Reduction of Time Complexity for CLS-DFE MIMO-OFDMA System

Abstract

OFDMA is a multiuser of digital modulation technique used to increase wireless transmission rate. As a one of promising technique, OFDMA still suffer from a few types of interference especially ISI. ISI is an interference that occurs due to the multipath propagation and can distort signal efficiency. Upgraded Cascaded Least Square (CLS) with Decision Feedback Equalizer (DFE) had been used in this research in order to mitigate ISI in OFDMA system. CLS is combination of two adaptive algorithms which are Least Mean Square (LMS) and Recursive Least Square (RLS). Although RLS is one of the best adaptive algorithm but it still suffer from high complexity. Wireless system should use algorithm that ran quickly and used available computing resources efficiently. Running time of an algorithm need to be considered in order to reduce cost when being implemented to hardware. Due to that reason, inverse matrix method is implemented for RLS instead of using basic RLS in order to overcome disadvantage of time complexity in RLS. For equalization technique, DFE as a nonlinear equalizer is used because of its performance which is not enhancing noise during simulation. The combination of CLS with DFE can minimize ISI better compare to conventional LMS and RLS alone. This research also justified that combination of CLS-DFE OFDMA with MIMO antenna enable to mitigate ISI too.