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\title{Coordinated Beamforming and Common Message Decoding for Intercell Interference Mitigation}

\author{
Hayssam Dahrouj and Wei Yu \\
Department of Electrical and Computer Engineering\\
University of Toronto, Toronto, ON, Canada\\
Emails: hayssam.dahrouj@utoronto.ca, weiyu@comm.utoronto.ca}


\maketitle

\begin{abstract}
Conventional multicell wireless systems operate with out-of-cell
interference treated as noise---interference detection is infeasible
as intercell interference is typically weak. This work considers the
benefits of coordinating base-stations across multiple cells, and
designing decodable interference signals by allowing common-private
message splitting at the transmitter and common message decoding by
users in adjacent cells. In particular, we consider a downlink
scenario, where base-stations are equipped with multiple transmit
antennas, the remote users are equipped with a single antenna, and
multiple remote users are active simultaneously via spatial division
multiplexing. We consider the problem of minimizing the total
transmit power across the base-stations subject to service rate
requirements for remote users. First consider the transmission of
private messages only. We derive an efficient algorithm for finding
the joint globally optimal beamformers across all base-stations
based on a generalization of uplink-downlink duality. An important
feature of the proposed algorithm is that it naturally leads to a
distributed implementation in time-division duplex (TDD) systems. It
also provides appreciable performance improvements as compared to
the conventional per-cell optimized network.  Next consider the
benefit of including common messages. We solve a network
optimization problem of jointly determining the appropriate users in
adjacent cells for rate splitting, the optimal beamforming vectors
for both common and private messages, and the optimal common-private
rates. Simulation results show that common message decoding can
significantly improve the network overall performance.
\end{abstract}


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