On Wed, Mar 9, 2016 at 3:24 PM, Tracie Perez <[email protected]> wrote:
> Hi all, > > If I open a new flow graph in GRC and select a QT GUI Bercurve Sink block, > the default parameters create 16 ports (connections) on the block. The > default in the "Num Curves" field is 1 and the default in the "esno" field > is numpy.arange(0.0, 4.0, .5), which is 8 values. I'm not sure why there > are 16 ports. > > If you then change "Num Curves" to 2, the number of ports on the block > changes to 32. Also, if you change the value of "esno" to a different range > of values, it changes the number of ports. Is that on purpose? Should the > specified number of esno values be related to the number of ports? > > I would expect that the number of ports on this block is simply equal to > the number of curves specified. i.e., 2 in the "num curves" field generates > 2 ports on the block. > > In fact, that is the behavior of the ber_curve_gen.grc example. However if > you start from a new flowgraph, there's a different behavior. > > Any clarification on this would be appreciated. I'm working with GNU Radio > v. 3.7.9.1. > > Thanks, > tracie > Tracie, Yes, this is pretty confusing. It's due to the fact that this block calculates the BER itself internally by comparing the original data (pre-distortion) from input i with the post-distortion and post-decoding data on input i+1. So input_items[i] ^ input_items[i+1] is the BER to plot for that particular Es/N0 point. This matches up to the behavior of a BER Curve Generator block (look at gr-fec/python/fec/bercurve_generator.py and gr-fec/python/fec/fec_test.py). It might make more sense from a simulation point of view to have something like the 0th input be the original data and inputs 1 to N be the N encoder/decoder pairs we are comparing. But the way it currently is allows each encoder/decoder pair to operate off completely independent streams. Does that clear things up? Perhaps we can put this explanation into the manual. Tom
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