Cross-layer Optimization of a CSMA Protocol with Adaptive Modulation for Improved Energy Efficiency in Wireless Sensor Networks

We investigate the energy efficiency in a wireless sensor networks that implements a non-persistent CSMA MAC protocol with adaptive MQAM modulation at the physical layer. The system throughput is estimated based on the number of received ACK packets. The backoff probability at the MAC layer and the modulation order at the physical layer are jointly adapted according to the traffic dynamics, leading to improved system energy efficiency while satisfying a given constraint on the packet retransmission delay. Through numerical examples and simulations, we verify the significant energy-efficiency improvements achieved by this joint optimization compared to the backoffprobability-only and the modulation-order-only adaptations.