A.L. Buzov – Dr.Sc.(Eng.), Professor, General Director, JSC «SIB RS» (Samara)
K.Yu. Morozov – Head of Department, JSC «SIB RS» (Samara)
This article is devoted to the problem of crest factor reduction for broadcasting transmitters of the DRM standard. Existing crest factor reduction methods for systems with the OFDM modulation are considered. Criteria for the selection of suitable methods in accordance with the limitations of the DRM standard are defined. The method of clipping with pre-filtering and post-filtering, the method of peak win-dowing, the method of active constellation extension are considered in detail. The effectiveness of these methods is analyzed; recom-mendations on the features of their application and the choice of their parameters are given. On the basis of the obtained results the ways of further research in the sphere of the crest factor reduction for broadcasting transmitters of the DRM standard are determined.
On September 11, 2018, the State Commission for Radio Frequencies (SCRF) decided to allocate frequencies in the ranges of 65.9−74.0 MHz and 87.5−108.0 MHz for the purposes of digital broadcasting in the DRM+ standard, which is fixed by the relevant proto-col of the meeting (Decision of the SCRF # 18-46-01). Therefore at present in Russia the issues of developing of the DRM standard equipment are particularly relevant.
For modulation of the signal in the DRM standard the COFDM technology –orthogonal frequency division of channels with coding is used. The COFDM technology in turn is a type of the OFDM technology. Due to a number of advantages the OFDM is an attractive communica-tion technology for broadcasters. However the main problem of systems with the OFDM modulation is the high crest factor, which causes strong non-linear distortions in the radio frequency components of the DRM equipment. Without a decrease of the crest factor it is im-possible to ensure a high power efficiency of the transmitter, the low power efficiency leads to its cost increase.
In systems with OFDM modulation various methods of the crest factor reduction are used, which can be divided into methods based on signal distortion and methods based on signal scrambling. Analysis of methods of the crest factor reduction for compliance with the re-quirements of the DRM standard shows that only few methods can be successfully applied for the transmitters of this standard. These in-clude of methods based on peak limiting (clipping) and filtering, as well as a method based on the active constellation extension.
Analysis of the above described methods shows that the most promising method of the crest factor reduction for the DRM standard is the method of active constellation extension with post-filtering. Also good results are obtained by the pre-filtering and post-clipping method, the advantage of which is the ease of implementation.
The obtained results provide an opportunity to significantly speed up the developing process of Russian broadcasting transmitters of the DRM standard.
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