Beamformer optimization with a constraint on user electromagnetic radiation exposure

Wireless technology is now a ubiquitous part of life worldwide. A continuing and evolving concern is the possibility of adverse health effects from long term exposure to electromagnetic radiation. In most countries, regulatory agencies set an exposure threshold in terms of the specific absorption rate (SAR). Surprisingly, portable wireless communication devices, such as mobile phones, are often designed with little attention to the SAR thresholds, instead focusing on transmit power constraints. As cellular handsets continue to become more and more multifunctional, designing devices that provide high rate performance and satisfy SAR constraints will become increasingly difficult. In this paper, we present a design strategy that considers both transmit power and SAR for multiple antenna transmit beamforming. Analytical and numerical results show substantial performance improvement over schemes that are designed using only the power constraint.