Many Media Access Control (MAC) protocols for Wireless Sensor Networks (WSN) use varia-tions of the popular copyright Sense Multiple Access (CSMA) protocol due to its simplicity and its high perfor-mance in low traffic scenarios.However, CSMA does not always represent a good choice for WSNs since typical low power click here transceivers require a significant time to switch between receiving and transmitting and vice versa.Sensor nodes are not able to detect a busy channel during the switching.Thus, the collision proba-bility 7gm pravana in WSNs is very high in case of correlated event-driven traffic.In this paper we introduce the BP-MAC protocol that uses a backoff preamble with variable length in order to mitigate the effect of Clear Channel As-sessment (CCA) delay.