Analysis and Compare of Slotted and Unslotted CSMA in IEEE 802.15.4

Abstract

This paper analyzes the non-persistent Carrier Sense Multiple Access (CSMA) mechanism, and simulates its application in IEEE 802. 15. 4. We find that throughputs are relevant to the normalized propagation delay and the Basic Time Period (BTP) of slotted CSMA. The throughputs of slotted and unslotted CSMA are almost equal when the normalized propagation delay is much less than 1 and the BTP is equal to the propagation delay. Moreover, for slotted CSMA, the BTP selection should be cautious because an unsuitable BTP will make the performance of the protocol worse. In IEEE 802. 15. 4, the normalized propagation delay is much less than 1, so it is inappropriate for the usage of a Slotted Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) mechanism whose BTP is 20 symbols. Finally, we compare the performance of slotted and unslotted CSMA/CA in IEEE 802. 15. 4 and verify the conclusion by simulation.