摘要 無線網路近幾年來的成熟發展，從早期的802.11a 、802.11b到最近的802.11g.，而正交分頻多工多載波調變系統也是其中的熱門的技術之一。透過正交分頻多工(OFDM)傳輸技術有效對抗載波間干擾(Inter-Carrier Interference，ICI)與符元間干擾(Inter-Symbol Interference，ISI)，而多載波系統隨著近來VLSI的製程進步，使得其在通訊當中更是扮演著愈來愈重要的角色，也是未來行動通訊系統當中，重要的關鍵技術之一。 本論文主要是針對802.11g的規格來實現，但為了配合我們硬體上的限制，我將規格稍微做了修改。基頻訊號利用matlab程式產生修改之後的OFDM調變訊號，並將程式寫入Ｔektronix 的任意波型產生器來幫我們產生真實的電壓形式的訊號，之後再將此基頻訊號，接到由駱達科技股份有限公司所生產的RF模組，來觀察發射到2.4GHz頻段的頻譜。之後經過測試確定無誤後，我們將發射訊號，接到另外一塊ＲＦ的模組來做降頻，並將其Ｉ、Ｑ訊號接出來，由Ｔektronix所生產的ＴＤＳ3032B的數位儲存示波器將資料儲存起來，利用ＰＣ的matlab 程式做數位訊號處理，以觀察我們實際網路卡上接收到的訊號的特性。此經驗乃是提供我們真實環境通道對於無線網路的影響，並且了解射頻電路特性，與基頻訊號處理的觀念，也提供學生能夠將理論與實務結合。 ABSTRACT With prevalence of wireless communication system such as 802.11a, 802.11b and 802.11g, Orthogonal Frequency Division Multiplexing (OFDM), which can effectively combat against Inter-Carrier Interference (ICI) as well as Inter-Symbol Interference (ISI), has grown to be one of popular techniques. Progress in VLSI manufacturing, furthermore, enables multi-carrier system to be of paramount importance in future mobile communication. Implementation in this paper is based on OFDM 802.11g specification. Base band modulation signals created by MATLAB were transformed into signals in the form of voltage through any Tektronix waveform generator. In order to observe the spectrum of signals in 2.4GHz, we cascaded voltage analog signals to RF module produced by AIROHA Corp. After verifying its validity, the other RF module was utilized to down convert signals from transmitter so that we can extract In-phase and Quadrature signals. Destined for analyzing characteristics of received signals from network card, I-Q signals were afterward stored in Tektronix TDS3032B digital oscilloscope and processed via MATALB. In theory and practice, this experiment enhanced our understanding of RF circuit characteristics, base band signal processing and how radio channel affects wireless LAN.
