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Michael Einhaus, ComNets, RWTH Aachen University
Dynamic Resource Allocation in Dynamic Resource Allocation in OFDMA SystemsOFDMA Systems
Michael Einhaus
Chair of Communication Networks RWTH Aachen University, Germany
13. ComNets-Workshop, Mobil- und TelekommunikationMarch 31st, 2006, Aachen, Germany
13. ComNets-Workshop 200613. ComNets-Workshop 2006
2Michael Einhaus, ComNets, RWTH Aachen University
OverviewOverview
• Introduction• OFDMA• Medium Access Control• Multi User Diversity• Interference Awareness• Conclusion
3Michael Einhaus, ComNets, RWTH Aachen University
IntroductionIntroduction
• 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 StructureOFDMA Subchannel Structure
clu
ster
edsu
bch
ann
eld
istr
ibu
ted
su
bch
ann
el
WIM
AX
WIG
WA
MW
INN
ER
Clustered subchannel interference/fading avoidance, exploitation of diversity, increased signaling overhead
Distributed subchannel averaging
5Michael Einhaus, ComNets, RWTH Aachen University
MAC Frame StructureMAC Frame Structure
• Centrally controlled (IEEE 802.16)
• 2-dimensional resources
• Scheduling within resource subsets
• Fast and slow adaptation
time slot (8 OFDMA symbols)
32
su
bc
ha
nn
els
signaling overhead
resources
544 s (40 x 13.6 s)
resource subset
6Michael Einhaus, ComNets, RWTH Aachen University
OFDMA Subchannel DiversityOFDMA Subchannel Diversity
• V = 50km/h fDoppler~230Hz• Τrms = 250ns• Δf = 78.125kHz (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 SchedulerBasic OFDMA Scheduler
• Perfect channel knowledge
• Uniform power allocation(no water-filling)
• Adaptive PHY-mode selection
resource
32
su
bc
ha
nn
els
time slot
8Michael Einhaus, ComNets, RWTH Aachen University
Exploitation of Multi User DiversityExploitation 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/s200 m
150 m
9Michael Einhaus, ComNets, RWTH Aachen University
SINR Estimation / PHY Mode SelectionSINR Estimation / PHY Mode Selection
iiii IFNLPSINR • 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 AllocationInterference Aware Resource Allocation
][~][~~
IIEI
• Perfect channel knowledge
• Interference estimation
= 0
• 2 cells (D = 500m, R = 150m)
• 8 mobile terminals
MT 1
MT 1(SINR0 = 15 dB)
11Michael Einhaus, ComNets, RWTH Aachen University
Interference Aware Resource Allocation (II)Interference Aware Resource Allocation (II)
12Michael Einhaus, ComNets, RWTH Aachen University
Conclusion and OutlookConclusion 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 [email protected]
Any questions?