Heterogeneous Networks in LTE-Advanced

A comprehensive summary of theoretical and practical developments in LTE Heterogeneous Networks

The last decade has witnessed the proliferation of mobile broadband data and the trend is likely to increase in the coming years. Current cellular networks are ill equipped to deal with this surge in demand. To satisfy user demand and maximize profits, a new paradigm to operate networks is needed. Heterogeneous networks, that deploy an overlay of small cells with limited coverage and transmit power, over a macro coverage area is the solution by providing capacity and coverage where it is needed.

This book presents a comprehensive overview of small cell based heterogeneous networks within the framework of 3GPP LTE-Advanced which is the major enabler of current and future heterogeneous networks. The book first establishes the basics of LTE standards 8 -10. Wherever relevant, the underlying theory of wireless communications is explained and the signaling and protocol aspects of LTE Releases 8-10 are presented. Next the book presents a systematic study of the inter cell interference (eICIC and FeICIC) mechanisms that have been standardized in LTE releases 10 and 11 to mitigate the interference arising in heterogeneous networks. From simple blank subframe design and implementation, the book discusses more advanced transceiver signal processing and carrier aggregation (CA) based mechanisms to improve performance. Besides data, control channel enhancements such as enhanced PDCCH (ePDCCH) are also discussed.

Subsequently the book discusses the possibility of base stations being allowed to coordinate to manage interference. This technique, called CoMP, has the potential of vastly improving network performance. However several practical challenges first have to be overcome before this potential can be realized. The book presents the different CoMP categories introduced in LTE release 11, the required signal processing and the changes that were introduced in Release-11 for supporting CoMP. The book then presents the state of the art developments in heterogeneous networks that are currently taking place in 3GPP with the initiation of Release 12. A whole array of new technologies have been introduced such as dynamic switching of small cells, new carrier types with reduced control signaling, dynamic reconfiguration of TDD-LTE, joint configuration of TDD and FDD via carrier aggregation and lastly advanced MIMO signal processing with three dimensional beamforming. All these technologies will work in unison leading to efficient operations of small cells.

The authors thus comprehensively summarize the advances in heterogeneous networks over the last couple of years as reflected in various LTE releases and then look ahead at what to expect in the future. Fully illustrated throughout and with an accompanying website including Matlab code for simulating heterogeneous networks, LTE channel models, and References to 3GPP specifications, contributions, and updates on recent standardization activities. The authors, being involved in LTE standardization, are well placed to give an excellent view on this topic, including valuable background and design rationale.

• A comprehensive summary of wireless communications theory and practical developments in LTE heterogeneous networks.
• Authors are experts in this field and are active members in standardization proceedings, enabling up-to-date coverage of current developments
• Multiple case studies explain network design optimization of various heterogeneous network deployments.
• Accompanying website includes Matlab code for simulating heterogeneous networks, LTE channel models, and References to 3GPP specifications, contributions, and updates on recent standardization activities

Essential reading for Engineers and practitioners in wireless industry.

About the Authors xi

Foreword xiii

Preface xv

Acknowledgements xvii

List of Acronyms xix

1 An Introduction to Heterogeneous Networks 1

1.1 Introduction 1

1.2 Heterogeneous Network Deployments 3

1.2.1 Distributed Antenna Systems 3

1.2.2 Public Access Picocells/Metrocells 4

1.2.3 Consumer-Grade Femtocells 4

1.2.4 WiFi Systems 5

1.3 Features of Heterogeneous Networks 5

1.3.1 Association and Load Balancing 5

1.3.2 Interference Management 6

1.3.3 Self-Organizing Networks 6

1.3.4 Mobility Management 7

1.4 Evolution of Cellular Technology and Standards 7

1.4.1 3GPP Standardization Process 9

References 10

Part I OVERVIEW

2 Fundamentals of LTE 15

2.1 Introduction 15

2.2 LTE Core Network 17

2.2.1 Control Plane 18

2.2.2 User Plane 19

2.2.3 Practical Implementations of the Core Network 19

2.3 LTE Radio Access Network 20

2.3.1 Control Plane 20

2.3.2 User Plane 23

2.4 Connectivity Among eNodeBs: The X2 Interface 24

2.4.1 Load- and Interference-Related Information 26

2.4.2 Handover-Related Information 26

2.5 Technologies in LTE 27

2.5.1 Orthogonal Frequency Division Multiplexing 27

2.5.2 Multiple Antenna Communications 36

References 42

3 LTE Signal Structure and Physical Channels 45

3.1 Introduction 45

3.2 LTE Signal Structure 45

3.3 Introduction to LTE Physical Channels and Reference Signals 48

3.4 Resource Block Assignment 51

3.5 Downlink Physical Channels 54

3.5.1 Physical Broadcast Channel (PBCH) 55

3.5.2 Physical Downlink Shared Channel (PDSCH) 57

3.5.3 Physical Multicast Channel (PMCH) 58

3.5.4 Physical Control Format Indicator Channel (PCFICH) 58

3.5.5 Physical Hybrid ARQ Indicator Channel (PHICH) 59

3.5.6 Physical Downlink Control Channel (PDCCH) 60

3.6 Uplink Physical Channels 67

3.6.1 Physical Uplink Shared Channel (PUSCH) 67

3.6.2 Physical Uplink Control Channel (PUCCH) 68

3.6.3 Physical Random Access Channel (PRACH) 70

References 71

4 Physical Layer Signal Processing in LTE 73

4.1 Introduction 73

4.2 Downlink Synchronization Signals 73

4.2.1 Primary Synchronization Signal 74

4.2.2 Secondary Synchronization Signal 76

4.3 Reference Signals 77

4.3.1 Downlink Reference Signals 77

4.3.2 Uplink Reference Signals 84

4.4 Channel Estimation and Feedback 85

4.4.1 Basics of Link Adaptation 85

4.4.2 Feedback for MIMO OFDM Channels 88

4.4.3 New Features in LTE-Advanced 92

4.5 Design Paradigm of LTE Signaling 94

4.6 Scheduling and Resource Allocation 94

4.6.1 Scheduling Algorithms 96

4.6.2 Inter-eNodeB Coordination for Resource Allocation in LTE 98

References 100

Part II INTER-CELL INTERFERENCE COORDINATION

5 Release 10 Enhanced ICIC 103

5.1 Introduction 103

5.2 Typical Deployment Scenarios 103

5.2.1 Macro–Pico Deployment Scenario 104

5.2.2 Macro–Femto Deployment Scenario 107

5.3 Time Domain Techniques 110

5.3.1 Almost Blank Subframe 110

5.3.2 ABS Use Cases 113

5.3.3 UE Measurement and Reporting 116

5.3.4 Backhaul Support 118

5.3.5 Simulation Results 119

5.4 Power Control Techniques 123

5.4.1 Target Scenario 123

5.4.2 Power Control Schemes 124

5.4.3 Results from Realistic Deployments 125

5.5 Carrier Aggregation-Based eICIC 127

References 130

6 Release 11 Further Enhanced ICIC: Transceiver Processing 133

6.1 Introduction 133

6.2 Typical Deployment Scenarios 133

6.3 Techniques for Mitigating CRS Interference 136

6.3.1 Receiver-Based Techniques 136

6.3.2 Transmitter-Based Techniques 140

6.4 Weak Cell Detection 142

6.5 Non-Zero-Power ABS 144

References 147

7 Release 11 Further Enhanced ICIC: Remaining Topics 149

7.1 Carrier-Based Interference Coordination 149

7.1.1 Operational Carrier Selection 150

7.1.2 Primary and Secondary Cell Selection 153

7.2 Enhanced PDCCH for Interference Coordination 154

References 159

Part III COORDINATED MULTI-POINT TRANSMISSION RECEPTION

8 Downlink CoMP: Signal Processing 163

8.1 Introduction 163

8.2 CoMP Scenarios in 3GPP 164

8.2.1 Homogeneous Networks with Intra-Site CoMP 164

8.2.2 Homogeneous Networks with High-Power RRHs 165

8.2.3 Heterogeneous Networks with Low-Power RRHs with Cell IDs Different from the Macro 165

8.2.4 Heterogeneous Networks with Low-Power RRHs with Cell IDs the Same as the Macro 166

8.3 CoMP Sets 167

8.3.1 RRM Measurement Set/CoMP Resource Management Set 167

8.3.2 CoMP Measurement Set 168

8.3.3 CoMP Cooperating Set 169

8.4 CoMP Transmission in 3GPP 169

8.4.1 Coordinated Scheduling/Beamforming 169

8.4.2 Dynamic Point Selection 172

8.4.3 Joint Transmission 177

8.5 Comparison of Different CoMP Categories 180

References 182

9 Downlink CoMP: Standardization Impact 185

9.1 Introduction 185

9.2 Modification of Reference Signals 185

9.2.1 Modifications in CSI-RS 185

9.2.2 Modifications in DMRS 186

9.3 CSI Processes 189

9.3.1 UE Processing Complexity and CSI Reference Resources 191

9.3.2 Inheritance and Reference Processes 192

9.4 PDSCH Rate Matching 193

9.5 Quasi-Co-Location of Antenna Ports 195

9.5.1 Quasi-Co-Location Between the Same Antenna Ports 197

9.5.2 Quasi-Co-Location Between Different Antenna Ports 198

9.6 New Transmission Mode and DCI Format 200

9.7 Backhaul Support for CoMP 201

9.8 Summary 203

References 203

Part IV UPCOMING TECHNOLOGIES

10 Dense Small Cell Deployments 207

10.1 Introduction 207

10.2 Evolution of Small Cells 207

10.2.1 Deployment Scenarios 209

10.3 Efficient Operation of Small Cells 212

10.3.1 Dual Connectivity 214

10.3.2 ICIC Mechanism 216

10.3.3 Small Cell Discovery 220

10.4 Control Signaling Enhancement 223

10.4.1 Multi-Subframe Scheduling 223

10.4.2 Cross-Subframe Scheduling 224

10.5 Reference Signal Overhead Reduction 225

10.5.1 Downlink DMRS 225

10.5.2 Uplink DMRS 227

References 228

11 TD-LTE Enhancements for Small Cells 231

11.1 Enhancements for Dynamic TDD 231

11.1.1 TDD UL/DL Reconfiguration Scenarios in 3GPP 232

11.1.2 Interference Mitigation Schemes 234

11.2 FDD-TDD Joint Operation 239

11.2.1 Deployment Scenarios 240

11.2.2 Issues and Potential Solutions 241

References 243

12 Full Dimension MIMO 245

12.1 Introduction 245

12.2 Antenna Systems Architecture: Passive and Active 245

12.3 Antenna Patterns 248

12.3.1 Passive Antenna Element Pattern 248

12.3.2 Active Antenna Systems 250

12.3.3 AAS with Additional Mechanical Tilt 253

12.3.4 Effect of Multipath Fading Channels 253

12.4 FD-MIMO Deployment Scenarios 254

12.4.1 UE-Specific FD-MIMO 254

12.4.2 Cell-Specific FD-MIMO 255

12.4.3 System-Specific FD-MIMO 255

12.5 Conclusion 256

References 256

13 Future Trends in Heterogeneous Networks 257

13.1 Summary 257

13.2 Small Cells and Cloud RAN 258

13.3 Small Cells, Millimeter Wave Communications and Massive MIMO 259

13.4 Small Cells and Big Data 260

13.5 Concluding Remarks 260

References 260

Index 263

Joydeep Acharya received his PhD degree in Electrical Engineering from Rutgers University in 2009. Currently he is a staff research engineer at Hitachi America's Wireless Systems Research Lab (WSRL) where he is involved in physical layer research and standardization in LTE-Advanced. Previously, he had worked as a research consultant in GS Sanyal School of Telecommunications, Indian Institute of Technology Kharagpur on Physical Layer design of WCDMA. He has been participating in 3GPP RAN 1 and 2 meetings since 2009. He is the author of several IEEE conference and journal papers and inventor of several patents filed worldwide. His research topics include MIMO signal processing, base station coordination, massive MIMO and spectrum regulation and resource allocation for wireless systems.

Long Gao received his B.S. degree from Beijing Jiaotong University, Beijing, China, in 2003 and his M.S. degree from Beijing University of Posts and Telecommunications, Beijing, China, in 2006, both in Electrical Engineering. He received his Ph.D. degree in Electrical Engineering from Texas A&M University, College Station, TX and joined Hitachi America, Ltd, Santa Clara, CA, in 2010. Since then, he has been involved in 3GPP LTE/LTE-Advanced standardization activities with focus on cooperative communication and heterogeneous networks. He has published several IEEE papers and submitted several technical contributions to 3GPP RAN1 conference. He has served as a TPC member in major IEEE conferences such as Globecom 2010-2013. He has presented tutorials on LTE-Advanced heterogeneous network in VTC 2012 and WCNC 2013.

Sudhanshu Gaur has over 10 years of research and industry experience in the field of wireless communications. He is currently the Principal Research Engineer at Hitachi America's Wireless System Research Lab (WSRL) where he leads LTE-Advanced standardization activities. Earlier he was also involved with IEEE 802.11aa standardization and cont