typical throughput in BLE 2M phy

[klaus1234]

Hi

my project is about live streaming of physiological data at high sampling rates over BLE. 

On the receiver side I have a Laptop(Windows/Mac/Linux) and not a NRF dongle. 

What are typical throughput values when connecting to laptops (not havong NRF modules on central/perpheral side)?

I am using:

• 2M PHY
• Connection interval: 7.5 ms
• 2M phy
• MTU: 247 bytes
• Total characteristics used: 1 (for notify)

On my windows machine I only get ~820 kbps. Is that normal? What are typical datarates? 

Here is my config file:

# Enable the UART driver

CONFIG_UART_ASYNC_API=y

CONFIG_NRFX_UARTE0=y

CONFIG_SERIAL=y

CONFIG_UART_ASYNC_API=y

CONFIG_GPIO=y

# CONFIG_POWEROFF=y

## CONFIG_PM_DEVICE=y

CONFIG_CONSOLE=y

CONFIG_UART_CONSOLE=n

CONFIG_HEAP_MEM_POOL_SIZE=25000

CONFIG_BT=y

CONFIG_BT_PERIPHERAL=y

CONFIG_DK_LIBRARY=y

CONFIG_MAIN_STACK_SIZE=10800

#4096

CONFIG_SYSTEM_WORKQUEUE_STACK_SIZE=10800

# Console

CONFIG_EARLY_CONSOLE=n

CONFIG_CONSOLE=y

CONFIG_UART_CONSOLE=n

CONFIG_STDOUT_CONSOLE=n

CONFIG_PRINTK=n

CONFIG_USE_SEGGER_RTT=y

CONFIG_RTT_CONSOLE=y

CONFIG_LOG_BACKEND_RTT=y

CONFIG_LOG=y

CONFIG_LOG_MODE_DEFERRED=n

CONFIG_LOG_BACKEND_UART=n

CONFIG_BOOTLOADER_MCUBOOT=y

CONFIG_NCS_SAMPLE_MCUMGR_BT_OTA_DFU=y

CONFIG_BT_GATT_CLIENT=y

CONFIG_BT_CENTRAL=n

CONFIG_BT_MAX_CONN=1

CONFIG_BT_MAX_PAIRED=1

CONFIG_BT_GATT_DM=y

CONFIG_BT_DEVICE_NAME_DYNAMIC=y

# Extended Data and Max Throughput

CONFIG_BT_USER_DATA_LEN_UPDATE=y

CONFIG_BT_USER_PHY_UPDATE=y

CONFIG_BT_GAP_AUTO_UPDATE_CONN_PARAMS=y

# Allow for large Bluetooth data packets.

CONFIG_BT_L2CAP_TX_MTU=247

CONFIG_BT_BUF_ACL_RX_SIZE=251

CONFIG_BT_BUF_ACL_TX_SIZE=251

CONFIG_BT_CTLR_DATA_LENGTH_MAX=251

CONFIG_BT_CTLR_PHY_2M=y

CONFIG_BT_CTLR_SDC_MAX_CONN_EVENT_LEN_DEFAULT=4000000

CONFIG_BT_PERIPHERAL_PREF_TIMEOUT=500

CONFIG_BT_PERIPHERAL_PREF_MIN_INT=6

CONFIG_BT_PERIPHERAL_PREF_MAX_INT=6

CONFIG_BT_CTLR_TX_PWR_PLUS_8=y

CONFIG_REBOOT=y

CONFIG_BT_AUTO_PHY_UPDATE=n

CONFIG_BT_PHY_UPDATE=y

CONFIG_BT_L2CAP_TX_BUF_COUNT=40

CONFIG_BT_BUF_ACL_TX_COUNT=40

# Enable GATT Write Command (Write Without Response) optimization

CONFIG_BT_CONN_TX_MAX=40

# Increase the number of Rx buffers for the controller

CONFIG_BT_BUF_EVT_RX_COUNT=40

# Ensure the controller has enough memory allocated for maximum TX/RX payloads

CONFIG_BT_CTLR_RX_BUFFERS=40

[Priyanka]

Hi,
Your observed ~820 kbps on Windows is actually a reasonable result when connecting to a laptop (non-Nordic central).
It is below the best-case Nordic-to-Nordic numbers, but laptop Bluetooth stacks often cap throughput because you do not control the central’s controller scheduling, connection-event length, number of packets per event, buffering, driver behavior, or OS GATT API overhead.

Please refer the following:

https://devzone.nordicsemi.com/guides/nrf-connect-sdk-guides/b/software/posts/building-a-bluetooth-application-on-nrf-connect-sdk-part-3-optimizing-the-connection#mcetoc_1ftnicups1 

The ~2 ms idle period at the end of each connection event (reserved by the central) doesn't scale with connection interval, so shorter intervals have lower radio duty cycle efficiency. A laptop's BLE host stack also introduces additional overhead compared to a Nordic dongle.

I would suggest you to try a longer connection interval, such as 15 ms, 30 ms, or 45 ms, not only 7.5 ms. Use one packed binary notification stream, as you are doing. Avoid multiple characteristics for parallel data unless you have a strong reason.

-Priyanka