動態碼率錯誤更正碼在OFDM系統上之效能

Performance of variable-rate error correcting code for OFDM systems

李大瑋(Da-Wei Li)

指導教授 ： 劉玉蓀

中原大學/工學院/電機工程研究所/碩士(2003年)

https://doi.org/10.6840/cycu200300185

摘要

本論文提出一個改變錯誤更正碼的碼率方法，試著提高正交分頻多工系統（Orthogonal Frequency Division multiplexing，OFDM）的效能。在系統中，我們使用渦輪碼、折積碼和Reed-Solomon碼做測試。信號在通道中會受到許多干擾，本文以frequency selective Rayleigh fading、都卜勒效應、多路徑干擾及白色高斯雜訊去模擬通道的效應。在接收端的部分，一般是採用等化器去接收信號，這個方法無法提升信號的SNR，如果要提升信號的SNR，就必須採用前置等化器。採用前置等化器的方法較複雜，我們嘗試利用在接收端部分加上門檻值測試的方式來做解碼計算，將未達到門檻值的信號在解碼時將信號資訊去除，試著利用錯誤更正碼的更正能力來提高系統效能。由模擬結果得知去除不佳的資訊，對於錯誤更正碼而言無法降低錯誤率，而且會因為不足的解碼資訊造成錯誤。

關鍵字

OFDM ； 都卜勒效應 ； Reed-Solomon碼 ； 折積碼 ； 渦輪碼 ； 多路徑干擾 ； frequency selective Rayleigh fading

並列摘要

In this thesis, we try to improve the performance of orthogonal frequency division multiplexing (OFDM) system over a frequency selective Rayleigh fading channel with Doppler effect and multipath interference. We use the method of threshold testing to increase the system performance. The method is to delete some information when signals’ energy is not big enough. As simulation results, we know we can’t decrease error probability of error correcting code by deleting some bad information and maybe increase errors by having not information enough.

並列關鍵字

OFDM ； convolutional code ； Reed-Solomon code. ； turbo code ； Doppler effect ； multipath interference

參考文獻

[1] R.W. Chang, “Synthesis of Band-limited Orthogonal Signals for Multichannel Data Transmission”, Bell System Tech. J., vol. 45, pp. 1775-1796, Dec. 1966.

[2] B.R. Saltzberg, “Performance of an efficient parallel data transmission system”, IEEE Trans. Commun. Technol., COM-15, no. 6, pp. 805-811, Dec. 1967.

[3] S.B. Weinstein and P.M. Ebert, “Data transmission by frequency-division multiplexing using the discrete Fourier transform”, IEEE Trans. Commun., COM-19, no.5, pp. 628-634, Oct. 1971.

[7] T. Keller and L. Hanzo, “Adaptive modulation techniques for duplex OFDM transmission”, Vehicular Technology, IEEE Transactions on, Volume: 49 Issue: 5, pp. 1893 –1906, Sept. 2000

[9] S.B. Weinstein and P.M. Ebert, “Data transmission by frequency-division multiplexing using the discrete fourier transform”, IEEE Trans. Commun. Technol., vol. COM-19, pp.628-634, Oct. 1971.