Hi!
LoRa uses chirp-signals whose frequency grows from -bandwidth/2 to bandwidth/2. Bandwidth can be 125, 250 or 500 kHz.
But in this impementation the modulator generates chirps changing from -pi to pi.
The modulator is followed by a resampler (.grc file is attached) that interpolates the signal sample_rate/bandwidth times (for example, 1e6/250e3 = 4 times) and sends it to the USRP-sink.
It is the same for the receiver, but the resampling rate is 1/4 for the example above.
The author of the block says: "The modulator and demodulator blocks do not resample or channelize input/output IQ streams; they expect to be provided a stream that is channelized to the bandwidth of the modulation." and "The width of the signal is determined by the sample rate." I'm familiar with the concepts of resampling and channelisation, but don't get this.
For the right work of the resampler the sampling frequency after the modulator should be of bandwidth rate (250e3, for example). But it isn't specified anywhere except the resampler.
The thing is that I want to add noise after the modulator and measure the error rate and can't figure out what signal bandwidth(sampling_freq/2) to choose to get the right noise power value.
That project seems abandoned, that's why I'm asking here.
Thank you
txrx_usrp.grc