A Two-Stage Dynamic Channel Assignment Scheme with Graph Approach for Dense Femtocell Networks

Se-Jin KIM  IlKwon CHO  Yi-Kang KIM  Choong-Ho CHO  

IEICE TRANSACTIONS on Communications   Vol.E97-B   No.10   pp.2222-2229
Publication Date: 2014/10/01
Online ISSN: 1745-1345
DOI: 10.1587/transcom.E97.B.2222
Type of Manuscript: PAPER
Category: Wireless Communication Technologies
dense femtocell networks,  OFDMA/FDD,  interference mitigation,  dynamic channel assignment,  graph coloring,  

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In dense femtocell networks (DFNs), one of the main issues is interference management since interference between femtocell access points (FAPs) reduces the system performance significantly. Further, FAPs serve different numbers of femtocell user equipments (FUEs), i.e., some FAPs have more than one FUE while others have one or no FUEs. Therefore, for DFNs, an intelligent channel assignment scheme is necessary considering both the number of FUEs connected to the same FAPs and interference mitigation to improve system performance. This paper proposes a two-stage dynamic channel assignment (TS-DCA) scheme for downlink DFNs based on orthogonal frequency division multiple access/frequency division duplex (OFDMA/FDD). In stage 1, using graph coloring algorithm, a femtocell gateway (FGW) first groups FUEs based on an interference graph that considers different numbers of FUEs per FAP. Then, in stage 2, the FGW dynamically assigns subchannels to FUE clusters according to the order of maximum capacity of FAP clusters. In addition, FAPs adaptively assign remaining subchannels in FUE clusters to their FUEs in other FUE clusters. Through simulations, we first find optimum parameters of the FUE clustering to maximize the system capacity and then evaluate system performance in terms of the mean FUE capacity, unsatisfied FUE probability, and mean FAP transmission energy consumption according to the different numbers of FUEs and FAPs with a given FUE traffic load.