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Green Radio Communication Networks Applying Radio-over-Fibre Technology for Wireless Access

Doctoral Thesis / Dissertation 2011 195 Pages

Engineering - Communication Technology

Excerpt

Table of Contents

Abstract

Acknowledgement

Author’s Declaration

List of Figures

List of Contributed Publication

Chapter 1
Introduction
1.1 Wireless Access Network
1.2 Research Motivation
1.3 Green Radio Communication
1.4 Fibre Optic Access Network
1.4.1 Radio over Fibre (RoF)
1.4.2 Challenges and Problems in RoF
1.5 Research Objective and Contributions
1.5.1 RoF base SMF, DCF, FBG and CFBG
1.5.2 WDM-RoF
1.5.3 GPON/CWDM-RoF
1.6 Thesis Structure

Chapter 2
Literature Review - Fundamental Concept of Fibre Optic Technology
Literature Review
2.1 Introduction
2.2 Propagation of Light
2.2.1 Refraction of Light Waves
2.2.2 Nonlinear Schrödinger Equation (NLS)
2.3 Optical Fibre
2.3.1 Multi Mode Fibre (MMF)
2.3.2 Single Mode Fibre (SMF)
2.4 Fibre Attenuation
2.4.1 Low Water Peak
2.4.2 Rayleigh Scattering
2.5 Dispersion
2.5.1 Intermodal or Modal Dispersion
2.5.2 Intra-modal or Chromatic Dispersion
2.5.2.1 Material Dispersion
2.5.2.2 Wave-guide Dispersion
2.6 Dispersion Compensating Modules (DCM)
2.6.1 Dispersion Compensating Fibre (DCF)
2.6.2 Fibre Bragg Grating (FBG)
2.6.3 Chirped Fibre Bragg Gratings (CFBG)
2.7 Radio over Fibre in Communication Networks
2.7.1 Direct Modulation
2.7.2 External Modulator
2.8 Applications in RoF Networks
2.8.1 RF over Fibre (Remote RoF)
2.8.2 Orthogonal Frequency-Division Multiplexing (OFDM)
2.8.3 Wavelength Division Multiplexing (WDM)
2.8.4 Dense Wavelength Division Multiplexing (DWDM)
2.8.5 Coarse Wavelength Division Multiplexing (CWDM)
2.9 Chapter Summary

Chapter 3
64-QAM WiMAX Signals Distributed via RoF Applying Different Compensators
3.1 Overview
3.2 Introduction
3.3 Methodology
3.4 Setups and Simulations of Green Radio Solutions for the Deployment of WiMAX
3.4.1 WiMAX-Tx via Air
3.4.1.1 Simulation Results and Discussion
3.4.2 WiMAX via RoF-SMF
3.4.2.1 Simulation Results and Discussion
3.4.3 WiMAX via RoF (SMF-DCF)
3.4.3.1 Simulation Results and Discussion
3.4.4 WiMAX via RoF (SMF-DCF-FBG)
3.4.4.1 Simulation Results and Discussion
3.4.5 Extended Mobile WiMAX Signal Transmission over RoF via Triple Symmetrical Dispersion System SMF, DCF and CFBG
3.4.5.1 Related Work
3.4.5.2 Theory and Analyses
3.4.5.3 WiMAX via RoF (SMF-DCF-CFBG)
3.4.5.4 Simulation Results and Discussion
3.5 Chapter Summary

Chapter 4
LTE and WiMAX Signal Transmission via WDM-RoF for a Length of 1800km
4.1 Overview
4.2 Introduction
4.3 Related Work
4.4 Theory and Analyses
4.5 System Description and Simulation
4.6 Simulation Results and Discussion
4.7 Chapter Summary

Chapter 5
Efficient Transmission of WiMAX, LTE and CWDM Channels via GPON-RoF
5.1 Overview
5.2 Introduction
5.3 Related Work
5.4 Passive Optical Network (PON) Technologies
5.4.1 APON / BPON
5.4.2 Ethernet Passive Optical Network (EPON)
5.4.3 Gigabit Passive Optical Network (GPON)
5.5 Simulation Design of GPON-CWDM via RoF and Discussion
5.5.1 GPON-CWDM via RoF for fibre length of 210km
5.5.2 SMF, DCF, and CFBG Extended GPON Network for Fibre length 600km
5.6 Simulation Results and Discussion
5.6.1 GPON/CWDM Based RoF for a SMF length of 210km
5.6.2 RoF Based GPON - CWDM System for Transmission of LTE/WiMAX/ Baseband
over 600km
5.7 Chapter Summary

Chapter 6
Conclusion and Future Work
6.1 Conclusion
6.1.1 Performance of WiMAX Signals Distributed via RoF Applying Symmetrical
Compensators
6.1.2 Performance of LTE and WiMAX Signal transmission via WDM-RoF for a length of 1800km
6.1.3 Performance of WiMAX, LTE and CWDM Channels via GPON-RoF
6.2 Future Work
6.2.1 WiMAX- Femtocell via RoF
6.2.2 Sleep Mode in the RoF System

References

Abstract

Wireless communication increasingly is becoming the first choice link to enter into the global information society. It is an essential part of broadband communication networks, due to its capacity to cover the end-user domain, outdoors or indoors. The use of mobile phones and broadband has already exceeded the one of the fixed telephones and has caused tremendous changes in peoples life, as not only to be recognised in the current political overthrows. The all-around presence of wireless communication links combined with functions that support mobility will make a roaming person-bound communication network possible in the near future. This idea of a personal network, in which a user has his own communication environment available everywhere, necessitates immense numbers of radio access points to maintain the wireless links and support mobility.

The progress towards “all-around wireless” needs budget and easily maintainable radio access points, with simplified signal processing and consolidation of the radio network functions in a central station. The RF energy consumption in mobile base stations is one of the main problems in the wireless communication system, which has led to the worldwide research in so called green communication, which offers an environmentally friendly and cost-effective solution. In order to extend networks and mobility support, the simplification of antenna stations and broadband communication capacity becomes an increasingly urgent demand, also the extension of the wireless signal transmission distance to consolidate the signal processing in a centralised site.

Radio-over-Fibre technology (RoF) was considered and found to be the most promising solution to achieve effective delivery of wireless and baseband signals, also to reduce RF energy consumption. The overall aim of this research project was to simulate the transmission of wireless and baseband RF signals via fibre for a long distance in high quality, consuming a low-power budget. Therefore, this thesis demonstrated a green radio communication network and the advantage of transmitting signals via fibre rather than via air. The contributions of this research work were described in the follows:

Firstly, a comparison of the power consumption in WiMAX via air and fibre is presented. As shown in the simulation results, the power budget for the transmission of 64 QAM WiMAX

IEEE 802.16-2005 via air for a distance of 5km lies at -189.67 dB, whereas for the transmission via RoF for a distance of 140km, the power consumption ranges at 65dB. Through the deployment of a triple symmetrical compensator technique, consisting of SMF, DCF and FBG, the transmission distance of the 54 Mbps WiMAX signal can be increased to 410km without increasing the power budget of 65dB. An amendment of the triple compensator technique to SMF, DCF and CFBG allows a 120Mbps WiMAX signal transmission with a clear RF spectrum of 3.5 GHz and constellation diagram over a fibre length of 792km using a power budget of 192dB. Secondly, the thesis demonstrates a simulation setup for the deployment of more than one wireless system, namely 64 QAM WiMAX IEEE 802.16-2005 and LTE, for a data bit rate of 1Gbps via Wavelength Division Multiplexing (WDM) RoF over a transmission distance of 1800km. The RoF system includes two triple symmetrical compensator techniques - DCF, SMF, and CFBG - to obtain a large bandwidth, power budget of 393.6dB and a high signal quality for the long transmission distance. Finally, the thesis proposed a high data bit rate and energy efficient simulation architecture, applying a passive optical component for a transmission span up to 600km. A Gigabit Optical Passive Network (GPON) based on RoF downlink 2.5 Gbps and uplink 1.25Gbps is employed to carry LTE and WiMAX, also 18 digital channels by utilising Coarse Wavelength Division Multiplexing (CWDM). The setup achieved high data speed, a lowpower budget of 151.2dB, and an increased service length of up to 600km.

Acknowledgement

In the Name of ALLAH, the Most Beneficent, the Most Merciful All Thanks to ALLAH for His favours and blessings.

I owe special thanks to my supervisors, Dr Jonathan Loo and Professor Richard Comley and my external supervisor Dr Dhananjay Singh from South Korea for their guidance and support. As my first supervisor, Dr Jonathan Loo provided me with the encouragement and freedom to pursue my own ideas. Therefore, I do want to express my sincere appreciation to him.

I owe great thank to my wife, for her support, understanding and patience during all these years. I would like to thank my son and my daughter, who allowed me to spend endless hours in front of the laptop instead of being with them.

I am also grateful to my colleagues for their continuous support and suggestions.

I would like to thank the staff in the School of Engineering and Information Sciences for their support and encouragement.

I owe thanks to Optiwave company, who provided me with Optisystem software without, respectively, a low charge also the staff of Optiwave, who always were there answering questions and giving advice.

Dedicated to My Family My Mother, My Wife

My Son Yacin and My Daughter Betul

Author’s Declaration

I certify that the work in this thesis has not previously been submitted for a degree nor has it been submitted as part of requirements for a degree except as fully acknowledged within the text.

I also certify that the thesis has been written by me. Any help that I have received in my research work and the preparation of the thesis itself has been acknowledged. In addition, I certify that all information sources and literature used are indicated in the thesis.

Mazin Al Noor

June 2011, London, UK

List of Figures

FIGURE 2-1 A-C: SNELL’S LAW OF REFRACTION
FIGURE 2-2: MMF AND SMF CORE DIAMETER
FIGURE 2-3: ACCEPTANCE ANGLE OF A FIBRE
FIGURE 2-4: WATER PEAK AREA OF CWDM FROM 1271 NM TO 1611 NM
FIGURE 2-5:VARIATION IN THE SILICA REFRACTIVE INDEX AS A FUNCTION OF OPTICAL WAVELENGTH
FIGURE 2-6: DIFFERENT TYPES OF DISPERSION
FIGURE 2-7: POLARISATION MODE DISPERSION
FIGURE 2-8: PRINCIPLE OF A FIBRE BRAGG GRATING
FIGURE 2-9: COVERAGE IN “DEAD ZONE”
FIGURE 2-10: DIRECT MODULATION
FIGURE 2-11: EXTERNAL MODULATION
FIGURE 2-12: DOWNLINK SIGNAL TRANSMISSION, EMPLOYING OFDM
FIGURE 2-13: WAVELENGTH DIVISION MULTIPLEXING
FIGURE 2-14: 18 CHANNEL PASS BAND OF CWDM FOR WAVELENGTH FROM 1271-1611NM

FIGURE 3-1: WIMAX TRANSMITTER’S RADIATION
FIGURE 3-2: POWER ATTENUATION IN AIR
FIGURE 3-3: SETUP SCHEMATIC OF DOWNLINK WIMAX VIA ROF-SMF LENGTH 180KM
FIGURE 3-4: OFDM MODULATOR PROPERTIES OF WIMAX-TX
FIGURE 3-5: OFDM DEMODULATOR PROPERTIES OF WIMAX-RX
FIGURE 3-6-A: CONSTELLATION FOR WIMAX SIGNAL TRANSMISSION AT WIMAX-TX
FIGURE 3-6-B: CONSTELLATION FOR WIMAX SIGNAL TRANSMISSION AT WIMAX-RX FOR
SMF LENGTH 20KM
FIGURE 3-7: RF SPECTRUM FOR WIMAX OVER ROF FOR SMF FIBRE LENGTH 20KM
FIGURE 3-8-A: CONSTELLATION AT WIMAX-RX AFTER 100KM SMF LENGTH
FIGURE 3-8-B: RF SPECTRUM OF WIMAX-RX AFTER 100KM SMF FIBRE LENGTH
FIGURE 3-9-A: 140KM SMF LENGTH, EDFAS POWER OF 35DB
FIGURE 3-9-B: CONSTELLATION AT WIMAX-RX AFTER 140 KM FIBRE LENGTH FOR EDFAS POWER 65DB
FIGURE 3-9-C: CONSTELLATION AFTER180KM SMF LENGTH FOR EDFAS POWER OF 65DB
FIGURE 3-10: SETUP SCHEMATIC OF WIMAX VIA ROF (SMF-DCF) FOR FIBRE LENGTH 288KM. .
FIGURE 3-11: RF SPECTRUM OF WIMAX-RX FOR SMF-DCF LENGTH OF 288KM
FIGURE 3-12: ELECTRICAL CONSTELLATION DIAGRAM FOR WIMAX-RX VIA ROF(SMF-DCF) FOR FIBRE LENGTH 288KM
FIGURE 3-13: FIBRE BRAGG GRATING
FIGURE 3-14: SETUP SCHEMATIC OF THE WIMAX OVER FIBRE SYSTEM USING SMF, DCF AND FBG FILTER FOR FIBRE LENGTH 410KM
FIGURE 3-15: ELECTRICAL CONSTELLATION DIAGRAM FOR WIMAX-RX OVER ROF(SMF- DCF-FBG) FOR A FIBRE LENGTH OF 410KM
FIGURE 3-16: RF SPECTRUM FOR FIBRE LENGTH SMF( 3×120KM), DCF( 2×24) AND (1×122)KM, AND FBG
FIGURE 3-17: OSNR & SNR FOR WIMAX-RX VIA ROF (SMF-DCF- FBG) FROM 20 TO 410KM .
FIGURE 3-18: ELECTRICAL POWER FOR WIMAX VIA ROF ( SMF-DCF-FBG) AFTER PHOTO DETECTOR DIODE
FIGURE 3-19: THE WAVELENGTH REFLECTION IN CFBG
FIGURE 3-20: SETUP SCHEMATIC OF WIMAX DOWNLINK VIA ROF (SMF, DCF AND CFBG) FOR THE INCREASED FIBRE LENGTH OF 792KM
FIGURE 3-21: SCHEMATIC OF MACH- ZEHNDER LINBO3 MODULATOR (MZM)
FIGURE 3-22: DISPERSION CHARACTERISTIC OF THE WAVELENGTHS
FIGURE 3-23: DCF COMPENSATE FOR SMF DISPERSION
FIGURE 3-24: TOTAL POWER IN THE DCF
FIGURE 3-25: WAVELENGTH DELAY IN CFBG
FIGURE 3-26: OSNR MEASUREMENT AT THE CFBG CHIRPED LENGTHS FROM 10MM TO 55MM
FIGURE 3-27: TOTAL POWER MEASUREMENT AT CFBG CHIRPED LENGTHS FROM 10-55MM
FIGURE 3-28-A: OPTICAL BANDWIDTH AFTER 264KM FIBRE LENGTH
FIGURE 3-28-B: OPTICAL BANDWIDTH AFTER 792KM FIBRE LENGTH
FIGURE 3-29: CONSTELLATION DIAGRAM OF 120MBIT/S WIMAX QAM-64 TRANSMISSION DOWNLINK FOR FIBRE LENGTH 792KM
FIGURE 3-30: CONSTELLATION DIAGRAM OF 120-MBIT/S WIMAX QAM-64 RECEIVER DOWNLINK FOR FIBRE LENGTH 528KM
FIGURE 3-31: CONSTELLATION DIAGRAM OF 120-MBIT/S WIMAX QAM-64 RECEIVED DOWNLINK FOR FIBRE LENGTH 792KM
FIGURE 3-32: 3.5GHZ WIMAX-TX FOR BANDWIDTH 20MHZ AND FFT 1024 BEFORE TRANSMITTING VIA ROF
FIGURE 3-33: WIMAX CARRIER FREQUENCY 3.5GHZ FOR BANDWIDTH 20MHZ AT WIMAX- RX AFTER TRANSMISSION VIA ROF FOR FIBRE LENGTH OF 792KM

FIGURE 4-1: POSITIVE AND NEGATIVE DISPERSION FOR SMF AND DCF FOR WAVELENGTH
FIGURE 4-2: SETUP SCHEMATIC OF WIMAX DOWNLINK VIA ROF (SMF, DCF AND CFBG) FOR 1800KM
FIGURE 4-3: OPTISYSTEM SOFTWARE PARAMETERS CONFIGURATION FOR SMF
FIGURE 4-4: OPTISYSTEM SOFTWARE DISPERSION PARAMETERS CONFIGURATION FOR SMF .. 103 FIGURE 4-5: OPTISYSTEM SOFTWARE NON-LINEARITY PARAMETERS CONFIGURATION FOR SMF
FIGURE 4-6: OPTISYSTEM SOFTWARE MAIN CONFIGURATION PARAMETERS FOR DCF
FIGURE 4-7: DISPERSION PARAMETERS FOR DCF
FIGURE 4-8: DCF NONLINEAR PARAMETERS CONFIGURATION
FIGURE 4-9-A: ELECTRICAL CONSTELLATION FOR 64QAM WIMAX-TX AND LTE-TX
FIGURE 4-9-B: ELECTRICAL CONSTELLATION FOR 64QAM AT WIMAX-RX AFTER 1800KM
FIGURE 4-10-A: OPTICAL SIGNAL TRANSMISSION OF WIMAX
FIGURE 4-10-B: OPTICAL SPECTRUM ODSB WIMAX AND LTE FOR WAVELENGTH
FIGURE 4-10-C: ODSB OF OPTICAL SPECTRUM FOR LTE AFTER 900KM
FIGURE 4-10-D: OPTICAL BANDWIDTH AFTER 1800KM
FIGURE 4-12: SNR OUTPUT FOR DIFFERENT CHIRP LENGTHS AFTER 1800KM
FIGURE 4.13: RF SPECTRUM OF 3.5GHZ-WIMAX-RX FOR FIBRE LENGTH 1800KM
FIGURE 4.14: RF SPECTRUM OF 2.6GHZ-LTE-RX FOR FIBRE LENGTH 1800KM

FIGURE 5-1: PON TECHNOLOGY TO THE HOME [120]
FIGURE 5-2: WIMAX AND LTE COMBINED WITH BASEBAND AND TRANSMITTED VIA GPON CWDM-ROF SYSTEM
FIGURE 5-3: DOWNSTREAM AND UPSTREAM OF GPON/CWDM NETWORK VIA ROF, USING SMF, DCF AND CFBG FOR FIBRE LENGTH 600KM
FIGURE 5-4-A: 64 QAM SIGNAL CONSTELLATION DIAGRAM OF WIMAX FOR 20KM FIBRE LENGTH
FIGURE 5-4-B: 64 QAM SIGNAL CONSTELLATION DIAGRAM OF WIMAX FOR 210KM FIBRE LENGTH
FIGURE 5-5: OPTICAL EMISSION SPECTRUM FOR 2.5 GBPS FOR COMBINED 18 CHANNELS CWDM SIGNAL, WIMAX-TX AND LTE-TX FOR SMF LENGTH 210KM
FIGURE 5-6: SIGNAL POWER ATTENUATION OF 8 CHANNELS IN SMF; DBM PER KM
FIGURE 5-7-A: EYE DIAGRAM AND Q-FACTOR AFTER SPLITTER FOR THE ONU MULTIPLE WAVELENGTH FOR A FIBRE LENGTH OF 160 KM
FIGURE 5-7-B: EYE DIAGRAM AND BIT ERROR RATE FOR BIDIRECTIONAL SMF 160
FIGURE 5-8-A: EYE DIAGRAM AND BER FOR WDM -ONU AFTER SMF LENGTH OF 210KM ..
FIGURE 5-8-B: EYE DIAGRAM AND Q-FACTOR AFTER 210KM
FIGURE 5-9-A: DOWNSTREAM RF SPECTRUM OF WIMAX-RX AFTER SMF 210KM
FIGURE 5-9-B: DOWNSTREAM RF SPECTRUM OF LTE-RX AFTER SMF 210KM
FIGURE 5-9-C: UPSTREAM RF SPECTRUM OF WIMAX-RX
FIGURE 5-10: OSNR FOR CFBG CHIRP LENGTH IN MM
FIGURE 5-11: TRANSMITTIVITY AND REFLECTIVITY OF WAVELENGTHS FROM 1.2μM - 1.6 μM 147 FIGURE 5-12: OPTICAL SPECTRUM 18 CHANNELS CWDM IN GPON- AND LTE-RF, AND WIMAX-RF FOR THE DISTANCE OF 600KM
FIGURE 5- 13-A: DOWNSTREAM EYE DIAGRAM FOR Q-FACTOR AFTER 300KM OF COMBINED SMF, DCF, CFBG FIBRE
FIGURE 5- 13-B: DOWNSTREAM EYE DIAGRAM FOR Q-FACTOR AFTER 600KM OF COMBINED SMF, DCF, CFBG FIBRE LENGTH
FIGURE 5-13-C: DOWNSTREAM EYE DIAGRAM FOR BER AFTER 600KM OF COMBINED SMF, DCF AND CFBG FIBRE LENGTH
FIGURE 5-14-A: DOWNSTREAM RF SPECTRUM OF LTE-RF AFTER 600 KM TRANSMISSION
FIGURE 5-14-B: DOWNSTREAM RF SPECTRUM OF WIMAX-RF AFTER 600 KM TRANSMISSION
FIGURE 5-14-C: UPSTREAM RF SPECTRUM FOR WIMAX- RF
FIGURE 5-14-D: UPSTREAM RF SPECTRUM FOR LTE- RF

List of Tables

TABLE 3-1: OSNR INPUT AND OUTPUT
TABLE 3-2 : TOTAL POWER AND SNR AT TRANSMITTER
TABLE 3-3 : TOTAL POWER AND SNR AT RECEIVER

TABLE 4-1: LTE AND WIMAX PARAMETERS
TABLE 4-2: TOTAL POWER AND SNR OF WIMAX-TX
TABLE 4-3: TOTAL POWER AND SNR OF WIMAX-RX

TABLE.5-1-A: OSNR AFTER 160KM FIBRE LENGTH
TABLE 5-1-B : OSNR AFTER 210KM FIBRE LENGTH

List of Abbreviations

illustration not visible in this excerpt

List of Contributed Publication

Conference

I. M. Al Noor, K.K. Loo, R. Comley, “WiMAX 54Mbit/s over Radio over Fibre Using

DCF, SMF Fibre and FGB for Fibre over 410km”, IEEE 7th International Symposium on Wireless Communication Systems (ISWCS 2010), The University of York, UK.

II. M. Al Noor, K.K. Loo, R. Comley, “120 Mbps Mobile WiMAX Scalable OFDMA-

PHY over Radio Over Fibre For Fibre Length 792 Km”, IEEE 6th International Conference on Wireless and Mobile Communications (ICWMC 2010), Valencia, Spain. Selected as one of twenty best papers in the conference.

Journal

I. M. Al-Noor, K.K. Loo, R. Comley “Extended Mobile WiMAX Signal Transmission

over RoF through Triple Symmetrical Dispersion System SMF, DCF and CFBG” International Journal on Advances in telecommunications (IARIA). Published 15.Aug.2011

II. M. Al-Noor, K.K. Loo, D. Singh “WiMAX, LTE & CWDM Signal Transmission via GPON-RoF“ Journal of Optical and Fibre Communications Research (Springer).Under review.

III. M. Al-Noor, K.K. Loo, D. Singh “”LTE/WiMAX Signal Transmission using WDM-RoF for Long Fibre Distance Network” Multimedia Tools and Applications (Springer).Under review Empty Page

Chapter 1 Introduction

1.1 Wireless Access Network

Wireless broadband, fixed and mobile, can be found almost everywhere, and it became a part of our modern life style. The data traffic in telecommunication networks has been growing tremendously over recent years, and experts predict accelerating data volumes from today three Exabyte a year to ninety Exabyte per year by 2015, where an Exabyte is equal to one million terabytes [1]. Wireless mobile services expanded in a range of 15 years (1990-2005) from worldwide 1 million to more than 2 billion subscribers. Delivering the Internet throughout the globe, the IEEE 802.16 committee aimed to engineer a wireless communication system based on new technologies in communications and digital signal processing to obtain a broadband Internet experience for nomadic users over a large area [2]. Long-term Evolution (LTE) is the next crucial step beyond High Speed Packet Access (HSPA) in the development of 3GPP technologies. Supporting and promoting the most fundamental aspects of mobile telephony and broadband, namely unparalleled mobility and coverage, LTE has an increased emphasis on quality and operational efficiency in the explosive growth of data service usage. The commercial launch of LTE single mode has started in Northern Europe at the end of 2009, and LTE dual mode services at the end of 2010 [3]. Both WIMAX and LTE are based on OFDM and provide wireless and fixed access. These technologies bring mobile broadband services to areas where currently fixed broadband access is not practicable due to excessive cost [4].

1.2 Research Motivation

The main challenge of wireless access networks is the vast amount of energy needed to power the base stations. A typical 3G base station needs 12.5 times more input power than it produces output RF power (500W input; 40W output), which adds up to an annual energy consumption of approximately 4.5MWh [5]. With 12,000 base stations building up a 3G mobile network, it consumes more than 50GWh a year. For example, Vodafone needs one million litres of diesel per day to operate its remote base stations worldwide [5]. The number of mobile subscribers is increasing continuously and at the same time the amount of energy consumption. The fact is that sending more data requires more RF energy. At the Mobile World Congress this year, a sale of worldwide 1.4 billion handsets in 2010 was announced, where the Chinese market had 842 million subscribers and presently only 15 per cent on 3G networks [5]. The global shift from 2G to 3G networks, with predicted 775 million handsets supporting 3G in 2011, takes part in the rising quantity of data and so the rising amount of energy needed to transfer the data [6] ; 30 to 40 per cent of the total cost of a base station is caused by the power amplifier [6]. The RF cable, carrying the signal between the power amplifier and the antenna introduce some loss that also increases the transmission cost. Furthermore, the cables are expensive, afford strong mechanical support, due to their heaviness, and are regarded as one of the main causes for mechanical problems in base stations. Another challenge for broadband wireless systems is the Mobility Management to find the right balance between capacity and coverage. The wireless network needs to provide the device to reach inactive/active users everywhere in the network, which is described as roaming also, to maintain a persisting session free from interruption while the user is moving (handoff).

1.3 Green Radio Communication

Over a period of ten years, the number of mobile phone subscribers increased from circa 700m to 5bn worldwide by July 2010 [7]. The fastest growth can be recognised in developing countries, like India and China, where wireless Internet has been adopted massively. Of course, this humongous increase of the use of wireless systems is associated with an increase in energy consumption. It is predicted that the majority of Internet access worldwide will be wireless on mobile devices. The future challenge is, to provide wireless Internet globally with significantly reduced energy consumption per bit and a reduction in network operating costs to operate profitably.

Discussions within the Mobile VCE (Virtual Centre of Excellence) group in 2006 / 2007 let the term” Green Radio” firstly appear. In October 2008, a three year Mobile VCE’s Green Radio programme was formally launched, jointly funded by Industrial Companies and the UK’s Engineering & Physical Sciences Research Council. The research in this programme is the responsibility of an integrated research team from five different universities in the UK [8] with the ambitious aim, to identify innovative methods to achieve a 100-fold reduction in the total energy consumption used to operate radio access networks. So far, there have been studies in areas like resource allocation, interference suppression, and multi-hop routing, which are able to lead to energy savings. Further key issues for investigation are the cell sizes of a base station, the backhaul method (wireless, fibre and free space optical), and the use of enterprise and femto-cell technologies [9].

1.4 Fibre Optic Access Network

The optical communication technology uses fibre cables to transfer data over long distances as well as for the last mile into the user’s home. This technology is capable to overcome the above described problems of wireless networks and participate in the responsible care for the environment and sustainable management of diminishing resources. The demand for and use of optical fibre has grown enormously and optical-fibre applications are widespread, ranging from global networks to desktop computers. The ability transmitting voice, data, or video over very short, respectively, very long distances provides considerable value for communication networks like mobile phone, wireless system and broadband, due to the reduction of energy consumption and cost. Fibre optic technology is understood as the promising technology for future networks and is a system trusted by users. For example, in April 2011, the Australian government has announced its £20bn plan to expand super-fast fibre-optic broadband across the country with FTTH (optical fibre to the home) for 90 per cent of its inhabitants. Additionally, the Australian healthcare service has reported that the investment in an intelligent system of patient records delivered via fibre optic technology could save $23bn over a 10-year time and save 1,300 lives every year [10].

1.4.1 Radio over Fibre (RoF)

This research focuses on RoF wireless access and RoF based on a passive optical network architecture aiming at efficient mobility, bandwidth management, and power behaviour. One of the most prominent applications in the fibre optic system is radio over fibre (RoF). This is a technology, which modulates light into radio frequency and transmits it via optical fibre to facilitate wireless access. Radio signals are carried over fibre utilising distributed antenna systems in fibre-optic cellular and micro-cellular radio networks. Radio signals in each cell are transmitted and received to and from mobile users by applying a separate little box that is connected to the base station via optical fibre. Cells are divided into microcells to enhance the frequency re-use and support a growing number of mobile users. The introduction of microcells has the following advantages: Firstly, the microcell is able to meet increasing bandwidth demands; secondly, reduces the power consumption also the size of the handset devices. The high-power radiating base station antenna is replaced by a divided antenna system connected to the base station via optical fibre [11]. RoF is commonly used for wireless access. RoF networks operate primarily at mm-wave bands, which require an additional attenuation, especially around 193.1THz, due to a limitation of the transmission range by oxygen absorption in outdoor environments. Compared to microwave bands such as 2.4 or 5 GHz, which require various BSs to support a wide service area, mm-wave band needs small cells. Networks operating with a large number of small cells have to cope with the issues of cost-effectiveness and mobility management [11]. RoF offers various benefits, like low attenuation, a large bandwidth, and immunity to radio frequency interference, operational flexibility, reduced power consumption, and a long signal transmission distance [11].

1.4.2 Challenges and Problems in RoF

There are two types of fibre optical cable: Multi mode fibre (MMF), used for a short distance signal transmission and Single mode fibre (SMF), used for long distances. The main challenge of the signal transmission via RoF for a long distance is the power attenuation and chromatic dispersion in SMF at wavelength 1550nm that can limit the signal transmission.

As this thesis considers an approach of green radio communication, the important question of high-energy consumption has to be solved, because most power is used for temperature regulation of the laser element in fibre optic networks. Additionally, the cooling system for the laser module needs itself to be cooled as well.

1.5 Research Objective and Contributions

This research presents a green radio communication system, which is based on RoF to deliver LTE, WiMAX and baseband for a long distance and low-power budget. As the RoF system is considered the future network technology, it has on one hand the capacity to meet the demands for decreasing electromagnetic smoking, wireless traffic, power, noise, cost, and antenna size and, on the other hand, to increase frequency bandwidth, data rate and capacity and eventually improves the spectral efficiency. By the deployment of RoF it is possible to avoid the transmission impairments via the air such as high power attenuation per km, cost of set up a base station (BS), non-line of sight (NLOS) coverage and limitation of signal transmission area. One research focus is the reduction of the power consumption of WiMAX and LTE central and base station by utilising fibre optic technology particularly, RoF, for a transmission range of more than 100km. Furthermore, the research aims for an improvement of the transmission distance in the RoF system and to overcome the problem of energy consumption caused by the laser’s temperature control. Addressing the impairment of chromatic dispersion in fibre optic systems, the deployment of different dispersion compensators is introduced in the following chapter.

1.5.1 RoF base SMF, DCF, FBG and CFBG

This thesis studies methods to control the chromatic dispersion in the SMF and power attenuation in the RoF system by utilising symmetrical compensators DCF, FBG, and CFBG. In a first step, the work focuses on WiMAX-LTE signals transmitted over RoF by using SMF, DCF, and CFBG. The thesis addresses the following areas: The theory of light dispersion in the fibre optic cable for SMF, DCF, FBG, and CFBG is presented. The description of the WiMAX -LTE via RoF system is introduced, followed by an explanation of the entire system setup design. Simulation results are presented to investigate the signal transmission over a long distance, with a special emphasis on signal dispersion.

1.5.2 WDM-RoF

In a second part, this research project presents a WDM-RoF network, operating with an increased bandwidth over fibre optic by transmitting multiple signals simultaneously at a different wavelength. Two wireless signals, WiMAX-RF 3.5GHz and LTE-RF 2.6GHz, for a data speed of 1Gbps, were merged into the wavelength division multiplexing (WDM) and transmitted via RoF. The WDM- RoF network raises the capacity also, and more importantly, enhances the number of base stations served by a single central station. The simulation results show the increase of the signal transmission area to 1800km also the improvement of OSNR and the signal attenuation.

1.5.3 GPON/CWDM-RoF

The final and third section of this thesis proposes the deployment of WiMAX-RF 3.5GHz, LTE-RF 2.6GHz wireless systems and 18 wavelengths as baseband signals with a bit rate of 2.5Gbps downlink and 1.25Gbps uplink in GPON-CWDM via RoF technology. The GPON system obtains the ability to deliver extremely high bit rates. The integration of an 18 channel coarse wavelength division multiplexing (CWDM) in the GPON, allows the use of less expensive, un-cooled lasers, operating with reduced energy consumption. The work achieved an extension of the transmission distance to 600km and a low-power budget.

1.6 Thesis Structure

This thesis comprises of six chapters, which are described in the following:

Chapter 1 presents the introduction consisting of the research background, formulation of problems and challenges, explanation of the research objectives and finally, the description of the thesis structure.

Chapter 2 provides the theoretical, respectively, technical basis of the thesis. This includes the propagation of light, optical fibre, Dispersion, Dispersion compensating modules, Radio over fibre communication networks and applications in RoF networks.

Chapter 3 compares the power consumptions of the WiMAX signal transmission via air and via RoF. To improve the transmission via RoF and extend the transmission distance, four different simulation setups for green radio solutions are described and their results, focussing on the power consumption, are discussed.

Chapter 4 examines the WDM-RoF system integrating two wireless systems, LTE and WiMAX, and increasing the fibre span to 1800km through the application of the triple compensators technique.

Chapter 5 focuses on CWDM-GPON for the last mile and describes the simulation design also the results for the transmission of 18 baseband channels, LTE & WiMAX via RoF.

Chapter 6 summarises the thesis and presents ideas for future research.

Chapter 2 Literature Review - Fundamental Concept of Fibre Optic Technology

Literature Review

2.1 Introduction

This chapter deals with the fibre optic theory, the problems of the transmissions via fibre, the Radio over fibre technology, and the fibre components related to the research project, as described in this thesis.

A look into the history of human communication reveals that the earliest optical communications systems consisted of fire or smoke signals along the Great Wall of China. Countless beacon towers were used to inform about the size of an invading enemy by the number of lanterns or the colour of smoke. Thus, a message could be spread over a distance of more than 7300km, from one end of the Great Wall to the other, in approximately one hour. This can be seen as the first stage of multilevel signalling [12].

Several centuries later, the first generation of fibre optic arose in the 1980s as a means to transport information in communication systems, operating at a wavelength of 0.8nm with 45 Mb/s data rate. One benefit was lower costs for installation and maintenance due to the greater repeater spacing of 10 km, compared to the coax systems. Currently, researchers focus on optical transmission of 100 Gbps per wavelength channel and beyond, by the application of multilevel coding and modulation schemes, polarisation-multiplexing, DSP, and coherent detection [12].

The limited capacity of narrowband wireless access systems is caused by their low carrier frequencies, which only can offer low bandwidth. For instance, GSM works at frequencies around 900 or 1800 MHz and 200 kHz allocated frequency spectrum; UMTS works at frequencies around 2 GHz and 4 MHz allocated bandwidth. The wireless system operates with large cells, which provide high mobility, but for the cost of poor spectrum efficiency and high-power consumption. An option to raise the capacity and economy of wireless communication systems is to utilise fibre optic systems, namely RoF.

RoF employs remote working inside the buildings, where normally the walls are a cause for high signal losses when a system operates with large cells.

2.2 Propagation of Light

The basis of fibre-optic communications is the principle that light in a glass medium is able to convey a high amount of data over a long distance. Information transport, via electrical signals in copper respectively coaxial cables or via radio frequencies over a wireless medium is, compared to fibre-optic cables, not hugely effective. Today, the purity of the glass fibre enables the transmission of digitised light signals for hundreds of kilometres without amplification. The optical fibre can be seen as an ideal transmission medium, due to low interference, minimal transmission loss, and broad bandwidth capacity.

An optical fibre works as follows: Like radio frequency (RF) signals are routed through coaxial cables, the light waves are guided through the core of the optical fibre. The light is reflected within the core to the other end of the fibre. The ability to reflect light is determined by the composition of the cladding relative to the core glass. Usually, the creation of a higher refractive index in the core class than in the surrounding cladding causes the reflection and creates the “waveguide.” A modest modification of the core glasses components increases the refractive index. Another option to create the waveguide is to reduce the refractive index of the cladding by the application of different doping agents [13].

The total internal reflection of the light, the light is reflected with 100% efficiency, reduces the attenuation in optical fibres to useful levels and enables optical fibre communication. Light can pass any transparent material, with a lower speed than in a vacuum.

2.2.1 Refraction of Light Waves

When a light wave travels from one transparent medium into another transparent medium, it changes direction. Firstly, the Muslim mathematician and optics engineer Ibn Sahl accurately described a law of refraction in Bagdad in 984. More than 600 years later, the Dutch astronomer W. Snellius (1580-1626) reinvented the law of refraction.

illustration not visible in this excerpt

Figure 2-1 a-c: Snell’s law of refraction [14]

Snell’s law describes the refraction of waves when travelling from one transparent medium into another with a different phase speed. This law is applicable for all waves. Figure 2-1-a shows the refraction of light, when passing from an optical thin (n1) into an optical dense medium (n2). The light refracts in the direction of the perpendicular; the angle of refraction

(β) is smaller than the angle of incidence (α). Figure 2-1-b displays the situation, when light passes from an optical dense medium into an optical thin medium; the angle of refraction is bigger than the angle of incidence. If the angle of incidence increases, as to be seen in Figure 2-1-c, the light beam will be reflected fully and will not enter the second medium[14].

illustration not visible in this excerpt

Equation 2.1 describes the refraction at the interface between two different light transmitting materials [14].

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Equations 2.2 and 2.3 describe the total reflection of the light beam.

Light travels through a dielectric transparent matter at a velocity, which depends on the dielectric constant of matter and its wavelength. The following equation describes the propagation of a monochromatic plane wave through a dielectric medium in the direction z:

illustration not visible in this excerpt

where A is the amplitude of the field, ω = 2π f ,and β is the propagation constant. Phase velocity is vφ , ωt − βx = constant [15].

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Or, equivalently, in terms of the wave's angular frequency ω and wavenumber k by (2.6)

The dielectric constant of a medium is a function of frequency; therefore, different optical frequencies propagate at different velocities through the medium. This is an important fact for optical communications, because the optical signal is not purely monochromatic. The optical signal consists of a frequencies band, where each frequency passes the medium at a slightly different velocity and different phase. Therefore, group velocity vg can be expressed as the velocity of the envelope of the frequencies of an optical signal. Also it can be described as the speed of the signal pulse [16].

illustration not visible in this excerpt

Where c = speed of light in a vacuum, m/s, β = phase propagation parameter, rad/m, ω = angular frequency, ω = 2πc/λ, rad/s, vg= group velocity of the signal, m/s ng= fibre‘s effective group refractive index at w or λ, L = fibre length, km.

2.2.2 Nonlinear Schrödinger Equation (NLS)

The Austrian physicist Erwin Schrödinger was the first person to describe a wave equation. As Einstein, he assumed that light is an electromagnetic ray, that consists of photons, which carry energy (E) and the momentum of the photon (p). Both parts of his equation together indicate the probability of the stay of a photon travelling through a medium. For fibre optic communication, the modified equation is used to take into account dispersion and nonlinear effects of the pulse propagation via the fibre.

The right-hand side of the equation refers to nonlinear effects; the Kerr effect, Raman scattering, and self-steepening. The right side equals 0, when there are no nonlinear effects to consider. The left- hand side refers to fibre attenuation and chromatic dispersion [16] [17].

illustration not visible in this excerpt

In Chapter 3, the SMF and DCF parameters, considered to the NLS, are described.

2.3 Optical Fibre

In optical communication systems, Silica-based optical fibres are the medium for long- distance and large-capacity signal transmission. The low-loss characteristics is the most prominent feature of optical fibre; achieving a loss of 0.154 dB/km at λ=1.55μm wavelength. This means that the original signal intensity of light decreases to its half after having travelled 20 km through the optical fibre [18].

There are two general categories of optical fibres: single-mode fibre (SMF) and multimode fibres (MMF). As shown in Figure 2-2, the core diameter of a MMF is six times bigger than the core of a SMF.

illustration not visible in this excerpt

Figure 2-2: MMF and SMF core diameter

2.3.1 Multimode Fibre (MMF)

MMFs have a large core diameter ranging from 50 up to 100 mm. The light waves are spread out into numerous paths, when travelling through the cable's core, typically with a wavelength of 850 or 1300nm. The multi-paths of light cause signal distortion, especially over cable lengths more than 900m, which leads to incomplete and unclear data transmission.

However, MMF offers high bandwidth at high speeds- 100Mbit/s for a distance up to 2km; 1 Gbps for 220-550m, and 10Gbps for 300m - over medium distances and is a low-cost application for short links, e.g., in buildings or on campuses. The deployment of MMF is attractive as it is easier to install than SMF; it is considerably larger, which eases splicing and connector zing. Additionally, it is easier to connect to transceiver modules than SMF, which is more cost-effective. Furthermore, the MMF can be used for the transmission of RF carriers over the modal dispersion limited 3-dB bandwidth [19] [20] [21].

2.3.2 Single Mode Fibre (SMF)

SMF is a small core (1-16mm) optical fibre, widely used in transport and access networks for long distances. This fibre obtains beneficial properties, like low attenuation, large wavelength area and high bandwidths over distance. Compared to MMF, they are less suitable for short link FTTH indoor cabling, due to high bending loss and high installation costs. Through the SMF, light rays propagate along a single mode or physical path. The refractive index between the core and the cladding is about 0.6%; for these fibres, the light source is a laser, due to a narrow numerical aperture (NA) [22].

illustration not visible in this excerpt

Figure 2-3: Acceptance angle of a fibre [23].

As illustrate in Figure 2-3, the numerical aperture measures the maximum angle at which the core of the fibre will take in light, described as the acceptance angle of an optical fibre. Regarding the fibre core axis, the measurement of NA is as follows [24]:

illustration not visible in this excerpt

Commonly, SMF is applied in amplitude modulation (AM), Quadrature amplitude modulation (QAM), community access television (CATV), and vestigial side band (VSB) transport. Compared to MMF, SMF obtains lower loss and eliminates intermodal dispersion and is, thus, applied in high-speed data rate channels over long distances. Group velocity dispersion (chromatic dispersion) is a significant problem in high-bit rate (>2.5 Gbps) transmission over SMF and will be discussed in Section 2.5.

2.4 Fibre Attenuation

Attenuation means the reduction of light power or signal strength over the length of the fibre cable and is measured in decibels per kilometre (dB/km). In optical communications, the terms fibre attenuation, fibre loss, power attenuation and power loss are used equivalently. Power attenuation within the fibre usually is a result of absorption and scattering. The absorption leads to a loss of the photons, and their energy is transformed into heat. Scattering means, that minor defects in the fibre redirect or scatter some light into rays that are no longer conducted by the fibre [25].

Attenuation of an optical signal changes as a function of wavelength; thus, the attenuation constant or fibre loss is not the same for all frequencies. For an attenuation constant α (λ), the optical power attenuation at a length L is expressed as follows [15] [26].

illustration not visible in this excerpt

Pr represents the minimum power acceptable at receiver; the maximum fibre length is determined by[15]:

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The optical power attenuation constant (j) is non-linear [15]:

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[...]


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Details

Pages
195
Year
2011
ISBN (eBook)
9783656235682
ISBN (Book)
9783656236894
File size
6 MB
Language
English
Catalog Number
v196589
Institution / College
Middlesex University in London – School of Engineering and Information Sciences
Grade
Pass
Tags
green radio communication networks applying radio-over-fibre technology wireless access

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Title: Green Radio Communication Networks Applying Radio-over-Fibre Technology for Wireless Access