Open Research Institute Weekly Reports, 28 May 2022

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From YouTube: Uplink Simulator Part 3

Description

Walks through the creation of a Phase 4 uplink simulator using M17 signals in an FDMA scheme. Details at https://github.com/phase4ground/documents/tree/master/Engineering/Uplink%20Modem/Simulator

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Here we have a new version of the three channel multi multi. Let me try that again.

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Here we have a new version of the three channel uplink simulator, this time, we're using the poly phase, synthesizer block to combine the signals, so three signals going through their conversions modulation.

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Now we're resampling them down to just the bandwidth that they occupy a 12.5 kilohertz channel and then the polyphase synthesizer takes three of them in and makes a four channel wide thing. So 50 kilohertz wide, then we're resampling up from 50 kilohertz to the two actually we're down to uh just over one.

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What's my sample right there is it still two megahertz yeah.

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Two megahertz increased buffer size for performance, and so let's play it.

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I removed the the time display because it wasn't really showing anything: here's our three channels with nice square edges and.

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Get the different speakers.

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Now, once we have the polyphase filter bank in place for combining them, it's easy to combine more and more channels. So the next thing we tried was combining nine channels.

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So, let's switch to the nine channel. This is the same thing. Only there's nine here you can't see them all off the bottom of the screen and a 10 channel poly phase synthesizer.

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So one interesting thing here is that I've changed the rational resamplers so that the numerator and denominator are calculated instead of entered manually.

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Now we've got nine signals.

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That one appears to be silent. I wonder why.

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Maybe here's some kelly k-e-w-l-y back in yards.

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It's silent well that needs to some investigating, but we have nine channels here all being transmitted in parallel.

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You may hear some glitches in the audio. There seems to be some case in which the cpu is getting overloaded, so we're already reaching the point where the flow graph can't do it all in real time. The intention is to run it all offline and then just play back the symbols when we're done.

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Notice, there's a tone interfering with that channel.

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We've reduced the amplitude of the interference signal by moving the radios around and that seems to have been sufficient to cause the problem.

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