EAGER: Multiple Transmitter Chains to Minimize Exposure to Electromagnetic Radiation in Portable Devices

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Portable wireless devices such as cell phones are becoming powerhouses of computational ability, with multiple processors, large amounts of memory, touch screens, cameras, and motion sensors all connected to WiFi, Bluetooth, 3G and 4G transceivers. Many of these transceivers can transmit concurrently, and each transmission exposes the user to some level of electromagnetic radiation. The total exposure is potentially cumulative. At the same time, regulatory agencies such as the Federal Communication Commission (FCC) are constantly being challenged to re-evaluate their thresholds for exposure to electromagnetic radiation as new science becomes available and as the public becomes more reliant on portable wireless devices. This research examines using multiple transmitters, commonly used to improve wireless performance, as a tool to minimize exposure. This research: (i) evaluates the exposure effects of a portable device as a function of its transmitter characteristics and the timing and phasing between transmitter elements; (ii) designs communication and constrained coding techniques that minimize exposure while not sacrificing wireless performance; (iii) evaluates the success of these techniques using accepted testing procedures for exposure such as the SAR (specific absorption rate) limit of 1.6 W/kg. The research characterizes the tradeoff between minimizing near-field energy, which determines exposure, and maximizing far-field energy, which determines wireless communication system performance.