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Most of Wireless Sensor Network (WSN) applications aim to utilize low data rates, consume very low energy, and operate in short range areas at low costs. IEEE 802.15. 4 standard is proposed in order to achieve such needs by putting standards for physical and Medium Access Control (MAC) layers. MAC operates in either beacon enabled or beaconless modes. Performance of the standard beacon enabled mode is basically affected by beacon frame parameters, which are Beacon Order (BO) and Superframe Order (SO). These two parameters determine node’s active and inactive periods, they also determine node’s duty cycle. BO and SO values must be chosen carefully when the standard MAC is parameterized since some combinations may degrade standard performance dramatically. Finding the optimal (BO, SO) combination is an application-based issue since diverse WSN applications work through different arrival rates at different duty cycles. This paper investigates the standard beacon enabled mode behavior through intensive simulation and revels the optimal range of (BO, SO) combinations for specific star topology with different number of nodes. The investigated application is evaluated in terms of energy consumption, average end to end delay and throughput. Moreover, this paper proposes an adaptive algorithm that converges to the network current performance and improves network performance accordingly, irrespective of the duty cycle. The performance of the new adaptive algorithm is compared to that of the original MAC algorithm using QualNet 5.2 simulator. The new adaptive algorithm outperforms the original MAC algorithm …