Hi there! I am working on PAPR measurement of OFDM signals connected to a RF amplifier.I created the OFDM signal from a signal studio. Then the signal is connected to RF amplifier and with the spectrum generators to see the input OFDM spectrum and output OFDM spectrum. The generated OFDM Spectrum from the Spectrum generator is stationary or it is changing for a particular input power of RF amplifier? I mean how can I fix the peak power and the average power of an output OFDM spectrum for a specific input power of RF amplifier? Can you help me how to measure the PAPR in such a case? Waiting to hear from you....... Regards Razib

# Measuring PAPR of OFDM signals

Started by ●August 3, 2007

Reply by ●August 3, 20072007-08-03

On Aug 3, 7:27 am, "razib3002" <razib3...@gmail.com> wrote:> Hi there! > > I am working on PAPR measurement of OFDM signals connected to a RF > amplifier.I created the OFDM signal from a signal studio. Then the signal > is connected to RF amplifier and with the spectrum generators to see the > input OFDM spectrum and output OFDM spectrum. > > The generated OFDM Spectrum from the Spectrum generator is stationary or > it is changing for a particular input power of RF amplifier? I mean how > can I fix the peak power and the average power of an output OFDM spectrum > for a specific input power of RF amplifier? > > Can you help me how to measure the PAPR in such a case? > > Waiting to hear from you....... > > Regards > RazibIn IEEE literature the PAPR for OFDM is computed as the magnitude squared of the largest sample divided by the average magnitude squared of a complete OFDM symbol. In a lab setting the symbol boundaries aren't known, so what is typically measured is the peak power divided by the average power measured over a relatively long time interval. The peak power is not fixed. John

Reply by ●August 5, 20072007-08-05

Hi Razib, [snip] "I mean how can I fix the peak power and the average power of an output OFDM spectrum for a specific input power of RF amplifier? " Hmm... I do not think that the above statement is correct. For the baseband waveform xt, the PAPR (peak-to-average-power ratio) is defined as PAPR_dB = 10*log10(max(xt.conj(xt))/E{xt.conj(xt)}). You can use your baseband waveform to find out the PAPR. For OFDM case, theoretically the PAPR is equal to 10*log10(N), where N is the number of used subcarriers. Typically, thanks to the scrambler, this maximum value of PAPR is never reached. To give margins for the peaks which may occur in the time domain waveform, the power amplifier needs to be operated such that the even the peaks in the waveform do not cause clipping or other non-linearities. Maybe this url helps: http://www.commsdesign.com/story/OEG20011023S0040 HTH, Krishna http://dsplog.blogspot.com

Reply by ●August 9, 20072007-08-09

>Hi Razib, > >[snip] >"I mean how >can I fix the peak power and the average power of an output OFDM >spectrum >for a specific input power of RF amplifier? " > >Hmm... I do not think that the above statement is correct. For the >baseband waveform xt, the PAPR >(peak-to-average-power ratio) is defined as PAPR_dB = >10*log10(max(xt.conj(xt))/E{xt.conj(xt)}). > >You can use your baseband waveform to find out the PAPR. For OFDM >case, theoretically the PAPR is equal >to 10*log10(N), where N is the number of used subcarriers. Typically, >thanks to the scrambler, this maximum value >of PAPR is never reached. > >To give margins for the peaks which may occur in the time domain >waveform, the power amplifier needs >to be operated such that the even the peaks in the waveform do not >cause clipping or other non-linearities. > >Maybe this url helps: http://www.commsdesign.com/story/OEG20011023S0040 > >HTH, >Krishna >http://dsplog.blogspot.com > >Thanks to John and Krishna.....I am actually trying to find the PAPR with respect to the Input power of the RF amplifier that I am using in my experiment. I want to see the effects of PAPR due to the variaion in RF amplifier power input. Thats why I need to know how can I measure PAPR for a specific input power value. Then I want to vary the input power of RF amp. to find the PAPR again......to eventually create a relationship.... I want to generate the OFDM signal using signal studio and then Signal Generator will download the created signal. After that , for every value of the input power of the RF amplifier, I want to measure peak value and average value of the OFDM signal to finally calculate PAPR. My question in this respect is..........should I hold the OFDM signal using the spectrum analyzer to find the peak value and average value for a particular RF amplifier input power? Hope you understood my query...:) Thanks> > > > > > > >