Area Spectral Efficiency of Co-Channel Deployed OFDMA Femtocell Networks

Deployment of femtocells is expected to increase the capacity of cellular networks several folds. However, since femtocells operate within the available spectrum of the macro-cellular network, the arising uncontrolled interference may limit the achievable gain. For the successful operation of femtocells, the area spectral efficiency (ASE) performance needs to be studied for useful insights. In this paper, we derive the ASE for orthogonal-frequency-division-multiple-access-based cochannel-deployed macrocell-femtocell networks considering uniformly distributed femtocell locations. The ASE is obtained from the area averaged signal to interference plus noise ratio (SINR) distributions of macrocell and femtocell networks. Since strength of the co-channel interference received by a user terminal is related to load condition in neighboring cells, the ASE is derived considering activity due to fractional load of interfering cells. We then investigate the impact of femtocell density, transmit power, and load of femtocells as well as macrocell transmit power and load on the ASE performance. We also look at the optimal femtocell radio parameters: transmit power and load that maximizes the ASE while satisfying the QoS constraints of macrocell and femtocell users at different network conditions. From the analysis, it is seen that in co-channel deployment mode, if femtocell radio parameters are suitably controlled according to varying network condition, the ASE gain can be increased several folds without affecting macrocell network performance. It is also shown that, by centrally coordinating the spectrum reuse and allocated power at each macro/femto tier, the overall performance can be improved.