Title: Maximizing the Mutual Information of Multi-Antenna Links Under an Interfered Receiver Power Constraint,
Abstract: Single-user multiple-input / multiple-output (SU-MIMO) communication systems
have been successfully used over the years and have provided a significant
increase on a wireless link's capacity by enabling the transmission of multiple
data streams. Assuming channel knowledge at the transmitter, the maximization
of the mutual information of a MIMO link is achieved by finding the optimal
power allocation under a given sum-power constraint, which is in turn obtained
by the water-filling (WF) algorithm. However, in spectrum sharing setups, such
as Licensed Shared Access (LSA), where a primary link (PL) and a secondary link
(SL) coexist, the power transmitted by the SL transmitter may induce harmful
interference to the PL receiver. While such co-existing links have been
considered extensively in various spectrum sharing setups, the mutual
information of the SL under a constraint on the interference it may cause to
the PL receiver has, quite astonishingly, not been evaluated so far. In this
paper, we solve this problem, find its unique optimal solution and provide the
power allocation policy and corresponding precoding solution that achieves the
optimal capacity under the imposed constraint. The performance of the optimal
solution and the penalty due to the interference constraint are evaluated over
some indicative Rayleigh fading channel conditions and interference thresholds.
We believe that the obtained results are of general nature and that they may
apply, beyond spectrum sharing, to a variety of applications that admit a
similar setup.