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From: | BHN66 |
Subject: | Re: [Discuss-gnuradio] problem with ofdm bandwidth and sampling rate |
Date: | Fri, 5 Jun 2015 10:15:19 +0200 |
Well, the measurable on-air bandwidth is always defined by the speed/rate at which your soundcard processes your digital samples. If you remember that B ~ 1/T and that the rate of your soundcard controls T it becomes obvious that changing the sample rate changes the bandwidth. If you don't want that, you could use a resampler that adapts its resampling ratio to the sampling rate of the soundcard.hello felix,>>please remember to always reply to the list.i'm sorry, i'm new at this. i have checked my configuration and i hope it works the next time.to mix up the baseband signal to 12khz or higher to short wave (3-30mhz) should be the same procedure. i have tested it by using a multiply block and a signal source block as the carrier frequency.but there is an other question: if i configured my system as described, can i be sure that the bandwidth of each sub carrier has the bandwidth and symbol duration as shown by the equations?used_bw = occupied_carriers * dfdf = used_bw / occupied_carriers = 10khz / 228df = 43.86hz --> tsym = 22.8msit's very confusing why i have to adjust my used bw by changing the sampling rate. when i follow the equations and the standard i choose one mode (RM A, SO 3). that means i have to use 228 carriers
and have a symbol duration with 24ms which leads to 41.66hz carrier spacing. so the used bw is 228 * 41.66hz = 9.5khz (approx. 10khz). this bw should be fix and should not change by the sampling rate.sorry for the maybe silly questions but i want to keep on that stuff.
@Marcusyou mean if there were pilots for a channel estimation in the transmitted signal?alphonso
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