On the Achievable Sum Rates of Iterative MIMO Receivers with Linear Front-Ends

In this paper, the rate achievable in Multiple-Input-Multiple-Output (MIMO) systems with iterative receivers based on linear front-end (FE) processing is investigated. First, the communication with Gaussian input signal is assumed and the Extrinsic Information Transfer (EXIT) chart is applied to evaluate the achievable sum rate. Then, the method for deriving the EXIT chart for a more practical case has been introduced. As a specific model, which fits the real turbo receivers better, communication with large size uniform constellations is discussed where the information being exchanged between the receiver´s iterative block are Log-Likelihood-Ratios (LLRs) of the transmitted bits. It is shown that, in this situation, the iterative process does not improve the performance from achievable sum rate point of view in both high and low SNR regimes. However, the iterative process is shown to help in the medium SNR range, which is the range of interest.