Re: [Discuss-gnuradio] problem with ofdm bandwidth and sampling rate

[Marcus Müller]

Hi Alphonso,

On 06/05/2015 11:22 AM, address@hidden wrote:

i think i have understand the concept now: the sampling rate is valid global for the hole graph.if there is a previous/following block or source with a different rate, i have to resample it with such a resampler block. i am right?

No. There is no sampling rate in GNU Radio, really. It's just a numerical concept for each block. For example, look at the standard "signal source". It takes a frequency and a sampling rate argument. If you use f=1000 and sampling rate=4000, the signal source (float mode) will just calculate how to scale the values that it puts into the sine function. You will get exactly the same signal (really, no difference *anywhere*) if you used f=0.5, rate=2, or f=1e9 and rate=4e9.
So, each block has only "sample" as a means to measure time, and 1/sample as a means to measure frequency. You need to start thinking relative to Nyquist frequency, i.e. to say "this signal source generates a signal at 0.25 of the sample rate, which is equivalent to 0.5 nyquist frequency, because this is real sampling".
You'll quickly see that the OFDM modulator and demodulator always uses the whole possible bandwidth (complex sampling, hence nyquist frequency == sampling rate), and your resampler generates a signal where only a part of the bandwidth is occupied.

Best regards,
Marcus