On Tue, Jun 28, 2016 at 6:14 PM, Raj Bhattacharjea <ra...@gatech.edu> wrote:
> Consider the identity channel that passes through it's input to its > output. This is an idealization of a very short run of high quality cable > between synchronized systems. Using GNURadio's channels_channel_model, I > expect that the following provides the identity channel: > > Noise voltage: 0 > Frequency offset: 0 > Epsilon: 1 > Taps: 1 > > That says add no noise, simulate no timing or carrier offset, and simulate > a channel impulse response that is a single impulse with amplitude 1. > However, I find that using such a channel model block introduces a delay > that can be corrected by applying the taps [0,0,0,1]. See the attached > flowgraph that subtracts the signals before and after the channel model; if > you let taps = 1, the two signals don't cancel. If you use taps = > [0,0,0,1], they do. Anyone know why this occurs? For my purposes, such a > channel model is a stand-in that is ideal for now, but general enough to > allow modeling of channel effects when I'm ready. > > -- > Raj Bhattacharjea, PhD > Georgia Tech Research Institute > Information and Communications Laboratory > http://www.prism.gatech.edu/~rb288/ > 404.407.6622 > For some value of "short" compared to the samples, otherwise, your cable is also introducing delay. Tom
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