Questions about Direction finding connectionless beacon setting parameters

RE: Questions about Direction finding connectionless beacon setting parameters

Elfving — Wed, 29 May 2024 07:41:11 GMT

In general I think it helps to transmit on 2M PHY instead of 1M, and choose an extended adv interval larger than the periodic one so that the periodic events won't be kicked out. However, in this case scheduling conflict typically won't be an issue. As long as the interval duration has sufficient airtime for all the chained PDUs and the two interval are multiples of each other then there should not any problem.

[quote user="Sho_Ri"]According to the default settings of the Beacon example, the intervals of periodic advertising is 1 second, and each periodic advertisement carries 5 CTE packets. Therefore, I assume that in one minute, 300 CTE packets are sent.[/quote]

The periodic adv interval is set between [BT_GAP_ADV_SLOW_INT_MIN, BT_GAP_ADV_SLOW_INT_MAX], and if you look up those values in gap.h, it says they are 1s and 1.2s respectively. However, those values are for extended advertising with a bit interval of 0.625ms. For periodic advertising, the bit interval is 1.25ms. That is why the actual periodic adv interval becomes 2.4s and why you are seeing 125 packets with CTE per minute (60s / 2.4s * 5 = 125). To fix this, use the values starting with BT_GAP_PER_ADV_ as they are calculated with the 1.25ms bit interval.

[quote user=""] In addition, is there a fixed time interval between [AUX SYNC IND] and [AUX CHAIN IND], or is there no time interval?[/quote]

yes, CONFIG_BT_CTLR_ADV_SYNC_PDU_BACK2BACK_AFS=300 the chain PDUs are placed with 300 us aux_offset

Regards,

Elfving

RE: Questions about Direction finding connectionless beacon setting parameters

Sho_Ri — Mon, 27 May 2024 05:15:40 GMT

Hi, Elfving

Thanks for your reply, it's very useful to me.
For the first question, I tested it under the following conditions:
1. Use two nrf52833-DKs, one as a Beacon tag and the other as a locator and connected to a 4X4 antenna array.
2. Use the direction_finding_connectionless_tx and direction_finding_connectionless_rx examples, and use the default settings.
3. In the electromagnetic anechoic chamber, set up Beacon tag in 9 different positions with a distance of 1 to 1.5 meters from the locator. Each position stayed for more than 2 minutes.
According to the default settings of the Beacon example, the intervals of periodic advertising is 1 second, and each periodic advertisement carries 5 CTE packets. Therefore, I assume that in one minute, 300 CTE packets are sent.
When I counted the logs of the locator, I found that as shown in the figure below, about 120 CTE data packets can be received in every locations, and the reception rate was about 40%.
I would like to ask, why is the reception rate in the electromagnetic anechoic chamber only 40%? Are there many CTE packets being ignored during the reception process?

For the second question, I would also like to know how the settings of the extended advertising interval and periodic advertising interval will affect the AoA accuracy calculation？ In addition, do you have any relevant suggestions on how to avoid scheduling conflicts between the two intervals?

Regards,

Elfving

RE: Questions about Direction finding connectionless beacon setting parameters

Elfving — Thu, 23 May 2024 06:51:35 GMT

Hello again,

For the first question, if CTE_COUNT is set to 5, the AUX_SYNC_IND and the first four AUX_CHAIN_IND packets in each periodic advertising event will contain CTE. The frame space between AUX_SYNC_IND and AUX_CHAIN_IN is defined by T_MAFS and it is implementation-specific. By core spec, the minimum T_MAFS is 300 us (Core spec Vol 6, Part B, 4.1.2 Minimum AUX Frame Space), and for the softdevice controller which we use in NCS, this value is 330 us.

For the second question, the two intervals should be independent, and depending on the data length and which PHY it is on, there could be scheduling conflicts. Is that what you are asking about how they affect each other?

Regards,

Elfving

RE: Questions about Direction finding connectionless beacon setting parameters

Sho_Ri — Wed, 22 May 2024 00:11:53 GMT

Hi, Elfving

Thank you for your contact and look forward to replying.

Regards,

Sho

RE: Questions about Direction finding connectionless beacon setting parameters

Elfving — Tue, 21 May 2024 14:24:43 GMT

Hello Sho, and thank you for your patience.

Both the 17th and Pentecost Monday are public holidays in Norway, which has unfortunately lead to some delays, as well as a rather high workload at the moment. As always, please contact your local RSM if you require more urgent assistance than what is provided.

I've forwarded your question to the relevant R&D team, and will let you know once I hear from them.

Regards,

Elfving