Set the bandwidth to 3.75KHz

[con2021]

Hi,

I would like to know how to set the service to NB-IOT Cat NB1,

and how then to set the UL subcarrier spacing to 3,75 KHz,

and how to fix the power to 23 dBm, not to 20 dBm, even in power save mode.

Thanks,

BR

[Heidi]

Hi!

Setting the system mode can be done in your application or through an AT command.

Application:

CONFIG_LTE_NETWORK_MODE_NB_IOT

AT Commands:

AT%XSYSTEMMODE=0,1,0,2

3.75 kHz bandwidth isn't supported in any LTE protocol. The lowest bandwidth supported with NB-IoT is 5 MHz. and the lowest bandwidth support by the nRF9160 SiP with NB-IoT is 10 MHz, on band 13.


For the transmission power, the closest thing we have is %XRFTEST. This is only for RF testing though, and doesn't work after %XPRODDONE is sent to the modem, indicating that the production is complete. 

Best regards,

Heidi

[con2021]

Thanks, I mean how to set the UL subcarrier spacing to 3,75 KHz or 15 KHz. I would like also to know for which subcarrier spacing value the modem uses more current consumption, and for which one we need more data usage to send the same data.

[Heidi]

Hi, I still don't have an answer regarding the UL Carrier spacing.

But here's a more thorough answer regarding fixing the power.

TX Power can't be "fixed" to anything. Not to 20dBm, not to 23dBm. A power class 3 device (which the nRF9160 is) has maximum power of 23 dBm, and that power is used only when operation according to 3GPP spec requires that.

A typical case is when a device far from eNB. Fixed power is not allowed because having one device "yell" very loudly near the eNB would prevent the eNB from hearing the other far-away devices. That's why there is automatic Tx power control required in LTE devices. It also obviously optimizes battery life.

A Power class 5 device would have a max power of 20dBm but we don't support that.

PSM does not affect maximum TX powers.

[con2021]

Thanks a lot for the information. I will wait for the information about how to set the UL subcarrier spacing to 3,75 KHz, or 15 KHz, and which value leads to more current consumption and more data usage. It would be really great and informative if you can push for that answer

[Heidi]

So the user cannot set the UL subcarrier spacing. It's set by the network and signaled in the random access response.

Would you still like me to find out which one leads to more current consumption and data usage?

[con2021]

Is that a limitation in the NRF9160 modem or is it network choice based on the standard? can we expect a possibility in future?

Yes if possible, I appreciate your support. I would like to know if 3.75 or 15KHz lead to more current consumption and/or data usage. We might figure out how to push the BS to set our connection to only one of these techniques

[Heidi]

Hi again, this is a network choice based on the standard. No, I don't think this is subject to change.

With regard to the current and data consumption, the honest answer is we don't know. This depends on your use case; expected data throughput requirements and also radio conditions.

Without solid evidence, we can maybe guess that it is typically more efficient to push data quickly into the air and then go to sleep. At least if the saving won't be spoiled by several retransmissions.

The transmitter is the power-hungry component in the modem and furthermore, the long transmission prevents the modem from going to sleep.