  This paper considers the beamforming design for a multiuser multiple-input
single-output (MISO) downlink with an arbitrary number of (context-specific)
shaping constraints. In this setup, the state-of-the-art beamforming schemes
cannot attain the well-known performance bound promised by the semidefinite
program (SDP) relaxation technique. To close the gap, we propose a
redundant-signal embedded linear beamforming (REEL-BF) scheme, where each user
is assigned with one information beamformer and several shaping beamformers. It
is shown that the proposed REEL-BF scheme can perform general rank-$K$
beamforming for user symbols in a low-complexity and structured manner. In
addition, sufficient conditions are derived to guarantee that the REEL-BF
scheme always achieves the SDP bound for linear beamforming schemes. Based on
such conditions, an efficient algorithm is then developed to obtain the optimal
REEL-BF solution in polynomial time. Numerical results demonstrate that the
proposed scheme enjoys substantial performance gains over the existing
alternatives.
