Short range on BLE Mesh app and rapid RSSI decay

[Santiago Castellano]

Hi everyone,
My teammates and I are currently developing a BLE Mesh–based application. At this stage, we’ve run range tests to verify connectivity performance. As a baseline, we used Nordic’s Mesh Chat sample to test the range between two nodes.

We set up two nRF52840 DKs, increased the SoC transmission power by setting CONFIG_BT_CTLR_TX_PWR_PLUS_8=y, logged RSSI values, and sent messages over increasing distances until we were unable to receive them. With this setup, we achieved a maximum transmission distance of about 240 meters, which met our expectations. Based on that, we proceeded to build our custom BLE Mesh app. However, when performing the same test on our custom app, we observed a much shorter range—around 15 meters—and a rapid drop in RSSI. Our custom app also sets CONFIG_BT_CTLR_TX_PWR_PLUS_8=y.

Sidenotes:

• Our custom app differs from Mesh Chat in some aspects regarding app logic:
  • There are two types of nodes. A central node and several peripheral nodes. 
  • Provisioning is performed by a DK (central node).
  • Peripheral nodes publish lightness and sensor values to the central node.
  • Nodes are made up of 3 elements with different models.

• The Mesh Chat range test was performed with the nRFConnect SDK v.2.9.0. Our app was built with v.2.8.0 of the SDK.

Peripheral node composition:

• Element 0:
  • Configuration Server
  • Health Server
  • Lightness Server
  • Sensor Server
  • Scheduler Server
  • Time Server
  • Location Server
• Element 1:
  • Level Server
• Element 2: 
  • Level Server

Central node composition:
The central node is composed of the equivalent client models.

Aside from these design and version differences, we haven’t identified any apparent reason for the drastic reduction in range.

• What could be causing such a significant decrease in transmission range?
• Are there any additional KConfigs that might be affecting radio performance?
• Could the SDK version difference (2.8.0 vs. 2.9.0) have any impact on BLE Mesh range?

Any insights or suggestions would be greatly appreciated.
Thanks in advance!

[Jennifer Gibbs]

Hello Santiago,

Please excuse my intrusion....

In your custom app, both the Central and Peripheral device(s) are nRF52840's and both are set to 8dB TX power? And, are the Mesh messages being sent from Peripherals to Central w/o response or w/ response?

Thank you,

Jennifer Gibbs

[Santiago Castellano]

Everybody, thanks for your support.

We identified the source of the problem! Our custom firmware had an erroneous configuration for the radio interface on the devicetree. We had set up an overlay node that configured the radio interface to use a Front-End Module through the generic-fem-two-ctrl-pins driver, while our hardware had no PA/LNA. Removing that overlay node resolved the transmission issue. Now our custom FW achieves the same range as Nordic samples, regardless of whether it's running on DKs or custom hardware. 

[Amanda Hsieh]

Happy to see the good news!