DiFuse: distributed frequency domain user selection for multi-user MIMO networks

Optimal user selection is important in increasing the capacity of Multi-User Multi-Input Multi-Output Wi-Fi networks, yet it faces a significant challenge; the multi-user diversity gain can be overwhelmed by the formidable Channel State Information (CSI) acquisition overhead. To lessen the overhead, existing schemes adopt the greedy user selection which generally takes the projected norm as the user selection metric, since it considers both the channel power gain and the orthogonality. However, the projected norm suffers from occasional poor user selection, since it does not take the optimal sum capacity gain into account. This paper proposes a new distributed user selection protocol called DiFuse. To employ the sum capacity gain as the user selection metric in DiFuse, each user cleverly computes its own estimated capacity gain by overhearing the CSI feedback from others. The users then simultaneously transmit their feedbacks at the frequency domain via the distributed feedback contention, which effectively reduces the feedback overhead. Then the AP collectively utilizes them for user selection that achieves the maximum positive increment to the sum capacity gain. We implemented the prototype of DiFuse on the USRP N210, and evaluated its performance via both testbed experiments and trace-driven emulations. The results showed that DiFuse outperforms the throughput of the existing scheme called OPUS by 1.8x on average, while maintaining better fairness.OAIID:RECH_ACHV_DSTSH_NO:T201620351RECH_ACHV_FG:RR00200001ADJUST_YN:EMP_ID:A001118CITE_RATE:1.006FILENAME:Difuse- distributed frequency domain user selection for multi-user MIMO Networks.pdfDEPT_NM:컴퓨터공학부EMAIL:[email protected]_YN:YFILEURL:https://srnd.snu.ac.kr/eXrepEIR/fws/file/458535f3-401c-40b1-abae-d2a01534178d/linkCONFIRM:

Towards Scalable Design of Future Wireless Networks

Wireless operators face an ever-growing challenge to meet the throughput and processing requirements of billions of devices that are getting connected. In current wireless networks, such as LTE and WiFi, these requirements are addressed by provisioning more resources: spectrum, transmitters, and baseband processors. However, this simple add-on approach to scale system performance is expensive and often results in resource underutilization. What are, then, the ways to efficiently scale the throughput and operational efficiency of these wireless networks? To answer this question, this thesis explores several potential designs: utilizing unlicensed spectrum to augment the bandwidth of a licensed network; coordinating transmitters to increase system throughput; and finally, centralizing wireless processing to reduce computing costs. First, we propose a solution that allows LTE, a licensed wireless standard, to co-exist with WiFi in the unlicensed spectrum. The proposed solution bridges the incompatibility between the fixed access of LTE, and the random access of WiFi, through channel reservation. It achieves a fair LTE-WiFi co-existence despite the transmission gaps and unequal frame durations. Second, we consider a system where different MIMO transmitters coordinate to transmit data of multiple users. We present an adaptive design of the channel feedback protocol that mitigates interference resulting from the imperfect channel information. Finally, we consider a Cloud-RAN architecture where a datacenter or a cloud resource processes wireless frames. We introduce a tree-based design for real-time transport of baseband samples and provide its end-to-end schedulability and capacity analysis. We also present a processing framework that combines real-time scheduling with fine-grained parallelism. The framework reduces processing times by migrating parallelizable tasks to idle compute resources, and thus, decreases the processing deadline-misses at no additional cost. We implement and evaluate the above solutions using software-radio platforms and off-the-shelf radios, and confirm their applicability in real-world settings.PhDElectrical Engineering: SystemsUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/133358/1/gkchai_1.pd

Improving MIMO Performance in Wi-Fi Networks by using Collision Resolution and User Selection

학위논문 (박사)-- 서울대학교 대학원 : 전기·컴퓨터공학부, 2015. 8. 김종권.Multiple-Input Multiple-Output (MIMO) technologies have emerged as a key component to increase the capacity of wireless networks. The MIMO scheme either simultaneously transmits to multiple users at a time or focuses energy towards a single user to enhance the data rate. A number of Wi-Fi standards based on MIMO technology have been developed, and recently, several commercial products have been successfully deployed on the market. Unfortunately, many commercial MIMO-based Wi-Fi products fail to fully exploit the advantages of the MIMO technology, even though the MIMO technology could play a key role in improving the wireless network performance. MIMO nodes cannot provide their higher data rates, especially when they coexist with SISO nodes. Meanwhile, in Wi-Fi networks, significant Channel State Information (CSI) feedback overhead has been obstacle to the performance of MU-MIMO transmission and user selection. Most of these problems are observed to root in the inefficient PHY and MAC design of current MIMO based Wi-Fi systems: the MAC simply abstracts the advancement of PHY technologies as a change of data rate. Hence, the benefit of new PHY technologies are either not fully exploited, or they even may harm the performance of existing network protocols. In this dissertation we introduce three co-designs of PHY/MAC layers for MIMO based Wi-Fi networks, in order to overcome the intrinsic limitations of the current MIMO based Wi-Fi network and improve the network capacity. First, we show the Interference Alignment and Cancelation (IAC) based collision resolution scheme for heterogeneous MIMO based Wi-Fi systems. Second, we present a practical user selection scheme for MU-MIMO Wi-Fi networks. Finally, we improve the proposed user selection scheme by exploiting a frequency domain signaling scheme and using a capacity gain as a selection metric. We have validated the feasibility and performance of our designs using extensive analysis, simulation and USRP testbed implementation.ABSTRACT i CONTENTS iii LIST OF FIGURES vi LIST OF TABLES ix CHAPTER I: Introduction 1 1.1 Background and Motivation 1 1.2 Goal and Contribution 8 1.3 Thesis Organization 9 CHAPTER II: MIMO based Collision Resolution 10 2.1 Introduction 10 2.2 Related Work 12 2.3 Background 14 2.3.1 Packet Collision Problems in MIMO Networks 14 2.3.2 IAC 15 2.4 802.11mc 17 2.4.1 Protocol Overview 17 2.4.2 Packet Collision Resolution via IAC 19 2.4.3 Collisions between Multiple CTSs 22 2.4.4 Optimal p 23 2.4.5 Discussion 28 2.5 USRP Experiments 33 2.5.1 Micro Benchmark 33 2.5.2 Macro Benchmark 39 2.6 NS-2 Simulations 43 2.6.1 Setting 43 2.6.2 Packet Loss Rate due to Collision 44 2.6.3 CWMin 45 2.6.4 Data Size 46 2.6.5 Number of Node Pairs (N) 49 2.6.6 Proportion of MIMO Receivers (q_2) 50 2.6.7 Postamble Probability (p) 52 2.6.8 Performance in Dynamic Network Configurations 54 2.7 Conclusion 55 CHAPTER III: User Selection for MU-MIMO Transmission 56 3.1 Introduction 56 3.2 Related Work 58 3.3 Background 60 3.3.1 System Model 60 3.3.2 User Selection 61 3.4 802.11ac+ 62 3.4.1 Overview 62 3.4.2 Channel Hint Broadcasting 63 3.4.3 Active CSI Feedback 66 3.5 Fair Scheduling 72 3.5.1 RR-11ac+ 72 3.5.2 PF-11ac+ 73 3.5.3 Summary 73 3.6 Performance Evaluation 75 3.6.1 Setting 75 3.6.2 802.11ac+ Performance 76 3.6.3 Fair Scheduling Protocol Performance 79 3.7 Conclusion 82 CHAPTER IV: Distributed Frequency Domain User Selection 83 4.1 Introduction 83 4.2 Motivation 84 4.3 DiFuse 88 4.3.1 Protocol Overview 88 4.3.2 Distributed Feedback Contention 89 4.3.3 Slot Threshold Design 95 4.3.4 Proportional Fair Selection 97 4.3.5 Discussions 98 4.4 Performance Evaluation 101 4.4.1 Micro Benchmark 101 4.4.2 System-Level Performance 105 4.5 Conclusion 113 CHAPTER V: Conclusion 114 BIBLIOGRAPHY 115 초 록 122Docto