A Comparison of TDMA, Dirty Paper Coding and Beamforming for Multiuser MIMO Relay Networks

A two-hop multiple-inputmultiple-output (MIMO) relay
network which comprises a multiple antenna source, an amplifyand-
forward MIMO relay and many potential users are studied in
this paper. Consider the achievable sum rate as the performance
metric, a joint design method for the processing units of the BS
and relay node is proposed. The optimal structures are given, which
decompose the multiuser MIMO relay channel into several parallel
single-input single-output relay channels.With these structures,
the signal-to-noise ratio at the destination users is derived; and the
power allocation is proved to be a convex problem. We also show
that high sum rate can be achieved by pairing each link according
to its magnitude. The sum rate of three broadcast strategies, time
division multiple access (TDMA) to the strongest user, dirty paper
coding (DPC), and beamforming (BF) are investigated. The sum
rate bounds of these strategies and the sum capacity (achieved by
DPC) gain over TDMA and BF are given. With these results, it
can be easily obtained that how far away TDMA and BF are from
being optimal in terms of the achievable sum rate.