Wireless sensor network consists of several tiny sensor nodes connected to each other in Ad hoc environment and coordinate with each other to form a network. The sensor nodes are typically battery powered, energy optimization and efficiency is extremely important in WSNs. Such networks have the ability to be self organized and failure-adaptive to provide an efficient and reliable network. Wireless sensor networks have a wide variety of applications such as intruder alert and tracking,

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... tal monitoring, industrial process monitoring, and tactical systems. In wireless sensor network deployments, reliably reporting data while consuming the least amount of power is the ultimate goal. Energy conservation is needed especially at MAC layer level. Medium access control (MAC) is an important technique that ensures the successful operation of the network. The performance of MAC protocols in congested wireless networks can be enhanced by the combined carrier-sense multiple access with collision avoidance (CSMA/CA) with that of time-division multiple access (TDMA). One of the main functions of the MAC protocol is to avoid collisions from interfering nodes and enhance the channel access performance in wireless networks. Designing power efficient MAC protocol is one of the ways to prolong the life time of the network. The proposed hybrid CSMA/CA-TDMA scheme can preserve the scalability property. Hybrid CSMA/CA-TDMA Schemes uses the transmission strategies based on Markov Decision Process (MDP) to access both contention period and contention-free period. This paper also deals with the performance comparison of proposed Hybrid CSMA/CA-TDMA scheme in NS-2 simulator.