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Downlink Resource Management for OFDMA Femtocells using Stochastic Subchannel Allocation

Downlink Resource Management for OFDMA Femtocells using Stochastic Subchannel Allocation. Hyunduk Jung Ubiquitous Network Lab. Yonsei University psychblue@yonsei.ac.kr. YONSEI UBIQUITOS NETWORK LAB. Introduction. Femtocell. Issues. Macrocell BS. Home Base Station (10~50m)

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Downlink Resource Management for OFDMA Femtocells using Stochastic Subchannel Allocation

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  1. Downlink Resource Management for OFDMA Femtocells using Stochastic Subchannel Allocation Hyunduk Jung Ubiquitous Network Lab. Yonsei University psychblue@yonsei.ac.kr YONSEI UBIQUITOS NETWORK LAB

  2. Introduction Femtocell Issues Macrocell BS • Home Base Station (10~50m) • High Speed Indoor Communication • IP backhaul (FTTH, xDSL,…) • WCDMA (UMTS) • OFDMA (3GPP H(e)NB, WiBro) • Frequency Operating • Access Scenario (open, closed) • Interference Management • Self-configuration • Security Femtocell 2

  3. Introduction Dedicated Channel Co-Channel Macrocell BS • Independent Frequency • Interference Avoid • Low Spectral Efficiency • Spatial Frequency Reuse • High Spectral Efficiency • High Interference Femtocell BS Femtocell BS Uplink Downlink < Interference Scenario of the Co-Channel Femtocell >

  4. System Model Topology • OFDMA macro-cellular networks with reuse factor 1 • Femtocells are uniformly distributed in the macrocell coverage Resources • The frequency resource is divided into Nsubchannels • The time domian is divides into several OFDM symbols. 4

  5. System Model SINR Subchannel allocation index Subchannel n is allocated to user k Otherwise : gain of subchannel n from BS i to user k Co-channel Interference (CCI) : user set of BS i : set of macrocell BS : set of femtocell BS Data rate 5

  6. Requirements Channel Allocation • Femtocells have not to use subchannels which are allocated to macrocell users in the femtocell coverage Power Allocation • Femtocells have to use transmission power as small as possible to reduce interference with macrocell BSs 6

  7. The Downlink Channel Allocation and Power Control Problem Subject to NP-hard combinatorial optimization problem 7

  8. Proposed Algorithm Stochastic Subchannel Selection Subchanneln is used by the femtocellf Subchannel used by uncertified macrocell user Otherwise Subchannel used by femtocell BS Subchanneloccupancy index frequency time frame 8

  9. Proposed Algorithm SubchannelAllocation • Greedy method Initialize: Calculate rk(n) with SINRk(n) Initialize: Set remk = Rk Do k’ = argmax(remk’) n’ = argmax(b(n)rk'(n)) ak’(n’) = 1 b(n’) = 0 remk’ = remk’ – rk’(n’) While ( max(b(n)rk’(n))>0 ) Higher data rate requirement -> Many subchannels 9

  10. Proposed Algorithm Power Allocation • Suboptimal problem Subject to the femtocell BS solves this problem by each user k independently 10

  11. Proposed Algorithm Power Allocation • KKT conditions Water filling problem 11

  12. Simulation Environments (Monte-Carlo) 12

  13. Simulation Results CDF of SINR for the uncertified macrocell users (20 femto/macro) The average SINR gain of the proposed algorithm is 34 dB (α=0.8) 13

  14. Simulation Results Average throughput of users The average throughput significantly increases 14

  15. Conclusions • This research proposes a stochastic subchannel allocation algorithm for the closed- access co-channel femtocell networks • The proposed algorithm is helpful to reduce the effect of co-channel interference • The performance of the uncertified users increases significantly. 15

  16. References [1] A. Ganz, C. M. Krishna, D. Tang, and Z. J. Haas, ”On optimal design of multitier wireless cellular systems,” IEEE Commun. Mag., vol. 35, no. 2, pp. 88-93, Feb. 1997. [2] A. Doufexi, E. Tameh, A. Nix, S. Armour, and A. Molina, ”Hotspot wireless LANs to enhance the performance of 3G and beyond cellular networks,” IEEE Commun. Mag., vol. 41, no. 7, pp. 58-65, July 2003. [3] H. Claussen, ”Perfromance of macro- and co-channel femtocells in a hierarchical cell structure,” in proc. IEEE PIMRC 2007, pp. 1-5. [4] T. Rappaport, Wireless Communications Principle and Practice. New York: Prentice-Hall, 1996. [5] G. Durgin, T. S. Rappaport, and H. Xu, ”Measurements and models for radio path loss and penetration loss in and around homes and trees at 5.85 GHz,” IEEE Trans. Commun., vol. 46, no. 11, pp. 1484-1998, Nov. 1998. [6] Ronal Y. Chang, Zhifeng Tao, Jinyun Zhang, and Jay Kuo, “Multi-Cell OFDMA Downlink Resource Allocation Using A Graphic Framework,” [7] Guoping Li, and Hui Liu, “Downlink Radio Resource Allocation for Multi-Cell OFDMA System,” IEEE Trans. Wireless Communications, vol. 5, no. 12, Dec . 2006 [8] Luca Venturino, Narayan Prasad, and Xiaodong Wang, “Coordinated Scheduling and Power Allocation in Downlink Multicell OFDMA Networks,” IEEE Trans. Vehicular Technology, vol. 58, no. 6, Jul. 2009 16

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