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An efficient superframe structure for 802.15. 4 Medium Access Control (MAC) layer that operates over 868, 915 and 2400MHz, is proposed in this paper. In this superframe structure, Contention Free Period (CFP) precedes the Contention Access Period (CAP) and more number of slots are used in the same CFP period as of original 802.15. 4 standard. As CFP precedes the CAP, the communication delay for the CFP traffic is exceptionally reduced. The Beacon frame is fine-tuned to achieve the above said superframe structure and makes it backward compatible with the original standard. Due to large number of small slots in CFP, more small amount of data requesting nodes can be assigned CFP space for communication. The analytical results show that our proposed superframe structure has nearly 50% less delay, accommodates almost double the number of CFP requesting nodes and has better link utilization compared to the original 802.15. 4 standard for all three frequency bands.