On the Impact of Uplink Interference Coordination When Using Multiple Antennas at the Base Station

Abstract

We consider the uplink of a multi-cell orthogonal frequency division multiple access (OFDMA) system that employs multiple (M > 1) receive antennas and maximum ratio combining at the base station. We propose a model that captures the impact of intercell interference coordination on the modulation and coding scheme dependent bit error rate (BER) performance. We analyze this model in two steps. First, we find a closed form formula to calculate the BER under Rayleigh fading for a single subcarrier. Second, we calculate the subcarrier collision probabilities under random and coordinated subcarrier allocation. Combining these two steps allows us to derive the average BER performance (over all OFDM subcarriers) without/with intercell interference coordination (ICIC). We perform extensive Monte Carlo simulations in order to compare these two schemes when mobile stations are positioned randomly in multi-cell cell system. We find that at low and medium load coordinated allocation is superior (for various values of M), while at higher loads the two schemes perform similarly. We also find that at load, it is beneficial to employ asymmetric as opposed to symmetric ICIC. Finally, we explain a somewhat counterintuitive result that shows that the ICIC gain can be larger with multiple antennas at the base station than when there is only one antenna, although this gain is in the very low BER regime.