전력 증폭기 효율 향상을 위한 통신 시스템에서의 신호 분해 및 편파 분할 다중화에 관한 연구

학위논문(박사) -- 서울대학교대학원 : 공과대학 전기·정보공학부, 2024. 2. 남상욱.This dissertation introduces polarization-division multiplexing (PDM) communication systems aimed at enhancing power amplifier (PA) efficiency. The proposed PDM systems undergo signal decomposition of original baseband signals, resulting in decomposed signals with Peak-to-Average Power Ratios (PAPRs) generally lower than the original signal. These signals are then separately amplified through dedicated PAs and subjected to PDM. Since each PA amplifies signals with reduced PAPR through decomposition, the overall PA efficiency in this system is enhanced. However, the transformation of the RF system introduces cross-polarization interference (XPI) resulted from PDM. PDM involves multiplexing different data into distinct polarization states. In PDM, complete separation of the multiplexed data is hindered by interference between polarization states, known as XPI. This interference leads to deteriorated error vector magnitude (EVM) at the Rx. Therefore, signal processing techniques are applied for demodulation at the Rx to mitigate EVM deterioration caused by XPI. The primary focus of this dissertation is on two modulation schemes: single carrier modulation (SCM) and orthogonal frequency division multiplexing (OFDM). Signal decomposition methods at the Tx for different modulation schemes are proposed, and corresponding Rx demodulation methods are suggested. The dissertation provides a comprehensive analysis of the proposed system's performance, presenting a reduction in total DC power consumption within the PAs while aligning the Symbol Error Rate (SER) with that of the original system. Performance analyses consider two channels: Additive White Gaussian Noise (AWGN) channel and frequency-selective Rayleigh fading channel. Additionally, a prototype operating at a 28 GHz carrier frequency is fabricated for experiments to verify the efficiency enhancement feasibility. Comparative analysis based on experimental results assesses the overall performance between the proposed and original systems. In SCM, a high-order Quadrature Amplitude Modulation (QAM) is decomposed into two asymmetric low-order QAMs, which are subjected to PDM. A technique for recovering the EVM which is deteriorated by XPI, enabled by the asymmetric decomposition, is proposed and applied. In the assumption of frequency-selective Rayleigh fading channel, the proposed system yields an average DC power reduction ratio of 54%/67%/72% (compared to original 16/64/256 QAM, respectively) when the optimized balanced scaling is applied for the two asymmetric low-order QAMs while it becomes 40%/52%/51% (compared to original 16/64/256 QAM, respectively) when balanced scaling is not applied. Furthermore, the experimental results show a DC power reduction ratio of 32.5%/43%/43.4% (compared to original 16/64/256 QAM, respectively) with no balanced scaling, while exhibiting improved SER. In OFDM, the original signal is decomposed into sub-signals with reduced effective PAPR of 5.4 and 5.9 dB based on a predefined threshold, which will be subjected to PDM. An EVM recovery technique enabled by sparsity of one of the sub-signals is proposed and filters are applied after channel equalization to mitigate noise amplification in channels with poor quality. The proposed system induces an average DC power consumption reduction of 46% in PAs compared to the original 16 QAM in the assumption of frequency-selective Rayleigh fading channel. Additionally, experimental results using a prototype demonstrate the feasibility of efficiency enhancement showing EVM performance comparable to that of the original system. In OFDM with suppressed out-of-band emission (OOBE), the original signal undergoes decomposition based on a predefined threshold, and the resulting sub-signals have significant OOBE. OOBE of them are suppressed and after that, they undergo PDM. An EVM recovery technique based on sparsity of one of the sub-signals (before the OOBE-suppression was applied) is proposed and applied. It involves solving a compressive sensing problem after a filter is applied in channel equalization to reject noise amplification at the channel with poor quality. The proposed system induces an average DC power consumption reduction of 36% in PAs compared to the original 16 QAM in the assumption of frequency-selective Rayleigh fading channel. Additionally, experimental results using a prototype demonstrate the feasibility of efficiency enhancement showing EVM performance comparable to that of the original system. Finally, the scalability of the proposed system to multiple-input and multiple-output (MIMO) is briefly addressed. In the context of MIMO scenarios, it is investigated whether replacing a portion of the RF chains connected to each Tx antenna with the proposed system and employing the suggested signal decomposition for PA DC power reduction would still yield advantages by MIMO in Tx performance.본 논문에서는 전력 증폭기의 효율을 향상시키기 위한 편파 분할 다중화 통신 시스템을 소개하고 제안한다. 제안된 편파 분할 다중화 시스템은 기존의 베이스밴드 신호를 분해하여 원신호보다 낮은 PAPR (Peak-to-Average Power Ratios)을 갖는 신호들을 생성한다. 이렇게 생성된 신호는 각기 다른 전력 증폭기를 통해 별도로 증폭되고 편파 분할 다중화를 통해 송신된다. 각 전력 증폭기가 PAPR이 감소한 신호를 증폭하기 때문에 이 시스템의 전반적인 전력 증폭기의 효율이 향상된다. 그러나 제안된 편파 분할 다중화 시스템에서는 교차 편파 간섭이 발생한다. 편파 분할 다중화 방식에서는 서로 다른 데이터를 직교하는 편파를 통해서 송신하는데, 교차 편파 간섭으로 인해 서로 다른 편파에 다중화된 데이터의 완전한 분리가 어려워진다. 이러한 교차 편파 간섭으로 수신단에서 복원한 신호의 오류 벡터 크기가 악화된다. 따라서 수신단에서는 교차 편파 간섭에 의한 오류 벡터 크기 악화를 완화하기 위해 신호 처리 기술이 적용된다. 본 논문에서는 단일 캐리어 변조와 직교 주파수 분할 다중화에 대한 전력 증폭기 효율 향상을 위한 편파 분할 다중화 통신 시스템을 제안한다. 각 변조 방식에 대한 송신단에서의 신호 분해 방법과 수신단에서의 복조 방법이 제안되었다. 제안된 시스템의 성능에 대한 분석으로서 심볼 오류율을 기존의 시스템과 일치시킨 상황에서 전력 증폭기 내의 총 DC 전력 소비 감소를 제시한다. 이러한 성능 분석은 가산 백색 가우시안 잡음 채널 및 주파수 선택적 레일리 페이딩 채널에서 진행되었다. 또한 28 GHz의 반송 주파수에서 동작하는 프로토 타입이 실험을 위해 제작되었다. 제안된 시스템과 기존의 시스템이 실험 결과를 기반으로 비교 분석되어 제안된 시스템 전반의 성능이 평가되었다. 단일 캐리어 변조의 경우 고차 직교 진폭 변조의 심볼이 두 개의 비대칭 저차 직교 진폭 변조 심볼로 분해되어 편파 분할 다중화 방식을 통해 송신된다. 비대칭 분해로 인한 교차 편파 간섭으로 악화된 오류 벡터 크기를 복구하기 위한 기법이 제안되었고 이를 적용했다. 주파수 선택적 레일리 페이딩 채널 상황에서 두 비대칭 저차 직교 진폭 변조에 최적의 전력 균형 스케일링이 적용되었을 때, 평균 DC 전력 감소 비율은 54%/67%/72%이다 (기존의 16/64/256 직교 진폭 변조 대비). 전력 균형 스케일링이 적용되지 않을 때 평균 DC 전력 감소 비율은 40%/52%/51%이다(기존의 16/64/256 직교 진폭 변조 대비). 전력 균형 스케일링이 적용되지 않은 경우에 대하여 실험이 진행되었으며 심볼 오류율이 더 낮게 측정되었고 기존의 16/64/256 직교 진폭 변조에 비해 DC 전력 감소 비율이 32.5%/43%/43.4%으로 측정되었다. 직교 주파수 분할 다중화의 경우 원신호는 특정한 임계 값을 기준으로 2개의 신호로 나누어진다. 이에 각 신호의 PAPR은 각각 5.4 dB와 5.9 dB로 개선되며 각 신호는 편파 분할 다중화 방식을 통해 송신된다. 나누어진 신호 중 하나의 희소성을 이용한 오류 벡터 크기 복구 기법이 제안되었으며, 채널 균등화 후 노이즈 증폭을 완화하기 위해 필터가 적용되었다. 주파수 선택적 레일리 페이딩 채널 상황에서, 제안된 시스템은 기존의 16 직교 진폭 변조 대비 전력 증폭기의 평균 DC 전력 감소 비율은 46%이다. 또한 실험 결과에서는 제안된 시스템과 기존의 시스템이 유사한 오류 벡터 크기 성능을 보여주며 전력 증폭기의 효율 향상의 가능성을 보여주었다. 대역 외 방사가 억제된 직교 주파수 분할 다중화의 경우 원신호가 특정한 임계 값을 기반으로 분해될 시 상당한 대역 외 방사를 가진 2개의 신호로 분해된다. 이 신호들의 대역 외 방사를 억제한 후에 해당 신호들은 편파 분할 다중화 방식을 통해 송신된다. 대역 외 방사가 억제되기 전의 한 신호는 희소성을 가지고 있으며 해당 희소성을 기반으로 한 오류 벡터 크기 복구 기법이 제안되었다. 이 기법은 압축 센싱 문제를 해결하는 것으로 설명되며, 채널 균등화시 저 품질 채널에서의 노이즈 증폭을 거부하기 위한 필터가 적용 후에 실행된다. 주파수 선택적 레일리 페이딩 채널 상황에서, 제안된 시스템은 기존의 16 직교 진폭 변조 대비 전력 증폭기의 평균 DC 전력 감소 비율은 36%이다. 또한 실험 결과에서는 제안된 시스템과 기존의 시스템이 유사한 오류 벡터 크기 성능을 보여주며 전력 증폭기의 효율 향상의 가능성을 보여주었다. 마지막으로, 제안된 시스템의 MIMO로의 확장 가능성에 대해 간단히 다루었다. MIMO 상황에서 각 송신 안테나에 연결된 일부 RF 체인을 제안된 시스템으로 교체하고 전력 증폭기의 DC 전력 감소를 위한 제안된 신호 분해를 사용했을 때 송신기 성능에 있어서 MIMO의 이점이 여전히 유효한지 확인했다.Abstract i Table of Contents v List of Figures ix List of Tables xvii Chapter 1. Introduction 1 1.1. PA Efficiency & PAPR Issue 1 1.2. Previous PAPR Reduction & Related Research 5 1.3. Proposal of PDM System 9 1.3.1. Performance Analysis (Comparison) Criterion 11 1.3.2. Performance Analysis in AWGN Channel 13 1.3.3. Performance Analysis in Frequency-Selective Rayleigh Fading Channel 14 1.3.4. Experimental Verification 16 1.4. Organization of the Dissertation 17 1.5. Notation 19 Chapter 2. System for SCM 20 2.1. Preliminary 20 2.2. System Configuration 23 2.3. Performance Analysis in AWGN Channel 33 2.3.1. DC Power Consumption at PAs 33 2.3.2. SER Equations 35 2.3.3. Comparison of the Original and Proposed Systems 38 2.4. Performance Analysis in Frequency-Selective Rayleigh Fading Channel 48 2.4.1. SER Equations 49 2.4.2. Comparison of the Original and Proposed Systems 58 2.5. Experiment 65 2.5.1. Experimental Setup 65 2.5.2. Experimental Results 69 Chapter 3. System for OFDM 73 3.1. Preliminary 73 3.2. System Configuration 75 3.3. Performance Analysis in AWGN Channel 88 3.3.1. DC Power Consumption at PAs 88 3.3.2. SER Equations 91 3.3.3. Comparison of the Original and Proposed Systems 92 3.4. Performance Analysis in Frequency-Selective Rayleigh Fading Channel 96 3.4.1. SER Equations 96 3.4.2. Comparison of the Original and Proposed Systems 98 3.5. Experiment 106 3.5.1. Experimental Setup 106 3.5.2. Experimental Results 108 Chapter 4. System for OOBE-suppressed OFDM 110 4.1. Preliminary 110 4.2. System Configuration 115 4.3. Performance Analysis in AWGN Channel 130 4.3.1. DC Power Consumption at PAs 130 4.3.2. Comparison of the Original and Proposed Systems 131 4.4. Performance Analysis in Frequency-Selective Rayleigh Fading Channel 137 4.4.1. Comparison of the Original and Proposed Systems 137 4.5. Experiment 146 4.5.1. Experimental Setup 146 4.5.2. Experimental Results 148 4.6. MIMO Compatibility 150 Chapter 5. Conclusion 155 Bibliography 159 Abstract in Korean 177 ACKNOWLEDGEMENT 180박

Calibration of Mobile Robot with Single Wheel Powered Caster

학위논문(석사) -- 서울대학교대학원 : 융합과학기술대학원 지능정보융합학과, 2022. 8. 박재흥.모바일 로봇의 제어와 오도메트리에 큰 영향을 주는 기구학적 파라미터를 보정하는 기구학적 캘리브레이션 방법은 다양한 종류의 모바일 로봇에서 연구되어왔다. 기구학적 캘리브레이션 방법은 모바일 로봇의 종류에 의존적이기 때문에 각 종류에 맞는 기구학적 캘리브레이션 방법이 필요하다. 캐스터 기반 모바일 로봇의 경우 복잡한 기구학적 형상 때문에 기구학적 파라미터가 부정확한 경우 제어 시 응력을 발생시켜 미끄러짐을 유발하기 때문에 정확한 기구학적 파라미터를 아는 것이 중요하다. 캐스터 기반 모바일 로봇을 위한 기구학적 캘리브레이션 방법은 특정 모델인 분할 캐스터에 한하여 연구가 진행되었다. 이전 연구는 캐스터 바퀴를 고정한 경우 바퀴와 바닥 사이에 회전이 일어나면 안 되기 때문에 바닥과 1점 접촉을 하는 단일 바퀴 캐스터에는 적용할 수 없다. 본 논문은 단일 바퀴 캐스터 기반 모바일 로봇의 정확한 기구학적 파라미터를 구하는 기구학적 캘리브레이션 방법을 제안한다. 제안하는 방법은 로봇에 장착된 캐스터 모듈 하나를 고정해 고정된 바퀴를 기준으로 로봇이 회전하는 경우 생기는 기하학적 관계와 로봇의 이동 정보 및 모터 엔코더 정보를 이용해 로봇의 기구학적 파라미터를 구한다. 시뮬레이션과 실제 환경에서 진행된 실험을 통해 제안하는 캘리브레이션 방법을 검증하고 이 방법이 정확한 기구학적 파라미터를 구해 오도메트리 정확도를 향상할 수 있음을 보인다.Kinematic parameters of mobile robot have a great influence on its odometry and control, so many researches were conducted to find accurate kinematic parameters of mobile robot. Since a kinematic calibration method, for finding accurate kinematic parameters, is dependent on the kinematic type of mobile robot, calibration method for certain type is hard to apply for another type. For caster type mobile robots which has complex kinematic model, kinematic parameters are important since inaccurate kinematic parameters cause internal force which results in wheel slippage, a non-systematic error. Previous study on kinematic calibration for caster type mobile robot proposed a method that can only calibrate double-wheeled caster type mobile robot and not single-wheeled caster type mobile robot. This paper proposes a kinematic calibration method for single-wheeled caster type mobile robot. Proposed method uses geometric relationship and movement information of robot and its motor when the robot rotates around its stationary caster wheel. Simulation and hardware experiments conducted in this paper validates the proposed calibration method and shows its performance.제 1 장 서론 1 제 1 절 오도메트리 오차 1 제 2 절 연구 동향 2 제 3 절 연구 기여 5 제 4 절 논문 구성 9 제 2 장 ASOC 기반 모바일 로봇의 캘리브레이션 10 제 1 절 캘리브레이션 방법 10 제 2 절 캘리브레이션 방법의 특징 11 제 3 장 SWPC 기반 모바일 로봇의 캘리브레이션 14 제 1 절 캘리브레이션 방법 14 제 2 절 캘리브레이션 방법의 특징 19 제 4 장 실험 21 제 1 절 시뮬레이션 환경 캘리브레이션 22 제 2 절 실제 환경 캘리브레이션 24 제 3 절 주행 실험 25 제 5 장 결론 33 참고 문헌 35 Abstract 39석

Word Recommendation System Using Featureless Clustering and Thesaurus

This thesis proposes a word recommendation system using information retrieval techniques. The concept of the proposed system is the opposite of the dictionary system which looks up a word with its meaning. That is, the input of the proposed system is the definition or the meaning of a word and the output of the system is the ranked words which are most proper for the meaning (input: meaning, output: word). In the proposed system, documents are definitions or meanings of words and document identifiers are words themselves, compared to information retrieval systems. In this case, the length of the documents is too short because the definitions in the dictionary is too short and then the performance of the proposed system might be degraded. To alleviate the problem, in this thesis, methods for document expansion: glossary expansion, synonym expansion, thesaurus expansion are used. The proposed system computes the similarity between expanded documents and user queries (the meanings of words) and recommends words using the several methods for document expansion. The performance (r-inclusion rate) amounts to almost 100% when the queries are meanings of words in the dictionary, and to 72.1% when the queries are meanings which users write in person. Through the several experiments, we have observed that the document expansion is very useful for the word recommendation system. In the future, new measures including the r-inclusion rate of our proposed measure are required for performance evaluation of word recommendation systems and new evaluation sets for objective assessment. Furthermore, antonyms as well as synonyms are needed for document expansion.Abstract - iv 제 1 장 서론 제 2 장 관련연구 2.1 정보 검색 2.2 질의 확장 2.3 단어 군집화 2.4 시소러스 제 3 장 단어 추천 시스템의 설계 및 구현 3.1 단어 수집 3.2 사전을 이용한 뜻풀이 확장 3.3 단어 군집화를 이용한 유의어 확장 3.4 시소러스를 이용한 확장 3.5 단어 추천 시스템 제 4 장 분석 및 성능 평가 4.1 사전 뜻풀이를 이용한 시스템 성능 평가 4.2 사용자 뜻풀이를 이용한 시스템 성능 평가 제 5 장 결론 참고 문헌 부록 #1 : 가장 낮은 성능을 보이는 사용자 뜻풀이 부록 #2 : 가장 높은 성능을 보이는 사용자 뜻풀

Performance of deep learning-based algorithm for detection of ileocolic intussusception on abdominal radiographs of young children

The purpose of this study was to develop and test the performance of a deep learning-based algorithm to detect ileocolic intussusception using abdominal radiographs of young children. For the training set, children (≤5 years old) who underwent abdominal radiograph and ultrasonography (US) for suspicion of intussusception from March 2005 to December 2017 were retrospectively included and divided into control and intussusception groups according to the US results. A YOLOv3-based algorithm was developed to recognize the rectangular area of the right abdomen and to diagnose intussusception. For the validation set, children (≤5 years old) who underwent both radiograph and US from January to August 2018 with the suspicion of intussusception were included. Diagnostic performances of an algorithm and radiologists were compared. Total 681 children including 242 children in intussusception group were included in the training set and 75 children including 25 children in intussusception group were included in the validation set. The sensitivity of the algorithm was higher compared with that of the radiologists (0.76 vs. 0.46, p = 0.013), while specificity was not different between the algorithm and the radiologists (0.96 vs. 0.92, p = 0.32). Deep learning-based algorithm can aid screening of intussusception using abdominal radiography in young children.ope

Feasibility of Using the Epidural Space Detecting Device (EPI-Detection TM) for Interlaminar Cervical Epidural Injection

Cervical epidural injection (CEI), which is widely used for the treatment of cervical radiculopathy, sometimes has been associated with post-operative complications. Recently, EPI-DetectionTM, which detects the negative pressure of the epidural space and notifies the proceduralist by flashing a light and producing a beeping sound, was introduced. We assumed that the newly developed device could be as safe and efficient as the conventional loss of resistance (LOR) method. Therefore, we aimed to evaluate the effectiveness of the EPI-DetectionTM and compare it to that of the conventional LOR method. We randomly assigned 57 patients to the LOR and EPI-Detection groups (29 and 28 patients, respectively). Subjects were treated with interlaminar CEI (ILCEI) using one of two methods. The measured parameters, i.e., operation time and radiation dose were lower in the EPI-DetectionTM group (4.6 ± 1.2 min vs. 6.9 ± 2.1 min; and 223.2 ± 206.7 mGy·cm2 vs. 380.3 ± 340.9 mGy·cm2, respectively; all p < 0.05) than in the LOR group. There were no complications noted in either group. Both the EPI-DetectionTM and LOR methods were safe and effective in detecting the epidural space, but the former was superior to the latter in terms of operation time and radiation exposure. The EPI-DetectionTM may help perform ILCEI safely.ope

Preoperative Cognitive Impairment as a Predictor of Postoperative Outcomes in Elderly Patients Undergoing Spinal Surgery for Degenerative Spinal Disease

Cognitive status has been reported to affect the peri-operative and post-operative outcomes of certain surgical procedures. This prospective study investigated the effect of preoperative cognitive impairment on the postoperative course of elderly patients (n = 122, >65 years), following spine surgery for degenerative spinal disease. Data on demographic characteristics, medical history, and blood analysis results were collected. Preoperative cognition was assessed using the mini-mental state examination, and patients were divided into three groups: normal cognition, mild cognitive impairment, and moderate-to-severe cognitive impairment. Discharge destinations (p = 0.014) and postoperative cardiopulmonary complications (p = 0.037) significantly differed based on the cognitive status. Operation time (p = 0.049), white blood cell count (p = 0.022), platelet count (p = 0.013), the mini-mental state examination score (p = 0.033), and the Beck Depression Inventory score (p = 0.041) were significantly associated with the length of hospital stay. Our investigation demonstrated that improved understanding of preoperative cognitive status may be helpful in surgical decision-making and postoperative care of elderly patients with degenerative spinal disease.ope

Balloon Bronchoplasty for the Treatment of Bronchial Stenosis After Lung Transplantation: A Single-Center 10-Year Experience

Objective: To assess the safety and efficacy of balloon dilatation under dual guidance using fluoroscopy and bronchoscopy for treating bronchial stenosis following lung transplantation (LT), and to elucidate the factors associated with patency after the procedure. Materials and Methods: From September, 2012, to April, 2021, 50 patients (mean age ± standard deviation, 54.4 ± 12.2 years) with bronchial stenosis among 361 recipients of LT were retrospectively analyzed. The safety of balloon dilatation was assessed by evaluating procedure-related complications. Efficacy was assessed by evaluating the technical success, primary patency, and secondary patency. Primary and secondary cumulative patency rates were calculated using the Kaplan-Meier method. The factors associated with patency after the procedure were evaluated using multivariable Cox hazard proportional regression analysis. Results: In total, 65 bronchi were treated with balloon dilatation in 50 patients. The total number of treatment sessions was 277 and the technical success rate was 99.3% (275/277 sessions). No major procedure-related complications were noted. During the mean follow-up period of 34.6 ± 30.8 months, primary patency was achieved in 12 of 65 bronchi (18.5%). However, the patency rate improved to 76.9% (50 of 65 bronchi) after repeated balloon dilatation (secondary patency). The 6-month, 1-year, 3-year, and 5-year secondary patency rates were 95.4%, 90.8%, 83.1%, and 78.5%, respectively. The presence of clinical symptoms was a significant prognostic factor associated with reduced primary patency (adjusted hazard ratio [HR], 0.465; 95% confidence interval [CI], 0.220–0.987). Early-stage treatment ≤ 6 months (adjusted HR, 3.588; 95% CI, 1.093– 11.780) and prolonged balloon dilatation > 5 min (adjusted HR, 3.285; 95% CI, 1.018–10.598) were associated with significantly higher secondary patency. Conclusion: Repeated balloon dilatation was determined to be safe and effective for treating bronchial stenosis following LT. Early-stage treatment and prolonged balloon dilatation could significantly promote long-term patency.ope

Surgical Strategies for Cervical Deformities Associated With Neuromuscular Disorders

Neuromuscular disorders (NMDs) are diseases involving the upper and lower motor neurons and muscles. In patients with NMDs, cervical spinal deformities are a very common issue; however, unlike thoracolumbar spinal deformities, few studies have investigated these disorders. The patients with NMDs have irregular spinal curvature caused by poor balance and poor coordination of their head, neck, and trunk. Particularly, cervical deformity occurs at younger age, and is known to show more rigid and severe curvature at high cervical levels. Muscular physiologic dynamic characteristics such as spasticity or dystonia combined with static structural factors such as curvature flexibility can result in deformity and often lead to traumatic spinal cord injury. In addition, postoperative complication rate is higher due to abnormal involuntary movement and muscle tone. Therefore, it is important to control abnormal involuntary movement perioperatively along with strong instrumentation for correction of deformity. Various methods such as botulinum toxin injection, physical therapy, muscle division technique, or intrathecal baclofen pump implant may help control abnormal involuntary movements and improve spinal stability. Surgical management for cervical deformities associated with NMDs requires a multidisciplinary effort and a customized strategy.ope