應用於正交分頻多工無線區域網路之碼框同步與自動增益控制

Abstract

本論文提出一個有效率，應用在IEEE所制訂的無線區域網路標準IEEE 802.11a之碼框同步(Frame synchronization)，符元同步(Symbol synchronization)，以及數位自動增益控制。IEEE 802.11a所使用的方式是正交分頻多工(Orthogonal Frequency Division Multiplexing), OFDM)，在一個多路徑衰減的室內通道之中，正交分頻多工被證明能有效的對抗由多路徑衰減所帶來的不理想因素，就由此調變可使傳輸率提升至54 Mbps。 所提出的架構利用安置在每個封包之前的preamble，在低訊號雜訊比和多路徑衰減的通道時可以快速，正確的達到框碼同步。在實現部分，使用了FPGA和DSP實現所提出的演算法。對於測試和量測部分，我們提出並建立一個快速且方便的測試方法，兩種實現方式皆經由此測試部分印證成功。

In this thesis, an efficient frame and symbol synchronization, and digital automatic gain control (AGC) for Orthogonal Frequency Division Multiplexing (OFDM) based wireless LAN (WLAN) defined in IEEE 802.11a had been proposed. The architecture contains frame detection, symbol timing estimation and signal power estimation. The estimated signal power can be used in AGC. The proposed method enables a rapid and accurate synchronization even under very low SNR and multi-path fading channel by using ten short training symbols at the start of every frame. For implementation part, DSP and FPGA are both used to implement. By writing c code and assembly code, the proposed frame synchronization is implemented by using TI TMS320CC6201 EVM and is verified. The implementation on FPGA by writing hardware description language is also verified. For the test and measurement, a fast and convenient test methodology is proposed and built. The two implementations are tested and measured under the proposed test methodology with real-time signal processing.