Simplified BER formulations for MC-CDMA systems with orthogonality restoring combining

Orthogonality restoring combining (ORC) performs better than maximum ratio combining (MRC) and equal gain combining (EGC) in multicarrier code division multiple access (MC-CDMA) systems under high load and high signal-to-noise-ratio (SNR) conditions. However, its exact bit error rate (BER) performance is complicated to evaluate. In this paper, the signal models for the MC-CDMA uplink and downlink channels are first unified. A lower bound and a tight approximation to the BER expressions of MC-CDMA with ORC are then developed. Both the lower bound and approximate BER expressions involve at most one-dimensional integration, hence they can be evaluated much more efficiently. The approximate BER expression is also numerically verified to be very tight under different fading conditions.