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Dynamic Resource Allocation in OFDMA Systems

13. ComNets-Workshop 2006. Dynamic Resource Allocation in OFDMA Systems. Michael Einhaus Chair of Communication Networks RWTH Aachen University, Germany 13. ComNets-Workshop, Mobil- und Telekommunikation March 31st, 2006, Aachen, Germany. Overview. Introduction OFDMA

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Dynamic Resource Allocation in OFDMA Systems

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  1. 13. ComNets-Workshop 2006 Dynamic Resource Allocation in OFDMA Systems Michael Einhaus Chair of Communication Networks RWTH Aachen University, Germany 13. ComNets-Workshop, Mobil- und Telekommunikation March 31st, 2006, Aachen, Germany

  2. Overview • Introduction • OFDMA • Medium Access Control • Multi User Diversity • Interference Awareness • Conclusion

  3. Introduction Why OFDMA? (Orthogonal Frequency Division Multiple Access) • Handling of ISI • Spectral efficiency • Exploitation of diversity • Refined resource granularity • High flexibility Challenges • Synchronization • Handling of diversity and flexibility

  4. OFDMA Subchannel Structure WIGWAM WINNER clustered subchannel distributed subchannel WIMAX Clustered subchannel  interference/fading avoidance, exploitation of diversity, increased signaling overhead Distributed subchannel  averaging

  5. MAC Frame Structure 544 s (40 x 13.6 s) signaling overhead resources resource subset 32 subchannels time slot (8 OFDMA symbols) • Centrally controlled (IEEE 802.16) • 2-dimensional resources • Scheduling within resource subsets • Fast and slow adaptation

  6. OFDMA Subchannel Diversity • Subchannel diversity depends on subcarrier grouping • Diversity exploitation requires sophisticated scheduling algorithms • Diversity exploitation increases signaling overhead • V = 50km/h  fDoppler~230Hz • Τrms = 250ns • Δf = 78.125kHz (80MHz/1024)

  7. Basic OFDMA Scheduler resource 32 subchannels time slot • Perfect channel knowledge • Uniform power allocation (no water-filling) • Adaptive PHY-mode selection

  8. Exploitation of Multi User Diversity • Single cell scenario • 32 mobile terminals • Downlink traffic (Poisson) • 100 byte packets • Different OFDMA schemes • Clustered subchannels (MUD) • Clustered subchannels (random) • Distributed subchannels (averaging) • Pathloss coefficient :  = 2.5 • TX Power : 30 dBm • QPSK¾, 16QAM¾, 64QAM¾ 2000 kbit/s 200 m 150 m

  9. SINR Estimation / PHY Mode Selection • SINR estimation is required for optimal resource and PHY mode selection • Afflicted with uncertainty • Fading • Interference • Variance depends on OFDMA scheme

  10. Interference Aware Resource Allocation • Perfect channel knowledge • Interference estimation MT 1 (SINR0 = 15 dB) • 2 cells (D = 500m, R = 150m) • 8 mobile terminals MT 1 a = 0

  11. Interference Aware Resource Allocation (II)

  12. Conclusion and Outlook Conclusion • OFDMA has the potential to provide high spectral efficiency • Exploitation of diversity implies problems in the estimation of interference • The design of an OFDMA system comprises a large set of parameters and options Open Issues • Averaging vs. avoidance • Adaptation to channel or interference • Joint scheduling of base stations • Uplink

  13. Thank you for your attention ! Michael Einhaus ein@comnets.rwth-aachen.de Any questions?

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