Capture Effect in IEEE 802.15.4 Networks: Modelling and Experimentation

In this paper capture effect in IEEE 802.15.4 networks is studied, by means of mathematical analysis and experimentation. A Personal Area Network (PAN) composed of multiple nodes, which transmit data to a given sink by using the beacon-enabled mode of 802.15.4 Medium Access Control (MAC) protocol, is considered. Upon reception of the beacon transmitted by the PAN coordinator, the nodes transmit their packets using the slotted Carrier Sense Multiple Access with Collision Avoidance algorithm defined by the standard. A test-bed composed of 802.15.4-compliant Freescale devices is used to measure the protection ratio, that is the minimum Signal-to-Interference Ratio (SIR) which ensures the correct reception of majority of the packets. The result is, then, used to extend the developed mathematical model for beacon-enabled 802.15.4 networks. In contrast to the literature on the 802.15.4 MAC modelling, our model allows to compute the Packet Success Probability (PSP) of a node when capture effect is considered, in the scenario described. The impact of capture effect on the PSP, by varying the number of nodes, the propagation parameters and the protection ratio, is shown. The model is validated through simulations and experimental measurements. In both cases a very good agreement is found.