A Study of Crest Factor Reduction for Wcdma and Is-95 Systems

This dissertation, "A Study of Crest Factor Reduction for WCDMA and IS-95 Systems" by Hoi, Kuo, 郭海, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: Abstract of thesis entitiled A Study of Crest Factor Reduction for WCDMA and IS-95 Systems Submitted by Kuo Hoi for the degree of Master of Philosophy at The University of Hong Kong in December 2006 In a Code-Division-Multiple-Access (CDMA) base station, the downlink signal consists of a group of signals from different users. This results a very high peak amplitude but a relatively low mean value of the CDMA signal, leading to a signal with a high crest factor (CF), also known as the peak-to-average ratio (PAR). To reduce the out-of-band radiations which may interfere the adjacent channels, it is desirable to operate the base-station power amplifier (PA) in its linear region. However, the high-crest-factor of the CDMA signal sets a tight linearity requirement for the high PA (HPA). The penalty is a high DC power consumption and hence a low power efficiency. To obtain good power efficiency in PAs, the CF of the signal needs to be reduced. A new peak-windowing technique has been proposed and studied to reduce the CF of signals. Since a window function with a particular window length and window type is envisaged, we have explored the performance of this technique using a number of different window functions and parameters, with a view to optimizing performance in reducing the signal CF. Computer simulation tests have been used to study the CFs for the clipped WCDMA signals using the proposed technique and different clipping and windowing techniques. Results have shown that the proposed peak-windowing technique has the largest reduction in the CF, achieving at least 1.9 dB more in reducing the CF than other simple clipping techniques and the conventional II windowing technique. Taking into account the bit-error-rate (BER) degradation, at -3 BER=10, the technique is 6.2 dB or 1.9 dB better than the unclipped signal and the adaptive envelope clipping respectively in reducing the CF. When both the conventional windowing and peak-windowing techniques are optimized by choosing an optimized window function and the window length, taking into account the bit- -3 error-rate (BER) degradation, at BER=10, the technique is 6.6 dB or 2.2 dB better than the unclipped signal and the conventional windowing technique respectively in reducing the CF. Furthermore, the performance in signal quality and the reduction in the CF are studied in the IS-95 systems. Taking into account the BER degradation, at -3 BER=10, the technique is 4.0 dB or 2.0 dB better than the unclipped signal and the conventional windowing technique in reducing the CF. The results are further verified by various hardware experiments. Finally the proposed peak windowing technique can successfully reduce the CF of WCDMA signals for 8.1 dB, 2.2 dB better than other CF reduction techniques. For IS-95 signals, the proposed technique reduces the CF for 5.5 dB and 2.0 dB better than any other techniques covered in this thesis. The superior performance of the peak-windowing technique is also supported by hardware experiments and the analysis of signal spectra and constellations of signals clipped by different techniques. Hence, the PA power efficiency is enhanced by using the proposed technique at the base stations. III DOI: 10.5353/th_b3877802 Subjects: Power amplifiers Signal processing - Digital techniques Code division multiple access