Michael Einhaus, ComNets, RWTH Aachen University 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 13. ComNets-Workshop 2006

2Michael Einhaus, ComNets, RWTH Aachen University Overview Introduction OFDMA Medium Access Control Multi User Diversity Interference Awareness Conclusion

3Michael Einhaus, ComNets, RWTH Aachen UniversityIntroduction Handling of ISI Spectral efficiency Exploitation of diversity Refined resource granularity High flexibility Why OFDMA? (Orthogonal Frequency Division Multiple Access) Challenges Synchronization Handling of diversity and flexibility

4Michael Einhaus, ComNets, RWTH Aachen University OFDMA Subchannel Structure clustered subchannel distributed subchannel WIMAX WIGWAM WINNER Clustered subchannel  interference/fading avoidance, exploitation of diversity, increased signaling overhead Distributed subchannel  averaging

5Michael Einhaus, ComNets, RWTH Aachen University MAC Frame Structure Centrally controlled (IEEE ) 2-dimensional resources Scheduling within resource subsets Fast and slow adaptation time slot (8 OFDMA symbols) 32 subchannels signaling overhead resources 544  s (40 x 13.6  s) resource subset

6Michael Einhaus, ComNets, RWTH Aachen University OFDMA Subchannel Diversity V = 50km/h  f Doppler ~230Hz Τ rms = 250ns Δf = kHz (80MHz/1024) Subchannel diversity depends on subcarrier grouping Diversity exploitation requires sophisticated scheduling algorithms Diversity exploitation increases signaling overhead

7Michael Einhaus, ComNets, RWTH Aachen University Basic OFDMA Scheduler Perfect channel knowledge Uniform power allocation (no water-filling) Adaptive PHY-mode selection resource 32 subchannels time slot

8Michael Einhaus, ComNets, RWTH Aachen University 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

9Michael Einhaus, ComNets, RWTH Aachen University 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

10Michael Einhaus, ComNets, RWTH Aachen University Interference Aware Resource Allocation Perfect channel knowledge Interference estimation  = 0 2 cells (D = 500m, R = 150m) 8 mobile terminals MT 1 (SINR 0 = 15 dB)

11Michael Einhaus, ComNets, RWTH Aachen University Interference Aware Resource Allocation (II)

12Michael Einhaus, ComNets, RWTH Aachen University Conclusion and Outlook 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 Conclusion Open Issues Averaging vs. avoidance Adaptation to channel or interference Joint scheduling of base stations Uplink

13Michael Einhaus, ComNets, RWTH Aachen University Thank you for your attention ! Michael Einhaus Any questions?