BER analysis of overloaded MC-CDMA cellular system employing sphere decoder in non-ideal sectorization scenario

New multiple access techniques aim to increase the spectral efficiency by overloading the system, i.e., with those techniques the number of users served is greater than the number of system radio channels. Multicarrier-code division multiple access (MC-CDMA) allows the system to be overloaded when multiuser-maximum-likelihood-detector (MU-MLD) is used. Nevertheless, an overloaded system may be affected by high levels of interference. Hence, in this work, the mean bit error rate (BER) of the uplink of MC-CDMA cellular systems with MU-MLD is evaluated by considering own-cell and co-cell interference. MU-MLD is implemented via a sphere decoder with MMSE QR decomposition. The analysis assumes Rayleigh fading, Stanford University Interim (SUI) path-loss model and non-ideal antenna sectorization. Thus, an expression to model antenna radiation patterns is also proposed. In this context, an upper bound expression to evaluate the BER is derived for BPSK modulation. Monte Carlo simulations verify the expression accuracy. Results show that MC-CDMA does not lose diversity when the number of own-cell interferers increases. Moreover, co-cell interference significantly affects the system performance. However, cell sectorization allows mitigation of co-cell interference and as result, the system can be overloaded, while it maintains reasonable BER.