Performance Optimization

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Transmit Power

Both esp_ble_tx_power_set and esp_ble_tx_power_set_enhanced can be used to set the transmission power. It is recommended to use the esp_ble_tx_power_set_enhanced function, as it supports a more granular range of power. Different chips support different power ranges, which can be defined in the corresponding macros in the esp_bt.h file.

Power Consumption Optimization

How to optimize power consumption:

  1. Use low power mode

    • Use the Auto Sleep mode to allow the RF and CPU to enter low power mode when idle.

  2. Use an external crystal oscillator

    • Using an external 32.768 kHz crystal can provide a more stable clock source.

    • Helps to improve timing accuracy in low power mode

    • Reduce the power consumption of the internal RC oscillator

  3. Choose appropriate connection parameters

    • Connection Interval: Choose an appropriate time interval based on application requirements. A longer interval can reduce power consumption.

    • Slave Latency: Allows the slave device to skip a certain number of connection events, further reducing power consumption.

    • Supervision Timeout: Set a reasonable timeout period to avoid unnecessary reconnections.

    • Use a larger MTU size to reduce the number of data transfers

  4. Other optimization suggestions

    • Design packet sizes reasonably to avoid fragmented transmission.

    • Use notifications (Notification) instead of indications (Indication) where possible.

    • Utilize the power management features of ESP32, such as dynamic frequency adjustment

  5. Appropriately reduce transmit power

Typical power consumption data:

BLE Power Consumption Data

Chip

Max Current

Modem Sleep

Light Sleep (Main XTAL)

Light Sleep (32KHz XTAL)

ESP32

231 mA

14.1 mA

X

1.9 mA

ESP32C3

262 mA

12 mA

2.3 mA

140 uA

ESP32S3

240 mA

17.9 mA

3.3 mA

230 uA

ESP32C6

240 mA

22 mA

3.3 mA

34 uA

ESP32H2

82 mA

16.0 mA

4.0 mA

24 uA

ESP32C2

130 mA

18.0 mA

2.5 mA

169 uA

Reference example: BLE Low Power Example

Transmission Rate Optimization

BLE 5.0 and above versions support multiple physical layers: - LE 1M UNCODED PHY: Bit transmission rate is 1M bit/s (Physical layer used by BLE 4.2) - LE 2M UNCODED PHY: Bit transmission rate is 2M bit/s - LE CODED PHY: Used for long-distance communication, bit transmission rate is 125 K bit/s or 500 K bit/s

Factors affecting the actual transmission rate:

  1. Protocol layer encapsulation overhead

    • Data needs to be encapsulated layer by layer from the ATT layer to the LL layer.

    • A protocol header (Header) is added to each layer.

    • The Preamble of LE 1M UNCODED PHY is 1 byte

    • The Preamble of LE 2M UNCODED PHY is 2 bytes

  2. Data Length Extension (DLE)

    • BLE 4.0/4.1: Maximum ATT Payload is 20 bytes

    • BLE 4.2/5.0: Supports DLE, maximum ATT Payload can reach 244 bytes

    • It is recommended to configure DLE to its maximum value to improve the utilization rate of single packet data.

  3. Inter-Frame Space (T_IFS)

    • The distance between two air packets on the same data channel is 150 us.

    • This is a fixed time consumption

  4. Connection event and connection interval

    • In each connection event, both parties need to complete a packet transmission and reception once.

    • Even if there is no data, an empty packet still needs to be sent.

    • A connection event can include multiple packet interactions

    • The number of packets is related to the size of the connection interval

Optimization suggestions:

  1. Application layer packet sending method

    • Use write command instead of write request

    • Use Notify instead of Indication

  2. Connection interval optimization

    • Adjust packet size to increase packet fill rate during connection events.

    • Adjust the connection interval appropriately to send more data packets in a single connection event.

  3. Use 2M PHY

    • NimBLE uses the ble_gap_set_prefered_le_phy function to set the physical layer for a specific connection, and the ble_gap_set_prefered_default_le_phy function to set the default physical layer.

    • Bluedroid uses the esp_ble_gap_set_preferred_phy function to set the physical layer of a specific connection, and uses the esp_ble_gap_set_preferred_default_phy function to set the default physical layer.

Reference examples