How get the RF center frequency in Zephyr

[upupsky]

1. in the file "Core_v5.2.pdf"

"The LE system operates in the 2.4 GHz ISM band at 2400-2483.5 MHz. The

LE system uses 40 RF channels. These RF channels have center frequencies

2402 + k * 2 MHz, where k = 0, ..., 39."

2. in the file "hci.c", in zephyr

Question: How can I get the 'AuxPtr chan_idx', in period adv? It seems not in "struct bt_le_scan_recv_info *info",not in"struct bt_le_per_adv_sync_recv_info *info",not in "struct bt_le_per_adv_sync *sync".

thks.

 

[Edvin]

Hello,

I am not sure I understand exactly what you mean. Where do you want to see what channel is being used? Are you scanning or advertising? Are you using the hci_uart sample? Or do you intend to use a standalone Bluetooth LE device? The reason I ask is that I don't think the hci.c is used in standalone BLE devices. Only in the hci_uart sample. 

BR,

Edvin

[upupsky]

I used project "ncs\v1.8.0\nrf\samples\bluetooth\direction_finding_connectionless_rx", the scanning. for aoa algorithm, I need the RF Center frequency, such as 2402MHz.

 

[Edvin]

At least from what I have found so far, it doesn't look like you can see the advertising channel in an advertising report. Why do you need to know the channel/frequency?

Best regards,

Edvin

[upupsky]

when I do AoA algorithm, the frequency is important for me to calibrate tag (x,y).

thanks.

[Edvin]

Hello,

Unfortunately, it looks like it isn't possible to extract the channel from an advertising report event. That information is not passed on from the Softdevice Controller. I am not familiar with the details of AoA, but seeing as this is working for others, are you sure that you really need to know the frequency of the channel being used? 

I understand that the time difference between the samples on different antennas are dependent on the channel being used, but seeing as the difference between the advertising channels are 80 MHz on a 2.4 GHz frequency band. So if you assume a frequency of 2440 (middle channel) you will only be 40/4240 = 0,016 ( = 1.6%) offset. I think that is well within the accuracy of AoA itself (but I don't remember the accuracy from the specification right now). 

Please prove me wrong, but I am trying to understand how other have done this, when the channel number isn't available from the softdevice controller. Currently, my conclusion is that it really doesn't matter, within the accuracy of the AoA specification.

Best regards,

Edvin