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Bluetooth LE advertising parameters and power consumption

This topic focuses on the impact of various Bluetooth LE advertising parameters to a device’s total power consumption.

Recall from Bluetooth LE communication methods; the different advertising types:

Basic advertising (legacy)
Extended advertising
Periodic advertising
Periodic advertising with responses (PAwR)
Encrypted advertising

This lesson focuses on the first three types, showing how to enable and configure them in your application and how different configurations affect the device’s overall power consumption.

Basic advertising (legacy)

Advertising interval

The advertising interval has a huge effect on the overall power consumption during the advertising process. A longer advertising interval would result in lower average power consumption; however, it would also affect the device’s discoverability, so it is a trade-off. Here are some examples of different advertising intervals and the resulting average power consumption.

The following example code adjusts the advertising interval. Pre-defined macros for the timers are defined in the version/zephyr/include/zephyr/bluetooth/gap.h file.

#define BT_GAP_ADV_FAST_INT_MIN_1               0x0030  /* 30 ms    */
#define BT_GAP_ADV_FAST_INT_MAX_1               0x0060  /* 60 ms    */
#define BT_GAP_ADV_FAST_INT_MIN_2               0x00a0  /* 100 ms   */
#define BT_GAP_ADV_FAST_INT_MAX_2               0x00f0  /* 150 ms   */
#define BT_GAP_ADV_SLOW_INT_MIN                 0x0640  /* 1 s      */
#define BT_GAP_ADV_SLOW_INT_MAX                 0x0780  /* 1.2 s    */

Copy

#define BT_GAP_ADV_FAST_INT_MIN_1               0x0030  /* 30 ms    */
#define BT_GAP_ADV_FAST_INT_MAX_1               0x0060  /* 60 ms    */
#define BT_GAP_ADV_FAST_INT_MIN_2               0x00a0  /* 100 ms   */
#define BT_GAP_ADV_FAST_INT_MAX_2               0x00f0  /* 150 ms   */
#define BT_GAP_ADV_SLOW_INT_MIN                 0x0640  /* 1 s      */
#define BT_GAP_ADV_SLOW_INT_MAX                 0x0780  /* 1.2 s    */

Note

Legacy advertising intervals are expressed in 0.625 ms units, so for example, 0x0030 = 48, and 48 * 0.625 = 30 ms

Legacy advertising does not allow you to set a fixed advertising interval; you can only set a minimum and a maximum interval, and a random delay of 0-10 ms is added before each advertisement packet to avoid packet collisions.

The following code defines the advertising parameters for non-connectable advertising with varying advertising intervals, using the BT_LE_ADV_PARAM() macro.

/* 100 ms */
#define APP_BT_LE_ADV_100 BT_LE_ADV_PARAM(0, 160, 160, NULL)
/* 200 ms */
#define APP_BT_LE_ADV_200 BT_LE_ADV_PARAM(0, 320, 320, NULL)
/* 500 ms */
#define APP_BT_LE_ADV_500 BT_LE_ADV_PARAM(0, 800, 800, NULL)
/* 1000 ms */
#define APP_BT_LE_ADV_1000 BT_LE_ADV_PARAM(0, 1600, 1600, NULL)
/* 2000 ms */
#define APP_BT_LE_ADV_2000 BT_LE_ADV_PARAM(0, 3200, 3200, NULL)
/* 5000 ms */
#define APP_BT_LE_ADV_5000 BT_LE_ADV_PARAM(0, 8000, 8000, NULL)

Copy

/* 100 ms */
#define APP_BT_LE_ADV_100 BT_LE_ADV_PARAM(0, 160, 160, NULL)
/* 200 ms */
#define APP_BT_LE_ADV_200 BT_LE_ADV_PARAM(0, 320, 320, NULL)
/* 500 ms */
#define APP_BT_LE_ADV_500 BT_LE_ADV_PARAM(0, 800, 800, NULL)
/* 1000 ms */
#define APP_BT_LE_ADV_1000 BT_LE_ADV_PARAM(0, 1600, 1600, NULL)
/* 2000 ms */
#define APP_BT_LE_ADV_2000 BT_LE_ADV_PARAM(0, 3200, 3200, NULL)
/* 5000 ms */
#define APP_BT_LE_ADV_5000 BT_LE_ADV_PARAM(0, 8000, 8000, NULL)

Note that _int_min and _int_max have the same value. This is allowed as long as min <= max. However, it is not recommended, because giving a range lets the controller optimize scheduling with other radio activity.

The following table presents the average power consumption of an nRF54L15 DK at different advertising intervals (TX only, 6 bytes payload, 0 dBm), when testing with the PPK2.

Disclaimer: These numbers will vary slightly depending on your board and power measurement setup. See the datasheet for the accurate numbers.

Advertising interval (ms)	Average power consumption (µA)
100	40
200	22
500	11
1000	7
2000	5
5000	3.5

Advertising only on channels 37 and 38

One way to minimize power consumption during advertising is to reduce the number of channels the device advertises on. The following code snippet ensures the device advertises only on the first two channels, 37 and 38, and skips channel 39.

This lowers power consumption but, in turn, makes the device less likely to be discovered.

const struct bt_le_adv_param *param = BT_LE_ADV_PARAM(BT_LE_ADV_OPT_NONE | BT_LE_ADV_OPT_DISABLE_CHAN_39, \
                                      BT_GAP_ADV_SLOW_INT_MIN, BT_GAP_ADV_SLOW_INT_MAX, NULL)

Copy

const struct bt_le_adv_param *param = BT_LE_ADV_PARAM(BT_LE_ADV_OPT_NONE | BT_LE_ADV_OPT_DISABLE_CHAN_39, \
                                      BT_GAP_ADV_SLOW_INT_MIN, BT_GAP_ADV_SLOW_INT_MAX, NULL)

Here, the advertising interval is set to be between 1 s and 1.2 s.

Exercise 1 of this lesson shows how this affects the average power consumption in the Power Profiler.

Minimum vs maximum advertising packet

The maximum size of an advertising packet in legacy advertising is 31 bytes.

The following code example defines bt_data ad_max to be the maximum advertising packet allowed in legacy advertising and bt_data ad_min to be the minimum advertising packet allowed, with no payload.

Flags: 3 bytes (1 len + 1 type + 1 data)
Manufacturer data: 28 bytes (1 len + 1 type + 2 company ID (0x0059) + 24 data)

static unsigned char mfg_data[] = {
	0x59, 0x00, /* Nordic Semiconductor Company ID (little endian) */
	0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
	0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
	0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff
};

static const struct bt_data ad_max[] = {
	BT_DATA_BYTES(BT_DATA_FLAGS, BT_LE_AD_NO_BREDR),
	BT_DATA(BT_DATA_MANUFACTURER_DATA, mfg_data, sizeof(mfg_data)),
};

static const struct bt_data ad_min[] = {
	BT_DATA_BYTES(BT_DATA_FLAGS, BT_LE_AD_NO_BREDR),
};

Copy

static unsigned char mfg_data[] = {
	0x59, 0x00, /* Nordic Semiconductor Company ID (little endian) */
	0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
	0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
	0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff
};

static const struct bt_data ad_max[] = {
	BT_DATA_BYTES(BT_DATA_FLAGS, BT_LE_AD_NO_BREDR),
	BT_DATA(BT_DATA_MANUFACTURER_DATA, mfg_data, sizeof(mfg_data)),
};

static const struct bt_data ad_min[] = {
	BT_DATA_BYTES(BT_DATA_FLAGS, BT_LE_AD_NO_BREDR),
};

The following images show the advertising event when advertising with the maximum advertising packet vs the minimum one.

Notice how the spikes are much wider. The advertising event now lasts much longer since the radio has to transmit on each channel for a longer period of time because the amount of data it is transmitting is larger. The event itself now consumes double the charge, from 3.75 µC to 7.47 µC, and the average current increased to 2.23 mA from 1.31 mA.

So minimizing the advertising packet used during advertising to smallest possible can be a key factor in minimizing the overall power consumption of your applications.

Advertising types

Recall: The different Bluetooth LE legacy advertising types were covered in Advertising types in Lesson 2 of the Bluetooth LE Fundamentals course.

Bluetooth LE legacy advertising types can be categorized as connectable or non-connectable, and scannable or non-scannable.

Definition

Connectable vs. non-connectable: Determines whether the central can connect to the peripheral or not.
Scannable vs. non-scannable: Determines if the peripheral accepts scan requests from a scanner.

With regard to power consumption, non-connectable and non-scannable advertising combined use the least amount of power. Non-connectable non-scannable advertising keeps the radio in TX-only mode. It transmits and then immediately goes to sleep, without waiting for incoming packets. This skips the RX window entirely, reducing the time the radio is active.

The following code example shows how to set up the four main advertising types, using bt_le_adv_start() and BT_LE_ADV_PARAM().

/* Define the advertising parameter for connectable advertising */
#define APP_BT_LE_ADV_CONN BT_LE_ADV_PARAM(BT_LE_ADV_OPT_CONN, BT_GAP_ADV_SLOW_INT_MIN, BT_GAP_ADV_SLOW_INT_MAX, NULL)

/* Define the advertising parameter for non-connectable advertising */
#define APP_BT_LE_ADV_NONCONN BT_LE_ADV_PARAM(0, BT_GAP_ADV_SLOW_INT_MIN, BT_GAP_ADV_SLOW_INT_MAX, NULL)

/* Start connectable, scannable advertising */
err = bt_le_adv_start(APP_BT_LE_ADV_CONN, ad, ARRAY_SIZE(ad), sd, ARRAY_SIZE(sd));

/* Start connectable, non-scannable advertising */
err = bt_le_adv_start(APP_BT_LE_ADV_CONN, ad, ARRAY_SIZE(ad), NULL, 0);

/* Start non-connectable, scannable advertising */
err = bt_le_adv_start(APP_BT_LE_ADV_NONCONN, ad, ARRAY_SIZE(ad), sd, ARRAY_SIZE(sd));

/* Start non-connectable, non-scannable advertising */
err = bt_le_adv_start(APP_BT_LE_ADV_NONCONN, ad, ARRAY_SIZE(ad), NULL, 0);

Copy

/* Define the advertising parameter for connectable advertising */
#define APP_BT_LE_ADV_CONN BT_LE_ADV_PARAM(BT_LE_ADV_OPT_CONN, BT_GAP_ADV_SLOW_INT_MIN, BT_GAP_ADV_SLOW_INT_MAX, NULL)

/* Define the advertising parameter for non-connectable advertising */
#define APP_BT_LE_ADV_NONCONN BT_LE_ADV_PARAM(0, BT_GAP_ADV_SLOW_INT_MIN, BT_GAP_ADV_SLOW_INT_MAX, NULL)

/* Start connectable, scannable advertising */
err = bt_le_adv_start(APP_BT_LE_ADV_CONN, ad, ARRAY_SIZE(ad), sd, ARRAY_SIZE(sd));

/* Start connectable, non-scannable advertising */
err = bt_le_adv_start(APP_BT_LE_ADV_CONN, ad, ARRAY_SIZE(ad), NULL, 0);

/* Start non-connectable, scannable advertising */
err = bt_le_adv_start(APP_BT_LE_ADV_NONCONN, ad, ARRAY_SIZE(ad), sd, ARRAY_SIZE(sd));

/* Start non-connectable, non-scannable advertising */
err = bt_le_adv_start(APP_BT_LE_ADV_NONCONN, ad, ARRAY_SIZE(ad), NULL, 0);

Extended advertising

Extended advertising increases the maximum advertising packet size from 31 bytes to 254 bytes by moving the payload from primary to secondary channels.

The primary channels carry a short packet that points to the full advertising data on a secondary channel.

The following code example shows how to enable extended advertising, using bt_le_ext_adv_create(), bt_le_ext_adv_set_data(), and bt_le_ext_adv_start().

static void adv_sent_cb(struct bt_le_ext_adv *adv, struct bt_le_ext_adv_sent_info *info);

const static struct bt_le_ext_adv_cb adv_callbacks = {
	.sent = adv_sent_cb,
};

static struct bt_le_ext_adv *adv_set;

#define APP_BT_LE_EXT_ADV_PARAM BT_LE_ADV_PARAM(BT_LE_ADV_OPT_EXT_ADV, 160, 320, NULL);

err = bt_le_ext_adv_create(&param, &adv_callbacks, &adv_set);
if (err) {
	LOG_ERR("Failed to create advertising set (err %d)\n", err);
	return 0;
}

err = bt_le_ext_adv_set_data(adv_set, ad, ARRAY_SIZE(ad), NULL, 0);
if (err) {
	LOG_ERR("Failed to set advertising data (err %d)\n", err);
	return 0;
}

err = bt_le_ext_adv_start(adv_set, &ext_adv_start_param);
if (err) {
	LOG_ERR("Failed to start extended advertising (err %d)\n", err);
	return 0;
}

Copy

static void adv_sent_cb(struct bt_le_ext_adv *adv, struct bt_le_ext_adv_sent_info *info);

const static struct bt_le_ext_adv_cb adv_callbacks = {
	.sent = adv_sent_cb,
};

static struct bt_le_ext_adv *adv_set;

#define APP_BT_LE_EXT_ADV_PARAM BT_LE_ADV_PARAM(BT_LE_ADV_OPT_EXT_ADV, 160, 320, NULL);

err = bt_le_ext_adv_create(&param, &adv_callbacks, &adv_set);
if (err) {
	LOG_ERR("Failed to create advertising set (err %d)\n", err);
	return 0;
}

err = bt_le_ext_adv_set_data(adv_set, ad, ARRAY_SIZE(ad), NULL, 0);
if (err) {
	LOG_ERR("Failed to set advertising data (err %d)\n", err);
	return 0;
}

err = bt_le_ext_adv_start(adv_set, &ext_adv_start_param);
if (err) {
	LOG_ERR("Failed to start extended advertising (err %d)\n", err);
	return 0;
}

For the same advertising interval, TX power, and payload, extended advertising generally draws more average current than legacy advertising. However, it allows for the transmission of more data.

Periodic advertising

Periodic advertising allows non-connectable advertising to be sent at a fixed interval, eliminating the need for the 0-10 ms random delay. Because the advertising interval is deterministic, scanners can wake up for short periods to listen for packets, saving power.

The following code example shows how to enable periodic advertising.

static struct bt_le_ext_adv *adv_set;

const static struct bt_le_per_adv_param per_adv_param = {
	.interval_min = BT_GAP_PER_ADV_SLOW_INT_MIN,
	.interval_max = BT_GAP_PER_ADV_SLOW_INT_MAX,
	.options = BT_LE_ADV_OPT_USE_TX_POWER,
};

err = bt_le_per_adv_set_param(adv_set, &per_adv_param);
if (err) {
	LOG_ERR("Failed to set periodic advertising parameters (err %d)\n", err);
	return 0;
}

err = bt_le_per_adv_start(adv_set);
if (err) {
	LOG_ERR("Failed to start periodic advertising (err %d)\n", err);
	return 0;
}

Copy

static struct bt_le_ext_adv *adv_set;

const static struct bt_le_per_adv_param per_adv_param = {
	.interval_min = BT_GAP_PER_ADV_SLOW_INT_MIN,
	.interval_max = BT_GAP_PER_ADV_SLOW_INT_MAX,
	.options = BT_LE_ADV_OPT_USE_TX_POWER,
};

err = bt_le_per_adv_set_param(adv_set, &per_adv_param);
if (err) {
	LOG_ERR("Failed to set periodic advertising parameters (err %d)\n", err);
	return 0;
}

err = bt_le_per_adv_start(adv_set);
if (err) {
	LOG_ERR("Failed to start periodic advertising (err %d)\n", err);
	return 0;
}

Note

Unlike legacy advertising, periodic advertising intervals are expressed in 1.25 ms units, which is why the macros BT_GAP_PER_ADV_SLOW_INT_MIN and BT_GAP_PER_ADV_SLOW_INT_MAX specific for periodic advertising are used.

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Designing Low-Power Bluetooth LE Products

Bluetooth LE advertising parameters and power consumption

Basic advertising (legacy)

Advertising interval

Note

Advertising only on channels 37 and 38

Minimum vs maximum advertising packet

Advertising types

Definition

Extended advertising

Periodic advertising

Note

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