應用於無線基頻應用之前端訊號處理研究

Abstract

採用直接序列展頻的標準包含802.11, 802.11b 以及 802.11g等無線區域網路系統。無線通訊使用空氣當作介質，比有線通訊多了更多的不確定性，因此，無線通訊系統的封包裡一般都會定義preamble欄位作為接收端封包偵測及同步之用。 而本論文提出一個有效率，應用於802.11b標準之自動增益控制、封包偵測及符元邊界決策。所提出的方法利用安置在每個封包之前的preamble，在低訊號雜訊比、載波頻率偏移、多路徑衰減及路徑損失的通道時可以快速，正確的達到前端訊號處理的完成。而其中提出的自動增益控制演算法可在單一系統(直接序列展頻系統)以及雙系統(直接序列展頻系統和正交多工分頻系統)上使用。 為了瞭解整個系統，我們使用Matlab建立了系統模擬平台。我們可以觀察系統中任一訊號的波形，並且可以得知通道中的非理想效應對整個系統或某些訊號有何影響。此平台更可以用來驗證我們所提出的演算法，本論文中也放了一些模擬結果圖，也驗證了演算法的成功。

Direct sequence spread spectrum (DSSS) technique is used in IEEE 802.11, 802.11b and 802.11g wireless LAN systems. Unlike the wire channel, wireless communication uses radio as its medium and has more uncertainty with it. Therefore, WLAN frame format generally contains preamble field for packet diction and synchronization. In this thesis, an efficient automatic gain control (AGC), packet detection and symbol boundary decision for DSSS based WLAN defined in IEEE 802.11b had been proposed. The proposed methods enables a rapid and accurate front-end signal process even under very low SNR, carrier frequency offset multi-path fading and path loss channel by using preamble at the start of every frame. The proposed AGC algorithms could be used on single system (DSSS system) and dual system (DSSS system and OFDM system). To get familiar with IEEE standards, simulation platforms were set up with Matlab mathematical software which let us have a chance to probe signals in every place inside the system and visual view of the channel effects. And with this system, our algorithms could be verified. Some simulation results were shown in this thesis, and the accomplishment of the proposed algorithms are also verified with these simulation results.