  In this paper, we consider the joint design of the transceivers for a
multiple access Multiple Input and Multiple Output (MIMO) system having
Inter-Symbol Interference (ISI) channels. The system we consider is equipped
with the Minimum Mean Square Error (MMSE) Decision-Feedback (DF) detector.
Traditionally, transmitter designs for this system have been based on
constraints of either the transmission power or the
signal-to-interference-and-noise ratio (SINR) for each user. Here, we explore a
novel perspective and examine a transceiver design which is based on a fixed
sum mutual information constraint and minimizes the arithmetic average of mean
square error of MMSE-decision feedback detection. For this optimization
problem, a closed-form solution is obtained and is achieved if and only if the
averaged sum mutual information is uniformly distributed over each active
subchannel. Meanwhile, the mutual information of the currently detected user is
uniformly distributed over each individual symbol within the block signal of
the user, assuming all the previous user signals have been perfectly detected.
