On EIRP Control in Downlink Precoding for Massive MIMO Arrays

The usual performance comparisons of wireless systems are based on a constrained sum-power at the transmitter. However, many wireless systems are actually constrained in their equivalent isotropic radiated power (EIRP). So far, research effort in the area of beamforming under constrained EIRP seems to be done solely for single-user systems. As an original contribution, this contribution develops a theoretical description of an EIRP-limited multi-user system with joint consideration of the EIRP and the capacity. Accordingly, the EIRP is interpreted as a function of the precoding matrix instead of a static measure of the antenna. The theoretical formulations is applicable to arbitrary antenna designs, including multi-mode antennas. Down-scaling of any coventional linear precoding solution is proposed as a simple strategy to comply with the EIRP limit. Numerical results are provided in the context of massive MIMO with simple linear precoding techniques.