Reducing Energy Consumption of a Modem via Selective Packet Transmission Delaying

학위논문 (박사)-- 서울대학교 대학원 : 전기·컴퓨터공학부, 2017. 2. 홍성수.스마트폰을 비롯한 생활 밀착형 모바일 장치에서 모뎀이 소모하는 전력량을 줄이고자 하는 노력들이 끊임없이 경주되고 있다. 이러한 모뎀의 전력 소모량 절감 방안에 대한 연구들은 주로 패킷 전송 지연 기법에 기반한다. 패킷 전송 지연 기법이란 모바일 장치에서 지연 전송이 가능한 패킷의 전송 요청이 발생하는 경우, 해당 패킷의 전송을 지연시켰다가 이후에 전송 요청된 패킷들과 함께 한 번에 전송하는 기법이다. 이 기법은 모뎀이 여러 개의 패킷을 긴 시간에 걸쳐 산발적으로 전송하는 것에 비해서, 같은 패킷들을 짧은 시간 동안 한꺼번에 전송할 때 훨씬 적은 양의 전력을 소모하는 특성을 가지고 있다는 점에 착안하여 개발된 기법이다. 기존 연구들은 패킷 전송 지연 기법을 모바일 장치의 다양한 동작 상황에서 효과적으로 적용하는 각기 다른 방안들을 제시한다. 그러나 스마트폰과 같은 최신 모바일 장치의 복잡한 동작 환경에서 모뎀의 무선 자원 제어 상태를 치밀하게 고려하지 않고 적용하는 패킷 전송 지연 기법은 오히려 예기치 못한 추가적인 전력 소모를 야기하기도 한다. 이 문제는 기존의 모뎀 전력 소모량 절감 기법들의 효용성을 크게 해침으로써 실제 산업에 적용되기 어렵게 만든다. 본 학위논문에서는 앞서 설명한 문제를 해결하기 위해 선별적 패킷 전송 지연 기법을 제안한다. 제안하는 기법은 패킷 전송을 지연한 결과로 모뎀의 전력 소모량이 줄어들 것으로 예상될 때에만 선별적으로 패킷 전송을 지연한다. 이 기법의 핵심 골자는 패킷 전송 지연에 따른 전력량 이득 추산 모델이다. 이 모델은 모바일 장치에서 어떤 패킷의 전송 요청이 발생했을 때, 해당 시점의 모뎀의 무선 자원 제어 상태와 다음 번 패킷 전송 요청의 예상 발생 시점을 사용하여, 해당 패킷을 지연 전송하는 경우 모뎀의 전력 소모량이 어떻게 변화할지를 계산하는 모델이다. 제안하는 선별적 패킷 전송 지연 기법은 세 개의 핵심 컴포넌트들로 구성된다. 첫 번째는 지연 가능 패킷 판별기(Deferrable Packet Identifier)이다. 이 컴포넌트는 패킷 전송 요청이 발생했을 때, 해당 패킷의 전송 지연을 모바일 장치의 사용자가 인지할 수 있는지 여부를 사용하여 그 패킷의 지연 가능 여부를 판단한다. 두 번째는 패턴 기반 다음 패킷 예측기(Pattern-based Next Packet Predictor)이다. 이 컴포넌트는 사전 학습 단계와 온라인 적용 단계로 나누어 동작한다. 먼저 사전 학습 단계에서는 모바일 장치에서 수행되는 응용들의 패킷 전송 요청들을 모니터링하고, 이를 통해 각 응용의 패킷 전송 요청 패턴들을 도출한다. 이후 온라인 적용 단계에서는 도출된 패턴들을 사용하여 모바일 장치에서 다음 패킷 전송 요청이 언제 발생할지를 예측한다. 마지막 컴포넌트는 패킷 전송 시점 결정기(Packet Transmission Time Designator)이다. 이 컴포넌트는 패킷 전송 요청이 발생했을 때, 앞서 언급한 두 컴포넌트의 수행 결과와 패킷 전송 지연에 따른 전력량 이득 추산 모델을 사용하여 최종적으로 모뎀의 전력 소모량이 절감되도록 해당 패킷의 실제 전송 시점을 결정한다. 본 연구에서 제안한 기법의 효용성을 검증하기 위해서 실제 이동통신 네트워크망에 연결된 상용 스마트폰을 사용하여 다양한 실험을 수행하였다. 구체적으로, KT의 4세대 LTE 네트워크 망에 연결된 Google Nexus 5 스마트폰에 앞서 설명한 세 가지 핵심 컴포넌트들을 구현하고 실험적으로 모뎀의 전력 소모량 절감 효과를 평가하였다. 실험 결과, 제안된 기법을 적용함으로써 모뎀의 전력 소모량이 최대 22.5% 줄어드는 것을 확인하였다. 이러한 결과는 본 논문에서 제안하는 패킷 전송 지연에 따른 전력량 이득 추산 모델과 이를 활용한 선별적 패킷 전송 지연 기법이 최신 모바일 장치에 탑재된 모뎀의 전력 소모량을 줄이는 실용적이고 효과적인 수단임을 보여준다.1. 서론 1 1.1 연구 동기 3 1.2 연구 내용 5 1.3 논문 구성 9 2. 배경 지식과 관련 연구 10 2.1 무선 자원 제어 프로토콜과 비연속적 수신 기법 10 2.2 모뎀의 전력 소모량 절감 기법 19 2.1.1 Tail 시간의 빠른 종료 24 2.2.2 Tail 시간들의 중첩 28 3. 문제 설명과 해결 방안 개관 33 3.1 시스템 모델 33 3.2 문제 설명 39 3.3 해결 방안 개관 45 4. 선별적 패킷 전송 지연 기법 50 4.1 지연 가능 패킷의 판별 50 4.2 모바일 장치의 다음 패킷 전송 요청 시점 예측 53 4.2.1 패킷 전송 요청 그룹의 생성 53 4.2.2 패턴 검출 57 4.2.3 다음 패킷 전송 요청 시점의 예측 63 4.3 예상 전력 이득에 기반한 패킷 전송 시점의 결정 66 5. 구현과 실험적 평가 78 5.1 선별적 패킷 전송 지연 기법의 구현 78 5.2 실험 설정 89 5.3 실험 결과 92 5.4 분석적 평가 99 6. 결론 104 참고 문헌 107 Abstract 115Docto

Satellite technology : reinforcement of computer data transmission technology : implications for the maritime world communications, data transfer and maritime education

This dissertation is a study of the impact of data transmission via satellite on the maritime world of communication, data transfer and education. The aim of the study is to understand the technological reinforcement of the maritime industry and the changes taking place in it. With the avalanche of changes that are taking place in the field of information technology, they can be used to facilitate the shipping industry. This dissertation assists in understanding some of the technological evolution of satellite technology and data communication and in the needs of the maritime industry as well. This dissertation describes satellite technology and data communication and analyses the data communication software (protocols), compression software, and other application software combinations with maritime communication system provided to improve ship operation and management for safety. The conclusion and recommendations chapter examines the implications of the technology changes on developing countries, the need to be harmonised in training and education for the maritime industry, maritime communication systems and the equipment, policy of shipping companies and communication costs

Smart grid

Tese de mestrado integrado em Engenharia da Energia e do Ambiente, apresentada à Universidade de Lisboa, através da Faculdade de Ciências, 2016The SG concept arises from the fact that there is an increase in global energy consumption. One of the factors delaying an energetic paradigm change worldwide is the electric grids. Even though there is no specific definition for the SG concept there are several characteristics that describe it. Those features represent several advantages relating to reliability and efficiency. The most important one is the two way flow of energy and information between utilities and consumers. The infrastructures in standard grids and the SG can classified the same way but the second one has several components contributing for monitoring and management improvement. The SG’s management system allows peak reduction, using several techniques underlining many advantages like controlling costs and emissions. Furthermore, it presents a new concept called demand response that allows consumers to play an important role in the electric systems. This factor brings benefits for utilities, consumers and the whole grid but it increases problems in security and that is why the SG relies in a good protection system. There are many schemes and components to create it. The MG can be considered has an electric grid in small scale which can connect to the whole grid. To implement a MG it is necessary economic and technical studies. For that, software like HOMER can be used. However, the economic study can be complex because there are factors that are difficult to evaluate beyond energy selling. On top of that, there are legislation and incentive programs that should be considered. Two case studies prove that MG can be profitable. In the first study, recurring to HOMER, and a scenario with energy selling only, it was obtained a 106% reduction on production cost and 32% in emissions. The installer would have an $8 000 000 profit in the MG’s lifetime. In the second case, it was considered economic services related to peak load reduction, reliability, emission reduction and power quality. The DNO had a profit of$41,386, the MG owner had $29,319 profit and the consumers had a$196,125 profit. We can conclude that the MG with SG concepts can be profitable in many cases

Unified Framework for Multicarrier and Multiple Access based on Generalized Frequency Division Multiplexing

The advancements in wireless communications are the key-enablers of new applications with stringent requirements in low-latency, ultra-reliability, high data rate, high mobility, and massive connectivity. Diverse types of devices, ranging from tiny sensors to vehicles, with different capabilities need to be connected under various channel conditions. Thus, modern connectivity and network techniques at all layers are essential to overcome these challenges. In particular, the physical layer (PHY) transmission is required to achieve certain link reliability, data rate, and latency. In modern digital communications systems, the transmission is performed by means of a digital signal processing module that derives analog hardware. The performance of the analog part is influenced by the quality of the hardware and the baseband signal denoted as waveform. In most of the modern systems such as fifth generation (5G) and WiFi, orthogonal frequency division multiplexing (OFDM) is adopted as a favorite waveform due to its low-complexity advantages in terms of signal processing. However, OFDM requires strict requirements on hardware quality. Many devices are equipped with simplified analog hardware to reduce the cost. In this case, OFDM does not work properly as a result of its high peak-to-average power ratio (PAPR) and sensitivity to synchronization errors. To tackle these problems, many waveforms design have been recently proposed in the literature. Some of these designs are modified versions of OFDM or based on conventional single subcarrier. Moreover, multicarrier frameworks, such as generalized frequency division multiplexing (GFDM), have been proposed to realize varieties of conventional waveforms. Furthermore, recent studies show the potential of using non-conventional waveforms for increasing the link reliability with affordable complexity. Based on that, flexible waveforms and transmission techniques are necessary to adapt the system for different hardware and channel constraints in order to fulfill the applications requirements while optimizing the resources. The objective of this thesis is to provide a holistic view of waveforms and the related multiple access (MA) techniques to enable efficient study and evaluation of different approaches. First, the wireless communications system is reviewed with specific focus on the impact of hardware impairments and the wireless channel on the waveform design. Then, generalized model of waveforms and MA are presented highlighting various special cases. Finally, this work introduces low-complexity architectures for hardware implementation of flexible waveforms. Integrating such designs with software-defined radio (SDR) contributes to the development of practical real-time flexible PHY.:1 Introduction 1.1 Baseband transmission model 1.2 History of multicarrier systems 1.3 The state-of-the-art waveforms 1.4 Prior works related to GFDM 1.5 Objective and contributions 2 Fundamentals of Wireless Communications 2.1 Wireless communications system 2.2 RF transceiver 2.2.1 Digital-analogue conversion 2.2.2 QAM modulation 2.2.3 Effective channel 2.2.4 Hardware impairments 2.3 Waveform aspects 2.3.1 Single-carrier waveform 2.3.2 Multicarrier waveform 2.3.3 MIMO-Waveforms 2.3.4 Waveform performance metrics 2.4 Wireless Channel 2.4.1 Line-of-sight propagation 2.4.2 Multi path and fading process 2.4.3 General baseband statistical channel model 2.4.4 MIMO channel 2.5 Summary 3 Generic Block-based Waveforms 3.1 Block-based waveform formulation 3.1.1 Variable-rate multicarrier 3.1.2 General block-based multicarrier model 3.2 Waveform processing techniques 3.2.1 Linear and circular filtering 3.2.2 Windowing 3.3 Structured representation 3.3.1 Modulator 3.3.2 Demodulator 3.3.3 MIMO Waveform processing 3.4 Detection 3.4.1 Maximum-likelihood detection 3.4.2 Linear detection 3.4.3 Iterative Detection 3.4.4 Numerical example and insights 3.5 Summary 4 Generic Multiple Access Schemes 57 4.1 Basic multiple access and multiplexing schemes 4.1.1 Infrastructure network system model 4.1.2 Duplex schemes 4.1.3 Common multiplexing and multiple access schemes 4.2 General multicarrier-based multiple access 4.2.1 Design with fixed set of pulses 4.2.2 Computational model 4.2.3 Asynchronous multiple access 4.3 Summary 5 Time-Frequency Analyses of Multicarrier 5.1 General time-frequency representation 5.1.1 Block representation 5.1.2 Relation to Zak transform 5.2 Time-frequency spreading 5.3 Time-frequency block in LTV channel 5.3.1 Subcarrier and subsymbol numerology 5.3.2 Processing based on the time-domain signal 5.3.3 Processing based on the frequency-domain signal 5.3.4 Unified signal model 5.4 summary 6 Generalized waveforms based on time-frequency shifts 6.1 General time-frequency shift 6.1.1 Time-frequency shift design 6.1.2 Relation between the shifted pulses 6.2 Time-frequency shift in Gabor frame 6.2.1 Conventional GFDM 6.3 GFDM modulation 6.3.1 Filter bank representation 6.3.2 Block representation 6.3.3 GFDM matrix structure 6.3.4 GFDM demodulator 6.3.5 Alternative interpretation of GFDM 6.3.6 Orthogonal modulation and GFDM spreading 6.4 Summary 7 Modulation Framework: Architectures and Applications 7.1 Modem architectures 7.1.1 General modulation matrix structure 7.1.2 Run-time flexibility 7.1.3 Generic GFDM-based architecture 7.1.4 Flexible parallel multiplications architecture 7.1.5 MIMO waveform architecture 7.2 Extended GFDM framework 7.2.1 Architectures complexity and flexibility analysis 7.2.2 Number of multiplications 7.2.3 Hardware analysis 7.3 Applications of the extended GFDM framework 7.3.1 Generalized FDMA 7.3.2 Enchantment of OFDM system 7.4 Summary 7 Conclusions and Future work

On Providing Energy-efficient Data Transmission to Mobile Devices

The transformation from telephony to mobile Internet has fundamentally changed the way we interact with the world by delivering ubiquitous Internet access and reasonable cost of connectivity. The mobile networks and Internet services are supportive of each other and together drive a fast development of new services and the whole ecosystem. As a result, the number of mobile subscribers has skyrocketed to a magnitude of billions, and the volume of mobile traffic has boomed up to a scale no-one has seen before with exponential growth predictions. However, the opportunities and problems are both rising. Therefore, to enable sustainable growth of the mobile Internet and continued mobile service adaption, this thesis proposes solutions to ensure that the reduction of overall environmental presence and the level of QoE are mutually addressed by providing energy-efficient data transmission to mobile devices. It is important to understand the characteristics of power consumption of mobile data transmission to find opportunities to balance the energy consumption and the growth of mobile services and the data volumes. This research started with power consumption measurements of various radio interfaces and investigations of the trade-off between computation and communication of modern mobile devices. Power consumption models, state machines and the conditions for energy-efficient mobile data transmission were proposed to guide the development of energy-saving solutions. This research has then employed the defined guideline to optimise data transmission for energy-efficient mobile web access. Proxy-based solutions are presented in this thesis, utilising several strategies: bundling-enabled traffic shaping to optimise TCP behaviour over congested wireless links and keep the radio interface in low power consumption states as much as possible, offloading HTTP-object fetching to shorten the time of DNS lookups and web content downloading, and applying selective compression on HTTP payload to further reduce energy consumption of mobile data transmission. As a result, the solutions dramatically reduce the energy consumption of mobile web access and download time, yet maintain or even increase user experience