LATENCY, COOPERATION, AND CLOUD IN RADIO ACCESS NETWORK Navid Nikaein Thesis submitted to University of Nice in partial fulfilment for the award of the degree of Habilitation a` Diriger des Recherches 19 March 2015 AUTHOR’S ADDRESS: Navid Nikaein Eurecom Mobile Communication Department Campus SophiaTech 450 Route des Chappes 06410 Biot Sophia Antipolis – France Email: [email protected] URL: http://www.eurecom.fr/˜nikaeinn Forward This document is written as support to my French ”Habilitation a` diriger des recherches” (HDR) degree. Unlike a Ph.D. thesis, a HR thesis does not aim at providing a detailed description of a particular research problematic, but rather describes the various facets of responsibilities that I experienced as researcher and assistant professor since I obtained my Ph.D. My post-doctoral career started at Eurecom in January 2004, after having completed my Ph.D. entitled “Architecture and protocols for supporting routing and quality of service for mobile ad hoc networks” at Ecole´ Polytechnique Fed´ erale´ de Lausanne EPFL, Switzerland in September 2003. After the postdoc, I joined the founding team of a startup company in Sophia-Antipolis, France, working towards a range of intelligent wireless backhaul routing products for private and public networks. Four years later, I deliberately chose to join Eurecom as an assistant pro- fessor because of the experimental platform OpenAirInterface, which allowed me to work on practical aspects of wireless access network. This means working on aspects that are sometimes overlooked or not found interesting or even old fashioned by other researchers, or collecting and analyzing data from experiments to prove a concept or a point. Working with this platform is a unique experience, since one has to deal with many practical problems that sometimes lead to very interesting research avenues. Furthermore the platform is ideal for teaching, giving students hands-on experience and showing them the problems of real implementations. This document is composed of two parts. The first part describes the highlights of my research work I have been conducting after my Ph.D. The bulk of the text is based on existing and ongo- ing publications, but I have also added many new results, an introductory chapter summarizing all the works and putting them in context to each other, a chapter on the critical issues in cloud radio access network, and a conclusion chapter elaborating on my research methodology and giving directions for future work. The second part contains an extended CV, which includes teaching and supervising activities, project management and acquisition, as well as a selected list of my post-Ph.D. publications. Contents 1 Introduction5 1.1 Synopsis and Contributions . .6 1.1.1 OpenAirInterface: An Open Cellular Ecosystem . .6 1.1.2 LTE Unified Scheduler Framework . .8 1.1.3 Low Latency Contention-Based Access . .8 1.1.4 Evolving UEs for Collaborative Wireless Backhauling . .9 1.1.5 Closer to Cloud Radio Access Network: Study of Critical Issues . 10 1.1.6 Conclusion . 10 2 OpenAirInterface : An Open Cellular Ecosystem 11 2.1 Software Platform . 12 2.2 Hardware Platform . 13 2.3 Build-in Emulation Platform . 15 2.3.1 Experiment Design Workflow . 17 2.3.2 Discrete Event Generator . 18 2.3.3 Protocol Vectorization and Emulation Data Transport . 19 2.3.4 PHY Abstraction [1]........................... 21 2.4 Comparison of OAI with Other Platforms and Approaches . 24 2.5 Validation . 25 2.6 Conclusion . 27 3 Unified Scheduler Framework for LTE/LTE-A 31 3.1 Scheduling Parameters . 32 3.1.1 Packet-Level Parameters . 32 3.1.2 Logical Channel-Level Parameters . 33 3.1.3 User-level parameters . 33 2 CONTENTS 3.1.4 System-level parameters . 33 3.2 Scheduling Framework . 34 3.2.1 MAC-layer Interfaces . 34 3.2.2 MAC-layer Modules . 36 3.3 Comparative Analysis . 37 3.3.1 Simulation Setup . 40 3.3.2 Results . 40 3.4 Initial Experimentation and Validation . 42 3.5 Conclusion . 43 4 Low Latency Contention-Based Access 45 4.1 Latency in LTE . 47 4.1.1 Definitions . 47 4.1.2 Analysis [2]................................ 48 4.1.3 Measurements [3]............................. 51 4.2 General Idea of Contention Based Access . 54 4.3 Implementation of Contention Based Access in LTE . 57 4.3.1 Enhancements to the RRC Signaling Related to 3GPP TS 36.331 . 57 4.3.2 Enhancement to the PHY Signaling Related to 3GPP TS 36.212 . 57 4.3.3 Enhancement to the PHY Procedures related to 3GPP TS 36.213 . 59 4.3.4 CBA Operation . 60 4.4 Resource Allocation Scheme for Contention Based Access . 62 4.4.1 Estimation of the Probabilities of Events in Step 3 . 64 4.4.2 Estimation of the Latency in Step 4 . 67 4.5 Simulation Results . 67 4.5.1 Performance Evaluation . 68 4.5.2 Performance of the Resource Allocation Scheme . 70 4.6 Experimental Results . 72 4.6.1 Experiment Setup . 72 4.6.2 Applied Grouping Scheme and Scheduling Algorithm . 74 4.6.3 Results . 74 4.6.4 General CBA Latency Trend . 74 4.6.5 Uncoordinated Traffic Pattern . 76 4.6.6 Coordinated Traffic Pattern . 81 CONTENTS 3 4.7 Comparison . 82 4.8 Conclusion . 84 5 Evolving UEs for Collaborative Wireless Backhauling 87 5.1 Design Challenges and Contribution . 88 5.2 Explore for New Use Cases . 90 5.2.1 Moving Cells . 90 5.2.2 Small Cells . 91 5.3 Architecture . 92 5.3.1 LTE Mesh Network Topology . 92 5.3.2 Virtual Overlay - Enable Mesh Networking . 93 5.3.3 PHY Layer Design . 96 5.3.4 MAC Layer Design . 97 5.4 Performance Evaluation . 103 5.4.1 Experimentation . 104 5.5 Related Work . 108 5.6 Conclusion . 109 6 Closer to Cloud Radio Access Network: Study of Critical Issues 111 6.1 From Analog to Virtual Radio . 111 6.2 Background . 111 6.3 Cloud Radio Access Network Concept . 113 6.4 C-RAN Use Cases . 114 6.5 C-RAN Critical Issues . 115 6.5.1 Fronthaul Capacity . 116 6.5.2 BBU Processing . 116 6.5.3 Real-time Operating System and Virtualization Environment . 117 6.5.4 Candidate Architectures . 120 6.6 Evaluation . 121 6.6.1 Experiment Setup . 121 6.6.2 CPU Architecture Analysis . 122 6.6.3 CPU Frequency Analysis . 123 6.6.4 Virtualization Technique Analysis . 124 6.6.5 I/O Performance Analysis . 124 4 CONTENTS 6.6.6 Discussion . 125 6.7 Modelling BBU Processing Time . 126 6.8 Conclusion . 128 7 Conclusion 131 7.1 Open-Source Tools for 5G Cellular Evolution . 131 7.2 RANaaS . 131 7.3 Software-Defined Wireless Networking . 133 7.4 Mobile Cloud and Edge Computing . 134 7.5 Dynamic Meshing of the Base stations . 135 Bibliography 136 Appendices A CBA Protocol Validation 149 B Virtual Link Validation 153 List of Tables 156 List of Figures 157 Chapter 1 Introduction The main volume of the work presented here considers protocol and algorithm design and validation through experimentation for radio access networks (RAN) in a cellular, mesh, and cloud settings. Protocol and algorithm are the essential part of the wireless communication system allowing two or more nodes to communicate with each other according to a set of predefined communi- cation messages and rules. It is generally divided into a control plane and a data-plane, whose signalling determines (a) the type of communication and the resulted network topology, and (b) the efficiency of communication on the top of what is achievable by the physical link. However new application scenarios found in namely machine-type communication, public safety net- works, interactive online gaming, moving cells, and device-to-device communication, require more complex and dynamic protocols and algorithms. While in 4G systems, this represents an opportunity to limit the modifications in the physical layer and redesign the radio access protocols and algorithm to obtain the desired features, in 5G it rather calls for a new MAC/- PHY co-design that exploits new waveform, frame structure, and advanced (non-orthogonal) multiple access schemes among the others [4,5]. Experiment is also an integral part of wireless communications. An experiment is a procedure carried out with the goal of verifying, refuting, or establishing the validity of a hypothesis in a real-world.1 One of the very first experiments in this field was carried out by Heinrich Hertz in 1887, proving the fact that electromagnetic waves can travel over free space. Another more recent example is the concept of cloud RAN that decouples the baseband unit (BBUs) from the radio units by locating a pool of BBUs at the high performance cloud infrastructure. The concept was first proposed by Y. Lin et al. IBM Research Division, China Research Laboratory in 2010 [6], and was partially proven (only centralization) by experiments some years later by Chih-Lin I et al. in 2014 [7]. Experiments can also be used to characterize the behaviour of the system and/or analyse a specific phenomenon not yet very well understood. For example, processing time measurement of RAN functions can be used to analyse the required computa- tional power as a function bandwidth, modulation and coding scheme and assess the feasibility of RAN virtualization in the cloud infrastructure. Because wireless communications systems have become very complex and comprise many 1en.wikipedia.org/wiki/Experiment 6 Chapter 1. Introduction different fields, ranging from information and communication theory, signal processing to pro- tocols and networking, performing a reliable experiment is becoming an expensive and time consuming task. There are three main approaches to perform an experiment [8]: • Simulation: typically done.