esp_ble_tx_power_set has no effect

espdude
Posts: 4
Joined: Fri Jul 27, 2018 4:21 am

esp_ble_tx_power_set has no effect

Postby espdude » Fri Jul 27, 2018 4:46 am

Hi All,

I am playing with esp_ble_tx_power_set API to set maximum BLE TX power during advertisement and communication.
I run my code on WROVER-I module acting as BLE peripheral, latest IDF version, however I observe the issue for at least six months with latest IDF version.

What I have noticed is that changing esp_ble_tx_power_set has no effect on advertised TX level and also very limited (if any) effect on BLE connection distance (it is always around 10 meters indoors).

In my esp_ble_adv_data_t I set .include_txpower = true, and can observe advertised TX power using NRF Connect, however it is always -21dbm regardless of the value passed to esp_ble_tx_power_set.

Also, as I mentioned I do not notice any significant difference between ESP_PWR_LVL_P9 and ESP_PWR_LVL_N12, while I expect it to be clearly noticeable by communication distance.

Below is the code I use to change the TX level. Use both together with WiFi and without it. Can anyone suggest if this API has bugs, should I do it differently, or my expectations are just wrong?

Code: Select all

	esp_err_t ret;
    ret = esp_bt_controller_init(&bt_cfg);
    if (ret) {
        ESP_LOGE(BLE_TAG, "%s initialize controller failed\n", __func__);
        return;
    }
    ESP_LOGI(BLE_TAG, "%s initialize controller success\n", __func__);

    ret = esp_bt_controller_enable(ESP_BT_MODE_BLE);
    if (ret) {
        ESP_LOGE(BLE_TAG, "%s enable controller failed\n", __func__);
        return;
    }
    ESP_LOGI(BLE_TAG, "%s enable controller success\n", __func__);

    ESP_LOGI(BLE_TAG, "%s Successfully set BLE Tx power level\n", __func__);

    ret = esp_bluedroid_init();
    if (ret) {
        ESP_LOGE(BLE_TAG, "%s init bluetooth failed\n", __func__);
        return;
    }
    ESP_LOGI(BLE_TAG, "%s init bluetooth success\n", __func__);

    ret = esp_bluedroid_enable();
    if (ret) {
        ESP_LOGE(BLE_TAG, "%s enable bluetooth failed\n", __func__);
        return;
    }
    ESP_LOGI(BLE_TAG, "%s enable bluetooth success\n", __func__);

    ret = esp_ble_tx_power_set(ESP_BLE_PWR_TYPE_DEFAULT, ESP_PWR_LVL_P9);
    if (ret) {
        ESP_LOGE(BLE_TAG, "%s Unable to set BLE Tx power level\n", __func__);
        return;
    }
    ESP_LOGI(BLE_TAG, "%s Successfully set BLE Tx power level\n", __func__);

    ret = esp_ble_tx_power_set(ESP_BLE_PWR_TYPE_ADV, ESP_PWR_LVL_P9);
    if (ret) {
        ESP_LOGE(BLE_TAG, "%s Unable to set BLE Tx power level\n", __func__);
        return;
    }

User avatar
billiam
Posts: 4
Joined: Tue Jul 24, 2018 8:20 pm

Re: esp_ble_tx_power_set has no effect

Postby billiam » Mon Jul 30, 2018 4:41 pm

My code looks just like yours.

I am seeing a 20dbm difference in advertising RSSI using a ble monitor app between LVL_P7 and LVL_N14. I have not tested transmit power when connected. I am disappointed that N14 is as low as it can go. It is still, at N14, a stronger signal (rssi=-70) at 4 feet than any of my test sensors and I am kind of desperate to (further) reduce power consumption.

My range is much better than 10M using defaults. More like 100M through walls. I am using a WROVER-KIT.

genedyne
Posts: 15
Joined: Wed Jun 06, 2018 12:47 pm

Re: esp_ble_tx_power_set has no effect

Postby genedyne » Thu Aug 16, 2018 4:05 pm

I'm seeing the same as you describe.
I set the 'default' power for advertising using:

Code: Select all

esp_ble_tx_power_set( ESP_BLE_PWR_TYPE_DEFAULT, ESP_PWR_LVL_P9 );
This function is called prior to starting advertisment, and the flag is set in advertising data to include Tx power. According to esp_ble_power_t defintion in esp_bt.h, this default power should be used for advertising, scans & connections if not explicitly set.

nRF Connect always reports the Tx Power listed in the ADV data as -21dBm.

Thinking this might be stale information, that the IDF (incorrectly) never updates, I also tried explicitly setting the connection Tx power
using:

Code: Select all

esp_ble_tx_power_set( ESP_BLE_PWR_TYPE_ADV, ESP_PWR_LVL_P9 );
This produced the same result: ADV data still shows Tx Power is -21dBm.

I then enabled the RSSI graph (on the nRF Connect 'scanner' screen, open the '3 dots' menu).
The image below shows RSSI at ESP_PWR_LVL_P9 (only the red trace is relevant):
RSSI_ESP_PWR_LVL_P9.jpg
RSSI_ESP_PWR_LVL_P9.jpg (106.24 KiB) Viewed 2226 times
The image below shows RSSI at ESP_PWR_LVL_DEFAULT:
RSSI_ESP_PWR_LVL_DEFAULT.jpg
RSSI_ESP_PWR_LVL_DEFAULT.jpg (106.49 KiB) Viewed 2226 times
The image below shows RSSI at ESP_PWR_LVL_N12:
RSSI_ESP_PWR_LVL_N12.jpg
RSSI_ESP_PWR_LVL_N12.jpg (102.46 KiB) Viewed 2226 times
Averaging the RSSI of the top image, and comparing with average RSSI of the bottom image does show a clear difference. The change from defaults to P9 appears nominal at best. The comment at the top of esp_ble_power_type_t in esp_bt.h indicates ESP_PWR_LVL_P3 (+3dBm) is used as default, if nothing has been set.

I also tried explicitly setting the connection Tx power using:

Code: Select all

esp_ble_tx_power_set( ESP_BLE_PWR_TYPE_CONN_HDL0, ESP_PWR_LVL_P9 );
Following comment at top of esp_ble_power_type_t defintion in esp_bt.h, this function is called when a connection has been established (handling 'ESP_GATTS_CONNECT_EVT', so connection handle 0 is valid). I found only a (possible) nominal affect on range with ESP_PWR_LVL_P9 compared to operating with default (P3) settings.

I've tested with ESP IDF branch v3.1, & with current master (020ade6), with the same results.

In any event, it appears the TxPower parameter in ADV data is NOT being updated when Tx Power setting is changed.

genedyne
Posts: 15
Joined: Wed Jun 06, 2018 12:47 pm

Re: esp_ble_tx_power_set has no effect

Postby genedyne » Fri Aug 17, 2018 12:10 pm

Could you post snapshots of the nRF Connect RSSI graph of your modules, running at PWR_LVL_N12 & PWR_LVL_P9?
That should provide some clue if the modules are somehow at fault.
At least we know you can ignore the -21dBm TxPower in the advertising packet.

Who is online

Users browsing this forum: MSN [Bot], thethinker and 18 guests