Institute of Electrical & Electronic Engineers
In this paper, the authors investigate the outage and ergodic capacity of downlink Distributed Antenna Systems (DAS) where each Distributed Antenna Unit (DAU) has multiple antennas with per-DAU power constraint. They first derive the optimal beamforming vector in a closed form by applying a matrix minor condition to relax the positive semi-definite constraint. They observe that their derived solution has a form of maximum ratio transmission per each DAU with full power according to each DAU power constraint. Based on the derived optimal beamforming, the outage and ergodic capacity under Rayleigh fading channels are analyzed.