Link Scheduling Algorithms For In-Band Full-Duplex Wireless Networks

In the last two decades, wireless networks and their corresponding data traffic have grown significantly. This is because wireless networks have become an indispens- able and critical communication infrastructure in a modern society. An on-going challenge in communication systems is meeting the continuous increase in traffic de- mands. This is driven by the proliferation of electronic devices such as smartphones with a WiFi interface along with their bandwidth intensive applications. Moreover, in the near future, sensor devices that form the Internet of Things (IoTs) ecosystem will also add to future traffic growth. One promising approach to meet growing traffic demands is to equip nodes with an In-band-Full-Duplex (IBFD) radio. This radio thus allows nodes to transmit and receive data concurrently over the same frequency band. Another approach to in- crease network or link capacity is to exploit the benefits of Multiple-Input-Multiple- Output (MIMO) technologies; namely, (i) spatial diversity gain, which improves Signal-to-Noise Ratio (SNR) and thus has a direct impact on the data rate used by nodes, and (ii) spatial multiplexing gain, whereby nodes are able to form concurrent links to neighbors

Capacity Enhancement of Multiuser Wireless Communication System through Adaptive Non-Linear Pre coding

Multiuser multiple-input multiple-output (MIMO) nonlinear pre coding techniques face the issue of poor computational scalability of the size of the network. But by this nonlinear pre coding technique the interference is pre-cancelled automatically and also provides better capacity. So in order to reduce the computational burden in this paper, a definitive issue of MU-MIMO scalability is tackled through a non-linear adaptive optimum vector perturbation technique. Unlike the conventional (Vector Perturbation) VP methods, here a novel anterograde tracing is utilized which is usually recognized in the nervous system thus reducing complexity. The tracing of distance can be done through an iterative-optimization procedure. By this novel non-linear technique the capacity is improved to a greater extend which is explained practically. By means of this, the computational complexity is managed to be in the cubic order of the size of MUMIMO, and this mainly derives from the inverse of the channel matrix. The proposed signal processing system has been implemented in the working platform of MATLAB/SIMULINK. The simulation results of proposed communication system and comparison with existing systems shows the significance of the proposed work

Design and Testbed Deployment of Frequency-Domain Equalization Full Duplex Radios

Full-duplex (FD) wireless can significantly enhance spectrum efficiency but requires effective self-interference (SI) cancellers. RF SI cancellation (SIC) via frequency-domain equalization (FDE), where bandpass filters channelize the SI, is suited for integrated circuits (ICs). In this paper, we explore the limits and higher layer challenges associated with using such cancellers. We evaluate the performance of a custom FDE-based canceller using two testbeds; one with mobile FD radios and the other with upgraded, static FD radios in the PAWR COSMOS testbed. The latter is a lasting artifact for the research community, alongside a dataset containing baseband waveforms captured on the COSMOS FD radios, facilitating FD-related experimentation at the higher networking layers. We evaluate the performance of the FDE-based FD radios in both testbeds, with experiments showing 95 dB overall achieved SIC (52 dB from RF SIC) across 20 MHz bandwidth, and an average link-level FD rate gain of 1.87x. We also conduct experiments in (i) uplink-downlink networks with inter-user interference, and (ii) heterogeneous networks with half-duplex and FD users. The experimental FD gains in the two types of networks depend on the users' SNR values and the number of FD users, and are 1.14x-1.25x and 1.25x-1.73x, respectively, confirming previous analytical results.Comment: 13 pages, 22 figures. arXiv admin note: substantial text overlap with arXiv:1812.0112

Full-duplex wireless communications: challenges, solutions and future research directions

The family of conventional half-duplex (HD) wireless systems relied on transmitting and receiving in different time-slots or frequency sub-bands. Hence the wireless research community aspires to conceive full-duplex (FD) operation for supporting concurrent transmission and reception in a single time/frequency channel, which would improve the attainable spectral efficiency by a factor of two. The main challenge encountered in implementing an FD wireless device is the large power difference between the self-interference (SI) imposed by the device’s own transmissions and the signal of interest received from a remote source. In this survey, we present a comprehensive list of the potential FD techniques and highlight their pros and cons. We classify the SI cancellation techniques into three categories, namely passive suppression, analog cancellation and digital cancellation, with the advantages and disadvantages of each technique compared. Specifically, we analyse the main impairments (e.g. phase noise, power amplifier nonlinearity as well as in-phase and quadrature-phase (I/Q) imbalance, etc.) that degrading the SI cancellation. We then discuss the FD based Media Access Control (MAC)-layer protocol design for the sake of addressing some of the critical issues, such as the problem of hidden terminals, the resultant end-to-end delay and the high packet loss ratio (PLR) due to network congestion. After elaborating on a variety of physical/MAC-layer techniques, we discuss potential solutions conceived for meeting the challenges imposed by the aforementioned techniques. Furthermore, we also discuss a range of critical issues related to the implementation, performance enhancement and optimization of FD systems, including important topics such as hybrid FD/HD scheme, optimal relay selection and optimal power allocation, etc. Finally, a variety of new directions and open problems associated with FD technology are pointed out. Our hope is that this treatise will stimulate future research efforts in the emerging field of FD communication

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