Re: [Discuss-gnuradio] Channel model - the identity channel

[Tom Rondeau]

On Tue, Jun 28, 2016 at 6:14 PM, Raj Bhattacharjea <address@hidden> 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