即時無線感測網路之IEEE 802.15.4時槽型CSMA/CA分析與改善

Abstract

In this paper, we propose the effective analysis methodology to be applied to the monitoring network of synchronous under the IEEE 802.15.4 standard, we call it real-time wireless sensor network (RT-WSN) in this network that is build for the “real-time” specific application. We aim at the slotted Carrier Sense Multiple Access/Collision Avoidance (CSMA/CA) of algorithm of channel access mechanism in IEEE 802.15.4 MAC layer to build the network model and analyze the average packet delay over RT-WSN based on probability theory. The proposed theoretical analysis was nearly consistent with the correct result of simulation and the experiment. The result shows that this slotted CSMA/CA cannot be effectively applied to RT-WSN since it cannot avoid the high packet collision in the saturation throughput conditions. When receiving 10 sensor nodes, the packet delay caused by packet collision is 6.29 times more than one ideal model. Hence, we propose the like Time Division Multiple Access (TDMA) to improve CSMA/CA in packet collision problem. With neighbor table, TDMA can record the network states and implement the dynamic network configuration. Our experimental results show that TDMA can own the characteristics of the stable and limited packet delay. Once the total traffic load is lower than maximum throughput, it can guarantee the packet transmission of real-time without considering the amount of sensor nodes in network. Moreover, compare with CSMA/CA in 10 sensor nodes conditions, 57 % of the maximum throughput is improved. Therefore, we can meet with the QoS requirement of packet delay in RT-WSN. In the end, we install a remote ECG monitoring system for an example of application situation in the sanatorium. We provide steady wireless transmission media for the front of this system and reach the purpose of real-time remote medical care.