Network-Coded Multiple Access

This paper proposes and experimentally demonstrates a first wireless local area network (WLAN) system that jointly exploits physical-layer network coding (PNC) and multiuser decoding (MUD) to boost system throughput. We refer to this multiple access mode as Network-Coded Multiple Access (NCMA). Prior studies on PNC mostly focused on relay networks. NCMA is the first realized multiple access scheme that establishes the usefulness of PNC in a non-relay setting. NCMA allows multiple nodes to transmit simultaneously to the access point (AP) to boost throughput. In the non-relay setting, when two nodes A and B transmit to the AP simultaneously, the AP aims to obtain both packet A and packet B rather than their network-coded packet. An interesting question is whether network coding, specifically PNC which extracts packet (A XOR B), can still be useful in such a setting. We provide an affirmative answer to this question with a novel two-layer decoding approach amenable to real-time implementation. Our USRP prototype indicates that NCMA can boost throughput by 100% in the medium-high SNR regime (>=10dB). We believe further throughput enhancement is possible by allowing more than two users to transmit together

Energy Efficiency in Communications and Networks

The topic of "Energy Efficiency in Communications and Networks" attracts growing attention due to economical and environmental reasons. The amount of power consumed by information and communication technologies (ICT) is rapidly increasing, as well as the energy bill of service providers. According to a number of studies, ICT alone is responsible for a percentage which varies from 2% to 10% of the world power consumption. Thus, driving rising cost and sustainability concerns about the energy footprint of the IT infrastructure. Energy-efficiency is an aspect that until recently was only considered for battery driven devices. Today we see energy-efficiency becoming a pervasive issue that will need to be considered in all technology areas from device technology to systems management. This book is seeking to provide a compilation of novel research contributions on hardware design, architectures, protocols and algorithms that will improve the energy efficiency of communication devices and networks and lead to a more energy proportional technology infrastructure

Recent Advances in Wireless Communications and Networks

This book focuses on the current hottest issues from the lowest layers to the upper layers of wireless communication networks and provides "real-time" research progress on these issues. The authors have made every effort to systematically organize the information on these topics to make it easily accessible to readers of any level. This book also maintains the balance between current research results and their theoretical support. In this book, a variety of novel techniques in wireless communications and networks are investigated. The authors attempt to present these topics in detail. Insightful and reader-friendly descriptions are presented to nourish readers of any level, from practicing and knowledgeable communication engineers to beginning or professional researchers. All interested readers can easily find noteworthy materials in much greater detail than in previous publications and in the references cited in these chapters

MAC/PHY Co-Design of CSMA Wireless Networks Using Software Radios.

In the past decade, CSMA-based protocols have spawned numerous network standards (e.g., the WiFi family), and played a key role in improving the ubiquity of wireless networks. However, the rapid evolution of CSMA brings unprecedented challenges, especially the coexistence of different network architectures and communications devices. Meanwhile, many intrinsic limitations of CSMA have been the main obstacle to the performance of its derivatives, such as ZigBee, WiFi, and mesh networks. Most of these problems are observed to root in the abstract interface of the CSMA MAC and PHY layers --- the MAC simply abstracts the advancement of PHY technologies as a change of data rate. Hence, the benefits of new PHY technologies are either not fully exploited, or they even may harm the performance of existing network protocols due to poor interoperability. In this dissertation, we show that a joint design of the MAC/PHY layers can achieve a substantially higher level of capacity, interoperability and energy efficiency than the weakly coupled MAC/PHY design in the current CSMA wireless networks. In the proposed MAC/PHY co-design, the PHY layer exposes more states and capabilities to the MAC, and the MAC performs intelligent adaptation to and control over the PHY layer. We leverage the reconfigurability of software radios to design smart signal processing algorithms that meet the challenge of making PHY capabilities usable by the MAC layer. With the approach of MAC/PHY co-design, we have revisited the primitive operations of CSMA (collision avoidance, carrier signaling, carrier sensing, spectrum access and transmitter cooperation), and overcome its limitations in relay and broadcast applications, coexistence of heterogeneous networks, energy efficiency, coexistence of different spectrum widths, and scalability for MIMO networks. We have validated the feasibility and performance of our design using extensive analysis, simulation and testbed implementation.PHDComputer Science & EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/95944/1/xyzhang_1.pd

고밀도 무선랜 동시 전송 향상 기법

학위논문 (박사)-- 서울대학교 대학원 공과대학 전기·컴퓨터공학부, 2017. 8. 최성현.무선 통신에 대한 수요가 증가함에 따라, Wi-Fi로 흔히 알려진 IEEE 802.11 표준 기반 무선랜(WLAN, Wireless Local Area Network)은 어디에서나 찾아볼 수 있는 기술로 거듭났다. 이로 인해 무선랜의 고밀화, 즉 공간적으로 인접한 많은 AP(Access Point)와 STA(station)들이 동일한 주파수 채널을 사용하며 이로 인해 한 단말이 얻을 수 있는 성능이 제한되는 현상이 두드러지고 있다. 따라서 이러한 고밀도 무선랜 환경에서는 단일 전송에 대한 스펙트럼 효율 뿐만 아니라 주파수 자원의 공간 재사용(spatial reuse)의 중요성 또한 강조된다. 즉, 특정 공간 내에서 얼마나 많은 동시 전송이 가능한지가 중요한 이슈로 자리매김하고 있다. 본 학위논문에서는 고밀도 무선랜 환경에서 더 많은 동시 전송을 성공시키기 위하여 다음과 같은 세 가지 전략을 고려한다. (i) 매체접근제어(MAC, Medium Access Control) 계층의 ACK(Acknowledgment) 및 CTS(Clear-To-Send) 프레임에 대한 송신 전력 제어, (ii) 반송파 감지 임계값(CST, Carrier-Sense Threshold) 적응, (iii) 동시 송신 및 수신 (STR, Simultaneous Transmit and Receiver), 즉 동일대역 전이중 통신(in-band full duplex). 첫번째로, 본 학위 논문에서는 데이터 프레임에 의한 동일 채널 간섭(CCI, Co-Channel Interference)보다 덜 조명되어 왔던 MAC ACK 프레임에 의해 발생하는 CCI에 주목한다. 확률적 기하 분석(stochastic geometry analysis)을 기반으로 ACK 프레임의 송신 전력 조절의 필요성을 확인하였으며, 이를 바탕으로 동적 ACK 프레임 송신 전력 제어 알고리즘인 Quiet ACK(QACK)을 제안한다. QACK은 데이터 프레임 수신 중 수행되는 CCI 검출 및 CCI 전력 추정 기법과 ACK 프레임 전송 통계를 활용하여 세밀하고 신속하게 ACK 프레임의 송신 전력을 조절한다. 더불어, QACK을 바탕으로 CTS 프레임 송신 전력을 조절하여 더 많은 동시 전송이 시도될 수 있게 하는 Quiet CTS(QCTS)라는 알고리즘 또한 제안한다. QACK의 실현 가능성과 성능은 SDR(Software-Defined Radio) 기반 프로토타입을 통해 검증하며 기존 방식 대비 약 1.5배 높은 수율을 얻을 수 있음을 확인한다. 보다 일반적인 무선랜 환경에서의 QACK 및 QCTS의 성능은 ns-3를 사용한 다양한 시뮬레이션을 통해 평가한다. 다음으로, 동시에 더 많은 동시 전송이 시도될 수 있도록 간섭원(interferer node)과 목적 노드(destination node)에 따라 CST를 제어하는 ​​CST 적응 방법, FACT(Fine-grained Adaptation of Carrier-sense Threshold)를 제안한다. 제안하는 방법은 무선랜 표준에서 이미 정의되어 있는 기능을 사용하므로 상용 무선랜 기기에서 쉽게 구현할 수 있다. 또한 FACT 및 다른 CST 적응 기법과 함께 동작할 수 있는 CCA(Clear Channel Assessment) 오버헤드 감소 기법을 제안하며, 제안한 기법들의 성능을 ns-3 시뮬레이션을 통해 비교평가한다. 시뮬레이션 결과를 통해 제안한 방법이 기존 방법에 비해 네트워크 전체 수율을 큰 폭으로 향상시킬 수 있음을 확인한다. 마지막으로, 무선랜에서 STR을 가능하게하는 새로운 MAC 프로토콜, 즉 MASTaR(MAC Protocol for Access points in Simultaneous Transmit and Receive mode)를 기존 무선랜 표준을 준수하는 방법으로 제안한다. 또한 MASTaR 동작을 위해 필요한 물리계층에서 디지털 자가 간섭 상쇄(SIC, Self-Interference Cancellation) 전략을 제안하며 그 실현 가능성과 성능을 3차원 광선 추적(3D-ray tracing) 기반 시뮬레이션을 통해 다양한 측면에서 평가한다. 시뮬레이션 결과는 현재 무선랜 MAC 프로토콜보다 최대 2.58배 높은 수율이 MASTaR를 통해 얻어질 수 있음을 보인다. 요약하면, 본 학위논문에서는 ACK 및 CTS 프레임의 송신 전력 제어 알고리즘과 CST 적응 및 STR을 위한 프로토콜을 제안한다. 제안한 알고리즘 및 프로토콜의 실현 가능성과 성능은 수치 해석, 3차원 광선 추적, ns-3 기반 시스템 수준(system-level) 시뮬레이션, SDR 기반 프로토타입 등 다양한 방법론을 통해 입증한다.With increasing demand for wireless connectivity, IEEE 802.11 wireless local area network (WLAN), a.k.a. Wi-Fi, has become ubiquitous and continues to grow in number. This leads to the high density of WLAN, where many access points (APs) and client stations (STAs) operate on the same frequency channel. In a densely deployed WLAN, greater emphasis is placed on the importance of spatial reuse as well as spectral efficiency. In other words, it is of particular importance how many simultaneous transmissions are possible in a given area. In this dissertation, we consider the following three strategies to increase the number of successful simultaneous transmissions: (i) Transmit power control for medium access control (MAC) acknowledgment (ACK) and clear-to-send (CTS) frames, (ii) carrier sense threshold (CST) adaptation, and (iii) simultaneous transmit and receive (STR), i.e., in-band full-duplex communication. First, this dissertation sheds light on the co-channel interference (CCI) caused by 802.11 MAC ACK frames, which has been less studied than the CCI caused by data frames. Based on stochastic geometry analysis, we propose Quiet ACK (QACK), a dynamic transmit power control algorithm for ACK frames. Fine-grained transmit power adjustment is enabled by CCI detection and CCI power estimation in the middle of a data frame reception. A power control algorithm for clear-to-send (CTS) frame transmission, namely Quiet CTS (QCTS) is also proposed based on QACK. Our prototype using software-defined radio shows the feasibility and performance gain of QACK, i.e., 1.5X higher throughput than the legacy 802.11 WLAN. The performance of QACK and QCTS is further evaluated in more general WLAN environments via extensive simulations using ns-3. Second, a fine-grained CST adaptation method, which controls CST depending on both interferer and destination nodes, is proposed to improve spatial reuse in WLAN. The proposed method utilizes pre-defined functions in the WLAN standard, thus making itself easily implementable in commercial WLAN devices. Supplementary clear channel assessment (CCA) method is also proposed to further enhance network performance by reducing CCA overhead. The performance of the proposed methods is comparatively evaluated via ns-3 simulation. Simulation results show that the proposed methods significantly improve network throughput compared with the legacy method. Finally, a novel MAC protocol that enables STR in 802.11 WLAN, namely MASTaR, is proposed based on standard-compliant methods. Also, a digital self-interference cancellation (SIC) strategy is proposed to support the operation of MASTaR. The feasibility and the performance of MASTaR are extensively evaluated via 3D ray tracing-based simulation. The simulation results demonstrate that significant performance enhancement,e.g., up to 2.58X higher throughput than the current 802.11 MAC protocol, can be achieved by an STR-capable access point. In summary, we propose an algorithm for ACK and CTS transmission power control and two protocols each for CST adaptation and STR which enhance the efficiency of WLAN by enriching simultaneous transmission. The feasibility and the performance of the algorithm and protocols are demonstrated via various methodologies including numerical analysis, 3D ray-tracing, ns-3 based system-level simulation, and prototype using a software-defined radio.1 Introduction 1 1.1 Motivation 1 1.2 Overview of Existing Approaches 3 1.2.1 Transmit power control for CCI reduction 3 1.2.2 CST adaptation for better spatial reuse 3 1.2.3 MAC protocol for STR in WLAN 4 1.3 Main Contributions 7 1.3.1 Quiet ACK: ACK Transmit Power Control 7 1.3.2 FACT: CST adaptation scheme 8 1.3.3 MASTaR: MAC protocol for STR in WLAN 8 1.4 Organization of the Dissertation 9 2 Quiet ACK: ACK Transmit Power Control in IEEE 802.11 WLANs 10 2.1 Introduction 10 2.2 Numerical Analysis 12 2.2.1 System Model 13 2.2.2 AISR Expansion by ACK Power Control 18 2.2.3 Optimization of ACK Outage Tolerance 19 2.3 QACK: Proposed ACK power Control 21 2.3.1 CCI Detection and CCI Power Estimation 22 2.3.2 Link Margin Estimation 26 2.3.3 ACK Power Adjustment 29 2.3.4 Conditional QACK Enabling/Disabling 30 2.4 Prototyping-Based Feasibility Evaluation 30 2.4.1 Feasibility of CCI Detection and CCI Power Estimation 30 2.4.2 Throughput Enhancement by QACK 33 2.5 Simulation-based Performance Evaluation 34 2.5.1 Two BSS Topology 35 2.5.2 Multiple BSS Environment 38 2.5.3 Coexistence with Legacy Devices 41 2.6 Quiet CTS: Proposed CTS Power Control 41 2.6.1 Problem Statement 41 2.6.2 CTS Power Control 42 2.6.3 Relationship with Quiet ACK 44 2.6.4 Simulation Results 45 2.7 Summary 48 3 FACT: Fine-Grained Adaptation of Carrier Sense Threshold in IEEE 802.11 WLANs 49 3.1 Introduction 49 3.2 Preliminaries 50 3.2.1 IEEE 802.11h Transmit Power Control (TPC) 50 3.2.2 IEEE 802.11ah Basic Service Set (BSS) Color 52 3.3 FACT: Proposed CST Adaptation Scheme 52 3.3.1 Basic Principle 53 3.3.2 Challenges and Solutions 54 3.3.3 Specification 54 3.3.4 Transmit Power Adjustment 56 3.3.5 Conditional Update of CST 57 3.4 Blind CCA and Backoff Compensation 57 3.4.1 Blind CCA 58 3.4.2 Backoff Compensation 59 3.5 Performance Evaluation 59 3.6 Summary 63 4 MASTaR: MAC Protocol for Access Points in Simultaneous Transmit and Receive Mode 64 4.1 Introduction 64 4.2 Preliminaries 68 4.2.1 Explicit Block ACK 68 4.2.2 Capture Effect 69 4.3 MASTaR: Proposed MAC Protocol 70 4.3.1 PTX Identification 70 4.3.2 Initial Training 73 4.3.3 Link Map Management 73 4.3.4 Secondary Transmission 74 4.4 Feasibility Study 76 4.4.1 Analog SIC and Channel Modeling 76 4.4.2 Digital SIC for WLAN 79 4.5 Performance Evaluation 83 4.5.1 Simulation with UDP Data Traffic 87 4.5.2 Simulation with Voice and Data Traffic 100 4.6 Summary 102 5 Concluding Remarks 103 5.1 Research Contributions 103 5.2 Future Work 104 Abstract (In Korean) 110Docto

Improving the performance and efficiency of wireless networks using rate adaptation

Recent years have seen a staggering increase in the deployment and utilization of wireless networks. More and more devices are being equipped with Wireless LAN (WLAN) cards to take advantage of the omnipresence of WLAN networks. Therefore, it has become necessary that the protocols used by WLANs are efficient and provide good performance. Rate Adaptation protocols are an important mechanism employed by WLANs to improve network performance. This dissertation develops three complementary techniques, which use rate adaptation to optimize and improve performance by i) performing rate adaptation to optimize energy consumption, ii) developing a more accurate technique to predict the frame delivery ratio that is used by rate adaptation protocols, and iii) jointly optimizing rate adaptation with data retransmission to maximize throughput. More specifically, in i), we use extensive measurements to develop a simple yet accurate energy consumption model for 802.11n wireless cards. We use the model to drive the design of an energy aware rate adaptation scheme. A major benefit of a model-based rate adaptation is that applying a model allows us to eliminate frequent probes required in many existing rate adaptation schemes. In ii), we find that the accuracy of existing delivery ratio calculation techniques is still limited due to bursty errors inherent to the wireless channel. We develop a new method for computing packet delivery rate that captures the burstiness of errors. Furthermore, we propose a new data interleaving technique, which leverages our framework to reduce the burstiness of errors, thereby improving frame delivery ratio. Finally, in iii), we address the susceptibility of wireless networks to transmission failures due to dynamic channel conditions and unpredictable interference. To efficiently recover from failures, we propose a retransmission scheme where the receiver combines information received from multiple failed transmissions associated with the same frame. The protocol has two distinguishing features. First, it simultaneously supports partial retransmission and combines bits with low confidence. Second, it jointly optimizes the data rate of the retransmission and the information to be retransmitted to maximize throughput.Electrical and Computer Engineerin

Cross-Layer Optimization and Dynamic Spectrum Access for Distributed Wireless Networks

We proposed a novel spectrum allocation approach for distributed cognitive radio networks. Cognitive radio systems are capable of sensing the prevailing environmental conditions and automatically adapting its operating parameters in order to enhance system and network performance. Using this technology, our proposed approach optimizes each individual wireless device and its single-hop communication links using the partial operating parameter and environmental information from adjacent devices within the wireless network. Assuming stationary wireless nodes, all wireless communication links employ non-contiguous orthogonal frequency division multiplexing (NC-OFDM) in order to enable dynamic spectrum access (DSA). The proposed approach will attempt to simultaneously minimize the bit error rate, minimize out-of-band (OOB) interference, and maximize overall throughput using a multi-objective fitness function. Without loss in generality, genetic algorithms are employed to perform the actual optimization. Two generic optimization approaches, subcarrier-wise approach and block-wise approach, were proposed to access spectrum. We also proposed and analyzed several approaches implemented via genetic algorithms (GA), such as quantizing variables, using adaptive variable ranges, and Multi-Objective Genetic Algorithms, for increasing the speed and improving the results of combined spectrum utilization/cross-layer optimization approaches proposed, together with several assisting processes and modifications devised to make the optimization to improve efficiency and execution time