Supervisor: Prof. Riku J ä ntti Instructor: Lic. Tech. Boris Makarevitch
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Transcript of Supervisor: Prof. Riku J ä ntti Instructor: Lic. Tech. Boris Makarevitch
Performance Evaluation of WiMAX / IEEE 802.16 OFDM Physical Layer
Mohammad Azizul Hasan
Master’s thesis presentation, 5th June, Espoo
Supervisor: Prof. Riku JänttiInstructor: Lic. Tech. Boris Makarevitch HELSINKI UNIVERSITY OF TECHNOLOGY
Communications Laboratory
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Agenda
Introduction
IEEE 802.16 and Wireless Broandband Access
IEEE 802.16 Physical Layer
Simulation Model
Simulation Results
Conlusion and Futurework
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Introduction Background and Motivation
Broadband Wireless Access Promising solution for last mile access High speed internet access in residential as well as small and medium sized enterprise sector
Advantages of BWA– Ease of deployment and installation– Much higher data rates can be supported– Capacity can be increased by installing more base stations
Challenges for BWA
– Price
– Performance– Interoperability issues
Broadband access is currently dominated by DSL and cable modem technologiesLimitations:
• dsl can reach only three miles from central office switch
• Lack of return channel in older cable network
• Commercial areas are often not covered by cable networks
IEEE 802.16 is the first industry based standard for BWA Objective
Evaluate the effect of various modulation and coding schemes as well as interleving on PHY layer performance Methodology
PHY layer simulation is used to investigate the performance
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IEEE 802.16 and Broadband Wireless Access (BWA) (1/5)
• Evolution of IEEE family of standard for BWA
-EEE 802.16 Working group on BWA is responsible for development of the standards-The standard provides secification for PHY and MAC layer
IEEE 802.16-2001-First issue of the family intend to provide fixed BWA access in a point-to-point (PTP) topology.-Single carrier modulation-10-66 GHz frequency range-QPSK, 16-QAM (optional in UL) and 64-QAM (optional) modulation scheme
IEEE 802.16a-Added physical layer support for 2-11 GHz-Non Line of Sight (NLOS) operation becomes possible-Advanced power management technique and adaptive antenna arrays were included -OFDM was included as an alternative to single carrier modulation-BPSK, QPSK, 16-QAM, 64-QAM, 256-QAM (optional)
IEEE 802.16-2004-2-11 GHZ frequency range-256 subcarriers OFDM Technique-BPSK, QPSK, 16-QAM, 64-QAM-Fixed and Nomadic access
IEEE 802.16e-Scalable OFDMA-Mobile BWA
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IEEE 802.16 and BWA (2/5)
IEEE 802.16 Protocol Stack
MAC Layer
Service specific convergence Sublayer(CS)-MAC CS receives higher level data
-provides transformation and mapping into MAC SDU
-ATM CS and packet CS
MAC Common Part Sublayer (CPS)
- System access, bandwidth allocation, connection
management
-QoS provisioning
Privacy Sublayer
-Authentication, secure key exchange, encryption
PHY Layer-Four different physical layer specifications
-SC, SCa, OFDM, OFDMA
Service-Specific Convergence Sublayer
(CS)
MAC Common Part Sublayer (MAC CPS)
Security Sublayer
Physical Layer (PHY)
CS SAP
PHY SAP
MAC SAP
Data /Control Plane
PHY
MAC
Scope of standard
Management Entity
Service Specific CS
Management Entity
MAC CPS
Security Sublayer
Management EntityPHY
Management Plane
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IEEE 802.16 and BWA (3/5)
Network Architecture and Deployment Topology
Architecture Resembled to cellular networks Each cell consists of a BS and one or
more SS BS provides connectivity to core network
Topology Point to point (PTP) Point to multi point (PTM) Mesh
BS
SSsBS
SSs
BS
SSs
Core Network
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IEEE 802.16 and BWA (4/5)
Application-Supports ATM, IPv4, IPv6, Ethernet and VLAN
Cellular Backhaul
- hotspots, PTP back haul
Residential Broadband
-fill the gaps in cable and dsl coverage
Underserved Areas
-rural areas
Always Best Connected
- roaming
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IEEE 802.16 and BWA (5/5)
WiMAX Forum and IEEE 802.16
Worldwide Interoperability for Microwave Access (WiMAX) An allince of telecommunication equipment and component manufacturers and service
providers Promotes and certify the compatibility and interoperability of BWA products Adopted two version of the IEEE 802.16 standard
Fixed/nomadic access: IEEE 802.16-2004 OFDM PHY layer
Portable/Mobile access: IEEE 802.16e
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IEEE 802.16 Physical Layer (1/4)
PHY Layer attributes:
Defines duplexing techniques (TDD, FDD)
Supports multiple RF bands 10-66 GHz for LOS below 11GHz for NLOS
Flexible bandwidths Up to 134 MHz in 10-66 GHz band Up to 20 MHz in < 11GHz band
Defines multiple PHYs for different Applications SC for point-to-point long range application OFDM for efficient Point-to-Multi-Point high data rate applications OFDMA more optimized for mobility, using sub-channelizationon on Downlink and Uplink
Specifies Modulation and channel coding schemes
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IEEE 802.16 Physical Layer (2/4)
Desgnation Band of operation Duplexing Technique Notes
WirelessMAN-SC™ 10-66 GHz TDD,
FDD
Single Carrier
WirelessMAN-SCa™ 2-11 GHz
Licensed band
TDD,
FDD
Single Carrier technique for NLOS
WirelessMAN-OFDM™ 2-11 GHz
Licensed band
TDD,
FDD
OFDM for NLOS operation
WirelessMAN-OFDMA™ 2-11 GHz
Licensed band
TDD,
FDD
OFDM Broken into subgroups to provide multiple access in a
single frequency band
WirelessHUMAN™ 2-11 GHz
Licensed Exempt Band
TDD May be SC, OFDM, OFDMA. Must include Dynamic Frequency Selection to mitigate interfarence
IEEE 802.16 Airinterface nomenclature and description
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IEEE 802.16 Physical Layer (3/4)
WirelessMANTM OFDM PHY Layer
Flexible Channel Bandwidth integer multiple of (1.25 1.5, 1.75, 2 or 2.75) MHz with a maximum of 20 MHz
Robust Error Control Mechanism outer Reed-Solomon (RS) code and inner Convolutional code (CC). Turbo Coding (optional)
Adaptive Modulation and Coding 8 different scheme
Adaptive Antenna System Transmission of DL and UL burst using
directed beams
Transmit Diversity
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IEEE 802.16 Physical Layer (4/4)
OFDM Special form of MCM technique Dividing the total bandwidth into a number of sub-carriers
Densely spaced and orthogonal sub-carriers Orthogonality is acheived by FFT ISI is mitigated
Comparison between conventional FDM and OFDM
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Simulation Model (1/5)
PHY Layer Setup
Random data generation
Channel Encoding
Mapping
Cyclic Prefix removal
FFT
IFFT Cyclic Prefix insertion
De-mappingChannel decoding
Output Data
Transmitter
Receiver
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Simulation Model (2/5)
Channel coding
Mandatory channel coding per modulation
Modulation Uncoded Block Size
(bytes)
Coded Block Size
(bytes)
Overall coding rate
RS code CC code rate
BPSK 12 24 1/2 (12,12,0) 1/2
QPSK 24 48 1/2 (32,24,4) 2/3
QPSK 36 48 3/4 (40,36,2) 5/6
16-QAM 48 96 1/2 (64,48,8) 2/3
16-QAM 72 96 3/4 (80,72,4) 5/6
64-QAM 96 144 2/3 (108,96,6) 3/4
64-QAM 108 144 3/4 (120,108,6) 5/6
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Simulation Model (3/5)
Channel Coding (contd.)
Data randomization• Implemented with PRBS generator• 15-stage shift register• XOR gates in feedback
RS-encoding• Derived from RS(N=255, K=239, T=8)
• Shortend and punctured
CC Encoder• Native code rate ½• Supports punctureing to acheive variable code rate
Interleaver• Two step permutation• First step:adjacent coded bits are mapped onto non-adjacent subcarriers • Second step: adjacent coded bits are mapped alternately onto less or more significant bits of the constellation
Data Randomization
Reed-SolomonEncoding
ConvolutionalEncoding
Interleaving
FEC
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Simulation Model (4/5)
Simulator Description
Each block of the transmitter, receiver and channel is written in separate ’m’ file
The main procedure call each of the block in the manner a communication system works
initialization parameters: number of simulated OFDM symbols, CP length, modulation and coding rate, range of SNR values and SUI channel model for simulation.
The input data stream is randomly generated
Output variables are available in Matlab™ workspace
BER and BLER values for different SNR are stored in text files
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Simulation Model (5/5)
Channel model wireless channel is characterized by: Path loss Multipath delay spread Fading characteristics Doppler spread Co-channel and adjacent channel interference
Stanford University Interim (SUI) channel models -empirical model -six channel model to address three different terrain types -3 taps used to model multipath -tap delay: 0-20 µs
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Simulation results (1/10)
Scatter plots• '+' transmitted data
• '*' received data.
Sppead reduction is taking place with
the increaseing values of SNR
Validates the implementation
of channel model
Scatter Plots for 16-QAM modulation (RS-CC 1/2) in SUI-1 channel model
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Simulation results (2/10)
BER Performance
BER vs. SNR plot for different coding profiles on SUI-2 channel
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Simulation results (3/10)
BPSK ½ QPSK ½ QPSK ¾ 16-QAM ½ 16-QAM ¾ 64-QAM 2/3 64-QAM 3/4
Channel SNR (dB) at BER level 10-3
SUI-1 4.3 6.6 10 12.3 15.7 19.4 21.3
SUI-2 7.5 10.4 14.1 16.25 19.5 23.3 25.4
SUI-3 12.7 17.2 22.7 22.7 28.3 30 32.7
SNR required at BER level 10-3 for different modulation and coding profile
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Simulation results (4/10)
BER performance:variations with the change in channel conditions
Severity of corruption is highest on SUI-3 Lowest in SUI-1
Tap power dominates in determining
the order of severity of corruption
BER vs. SNR plot for 16-QAM 1/2 on different SUI channel
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Simulation results (5/10)
BLER performance
BLER vs. SNR plot for different modulation and coding profile on SUI-1
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Simulation results (6/10)
BLER Performance
BPSK ½ QPSK ½ QPSK ¾ 16-QAM ½ 16-QAM ¾ 64-QAM 2/3
64-QAM 3/4
Channel SNR (dB) at BLER level 10-2
SUI-1 7.3 7 11 12.6 15.6 19.6 21.3
SUI-2 10.7 12.7 15.4 16.5 20.8 23.8 26.1
SUI-3 15 17.7 22.7 24.4 28.8 31.2 33.8
SNR required at BLER level 10-2 for different modulation and coding profile
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Simulation results (7/10)
BLER performance:variations with the change in channel conditions
• Results are consistant with
the BER performance
BLER vs. SNR plot for 64-QAM 2/3 modulation and coding profile on different SUI channel
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Simulation results (8/10)
Effect of Forward Error Correction
FEC gains 4.5 dB improvement
at BER level of 10-3
Effect of FEC in 64-QAM 2/3 on SUI-3 channel model
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Simulation results (9/10)
Effect of Reed-Solomon Encoding
QPSK ½ 16-QAM ½ 64-QAM 2/3
SNR(dB) at BER 10-3
1 1.2 1.4
SNR(dB) at BLER 10-2
3 4.5 5
Performance improvement due to RS Coding
Effect of Reed Solomon encoding in QPSK ½ on SUI-3 channel model
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Simulation results (10/10)
Effect of Bit interleaver
Effect of Block interleaver in 64-QAM 2/3 on SUI-2 channel model
BPSK 1/2 QPSK ½ 16-QAM ½ 64-QAM 2/3
SNR(dB) at BER 10-
3
2.2 0.8 1.4 2.2
SNR(dB) at BLER 10-2
1 1.2 1.7 2.5
Performance improvement due to bit interleaving
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Conclusion and Future Work
Conclusion
• Lower modulation and coding scheme provides better performance with less SNR• The results are ovious from constallation mapping point of view• Results obtain from the simulation can be used to set threshold SNR to implement adaptive modulation scheme
to attatin highest transmission speed with a target BER• FEC improves the BER performance by 6 dB to 4.5 dB at BER level 10 -3
• RS encoding improves the BER performance by 1dB to 1.4 dB at BER level 10 -3 • RS encoder provides tremendous performance when it is concatenated with CC
Future Works
The implemented PHY layer model still needs some improvement. The channel estimator can be implemented to obtain a depiction of the channel state to combat the effects of the channel using an equalizer.
The IEEE 802.16 standard comes with many optional PHY layer features, which can be implemented to further improve the performance. The optional Block Turbo Coding (BTC) can be implemented to enhance the performance of FEC. Space Time Block Code (STBC) can be employed in DL to provide transmit diversity.
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Thank You !