MultiNav Pro+ BLE - does link quality degrade gracefully or just drop?

@Joseph Gonzalez yeah this is exactly the right question to be asking before you deploy rather than after — good instinct.

 

The module does expose RSSI readings you can pull in firmware, so you're not flying blind as the link gets marginal. In practice what you'll see is a gradual degradation — RSSI climbing toward the noise floor, packet retries increasing — before you actually lose the connection. It's not a hard cliff in normal conditions, but the "graceful" part depends a lot on your environment. Line of sight with a slow-moving vehicle on flat terrain is about as favorable as it gets, so you should have a decent warning window.

 

What I'd suggest is building a simple RSSI threshold into your firmware logic — flag a warning state when you hit, say, -90 dBm or wherever you find the retries start climbing, so your application layer knows to reduce data rate or switch to essential-only telemetry before the link actually drops. The AI Firmware Builder in the Dev Hub is honestly pretty useful for scaffolding exactly this kind of conditional logic if you want a starting point rather than writing it from scratch.

 

If you want to share more about your data rate requirements and what you're actually transmitting, I can give you more specific advice on how aggressive to be with the threshold.

Yeah the MultiNav Pro+ does expose RSSI through the BLE stack so you can absolutely poll that in firmware and use it as an early warning before the link degrades too far - I've been doing exactly this on a similar outdoor tracking project and it gives you enough headroom to trigger a fallback behavior before you actually lose the connection. That said, from what I've seen the drop-off when you're really pushing range can still be pretty abrupt depending on terrain and interference, so I'd reccomend setting your threshold conservatively rather than waiting until RSSI is already in the basement.

Seconding what Michael said about conservative thresholds - I'd also suggest logging RSSI over a few test runs along your actual route before you set that value in stone, because the rolloff profile can vary a lot depending on whether you've got line of sight or any obstacles in the way. On my setup I paired the RSSI polling with a simple moving average to smooth out the noise so I wasn't triggering fallback on a momentary spike.

Good points all round - one thing worth adding is that the MultiNav Pro+ also has a connection interval you can tune, and tightening that up when you're operating near the edge of range can help you catch degradation faster before the link actually drops. Doesn't replace the RSSI threshold approach but it complements it nicely, especially if your vehicle speed means the signal environment is changing quickly.

Solid thread - one more thing to layer in if you haven't already is using the connection event callbacks to track consecutive missed events alongside your RSSI averaging, because sometimes the signal looks ok on paper right before it falls apart and having that second signal gives you an earlier nudge to bail to your fallback. Saved me from a few ugly disconnects on a similar build.

One thing I haven't seen mentioned yet - if you can swing it, also keep an eye on the TX power level the module is reporting alongside RSSI, because watching those two diverge can give you a pretty early read on whether you're heading into a multipath situation vs just straight distance loss, and those two scenarios can call for pretty different fallback strategies. Caught me off guard the first time I didn't account for it.

Really solid thread - just want to +1 Karen's point about TX power vs RSSI divergence, that's caught me out before too. One thing I'd add from my own testing is that if you're building in a fallback mode, consider making the re-acquisition logic a bit hysteretic so you don't end up ping-ponging in and out of fallback at the edge of range - gives the system a chance to actually stabilize before you hand control back.

Thomas's hysteresis point is really important and something I burned a few hours learning the hard way - I'd suggest making the re-entry threshold at least 6-8dB above where you bailed out, because anything tighter and you're basically just fighting the fade margin. Also worth logging the timestamps on those fallback transitions during your range testing so you can see if the ping-ponging pattern correlates with specific terrain or multipath zones you can anticipate in firmware.

Late to this but just wanted to say the hysteresis + timestamp logging combo Sarah mentioned is genuinely the move - I did something similar on a drone telemetry build and being able to replay exactly when and where the transitions happened made it way easier to tune the thresholds against real-world terrain rather than just guessing in the lab. Also seconding the RSSI averaging from earlier in the thread, raw RSSI on its own is noisy enough that you'll drive yourself crazy reacting to every blip.