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802.16 comiitee broadband wireless access based on OFDMA.

Physical layer should mitigate non LOS environments in indoor.

802.16 10-66GHz

802.16a 2-11GHz

- 1. QoS Aware Adaptive Subcarrier Allocation in OFDMA Systems Mustafa Ergen & Sinem Coleri {ergen,csinem}@eecs.berkeley.edu University of California Berkeley
- 2. Introduction Motivation Orthogonal Frequency Division Multiple Access(OFDMA) OFDMA System Resource Allocation Problem Algorithms Optimal Suboptimal Simulation Conclusion
- 3. Motivation Broadband Wireless Access Ex: IEEE 802.16, Wireless MAN OFDM Eliminates OFDMA InterSymbol Interference
- 4. OFDM Diagram
- 5. OFDM-TDMA Multiuser OFDM Time Subcarrier OFDM-FDMA Time OFDM-TDMA OFDM-FDMA OFDMA Subcarrier OFDMA Time User 1 User 2 User 3 … … Subcarrier
- 6. Resource Allocation Goals: Dynamic subcarrier selection Improve system performance with adaptive modulation More bits transmitted in large channel gain carriers Provide QoS Rate and BER
- 7. Resource Allocation ri ar bc su Assumptions: Base station knows the channel Base station informs the mobiles for allocation er Base Station user
- 8. System oCoS=Ptotal for downlink oCoS=Pu for uplink Application Network rQoS=[rR,rBER] oQoS=[oR,oBER,oCoS] Resource Allocation [User x Subcarrier] Physical Layer
- 9. OFDMA
- 10. Resource Allocation RATE: BER: [12 6 6 8 ] [1e-2 1e-2 1e-4 1e-4] Resource Allocation Subcarrier r es U Channel QoS 64-QAM 16-QAM 4-QAM
- 11. Notation Transmit Power : Pkc,n = f k (ck , n ) α k2,n user : k ∈ {1,..., K } subcarrier : n ∈ {1,..., N } assigned bit : c ∈ {0,1,..., M } k, n channel gain : α 2 k, n No −1 BER M − QAM : f (c) = Q ( 3 4 2 ) (2c − 1)
- 12. K min γ k ,n ,c N M ∑∑∑ f ( ck , n ) k =1 n =1 c =1 subject to Rk = α N 2 k ,n γ k ,n ,c for γ k ,n ,c ∈{0,1} M ∑∑ c k ,n .γ k ,n ,c for all k , n =1 c =1 and 0 ≤ K M ∑∑ γ k , n ,c Pc2 Pc3 r es U Integer Programming ≤ 1, for all n. Subcarrier Subcarrier Subcarrier k =1 c =1 es U Pc1 r es U Optimal r es U Subcarrier
- 13. Motivation for Sub-optimal Algorithms IP is complex Allocation should be done within the coherence time Time increases exponentially with the number of constraints
- 14. Current Suboptimal Algorithms 2-step: Subcarrier Allocation Assume the data rate for all subcarriers Assume modulation rate is fixed Assign the subcarriers Bit Loading Greedy approach to assign the bits of user
- 15. Current Suboptimal Algorithms Subcarrier Hungarian algorithm Optimal, very complex LP approximation to IP problem Bit Loading For each k , repeat the following Rk times : n = arg min ∆Pk ,n (ck ,n ) n∈S k c k ,n =c Subcarrier Close to optimal r es U r es U Subcarrier Allocation k ,n +1 evaluate ∆P (c ). k ,n k ,n r es U Subcarrier
- 16. Problems in Current Suboptimal Algorithms Subcarrier assignment and bit loading are separated Users with bad channels may need higher number of subcarriers Not iterative subcarrier assignment
- 17. Iterative Algorithm Iterative algorithm based on Assignment of bits according to highest modulation Finding the best places Distributing the assigned bits to other subcarriers or to non-assigned subcarriers Exchanging the subcarriers among user pairs for power reduction.
- 18. Iterative Algorithm Fair Selection(FS) Greedy Release(GR) Horizontal Swaping(HS) Vertical Swaping(VS)
- 19. Iterative Algorithm Start ASSIGNMENT Modulation-- ITERATION PA W L A C T REV S I GREEDY RELEASE PA W L AT N OZ R OH S I Ptotal<Pmax FAIR SELECTION
- 20. Simulation Environment Build the OFDMA system Modulations:4-QAM,16-QAM,64-QAM Independent Rayleigh fading channel to each user Number of subcarriers =128 Nodes are perfectly synchronized
- 21. CDF of total transmit power without Pmax constraint
- 22. CDF of total transmit power with Pmax constraint
- 23. Average bit SNR vs. RMS delay spread As RMS delay spread increases, the fading variation increases hence higher gains are obtained by adaptive allocation
- 24. Average bit SNR vs. number of users As the number of users increases, the probability of obtaining good channel at a subcarrier increases
- 25. Instantaneous Average bit SNR vs Time Iterative Algorithm improves its Average Bit SNR by the time.
- 26. Conclusion OFDMA Broadband Wireless Access Resource Allocation Channel Information QoS Requirement Optimal Algorithms complex Iterative Algorithms

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