Performance Analysis of Slotted CSMA/CA IEEE 802.15.4 with Heterogeneous No-Acknowledged Uplink Traffic

IEEE 802.15.4 Wireless Sensor Networks (WSN) often are used in cluster topologies, where one or more reduced function devices (RFD) exchange messages with full function devices (FFD). FFD´s, in turn, may exchange messages among themselves in a tree topology. To be energy efficient, these devices will collect received messages and regroup them in order to reduce the protocol overhead associated to communications. As a result, WSN messages may differ in size and periodicity, a fact that has not been studied in performance analysis of this kind of networks. An analytical model that considers variable message size, transmission scheduling and the impact of these on energy consumption is presented and then validated by simulations.