  Recently, a structure of an optimal linear precoder for multi cell downlink
systems has been described in [1, Eq (3.33)]. Other references (e.g., [2,3])
have used simplified versions of the precoder to obtain promising performance
gains. These gains have been hypothesized to stem from the additional degrees
of freedom that allow for interference mitigation through interference
relegation to orthogonal subspaces. However, no conclusive or rigorous
understanding has yet been developed. In this paper, we build on an intuitive
interference induction trade-off and the aforementioned precoding structure to
propose an interference aware RZF (iaRZF) precoding scheme for multi cell
downlink systems and we analyze its rate performance. Special emphasis is
placed on the induced interference mitigation mechanism of iaRZF. For example,
we will verify the intuitive expectation that the precoder structure can either
completely remove induced inter-cell or intra-cell interference. We state new
results from large-scale random matrix theory that make it possible to give
more intuitive and insightful explanations of the precoder behavior, also for
cases involving imperfect channel state information (CSI). We remark especially
that the interference-aware precoder makes use of all available information
about interfering channels to improve performance. Even very poor CSI allows
for significant sum-rate gains. Our obtained insights are then used to propose
heuristic precoder parameters for arbitrary systems, whose effectiveness are
shown in more involved system scenarios. Furthermore, calculation and
implementation of these parameters does not require explicit inter base station
cooperation.
