Wireless Sensor Network (WSN) acts as one of the fundamental elements of network infrastructure, requiring to establish a wireless communication network for the reliable frame transmission. The channel access in IEEE 802.15.4 employs Carrier Sense Multiple Access with Collision Avoidance (CSMA) without amendment. However, the contention collision of typical technique, IEEE 802.15.4, could not guarantee the reliable frame transmission because of the difficulties avoiding the collision. To tackle the aforementioned challenges, we propose a new collision resolution scheme, Next-Transmission Backoff Reservation (N-TBR) Scheme, for IEEE 802.15.4 to guarantee a reliable transmission especially for the contention collision of messages with the reservation scheme. The proposed scheme consists of two sub-schemes. The main contributions of this paper are twofold: Next-Transmission Backoff Reservation Process that reserves a backoff counter for next transmission, Reservation Window Adjust Process to avoid conflicts.