DRM數位廣播帶外功率降低研究

Reduction Proposal of Out-of-Band Power Radiation in DRM System

張金山(Jin-Shan Chang)

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(2007年)

摘要

廣播的數位化為未來必然的趨勢，DRM系統被設計用來取代現有的類比調幅廣播。而此數位系統的先期設計允許與現有的類比廣播系統共存，因此在這有限寬度的頻帶上，頻帶間干擾的抑制將是一個重要的議題。
為了降低DRM頻帶外頻譜功率的散逸，我們提出有效的方法來改善降低對鄰近頻帶的干擾。並且我們利用空的副載波加入額外資料，來降低自身頻道對相鄰頻道的干擾。另外我們也改善本方法在主頻帶高頻處產生過高功率值的缺點。
眾所周知“消除載波插入法”利用OFDM的頻譜邊界來降低帶外頻譜的功率發散，但其方法除了增加運算的複雜度也影響了BER的表現。而我們的方法不會有這一方面的缺失。
依據我們模擬的結果，有下列的優點：
1. 我們僅需要將輔助資訊安插入兩個或四個無傳送資料的副載波內，而不需要改變系統設定。
2. 峰值功率的現象明顯有效地被控制。
3. 當我們使用門檻值為1的Zero Forcing方法，在同頻廣播的5.3kHz邊界可以降低帶外功率2.68dB，在鄰頻廣播的21.2kHz處可以降低帶外功率13.05dB。
4. 我們使用門檻值為1的Tail Tracking方法，在同頻廣播的5.3kHz邊界可以降低帶外功率1.17dB，在鄰頻廣播的21.2kHz處可以降低帶外功率12.67dB。同時可改善峰值功率。

關鍵字

數位廣播 ； 帶外功率 ； 強迫為零平滑處理方法 ； 尾隨平滑處理方法 ； 峰值功率

並列摘要

The broadcasting be digitized is an inevitable trend in the future, the DRM system was designed as an eventual replacement for current analogue AM broadcasting, but allow these new digital transmissions to co-exist with current analogue services from the outset. In order to make the best use in these limited and crowded bandwidth, the interference rejection between adjacent channels becomes an important issue.
The reduction of DRM out-of-band power is proposed in this thesis and it improved to reduce the adjacent interference indeed in order to gain high bandwidth efficiency. To eliminate this problem, we add the power of additional carriers with extra information, and solve it indeed for adjacent channel even better for co-channel with digital and current analogue AM service. Otherwise we did not impact the existing system, the object of gaining high bandwidth efficiency can achieve and more channels may be allowed in the specific frequency band.
As we knew a method called “Reduction of Out-of-Band Radiation in OFDM Systems by Insertion of Cancellation Carriers”. They use cancellation carriers at borders of the OFDM spectrum to reduce the out-of-band radiation of the OFDM signal. There is cost consumption for these results with a loss in BER performance and an increased computation complexity.
To compare with cancellation carriers method, our proposed methods has treated the boundary between current symbol and next symbol, but cancellation carriers method doesn’t. So out-of-band radiation of cancellation carriers method will still exist.
Based on our simulation, the advantages can be achieved below:
1. We only need to insert two or four auxiliary data into the original null subcarriers to reduce out-of-band power. It presents fully compatible to current existing system but don’t need to change any system’s set up.
2. The peak-power phenomenon can be controlled.
3. The simulated results indicates to improve the reduction out of band power with 2.68dB at 5.3kHz for co-exist channel using Zero Forcing Method with 1 of threshold value, and 13.05dB at 21.2kHz for adjacent channel.
4. To improve the reduction out of band power with 1.17dB at 5.3kHz for co-exist channel using Tail Tracking Method with 1 of threshold value, and 12.67dB at 21.2kHz for adjacent channel as well as can improve the peak power.

並列關鍵字

DRM ； out-of-band power ； zero forcing ； tail tracking ； peak power

參考文獻

[2] DRM publication, Broadcasters’ User Manual, 2nd edition, August 2006.

[6] European Telecommunications Standards Institute: Digital Radio Mondiale (DRM); System Specification ETSI ES 201 908 v2.2.1, 2005.

[9] Sinja Brandes,Ivan Cosovic,and Michael Sshnell,” Reduction of Out-of-Band Radiation in OFDM Systems by Insertion of Cancellation Carriers”, IEEE Communications Letters, Vol. 10, No.6, pp.420-422, June, 2006.

[1] Berker Sklar, Digital Communications-Fundamentals and Applications, 2nd edition, Prentice-Hall Inc., 2004.

[3] Yuong-Fong Lin, Study on Reduction of Out-of-Band Power in DAB Eureka-147, Master Thesis of Tatung University, pp.2, January 2007.