An Energy Efficient Hybrid Medium Access Control Scheme for Wireless Sensor Networks with Quality of Service Guarantees

In this paper, we present a new MAC layer protocol for wireless sensor networks that reduces energy consumption and provides Quality of Service (QoS) guarantees through the use of service differentiation concept. The proposed protocol (named as EQ-MAC) consists of two sub-protocols: Classifier MAC (C-MAC), and Channel Access MAC (CA-MAC). C-MAC is responsible of classifying gathered data at sensor nodes based on its importance and then stores it in the appropriate queue of the node´s queuing system. The CA-MAC is an energy efficient medium access mechanism that uses a hybrid approach of both scheduled and unscheduled schemes to gain a save in energy, and hence prolonging the network´s lifetime. The save in energy achieved by CA-MAC is coming from the differentiation between control and data messages. Data messages are assigned scheduled slots with no contention (here we have to emphasize that slots are assigned only to those nodes which have data to send, this allows an efficient energy use of the TDMA slots), while short periodic control messages are assigned random access slots. To study the performance of the EQ-MAC protocol, several simulation experiments were conducted. EQ-MAC is compared with both Q-MAC and S-MAC protocols. Simulation results demonstrate that EQ-MAC outperforms the other two protocols and achieves a significant improvement in terms of energy expenditure. Under prioritized traffic, EQ-MAC is comparable to Q-MAC in average latency, while achieving less energy consumption.