| Summary: | 碩士 === 國立臺北科技大學 === 電機工程系研究所 === 99 === This thesis presents a retransmission mechanism with frequency-hopping media access control to achieve the goal of higher reliability of low-power consumption sensor networks without interference in communication from other networks. This mechanism can also be applied to the media access control protocol (e.g. F-MAC) for ecological monitoring.
In the F-MAC protocol, lost data can be retransmitted by the multi-path mechanism, but no mechanism exists to confirm a successful transmission. Therefore, the thesis proposes a modified synchronization mechanism for F-MAC and a more reliable data transmission method . Based on the adaptive frequency hopping (AFH) of the Bluetooth technology, a simplified Bluetooth frequency-hopping mechanism is developed, while taking the interference from other networks that also use the 2.4 GHz frequency band to transmit data into account. Before the transmission, a sender (node) determines the amount of data that will be transmitted to a receiver (node) and the sequence number of the data. The receiver will immediately reply an acknowledgement (ACK) message to the sender to confirm that the data which has been received. When data is lost during transmission, the sender records the number of missing ACK messages. This number will serve as the frequency hopping input that corresponds to the frequency hopping sequence table generated by the hash method to complete the frequency-hopping action.
Finally, the experimental results show that the average package receiving rate using the proposed mechanism is higher than the rate using a single channel to transmit data after packet loss, network traffic and the performance of frequency hopping are examined. Besides, the successful transmission rate generated by the frequency-hopping retransmission mechanism is 2.09 % higher than the rate using the retransmission mechanism built in the F-MAC. The proposed mechanism will be applied to ecological monitoring systems in the future to improve the data transmission reliability.
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