Slotted CSMA/CA is an algorithm proposed by IEEE 802.15.4 in order to deal with the contention of energy constrained nodes. Slotted CSMA/CA is used during a limited time interval, included in a superframe. Two specific mechanisms defer the transmissions that would occur towards the end of the contention period. Multiple models of the average delay or throughput of slotted CSMA/CA have been proposed recently, but they do not take into account the deference mechanisms.In this paper, we show that the deference mechanisms occurring at the end of the superframe have a significant impact on the performance of slotted CSMA/CA. We prove this by giving the distribution of the delay in a simple scenario, obtained by simulation. Then, we compute the average delay t MAC of traversing the MAC layer, as the MAC parameters or the frame size vary. We show that for either reactive WPANs and energyefficient WPANs, the impact of the deference mechanisms is important.
Wireless sensor networks, widely used in the industry, must comply to severe energy constraints. IEEE 802.15.4 proposes a mode where the sensors access to the channel with slotted CSMA/CA mechanism, and save energy during an inactive period. In this paper, we study the impact of the inactive period on the performance of the slotted CSMA/CA algorithm. We notice that the slotted CSMA/CA algorithm induces a lot of packet loss because of collisions and channel access failures. We reduce these problems by proposing an adaptive slotted CSMA/CA algorithm. The simulation results show that our algorithm is better than the standard.
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