Energy Harvesting Based MAC Protocol Of Wireless Body Area Network

Wireless Body Area Network(WB AN) is a kind of body-centered, low-power Wire-less Sensor Networks, which is widely applied in many areas, such as military, health-care, sports training and entertainment. The energy issue is always the most impor-tant challenges for WBAN for the limitation of battery. The emerging power supply technology-Energy Harvesting(EH), become a promising solution of WBAN energy problem. In conventional WBAN powered by battery, WBAN node would enter the state of permanent sleep when battery depleted, but WBAN node powered by EH would just sleep for a moment and wake up again when harvested energy becomes enough. Therefore, the primary mission of EH-based WBAN is how to utilize the EH-energy to improve performance of WBAN.In this work, we consider the medium access control(MAC) protocol design for En-ergy Harvesting based WBAN. We proposed distributed MAC EH-based MAC proto-col and centralized EH-based MAC protocol respectively to improve data transmission performance, in which the factors considered are decision-making speed and decision-making optimization.· In the distributed MAC scheme, we observe the transmission process and node make decision for channel access from the perspective of WBAN node. We build an infinite-horizon Markov Decision Process(MDP) problem for this decision combined with node’s packets in buffer and available EH-energy, then we de-sign the reward function according to the packets transmitted and the waste of contention-free slots. After that, we resolve the MDP problem and get a optimal policy, then WBAN node can make dynamic channel access decision based on the optimal policy and its real-time state. Simulation results validate that our dis-tributed EH-based MAC protocol has higher packets transmission efficiency but fewer packets overflowed from buffer contrasting with slotted CSMA/CA..· In the centralized MAC scheme, We regard the number of packets in buffer and available EH-energy for all the WBAN nodes as the state of system and the ac-tion set contains all kinds of slot allocation, then we build a more complicated infinite-horizon MDP problem for slot allocation decision of WBAN hub. Let the reward function represents the packets transmission of the whole WBAN, we can obtain a optimal slot allocation that maximize the packets delivered in WBAN with an approximate resolution. The simulations show that the centralized EH-based MAC protocol outperform the aforementioned distributed EH-based MAC protocol and slotted CAMA/CA in terms of packets delivery and delay. In the distributed MAC scheme, a node make decision for channel access based on its packets in buffer and available EH-energy. Because of small state space of packets and energy, a node could obtain a optimal channel access fast. But the channel access is local optimal for the lack of other WBAN nodes’state and behavior information. How-ever, the centralized MAC scheme regard the states of all WBAN nodes as the union state of system, by which the hub make channel access decision then send the decision results to every nodes in WBAN. Because the system state contains state information of all nodes, centralized MAC scheme could obtain a global optimal channel access. Nevertheless, the time for computing the optimal channel access in centralized MAC scheme is far more than that in distributed MAC scheme on account of the huge state space.