Capacity Enhancement of MCCDMA Systems through MAI Cancellation Using Switched Interleaving Technique and Correlation Reconstruction based MRC with Diversity Gain

The multi-carrier code division multiple access (MCCDMA) is a attractive choice for the future wireless systems where multiplexing and diversity in space, time and frequency are joined together through multiple input multiple output (MIMO) and space time block coding (STBC) in order to increase user capacity. In this study, the orthogonal complete complementary (OCC) spreading codes are employed along with unique spreading modulation for synchronous downlink transmission of MCCDMA systems. However, MC-CDMA suffers from multiple access interference (MAI) due to frequencyselective fading and multipath effects. To mitigate this MAI effect and achieve diversity gain, adaptive switched interleaving technique is proposed based on the concept of Minimum Distance Conditional Bit Error Rate (MDCBER) criterion. Furthermore, simple correlation reconstruction based maximal ratio combing (CRMRC) scheme is introduced at the receiver to compensate the diversity fading and suppress the effect of MAI at the receiver. The proposed technique modifies interleaving pattern adaptively for STBC encoded sequence of the users to reconstruct the orthogonality among the users to counteract the fading and multipath effects. For this purpose only a quantized detail of the Squared Minimum Distance Estimation (SMDE) is enough at the users such that the associated overhead is nominal compared to perfect channel state information (CSI) at the users. The simulation result shows that the MCCDMA system using switched interleaving technique along with CRMRC scheme achieves significant performance improvement in terms of BER. It also shows that the proposed technique reduces the MAI and increases user capacity.