I-CUBE-LRWAN (AT-SLAVE) downlink issue for CMWX1ZZABZ-091

[JGuembe.1]

Hello!

We have developed a LoRaWAN network using as end-nodes MURATA CMWX1ZZABZ-091 module (with a ST microprocessor inside).

For this mode device, we use “I-CUBE-LRWAN” – (Lorawan Software Expansion from STMicroelectronics) and the code related to AT_SLAVE, to control this module via another MCU.

Communication is implemented in both directions:

    - Uplink (from node to gateway)

    - Downlink (from gateway to node).

We have experimentally verified that the distance achieved in the uplink direction is much higher than the distance achieved in the downlink.

Analyzing the rssi values at the gateway and at the node device, we have detected a difference of approx 30dB (-70dBm at the gateway and approx -100dBm at the device). It matches with the experimental behavior, where the downlink shows worse behavior than the uplink.

We have also checked that both the gateway and the MURATA module are configured to transmit with the same power (+14dBm), and that the sensitivity of both devices is also similar (between - 120dBm and -125dBm).

In the SX1276SetOpMode function from the file sx1276.c, we have added the RFLR_OPMODE_RECEIVER_SINGLE condition, so:

• Without the condition, signal difference between downlink and uplink was 30dB.
• Adding the condition, the difference between downlink and uplink is quite satisfactory, but we still detect a difference of 6dB.

• Has anyone had a similar problem?
• Is there any other code we should modify in order to reach equal downlink and uplink rssi level?

Thank you in advance and best regards,

[Issamos]

Hello @JGuembe.1 

I think this can be related to the difference of length between the two packets (Uplink and Downlink). Also, the power used in both end_node and Gateway can be cause of this difference.

Best regards.

II

[Tesla DeLorean]

Why would they be entirely symmetrical? Likely using different IC's, RF paths and antennas.

Check the gain and current limiting settings.

[JGuembe.1]

We detected a posible issue in the AT_SLAVE firmware of "I-CUBE-LRWAN" Software Expansion Pack.

In the SX1276SetOpMode function from the file sx1276.c, we have added the RFLR_OPMODE_RECEIVER_SINGLE condition, so:

• Without the condition, signal difference between downlink and uplink was 30dB.
• Adding the condition, the difference between downlink and uplink is quite satisfactory, but we still detect a difference of 6dB.

• Is correct the modification?
• Is there any other code we should modify in order to reach equal downlink and uplink rssi level?