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Tham khảo tài liệu 'emerging communications for wireless sensor networks part 5', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | A Survey of Low Duty Cycle MAC Protocols in Wireless Sensor Networks 73 cluster s members. The cluster is formed completely when all the cluster members are synchronised to the TDMA schedule. The cluster head creates and maintains the TDMA schedule. The LEACH protocol implements two strategies to ensure energy efficient operation. The first strategy is to shift the total burden of energy consumption of a single cluster head by rotating the assignment of the cluster head to the other members in the cluster. The aim behind this strategy is to distribute evenly the energy usage between the members of the cluster. The second strategy is to switch the ordinary nodes in a cluster into the sleep mode whenever they enter inactive TDMA slots. In this way we actually create a duty cycle mechanism through the implementation of an active and inactive TDMA time slots schedule. However high transmission power during direct communication between cluster heads and the base station may dominate the total energy consumption in the network. Furthermore the fixed clustering structure and the need for global synchronisation make the network not scalable whenever nodes join or leave the network. The condition becomes worse when we consider mobile nodes. 3.3 Self-Organizing Slot Allocation SRSA The Self-Organising Slot Allocation or SRSA protocol Wu Biswas 2005 was proposed to improve the LEACH MAC protocol in terms of energy efficiency and network scalability. The SRSA protocol is a TDMA-based MAC and has a similar network topology as LEACH. The strategy to increase energy efficiency is by utilising multiple base stations instead of only one base station as in the LEACH architecture. Thus cluster heads can communicate directly with the nearest base station which reduces transmission energy significantly. Moreover in order to increase network scalability SRSA provides local synchronisation where each cluster maintains its own local TDMA MAC frame. The main idea is to initiate .
