Performance Evaluation of WiMAX / IEEE 802.16 OFDM Physical Layer Mohammad Azizul Hasan Master

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Performance Evaluation of WiMAX / IEEE 802.16
OFDM Physical LayerMohammad Azizul
HasanMasters thesis presentation, 5th June,
Espoo

• Supervisor Prof. Riku Jäntti
• Instructor 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 technologies
• Limitations
• dsl can reach only three miles from central
  office switch
• Lack of return channel in older cable network

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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

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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

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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

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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 lt 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)
IEEE 802.16 Airinterface nomenclature and
description
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
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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

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(N255, K239, T8)
• Shortend and punctured
• CC Encoder
• Native code rate ½
• Supports punctureing to acheive variable code
  rate
• Interleaver
• Two step permutation
• First stepadjacent 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

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)
SNR required at BER level 10-3 for different
modulation and coding profile
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 SNR (dB) at BER level 10-3 SNR (dB) at BER level 10-3 SNR (dB) at BER level 10-3 SNR (dB) at BER level 10-3 SNR (dB) at BER level 10-3 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
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Simulation results (4/10)

• BER performancevariations 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

SNR required at BLER level 10-2 for different
modulation and coding profile
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 SNR (dB) at BLER level 10-2 SNR (dB) at BLER level 10-2 SNR (dB) at BLER level 10-2 SNR (dB) at BLER level 10-2 SNR (dB) at BLER level 10-2 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
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Simulation results (7/10)

• BLER performancevariations 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

Performance improvement due to RS Coding
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
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

Performance improvement due to bit
interleaving
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
Effect of Block interleaver in 64-QAM 2/3 on
SUI-2 channel model
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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 !