Low Energy Consumption And Low Delay MAC Protocls For WBANS

With the popularization of e-health service, as one of the most promising technology, wireless body area network(WBAN) has drawn increasing attention. WBAN consists of serval sensor nodes placed on human body, which are used to collect life signals and transmit to the remote data center for further analysis. Since the sensors are minimized but required to work as long as possible, energy consumption becomes a paramount issue. Besides, since WBAN deals with medical data, it should be transmitted at time. For the above reasons, it is necessary to design MAC protocols of low energy consumption and low delay, tailored for the requirements of WBAN. Since the design of MAC protocols is directly affected by the specific topology of the network, we design proper MAC protocols for star-topology and tree-topology WBAN respectively.First, for a star-topology WBAN adopting superframe, since the superframe structure of IEEE802.15.6 duplicates in some parts and lacks of practicality, we propose an enhance superframe structure. In the enhanced superframe structure, different parts are more compact and complementary. Besides, the length of each part can change adaptively based on the status of the whole network. Furthermore, in order to be compatible with IEEE802.15.6 physical layer, consider the specific physical-layer implementation of the enhanced superframe structure. The simulation results validate that the enhanced superframe structure can increase throughput and decrease the delivery latency.Next, for a star topology not adopting superframe, we propose a queue length based CSMA/CA. We use a mathematic mode to prove that the channel occupation of one node is related to the ratio of average backoff time and average transmission time. And point out that fact that in current CSMA/CA, since it does not take the traffic property into account, it lacks the ability to adapt to the variation of data rate. By contrast, since the backoff time and transmission time are related to the queue length in the newly proposed CSMA/CA. The simulation experiments also show that the queue length based CSMA/CA can increase the throughput capacity of the network, while decreasing the delivery latency.At the last part, we propose a cross-layer design MAC protocol: QS-PS. We find that the existing MAC protocols applying for tree-topology do not make a good balanced between energy consumption and delay. In the newly proposed QS-PS, node transmits packets in the dedicated slot(s) and enters a quasi-sleep mode to save energy. Moreover, when a node generates an emergency-type packet but the current slot may not belong to it, it can broadcast a special designed awakening message to wake up the whole network and preempt the right to use the current slot to transmit the emergency-type packet without interference from other nodes. The simulation results prove that QS-PS can provide good delivery service to both normal-type packet and emergency-type packet, and make a better balance between energy consumption and delay.