Frequency domain equalization with user interference cancellation for 2-dimensional block spread CDMA system

The 2-Dimension orthogonal variable spreading factor (OVSF) block spread code divide multiple access (CDMA) has been regarded as a promising multiple access interference (MAI) free transmission scheme. But as the spreading factor increases, the performance will degrade significantly due to the time domain fast fading. In this paper, we will propose frequency-domain equalization (FDE) based on minimal mean square error (MMSE) criterion combining user interference cancellation (UIC) for 2D OVSF block spread CDMA systems. The orthogonalilty loss among users caused by channel time-domain fast fading is analyzed, and the residual interference between users after block-level de-spreading is cancelled by a proposed algorithm using QR decomposition. Its complexity is quite low compared to the traditional direct sequence CDMA (DS-CDMA) scheme with multi-user detection (MUD) technique. Simulation results have shown that the block spread CDMA systems with the proposed MMSE-FDE with UIC can achieve almost the same performance with the traditional DS-CDMA and MC-CDMA systems.