tailieunhanh - Emerging Communications for Wireless Sensor Networks Part 3

Tham khảo tài liệu 'emerging communications for wireless sensor networks part 3', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Wireless sensor network for monitoring thermal evolution of the fluid traveling inside ground heat exchangers 33 this state the microcontroller is sleeping between two acquisitions and is characterized by using the secondary oscillator which only drives the peripheral that remains in operation the timer that sets the sampling period. The circuit that conditions the signal from the Pt100 is activated moments before the measurement and immediately returns to the low power state. At the conclusion of the scheduled number of acquisitions the probe goes to the Down load state recovering the main oscillator and establishing communication with the control system to transfer data. When the transfer is finished it is passed to the Power down state. The communications protocol is a simple design because it is during the wireless communications that thee consumption is higher Therefore the fewer bits are transmitted more energy savings are achieved. All the messages that are exchanged between the transceivers are 6 bytes of data a CRC-16 plus a header of 7 bytes for synchronization. The only exception is in the downloading of data where the number of bytes transmitted is twice the number of acquisitions. The transfer rate is set at the highest rate possible kbs. The transmission power is also set at the minimum because the distance between transceivers is less than a meter and the CC1010 can reach 100 meters at full power. Fig. 4. Protocol communication 34 Emerging Communications for Wireless Sensor Networks 5. Time synchronization considerations Another key to the reliability of the obtained data is the time synchronization all probes must have the same clock as a reference for the estimated time of acquisition. Since the evolution of temperature on the heat exchanger is slow the accuracy in time between all the probes must be better than 100ms. There are different synchronization techniques in wireless sensor networks Sundararaman 2005 Jones 2001 but to meet the energy

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