development of WiMAX OFDM Physical Layer Building Blocks using. MATLAB and .... Figure 2.4 WiMAX provides better data application support compared to ...
AIN SHAMS UNIVERSITY FACULTY OF ENGINEERING ELECTRONICS AND COMMUNICATIONS ENGINEERING DEPARTMENT
Development of Wimax Physical Layer Building Blocks A Thesis Submitted for Partial Fulfillment of the Requirements of the Degree of Master of Science in Electrical Engineering (Electronics and Communications Engineering)
Submitted by
Eng. Amiro George Roushdy Gaballah Hanna B.Sc. of Electrical Engineering Ain Shams University, 2005
Supervised by Prof. Dr. Abdel Haliem Zekry Professor of Communication Engineering Electronics and Communication Engineering Dept. Faculty of Engineering Ain Shams Univeristy
Cairo 2012
STATEMENT This thesis is submitted to Ain Shams University for the degree of Master of Science in Electrical Engineering (Electronics and communication Engineering) The work included in this thesis was carried out by the author in the Department of Electronics and Communication Engineering, Ain Shams University. No Part of this thesis has been submitted for a degree or a qualification at any other university or institute.
Name Signature Date
: Amiro George Roushdy Gaballah Hanna : : / / 2012
C.V. Name of Researcher Date of Birth Nationality University Degree
Date of Degree
: : : :
Amiro George Roushdy Gaballah Hanna 4 October 1983 Egyptian B.Sc. in Electronics and Communication
:
Engineering. Faculty of Engineering. Ain Shams University. 2005
ACKNOWLEDGMENT
I wish to express my sincere appreciation to my supervisors Prof. Abdel Haliem Zekry for his precious instructions, kind care, his constructive advices, helpful and valuable guidance, heartfelt cooperation, strong encouragement and valuable comments during the course of this work. Moreover, Prof. Abdel Haliem Zekry, has a continuous guidance during the whole work through numerous discussions and meetings from which I learnt a great deal. I would like to express my gratitude to my mother, father and my wife whom without their support, this thesis would have never been finalized.
i
ABSTRACT Amiro George Roushdy Gaballah Hanna, Development of Wimax Physical Layer building blocks. Master of Science, Ain Shams University, Faculty of Engineering, Electronics and Communication Engineering Department, 2012. WiMAX has commercial networks in 149 countries and subscriptions have reached 10 million globally today and are projected to grow to 130 million subscribers by 2014. This Thesis is covering the development of WiMAX OFDM Physical Layer Building Blocks using MATLAB and Simulink, based on the ETSI TS 102 177 V1.5.1 “Broadband Radio Access Networks (BRAN) HiperMan Physical Layer Standard”, the scope and complexity of the standard creates challenges for designers of a standard compliant components. Model-Based Design for a WiMAX transceiver with Simulink addresses these challenges by placing a system model at the center of the development process from requirements capture to implementation, testing and Analysis. Key words: U
WiMAX, BRAN, IEEE 802.16, HiperMAN, OFDM
Thesis supervisor: U
Prof. Dr. Abdel Haliem Zekry Professor of Communication Engineering, Electronics and Communications Engineering Department, Faculty of Engineering, Ain Shams University, Cairo, Egypt.
ii
PUBLICATION ARISING FROM THIS THESIS
CONFERENCE PAPERS (FULLY REFEREED)
1. Amiro.G. R. G. Hanna, Prof. Abdel Haliem Zekry “Development of Wimax Physical Layer Building Blocks ", ISMS2012. 3rd International Conference on Intelligent Systems, Modeling and Simulation, Kota Kinabalu, Malaysia, 8-10 February 2012.Paper ID: # 1569554583
iii
Table of Contents Acknowledgment Abstract Publication Arising From This Thesis
i ii iii
Table of Contents List of Figures List of Tables List of Abbreviations
iv viii xiii xiv
CHAPTER 1
1
INTRODUCTION AND MOTIVATION 1.1 Introduction 1.2 Problem Statement 1.3 Thesis Contribution 1.4 Thesis Structure
1 4 4 4
CHAPTER 2 WIRELESS BROADBAND EVOLUTION
6
2.1 Introduction to Wireless Broadband 2.2 Evolution of Wireless Broadband
6 7
2.3 Wireless Broadband Races to Substitute ADSL 2.3.1 Better Data Application Support 2.4 Emergence of Standards-Based Technology 2.5 WiMAX and Other Broadband Wireless Technologies 2.5.1 3G Cellular Systems 2.5.2 Wi-Fi Systems
8 9 10 11 12 13
2.5.3 WiMAX versus 3G and Wi-Fi 2.5.4 4G Cellular Systems 2.5.5 WiMAX and LTE 2.5.6 The Power of WiMAX and LTE
14 16 17 18
iv
2.5.7 The Drill-Down on Both Technologies 2.5.8 Focus on WiMAX 2.5.9 WiMAX and LTE Comparison 2.6 OFDM & MIMO: Technologies of Choice for Mobile Broadband
19 20 21 21
2.7 WiMAX is a Premier 2.8 WiMAX Architecture 2.9 Advantages of WiMAX 2.10 Conclusion
23 24 25 26
CHAPTER 3 WIMAX OVERVIEW
28
3.1 Introduction 3.2 Background on IEEE 802.16 and WiMAX 3.3 Global Deployment Update 3.4 Features of WiMAX 3.5 WiMAX Physical Layer
28 28 31 32 35
3.5.1 OFDM Basics 3.5.2 OFDM Pros and Cons 3.5.3 OFDM Parameters in WiMAX 3.5.3.1 Fixed WiMAX OFDM-PHY 3.5.3.2 Mobile WiMAX OFDMA-PHY: 3.5.4 Subchannelization: OFDMA
35 37 38 38 39 40
3.5.5 Slot and Frame Structure 3.5.6 Adaptive Modulation and Coding in WiMAX 3.5.7 PHY-Layer Data Rates 3.6 Summary and Conclusions
41 43 44 45
CHAPTER 4 WiMAX PHYSICAL LAYER
47
4.1 Introduction 4.2 Channel Coding 4.2.1 Data Randomization
47 47 47
v
4.2.2 Forward Error Correction (FEC) 4.2.2.1 Reed Solomon Encoding 4.2.2.2 Convolutional Encoding 4.2.3 Interleaving
49 49 51 52
4.2.4 Modulation 4.2.4.1 Rate ID encodings 4.3 OFDM Symbol Construction 4.4 Transmitted Signal
54 55 55 57
CHAPTER 5 SIMULATION MODEL
58
5.1 Introduction 5.2 Model Building Blocks 5.2.1 Data Source Generator 5.2.2 Data Randomizer 5.2.3 Reed Solomon Encoding
58 59 60 61 62
5.2.4 Convolutional Encoding 5.2.5 Interleaving 5.2.6 Modulation 5.2.7 OFDM Symbol Construction 5.2.8 AWGN Channel 5.2.9 Data Construction
64 65 65 66 69 68
5.2.10 De-Modulation 5.2.11 De-Interleaver 5.2.12 Viterbi Decoding 5.2.13 Reed Solomon Decoding 5.2.14 De-Randomizer 5.2.15 Error Rate Calculator
69 70 70 71 73 74
5.3 Testing 5.3.1 Test Vectors 5.3.1.1 Input Data (Hex) 5.3.1.2 Randomized Data (Hex)
75 75 75 75
vi
5.3.1.3 Reed-Solomon encoded Data (Hex) 5.3.1.4 Convolutionally Encoded Data (Hex) 5.3.1.5 Interleaved Data (Hex) 5.3.1.6 Carrier Mapping (frequency offset index: I value Q value)
76 76 76 76
5.3.2 Test Benches 5.4 Conclusion
77 79
CHAPTER 6 SIMULATION RESULTS
80
6.1 Introduction
80
6.2 Scatter Plots 6.2.1 Scatter Plots for Rate_ID “0” BPSK ½ 6.2.2 Scatter Plots for Rate_ID “1” QPSK 1/2 6.2.3 Scatter Plots for Rate_ID “2” QPSK 3/4 6.2.4 Scatter Plots for Rate_ID “3” 16-QAM 1/2 6.2.5 Scatter Plots for Rate_ID “4” 16- QAM 3/4
80 81 82 84 86 88
6.2.6 Scatter Plots for Rate_ID “5” 64- QAM 2/3 6.2.7 Scatter Plots for Rate_ID “6” 64- QAM 3/4 6.3 BER Plots
90 92 94
CHAPTER 7 CONCLUSION AND FUTURE WORK
99
7.1 Conclusion 7.2 Future Work
99 99
100 101
REFERENCES APPENDIX
vii
LIST OF FIGURES Figure Figure 1.1 Figure 2.1 Figure 2.2 Figure 2.3 Figure 2.4
Page WiMAX blankets large areas with broadband Internet 3 Wireless Evolution Roadmap 7 Global Wireless Spectrum Allocations 8 Rapid growth of global wireless broadband 9 subscribers WiMAX provides better data application support 10 U
Figure 2.5 Figure 2.6 Figure 2.7 Figure 2.8
compared to ADSL2+ 4G Technology Evolution WiMAX and LTE: History and Evolution All roads lead to OFDM & MIMO WiMAX as a Data Overlay to Existing 2G & 3G Networks
17 18 23 23
Figure 2.9 Figure 2.10 Figure 3.1 Figure 3.2 Figure 4.1 Figure 4.2
A Comparison of Networks WiMAX Frequency Allocations Worldwide Deployments A sample TDD frame structure for mobile WiMAX Data Randomization PRBS Scrambler DL initialization vector
25 26 32 42 48 48
Figure 4.3 Figure 4.4 Figure 4.5 Figure 4.6 Figure 4.7 Figure 5.1
Scrambler UL initialization vector Convolutional Encoder of rate ½ Modulation Constellation OFDM symbol time structure OFDM symbol frequency structure Framework for Wimax Transmitter
48 52 55 56 56 58
Figure 5.2 Figure 5.3 Figure 5.4 Figure 5.5
Input Data Test Vector Transceiver Structure Bernoulli Binary Generator Parameters of the Bernoulli Binary Generator
58 59 60 60
viii
Figure 5.6 Figure 5.7 Figure 5.8 Figure 5.9
Data Randomizer in Simulink Parameters of the Randomizer PN Sequence Generator Parameters of the Randomizer Zero Pad Reed Solomon Encoder in Simulink
61 61 62 62
Figure 5.10 Figure 5.11 Figure 5.12 Figure 5.13 Figure 5.14
Parameters of the Reed Solomon Encoder Zero Pad Parameters of the RS Encoder Parameters of the Reed Solomon Encoder Selector Parameters of the Reed Solomon Encoder Puncture Convolutional Encoder in Simulink
63 63 63 64 64
Figure 5.15 Figure 5.16 Figure 5.17 Figure 5.18 Figure 5.19 Figure 5.20
Parameters of the Convolutional Encoder Interleaver in Simulink Parameters of the Interleaver Modulator in Simulink Parameters of the QAM Modulator OFDM symbol construction in Simulink
64 65 65 65 65 66
Figure 5.21
Parameters of the OFDM Symbol Construction 66 Selector Parameters of the OFDM Symbol Construction Matrix 67 Concatenation Parameters of the OFDM Symbol Construction Cyclic 67 Prefix
Figure 5.22 Figure 5.23 Figure 5.24 Figure 5.25 Figure 5.26 Figure 5.27 Figure 5.28 Figure 5.29 Figure 5.30 Figure 5.31 Figure 5.32 Figure 5.33
AWGN Channel Parameters of the AWGN Channel Data Construction Parameters of the Data Construction Remove Cyclic Prefix block Parameters of the Remove Zero Padding block
67 68 68 69
Parameters of the Data Construction Remove Pilots block QAM De-Modulator Parameters of the QAM De-Modulator De-Interleaver Parameters of the De-Interleaver
69
ix
69
69 69 69 70
Figure 5.34 Figure 5.35 Figure 5.36 Figure 5.37
Viterbi Decoder Parameters of the Viterbi Decoder RS Decoder Parameters of the RS Decoder
70 71 71 72
Figure 5.38 Figure 5.39 Figure 5.40 Figure 5.41 Figure 5.42
Parameters of the Reed Solomon Decoder Insert-Zero Parameters of the Reed Solomon Decoder Pad Parameters of the Reed Solomon Decoder Selector De-Randomizer Parameters of the De-Randomizer PN Sequence
72 72 73 73 74
Figure 5.43 Figure 5.44 Figure 5.45 Figure 5.46 Figure 5.47
Generator Parameters of the De- Randomizer Selector Error Rate Calculator Parameters of the Error Rate Calculator Test Bench for the Data Randomization Block Test Bench for the Convolutional Encoder Block
74 74 75 77 77 77 77
Figure 5.50 Figure 5.51 Figure 5.52
Test Bench for the Interleaver Block Test Bench for the Modulator and the OFDM Symbol Create Blocks Test Bench for the Reed Solomon Encoder Test Bench for the Reed Solomon Decoder Test Bench for the Data De-Randomization Block
Figure 5.53 Figure 5.54 Figure 5.55 Figure 5.56 Figure 5.57 Figure 6.1
Test Bench for the De- Interleaver Block Test Bench for the Viterbi Decoder Block Test Bench for the OFDM Symbol Extract Blocks Test Bench for the De-Modulator Test Bench for the Transceiver Bit Error Rate Test Model
78 78 78 78 79 80
Figure 6.2 Figure 6.3 Figure 6.4 Figure 6.5 Figure 6.6 Figure 6.7
Simulation Model for Rate_ID “0 “ Input Signal Constellation Diagram for Rate_ID “0 “
81 81 82 82 82 83
Figure 5.48 Figure 5.49
Constellation Diagram @ SNR= 8dB for Rate_ID “0 “ Constellation Diagram @ SNR=1 dB for Rate_ID “0 “ Simulation Model for Rate_ID “1 “ Input Signal Constellation Diagram for Rate_ID “1 “
x
78 78 78
Figure 6.8 Figure 6.9 Figure 6.10 Figure 6.11
Constellation Diagram @SNR= 8 dB for Rate_ID “1 “ Constellation Diagram @SNR=15dB for Rate_ID “1 “ Constellation Diagram @SNR= 24 dB for Rate_ID “1 Simulation Model for Rate_ID “2 “
83 83 84 84
Figure 6.12 Figure 6.13 Figure 6.14 Figure 6.15 Figure 6.16
Input Signal Constellation Diagram for Rate_ID “2 “ Constellation Diagram @SNR= 8 dB for Rate_ID “2 “ Constellation Diagram @ SNR=16dB for Rate_ID “2“ Constellation Diagram @SNR=24 dB for Rate_ID “2“ Simulation Model for Rate_ID “2 “
84 85 85 85 86
Figure 6.17 Figure 6.18 Figure 6.19 Figure 6.20 Figure 6.21 Figure 6.22
Input Signal Constellation Diagram for Rate_ID “2 “ 86 Constellation Diagram @ SNR= 8 dB for Rate_ID “2“ 86 Constellation Diagram @SNR=16dB for Rate_ID “2 “ 87 Constellation Diagram @SNR=24dB for Rate_ID “2 “ 87 Constellation Diagram @SNR=32dB for Rate_ID “2 “ 87 Simulation Model for Rate_ID “4 “ 88 Input Signal Constellation Diagram for Rate_ID “4 “ 88 Constellation Diagram @SNR= 8 dB for Rate_ID “4 “ 88 Constellation Diagram @SNR= 16dB for Rate_ID “4“ 89 Constellation Diagram @SNR=24 dB for Rate_ID “4“ 89 Constellation Diagram @SNR=32 dB for Rate_ID “4“ 89 Simulation Model for Rate_ID “5 “ 90
Figure 6.23 Figure 6.24 Figure 6.25 Figure 6.26 Figure 6.27 Figure 6.28 Figure 6.29 Figure 6.30 Figure 6.31 Figure 6.32 Figure 6.33 Figure 6.34 Figure 6.35 Figure 6.36 Figure 6.37 Figure 6.38 Figure 6.39
Input Signal Constellation Diagram for Rate_ID “5 “ Constellation Diagram @SNR= 8 dB for Rate_ID “5 “ Constellation Diagram @SNR= 16dB for Rate_ID “5“ Constellation Diagram @ SNR=24dB for Rate_ID “5“
90 90
91 91 Constellation Diagram @SNR= 32dB for Rate_ID “5“ 91 Simulation Model for Rate_ID “6 “ 92 Input Signal Constellation Diagram for Rate_ID “6 “ 92 Constellation Diagram@ SNR= 8 dB for Rate_ID “6 “ 92 Constellation Diagram@ SNR=16dB for Rate_ID “6 “ 93 Constellation Diagram@ SNR=24dB for Rate_ID “6 “ 93 Constellation Diagram@ SNR=32dB for Rate_ID “6 “ 93
xi
Figure 6.40 Figure 6.41 Figure 6.42 Figure 6.43
BER vs SNR for Rate_ID “0 “ BER vs SNR for Rate_ID “1 “ BER vs SNR for Rate_ID “2 “
Figure 6.44 Figure 6.45 Figure 6.46 Figure 6.47
BER vs SNR for Rate_ID “4 “ BER vs SNR for Rate_ID “5 “
BER vs SNR for Rate_ID “3 “
BER vs SNR for Rate_ID “6 “ BER vs SNR for Different Rate_ID
xii
94 95 95 96 96 97 97 98
LIST OF TABLES Table Table 2.1 Table 2.2
Page 16 U
Comparison of WiMAX with Other Broadband Wireless Technologies WiMAX and LTE features
19 20 21 30
Table 3.2 Table 3.3
Technology Comparative WiMAX and LTE Comparison Fixed and Mobile WiMAX Initial Certification Profiles Deployments by Region Deployments by Frequency
Table 3.4 Table 3.5 Table 3.6 Table 4.1 Table 4.2 Table 4.3
OFDM Parameters Used in WiMAX Modulation and Coding Supported in WiMAX PHY-Layer Data Rate at Various Channel Bandwidths Channel Encoding Convolutional code puncturing configuration Block Size of bit Interleaver
39 44 45 51 52 54
Table 4.4 Table 4.5 Table 5.1
Rate ID encodings OFDM symbol parameters OFDM Subcarrier Parameters
55 57 60
Table 2.3 Table 2.4 Table 3.1
xiii
31 31
LIST OF ABBREVIATIONS 1x evolution—data optimized
1xEV-DO
1x evolution—data and voice Second and Half Generation Wireless Second Generation Wireless Triple data encryption standard Third generation Third-generation partnership project
1xEV-DV 2.5G 2G 3DES 3G 3GPP
Third Generation Partnership Project 2 Authentication, authorization, and accounting Advanced antenna systems Admission control analog-to-digital converter asymmetric digital subscriber loop
3GPP2 AAA AAS AC ADC ADSL
advanced encryption standard amplitude modulation adaptive modulation and coding automatic repeat request asynchronous transfer mode additive white Gaussian noise
AES AM AMC ARQ ATM AWGN
advanced wireless services bit error probability bit error rate block error rate Binary Phase Shift Keying broadband radio services
AWS BEP BER BLER BPSK BRS
Base Station base station controller Base Station IDentification block sequence number base station transceivers
BS BSC BSID BSN BTS
xiv
BandWidth Capital Expenditure constant bit rate Convolutional Coding
BW Capex CBR CC
Control subCHannel cochannel interference Code Division Multiple Access Connection IDentifier Carrier to Interference Noise Ratio
CCH CCI CDMA CID CINR
Convergence Layer cubic metric Carrier to Noise Ratio Cyclic Prefix Customer Premises Equipment call-processing language
CL CM CNR CP CPE CPL
cyclic redundancy check carrier sense multiple access Convolutional Turbo Code digital-to-analog converter Direct Current Downlink Channel Descriptor
CRC CSMA CTC DAC DC DCD
digital-enhanced cordless telephony data encryption standard decision-feedback equalizer discrete Fourier transform dynamic host control protocol Downlink Interval Usage Code
DECT DES DFE DFT DHCP DIUC
DownLink Data Link Control DownLink Frame Prefix domain name system direction of arrival data over cable service interface specification
DL DLC DLFP DNS DoA DOCSIS
xv
decision point data path function digital rights management delay spread
DP DPF DRM DS
dynamic service change digital subscriber line digital-signal processing digital video broadcasting-handheld extensible authentication protocol
DSC DSL DSP DVB-H EAP
Enhanced Data for GSM Evolution effective isotopic radiated power Electronics and Telecommunications Research Institute European Telecommunications Standards Institute Evolution Data Only Federal Communications Commission
EDGE EIRP ETRI ETSI EVDO FCC
Frame Control Header Frequency Division Duplexing frequency division multiple access Forward Error Correction frequency-domain equalization frame error rate
FCH FDD FDMA FEC FEQ FER
Fast Fourier Transform frequency-hopping diversity code finite impulse response frequency modulation fragmentation subheader file transfer protocol
FFT FHDC FIR FM FSH FTP
fiber-to-the-home full usage of subcarriers fixed wireless access General Packet Radio Service Global System for Mobile Communications gateway
FTTH FUSC FWA GPRS GSM GW
xvi
hybrid-ARQ Header Check Sequence high-definition television Half duplex Frequency Division Duplexing
HARQ HCS HDTV H-FDD
high-performance metropolitan area network high-power amplifier high-speed downlink packet access high-speed packet access home subscriber server
HIPERMAN HPA HSDPA HSPA HSS
high-speed uplink packet access hypertext transfer protocol input backoff intercarrier interference Internet control message protocol inverse discrete Fourier transform
HSUPA HTTP IBO ICI ICMP IDFT
Information Element Institute of Electrical and Electronics Engineers Internet Engineering Task Force Inverse Fast Fourier Transform Internet group management protocol instant messaging
IE IEEE IETF IFFT IGMP IM
IP multimedia subsystem intelligent network integrated services Internet Protocol IP security Internet protocol television
IMS IN IntServ IP IPsec IP-TV
integrated services integrated services digital network inter-symbol interference International Telecommunications Union Java for advanced intelligence network local area network
IS ISDN ISI ITU JAIN LAN
xvii
lightweight directory access protocol low-density parity codes linear minimum mean square error local multipoint distribution system
LDAP LDPC LMMSE LMOS
line of sight least squares least Significant Bit label switched path label switching router
LOS LS LSB LSP LSR
long-term evolution Media Access Control Metropolitan Area Network multicast broadcast service multicarrier CDMA modulation and coding scheme
LTE MAC MAN MBS MC-CDMA MCS
message-digest 5 algorithm macrodiversity handover mean instantaneous capacity Multiple Input Multiple Output mobile IP mobile IP home agent
MD5 MDHO MIC MIMO MIP MIP-HA
multiple input/single output maximum likelihood maximum likelihood detection maximum-likelihood sequence detection multichannel multipoint distribution services multimedia messaging service
MISO ML MLD MLSD MMDS MMS
minimum mean square error mobile node MAC protocol data unit Motion Picture Experts Group Multiprotocol Label Switching multilevel QAM
MMSE MN MPDU MPEG MPLS M-QAM
xviii
maximal ratio combining maximum ratio transmission mobile station Most Significant Bit
MRC MRT MS MSB
MAC service data unit mean square error master session key minimum signal level maximum sum rate
MSDU MSE MSK MSL MSR
network access provider network access server network address translation non–line-of-sight network services provider network timing protocol
NAP NAS NAT NLOS NSP NTP
other-cell interference Orthogonal Frequency Division Multiplexing Orthogonal Frequency Division Multiple Access Operational Expenditure open systems architecture open systems interconnect
OCI OFDM OFDMA OPEX OSA OSI
parallel to serial peak-to-average-power ratio peak-to-average ratio probability density function policy decision point Protocol Data Unit
P/S PAPR PAR PDF PDP PDU
packet error rate packet header suppression PHS field PHS index PHS mask PHS verify
PER PHS PHSF PHSI PHSM PHSV
xix
PHYsical public key infrastructure privacy and key management phase modulation
PHY PKI PKM PM
proxy mobile IP pairwise master key Point-to-MultiPoint pseudonoise point of attachment
PMIP PMK PMP PN PoA
point-to-point protocol policy rule Pseudo Random Binary Sequence proportional rate constraints Physical Slot packing subheader
PPP PR PRBS PRC PS PSH
preshared key Public Switch Telephony Network partial transmit sequence partial usage of subcarriers Quadrature Amplitude Modulation Quality of Service
PSK PSTN PTS PUSC QAM QoS
Quadrature Phase Shift Keying remote access dial-in user service REQuest Radio Frequency request for comments Root Mean Square
QPSK RADIUS REQ RF RFC RMS
robust header compression reference point round-robin radio resource radio resource agent radio resource controller
ROHC RP RR RR RRA RRC
xx
radio resource management Reed-Solomon Rivest-Shamir-Adleman Reed-Solomon / Convolutional Code
RRM RS RSA RS-CC
received signal strength reduced-state sequence estimation Received Signal Strength Indicator received signal strength indicator resource reservation protocol
RSS RSSE RSSI RSSI RSVP
real-time control protocol Receive-Transmit Transition Gap real-time transport protocol real-time polling service roundtrip time removable user identity module
RTCP RTG RTP rtPS RTT RUIM
Receive serial to parallel security association selection combining serving call session control function stream control transport protocol
Rx S/P SA SC S-CSCF SCTP
session description protocol service data unit secure electronic transactions service flow; shadow fading service flow authorization space/frequency block code
SDP SDU SET SF SFA SFBC
service flow identifier service flow management serving GPRS support node subheader secure hash algorithm successive interference cancellation
SFID SFM SGSN SH SHA SIC
xxi
system identity information subscriber identity module single input/multiple output signal-to-interference-plus-noise ratio
SII SIM SIMO SINR
session initiation protocol signal-to-interference ratio single input/single output service-level agreement selected mapping
SIP SIR SISO SLA SLM
spatial multiplexing small and medium enterprise short messaging service signal-to-noise and distortion ratio Signal to Noise Ratio sealable OFDMA
SM SME SMS SNDR SNR SOFDMA
small office/home office soft input/soft output security parameter index subpacket identity spatial-channel model Service Provider Working Group
SOHO SOVA SPI SPID SPM SPWG
Subscriber Station secure sockets layer Subscriber Station Receive Transmit Gap space/time block code Space Time Coding singular-value decomposition
SS SSL SSRTG STBC STC SVD
Transmission Convergence transport control protocol Time Division Duplexing tap-delay line time division multiplexing time division multiple access
TC TCP TDD TDL TDM TDMA
xxii
time division/synchronous CDMA traffic engineering traffic encryption key transport-layer security
TD-SCDMA TE TEK TLS
Type Length Value Transmission Opportunities type of service tone reservation transmit selection diversity
TLV TOs TOS TR TSD
Transmit-receive Transition Gap tunneled transport layer security tile usage of subcarriers Transmit user agent Uplink Channel Descriptor
TTG TTLS TUSC Tx UA UCD
user datagram protocol unsolicited grant services ultrahigh frequency universal integrated circuit card Uplink Interval Usage Code UpLink
UDP UGS UHF UICC UIUC UL
uniform linear array Universal Mobile Telecommunications System unlicensed national information infrastructure universal resource locator universal subscriber identity module virtual circuit identifier
ULA UMTS U-NII URL USIM VCI
very high data rate digital subscriber loop very high frequency virtual local area networking video on demand voice over Internet protocol virtual path indicator
VDSL VHF VLAN VoD VoIP VPI
xxiii
virtual private network Wide Area Network wireless access protocol wideband code division multiple access
VPN WAN WAP WCDMA
wireless communications services wireless broadband wireless fidelity Worldwide Interoperability for Microwave Access2.5GHz wireless Internet service provider
WCS WiBro Wi-Fi WiMAX WISP
Wireless Local Area wireless local loop wireless metropolitan area network wireless regional area network wide-sense stationary wide-sense stationary uncorrelated scattering
WLAN WLL WMAN WRAN WSS WSSUS
eXclusive OR zero forcing
XOR ZF
xxiv
Chapter 1
Introduction and Motivation
CHAPTER 1 INTRODUCTION AND MOTIVATION 1.1 Introduction Mobile broadband offers many potential benefits to subscribers, but to fully take advantage of them it needs to meet several requirements. Mobile broadband has to provide robust support for applications that require high throughput (e.g. video and audio streaming, video calls, large downloads or heavy Virtual Private Network [VPN] use), or low latency (e.g. Voice over Internet Protocol [VoIP], online gaming and streaming). It also has to be affordable to promote mass adoption, which in turn is necessary to offset infrastructure costs. WiMAX was designed from the ground up to meet these requirements. It is a next-generation technology that makes it possible to capitalize on the currently unmet demand for mobile broadband services by widening their market beyond business users, and by including more pricesensitive consumer users. A combination of factors explains why WiMAX technology is the best candidate for successful deployment of mobile broadband services: Advanced performance: WiMAX high-capacity base stations offer high throughput per-user and low latency, and support all those applications supported by a wired broadband connection, including real-time and bandwidth-intensive applications. A wide variety of devices: Laptop add-in cards and modules will be the first WiMAX subscriber devices to be introduced in the market. A wide variety of form factors will soon follow including PDAs, phones, game consoles, ultra-mobile PCs, MP3 players. Internet Protocol (IP) architecture
1
Chapter 1
Introduction and Motivation
offered through WiMAX technology makes it easier to integrate and support these new devices. Cutting-edge technology: WiMAX is a technology developed and optimized for packet-based data applications and offers some of the most advanced functionality and spectral efficiency among commercially available wireless data technologies. Its native IP core network and support of IP Multimedia Subsystem (IMS) and MultiMedia Domain (MMD) will make it easier and cheaper to deploy new data applications and to interwork with other IP-based technologies. The use of Orthogonal Frequency Division Multiple Access (OFDMA), the multiplexing mechanism that is at the core of most next-generation technologies, including Third Generation Partnership Project’s (3GPP) Long Term Evolution (LTE), brings higher throughput and improved indoor coverage. Quality of Service (QoS) functionality enables mobile operators to offer advanced services and to prioritize traffic from different applications. Finally, advanced antenna techniques like Multiple Input Multiple Output (MIMO) and beam forming bring further enhancements in throughput and range. Support for mobility: WiMAX technology supports seamless handoffs at vehicular speeds that enable subscribers to maintain their connection as they move across areas covered by different base stations. Cost effectiveness: WiMAX technology features spectral efficiency that enables network operators to carry more traffic and to deploy a costeffective infrastructure. Manufacturing economies of large scale are expected to drive down product production costs and promote wide product availability. Operator cost savings can be passed on to subscribers, thus widening the appeal and adoption of mobile broadband services to the mass market. Commercial availability: Mobile WiMAX technology is based on the Institute of Electrical and Electronics Engineers (IEEE) 802.16e-2005
2
Chapter 1
Introduction and Motivation
standard, approved in December 2005, and on European Telecommunications Standards Institute (ETSI) High Performance Radio Metropolitan Area Network (HiperMAN). Worldwide availability: Mobile WiMAX operates in three spectrum bands (2.3-2.4 GHz, 2.496-2.69 GHz, and 3.4-3.6 GHz) which have common allocations in most countries. It is a global technology that subscribers can use worldwide with a single device. WiMAX fully supports roaming capabilities and the WiMAX Forum is already working towards a worldwide roaming framework. WiMAX combines the familiarity of Wi-Fi with the mobility of cellular that will deliver personal mobile broadband that moves with us. It will let us get connected to the Internet, miles from the nearest Wi-Fi hotspot. Soon, Mobile WiMAX will blanket large areas—metropolitan, suburban, or rural—delivering mobile broadband Internet access at speeds similar to existing broadband. WiMAX is built for the future with advanced, efficient wireless technology that provides higher speeds than today’s wide area wireless technologies. It will be able to completely transform our mobile Internet lifestyle, enabling us to connect in ways we’ve only dreamed about.
Figure 1.1 WiMAX blankets large areas with broadband Internet
3
Chapter 1
Introduction and Motivation
1.2 Problem Statement: 1. The WiMAX OFDM physical layer different building blocks need to be dimensioned and how to benchmark the different supported channel coding and rates. 2. The design and analysis of WiMAX Transceiver model is needed to be identified. 3. The performance and the compliance of WiMAX Transceiver model need to be tested in order to know the behavior of the Transceiver with respect to the standard.
1.3 Thesis Contribution: This thesis covers the topic of design, testing and analysis of the WiMAX physical Layer. The primary contributions of this dissertation are as follows: 1. Proposing a robust and scalable method that can be used to build an executable specification model for a Wimax physical layer. 2. Developing a MATLAB and a Simulink model to the WiMAX physical layer. 3. Testing and verification of the model performance with respect to the WiMAX Standard. 4. Developing a method for measuring and simulation of the Transceiver Model
1.4 Thesis Structure: The rest of the thesis is organized as follows. In chapter 2, the wireless broadband evolution is presented. The WiMAX overview is introduced in chapter 3. The WiMAX physical layer is presented in chapter 4. Chapter 5 depicts the methodology behind the implementation of the WiMAX transceiver in the Simulator and the testing procedures to verify the matching between our model and the standard [1] specification.
4
Chapter 1
Introduction and Motivation
Simulation results and discussion of the model performance in terms of bit error rate and scatter plots are presented in chapter 6. Finally, chapter 7 concludes the thesis with recommendations for future work.
5
Chapter 2
Wireless Broadband Evolution
CHAPTER 2 WIRELESS BROADBAND EVOLUTION 2.1 Introduction to Wireless Broadband Broadband wireless sits at the confluence of two of the most remarkable growth stories of the telecommunications industry in recent years. Both wireless and broadband have on their own enjoyed rapid mass-market adoption. The staggering growth of the Internet is driving demand for higher-speed Internet-access services, leading to a parallel growth in broadband adoption. In less than a decade, broadband subscription worldwide has grown from virtually zero to over 200 million. Digital subscriber line (DSL) technology, which delivers broadband over twisted-pair telephone wires, and cable modem technology, which delivers over coaxial cable TV plant, are the predominant mass-market broadband access technologies today. Both of these technologies typically provide up to a few megabits per second of data to each user, and continuing advances are making several tens of megabits per second possible. Since their initial deployment in the late 1990s, these services have enjoyed considerable growth. The availability of a wireless solution for broadband could potentially accelerate this growth. The market is rapidly advancing toward 4G mobile communications and ubiquitous broadband. Today, operators are in an excellent position to take advantage of both today’s widely-deployed WiMAX and emerging LTE (Long-Term Evolution) standards in order to leverage the power of both and deliver anywhere, anytime wireless broadband communications with a rich ecosystem and uncompromising economies of scale. Broadband access not only provides faster Web surfing and quicker file downloads but also enables several multimedia applications, such as real-time audio and video streaming, multimedia conferencing, and interactive gaming. Broadband connections are also being used for voice telephony using voice-over-Internet Protocol (VoIP) technology. More advanced broadband access systems, such as fiber-to-the-home (FTTH) and very high data rate digital subscriber loop (VDSL), enable such applications as entertainment-quality video, including high-definition TV (HDTV) and video on demand (VoD). As the broadband market continues to grow, several new applications are likely to emerge, and it is difficult to predict which ones will succeed in the future. So what is broadband wireless? Broadband wireless is about bringing the broadband experience to a wireless context, which offers users certain unique benefits and convenience. There are two fundamentally different types of broadband wireless services. The first type
6
Chapter 2
Wireless Broadband Evolution
attempts to provide a set of services similar to that of the traditional fixed-line broadband but using wireless as the medium of transmission. This type, called fixed wireless broadband, can be thought of as a competitive alternative to DSL or cable modem. The second type of broadband wireless, called mobile broadband, offers the additional functionality of portability, nomadicity and mobility. Mobile broadband attempts to bring broadband applications to new user experience scenarios and hence can offer the end user a very different value proposition. WiMAX (worldwide interoperability for microwave access) technology is designed to accommodate both fixed and mobile broadband applications. In this chapter, we provide a brief overview of broadband wireless.
2.2 Evolution of Wireless Broadband The history of broadband wireless as it relates to WiMAX can be traced back to the desire to find a competitive alternative to traditional wireline-access technologies. Spurred by the deregulation of the telecom industry and the rapid growth of the Internet, several competitive carriers were motivated to find a wireless solution to bypass incumbent service providers. During the past decade or so, a number of wireless access systems have been developed, mostly by start-up companies motivated by the disruptive potential of wireless. These systems varied widely in their performance capabilities, protocols, frequency spectrum used, applications supported, and a host of other parameters. Some systems were commercially deployed only to be decommissioned later. Successful deployments have so far been limited to a few niche applications and markets. Clearly, broadband wireless has until now had a checkered record, in part because of the fragmentation of the industry due to the lack of a common standard. The emergence of WiMAX as an industry standard is expected to change this situation.
Figure 2.1 Wireless Evolution Roadmap
7
Chapter 2
Wireless Broadband Evolution
Figure 2.2 Global Wireless Spectrum Allocations
2.3 Wireless Broadband Races to Substitute ADSL For many years, users around the world have relied on fixed Internet connections, from the humble beginnings of dial-up to more generous portions of bandwidth though broadband connectivity. Recently, the emergence of wireless broadband has begun to challenge the landscape of fixed broadband. Though during its infancy stage, wireless broadband was regarded as a complimentary technology to empower mobile broadband, a sector outside the service perimeters of fixed line broadband operators, the scene has now changed to a competing one. Especially in emerging markets, wireless broadband technologies such as Wimax are now in direct competition with fixed (ADSL) operators, where wireless broadband is positioned for fixed, indoor use that caters for home and small office users. Wimax holds this advantage as it began as a fixed wireless broadband connectivity (IEEE’s 802.16d standard). According to Qualcomm, the year 2010 will see the number of wireless broadband subscribers overtake fixed broadband subscribers as shown in Figure 2.3 below.
8
Chapter 2
Wireless Broadband Evolution
Figure 2.3 Rapid growth of global wireless broadband subscribers
The beauty of Wimax (based on the IEEE 802.16e standard) is its ability to support nomadic and mobile use which is not an option with ADSL. Wimax Operators have the flexibility of offering both fixed broadband and eventually graduate to economically offer nomadic broadband without major disruption to existing core network infrastructure. In fact, some Operators are bundling both fixed and nomadic Wimax for a wholesome connectivity experience
2.3.1 Better Data Application Support Compared to the dial-up era, emergence of broadband has tremendously fueled the datacraze globally. The availability of attractive bandwidth-hungry applications and services, such as YouTube, gaming, IPTV and more challenge the bandwidth capabilities of wired and wireless networks in a greater manner. According to Senza Fili Consulting, 80% of traffic usage occurs indoor which means users rely on their fixed broadband connections to enjoy data applications. As the demand for data is surely set to increase every year, Figure 2.4 illustrates that not all broadband networks are able to cope with the demand. WiMAX upholds a higher bandwidth (both downlink and uplink) compared to ADSL+2. Additionally, WiMAX’s core strength since conception is that this network is designed for data optimization which gives WiMAX an edge over other broadband technologies in the market. Hence, with the overwhelming demand for data, WiMAX handles data traffic efficiently and is easily scalable to contain future radical data needs.
9
Chapter 2
Wireless Broadband Evolution
Figure 2.4 WiMAX provides better data application support compared to ADSL2+
2.4 Emergence of Standards-Based Technology In 1998, the Institute of Electrical and Electronics Engineers (IEEE) formed a group called 802.16 to develop a standard for what was called a wireless metropolitan area network, or wireless MAN. Originally, this group focused on developing solutions in the 10GHz to 66GHz band, with the primary application being delivering high-speed connections to businesses that could not obtain fiber. These systems, like LMDS, were conceived as being able to tap into fiber rings and to distribute that bandwidth through a point-to-multipoint configuration to LOS businesses. The IEEE 802.16 group produced a standard that was approved in December 2001. This standard, Wireless MAN-SC, specified a physical layer that used single-carrier modulation techniques and a media access control (MAC) layer with a burst time division multiplexing (TDM) structure that supported both frequency division duplexing (FDD) and time division duplexing (TDD). After completing this standard, the group started work on extending and modifying it to work in both licensed and license-exempt frequencies in the 2GHz to 11GHz range, which would enable NLOS deployments. This amendment, IEEE 802.16a, was completed in 2003, with OFDM schemes added as part of the physical layer for supporting deployment in multipath environments. By this time, OFDM had established itself as a method of choice for
10
Chapter 2
Wireless Broadband Evolution
dealing with multipath for broadband and was already part of the revised IEEE 802.11 standards. Besides the OFDM physical layers, 802.16a also specified additional MAC-layer options, including support for orthogonal frequency division multiple access (OFDMA). Further revisions to 802.16a were made and completed in 2004. This revised standard, IEEE 802.16-2004, replaces 802.16, 802.16a, and 802.16c with a single standard, which has also been adopted as the basis for HIPERMAN (high-performance metropolitan area network) by ETSI (European Telecommunications Standards Institute). In 2003, the 802.16 group began work on enhancements to the specifications to allow vehicular mobility applications. That revision, 802.16e, was completed in December 2005 and was published formally as IEEE 802.16e-2005.It specifies scalable OFDM for the physical layer and makes further modifications to the MAC layer to accommodate high-speed mobility. As it turns out, the IEEE 802.16 specifications are a collection of standards with a very broad scope. In order to accommodate the diverse needs of the industry, the standard incorporated a wide variety of options. In order to develop interoperable solutions using the 802.16 family of standards, the scope of the standard had to be reduced by establishing consensus on what options of the standard to implement and test for interoperability. The IEEE developed the specifications but left to the industry the task of converting them into an interoperable standard that can be certified. The WiMAX Forum was formed to solve this problem and to promote solutions based on the IEEE 802.16 standards. The WiMAX Forum was modeled along the lines of the Wi-Fi Alliance, which has had remarkable success in promoting and providing interoperability testing for products based on the IEEE 802.11 family of standards. The WiMAX Forum enjoys broad participation from the entire cross-section of the industry, including semiconductor companies, equipment manufacturers, system integrators, and service providers. The forum has begun interoperability testing and announced its first certified product based on IEEE 802.16-2004 for fixed applications in January 2006. Many of the vendors that previously developed proprietary solutions have announced plans to migrate to fixed and/or mobile WiMAX. The arrival of WiMAX-certified products is a significant milestone in the history of broadband wireless.
2.5 WiMAX and Other Broadband Wireless Technologies WiMAX is not the only solution for delivering broadband wireless services. Several proprietary solutions, particularly for fixed applications, are already in the market. A few proprietary solutions, such as i-Burst technology from ArrayComm and Flash-OFDM from Flarion (acquired by QualComm) also support mobile applications. In addition to the proprietary solutions, there are standards-based alternative solutions that at least partially
11
Chapter 2
Wireless Broadband Evolution
overlap with WiMAX, particularly for the portable and mobile applications. In the near term, the most significant of these alternatives are third-generation cellular systems and IEEE 802.11-based Wi-Fi systems.
2.5.1 3G Cellular Systems Around the world, mobile operators are upgrading their networks to 3G technology to deliver broadband applications to their subscribers. Mobile operators using GSM (global system for mobile communications) are deploying UMTS (universal mobile telephone system) and HSDPA (high speed downlink packet access) technologies as part of their 3G evolution. Traditional CDMA operators are deploying 1x EV-DO (1x evolution data optimized) as their 3G solution for broadband data. In China and parts of Asia, several operators look to TD-SCDMA (time division-synchronous CDMA) as their 3G solution. All these 3G solutions provide data throughput capabilities on the order of a few hundred kilobits per second to a few megabits per second. HSDPA is a downlink-only air interface defined in the Third-generation Partnership Project (3GPP) UMTS Release 5 specifications. HSDPA is capable of providing a peak user data rate (layer 2 throughput) of 14.4Mbps, using a 5MHz channel. Realizing this data rate, however, requires the use of all 15 codes, which is unlikely to be implemented in mobile terminals. Using 5 and 10 codes, HSDPA supports peak data rates of 3.6Mbps and 7.2Mbps, respectively. Typical average rates that users obtain are in the range of 250kbps to 750kbps. Enhancements, such as spatial processing, diversity reception in mobiles, and multiuser detection, can provide significantly higher performance over basic HSDPA systems. It should be noted that HSDPA is a downlink-only interface; hence until an uplink complement of this is implemented, the peak data rates achievable on the uplink will be less than 384kbps, in most cases averaging 40kbps to 100kbps. An uplink version, HSUPA (highspeed uplink packet access), supports peak data rates up to 5.8Mbps and is standardized as part of the 3GPP Release 6 specifications; deployments are expected in 2007. HSDPA and HSUPA together are referred to as HSPA (high-speed packet access). 1x EV-DO is a high-speed data standard defined as an evolution to second-generation IS-95 CDMA systems by the 3GPP2 standards organization. The standard supports a peak downlink data rate of 2.4Mbps in a 1.25MHz channel. Typical user-experienced data rates are in the order of 100kbps to 300kbps. Revision A of 1x EV-DO supports a peak rate of 3.1Mbps to a mobile user; Revision B will support 4.9Mbps. These versions can also support uplink data rates of up to 1.8Mbps. Revision B also has options to operate using higher channel bandwidths (up to 20MHz), offering potentially up to 73Mbps in the downlink and up to 27Mbps in the uplink.
12
Chapter 2
Wireless Broadband Evolution
In addition to providing high-speed data services, 3G systems are evolving to support multimedia services. For example, 1x EV-DO Rev A enables voice and video telephony over IP. To make these service possible, 1xEV-DO Rev A reduces air-link latency to almost 30ms, introduces intrauser QoS, and fast intersector handoffs. Multicast and broadcast services are also supported in 1x EV-DO. Similarly, development efforts are under way to support IP voice, video, and gaming, as well as multicast and broadcast services over UMTS/HSPA networks. It should also be noted that 3GPP is developing the next major revision to the 3G standards. The objective of this long-term evolution (LTE) is to be able to support a peak data rate of 100Mbps in the downlink and 50Mbps in the uplink, with an average spectral efficiency that is three to four times that of Release 6 HSPA. In order to achieve these high data rates and spectral efficiency, the air interface will likely be based on OFDM/OFDMA and MIMO (multiple input/multiple output), with similarities to WiMAX. Similarly, 3GPP2 also has longer-term plans to offer higher data rates by moving to higher bandwidth operation. The objective is to support up to 70Mbps to 200Mbps in the downlink and up to 30Mbps to 45Mbps in the uplink in EV-DO Revision C, using up to 20MHz of bandwidth.
2.5.2 Wi-Fi Systems In addition to 3G, Wi-Fi based-systems may be used to provide broadband wireless. Wi-Fi is based on the IEEE 802.11 family of standards and is primarily a local area networking (LAN) technology designed to provide in-building broadband coverage. Current Wi-Fi systems based on IEEE 802.11a/g support a peak physical-layer data rate of 54Mbps and typically provide indoor coverage over a distance of 100 feet. Wi-Fi has become the defacto standard for “last feet” broadband connectivity in homes, offices, and public hotspot locations. In the past couple of years, a number of municipalities and local communities around the world have taken the initiative to get Wi-Fi systems deployed in outdoor settings to provide broadband access to city centers and metrozones as well as to rural and underserved areas. It is this application of Wi-Fi that overlaps with the fixed and nomadic application space of WiMAX. Metro-area Wi-Fi deployments rely on higher power transmitters that are deployed on lampposts or building tops and radiating at or close to the maximum allowable power limits for operating in the license-exempt band. Even with high power transmitters, Wi-Fi systems can typically provide a coverage range of only about 1,000 feet from the access point. Consequently, metro-
13
Chapter 2
Wireless Broadband Evolution
Wi-Fi applications require dense deployment of access points, which makes it impractical for large-scale ubiquitous deployment. Nevertheless, they could be deployed to provide broadband access to hot zones within a city or community. Wi-Fi offers remarkably higher peak data rates than do 3G systems, primarily since it operates over a larger 20MHz bandwidth. The inefficient CSMA (carrier sense multiple access) protocol used by Wi-Fi, along with the interference constraints of operating in the license-exempt band, is likely to significantly reduce the capacity of outdoor Wi-Fi systems. Further, Wi-Fi systems are not designed to support high-speed mobility. One significant advantage of Wi-Fi over WiMAX and 3G is the wide availability of terminal devices. A vast majority of laptops shipped today have a built-in Wi-Fi interface. Wi-Fi interfaces are now also being built into a variety of devices, including personal data assistants (PDAs), cordless phones, cellular phones, cameras, and media players. The large embedded base of terminals makes it easy for consumers to use the services of broadband networks built using Wi-Fi. As with 3G, the capabilities of Wi-Fi are being enhanced to support even higher data rates and to provide better QoS support. In particular, using multiple-antenna spatial multiplexing technology, the emerging IEEE 802.11n standard will support a peak layer 2 throughput of at least 100Mbps. IEEE 802.11n is also expected to provide significant range improvements through the use of transmit diversity and other advanced techniques.
2.5.3 WiMAX versus 3G and Wi-Fi How does WiMAX compare with the existing and emerging capabilities of 3G and Wi-Fi? The throughput capabilities of WiMAX depend on the channel bandwidth used. Unlike 3G systems, which have a fixed channel bandwidth, WiMAX defines a selectable channel bandwidth from 1.25MHz to 20MHz, which allows for a very flexible deployment. When deployed using the more likely 10MHz TDD (time division duplexing) channel, assuming a 3:1 downlink-to-uplink split and 2 × 2 MIMO, WiMAX offers 46Mbps peak downlink throughput and 7Mbps uplink. The reliance of Wi-Fi and WiMAX on OFDM modulation, as opposed to CDMA as in 3G, allows them to support very high peak rates. The need for spreading makes very high data rates more difficult in CDMA systems. More important than peak data rate offered over an individual link is the average throughput and overall system capacity when deployed in a multicellular environment. From a capacity standpoint, the more pertinent measure of system performance is spectral
14
Chapter 2
Wireless Broadband Evolution
efficiency. The fact that WiMAX specifications accommodated multiple antennas right from the start gives it a boost in spectral efficiency. In 3G systems, on the other hand, multipleantenna support is being added in the form of revisions. Further, the OFDM physical layer used by WiMAX is more amenable to MIMO implementations than are CDMA systems from the standpoint of the required complexity for comparable gain. OFDM also makes it easier to exploit frequency diversity and multiuser diversity to improve capacity. Therefore, when compared to 3G, WiMAX offers higher peak data rates, greater flexibility, and higher average throughput and system capacity. Another advantage of WiMAX is its ability to efficiently support more symmetric links—useful for fixed applications, such as T1 replacement—and support for flexible and dynamic adjustment of the downlink-to-uplink data rate ratios. Typically, 3G systems have a fixed asymmetric data rate ratio between downlink and uplink. What about in terms of supporting advanced IP applications, such as voice, video, and multimedia? How do the technologies compare in terms of prioritizing traffic and controlling quality? The WiMAX media access control layer is built from the ground up to support a variety of traffic mixes, including real-time and non-real-time constant bit rate and variable bit rate traffic, prioritized data, and best-effort data. Such 3G solutions as HSDPA and 1x EV-DO were also designed for a variety of QoS levels. Perhaps the most important advantage for WiMAX may be the potential for lower cost owing to its lightweight IP architecture. Using an IP architecture simplifies the core network—3G has a complex and separate core network for voice and data—and reduces the capital and operating expenses. IP also puts WiMAX on a performance/price curve that is more in line with general-purpose processors (Moore’s Law), thereby providing greater capital and operational efficiencies. IP also allows for easier integration with third-party application developers and makes convergence with other networks and applications easier. In terms of supporting roaming and high-speed vehicular mobility, WiMAX capabilities are somewhat unproven when compared to those of 3G. In 3G, mobility was an integral part of the design; WiMAX was designed as a fixed system, with mobility capabilities developed as an add on feature. In summary, WiMAX occupies a somewhat middle ground between Wi-Fi and 3G technologies when compared in the key dimensions of data rate, coverage, QoS, mobility, and price. Table 2.1 provides a summary comparison of WiMAX with 3G and Wi-Fi technologies.
15
Chapter 2
Wireless Broadband Evolution
Table 2.1 Comparison of WiMAX with Other Broadband Wireless Technologies
2.5.4 4G Cellular Systems The drive toward 4G mobile communications is progressing full speed ahead. The dizzying pace of growth in mobile data usage and new applications demands that solutions be deployed to meet today’s demand while work on new standards progresses. 4G solutions that deliver truly ubiquitous broadband will change the way many industries operate. Public utilities, smart grids, oil and gas, and video surveillance are just a few examples. Operators are in an excellent position to take advantage of the current state of the industry to establish 4G services today, enjoy a return on investment, and position themselves to take advantage of future technologies and platforms. Operators that embrace both widely-deployed WiMAX and emerging LTE will be uniquely positioned to leverage the power of both and deliver anywhere, anytime wireless broadband communications with a rich ecosystem and uncompromising economies of scale. WiMAX and LTE are the two principal 4G mobile broadband technologies and research indicates that they will remain in the forefront for the next five to ten years. WiMAX enables new revenue generating applications previously reserved to fixed line broadband. Both are all-IP, integrating mobile broadband with IP networking, and both offer an ecosystem for networks, devices and applications. Equipped with an arsenal that includes
16
Chapter 2
Wireless Broadband Evolution
today’s WiMAX and a clear migration path to LTE, operators will gain a valuable competitive edge and gain market share by taking advantage of access to broadband spectrum and be early to penetrate wireless broadband markets.
Figure 2.5 4G Technology Evolution
2.5.5 WiMAX and LTE For carriers looking at both the short and long term gains, the “WiMAX vs. LTE” question is short-sighted. And based on recent market trends and research, it is a moot point. It is clear that both WiMAX and LTE will be widely deployed. With the focus on delivering services and applications that exceed the customer expectations, the question is how to optimize and exploit both to deliver on the 4G promise and meet growing demand. A multi-technology approach is optimal and an extremely viable way for operators to grow their businesses – today and tomorrow. A multi-technology approach allows carriers to take more variables into consideration and turn them into opportunities. These include the environment topography, such as urban or rural, and the type of applications deployed. A dual approach lets carriers select the most suitable solution and technology for each situation, and as a result, be prepared to overcome challenges in a more broad range of scenarios. For instance, WiMAX’s lower cost of ownership, especially its cost efficient spectrum and IPR, and attractive time-to-market allows for more Greenfield operators to enter markets that were previously out of reach. 17
Chapter 2
Wireless Broadband Evolution
In all likelihood, when TD-LTE matures, it may be a compelling alternative for operators who have a large percentage of mobile subscribers. Its ecosystem is expected to offer a large selection of handheld devices and favorable conditions for roaming. WiMAX will continue to be the preferred choice for fixed/nomadic deployments and for rural – suburban environments. In any case it is clearly not advisable to transition before the ecosystem fully matures.
Figure 2.6 WiMAX and LTE: History and Evolution
2.5.6 The Power of WiMAX and LTE The undisputed principal mobile broadband platforms to be deployed over the next ten years: • Both are all-IP • Both use OFDM air interface • Current availability of market-tested and proven delivery of WiMAX services and applications • Available to be operated in licensed spectrums and both address globally available bands.
18
Chapter 2
Wireless Broadband Evolution
Table 2.2 WiMAX and LTE features
2.5.7 The Drill-Down on Both Technologies If we take a close look, we see that the differences in performance between the two technologies are minimal. This becomes even more evident if we analyze the unique advantages of both technologies; each leverages the advantages of the other. In terms of economies of scale, the strong market adoption rate of both WiMAX 802.16e-2005 and LTE delivers the volume needed to make them both economically viable. Today, WiMAX enjoys the benefits of commitments with major chipset manufacturers, and the market has a strong embedded base of WiMAX-enabled devices. Research indicates that both WiMAX 802.16e-2005 and LTE will have rich device ecosystems based on standardsbased designs, cooperation with chipset manufacturers, and the interest of developer communities and manufacturers of consumer electronics. And of course, performance is a crucial factor. WiMAX 802.16e, with a defined roadmap to 802.16m, will deliver similar performance to LTE Rev.10. Both approach the maximum spectral efficiencies of approximately 6 bits/Hz. Today, operators are delivering in excess of 3.5 bits/Hz. with 802.16e. Next on the WiMAX roadmap, and already proven in field tests, 802.16m, will deliver over 5.0 bits/Hz., greater than 100 Mbps per sector for a 20 MHz channel – and similar to the promise of LTE. On the technology side, both are based on all-IP network architecture. This means reduced network complexity, faster handovers, flexible service delivery and all-important scalability. Interoperability with existing wireless technologies is of course, essential, and 19
Chapter 2
Wireless Broadband Evolution
both WiMAX and LTE are seamlessly integrated with these platforms. The multi-antenna techniques used on both overcome all types of deployment challenges, such as interference, high-speed mobility and more. Spectral holdings are also a key factor, and early evidence indicates that operators will need both WiMAX and LTE to cover both TDD and FDD.
Table 2.3 Technology Comparative
2.5.8 Focus on WiMAX The WiMAX industry has clearly passed its inflection point, and offers a very competitive and broad end user device portfolio with attractive price levels. There are literally hundreds of types of devices, USBs, laptops, residential gateways, and handheld devices. This positions WiMAX as an operative and mature broadband wireless solution for operators with licensed TDD spectrum (2.x and 3.x GHz). Recent Infonetics market analysis indicates that the WiMAX industry reached a market level of $1.5 million TAM (Total Addressable Market) in 2009 and will continue to grow, reaching an estimated $3 million in 2012 with an annual CAGR of 24%.
20
Chapter 2
Wireless Broadband Evolution
2.5.9 WiMAX and LTE Comparison
Table 2.4 WiMAX and LTE Comparison
2.6 OFDM & MIMO: Technologies of Choice for Mobile Broadband 2.5 and 3G networks have enabled users around the world to access data on their handsets and laptops. However, as mobile data services increase and more PC users start using the same broadband Internet applications “on the go” as they do at home, the expectation is for mobile data traffic to grow by a factor of 10x between 2010 and 2015. And this requirement could easily exceed expectations with a surge in applications like rich social networking which combine Internet multimedia and mobility. Although 2.5 and 3G networks will continue to serve up voice and mobile data for the foreseeable future, these networks will become capacity constrained as mobile broadband data use increases. Hence, the deployment of new networks to offload data-intensive mobile broadband applications is inevitable. Along with increased and scalable data capacity, these new networks will be
21
Chapter 2
Wireless Broadband Evolution
capable of supporting new, open Internet models and new device distribution and subsidy models -- flexibly accommodating operators’ business model needs. OFDM & MIMO have emerged as the technologies of choice to satisfy this growth, not only for WiMAX, but also for 3GPP’s LTE standard as well as Wi-Fi (802.11n). The combination of OFDM and MIMO is highly scalable and systems based upon it are best positioned to satisfy the headroom requirements for mobile broadband data over the next decade. In 2007, commercial Mobile WiMAX Release 1.0 systems which have not yet incorporated MIMO capability, showed a consistent 3x capacity improvement over other mobile wireless solutions in the same amount of spectrum. And that’s just the start. In 2008, MIMO-enabled WiMAX systems are expected to deliver 50% gains over the current SISO implementations. In 2010, wider channel bandwidth support in Release 1.5 will enable peak data rates well in excess of 100 Mbps using 20 MHz channels. In the future, when equipment can cost effectively support 4x4 MIMO configurations, peak data rates of over 300 Mbps will be achievable. New, data-optimized networks based upon OFDMA & MIMO (e.g., today’s WiMAX or 3GPP’s future LTE) will be deployed in entirely new spectrum, and will take years to reach the coverage levels of today’s 2G & 3G networks. These combined factors point towards operators maintaining their existing 2G & 3G networks for voice & narrower-band data, and deploying WiMAX for more data intensive applications. This is precisely what KT is doing with HSPA + Wibro and EV-DO + Wibro; likewise Sprint is planning EV-DO + WiMAX handsets. Operators will offer multi-mode handsets & modems to provide the best of both worlds -- coverage + high speed -- to their subscribers while they build out their 4G networks over several years. For portable devices such as laptops, the multi-mode combination of Wi-Fi + WiMAX will be the more common embedded solution for ensuring coverage.
22
Chapter 2
Wireless Broadband Evolution
Figure 2.7 All roads lead to OFDM & MIMO
Figure 2.8: WiMAX as a Data Overlay to Existing 2G & 3G Networks
2.7 WiMAX is a Premier A growing number of wireless service providers are looking at WiMAX 802.16e as the optimal technology for evolving their cellular networks. WiMAX will enable them to create a seamless broadband wireless fabric that empowers end users in all their environments: home, office and mobile. 23
Chapter 2
Wireless Broadband Evolution
WiMAX 802.16e is an IP-based broadband wireless access technology developed from the ground up to provide high-speed data and voice capabilities combined with advanced interactivity, ubiquitous mobility and exceptional cost-effectiveness. WiMAX delivers standards-based high-speed voice, data and Internet connectivity in licensed spectrum. It is the first technology that delivers true broadband mobility at speeds that enable powerful applications—such as VoIP, online gaming, mobile TV and other personalized, interactive media experiences—that differentiate networks, enhance revenues and reduce churn. Mobile WiMAX offers the industry a very capable platform by which to deliver the demanding service requirements for wireless access today and tomorrow. With the added support for a variety of advanced multi-antenna implementations such as MIMO (multiple input multiple output) and beamforming, mobile WiMAX offers the wireless operator considerable relief in meeting their growing network demands with higher performance, fewer sites, less spectrum and reduced cost. The WiMAX 802.16e standard enjoys remarkable industry wide acceptance. That means WiMAX is well positioned to be embedded in a wide range of low-cost, off-the shelf CPEs—including handsets, laptops, digital cameras, gaming consoles, mp3 players, television sets and more—that can virtually eliminate costly end user CPE subsidies.
2.8 WiMAX Architecture The WiMAX distributed architecture is a simpler, more powerful alternative to traditional hierarchical cellular networks based on complex layers of control. WiMAX networks and supplemental solutions take maximum advantage of the power of IP technology, utilizing the latest advancements in mobility management and providing a robust and versatile services platform. How does IP-based WiMAX technology compare with 2G and 3G mobile networks? WiMAX is simpler and more efficient, providing both “Broadband-on-the-Go” capabilities and significantly reduced CAPEX and OPEX. As shown in Figure 2.9 traditional 2G and 2.5G network traffic must go through the equivalent of an MSC (Mobile Switching Center). The backhaul from the base stations to the MSC is either through low throughput frame relay or E1/T1 connection. Traffic is rerouted to a data network or a circuit network for voice. Furthermore, data traffic is directed to the SGSN/GGSN in a GPRS/EDGE network or through a PDSN in a CDMA network. In contrast, the WiMAX network has a flat IP architecture with high throughput backhaul using Ethernet (10/100/1000 BaseT Ethernet) that is remarkably easy, efficient and cost-effective, significantly reducing CAPEX and OPEX. 24
Chapter 2
Wireless Broadband Evolution
Figure 2.9 A Comparison of Networks.
2.9 Advantages of WiMAX Mobile operators considering deployment of a new stand-alone WiMAX network, or using WiMAX as an extension or overlay to their existing networks, can look forward to a number of critical advantages, including: True Mobile Broadband: WiMAX IP-based technology is an efficient and cost-effective solution for delivering the dramatically higher speeds necessary to give end users the bandwidth-intensive applications they demand and the mobility to provide them anywhere and everywhere. Substantial Reductions in Interference: Because WiMAX operates in licensed spectrum, it effectively does away with most of what can be substantial interference challenges posed by solutions that work in unlicensed spectrum. Lower Cost of Ownership: The WiMAX IP-based architecture enables highly cost-effective implementation for both small- and large-scale deployments. The WiMAX distributed architecture eliminates costly centralized boxes, enables efficient remote management and allows for software-driven upgrades. Shorter Time-To-Market: In a market moving as quickly as mobile broadband, WiMAX networks offer distinct advantages in both ease of deployment and reduced time-to-market. Outstanding Revenue Opportunities: The WiMAX open IP-based architecture encourages developers to supply applications that provide the rich media experiences today’s consumers want. Current applications such as VoIP, streaming video and gaming can help you
25
Chapter 2
Wireless Broadband Evolution
maximize revenues and profitability today, and next-generation applications such as mobile TV, real-time trading and video telephony can keep profitability growing tomorrow. Widespread Acceptance: WiMAX technology enjoys exceptional industry acceptance with over 400 member companies currently in the WiMAX Forum. The WiMAX Forum includes not only WiMAX vendors and providers but also application developers, content developers and component suppliers. As shown in Figure 2.10, significant spectrum has been allocated worldwide in the 3.5, 2.5, and 2.3 GHz bands for wireless broadband solutions such as WiMAX.
Figure 2.10 WiMAX Frequency Allocations
2.10
Conclusion
Personal Broadband is the promise of always on, always available connectivity, allowing users to take their information and services with them when they leave the confines of their home or office. Just as cellular technology freed the world to roam and talk, personal broadband services over mobile WiMAX frees the world to connect anywhere, any time. Compelling multi-modal devices will allow operators to seamlessly transition across multiple networks: cellular, WiFi, WiMAX, wireline. End-Users will have ubiquitous broadband connections that follow them wherever they may be for ready access to bandwidth-intensive, personalized, rich-media content. The IP-based, flat WiMAX architecture is inherently more interoperable with legacy cellular networks, in large part, because the design is not encumbered by the requirement to
26
Chapter 2
Wireless Broadband Evolution
support a number of proprietary components. This makes interconnectivity to existing operator systems more agnostic when integrating common subscriber management, messaging and other services. With WiMAX we have the opportunity to free the tethers of wired broadband and transform the way we share, connect, and communicate with seamless mobility.
27
Chapter 3
WiMAX Overview
CHAPTER 3 WiMAX OVERVIEW
3.1
Introduction
After years of development and uncertainty, a standards-based interoperable solution is emerging for wireless broadband. A broad industry consortium, the Worldwide Interoperability for Microwave Access (WiMAX) Forum has begun certifying broadband wireless products for interoperability and compliance with a standard. WiMAX is based on wireless metropolitan area networking (WMAN) standards developed by the IEEE 802.16 group and adopted by both IEEE and the ETSI HIPERMAN group. In this chapter, we present a concise technical overview of the emerging WiMAX solution for broadband wireless. The purpose of this chapter is to provide an executive summary before offering a more detailed exposition of WiMAX in later chapters. We begin the chapter by summarizing the activities of the IEEE 802.16 group and its relation to WiMAX. Next, we discuss the salient features of WiMAX and briefly describe the physical layer characteristics of WiMAX.
3.2
Background on IEEE 802.16 and WiMAX
The IEEE 802.16 group was formed in 1998 to develop an air-interface standard for wireless broadband. The group’s initial focus was the development of a LOS-based point-to-multipoint wireless broadband system for operation in the 10GHz–66GHz millimeter wave band. The resulting standard—the original 802.16 standard, completed in December 2001—was based on a single-carrier physical (PHY) layer with a burst time division multiplexed (TDM) MAC layer. Many of the concepts related to the MAC layer were adapted for wireless from the popular cable modem DOCSIS (data over cable service interface specification) standard. The IEEE 802.16 group subsequently produced 802.16a, an amendment to the standard, to include NLOS applications in the 2GHz–11GHz band, using an
28
Chapter 3
WiMAX Overview
orthogonal frequency division multiplexing (OFDM)-based physical layer. Additions to the MAC layer, such as support for orthogonal frequency division multiple access (OFDMA), were also included. Further revisions resulted in a new standard in 2004, called IEEE 802.16-2004, which replaced all prior versions and formed the basis for the first WiMAX solution. These early WiMAX solutions based on IEEE 802.162004 targeted fixed applications, and we will refer to these as fixed WiMAX. In December 2005, the IEEE group completed and approved IFEEE 802.16e2005, an amendment to the IEEE 802.16-2004 standard that added mobility support. The IEEE 802.16e-2005 forms the basis for the WiMAX solution for nomadic and mobile applications and is often referred to as mobile WiMAX . The basic characteristics of the various IEEE 802.16 standards are summarized in Table 3.1.Note that these standards offer a variety of fundamentally different design options. For example, there are multiple physical-layer choices: a single-carrier-based physical layer called Wireless- MAN-SCa, an OFDM-based physical layer called WirelessMAN-OFDM, and an OFDMA based physical layer called Wireless-OFDMA. Similarly, there are multiple choices for MAC architecture, duplexing, frequency band of operation, etc. These standards were developed to suit a variety of applications and deployment scenarios, and hence offer a plethora of design choices for system developers. In fact, one could say that IEEE 802.16 is a collection of standards, not one single interoperable standard. For practical reasons of interoperability, the scope of the standard needs to be reduced, and a smaller set of design choices for implementation need to be defined. The WiMAX Forum does this by defining a limited number of system profiles and certification profiles. A system profile defines the subset of mandatory and optional physical- and MAC-layer features selected by the WiMAX Forum from the IEEE 802.16-2004 or IEEE 802.16e-2005 standard. It should be noted that the mandatory and optional status of a particular feature within a WiMAX system profile may be different from what it is in the original IEEE standard. Currently, the WiMAX Forum has two different system profiles: one based on IEEE 802.16-2004, OFDM PHY, called the fixed system profile; the other one based on IEEE 802.16e-2005 scalable OFDMA PHY, called the mobility system profile. A certification profile is defined as a particular instantiation of a system profile where the operating
29
Chapter 3
WiMAX Overview
frequency, channel bandwidth, and duplexing mode are also specified. WiMAX equipment are certified for interoperability against a particular certification profile. The WiMAX Forum has thus far defined five fixed certification profiles and fourteen mobility certification profiles. To date, there are two fixed WiMAX profiles against which equipment have been certified. These are 3.5GHz systems operating over a 3.5MHz channel, using the fixed system profile based on the IEEE 802.162004 OFDM physical layer with a point-to-multipoint MAC. One of the profiles uses frequency division duplexing (FDD), and the other uses time division duplexing (TDD).
Table 3.1 Fixed and Mobile WiMAX Initial Certification Profiles
30
Chapter 3
WiMAX Overview
With the completion of the IEEE 802.16e-2005 standard, interest within the WiMAX group has shifted sharply toward developing and certifying mobile WiMAX system profiles based on this newer standard. All mobile WiMAX profiles use scalable OFDMA as the physical layer. At least initially, all mobility profiles will use a point-to-multipoint MAC. It should also be noted that all the current candidate mobility certification profiles are TDD based. Although TDD is often preferred, FDD profiles may be needed for in the future to comply with regulatory pairing requirements in certain bands.
3.3
Global Deployment Update
This section describes the current state of WiMAX deployments across the world. The data for this tool is delivered to us courtesy of Informa Telecoms & Media, and can be viewed online in more detail at www.wimaxmaps.org.
Table 3.2 Deployments by Region
Table 3.3 Deployments by Frequency
31
Chapter 3
WiMAX Overview
Figure 3.1 Worldwide Deployments
3.4
Features of WiMAX
WiMAX is a wireless broadband solution that offers a rich set of features with a lot of flexibility in terms of deployment options and potential service offerings. Some of the more salient features that deserve highlighting are as follows: OFDM-based physical layer: The WiMAX physical layer (PHY) is based on orthogonal frequency division multiplexing, a scheme that offers good resistance to multipath, and allows WiMAX to operate in NLOS conditions. OFDM is now widely recognized as the method of choice for mitigating multipath for broadband wireless. Very high peak data rates: WiMAX is capable of supporting very high peak data rates. In fact, the peak PHY data rate can be as high as 74Mbps when operating using a 20MHz wide spectrum. More typically, using a 10MHz spectrum operating using TDD scheme with a 3:1 downlink-to-uplink ratio, the peak PHY data rate is about 25Mbps and 6.7Mbps for the downlink and the uplink, respectively. These peak PHY data rates are achieved when using 64 QAM modulation with rate 5/6 error32
Chapter 3
WiMAX Overview
correction coding. Under very good signal conditions, even higher peak rates may be achieved using multiple antennas and spatial multiplexing. Scalable bandwidth and data rate support: WiMAX has a scalable physical-layer architecture that allows for the data rate to scale easily with available channel bandwidth. This scalability is supported in the OFDMA mode, where the FFT (fast fourier transform) size may be scaled based on the available channel bandwidth. For example, a WiMAX system may use 128-, 512-, or 1,048-bit FFTs based on whether the channel bandwidth is 1.25MHz, 5MHz, or 10MHz, respectively. This scaling may be done dynamically to support user roaming across different networks that may have different bandwidth allocations. Adaptive modulation and coding (AMC): WiMAX supports a number of modulation and forward error correction (FEC) coding schemes and allows the scheme to be changed on a per user and per frame basis, based on channel conditions. AMC is an effective mechanism to maximize throughput in a timevarying channel. The adaptation algorithm typically calls for the use of the highest modulation and coding scheme that can be supported by the signal-to-noise and interference ratio at the receiver such that each user is provided with the highest possible data rate that can be supported in their respective links. Link-layer retransmissions: For connections that require enhanced reliability, WiMAX supports automatic retransmission requests (ARQ) at the link layer. ARQenabled connections require each transmitted packet to be acknowledged by the receiver; unacknowledged packets are assumed to be lost and are retransmitted. WiMAX also optionally supports hybrid-ARQ, which is an effective hybrid between FEC and ARQ. Support for TDD and FDD: IEEE 802.16-2004 and IEEE 802.16e-2005 supports both time division duplexing and frequency division duplexing, as well as a halfduplex FDD, which allows for a low-cost system implementation. TDD is favored by a majority of implementations because of its advantages: • flexibility in choosing uplink-to-downlink data rate ratios, • ability to exploit channel reciprocity, • ability to implement in nonpaired spectrum, and • less complex transceiver design. All the initial WiMAX profiles are based on TDD, except for two fixed WiMAX profiles in 3.5GHz. 33
Chapter 3
WiMAX Overview
Orthogonal frequency division multiple access (OFDMA): Mobile WiMAX uses OFDM as a multiple-access technique, whereby different users can be allocated different subsets of the OFDM tones. OFDMA facilitates the exploitation of frequency diversity and multiuser diversity to significantly improve the system capacity. Flexible and dynamic per user resource allocation: Both uplink and downlink resource allocation are controlled by a scheduler in the base station. Capacity is shared among multiple users on a demand basis, using a burst TDM scheme. When using the OFDMA-PHY mode, multiplexing is additionally done in the frequency dimension, by allocating different subsets of OFDM subcarriers to different users. Resources may be allocated in the spatial domain as well when using the optional advanced antenna systems (AAS). The standard allows for bandwidth resources to be allocated in time, frequency, and space and has a flexible mechanism to convey the resource allocation information on a frame-by-frame basis. Support for advanced antenna techniques: The WiMAX solution has a number of hooks built into the physical-layer design, which allows for the use of multipleantenna techniques, such as beamforming, space-time coding, and spatial multiplexing. These schemes can be used to improve the overall system capacity and spectral efficiency by deploying multiple antennas at the transmitter and/or the receiver. Quality-of-service support: The WiMAX MAC layer has a connection-oriented architecture that is designed to support a variety of applications, including voice and multimedia services. The system offers support for constant bit rate, variable bit rate, real-time, and non-real-time traffic flows, in addition to best-effort data traffic. WiMAX MAC is designed to support a large number of users, with multiple connections per terminal, each with its own QoS requirement. Robust security: WiMAX supports strong encryption, using Advanced Encryption Standard (AES), and has a robust privacy and key-management protocol. The system also offers a very flexible authentication architecture based on Extensible Authentication Protocol (EAP), which allows for a variety of user credentials, including username/password, digital certificates, and smart cards.
34
Chapter 3
WiMAX Overview
Support for mobility: The mobile WiMAX variant of the system has mechanisms to support secure seamless handovers for delay-tolerant full-mobility applications, such as VoIP. The system also has built-in support for power-saving mechanisms that extend the battery life of handheld subscriber devices. Physical-layer enhancements, such as more frequent channel estimation, uplink subchannelization, and power control, are also specified in support of mobile applications. IP-based architecture: The WiMAX Forum has defined a reference network architecture that is based on an all-IP platform. All end-to-end services are delivered over an IP architecture relying on IP-based protocols for end-to-end transport, QoS, session management, security, and mobility. Reliance on IP allows WiMAX to ride the declining costcurves of IP processing, facilitate easy convergence with other networks, and exploit the rich ecosystem for application development that exists for IP.
3.5
WiMAX Physical Layer
The WiMAX physical layer is based on orthogonal frequency division multiplexing. OFDM is the transmission scheme of choice to enable high-speed data, video, and multimedia communications and is used by a variety of commercial broadband systems, including DSL, Wi-Fi, Digital Video Broadcast-Handheld (DVB-H), and MediaFLO, besides WiMAX. OFDM is an elegant and efficient scheme for high data rate transmission in a non-line-of-sight or multipath radio environment. In this section, we cover the basics of OFDM and provide an overview of the WiMAX physical layer.
3.5.1 OFDM Basics OFDM belongs to a family of transmission schemes called multicarrier modulation, which is based on the idea of dividing a given high-bit-rate data stream into several parallel lower bit-rate streams and modulating each stream on separate carriers—often called subcarriers, or tones. Multicarrier modulation schemes eliminate or minimize intersymbol interference (ISI) by making the symbol time large enough so that the channelinduced delays—delay spread being a good measure of this in wireless channels are an insignificant (typically,
