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Dynamic Resource Allocation in OFDMA Systems

This presentation, delivered by Michael Einhaus at the ComNets Workshop 2006, explores dynamic resource allocation in Orthogonal Frequency Division Multiple Access (OFDMA) systems. Key topics include the introduction to OFDMA, its medium access control mechanisms, multi-user diversity, and interference awareness. The talk highlights the significant potential of OFDMA for enhancing spectral efficiency through refined resource granularity and diversity exploitation. It also discusses the ongoing challenges in synchronization, diversity handling, and efficient scheduling strategies necessary for optimizing performance in rapidly changing environments.

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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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