삭력을 유지하면서 작업부의 각도변화를 최소화 하였다. 그 결과 굴삭력은 12.6 ton으로 지-바 타입 수준의 굴삭력(12.7 ton)을 확보하였으며, 작업부의 각도변화는 틸팅(tilting) 시 12.5˚, 노-틸팅(no-tilting) 시 3.4˚로 지-바 타입 대비 각각 38.1 %, 91.3 % 향상되었음을 확인하였다.There are two typical type of wheel loader front linkage, Z-bar type and Parallel type. Z-bar type has a high breakout force, but a big angle change of attachment. On the other hand, parallel type has a small angle change of attachment but a low breakout force. So it is needed to develop new front linkage retaining merit of two type of wheel loader This paper presents to develop the new wheel loader front linkage simultaneously retaining a high breakout force of the Z-bar type level and a small angle change of attachment in a trajectory. Also it is presented to derive a angle change of attachment by kinematic analysis, breakout force by static analysis, and reaction force acted on cylinder by dynamic analysis. In addition, position of pin-point is optimized through branch stretching type exhaustive search method. As a result, breakout force of new front linkage is 12.6 ton that is similar to Z-bar type. Also angle change of an attachment is 12.5˚in tilting trajectory and 3.4˚in no-tilting trajectory초록 1. 서론 1.1 연구배경 및 연구동기 1.2 관련 연구 조사 1.3 연구목표 및 내용 2. 휠로더 신규 프런트 링키지 고안 3. 기구학 해석 4. 역학해석 4.1 정역학 해석을 통한 굴삭력 도출 4.2 동역학 해석을 통한 실린더 반력 도출 5. 이론해석결과의검증 5.1 기구학 해석의 검증 5.2 정역학 해석의 검증 5.2 동역학 해석의 검증 6. 핀 포인트 위치 최적 설계 6.1 핀 포인트 위치 최적화 6.2 최적화 수행 결과 7. 결론 8. 참고문헌 AbstractMaste

Development of an efficient microbial process using non-edible biomass by engineering Vibrio sp. dhg

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Lignocellulosic sugar conversion by Vibrio sp. dhg

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Vibrio-based microbial platform for accelerated lignocellulosic biomass refinery

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