Performance of LDPC based turbo equalization for spatial multiplexing

The performance of the turbo equalization algorithm combined minimum mean square error (MMSE) filter with low-density parity-check (LDPC) codes is investigated under frequency selective fading environment. Spatial multiplexing scheme can improve frequency efficiency without channel knowledge at the transmitter. In this system different users transmit LDPC encoded information on the same carrier frequency at the same time. The receiver separates multiplexed signals into individual signals of each user by MMSE filter. After that, each information bit is decoded by sum-product algorithm and log likelihood ratio (LLR) of them are updated. The soft replica is generated from its LLR. Interference components are subtracted from the received signal. The MMSE filtering is reapplied to the resultant signal. This paper shows the performance of this scheme in 4x4 multiple-input multiple-output (MIMO) system and reveals the effect of iteration and channel estimation on the bit error rate (BER) performance.