Interference Alignment and Cancellation

The throughput of existing MIMO LANs is limited by the number of antennas on the AP. This paper shows how to overcome this limit. It presents interference alignment and cancellation (IAC), a new approach for decoding concurrent sender-receiver pairs in MIMO networks. IAC synthesizes two signal processing techniques, interference alignment and interference cancellation, showing that the combination applies to scenarios where neither interference alignment nor cancellation applies alone. We show analytically that IAC almost doubles the throughput of MIMO LANs. We also implement IAC in GNU-Radio, and experimentally demonstrate that for 2x2 MIMO LANs, IAC increases the average throughput by 1.5x on the downlink and 2x on the uplink.United States. Defense Advanced Research Projects Agency. Information Theory for Mobile Ad-Hoc Networks Progra

Stable and Efficient Sparse Recovery for Machine Learning and Wireless Communication

Recent theoretical study shows that the sparsest solution to an underdetermined linear system is unique, provided the solution vector is sufficiently sparse, and the operator matrix has sufficiently incoherent column vectors. In addition, efficient algorithms have been discovered to find such solutions. This intriguing result opens a new door for many potential applications. In this thesis, we study the design of a class of greedy algorithms that are extremely efficient, e.g., Orthogonal Matching Pursuit (OMP). These greedy algorithms suffer from a stability issue that the greedy selection approach always make locally optimal decisions, thereby easily biasing and mistaking the solutions in particular under data noise. We propose a solution approach that in designing greedy algorithms, new constraints can be devised by leveraging application-specific insights and incorporated into the algorithms. Given that sparse recovery problems by definition are underdetermined, introducing additional constraints can significantly improve the stability of greedy algorithms, yet retain their efficiency.Engineering and Applied Science

A random access MAC protocol for MPR satellite networks

Dissertação apresentada para obtenção do Grau de Mestre em Engenharia Electrotécnica e de Computadores, pela Universidade Nova de Lisboa, Faculdade de Ciências e TecnologiaRandom access approaches for Low Earth Orbit (LEO) satellite networks are usually incompatible with the Quality of Service (QoS) requirements of multimedia tra c, especially when hand-held devices must operate with very low power. Cross-Layered optimization architectures, combined with Multipacket Reception (MPR)schemes are a good choice to enhance the overall performance of a wireless system. Hybrid Network-assisted Diversity Multiple Access (H-NDMA) protocol, exhibits high energy e ciency, with MPR capability, but its use with satellites is limited by the high round trip time. This protocol was adapted to satellites, in Satellite-NDMA, but it required a pre-reservation mechanism that introduces a signi cant delay. This dissertation proposes a random access protocol that uses H-NDMA, for Low Earth Orbit (LEO) satellite networks, named Satellite Random-NDMA (SR-NDMA). The protocol addresses the problem inherent to satellite networks (large round trip time and signi cant energy consumption) de ning a hybrid approach with an initial random access plus possible additional scheduled retransmissions. An MPR receiver combines the multiple copies received, gradually reducing the error rate. Analytical performance models are proposed for the throughput, delay, jitter and energy e ciency considering nite queues at the terminals. It is also addressed the energy e ciency optimization, where the system parameters are calculated to guarantee the QoS requirements. The proposed system's performance is evaluated for a Single-Carrier with Frequency Domain Equalization (SC-FDE) receiver. Results show that the proposed system is energy e cient and can provide enough QoS to support services such as video telephony

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