Comparison of bit error rate and convergence of four different iterative receivers for wireless OFDM-CDM

In this paper we investigate four different detection methods for Orthogonal Frequency Division Multiplexing Code Division Multiplexing (OFDM-CDM). The first method applies the Maximum A Posteriori (MAP) algorithm. The second and the third method use detection algorithms which are based on the Minimum Mean Squared Error (MMSE) criterion. The second method uses the Soft Symbol Based (SSB)-MMSE algorithm whereas the third receiver applies the Soft Chip Based (SCB)-MMSE algorithm. The fourth detection method uses a hybrid detection scheme which applies the SCB-MMSE and the Soft Interference Cancellation (SIC) detection method. We concatenate each detection method with the outer channel decoder which allows for iterative decoding at the receiver side. This system can be considered as a serially concatenated iterative decoding scheme whereby the inner decoder is replaced by the respective detection method. For the comparison of the four different detection methods the Bit Error Rate as a function of the signal to noise ratio is used as a performance measure. In addition the convergence of the iterative decoding loop is studied with the Extrinsic Information Transfer (EXIT) chart.