Channel Estimations Schemes for OFDM Radio Systems with Pilot Channels 劉允中、李金椿
E-mail: 9315049@mail.dyu.edu.tw
ABSTRACT
The channel estimation schemes of the OFDM systems with pilot channels are investigate for frequency selective fading channels.
Firstly, the performance of the conventional linear interpolation and weight interpolation schemes are considered. Secondly, the time correlation coefficient estimation scheme with linear and weight interpolation are proposed, and their simulations are performed and compared. Consider the OFDM system that has two pilot channels and a data length of 512 bytes per frame. According to the simulation results and referring to a performance of BER=10-3, the performance of the time correlation estimation with linear interpolation can provide over 10dB than the conventional linear and weight interpolation schemes. Time correlation with weight interpolation has the same performance as the conventional weight interpolation schemes, but has more 4dB than that of the conventional linear interpolation scheme. When the number of pilot channels is increase to four, the performance of the time correlation estimation scheme and the conventional weight interpolation schemes remain the same, while a 5dB improvement can be obtained for the conventional linear interpolation scheme. In time correlation estimation schemes, because the number of pilot channels can be reduced without performance degradation, the data transmission capacity is increase accordingly. From the simulations, we find the performance improvement decrease 5dB when the data length frame is increase for 512bytes to 1024bytes.
In general, the proposed time correlation estimation schemes are able to provide better channel estimation performance, while performance is inversely proportional to the frame length.
Keywords : OFDM ; conventional linear interpolation ; weight interpolation channel estimation ; time correlation estimation scheme
; pilot ; IEEE802.11a
Table of Contents
封面內頁 簽名頁 授權書．．．．．．．．．．．．．．．．．．．．．．．．．iii 中文摘要．．．．．．．．．．．．
．．．．．．．．．．．．iv 英文摘要．．．．．．．．．．．．．．．．．．．．．．．．v 誌謝．．．．．．．．．
．．．．．．．．．．．．．．．．．vii 目錄．．．．．．．．．．．．．．．．．．．．．．．．．．viii 圖目錄．．
．．．．．．．．．．．．．．．．．．．．．．．xi 表目錄．．．．．．．．．．．．．．．．．．．．．．．．．xiii 第一章 緒論．．．．．．．．．．．．．．．．．．．．．．1 第二章 無線通道及OFDM技術原理．．．．．．．．
．．．．4 2.1無線通道．．．．．．．．．．．．．．．．．．．4 2.1.1 大範圍衰減模型與小範圍衰減模型．．．．．5 2.1.2多重路徑衰變．．．．．．．．．．．．．．7 2.1.3多路徑延遲功率．．．．．．．．．．．．．9 2.2 OFDM調變技 術．．．．．．．．．．．．．．．11 2.2.1 OFDM和傳統分頻多工系統．．．．．．．12 2.2.2 OFDM架構．．．．．．
．．．．．．．．15 2.2.3保護區間和前置循環信號．．．．．．．．17 第三章 無線區域網路IEEE 802.11a標準．．．．
．．．．．19 3.1無線區域網路簡介．．．．．．．．．．．．．．19 3.2 IEEE 802.11a頻帶分配．．．．．．．．．．．
．19 3.3 IEEE 802.11a系統架構．．．．．．．．．．．．20 3.4 IEEE 802.11a實體層與Frame結構及系統參數．．23 3.4.1 IEEE 802.11a frame format．．．．．．．．24 3.4.2 PLCP 表頭．．．．．．．．．．．．．．26 3.4.3 Signal Field、Data Field．．．．．．．．．29 3.5 IEEE 802.11a系統方塊介紹．．．．．．．．．．29 3.5.1 Add pad bits．．．．．．．．．
．．．．．29 3.5.2 Scrambler．．．．．．．．．．．．．．．30 3.5.3 Convolutional encoder．．．．．．．．．．31 3.5.4 Data interleaving．．．．．．．．．．．．．33 3.5.5 Symbol Mapping．．．．．．．．．．．．34 3.5.6訊符插入方 式．．．．．．．．．．．．．36 3.5.7 Guard Interval addition．．．．．．．．．．38 3.5.8 Window function．．．．．
．．．．．．．38 3.6 IEEE 802.11a 接收端架構．．．．．．．．．．．40 第四章 通道估測與效能模擬．．．．．．．
．．．．．．．．41 4.1通道估測．．．．．．．．．．．．．．．．．．41 4.1.1一階線性內插法．．．．．．．．．．
．．42 4.1.2內插權重法．．．．．．．．．．．．．．45 4.1.3時間相關係數估測法．．．．．．．．．．47 4.2模擬．．
．．．．．．．．．．．．．．．．．．51 4.2.1系統架構．．．．．．．．．．．．．．．52 4.2.2參數設定．．．．．
．．．．．．．．．．52 4.2.3模擬結果．．．．．．．．．．．．55 4.2.4討論．．．．．．．．．．．．．．．．．58 第五章 結論．．．．．．．．．．．．．．．．．．．．．59 參考文獻．．．．．．．．．．．．．．．．．．．．．
．．60
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