EXIT Analysis of a Soft-Input/Soft-Output Iterative Multiuser Detector

This paper applies extrinsic information (EXIT) analysis to an internally iterative multiuser detector (IMUD) in serial concatenation with convolutional codes. The focus is overloaded conditions, in which the number of transmitters exceeds the number of receiver antennas. The study seeks to verify if EXIT charts can be used as a design tool under these circumstances. The use of non-Gaussian LLR distributions in performance estimation is discussed. The mutual information of the extrinsic information from IMUD is characterized under a variety of situations. It is shown that the EXIT charts do provide a means to determine both the minimum SNR and necessary number of iterations for convergence. However, estimating the bit error rate from the EXIT chart does not seem to be possible except in special circumstances.