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WiMax-Optimal Throughput Scheduling

WiMax-Optimal Throughput Scheduling. SURVEY. Optimal Throughput Scheduling. Reason The bit rate can be significantly increased. Objective Analytically characterize the performance achieved by multiuser OFDM-TDMA and OFDMA systems from the scheduling viewpoint.

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WiMax-Optimal Throughput Scheduling

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  1. WiMax-Optimal Throughput Scheduling SURVEY

  2. Optimal Throughput Scheduling • Reason • The bit rate can be significantly increased. • Objective • Analytically characterize the performance achieved by multiuser OFDM-TDMA and OFDMA systems from the scheduling viewpoint.

  3. WiMax (IEEE 802.16) Physical Layer - Specifications • OFDMA • OFDM • Adaptive Modulation and Coding • Turbo-Coding, LDPC, Convolutional Coding • QPSK, 16QAM, 64QAM etc.

  4. OFDM & OFDMA • Dividing the total bandwidth into number of subcarriers • Densely spaced and orthogonal sub-carriers • Orthogonality is acheived by FFT • ISI is mitigated • OFDM, access is done via TDMA • OFDMA, access is done via FDMA

  5. System Preliminaries • Channel • Frequency Selective MIMO channel • Perfect CSI at TX and RX • Yn = Hnx xn + N • Remains same within a frame • Scheduling Scenario • Downlink multi-user system • Poisson distributed packet arrival process • Queue length is of an infinite size • Select user, u

  6. Delay Throughput Analysis • M/G/1 model is adopted for analysis • Poisson packet Arrival Rate = λ • Poisson Packet Service Time = S • Number of subcarriers = Ns • Fixed packet size in unit of bits = α • Number of bits loaded to subcarrier i = μi • Average Delay

  7. Average Service Time • Packet is served by allocation of subcarrier in transmission systems • Service measured in the unit of the number of subcarriers

  8. Second Moment and Lower Bound • By Schwartz inequality and the fact that μi and μj are non-negative we have

  9. Markov Models for Wireless Channel • Gilbert-Elliot • Finite-State Markov Channel

  10. Adaptive Modulation and Coding • Divide received SNR value into disjoint regions • Select proper modulation method • FSMC

  11. Steady-State Probabilities • Steady-state probabilities can be obtained by integrating pdf of received SNR • PDF of received SNR for Rayleigh fading channel with OFDM • PDF for received SNR for Rayleigh fading channel with OFDMA

  12. Results • Service Time-First and Second Moments as: Dynamic OFDMA outperforms dynamic OFDM

  13. Future Work • Performance analysis with finite buffer length • Heterogonous traffic among the users • Limited Feedback CSIT

  14. References • Javad Razavilar, K. J. Ray Liu, “Jointly Optimized Bit-Rate/Delay Control Policy for Wireless Packet Networks With Fading Channels”, IEEE Transactions on Communications, Volume 50, Issue: 3, pp. 484-494, Mar 2002 • Yu-Jung Changy, Feng-Tsun Chienz and C.C. Jay “Performance Comparison of OFDM-TDMA and OFDMA with Cross-Layer Consideration” Vehicular Technology Conference, 2006. VTC-2006 Fall. 2006 IEEE 64t, pp. 1-5,Sept. 2006 • Zhendong Zhou and Branka Vucetic, “MIMO Systems with Adaptive Modulation” Vehicular Technology Conference, 2004. VTC 2004-Spring. 2004 IEEE 59th,Volume 2, Issue , 17-19 May 2004 Page(s): 765 - 769 Vol.2 • Manish Airy, Sanjay Shakkottai and Robert W. Heath Jr, “Limiting Queueing Models for Scheduling in Multi-user MIMO Wireless Systems”

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