Analysis of Uplink Inter-Carrier-Interference Observed at Femtocell Networks

In a typical macrocell network, all macrocell mobile stations (mMSs) are synchronized to the macrocell base station (mBS) during the uplink. The mMSs that are closer to the mBS transmit their signals at a later time instant so that signals of all the all mMSs arrive at the mBS at the same time. However, signals of the mMSs reach at the femtocell base stations (fBSs) with different delays, which may cause interference problems for femtocell users. For orthogonal frequency division multiple access (OFDMA) based networks, interference due to delays larger than the cyclic prefix of the desired signal will appear as inter-carrier interference (ICI) and inter-symbol-interference (ISI). In this paper, statistics of the ICI power received from the mMSs at the fBSs is derived considering different locations of the fBSs in the macrocell network. The concept of zero-ICI region is introduced and its implications for coexisting macrocell/femtocell networks are presented. Theoretical findings are verified via simulation results.