Vimtakhul Azis (master program FH Darmstadt)
Prof. Dr.-Ing. Werner Henkel
February – July 2003
We appreciate funding by Infineon
The major drawback of multi-carrier transmission is the high peak-to-average power ratio of the time-domain signal resulting from the combination of many carriers (central limit theorem). Without countermeasures, the analog circuitry, A/D and D/A converters, and the voltage supplies have to be designed for very high peaks, although they may not occur very often. This would require high resolution and costly converters and due to the high voltage power supplies, also a high power dissipation. Especially, the power dissipation and with it the heat is a critical issue when increasing the number of xDSL lines per circuit board, i.e., also per rack. In the wireless domain, power dissipation is of similar importance. There, battery power is a very limited resource.
Without any countermeasures, clipping will occur. In a recent paper by Bahai et al. , for the first time, the impact of clipping is studied as an impulse-noise process. They especially model the excursions above the clipping level as parabolic arcs and even derive bit-error rate expressions. Although this paper is an essential step into the right direction compared to former simplistic approaches, modeling the noise to be white Gaussian, colleagues reported the actual results to be not very exact or simply wrong. Since the results may also have very practical implementation aspects regarding the error-correction procedures, in this study, we will investigate the assumptions and derivations of this paper in more detail and will try to improve the results.
Furthermore, we are also planning to improve on clipping procedures. Especially, ideas have been already developed that should be investigated in this study. Due to IP issues, we cannot yet present details in here. However, earlier proposals can,e.g., be found in [2-3].
 Bahai, A.R.S., Singh, M., Goldsmith, A.J., Saltzberg, B.R., A new approach for evaluating clipping distortion in multicarrier systems, IEEE Journal on Selected Areas in Communications, Vol. 20 , No. 5 , June 2002, pp. 1037-1046.
 Henkel, W., Analog codes for peak-to-average ratio reduction, 3rd ITG Conference Source and Channel Coding, Munich, Jan. 17-19, 2000.
 Henkel, W., Zrno, V., PAR reduction revisited: an extension to Tellado’s method, 6th International OFDM-Workshop, Hamburg, Sept. 18-19, 2001.
[Thesis] Impact of Clipping on a Multicarrier Signal and Countermeasures
Note: Please check later publications that contain some corrections!