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:
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.
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Raj Bhattacharjea, PhD
Georgia Tech Research Institute
Information and Communications Laboratory
404.407.6622
identity_channel_model.grc