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研究生:王歷信
研究生(外文):Li-Shin Wang
論文名稱:OFDM無線區域網路在頻率選擇性衰減通道下之效能研究
論文名稱(外文):Performance Study of OFDM-based Wireless LANs over Frequency Selective Fading Channels
指導教授:竇奇
指導教授(外文):Chie Dou
學位類別:碩士
校院名稱:國立雲林科技大學
系所名稱:通訊工程研究所碩士班
學門:工程學門
學類:電資工程學類
論文種類:學術論文
論文出版年:2009
畢業學年度:97
語文別:中文
論文頁數:92
中文關鍵詞:鏈路調適通道增益802.11a頻率選擇性衰減封包錯誤率BRAN
外文關鍵詞:channel gainlink adaptationpacket error rate802.11afading channel
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OFDM-based的IEEE 802.11a無線網路在頻率選擇性衰減通道下,各target Eb/No的鏈路調適,以獲得無線網路系統的最佳效能。論文中,展現了頻率衰減性通道下,target Eb/No(訊雜比)與received SNR的關係,並以各封包received SNR觀念,做為鏈路調適的基礎。採用迴旋編碼與hard-decision viterbi 解碼,以各封包的次通道增益,來計算各received SNR的封包錯誤率上限值(upper bound)。由於封包的received SNR取決於,target Eb/No、平均通道增益與傳輸速率模式,因此論文中,模擬了target Eb/No從3到26 dB的平均封包錯誤率,並呈現了ETSI/BRAN A與C通道的平均通道增益機率分佈,其結果可進一步瞭解received SNR的分佈並比較兩衰減通道在各種傳輸速率模式下的平均封包錯誤率情形。論文中,除了以分析計算方式獲得平均封包錯誤率,並以模擬方式來驗證所獲得的平均封包錯誤率。本論文發現,考量到衰減通道造成的影響,對各種傳輸速率模式而言,在received SNR相同的情況下,低target Eb/No擁有較低的封包錯誤率現象。並由以上獲得的結果得知,傳統IEEE 802.11a鏈路調適只選取一組固定的平均訊雜比,做為傳輸速率調適的門檻值,是無法在每個target Eb/No之下獲得最佳的系統效能。而本論文,則是考量在不同target Eb/No之下,根據平均通道增益機率分佈,產生一組傳輸速率門檻值,以獲得最佳的傳輸量系統效能。在ETSI/BRAN A通道下,對不同target Eb/No作模擬,所獲得的傳輸速率門檻值,也一併呈現於本論文中。
This paper performs link adaptation on a per base the OFDM-based IEEE 802.11a WLAN over frequency selective fading channels. First clarifies the relationship between the target Eb/No and the received SNR (signal-to-noise ratio) of the packet in the rate adaptive IEEE 802.11a WLANs over the fading channels. Packet error rate (PER) expression for convolutional-coded hard-decision decoded OFDM systems is analytically derived on a fading realization basis. The initial SNR per subcarrier is calculated directly from the target Eb/No. Due to channel fading effects, the received SNR of transmitted packets forms a probabilistic distribution with the initial SNR as the approximate mean. The received SNR depends on the given target Eb/No, the selected rate mode and the average channel gain of the fading realization experienced by the packet. This paper shows that the probability distribution of the average channel gain of the multipath fading channel governs the pattern of the probability distribution of the received SNR. Through this pattern the effective region of the received SNR, that represents the occurring probability of any received SNR falling outside of this region is negligible, is determined. Given that the is fixed, the average PER performance for each individual received SNR within the effective region are obtained both by an analytical approach and the simulation for different rate modes. This paper demonstrates that by lowering the target Eb/No values, better PER performances under the same received SNR are obtained. This observation has a significant impact on the determination of the mode switching thresholds in the IEEE 802.11a link adaptation. Unlike conventional link adaptation technique that a set of mode switching thresholds is chosen to optimize the overall system performance, in this paper mode switching thresholds is determined for each individual target Eb/No. Thus, the optimal system performance can be obtained on a per target Eb/No basis. Throughput are investigated and compared for 802.11a WLANs over BRAN A and C channel models.
中文摘要 --------------------------------------------------------------- i
英文摘要 --------------------------------------------------------------- ii
誌謝 --------------------------------------------------------------- iv
目錄 --------------------------------------------------------------- v
表目錄 --------------------------------------------------------------- vii
圖目錄 --------------------------------------------------------------- viii
第一章 緒論----------------------------------------------------------- 1
1.1 研究動機------------------------------------------------------- 1
1.2 研究目的------------------------------------------------------- 1
1.3 研究方法與內容------------------------------------------------- 2
1.4 各章提要------------------------------------------------------- 3
第二章 IEEE 802.11a 簡介---------------------------------------------- 4
2.1 IEEE 802.11a -------------------------------------------------- 4
2.2 正交分頻多工簡介----------------------------------------------- 4
2.2.1 多載波傳輸與載波正交性----------------------------------------- 5
2.2.2 正交分頻多工之優缺點------------------------------------------- 6
2.3 IEEE 802.11a OFDM系統架構-------------------------------------- 8
2.3.1 IEEE 802.11a 系統操作------------------------------------------ 9
2.3.2 錯誤更正碼----------------------------------------------------- 10
2.3.3 位元交錯------------------------------------------------------- 12
2.3.4 保護區間------------------------------------------------------- 12
2.3.5 Windowing ----------------------------------------------------- 14
2.4 IEEE 802.11a 系統參數與特色------------------------------------ 15
2.4.1 操作頻段------------------------------------------------------- 15
2.4.2 系統參數------------------------------------------------------- 16
2.5 IEEE 802.11a 訊框格式------------------------------------------ 18
2.5.1 同步訊號------------------------------------------------------- 19
2.5.2 訊號欄位(SIGNAL)----------------------------------------------- 20
2.5.3 資料欄位(DATA)------------------------------------------------- 21
2.6 模擬環境------------------------------------------------------- 22
第三章 無線通道模型--------------------------------------------------- 24
3.1 無線通道模型簡介----------------------------------------------- 24
3.2 可加性白高斯雜訊----------------------------------------------- 24
3.3 多重路徑衰減--------------------------------------------------- 27
3.3.1 訊號延遲擴散--------------------------------------------------- 27
3.3.2 相位偏移------------------------------------------------------- 28
3.3.3 瑞利衰減------------------------------------------------------- 29
3.4 ETSI/BRAN通道模型---------------------------------------------- 31
3.4.1 ETSI/BRAN A通道模型-------------------------------------------- 31
3.4.2 ETSI/BRAN C通道模型-------------------------------------------- 33
第四章 無線通道模擬與通道估測分析------------------------------------- 35
4.1 通道模擬簡介--------------------------------------------------- 35
4.1.1 頻率選擇性衰減通道數學模型------------------------------------- 35
4.1.2 通道增益的機率分佈--------------------------------------------- 37
4.2 系統錯誤率----------------------------------------------------- 38
4.2.1 錯誤率上限值--------------------------------------------------- 39
4.2.2 系統錯誤率(simulation)----------------------------------------- 43
第五章 通道效應與鏈結調適(link adaptation)---------------------------- 46
5.1 通道效應------------------------------------------------------- 46
5.1.1 通道與錯誤率關係----------------------------------------------- 47
5.2 鏈結調適簡介--------------------------------------------------- 54
5.2.1 Throughput-based鏈路調適--------------------------------------- 55
5.2.2 傳輸速率模式門檻值--------------------------------------------- 56
5.3 Link Adaptation應用-------------------------------------------- 62
第六章 結論與未來研究方向--------------------------------------------- 65
6.1 結論----------------------------------------------------------- 65
6.2 未來研究方向--------------------------------------------------- 66
參考文獻 --------------------------------------------------------------- 67
附 錄 一 各 的傳輸速率門檻選擇-------------------------------------------69
作者簡歷 --------------------------------------------------------------- 81
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