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標題: 無線區域網路不同調變技術之效益分析
Performance Analysis on Wireless Local Area Networks with Different Modulations
作者: 余偉聲
關鍵字: WLAN;無線區域網路;CCK Modulation;OFDM;wireless channel model;soft decision;互補碼調變;正交分頻多工系統;無線通道模型;軟式決策
出版社: 電機工程學系
自從網際網路被發明以來,資料需求量可說是與日俱增,所以高速無線區域網路標準也不斷的被推出。從早期的IEEE 802.11、IEEE 802.11b及 IEEE 802.11a乃至於目前最新的無線區域網路標準IEEE 802.11g,其最高傳輸速率可以達到54M bits/s。本論文將針對目前兩種主要無線區域網路標準 IEEE 802.11b及IEEE 802.11a 做為研究主題。
在本論文中,首先研究無線區域網路通道特性,並且考慮實際上硬體所造成如頻率偏移、直流位準偏移等不良效應,最後建立一個近似真實無線通道的模型,在系統方面分別以IEEE 802.11b及 IEEE 802.11a 為架構並以上述所建立通道模型進行模擬,並分析比較兩種系統效能。
最後針對IEEE 802.11a部份,分析比較了軟式決策法與硬式決策法的效能差異,經由模擬結果證明採用軟式決策法相較於硬式決策法,即使在惡劣的通道環境下,亦可以有效提升系統性能1~2 dB。

Since internet was invented, the needs of the information gradually increase. Hence, the standard of the high-speed Wireless LAN is usually performed. From the early IEEE 802.11 , IEEE 802.11b and IEEE 802.11a to the newest wireless LAN standard, IEEE 802.11g, the highest speed is up to 54M bits/s. This thesis aims directly at the two main standards of wireless LAN, IEEE 802.11b and IEEE 802.11a, being the topics of this research .
In this thesis, we investigate the channel characteristics of the Wireless LAN, first and concerned about the harmful effects such as DC shift, frequency offset caused by the hardware. The model which is similar to the real wireless channel is builded and simulatied . The system which is structured by the two main high-speed standard wireless LAN, IEEE 802.11b and IEEE 802.11a, and are analyzed in the system performance
Finally, In the part of IEEE 802.11a, the effects of the policy making decision in hard and soft ways are analyzed, and the simulation result proves that the policy making in soft way can promote 1~2 dB in the system's performance, even under the worst channel condition.
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