Tiny Codes for Guaranteeable Delay

Future 5G systems will need to support ultra-reliable low-latency communications scenarios. From a latency-reliability viewpoint, it is inefficient to rely on average utility-based system design. Therefore, we introduce the notion of guaranteeable delay which is the average delay plus three standard deviations of the mean. We investigate the trade-off between guaranteeable delay and throughput for point-to-point wireless erasure links with unreliable and delayed feedback, by bringing together signal flow techniques to the area of coding. We use tiny codes, i.e. sliding window by coding with just 2 packets, and design three variations of selective-repeat ARQ protocols, by building on the baseline scheme, i.e. uncoded ARQ, developed by Ausavapattanakun and Nosratinia: (i) Hybrid ARQ with soft combining at the receiver; (ii) cumulative feedback-based ARQ without rate adaptation; and (iii) Coded ARQ with rate adaptation based on the cumulative feedback. Contrasting the performance of these protocols with uncoded ARQ, we demonstrate that HARQ performs only slightly better, cumulative feedback-based ARQ does not provide significant throughput while it has better average delay, and Coded ARQ can provide gains up to about 40% in terms of throughput. Coded ARQ also provides delay guarantees, and is robust to various challenges such as imperfect and delayed feedback, burst erasures, and round-trip time fluctuations. This feature may be preferable for meeting the strict end-to-end latency and reliability requirements of future use cases of ultra-reliable low-latency communications in 5G, such as mission-critical communications and industrial control for critical control messaging.Comment: to appear in IEEE JSAC Special Issue on URLLC in Wireless Network

Explainable expert systems: A research program in information processing

Our work in Explainable Expert Systems (EES) had two goals: to extend and enhance the range of explanations that expert systems can offer, and to ease their maintenance and evolution. As suggested in our proposal, these goals are complementary because they place similar demands on the underlying architecture of the expert system: they both require the knowledge contained in a system to be explicitly represented, in a high-level declarative language and in a modular fashion. With these two goals in mind, the Explainable Expert Systems (EES) framework was designed to remedy limitations to explainability and evolvability that stem from related fundamental flaws in the underlying architecture of current expert systems

Programming Language Tools and Techniques for 3D Printing

We propose a research agenda to investigate programming language techniques for improving affordable, end-user desktop manufacturing processes such as 3D printing. Our goal is to adapt programming languages tools and extend the decades of research in industrial, high-end CAD/CAM in order to help make affordable desktop manufacturing processes more accurate, fast, reliable, and accessible to end-users. We focus on three major areas where 3D printing can benefit from programming language tools: design synthesis, optimizing compilation, and runtime monitoring. We present preliminary results on synthesizing editable CAD models from difficult-to-edit surface meshes, discuss potential new compilation strategies, and propose runtime monitoring techniques. We conclude by discussing additional near-future directions we intend to pursue

무선 통신 네트워크 환경에서의 효과적인 비디오 스트리밍 기법 연구

학위논문 (박사)-- 서울대학교 대학원 : 전기정보공학부, 2013. 8. 최성현.오늘날 무선 네트워크 통신 기술의 발달로 인해 고품질의 비디오 스트리밍 서비스에 대한 요구가 급증하고 있다. 새로운 60~GHz 광대역 고속 무선 통신 기술은 기존의 무선 통신 기술에서는 불가능했던, 고품질의 무압축 비디오 스트리밍을 가능하게 한다. 제한된 무선 자원 환경에서 고품질의 비디오 서비스를 지원하기 위해 주어진 채널 환경에서 적절한 변조 및 코딩 기술을 선택하는 효율적인 링크 적응 기법이 필요하다. 비디오 스트리밍의 품질을 수치로 평가하는 ePSNR을 정의하고, 불평등 오류 보호 기법(UEP)을 추가로 도입하여 보다 세밀한 링크 적응 기법을 가능케 한다. 정의한 ePSNR을 기반으로 (1) 주어진 무선 자원에서 비디오 품질을 최대화, 혹은 (2) 목표 비디오 품질을 만족하는 무선 자원 사용을 최소화, 하는 두가지 링크 적응 기법들을 제안한다. 다양한 시뮬레이션 결과를 통해, 정의한 ePSNR이 비디오 품질을 잘 표현하고 있음을 확인하였다. 또한, 제안한 링크 적응 기법들이 비디오 스트리밍 서비스를 위한 적절한 품질을 제공하면서, 동시에 자원 효율성을 향상시킴을 검증하였다. 한편, 순방향 오류 정정 기법(FEC)은 무선랜 환경에서 고품질의 신뢰성있는 비디오 멀티캐스트를 지원한다. 무선랜 환경에서 복수개의 액세스포인트(AP)간의 조정을 통한 신뢰성있는 비디오 멀티캐스트 기법을 제시한다. 복수개의 AP간의 조정을 통해 각각의 AP들이 (1) 완전히 서로 다른, 혹은 (2) 부분적으로 서로 다른, 인코딩된 패킷들을 전송하게 하여, 공간 및 시간적 다양성을 멀티캐스트 유저에게 제공할 수 있다. 추가로, 제한된 무선 자원을 보다 효율적으로 사용하기 위해, 순방향 오류 정정 기법의 코딩 비율 적응 기법을 위한 자원 할당 알고리즘을 제안한다. 또한, FEC 디코딩 후의 비디오 패킷의 전송율를 예측할 수 있는 방법을 제안한다. 다양한 시뮬레이션과 실험을 통해 제안한 기법들의 우수성을 확인하였다. 멀티캐스트 전송은 기본적으로 무선 채널 오류로 인해 전송 실패가 발생할 가능성을 내포한다. 그러나 기존의 무선랜 표준에서는 멀티캐스트 환경에서 자동 반복 요청 기법(ARQ)을 통한 손실 조정 방법을 제공하지 않았다. 멀티캐스트 전송의 비신뢰성 문제를 해결하기 위해, 자동 반복 요청 기법(ARQ)과 순방향 오류 정정 기법(FEC)를 함께 고려한 신뢰성 있는 멀티캐스트 전송 기법을 제안한다. 신뢰성 있는 멀티캐스트 전송을 위한 피드백 교환의 오버헤드를 줄이기 위한 복수개의 효율적인 피드백 기법을 제시한다. 제안한 피드백 기법은 액세스포인트(AP)가 멀티캐스트 유저들의 손실된 패킷들의 복원을 위해 필요한 패리티(parity) 패킷의 개수를 쉽게 알 수 있도록 한다. 피드백 간의 충돌을 감안한 의도적인 동시 전송을 통해 피드백 오버헤드를 감소시킬 수 있다. 추가로, 효율적인 피드백 프로토콜을 활용하여, 변조 및 코딩 기법(MCS)의 폐쇄적 피드백 기반의 물리 전송 속도 적응 기법을 제안한다. 성능 검증을 통해 제안한 기법들이 효율적으로 피드백 오버헤드를 감소시키며, 동시에 신뢰성있는 멀티캐스트 전송을 보장함을 검증하였다.Today, along with the rapid growth of the network performance, the demand for high-quality video streaming services has greatly increased. The emerging 60 GHz multi-Gbps wireless technology enables the streaming of high-quality uncompressed video, which was not possible with other existing wireless technologies. To support such high quality video with limited wireless resources, an efficient link adaptation policy, which selects the proper Modulation and Coding Scheme (MCS) for a given channel environment, is essential. We introduce a new metric, called expected Peak Signal-to-Noise Ratio (ePSNR), to numerically estimate the video streaming quality, and additionally adopt Unequal Error Protection (UEP) schemes that enable flexible link adaptation. Using the ePSNR as a criterion, we propose two link adaptation policies with different objectives. The proposed link adaptation policies attempt to (1) maximize the video quality for given wireless resources, or (2) minimize the required wireless resources while meeting the video quality. Our extensive simulation results demonstrate that the introduced variable, i.e., ePSNR, well represents the level of video quality. It is also shown that the proposed link adaptation policies can enhance the resource efficiency while achieving acceptable quality of the video streaming. Meanwhile, Forward Error Correction (FEC) can be exploited to realize reliable video multicast over Wi-Fi with high video quality. We propose reliable video multicast over Wi-Fi networks with coordinated multiple Access Points (APs) to enhance video quality. By coordinating multiple APs, each AP can transmit (1) entirely different or (2) partially different FEC-encoded packets so that a multicast receiver can benefit from both spatial and time diversities. The proposed scheme can enlarge the satisfactory video multicast region by exploiting the multi-AP diversity, thus serving more multicast receivers located at cell edge with satisfactory video quality. We propose a resource-allocation algorithm for FEC code rate adaptation, utilizing the limited wireless resource more efficiently while enhancing video quality. We also introduce the method for estimating the video packet delivery ratio after FEC decoding. The effectiveness of the proposed schemes is evaluated via extensive simulation and experimentation. The proposed schemes are observed to enhance the ratio of satisfied users by up to 37.1% compared with the conventional single AP multicast scheme. The multicast transmission is inherently unreliable due to the transmission failures caused by wireless channel errors, however, the error control with Automatic Repeat reQuest (ARQ) is not provided for the multicast transmission in legacy IEEE 802.11 standard. To overcome the unreliability of multicast transmission, finally, we propose the reliable multicast protocols considering both ARQ and packet-level FEC together. For the proposed reliable multicast protocol, to reduce the overheads of feedback messages while providing the reliable multicast service, the multiple efficient feedback protocols, i.e., Idle-time-based feedback, Slot-based feedback, Flash-based feedback, and Busy-time-based feedback, are proposed. The proposed feedback protocols let the AP know easily the number of requiring parity frames of the worst user(s) for the recovery of the lost packets. The feedback overheads can be reduced by intending the concurrent transmissions, which makes the collisions, between feedback messages. In addition, utilizing the efficient feedback protocols, we propose the PHY rate adaptation based on the close-loop MCS feedback in multicast transmissions. From the performance evaluations, the proposed protocols can efficiently reduce the feedback overheads, while the reliable multicast transmissions are guaranteed.1 Introduction 1 1.1 Video Streaming over Wireless Networks 1 1.1.1 Uncompressed Video Streaming over 60 GHz band 2 1.1.2 Video Multicast over IEEE 802.11 WLAN 3 1.2 Overview of Existing Approaches 5 1.2.1 Link Adaptation over Wireless Networks 5 1.2.2 Video Streaming over IEEE 802.11 WLAN 6 1.2.3 Reliable Multicast over IEEE 802.11 WLAN 8 1.3 Main Contributions 9 1.4 Organization of the Dissertation 11 2 Link Adaptation for High-Quality Uncompressed Video Streaming in 60 GHz Wireless Networks 12 2.1 Introduction 12 2.2 ECMA-387 and Wireless HDMI 17 2.2.1 ECMA-387 18 2.2.2 Wireless HDMI (HDMI PAL) 21 2.2.3 UEP Operations 22 2.2.4 ACK Transmissions for Video Streaming 23 2.2.5 Latency of Compressed and Uncompressed Video Streaming 24 2.3 ePSNR-Based Link Adaptation Policies 25 2.3.1 ePSNR 28 2.3.2 PSNR-based Link Adaptation 30 2.4 Performance Evaluation 33 2.4.1 Evaluation of ePSNR 34 2.4.2 Performance of Link Adaptation 40 2.5 Summary 45 3 Reliable Video Multicast over Wi-Fi Networks with Coordinated Multiple APs 47 3.1 Introduction 47 3.2 System Environments 50 3.2.1 Time-Slotted Multicast 50 3.2.2 FEC Coding Schemes 52 3.3 Reliable Video Multicast with Coordinated Multiple APs 52 3.3.1 Proposed Video Multicast 52 3.3.2 Video Multicast Procedure 55 3.4 FEC Code Rate Adaptation 58 3.4.1 Estimation of Delivery Ratio 59 3.4.2 Greedy FEC Code Rate Adaptation 61 3.5 Performance Evaluation 63 3.5.1 Raptor Code Performance 64 3.5.2 Simulation Results: No Fading 66 3.5.3 Simulation Results: Fading Channel 69 3.5.4 Simulation Results: Code Rate Adaptation 70 3.5.5 Experimental Results 74 3.5.6 Prototype Implementation 76 3.6 Summary 79 4 Reliable Video Multicast with Efficient Feedback over Wi-Fi 81 4.1 Introduction 81 4.2 Motivation 85 4.3 Proposed Feedback Protocols for Reliable Multicast 87 4.3.1 Idle-time-based Feedback 88 4.3.2 Slot-based Feedback 89 4.3.3 Flash-based Feedback 91 4.3.4 Busy-time-based Feedback 92 4.4 PHY Rate Adaptation in Multicast Transmission 93 4.5 Performance Evaluation 96 4.5.1 Performance evaluation considering feedback error 104 4.6 Summary 109 5 Conclusion and Future Work 110 5.1 Research Contributions 110 5.2 Future Research Directions 111 Abstract (In Korean) 121Docto