After updating device firmware to version 2.4.1, our asset tracking payloads started dropping location fields intermittently. The MQTT publish pattern looks correct, but we’re seeing null latitude/longitude values in about 15% of messages.
{"deviceId":"TRK-8821","timestamp":1710493380,
"lat":null,"lng":null,"status":"active"}
The firmware publish logic seems to handle GPS timeout differently now. We suspect the Device SDK might not be handling null values properly before publishing. This creates significant data gaps in our tracking dashboard, making fleet management unreliable. Has anyone encountered similar MQTT payload schema issues after firmware updates?
Thanks for the insights. I checked the SDK config and found gpsTimeout was reduced from 60s to 30s in the new firmware. That explains why we’re seeing more null values in areas with poor satellite visibility. How do you handle buffering on the device side when GPS isn’t ready?
Don’t forget to check your MQTT QoS settings too. If you’re using QoS 0, you might be losing messages during brief network drops when the device is trying to get GPS lock. QoS 1 ensures at-least-once delivery which helps with intermittent connectivity issues. We switched to QoS 1 for location data and it reduced our null value rate significantly.
Check your GPS timeout settings in the device SDK configuration. The 2.4.x firmware changed how it handles satellite lock failures. If GPS can’t get a fix within the timeout window, it might be publishing with nulls instead of buffering the message. Look at your device-side retry logic.
We had this exact issue last month. The problem is that the new firmware publishes immediately regardless of GPS lock status, whereas the old version would wait or skip the publish. You need to add validation in your MQTT publish handler to check if location fields are populated before sending. Also review your payload schema - consider making lat/lng optional fields with a ‘gpsValid’ boolean flag so downstream systems know when to trust the data.
I can see you’re hitting multiple issues that compound each other. Let me address all three focus areas systematically:
MQTT Payload Schema:
First, update your schema to include a gpsStatus field that explicitly indicates data validity:
{"deviceId":"TRK-8821","timestamp":1710493380,
"gpsStatus":"no_lock","lat":null,"lng":null}
This makes null handling intentional rather than ambiguous. Configure Watson IoT Platform rules to filter or flag messages where gpsStatus != “valid”.
Firmware Publish Logic:
The 2.4.1 firmware changed from blocking to non-blocking GPS reads. Modify your device SDK configuration:
- Increase gpsTimeout back to 60 seconds for initial lock attempts
- Implement a message queue that buffers up to 50 messages locally
- Add retry logic: attempt GPS lock 3 times with 20-second intervals before publishing with nulls
- Use the Device SDK’s publishWhenReady() method instead of immediate publish()
Device SDK Handling of Nulls:
The SDK’s default behavior now publishes all fields regardless of value. Add pre-publish validation:
if (locationData.lat === null || locationData.lng === null) {
locationData.gpsStatus = "no_lock";
locationData.lastValidLat = deviceState.lastKnownLat;
locationData.lastValidLng = deviceState.lastKnownLng;
}
Implement a device-side state manager that caches the last valid GPS coordinates and includes them as fallback values. This gives your dashboard something to work with while clearly marking the data as stale.
For your 15% null rate, also check if these devices are in specific geographic areas with poor GPS coverage (urban canyons, underground parking). You might need location-specific timeout adjustments or consider adding Wi-Fi/cellular triangulation as a backup positioning method.
Finally, update your Watson IoT Platform device type schema to make lat/lng nullable and add validation rules that trigger alerts when null rates exceed thresholds per device or fleet segment.