  In this paper, linear beamforming design for amplify-and-forward relaying
cellular networks is considered, in which base station, relay station and
mobile terminals are all equipped with multiple antennas. The design is based
on minimum mean-square-error criterion, and both uplink and downlink scenarios
are considered. It is found that the downlink and uplink beamforming design
problems are in the same form, and iterative algorithms with the same structure
can be used to solve the design problems. For the specific cases of fully
loaded or overloaded uplink systems, a novel algorithm is derived and its
relationships with several existing beamforming design algorithms for
conventional MIMO or multiuser systems are revealed. Simulation results are
presented to demonstrate the performance advantage of the proposed design
algorithms.
