From myth to methodology: cross-layer design for energy-efficient wireless communication

During the last decade, wireless communication has seen a trend towards application diversification leading to a significant growth in users. With the availability of - however energy-limited - nomadic devices and real-time multimedia applications, user demand is shifting from simply asking for higher data rates to more complex requirements in terms of quality of service (QoS) and energy-efficiency. In this new context energy management is becoming a key success factor. Optimized energy-efficiency requires an energy management that continuously trades off QoS and energy adapting to varying user expectations and environment dynamics. But, QoS can only be evaluated on top of the whole protocol stack while energy consumption largely appears at the lower layers. To minimize overhead during the transitions between layers, we need to address the problem from a cross-layer perspective. We present a methodology that, based on systematic exploration, effective problem partitioning and minimal cross-layer interface, allows energy management in a cross-layer way, while maintaining efficient layered semantics. Different case studies in the context of wireless LAN (WLAN) for multimedia and data traffic transport are discussed, to show how cross-layer energy management can easily be included in systems running state-of-the-art protocols.