Modeling and mitigation of extra-SoC thermal coupling effects and heat transfer variations in mobile devices

In smartphones and tablets, a number of components, such as display and communication subsystem, dissipate a significant amount of heat. This influences the SoC thermal envelope, because of the absence of a fan. Thus the thermal conditions of the SoC cannot simply be modeled as only a function of the SoC component power. In addition, contact surfaces and phone orientation variations (e.g., phone inside a pocket, phone held in a hand, and phone laying on a desk) change the heat transfer coefficients of the device over time and influence the SoC temperature. In this work, we analyze the thermal behavior of a commercial mobile device in varying user interaction profiles and under different environmental conditions. Next, we propose a system-variation aware thermal modeling strategy that only uses available power and thermal sensors. Lastly, we devise a novel ambient-aware proactive thermal management algorithm. Our approach is able to meet the given thermal constraints while providing stable performance and comparable power consumption with respect to existing techniques. In contrast, the state-of-the-art approaches, which do not consider ambient condition variations, violate the thermal constraints and lead up to 2.6× higher performance variations.