正交分頻多工帶外功率譜降低法

THE REDUCTION OF OUT-OF-BAND POWER SPECTRUM FOR OFDM

陳思豪(Szu-Hao Chen)

指導教授 ： 許超雲

大同大學/電機資訊學院/通訊工程研究所/碩士(2004年)

摘要

近年來對於高速資料傳輸率的無線通訊的需求正在快速地成長中。而正交分頻多工(OFDM)是一種能夠達到高資料傳輸量及高頻寬效益兩大需求的技術，也已經被普遍地應用在無線通訊的各種應用上。在1998年7月，訂定IEEE標準的團隊決定選擇OFDM作為5G-Hz頻帶標準的基礎技術，且目標是希望資料流的速率可以高達6~54Mbps。
然而由於OFDM不同符號(symbol)之間的不連續性，將會導致頻帶外的功率發散，這些發散都是我們不希望對鄰近頻道所造成的干擾，換句話說，由鄰近頻道所發散出的干擾會降低頻帶內的信號品質。為了改善這種現象，我們嘗試做一些信號上的處理來維持符號間邊界的連續性。最後頻帶外的發散功率的確會被降低。此外我們也將會在本篇論文中探討當我們的方法通過實際的無線傳輸通道之後是否仍能有令人滿意的效果。
根據我們的模擬方法，會有如下的兩項優點:
1. 我們僅需將所需的輔助資訊安插在原本沒有傳送資料的子載波裡而不需要增加其他的子載波。
2. 即使沒有做波形調整的處理依然能達到降低帶外功率的效果。

關鍵字

鄰頻干擾 ； 正交分頻多工

並列摘要

The demand for high data rate wireless communications is rapidly growing recently. Orthogonal Frequency Division Multiplexing (OFDM) is a technique that can achieve the high data capacity and spectral efficiency requirements, and is already commonly adapted in all kinds of wireless applications. In July 1998, the IEEE standardization group decided to select OFDM as the basis for their new 5-GHz standard, targeting a range of data stream from 6 to 54 Mbps.
However, it will cause out-of-band emissions due to the discontinuities at boundary between two different OFDM symbols. These emissions are undesired interference to adjacent channels, and will lower the quality of in-band signal. In order to improve this phenomenon, we try to do some signal processing to keep continuous at the boundary between symbols. Finally the out-of-band power will be reduced by our method. And we will also discuss whether the effect is good enough after transmitting through the real wireless channel.
According to our simulation, two advantages can be achieved as follows:
(1) We only insert the necessary data into the originally null subcarriers and do not need to add other subcarriers.
(2) The out-of-band power can be reduced even without pulse shaping.

並列關鍵字

adjacent interference ； OFDM

參考文獻

[1]R. van Nee and R. Prasad, OFDM for Wireless Multimedia Communications. 2000.

[4]A. V. Oppenheim and R. W. Schafer, Discrete-time signal processing, Prentice Hall, 1998.

[7]Theodore S. Rappaport, Wireless communications, Prentice Hall Press, 1996.

[8]B.Sklar and E. Okamoto, “ Rayleigh fading channels in mobile digital communication systems .I. Characterization,” IEEE Communications Magazine, vol. 35, pp.90-100, July 1997.

[9]B. Sklar and E. Okamoto, “Rayleigh fading channels in mobile digital communication systems. II. Characterization,” IEEE Communications Magazine, vol. 35, pp.148-155, Sept 1997.