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Frequency Hopping Added

A project log for QMesh: A LoRa-based Voice Mesh Network

Developing a synchronized, flooded mesh network to carry codec2-encoded voice over LoRa

Dan FayDan Fay 12/01/2020 at 03:520 Comments

I decided to play around with the CAD feature on the SX126X a bit, and developed a simple scanning-based frequency hopping scheme. As a result, QMesh can now do a hybrid spread-spectrum scheme (CSS+FHSS).

Some things I learned along the way:

1. The CAD has a lot of false positives. Doing a "double CAD" helps reduce this issue. Basically, do a CAD, and if it comes back positive, do a CAD+Rx for the final receive.

2. The CAD starts the oscillator "fresh". This means that, with a TCXO, the CAD will not start until the programmed TCXO stabilization delay completes. I may consider cutting the stabilization time for CADs, as a bunch of correlators just trying to detect some chirps probably doesn't need the TCXO's full accuracy.

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