Analysis of Uplink Intercarrier Interference in OFDMA Femtocell Networks

The femtocell has been considered to be a promising and cost-effective technology to enhance cellular coverage and capacity. However, in the uplink of orthogonal frequency-division multiple access (OFDMA)-based femtocell systems, the signals from macrocell users (MUs) generally arrive at the femtocell base station (FBS) asynchronously because their transmissions are scheduled to be synchronized at the macrocell base station (MBS). When the timing misalignment caused by the asynchronous reception at the FBS is greater than the cyclic prefix length, intercarrier interference (ICI) will arise in demodulation. In this paper, a performance analysis of uplink OFDMA femtocell network is presented. First, the cumulative distribution function (CDF) of MU arrival time is derived. Evaluation shows that the derived CDF is accurate and agrees with simulation results. With the CDF, a closed-form expression of probability mass functions (PMFs) of relative delay of MU signal and probability of ICI occurrence for two synchronization schemes are developed. Based on the PMF of relative delay, ICI power averaged over MU locations for the macrocell using fractional power control is derived for the two synchronization schemes. This new theoretical result helps analyze the signal-to-interference-plus-noise ratio (SINR) of the femtocell, femtocell capacity, and symbol error rate (SER). The theoretical analysis provides a solid evaluation of the effects of ICI for different FBS locations on system performance. It is shown that the performance analysis is quite agreeable with computer simulation. Theory and simulation results show that the system performance of the femtocell using first MU arrival time for synchronization is close to that of no ICI and better than that of using the earliest permissible arrival time.