LTE Communications and Networks E-Book

• Herausgeber: John Wiley & Sons
• Kategorie: Wissenschaft und neue Technologien
• Sprache: Englisch

Seitenzahl: 440

Veröffentlichungsjahr: 2018

Beschreibung

A comprehensive resource to the latest developments of system enhancement techniques of Femtocells, power management, interference mitigation and antenna design LTE Communications and Networks fills a gap in the literature to offer a comprehensive review of the most current developments of LTE Femtocells and antennas and explores their future growth. With contributions from a group of experts that represent the fields of wireless communications and mobile communications, signal processing and antenna design, this text identifies technical challenges and presents recent results related to the development, integration and enhancement of LTE systems in portable devices. The authors examine topics such as application of cognitive radio with efficient sensing mechanisms, interference mitigation and power management schemes for the LTE systems. They also provide a comprehensive account of design challenges and approaches, performance enhancement techniques and effects of user's presence on the LTE antennas. LTE Communications and Networks also highlights the promising technologies of multiband, multimode and reconfigurable antennas for efficient design of portable LTE devices. Designed to be a practical resource, this text: * Explores the interference mitigation, power control and spectrum management in LTE Femtocells and related issues * Contains information on the design challenges, different approaches, performance enhancement and application case scenarios for the LTE antennas * Covers the most recent developments of system enhancement techniques in terms of Femtocells, power management, interference mitigation and antenna design * Includes contributions from leading experts in the field Written for industry professionals and researchers, LTE Communications and Networks is a groundbreaking book that presents a comprehensive treatment to the LTE systems in the context of Femtocells and antenna design and covers the wide range of issues related to the topic.

Leseprobe

Table of Contents

Cover

Title Page

List of Contributors

Preface

1 Introduction

1.1 Evolution of Wireless and Cellular Communication

1.2 LTE Architecture

1.3 LTE Antennas

1.4 LTE Applications

1.5 Book Organization

References

Part I: LTE Femtocells

2 LTE Femtocells

2.1 Introduction

2.2 Platform for Femtocell Deployment

2.3 LTE Architecture Overview

2.4 LTE Femtocell Interference Analysis

2.5 Interference Mitigation: Current State of the Art

2.6 Cognitive Femtocells: A Smart Solution to a Complex Problem

2.7 Summary

References

3 Interference Mitigation in Cognitive Radio‐Based LTE Femtocells

3.1 Introduction

3.2 Femtocells

3.3 Interference Mitigation in Femtocells using Cognitive Radio

3.4 Summary

4 Coverage Area‐Based Power Control for Interference Management in LTE Femtocells

4.1 Introduction

4.2 Coverage Radius Based Power Control Scheme (PS)

4.3 System Model

4.4 Performance Analysis

4.5 Summary

References

5 Energy Management in LTE Femtocells

5.1 Introduction

5.2 Architecture of LTE Networks

5.3 Classification of ES Schemes

5.4 Energy Efficient Resource Allocation

5.5 Bandwidth Expansion Schemes

5.6 Load Balancing Schemes

5.7 Comparative Analysis

5.8 Open Research Issues

5.9 Summary

6 Spectrum Sensing Mechanisms in Cognitive Radio Based LTE Femtocells

6.1 Fundamentals of Signal Processing

6.2 Spectrum Sensing Techniques

6.3 History Assisted Spectrum Sensing

6.4 Model‐ and Statistics‐Based Spectrum Sensing Classification

6.5 Challenges and Issues

6.6 Summary

References

Part II: Antennas for LTE Femtocells

7 Antenna Consideration for LTE Femtocells

7.1 Antenna Fundamentals

7.2 Antenna Requirements for LTE Femtocells

References

8 Multiband Antennas for LTE Femtocells

8.1 Fundamentals of Multiband Antennas

8.2 Types of Multiband Antennas

8.3 Multiband Antenna Design: Case Studies

8.4 Open Research Issues

References

9 Reconfigurable Antennas for LTE Femtocells

9.1 Fundamentals of Reconfigurable Antennas

9.2 Realization of Reconfigurable Antennas

9.3 Rectangular Patch Reconfigurable LTE Femtocell Antenna

9.4 Circular Patch Reconfigurable LTE Femtocell Antenna

9.5 Open Research Issues

References

10 Multimode Antennas for LTE Femtocells

10.1 Multimode Antennas: Fundamentals and Types

10.2 Design of a Compact Multimode LTE Femtocell Antenna for Handheld Devices

10.3 Design of a Multifunctional Compact Antenna for LTE Femtocells and GNSS Systems

10.4 Summary

10.5 Open Challenges and Issues

References

11 Human Body Effects on LTE Femtocell Antennas

11.1 Interaction of the Human Body with Antennas

11.2 Numerical Modelling of the Human Body

11.3 Evaluation of Human Body Effects on LTE Femtocell Antennas

11.4 Open Research Issues

References

12 The Road Ahead for LTE Femtocells

12.1 Future Prospects and Challenges

References

Index

End User License Agreement

List of Tables

Chapter 01

Table 1.1 Comparison of mobile technologies.

Table 1.2 LTE network components.

Chapter 02

Table 2.1 Cost of using CR in femtocells.

Chapter 03

Table 3.1 Classification of safe/victim UE.

Table 3.2 Pros and cons of cognitive interference mitigation schemes.

Table 3.3 Synopsis of CR enabled interference mitigation schemes.

Chapter 04

Table 4.1 Simulation parameters.

Table 4.2 Percentage drop due to change in scenario (single to multicell).

Chapter 05

Table 5.1 LTE network components.

Table 5.2 Critical analysis of existing ES schemes.

Table 5.3 QoS factors involved in ES schemes.

Table 5.4 Open research issues.

Chapter 06

Table 6.1 Pros and cons of standard spectrum sensing techniques.

Table 6.2 Spectrum sensing methods and the models implemented.

Table 6.3 Statistics used in different spectrum sensing methods.

Table 6.4 Table of acronyms.

Chapter 07

Table 7.1 LTE frequency bands.

Chapter 08

Table 8.1 Optimized design parameters for the multislot patch multiband antenna

Chapter 09

Table 9.1 Comparison of switching technologies.

Table 9.2 Optimized dimensions of the proposed rectangular patch frequency reconfigurable antenna.

Table 9.3 Comparison of performance metrics for the rectangular patch frequency reconfigurable LTE antenna at two operating frequencies.

Table 9.4 Comparison of circular patch frequency reconfigurable antenna performance at the two LTE frequency bands.

Chapter 11

Table 11.1 Electric properties of specific human tissues at 2.45 GHz used within the constructed homogeneous body models [39].

Table 11.2 Comparison of the 10 g, 1 g and whole‐body averaged SAR values at 2.45 GHz for a handset antenna using high, medium and low resolution numerical models of the human body.

Table 11.3 Comparison of simulated parameters of on‐body Bluetooth communication channel using high‐, medium‐ and low‐resolution human body models (with reference to high‐resolution model).

Table 11.4 Comparison of the 1 g averaged SAR values at different frequencies of operation for the on‐body multiband antenna.

List of Illustrations

Chapter 01

Figure 1.1 LTE architecture.

Figure 1.2 Downlink resource block and sub‐frame structure in downlink LTE.

Chapter 02

Figure 2.1 Femtocell and interference in a two‐tiered network.

Figure 2.2 Cross‐tier analysis with; (a) the detriment and (b) importance of femtocells in a heterogeneous network.

Figure 2.3 Effect of femtocell access mode on MUEs.

Figure 2.4 Co‐tier interference in femtocells.

Figure 2.5 Varying FAP power levels and effect on MUEs.

Chapter 03

Figure 3.1 Femtocell deployment.

Figure 3.2 Femtocell scenario with co‐tier and cross‐tier interference.

Figure 3.3 Femtocell deployment scenarios.

Figure 3.4 Open access versus CSG.

Figure 3.5 Interference mitigation – hybrid spectrum allocation.

Figure 3.6 Interference mitigation – PC.

Figure 3.7 Interference mitigation – antenna schemes.

Figure 3.8 White spaces denoting availability of spectrum.

Figure 3.9 Cognitive interference mitigation schemes.

Figure 3.10 Interference mitigation on a per‐time slot basis.

Figure 3.11 Distributed carrier selection process – PCC and SCC.

Figure 3.12 Interference mitigation scenario to illustrate safe/victim UE.

Figure 3.13 Spectrum reuse – FAP assigns RBs of a far away MUE to FUE.

Figure 3.14 SCFN: Interference mitigation with main beam direction.

Figure 3.15 Interference mitigation through FPC.

Figure 3.16 CR enabled interference mitigation.

Chapter 04

Figure 4.1 Blind placement of a FAP and power spillage.

Figure 4.2 Coverage radius based PS.

Figure 4.3 Comparison of PS with other schemes.

Figure 4.4 SINR cross‐tier (single cell).

Figure 4.5 SINR co‐tier (single cell).

Figure 4.6 Downlink throughput (single cell).

Figure 4.7 Co‐tier SINR comparison (single versus multicell).

Figure 4.8 Cross‐tier SINR comparison (single versus multicell).

Figure 4.9 Percentage droppage in SINR (single‐ versus multicell).

Figure 4.10 Coverage radius bounds and effect on SINR (single‐ versus multicell).

Chapter 05

Figure 5.1 Architecture of LTE networks.

Figure 5.2 Classification of energy saving schemes.

Figure 5.3 Hybrid FBS and MBS based ES scheme.

Figure 5.4 Link adaptation scheme – LTE based downlink transmission.

Figure 5.5 MBSFN based frame architecture.

Figure 5.6 CoMP based coverage expansion.

Figure 5.7 OFDMA frame architecture.

Figure 5.8 Resource allocation through load balancing.

Figure 5.9 Carrier aggregation.

Figure 5.10 OFDMA‐based CC ES scheme.

Figure 5.11 Distance aware based BS communication.

Figure 5.12 BS coverage expansion for ES.

Figure 5.13 Distributed schemes: sectorization in BS.

Figure 5.14 State diagram for CRN based ES.

Figure 5.15 REHO ES scheme.

Figure 5.16 REHO dynamic power consumption.

Figure 5.17 Percentage of energy saved in each ES scheme.

Chapter 06

Figure 6.1 Additive Gaussian noise channel.

Figure 6.2 Linear filter channel with additive noise.

Figure 6.3 OFDM block diagram.

Figure 6.4 Spectrum sensing mechanisms.

Figure 6.5 (a) Energy detector implementation using analogue pre‐filter and square‐law device. (b) Energy detector implementation using periodogram FFT and averaging.

Figure 6.6 Main blocks of matched filter spectrum sensing technique.

Figure 6.7 Implementing pilot detection using matched filter technique.

Figure 6.8 Implementation of cyclostationary feature detection.

Figure 6.9 Implementation of a wavelet detector [34].

Figure 6.10 Centralized cooperative network.

Figure 6.11 Distributed cooperative network.

Figure 6.12 History assisted CR model using an analytical database [62].

Figure 6.13 Classification of spectrum sensing techniques based on models and statistics implemented.

Chapter 07

Figure 7.1 Input impedance model of an antenna.

Figure 7.2 Bandwidth of two antennas using

S

11

plotted against frequency.

Figure 7.3 3D radiation pattern of an electrically small antenna.

Figure 7.4 2D radiation pattern in elevation and azimuth planes of an electrically small antenna.

Figure 7.5 Spherical coordinate system and antenna radiation pattern features.

Figure 7.6 Propagation of a plane wave.

Figure 7.7 Polarization states of an electromagnetic wave.

Figure 7.8 Multipath propagation.

Figure 7.9 A typical MIMO arrangement in LTE systems.

Chapter 08

Figure 8.1 Generation of multiple resonances for multiband antenna operation via higher order resonance techniques.

Figure 8.2 Multiple resonant structures for multiband antenna operation using single feed and proximity feed methods.

Figure 8.3 Geometry and dimensions of the multislot patch antenna for multiband operation (all units are in mm) [28].

Figure 8.4 Reflection coefficient response of the multislot patch antenna [28].

Figure 8.5 Three‐dimensional radiation patterns of the multi‐slot antenna for multiband operation at 2.1, 3.6, 4.9 and 5.7 GHz [28].

Figure 8.6 Simulated peak gain values of the proposed multiband slotted patch antenna [28].

Figure 8.7 Simulated efficiency of the proposed multiband slotted patch antenna [28].

Figure 8.8 Geometry and dimensions of the patch‐loop microstrip patch multiband antenna operating at GPS/4G/Wi‐Fi frequencies (all units are in mm) [30].

Figure 8.9 Reflection coefficient response of the patch‐loop antenna for GPS/4G/Wi‐Fi multiband operation [30].

Figure 8.10 Two‐dimensional radiation patterns for the patch‐loop microstrip patch antenna for multiband operation at 1.575 GHz and 2.1 GHz in XZ and YZ planes [30].

Figure 8.11 Two‐dimensional radiation patterns for the proposed patch‐loop antenna for multiband operation at 1.575 and 2.1 GHz in XZ and YZ planes [30].

Figure 8.12 Peak gain values of the patch‐loop combination antenna for GPS/4G/Wi‐Fi multiband operation [30].

Figure 8.13 Efficiency of the patch‐loop combination antenna for GPS/4G/Wi‐Fi multiband operation [30].

Figure 8.14 Surface current distribution at 1.575 GHz and 2.1 GHz for the patch‐loop multiband antenna [30].

Figure 8.15 Surface current distribution at 3.68 GHz and 5.37 GHz for the patch‐loop multiband antenna [30].

Chapter 09

Figure 9.1 Use of PIN diode to achieve switching between two frequencies through changed effective length of a simple patch antenna.

Figure 9.2 Use of varactor to vary the effective length of a PIFA to achieve reconfigurable antenna operation.

Figure 9.3 Geometry and dimensions of the rectangular patch reconfigurable LTE antenna (all units are in mm).

Figure 9.4 Surface current distribution of the rectangular patch reconfigurable antenna in the filled configuration at 1.575 and 2.45 GHz.

Figure 9.5 Surface current distribution of the rectangular patch reconfigurable antenna in the unfilled configuration at 1.575 and 2.45 GHz.

Figure 9.6 Reflection coefficient response of the rectangular patch reconfigurable LTE antenna operating at two frequencies.

Figure 9.7 Three‐dimensional radiation pattern of the rectangular patch reconfigurable antenna in unfilled configuration operating at 2.45 GHz.

Figure 9.8 Three‐dimensional radiation pattern of the rectangular patch reconfigurable antenna in filled configuration operating at 1.575 GHz.

Figure 9.9 Geometry and dimensions of the circular patch reconfigurable LTE antenna (all units are in mm) [48].

Figure 9.10 Surface current distribution on the circular patch reconfigurable antenna in a filled configuration at 3.6 and 5 GHz.

Figure 9.11 Surface current distribution on the circular patch reconfigurable antenna in an unfilled configuration at 3.6 and 5 GHz.

Figure 9.12 Reflection coefficient response of the circular patch reconfigurable LTE antenna operating at two frequencies.

Figure 9.13 Three‐dimensional radiation pattern of the circular patch reconfigurable antenna in a filled configuration operating at 3.6 GHz.

Figure 9.14 Three‐dimensional radiation pattern of the circular patch reconfigurable antenna in an unfilled configuration operating at 5 GHz

Chapter 10

Figure 10.1 Geometry of the proposed CWSGP antenna showing the (a) top view and (b) back view of the antenna.

Figure 10.2 Simulated axial ratio of different truncated inner patch, C.

Figure 10.3 Different stages of the ground plane slots in the proposed CWSGP antenna. (a) Four horizontal slots. (b) Eight horizontal slots. (c) Ten horizontal slots. (d) Ten horizontal and two vertical slots.

Note: a1 = 17 mm, a2 = 21 mm, a3 = 4 mm, a4 = 1 mm, b1 = 24 mm, b2 = 14 mm, a5 = 6.5 mm, d1 = d4 = 10.5 mm, d2 = 5.5 mm and d4 = 9.5 mm, m = 3.1 mm and l = 23.5 mm

Figure 10.4 Simulated reflection coefficients and axial ratios of different stages of the grounded slots in the proposed CWSGP antenna. (a) Reflection coefficients and (b) axial ratios.

Figure 10.5 Fabricated prototyped CWSGP antenna: (a) top view and (b) back view.

Figure 10.6 Measured and simulated reflection coefficient and axial ratio of the proposed CWSGP antenna: (a) measured and simulated reflection coefficient and [40] (b) simulated axial ratio.

Figure 10.7 Measured and simulated radiation pattern at 2.6 GHz showing the RHCP and LHCP of the proposed CWSGP antenna.

Figure 10.8 Measured and simulated radiation pattern at 2.3 GHz showing the RHCP and LHCP of the proposed CWSGP antenna.

Figure 10.9 Simulated current distribution of the proposed CWSGP antenna at 2.6 GHz.

Figure 10.10 Simulated current distribution of the proposed CWSGP antenna at 2.3 GHz.

Figure 10.11 Geometry of the proposed stacked patch triple‐band dual‐polarized antenna: (a) configuration of the antenna and (b) top view of the antenna [41].

Figure 10.12 Variation of the antenna parameters for different values of breadth g of I‐slot (lower patch): (a) reflection coefficient and (b) AR [41].

Figure 10.13 Variation of the antenna parameters for different values of length, c (middle patch I‐slot): (a) reflection coefficient and (b) AR [41].

Figure 10.14 Variation of the antenna parameters for different values of breadth g of I‐slot (lower patch): (a) reflection coefficient and (b) AR [41].

Figure 10.15 Fabricated prototype of the stacked patch triple‐band dual‐polarized antenna: (a) top view and (b) bottom view [41].

Figure 10.16 Measured and simulated reflection coefficient and AR of the stacked patch triple‐band, dual‐polarized antenna: (a) measured and simulated reflection coefficient and (b) measured and simulated AR [41].

Figure 10.17 Measured and simulated RHCP and LHCP radiation patterns in XZ‐plane of the stacked patch triple‐band, dual‐polarized antenna at 1.227 GHz [41].

Figure 10.18 Measured and simulated RHCP and LHCP radiation patterns in XZ‐plane of the stacked patch triple‐band, dual‐polarized antenna at 1.575 GHz [41].

Figure 10.19 Linear polarized radiation pattern at 1.800 GHz showing both the measured and simulated co and cross polarization at XZ‐plane [41].

Figure 10.20 3D radiation pattern showing the RHCP and LHCP of the stacked patch triple‐band, dual‐polarized antenna at 1.227 GHz [41].

Figure 10.21 3D radiation pattern showing the RHCP and LHCP of the stacked patch triple‐band, dual‐polarized antenna at 1.575 GHz [41].

Figure 10.22 3D radiation pattern showing the THETA and PHI of the stacked patch triple‐band, dual‐polarized antenna at 1.800 GHz [41].

Figure 10.23 Simulated Cartesian plots of the stacked patch triple‐band, dual‐polarized antenna showing a wider beamwidth at the upper hemisphere for 1.227 GHz and 1.575 GHz at

 = 0°, 45° and 90° [41].

Chapter 11

Figure 11.1 Structure of realistic high‐resolution, simplified medium‐resolution and basic low‐resolution numerical models of the human body with on‐body positioned headset and handset antennas (all lengths are in mm) [40].

Figure 11.2 Simulation set‐up (showing on‐body test configurations with headset and handset antenna positions, location of cross‐section plane and definition of curves for the observation of electric field distribution), antenna prototypes and measurement set‐up in an anechoic chamber (all lengths are in mm) [40].

Figure 11.3 Comparison of simulated and measured average path gains for Bluetooth headset and handset antennas at 2.45 GHz [40].

Figure 11.4 Comparison of simulated 2D radiation patterns of headset meander line monopole antenna at 2.45 GHz using different human body models [40].

Figure 11.5 Comparison of simulated 2D radiation patterns of a handset PIFA antenna at 2.45 GHz using different human body models [40].

Figure 11.6 Comparison of normalized electric field distributions on the three human body models for handset LTE antenna on the cross section plane through a headset LTE antenna [40].

Figure 11.7 Electric field strength on the curves between the handset and the headset antennas in front of the three body models, corresponding to Figure 11.2(a) [40].

Figure 11.8 Comparison of maximum SAR distributions on the three human body models for handset antenna [40].

Figure 11.9 Geometry and dimensions of the slot‐ring microstrip patch multiband antenna operating at GPS/4G/Wi‐Fi frequencies (all units are in mm [46, 47]).

Figure 11.10 Structure of a realistic high‐resolution numerical model of the human body (all lengths are in mm) [47].

Figure 11.11 Reflection coefficient response of the multiband microstrip patch antenna with and without human body presence [47].

Figure 11.12 On‐body placement of the antenna at different body locations [47].

Figure 11.13 Reflection coefficient response of the multiband microstrip patch antenna while placed at different on‐body positions.

Figure 11.14 Antenna placement at different separations from the human body.

Figure 11.15 Reflection coefficient response of the multiband microstrip patch antenna with varying separations between the human body and the antenna.

Figure 11.16 Path gain response of the multiband microstrip patch antenna in different on‐body channels.

Figure 11.17 Considered scenarios for evaluation of the antenna performance in on‐off body and body‐body channels.

Figure 11.18 Path gain performance of the multiband microstrip patch antenna in on‐off body LOS and NLOS configurations [47].

Figure 11.19 Path gain performance of the multiband microstrip patch LTE antenna in body‐to‐body LOS and NLOS configurations.

Guide

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LTE Communications and Networks

Femtocells and Antenna Design Challenges

Edited by Masood Ur Rehman and Ghazanfar Ali Safdar

School of Computer Science and Technology, University of Bedfordshire, Luton, UK

This edition first published 2018© 2018 John Wiley & Sons Ltd

All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, except as permitted by law. Advice on how to obtain permission to reuse material from this title is available at http://www.wiley.com/go/permissions.

The right of Masood Ur Rehman and Ghazanfar Ali Safdar to be identified as the authors of the editorial material in this work has been asserted in accordance with law.

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Library of Congress Cataloging‐in‐Publication DataNames: Ur‐Rehman, Masood, editor. | Safdar, Ghazanfar Ali, 1973– editor.Title: LTE communications and networks : femtocells and antenna design challenges / edited by Masood Ur Rehman, Ghazanfar Ali Safdar.Description: First edition. | Hoboken, NJ : John Wiley & Sons, 2018. | Identifiers: LCCN 2017056167 (print) | LCCN 2018006050 (ebook) | ISBN 9781119385240 (pdf) | ISBN 9781119385257 (epub) | ISBN 9781119385226 (cloth)Subjects: LCSH: Long‐Term Evolution (Telecommunications) | Femtocells. | Antennas (Electronics)–Design and construction.Classification: LCC TK5103.48325 (ebook) | LCC TK5103.48325 .L7346 2018 (print) | DDC 621.3845/6–dc23LC record available at https://lccn.loc.gov/2017056167

Cover design by WileyCover image: © Jan Jirous/Shutterstock

To my parents, Khalil Ur Rehman and Ilfaz Begum and my siblings, Habib Ur Rehman, Waheed Ur Rehman and Tahera Kalsoom.Masood Ur Rehman

To my late parents, Safdar Hussain and Sadiq Sultana and my two little angels, Taha and Taqi and my wife, Misbah.Ghazanfar Ali Safdar

List of Contributors

Qammer Hussain AbbasiSchool of EngineeringUniversity of Glasgow, Glasgow, UK

Xiaodong ChenSchool of Electronic Engineering and Computer ScienceQueen Mary, University of London, London, UK

Oluyemi Peter FaladeTempfad Limited, Leyton, London, UK

Waqas FarooqSchool of Computer Science and TechnologyUniversity of Bedfordshire, Luton, UK

Kapil KanwalSchool of Computer Science and TechnologyUniversity of Bedfordshire, Luton, UK

Masood Ur RehmanSchool of Computer Science and TechnologyUniversity of Bedfordshire, Luton, UK

Ghazanfar Ali SafdarSchool of Computer Science and TechnologyUniversity of Bedfordshire, Luton, UK

Tazeen S. SyedSchool of Computer Science and TechnologyUniversity of Bedfordshire, Luton, UK

Xiaodong YangSchool of Electronic EngineeringXidian University, Xi’an, China

Preface

Long Term Evolution (LTE) technology has brought about a revolution in the field of wireless communications. It has attracted huge attention due to its essential features of being an easily deployable network, offering high data rates and low latencies over long distances. Almost all new cellular and portable communication devices are now LTE enabled. It is also being used as a basis for the upcoming 5G technology and Internet‐of‐Things (IoT) concept, which will allow connectivity anywhere and anytime. It is growing fast to fulfil the ever‐increasing demand from millions of users worldwide with applications ranging from communications to infotainment, healthcare to surveillance and transportation to manufacturing. Sales of LTE‐enabled smart phones alone were expected to grow from 450 million units in 2015 to over 900 million units in 2017.

With huge benefits on offer, the LTE faces challenges of spectrum cognition, interference mitigation and power control. Efficient solutions to these challenges are necessary to enhance the performance of this technology. Femtocells are envisioned as a step forward to smart and low‐interference LTE systems. Moreover, the performance of the overall wireless devices is dictated by the working of embedded antennas. Design of the LTE antennas is getting more complex day‐by‐day due to the advent of new design methodologies, innovative material technologies, miniaturization of devices and performance degradations caused by the user.

The current developments and expected future growth of the LTE demands availability of a comprehensive reference that deals with these systems in the context of femtocells and antennas. This book is an effort to fill this gap by educating the reader on the most important aspects of LTE femtocells and lays the foundations for future advancements. It brings together multidisciplinary contributions in the field of wireless and mobile communications, signal processing and antenna design to identify technical challenges and present recent results related to the development, integration and enhancement of LTE systems in portable devices. Both state‐of‐the‐art and advanced topics including application of cognitive radio with efficient sensing mechanisms, interference mitigation and power management schemes for the LTE systems are discussed. Moreover, a comprehensive account of design challenges and approaches, performance enhancement techniques and effects of a user’s presence on the LTE antennas is presented. Particular focus is put on the promising technologies of multiband, multimode and reconfigurable antennas for efficient design of portable LTE devices. Although the book is intended to be practical, theoretical details are revisited where it is required.

This is the first dedicated book that gives such a broad treatment to LTE systems in the context of femtocells and antenna design, covering wide range of issues related to the topic. The organization of the book makes it a valuable reference for the LTE system designers, as well as an introductory text for researchers, lecturers and students.

Masood Ur RehmanGhazanfar Ali Safdar

1Introduction

Ghazanfar Ali Safdar and Masood Ur Rehman

School of Computer Science and Technology, University of Bedfordshire, Luton, UK

Wireless communication has involved relentless years of research and design and comprises cellular telephony, broadcast and satellite television, wireless networking to today’s 3rd Generation Partnership Project (3GPP) and Long Term Evolution (LTE) technology. However, cellular telephony networks surpass the others in terms of usage [1]. Although cellular networks were designed to provide mobile voice services and low rate mobile data services, data services have excelled voice and findings show that global data traffic has grown by 280% since 2008 and is expected to double annually in the next 5 years [2]. Importantly, it already exceeded those expectations by 2010 by nearly tripling and it is further predicted that by 2020 nearly 1 billion people will access the Internet using a wireless mobile device [3].

The introduction of new or the upgrade of existing wireless standards such as the Institute of Electrical and Electronics Engineers (IEEE) Worldwide Interoperability for Microwave Access (WiMAX) and 3GPP’s LTE have been developed to meet traffic and high data rates. Most of the methods to increase spectrum capacity in practice today are aligned towards; (1) improving the macro layer by upgrading radio access, (2) densifying the macro layer by reducing inter‐site distances and (3) the use of low power nodes to complement the macro layer [4]. Macro layer deployment is a typical approach of deploying Base Station (BS) in proximity to each other covering large distances with reduced handover frequency. Although it is the backbone of most wireless networks, it has proven to be inefficient as it does not guarantee a high‐quality link in situations where the BS and Mobile Station (MS) are relatively far away. Moreover, a BS serving hundreds of contentious users all vying for resources is old fashioned [5]. Researchers indicate that 50% of all voice calls and most of the data traffic, more than 70%, originate indoors [6]. However, indoor users may suffer from a reduced Received Signal Strength (RSS) due to low signal penetration through the walls or attenuation leading to total loss of signal in situations where the distance between transmitter and receiver is large. There is a need to provide solutions for poor indoor coverage to satisfy consumers. According to [5] the solutions to poor indoor coverage can be classified into two types, Distributed Antenna Systems (DAS) and Distributed Radios.

Distributed Antenna Systems comprise a group of Remote Antenna Units (RAU) spaced apart, providing not only enhanced indoor signal quality by significantly reducing transmission distance but also reducing transmit power (the power of the reference signal) [7]. Some of the challenges involved in deploying DAS are the choice of antennas and selecting a suitable location [8, 9]. Distributed radios involve the introduction of smaller cells to complement the deficiencies of the larger macrocell and the gains include an efficient spatial reuse of spectrum [10]. These small cells, which include picocells and microcells, are overlaid in the macrocell to provide voice and data service. Due to the two‐tier nature of its architecture, it is prone to interference that may result in a low Signal to Interference plus Noise Ratio (SINR), throughput and in some cases a total disruption of service. As a result, there is a need to provide interference avoidance and mitigation schemes. Recently, a new distributed form of radio, LTE femtocells, has emerged that promises to be a viable solution to indoor cellular communication.

1.1 Evolution of Wireless and Cellular Communication

Communication has been essential for humanity to interact with one another where distance, quality of communication and high demand have always been important factors. Thus, it has evolved over the recent decades to overcome such factors in which newer and more obstacles have arrived in order to meet these challenges. Mobile communication has gradually evolved in shape of different generations as described next.

1.1.1 1 G

1G stands for the first generation of wireless mobile communication, which was first implemented in North America in the early 1980s. The technology was also known as Analogue Mobile Phone Systems (AMPS) based on an analogue system; that is, where information is transmitted by controlling a continuous transmission signal, such as amplifying signal strength or varying its frequency in relation to actual data. This system mainly provided services such as voice over a set radio frequency. In order for users to communicate, they would have to maintain a large distance from communicating points and use sufficiently large handsets. A mobile user would have to connect to the mobile base station that connects to the MTSO (Mobile Telecommunication Switching Office) that contains an MSC (Mobile Switching Centre) for routing mobile calls. The MTSO is then connected to the PSTN (Public Switch Telephony Network), which is a collection of unified voice‐oriented public telephone networks [11].

1.1.2 2 G

2G stands for the second generation of wireless mobile communication and finished its establishment in the late 1990s. It was based on the Global System for Mobile Communication (GSM). GSM is a digital cellular phone system and it uses a variation of TDMA (time‐division multiple access). 2G introduced digital traffic and voice encoded into digital signals. From its predecessor, it evolved and brought features such as SMS (short messaging service) and the quality of service for voice communication considerably improved [11].

1.1.3 2.5 G

2.5G GPRS (General Packet Radio Service) is a bridge between the second and third generations of wireless technology. GPRS supports MMS (multimedia messaging service), WAP (Wireless Application Protocol) Access and connects to the Internet. The first major step in the advancement of GSM networks to 3G (3rd Generation) of wireless mobile technology is GPRS. The service has added value to the GSM network by transmitting data by overlaying a packet based air interface on the existing circuit‐switch‐based GSM network. The voice traffic with this carrier is circuit switched, whereas the data is packet switched [12].

1.1.4 2.75 G

2.75G is based on an Enhanced Data rates for GSM Evolution (EDGE) and was the major breakthrough before the evolution of 3G. EDGE technology allows fast transmission of data and information and one of its major advantages is that the existing GSM networks can also support this technology and be upgraded. EDGE is preferred over GSM due to its flexibility and the provision of capacity, global roaming and data size as compared to GPRS [12].

1.1.5 3 G

3G stands for the third generation of mobile technology, which was introduced in 2005. It is based on set standards that are used for mobile devices meeting the terms of the ITU (International Telecommunication Union). 3G features CDMA (code division multiple access), a channel access method where a single channel can be used by multiple users to transmit data on the same frequency. The most common form of 3G usually identified as UMTS (Universal Mobile Telecommunications System/Standards) is WCDMA (Wideband Code Division Multiple Access). It can use both voice and data services consecutively and offers faster data rates compared to EDGE. Data is sent through packet switching while video traffic is managed through circuit switching. 3G provides services like web browsing, multimedia, navigation and smartphone applications that require higher data rates. It has backward compatibility with 2G mobile technology, which means a user is able to use services such as voice and SMS alongside data [13].

1.1.6 3.5 G

3.5G is an improvement of UMTS and also known as CDMA2000 and High Rate Packet Data (HRPD) or Evolution Data Optimised (EV'DO). With 3.5G technology, there is improved capacity featuring high‐speed packet access, almost five times faster than an average 3G mobile technology. HSPA (High‐Speed Packet Access) extends and improves the performance and working of existing WCDMA systems. Although there are some technical differences between CDMA2000 and UMTS, which includes the fact that CDMA2000 is backward compatible with IS‐95. Interim Standard 95 was the first CDMA‐based digital technology; that is, IS‐95 devices can communicate with CDMA2000 BS whereas UMTS is not compatible with 2G GSM. Furthermore, UMTS uses the same carrier frequency for all types of traffic such as voice and data whereas CDMA2000 separates the traffic to multiple carriers [13].

1.1.7 4 G/LTE

LTE is a standard introduced by the 3GPP (3rd Generation Partnership project). There are a number of factors that LTE has helped to overcome with its following characteristics.

High throughput – high data rates, which can be achieved in uplink and downlink

Low Latency – unnoticeable delays between an input being processed and the corresponding output providing real time characteristics; for example, establishing a connection to a nearby network within a few milliseconds

Improved Quality of Service

Smooth handover across heterogeneous networks

High network capacity to accommodate user demands for high bandwidth.

LTE is based on OFDMA (Orthogonal Frequency Division Multiple Access) in which the system transmits large amount of data; that is, large bandwidths up to 20 Mbps. Multiple access is achieved in OFDMA by assigning subnets of subcarriers to individual users. Table 1.1 briefly compares different generations of mobile technologies.

Table 1.1 Comparison of mobile technologies.

Technology

1G

2G/2.5G/2.75G

3G/3.5G

LTE/4G

Features

Makes use of analogue radio signals

Analogue voice service

No data service

Uses digital radio signals

Voice encoded to digital signals

GSM

Supports digital voice service, SMS messaging, improved voice clarity, Comparatively secure

GPRS

Supports MMS, Internet

Fast data transfer rate, improved spectral efficiency, greater network capacity

Enhanced audio video streaming, video conferencing support,

Web browsing at higher speeds, IPTV support

Converged data and voice over IP

Entirely packet switched network,

Higher bandwidth to provide multimedia services at lower cost

Enhanced audio, video streaming, IP telephony, HD mobile TV

Standards

MTS, AMTS,IMTS

2G: GSM2.5: GPRS2.75: EDGE

IMT‐20003.5G‐HSDPA3.75G: HSUPA

Single unified standard LTE, LTE adv. Mobile WiMAX

Web Standards

—

www

www (IPv4)

www (IPv4)

Technology

Analogue cellularTechnology 14.4 Kbps

Digital narrow bandcircuit data, Packet data171.2 Kbps (peak).20–40 Kbps

Digital BroadbandPacket data3.1 Mbps (peak)500–700 Kbps3.5G:14.4 Mbps (peak)1–3 Mbps

Digital Broadband Packet, Very high throughput100–300 Mbps (peak)3–5 Mbps100 Mbps (Wi‐Fi)

Service

Voice Calls

2G: Digital voice, SMS2.5: Higher capacitypacketized

Integrated high‐quality audio, video and data

Dynamic information access, wearable devices with AI capabilities

Switching

Circuit switching

2G: Circuit2.5G: Circuit for access network and air interface,packet for core network

Packet except for circuit for air interface

Packet switching,message switching

Handoff

Horizontal only

Horizontal only

Horizontal and vertical

Horizontal and vertical

Shortfall

Low capacity,unreliable handoff, poor QoS for voice, less secure

Reliant on location and proximity, required strong digital signals to help mobile phones

Requires highernetwork capacity to accommodate growing consumers

Being deployed

1.2 LTE Architecture

The LTE systems usually provide low latency, high data rate and packet optimized radio access. Compared to 3G, LTE additionally provides international roaming and compatibility with other legacy networks [14–16]. The 4G systems make use of OFDMA and Single Channel Frequency Division Multiple Access (SC‐FDMA) schemes to support flexible bandwidth [17–23]. LTE architecture is generally based on Evolved Packet Core (EPC), Universal Terrestrial Radio Access (UTRA) and Universal Terrestrial Radio Access Network (UTRAN), each of which communicates with core network air interfaces and radio access network [24, 25].

Figure 1.1 illustrates the overall architecture of the LTE networks showing both EPC and evolved UTRAN (E‐UTRAN) [26, 27] while Table 1.2 summarizes the core elements of the LTE architecture.

Figure 1.1 LTE architecture.

Table 1.2 LTE network components.

Components

Description

Evolved Packet System (EPS)

Provides IP connectivity using E‐UTRAN.

MobilityManagement Entity (MME)

Responsible for authorization, security, handover, roaming and mobility of users.

S1 Interface

It connects EPC with BSs (base stations).

Serving Gateway (S.GW)

EPC terminates at this node. It is connected to E‐UTRAN through S1 interfaces. Each user is allocated unique S.GW, which is responsible for handover, packet routing and forwarding functions.

Packet data network gateway (PDN‐GW)

PDN‐GW provides UEs with access to packet data network by allocating IP addresses. It is also responsible for secure connection with untrusted devices from non‐4G networks.

HnodeB

Femtocells that are employed to improve seamless connectivity in coverage holes.

eNodeB

Also known as BS that serves the UEs.

HnodeB GW

Provides connection to the core network.

X2 Interface

Provides communication between two BSs.

1.2.1 Communications Perspective Challenges in LTE Networks

Though LTE has proven to be a promising technology, it is a complex network and there are some challenges that need to be carefully addressed for optimum functionality.

1.2.1.1 Signalling System

In LTE networks, one of the major issues is to avoid or limit signalling overhead and overlapping in the control part of the network. A large number of connections between nodes and network fragmentation causes rapid increase in signalling traffic. Any failure in signalling system will drag operators towards increased system latency and outages resulting in to loss of revenues [28, 29]. Increased signalling traffic also leads to increased energy consumption and definitely needs to be looked into carefully.

1.2.1.2 Backward Compatibility

LTE is usually compatible with all other relevant major standards. The combination of devices, network interfaces and equipment to support other standards complicates end‐to‐end functionality testing and interoperability testing (IOT) [30, 31].

1.2.1.3 BS Efficiency

Due to the employment of OFDMA in LTE, signals have high amplitude variability known as Peak‐to‐Average Power Ratio (PAPR), which reduces transmitter efficiency. Furthermore, the BS provides high data rate at the cost of high dynamic transmission power. Since high transmission power results in increased energy consumption and thereby increases Operational Expenditure, energy management has become a major challenge in LTE networks to stay profitable and also to reduce global warming [32].

1.2.2 LTE Radio Frame

The radio frame of LTE is defined as having a length of 10 ms as illustrated in Figure 1.2. It is divided equally into 10 sub‐frames of duration per sub‐frame. Each sub‐frame is further divided into slots of length . Each sub‐frame contains or OFDM symbols on the length of the selected cyclic prefix. An extended cyclic prefix of 16.7 µs is allowed in LTE, which might be suitable in accommodating delay.

Figure 1.2 Downlink resource block and sub‐frame structure in downlink LTE.

However, in femtocells, a normal length cyclic prefix (TCP = 5.2 µs) might be enough due to its limited coverage area and short delay periods as compared with a Macrocell Base Station. More information about the frame structures can be found in [33].

1.3 LTE Antennas

The antenna acts as a transducer between the guided electromagnetic wave travelling in a radio frequency circuit or transmission line and the unguided electromagnetic wave travelling in free space. It is the fundamental building block in the development of any wireless communications system.

The requirements for LTE antennas depend on the specific application or where it will be used since there is a need to meet the increased demand for a high data rate. Varying LTE applications consideration of a number of specific factors in antenna selection such as polarization, multi‐frequency or multi‐mode operation, multiple‐input multiple‐output (MIMO) structure, reconfigurability, directionality and certain specific absorption rate on top of common requirements of size, bandwidth, gain, radiation pattern and efficiency. The antenna can be put on mobile handheld terminal, laptop, BS, access points, high‐speed trains or cars, aeroplanes and so on.

Antenna selection and design is a challenging task that necessitates the utmost care as a poorly chosen antenna can severely affect the cost and performance of the overall LTE system.

1.4 LTE Applications

LTE has become a global wireless foundation supporting continual enhancements. Its applications range from communications to health monitoring, surveillance to public safety and smart homes to entertainment.

1.4.1 Communications

The major application area of LTE technology is cellular communications. It carries inherent benefits of reduced latency and increased data rates offering peak downlink data rates of 300 Mbps, peak uplink rates of 75 Mbps and QoS measures allowing latency of less than 5 ms in the radio access networks. It can manage moving devices and supports multicast and broadcast streams. Both frequency division duplexing (FDD) and time‐division duplexing (TDD) can be used in LTE. These advantages have made LTE the front‐runner in mobile communications standards.

1.4.2 Public Safety

An important LTE application area is public safety. Initially, it was a broadband data service that eventually turned into mission‐critical voice service.

Micro‐location information from small cells allows emergency and health services to locate the emergency. The USA and the UK have developed authorities, namely the First Responder Network Authority (FirstNet) and Emergency Service Network, employing LTE for public safety. Use of LTE for this purpose has special requirements in terms of features, network deployment and device‐level approaches that differ from general communication application.

1.4.3 Device‐to‐Device Communications

LTE supports autonomous discovery and communication of a device with nearby devices and services in a battery‐efficient manner. A device can broadcast its needs and services and can also passively identify services without user intervention. In this application scenario, the LTE network performs configuration and authentication while communication can take place either via the network or directly between the devices. It is fast becoming popular for emergency scenarios and disaster management when the rest of the network is unavailable.

1.4.4 Video Streaming

LTE is widely used for video streaming that requires high data rates. An increasing number of video applications, such as Netflix and Skype, adapt their streaming rates based on available bandwidth enabling them to continue operation even when throughput rates drop. LTE also supports video streaming via multicast or broadcast functions.

1.4.5 Voice over LTE (VoLTE)

LTE offers a transition from circuit‐switched voice (VoIP) to Voice over LTE (VoLTE). Using VoLTE, high‐definition voice transfer is possible having improved clarity and intelligibility and reduced background noise using Multi‐Rate Wideband voice codecs. Other advantages of VoLTE include ability to combine it with other services, such as video calling and presence and high voice spectral efficiency.

1.4.6 Internet of Things

LTE is one of the key enabling technologies from the Internet of Things (IoT). Though not fully implemented yet, early IoT applications do exist in the form of Machine‐to‐Machine (M2M communications) including vehicle infotainment, remote health, smart metering, security and home automation, construction and heavy equipment and industrial manufacturing. “Smart cities” initiatives are also supporting vast research and development activities. Although promising, the IoT market has to deal with numerous challenges such as varying communications requirements, long battery requirements, cost sensitivity and security concerns to name a few. Research is continuing to devise efficient methods addressing these issues.

1.4.7 Wearable Systems

One of the major application areas of the LTE systems is wearable systems for health monitoring, emergency services and entertainment. The user wears a body‐worn LTE device, such as the smart phone, smart watch or health tracker. It gathers vital physiological parameters and transmits required information to the access point that relays the information to the relevant services such as hospitals or fire fighters for appropriate action. New Wearable Augmented Reality applications such as Google Goggles and Samsung Gear are also fast becoming available. These applications need micro‐location information provided by the LTE femtocells. Apart from the location information, the user’s interests, place and context can also be used in these applications to retrieve relevant information.

1.4.8 Cloud Computing

LTE is also being used in cloud computing where the delivery of computing services like servers, storage, databases, networking, software and analytics is made available over the Internet. Cloud computing eliminates the cost of buying site‐specific hardware and software, offers high mobility, scalability and reliability through data backup, disaster recovery and business continuity. However, issues of security and privacy are restricting its universal acceptance up to now.

1.5 Book Organization

LTE technology has brought a revolution in the field of wireless communications. It has attracted huge attention due to its essential features of being an easily deployable network, offering high speeds and low latencies over long distances. Femtocells are envisioned as a step forward to smart homes and low‐interference LTE systems. In this book, many challenging issues of LTE femtocells and LTE antennas are discussed giving solutions from a technology and application point of view.

The book is divided into two parts. Part I (Chapters 2–6) deals with femtocells and the topics of cognitive radio, interference mitigation and power management schemes for LTE femtocell systems. Part II (Chapters 7–11) discusses the design challenges, different approaches, performance enhancement and application case scenarios for LTE antennas. Chapter 12 presents the concluding remarks and future prospects for LTE femtocells.

Chapter 2 provides an introduction to the LTE communications in femtocells and the rationale for selecting this communication mode. Interference is one of the major hurdles in the deployment of an efficient, robust and reliable communications link. The ever‐growing communication sector with an increasing number of devices and introduction of new technologies demands methods to mitigate it without altering the communication quality. This chapter also discusses various techniques for interference mitigation.

Chapter 3 discusses cognitive radio applications in LTE femtocells, which is considered as one of the key techniques to manage the increasingly important problem of spectrum shortage by allowing unlicensed users to utilize the licensed spectrum when the licensed user is not occupying it. This chapter introduces the concept of cognitive radio femtocells and deals with the issue of the interference by employing various mitigation strategies. A comparative analysis of these techniques is also presented to recommend an optimal approach.

Chapter 4 explains the fundamentals of coverage area based power control scheme and describes its usability in LTE femtocells to mitigate interference within a cell as well as across multiple cells using metrics of SINR, throughput and droppage.

Chapter 5 discusses importance of energy management in LTE femtocells that is one of the major constraints for wireless devices. Different energy saving schemes for the LTE femtocells are discussed presenting a comparative study to highlight advantages and disadvantages of these schemes while identifying the optimal solution.

Chapter 6 gives detailed discussion on working principles and operation of different sensing mechanisms employed in cognitive radio LTE femtocells as efficient sensing mechanisms are required to increase usability of the spectrum and minimize interference and collision of the secondary user with the primary user. It also identifies the strengths and weaknesses of these techniques through thorough comparative analysis.

Chapter 7 introduces antenna technology for LTE systems discussing fundamental parameters including bandwidth, gain, directivity, polarization, radiation pattern and efficiency. Complexity of the LTE antenna design, due to specific operational requirements on top of fundamental parameters such as form factor, SAR, working on various frequency bands and MIMO, is also highlighted.

Chapter 8 discusses the basics of the multiband antennas operating at multiple frequency bands and their importance in LTE systems to support various technologies. The design procedure and performance evaluation of three candidate antenna solutions for LTE femtocells are also described.

Chapter 9 deals with the fundamentals of reconfigurable antennas for multiple frequency LTE operation with a controlled switching mechanism to meet with the device size and form factor requirements. Different design approaches of reconfigurable antennas are also detailed along with the study of two candidate antenna solutions for LTE femtocell systems.

Chapter 10 covers the design challenges and proposes an effective solution for multi‐mode antennas for LTE femtocells covering multi‐frequency bands. The efficiency of multi‐mode antennas in devising compact, cost effective, simple and highly efficient LTE devices is also discussed.

Chapter 11 investigates the performance of various LTE femtocell antennas for the human body effects considering different wearable scenarios as the human body is an integral part of practical portable LTE systems. Body‐to‐body communication is considered a special case of LTE communications for emergency services. The prospects of body‐to‐body communication between two LTE devices carried by two users are also discussed in this chapter in terms of antenna design.

Chapter 12 presents the applicability of the LTE femtocell systems in future communication devices. It also highlights potentials and discusses challenges that need to be addressed in order to maximize the abilities and benefits of the LTE Femtocell and LTE antennas.