Slow and Fast Adaptation of Partial Equalization for MC-CDMA Systems

This paper investigates and compares slow and fast adapting equalization techniques for multi-carrier code division multiple access (MC-CDMA) systems. In particular, a recently proposed partial equalization (PE) technique is considered since providing good performance and being analytically tractable. We analytically evaluate both the downlink instantaneous bit error probability (BEP) and the mean BEP, averaged over fast fading, as a function of the PE parameter. We consider a slow adaptive PE technique that adapts the PE parameter to the slow processes variation (e.g., the number of sub-carriers, the mean signal to noise ratio and the number of active users). Our results show that the slow adaptation of the PE parameter can provide a noticeable improvement in terms of BEP with respect to fixed schemes. The slow adaptation is then compared to the fast adaptive PE technique tracking fast fading evolutions. Results show that the performance of slow adaptation can be in many practical cases close to that of fast adaptation despite the fact that slow adaptation is less complex in terms of feedback rate.