Enhanced Clear Channel Assessment for Slotted CSMA/CA in IEEE 802.15.4
IEEE 802.15.4 Standard is defined for ultra-low complexity and ultra-low power consumption as well as for low cost implementation. Realization of Wireless Sensor Networks (WSNs) is possible by configuring IEEE 802.15.4 in peer-to-peer topology as it fits the requirements of WSNs. Underlying protocols should take care of energy consumption as most of the nodes are battery operated and inaccessible after deployment. Focus should also be given to delay introduced due to channel sensing. Carrier Sense Multiple Access with Collision Avoidance in IEEE 802.15.4 ensures reduced probability of collision with the use of sporadic backoff delay before channel assessment. Channel assessment is performed by either one Clear Channel Assessments (CCA) or two consecutive CCAs. In this paper efforts have been made to reduce energy consumption and to reduce average delay by reducing the number of backoff periods taken before channel sensing. Method mentioned in this paper also reduces the number of backoffs as well as channel access failures. Proposed method also reduces the number of collisions. To achieve these goals, proposed method takes two, three or four consecutive CCAs to decide upon current channel status. An analytical Markov Chain Model is developed for the derivation of various probabilities associated with proposed method and then it has been analyzed with the help of illustrations. The proposed algorithm is implemented and validated using Network Simulator-2. Simulation results show that proposed method reduces energy consumption as well as average Medium Access Control delay by reducing number of backoffs.
KeywordsWSN IEEE 802.15.4 CCA Energy Delay NS-2 Markov chain
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