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Performance Evaluation of WiMAX/IEEE 802.16 OFDM Physical Layer

This thesis presentation evaluates the performance of various modulation and coding schemes in the IEEE 802.16 WiMAX physical layer through simulation. The results and future work are discussed.

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Performance Evaluation of WiMAX/IEEE 802.16 OFDM Physical Layer

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  1. Performance Evaluation of WiMAX / IEEE 802.16 OFDM Physical LayerMohammad Azizul HasanMaster’s thesis presentation, 5th June, Espoo Supervisor: Prof. Riku Jäntti Instructor: Lic. Tech. Boris Makarevitch HELSINKI UNIVERSITY OF TECHNOLOGY Communications Laboratory

  2. Agenda • Introduction • IEEE 802.16 and Wireless Broandband Access • IEEE 802.16 Physical Layer • Simulation Model • Simulation Results • Conlusion and Futurework

  3. 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 • 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

  4. 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

  5. Scope of standard CS SAP Management Entity Service Specific CS Service-Specific Convergence Sublayer (CS) M A C Management Entity MAC CPS MAC Common Part Sublayer (MAC CPS) Security Sublayer Security Sublayer PHY SAP P H Y Management Entity PHY Physical Layer (PHY) Data /Control Plane Management Plane MAC SAP 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

  6. SSs SSs SSs BS Core Network BS BS 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

  7. 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

  8. 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

  9. 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

  10. IEEE 802.16 Physical Layer (2/4) IEEE 802.16 Airinterface nomenclature and description

  11. 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

  12. 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

  13. Random data generation Channel Encoding Mapping IFFT Cyclic Prefix insertion Output Data Channel decoding De-mapping FFT Cyclic Prefix removal Simulation Model (1/5) PHY Layer Setup Transmitter Receiver

  14. Simulation Model (2/5) • Channel coding Mandatory channel coding per modulation

  15. Data Randomization Reed-Solomon Encoding Convolutional Encoding Interleaving 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 FEC

  16. 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

  17. 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

  18. 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

  19. Simulation results (2/10) • BER Performance BER vs. SNR plot for different coding profiles on SUI-2 channel

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

  21. 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

  22. Simulation results (5/10) • BLER performance BLER vs. SNR plot for different modulation and coding profile on SUI-1

  23. Simulation results (6/10) • BLER Performance SNR required at BLER level 10-2 for different modulation and coding profile

  24. 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

  25. 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

  26. Simulation results (9/10) • Effect of Reed-Solomon Encoding Performance improvement due to RS Coding Effect of Reed Solomon encoding in QPSK ½ on SUI-3 channel model

  27. Simulation results (10/10) • Effect of Bit interleaver Performance improvement due to bit interleaving Effect of Block interleaver in 64-QAM 2/3 on SUI-2 channel model

  28. 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.

  29. Thank You !

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