Design And Optimization Of MAC Protocol For Hybrid Wireless Sensor Networks

Recently, Wireless Sensor Networks (WSNs) are widely applied in various scenarios, such as health management, industrial measurement and agricultural surveillance. However, since these applications are usually incorporated with large-scale deployment of WSNs, traditional battery-powered wireless sensor cannot meet the demand because of its limited lifetime. Thus, Energy-harvesting Wireless Sensor Networks (EH-WSNs) gains the spotlight. It consists ofenergy-harvesting wireless sensors that can harvest ambient energy (solar, wind,heat, electromagnetic, etc.); therefore, the lifetime of Energy-harvesting Wireless Sensor Networks (EH-WSNs) is ideally infinite. However, these networks are costly to implement, and unreliable due to unstable ambient energy.Consequently, Hybrid Wireless Sensor Networks (HWSNs) consisting of Energy-harvesting Sensor Nodes (EHSNs) and Battery-powered Sensor Nodes(BPSNs) gain the spotlight. Nevertheless, HWSNs confront the volatility of BPSNs that result in the unreliability of the whole network; this calls for new design of MAC protocols targeting HWSNs.When designing MAC protocol for HWSNs, there are several aspects to consider: first, the lifetime of battery-powered sensors is limited, so that the design of access mechanism should involve appropriate allocation of the energy in their batteries; second, energy-harvesting sensors have energy-renewable characteristics, and this renewable energy should be fully utilized to improve the network transmission performance and reliability; finally, energy-harvesting sensors located in different place have various energy-harvesting rates, so that the energy level states are heterogeneous. Two types of sensors bring new challenge to the design of MAC protocol of HWSNs.This thesis proposes two reliable MAC protocols targeting HWSNs-Hybrid Polling MAC and Hybrid Duty-cycle Scheduling MAC. The former emphasizes on setting different polling transmission probabilities for BPSNs and EHSNs, while the latter on configuring different duty cycles. Both mechanisms are designed to suppress the energy dissipation of BPSNs by effectively utilizing the renewable energy of EHSNs,so that the stability of network can be guaranteed within its lifetime. Simulation results demonstrate that the average lifetime of BPSNs is significantly increased compared to the baseline protocols.Furthermore, the network transmission performance is also promoted.This thesis discusses the system models used in evaluation of the two MAC protocols and elaborates them in detail. Evaluation results will also be provided and discussed to demonstrate the promotions on the network transmission performance and reliability.