TAILIEUCHUNG - Vehicular Technologies Increasing Connectivity Part 12

Tham khảo tài liệu 'vehicular technologies increasing connectivity part 12', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Peak-to-Average Power Ratio Reduction for Wavelet Packet Modulation Schemes via Basis Function Design 321 results presented in Rostamzadeh Vakily 2008 show that the iterative ML receiver based clipping approach can nearly mitigate the in-band distortion introduced by the clipping process with 3 iterations in an additive white Gaussian noise AWGN channel. However in a multipath fading channel it is generally difficult to estimate the nonlinear distortion component at the receiver Jiang Wu 2008 . Thus the iterative ML receiver based clipping approach proposed in Rostamzadeh Vakily 2008 may suffer performance degradation due to in-band distortion in a multipath fading environment. Other major disadvantages of the iterative ML receiver based clipping approach include increased out-of-band radiation and a higher receiver complexity. In Zhang Yuan Zhao 2005 an amplitude threshold based method is proposed for PAPR reduction in WPM systems. In this method the signal samples whose amplitudes are below a threshold T are set to zero and the samples with amplitudes exceeding T are unaltered. Since setting the low amplitude samples to zero is a nonlinear process this method also suffers from in-band distortion and introduces out-of-band power emissions. Another major disadvantage with the amplitude threshold based PAPR reduction scheme proposed in Zhang Yuan Zhao 2005 is that it results in an increase in the average power of the modified signal. Although the PAPR is reduced due to an increased average power this method will result in BER degradation when the transmitted signal is normalized back to its original signal power level Han Lee 2005 . Furthermore the amplitude threshold based PAPR reduction scheme also requires HPAs with large linear operation regions Jiang Wu 2008 . Lastly the criterion for choosing the threshold value T is not defined in Zhang Yuan Zhao 2005 and hence may depend on the characteristics of the HPA. An alternative amplitude threshold based scheme .

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