MultiNav Pro+ BLE - latency characteristics at long range, anyone measured?

Douglas Young•July 25, 2026

Been working on a remote sensing application where I'm pushing telemetry over the BLE link at somewhere around 30-40km and I'm trying to get a realistic picture of what round-trip latency actually looks like at that distance. I get that BLE isn't really designed with ultra-low latency in mind, but I'm trying to figure out if the delay I'm seeing is mostly connection interval overhead, propagation delay, or something else going on in the stack. At 40km the raw propagation delay should be like 0.13ms which is basically nothing, so I'm guessing the connection interval is dominating everything.

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Adam•July 25, 2026

@Douglas Young yeah your propagation math is right — 0.13ms is essentially irrelevant at that range, you're not fighting physics, you're fighting the connection interval scheduler.

The dominant latency source on the STM32WB07 stack is almost certainly the connection interval. If you're running with a default CI somewhere in the 45-100ms range, your round-trip floor is already 90-200ms before you factor in any retransmissions. At 30-40km you're going to have a higher packet error rate than close range, which means the link layer retry mechanism kicks in more often — each retry burns another full connection interval, so your average latency will be higher and your variance will be wider compared to shorter links.

The other thing worth checking is whether you're seeing any throughput-related queuing delay. At 2Mbps the raw pipe is fast, but if your telemetry bursts are hitting the notification queue faster than the CI can drain them, you'll see latency creep up as packets stack. Worth logging queue depth if you can.

If you share what connection interval you're currently negotiating and roughly what your packet error rate looks like at that range, I can probably help you narrow it down more specifically — there's also a firmware discussion started a while back in the Dev Hub around CI tuning for the WB07 that had some useful numbers in it.

Julia Chavez•July 25, 2026

At 40km you're looking at ~0.13ms of raw propagation so that's basically a rounding error compared to your connection interval overhead - BLE connection intervals are typically 7.5ms minimum and in practice most stacks run 20-100ms, so that's almost certainly where your latency is living. If you haven't already, try tuning the connection interval parameters directly and see if your peripheral lets you negotiate something tighter, that'll tell you pretty quick whether the stack is the culprit or if there's something else going on.