Certain communications transmitters are restricted by their equivalent isotropic radiated power (EIRP) rather than the total transmitted power. Important examples are ultra-wideband systems. Use of channel knowledge at transmission for such systems, when there are multiple transmit antennas, is complicated due to the need to consider the spatial directivities of the radiation. Thus it is computationally prohibitive to implement optimal EIRP constrained beamforming schemes. This work presents a novel low complexity transmit beamforming method for such systems. Motivated by the radiation due to optimal schemes, the algorithm is based on perturbing the dominant channel eigenvector such that the peak-to-average power ratio of the spatial radiation is reduced. Simulation results confirm the improved system performance compared to existing sub-optimal beamforming methods.
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