For a traditional linear MMSE detector, the transmitted user symbol can be estimated by multiplying an optimal weight matrix to the frequency domain signal, i.e.,b Sk =e wH ke Y.
Here, the weight matrix for each user,e wk, is the key design parameter and depends on performance criteria used.
The idea of FDO-MMSE receiver design is to firstly project those input signals needed fore wk to the FSFD, which contains more information about the operation of signal passing multipath fading channels.