How to maximize Conn CTE packet rate on nRF5340?

RE: How to maximize Conn CTE packet rate on nRF5340?

cheng — Wed, 21 Jan 2026 08:40:07 GMT

Thanks! Now I understand where its limitations come from.

RE: How to maximize Conn CTE packet rate on nRF5340?

tesc — Tue, 20 Jan 2026 13:02:26 GMT

Hi,

[quote user="cwdao"]Is this a limitation of the SDK, or a limitation of the BLE specification?[/quote]

As is, the SoftDevice Controller responds with LL_CTE_RSP on the next connection event, not the current one. This has to do with implications for the complexity of the scheduler. According to the Bluetooth specification, the response to a link layer procedure can be sent in either the same or during a later connection event. Hence the delay is not a limitation of the specification, but implementation specific to the SoftDevice Controller. This does mean one connection event of latency compared to the maximum possible according to the specification, but it is at the same time well within the specifications.

Further, also according to the Bluetooth specification, the CTE_Request_Interval parameter, which is what is set here for the device requesting CTE, is a suggestion (not a hard requirement). In the case of periodic operation (non-zero value), "the procedure is initiated every CTE_Request_Interval. However, the Controller may delay initiating the procedure beyond the requested interval (e.g., in order to prioritize other activities.)" Ref. Vol 4, Part E, 7.8.85 LE Connection CTE Request Enable command.

From what I can tell the SoftDevice Controller implementation will send requests every connection event as requested (to the extent allowed by the Bluetooth specification with respect to overlapping procedures etc.) This means the SoftDevice Controller as a requester acts as quickly as permitted by the Bluetooth specification, and as a responder responds on the following connection event.

Regards,
Terje

RE: How to maximize Conn CTE packet rate on nRF5340?

cheng — Mon, 19 Jan 2026 13:27:19 GMT

Hi tesc,

No need to apologize—no worries. This forum isn’t an instant-messaging tool.

I’m using Nordic’s sample:
https://github.com/nrfconnect/sdk-nrf/tree/main/samples/bluetooth/direction_finding_central

I use an nRF5340 as the central, and an nRF54L15 and nRF5340 as peripherals.

In this program, the CTE interval is specified by bt_df_conn_cte_req_params. The interval field is described as: if set to 0, the CTE runs only once; if non-zero, it runs periodically with the configured interval. Therefore, the minimum value I can set is 1. From my observations, this means I receive one CTE packet every 1 connection interval.

As far as I understand, connection-based CTE should be able to complete the request and the CTE response within a single connection interval. In other words, when I set the connection interval to 10 ms, I would like to receive one CTE every 10 ms; however, with the current configuration, I can only receive a CTE at best every 20 ms. Is this a limitation of the SDK, or a limitation of the BLE specification?

Best,
Cheng

RE: How to maximize Conn CTE packet rate on nRF5340?

tesc — Mon, 19 Jan 2026 12:07:53 GMT

Hi,

I am sorry for the delays. We are looking into your latest question about CTE happening every other connection interval. Which BLE controller are you using, the SoftDevice Controller or the Zephyr controller?

Regards,
Terje

RE: How to maximize Conn CTE packet rate on nRF5340?

cheng — Wed, 31 Dec 2025 10:41:19 GMT

Hi,
Thanks you! I tried this parameter and it worked. I really appreciate it!

I have one more question about the CTE update frequency. I noticed that when I set the BLE connection interval to 50 ms, I don’t receive a CTE extension packet every 50 ms. Instead, it looks like the SDK requests a CTE in one connection event, and the peripheral sends the CTE in the next event.

Is it possible to configure it so that the CTE request and the CTE transmission happen within the same connection event each time? If so, then with a 50 ms interval the central should be able to receive a CTE every 50 ms.

RE: How to maximize Conn CTE packet rate on nRF5340?

Kenneth — Mon, 29 Dec 2025 13:55:35 GMT

Hi,

Try to disable CONFIG_BT_GAP_AUTO_UPDATE_CONN_PARAMS.

Kenneth