  The sum-rate of the broadcast channel in a multi-antenna multi-user
communication system can be achieved by using precoding and adding a regular
perturbation to the data vector. The perturbation can be removed by the modulus
function, thus transparent to the receiver, but the information of the
precoding matrix is needed to decode the symbols. This paper proposes a new
technique to improve the multi-antenna multi-user system, by adding a
continuous perturbation to the data vector without the need of information on
the precoding matrix to be known at the receiver. The perturbation vector will
be treated as interference at the receiver, thus it will be transparent to the
receiver. The derivation of the continuous vector perturbation is provided by
maximizing the signal-to-interference plus noise ratio or minimizing the
minimum mean square error of the received signal.
