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CC1350: Sensor Periodically Disconnects from Collector

Part Number: CC1350

Hello Ti,

Context:

I am deploying 10 CC1350 sensors to 1 CC1350 collector, deployed in a non-beacon star topology utilizing the simplelink 4.x SDK, APIMAC_STD_US_915_PHY_1. Sensors utilize a push based model, with reporting interval of 1 minute. Polling occurs every 90 seconds. The devices are placed less than 15m from the collector

Problem:

I am occasionally seeing one sensor disconnect from the network. It is not consistently the same sensor, and appears to rotate between a few. I have sniffed the traffic. It appears the disconnecting sensor does not receive an ACK, and rapidly tries to retry the request, leading to itself disconnecting. It's unclear why the sensor is not receiving an ACK. Once disconnected, I observe the sensor sending beacon requests. These requests are not always answered by the collector, causing further delay in reconnecting. The sensor typically reconnects after 10 or so minutes.

I have tried increasing the MAC TX and RX queue, but did not see improvement. 

I'm looking for guidance on how to diagnose the root cause of this issue. Is this an interference issue? 

Potentially related:

https://e2e.ti.com/support/wireless-connectivity/sub-1-ghz/f/156/p/860083/3182600?tisearch=e2e-sitesearch&keymatch=CONFIG_SCAN_DURATION#3182600

Update:

I've confirmed the disconnect is being caused by macAckFailures, leading to syncLoss. From the Sensor_msgStats, I can see a packet loss of roughly 1%.

Given this, a new question:

From configuration, I see a few parameters that may make sense to change:

- CONFIG_MAC_MAX_CSMA_BACKOFFS # increasing this I believe will better mitigate the collisions I'm observing between two sensors

- CONFIG_MIN_BE  

- CONFIG_MAX_BE   

- CONFIG_MAX_DATA_FAILURES # increase this will allow more requests to fail before triggering a syncLoss

Open questions:

- What is the cause of the beacon request not being responded to by the collector?

- Is there a better way to mitigate packet loss?

- My understanding of CSMA/CA is the device will wait to transmit until the channel is idle. As the device is transmitting, but failing acks, this doesn't seem it would help. Is this a correct thought?