nRF9160-DK Minimum Required Signal Strength

[Jeff4BLE]

In certain situations, I and customer are having issues connecting to cell towers. The issue seems to be most consistent when the Link Monitor indicates a signal strength of -100 dBM or less. In some areas, I have a customer reporting signal strength of -120 dBm. In that area, a connection is made from time to time, but the connection is quickly lost.

1) What is the expected signal threshold needed to ensure reliable connection to a tower?

2) At what signal strength, according to the link monitor, would we expect not to be able to connect to a tower?

3) Is there anyway of improving this performance with the DK?

4) In the worst case location above, the customer uses T-Mobile as their mobile phone carrier. They have reliable connection with their phones, so the expectation is the nRF9160-DK should have a reliable connection. Please confirm if this may be do to T-Mobile using a lower frequency/band that the nRF9160-DK does not support? Or is this simply because T-Mobile hasn't approved us? The customer has tested with both iBasis and Hologram.io SIMs.

All feedback welcomed.

Cheers,

Jeff

[Håkon Alseth]

Hi Jeff,

1) What is the expected signal threshold needed to ensure reliable connection to a tower?

Greater than the RX sensitivity, which is specified to -108 dBm:

https://www.nordicsemi.com/DocLib/Content/Product_Spec/nRF9160/latest/nRF9160_html5_keyfeatures

 

2) At what signal strength, according to the link monitor, would we expect not to be able to connect to a tower?

I have around -90 to -100 dBm at my desk, and that works fine. However; the specification depends on which band is in use as well:

https://www.nordicsemi.com/DocLib/Content/Product_Spec/nRF9160/latest/_tmp/alta-nRF9160/autodita/RADIOLTE/parameters-rf_spec_rx_m1

 

Parameters are a bit better for NB-IoT:

https://www.nordicsemi.com/DocLib/Content/Product_Spec/nRF9160/latest/_tmp/alta-nRF9160/autodita/RADIOLTE/parameters-rf_spec_rx_nb

 

3) Is there anyway of improving this performance with the DK?

The customer could try with an external antenna for the specific band (returned by AT%XCBAND) that is used in their region, but trying to place the kit in another corner of the building or similar can also have an effect.

 

4) In the worst case location above, the customer uses T-Mobile as their mobile phone carrier. They have reliable connection with their phones, so the expectation is the nRF9160-DK should have a reliable connection. Please confirm if this may be do to T-Mobile using a lower frequency/band that the nRF9160-DK does not support? Or is this simply because T-Mobile hasn't approved us? The customer has tested with both iBasis and Hologram.io SIMs.

 Cat M1 can potentially use other channels or even towers. It depends on the coverage for Cat M1. It's hard to say without knowing the region and how the telecom vendor has deployed M1/NB-IoT in the area.

 

Kind regards,

Håkon

[Jeff4BLE]

Thanks Håkon,

To add an external antenna, I assume this would be accomplished by removing L2, L3, C6 and connecting an antenna to J1?

Cheers,

Jeff

[Håkon Alseth]

Hi Jeff,

 

No, just connect a SWF to SMA interconnect to "J1", and it'll break the connection to the antenna.

It's the same connector as used in the nRF52-DKs. Here's one from murata:

https://www.digikey.no/product-detail/en/murata-electronics-north-america/MXHS83QE3000/490-4982-ND/1775923

Cheers,

Håkon

[Jeff4BLE]

Thank you