Avoid external devices disrupt a Bluetooth connection

RE: Avoid external devices disrupt a Bluetooth connection

Tai — Mon, 25 Mar 2024 21:39:58 GMT

Hi hmolesworth . Sorry for not replying this earlier. Thanks for this tip! We now accepted data loss as long as it's less than 2% of whole data.

RE: Avoid external devices disrupt a Bluetooth connection

hmolesworth — Wed, 28 Feb 2024 04:22:12 GMT

In my testing 75 - 100cm height would degrade performance; maybe test at 1-2m to see if it makes a difference ..

Edit: Worth reviewing this, although short-range OR is not quite the same near-ground can be an issue: testreport

RE: Avoid external devices disrupt a Bluetooth connection

Tai — Wed, 28 Feb 2024 00:14:55 GMT

[quote userid="15146" url="~/f/nordic-q-a/108567/avoid-external-devices-disrupt-a-bluetooth-connection/471009"]If you think interference is an issue, you could confirm the packet loss, crc-error, etc with a sniffer trace: https://www.nordicsemi.com/Products/Development-tools/nrf-sniffer-for-bluetooth-le[/quote]

It's really hard for us to trace it when testing it in the OR. We tried to reproduce it in the benchtop test by moving the device far away the phone app.

[quote userid="15146" url="~/f/nordic-q-a/108567/avoid-external-devices-disrupt-a-bluetooth-connection/471009"]If you are creating a custom PCB, we could help review the design. If so, please create a new private case for the PCB review[/quote]

We're using a third-party one with FCC granted for portable use (body worn).

RE: Avoid external devices disrupt a Bluetooth connection

Tai — Tue, 27 Feb 2024 22:19:04 GMT

[quote userid="65515" url="~/f/nordic-q-a/108567/avoid-external-devices-disrupt-a-bluetooth-connection/471003"]Some thoughts: Trace antenna/aerial behaves poorly; chip antenna/aerial has much better results. Height above ground can affect performance, eg on bench vs on floor (say sole of foot). FDA and other regulatory bodies (used to) frown on using BLE in the OR so clearance may be an issue.[/quote]

Thanks for suggestions! We're using chip antenna, and we boosted Tx power to 8 dBm. With benchtop test, we barely get data drops unless we stress the device really hard (e.g., covering it with many isolated layers, moving it far away the phone app....).

In the OR setup, we currently put our phone app close to the floor and behind other medical equipment while the device is about 75 - 100cm height. Not sure if it affects the device performance.

FYI, as far as I know FDA does not have specific comments or regulations solely dedicated to devices using BLE technology in operating rooms.

RE: Avoid external devices disrupt a Bluetooth connection

Sigurd — Tue, 27 Feb 2024 12:42:54 GMT

If you think interference is an issue, you could confirm the packet loss, crc-error, etc with a sniffer trace: https://www.nordicsemi.com/Products/Development-tools/nrf-sniffer-for-bluetooth-le

By increasing the queue buffer for notifications, then during interference, you could then be able to "buffer" up packets, and get them through once the interference is lower/gone.

If you are creating a custom PCB, we could help review the design. If so, please create a new private case for the PCB review.

RE: Avoid external devices disrupt a Bluetooth connection

hmolesworth — Tue, 27 Feb 2024 12:26:01 GMT

Some thoughts: Trace antenna/aerial behaves poorly; chip antenna/aerial has much better results. Height above ground can affect performance, eg on bench vs on floor (say heel of foot). FDA and other regulatory bodies (used to) frown on using BLE in the OR so clearance may be an issue.

RE: Avoid external devices disrupt a Bluetooth connection

Tai — Tue, 27 Feb 2024 06:20:32 GMT

Hmm, we're developing an IOS application to receive data, and IOS limits number of packets (about 4-6 data packets) being sent for each connection interval. Thus, playing around with those you mentioned won't be much effective.

Any suggestions on grounding/shielding the device to prevent it from interference of other devices?Thanks!

RE: Avoid external devices disrupt a Bluetooth connection

Sigurd — Mon, 26 Feb 2024 15:35:35 GMT

Hi!

[quote user="Tai Le"]From what I understand, this parameter is linked with connection interval, deciding how many packets it can be transmitted during each connection interval.[/quote]

Correct, it also indirectly increase the queue buffer for notifications.

Alternatively, you can try set the buffer size directly.

    ble_cfg_t ble_cfg;
    memset(&ble_cfg, 0, sizeof ble_cfg);
    ble_cfg.conn_cfg.conn_cfg_tag           = APP_BLE_CONN_CFG_TAG;
    ble_cfg.conn_cfg.params.gatts_conn_cfg.hvn_tx_queue_size = 50;
    err_code = sd_ble_cfg_set(BLE_CONN_CFG_GATTS, &ble_cfg, ram_start);
    APP_ERROR_CHECK(err_code);

(should be added to ble_stack_init() in main.c )

RE: Avoid external devices disrupt a Bluetooth connection

Tai — Fri, 23 Feb 2024 18:15:55 GMT

Thanks for reply, Sigurd. I've read many posts regarding NRF_SDH_BLE_GAP_EVENT_LENGTH parameter. I'm still confused how much should I increase this parameter? From what I understand, this parameter is linked with connection interval, deciding how many packets it can be transmitted during each connection interval. Since my connection interval is 7.5 ms, I've set NRF_SDH_BLE_GAP_EVENT_LENGTH to 6 (6 x 1.25ms = 7.5ms), covering 100% transmission bandwidth.

I noticed its value is set to 400 (400 x 1.25ms = 500ms) with the following setup in the example of long-range demo. It seems this number is based on the max acceptable connection interval? Thanks!

#define CONN_INTERVAL_MIN               (uint16_t)(MSEC_TO_UNITS(7.5, UNIT_1_25_MS))    /**< Minimum acceptable connection interval, in 1.25 ms units. */
#define CONN_INTERVAL_MAX               (uint16_t)(MSEC_TO_UNITS(500, UNIT_1_25_MS))    /**< Maximum acceptable connection interval, in 1.25 ms units. */

RE: Avoid external devices disrupt a Bluetooth connection

Sigurd — Fri, 23 Feb 2024 13:14:17 GMT

Hi!

You could try to increase the NRF_SDH_BLE_GAP_EVENT_LENGTH in sdk_config.h