在無線傳輸環境中，信號會受到多路徑傳輸衰減影響，由於OFDM (Orthogonal Frequency Division Multiplexing) 對於ISI (Inter-symbol Interference) 、多路徑傳輸衰減有較大的抵抗能力。 本研究主要說明，以理論的 OFDM 系統，模擬分析在降雨通道下的 BER (Bit Error rate) 位元錯誤率與訊號雜訊比，降雨通道將使用，本實驗室(微波遙測實驗室)於太空所到遙測中心所量測分析出的降雨衰減值，降雨通道依據中央氣象局的雨量分級定義：大雨、豪雨、大豪雨、超大豪雨及瞬間大雨15mm/hr ~ 100mm/hr的情況下，探討OFDM系統使用QPSK、16-QAM、64-QAM調變技術時，OFDM系統將無法達到所要求的頻寬效益及誤碼率時的機率。 結果顯示，OFDM系統於BER=1e-6時所需使用的 ENR 值，將超過 OFDM 理論值，若將利用 IEEE 802.16d SPEC 的參數分析 OFDM 系統於 BER=1e-6 時所需使用的 ENR 值，將發現 QPSK 於降雨量 8.333mm/hr 以下時，可降低因降雨衰減下所需的接收功率，而16-QAM、64-QAM，於降雨量 100mm/hr 以下時，均在 IEEE 802.16d SPEC 所能接收的功率範圍內。 另一方面，在BER=1e-6 不同的降雨量條件下時，OFDM系統無法達到所要求誤碼率的機率，將大於70%以上。由此可知OFDM 系統於 Ka 波段下使用時，對頻率偏移很敏感，若使用精確的同步分析，將可能降低OFDM 系統於 Ka 波段下使用時，無法達到所要求誤碼率的機率。 In the environment of transmitting of wireless. it is influenced that the signal will be transmitted and decayed by multipath. because of OFDM (Orthogonal Frequency Division Multiplexing) To ISI (Inter-symbol Interference) . multipath is it have heavy ability of resisting to decay to transmit. This research proves mainly. in OFDM system of the theory. analyse BER under the rainfall passway in simulation (Bit Error rate) The error rate of location compares with miscellaneous news of signal. the rainfall passway will be used. The microwave remote sensing measurement laboratory Examine the rainfall decaying value analysed in the telemetering measurement centre quantity reached of space. the rainfall passway is according to the hierarchical definition of rainfall of Central Weather Bureau: Heavy rain, torrential rain. torrential rain. exceeding under the situations of the torrential rain and heavy rain 15mm/hr big 100mm/hr in twinkling of an eye. it probe into OFDM the systems it use QPSK、 16-QAM、 64-QAM while lasting technology of turning QAM into. have the getting more unable to last required benefit and the probability at the time of yards of rate by mistake not wide frequently in system OFDM. The result shows. OFDM system to BER=1e-6 When it need by ENR value use. it exceed OFDM theory value. if utilize parameter. IEEE of 802.16d SPEC to be analysed the OFDM systems at BER=1e-6 When need ENR value that use. Find it during rainfall, under 8.333mm/hr. can reduce lasting power of receiving needed to down rainfall QPSK. and 16-QAM、64- QAM. when being under rainfall 100mm/hr, in the power range that IEEE 802.16d SPEC can receive. On the other hand. in BER=1e-6 When under different rainfall conditions. OFDM system is unable to reach and require the probability of one yard of rates by mistake. be greater than more than 70% Known OFDM system is very sensitive in skew to frequency when use under Ka wave band by this. if use accurate synchronizing analysing, may reduce OFDM system when use under Ka wave band. it is unable to reach and require the probability of one yard of rates by mistake.
