ZigBee是一種新的無線感測網路協定,它的特徵包含有短傳輸距離、低傳輸率、低成本以及低能量消耗。近年來如何降低成本或者是減少耗能的議題不斷出現,但是無論成本怎麼壓低,如果不能保證傳輸品質並且提供穩定的準確性,那麼就算是成本再低也都沒有意義,因此本文提出了自動調整功率的機制來修正資訊傳輸準確性的問題。 本文使用MATLAB/Simulink軟體來實現IEEE 802.15.4物理層,IEEE 802.15.4物理層是由調變器和展頻器所組成,然後再經由改變訊號雜訊比來模擬傳輸錯誤率,模擬結果顯示出訊號雜訊比至少在0dB的情況下所產生的錯誤率我們較能接受,當訊號雜訊比到達5dB時沒有錯誤率。可變式發射功率這項機制,是當訊號雜訊比低於0dB或大於5dB時進行發射功率的調整,藉此達到穩定的傳輸品質或者是減少能量消耗的地步,改善後原本訊號雜訊比小於0dB的環境都能將錯誤率壓低至0.00028%。 接著使用硬體發展套件Zigbex來完成這項機制,並且利用接收到的訊號強度值來做判斷的依據。起初發射功率為-5dBm,當接收到的訊號強度值低於-65dBm時將發射功率提升至-3dBm或是更高的-1dBm以穩定傳輸品質,最後硬體測試的結果顯示使用可變式發射功率機制在一分鐘的測試當中可以減少137次左右的傳輸失敗。
ZigBee is a new protocol by wireless sensor network. It’s characteristics include low transmission range, low data rate, low cost and low power consumption. There are many people to research about to reduce cost or power consumption, but we do not want the product that we can not ensure the message is correct by transmission even the cost is the lowest, so I use the name of method is automatic power level to increase the correct of message by transmission. In this research MATLAB is use to simulation the IEEE 802.15.4 physical layer. The model of IEEE 802.15.4 physical layer includes spreader and modulation, that we can get the bit error rate by different Signal to Noise radio (SNR). The result show the bit error rate that we want at the SNR from 0dB to 5dB. Then use the method of automatic power level control to process the power level that the SNR not at 0dB to 5dB, the bit error rate is reduce to 0.00028 percent at least. Finally I complete the method by Zigbex, if the Received Signal Strength Indication (RSSI) small than -65dBm, then the power level up a step, and the result show it can reduce 137 times by transmission from a minute test.