Channel sounding with 2 antennas

Question

Hi,

I am currently testing the channel sounding capabilities of nRF54L15 with zephyr on NCS 3.2.3.
I used the sample code from nrf\samples\bluetooth\channel_sounding_ras_initiator and reflector and it works well but only use one antenna from both sides.

In my setup, I have one nRF54L15DK as initiator and one custom board as reflector using nRF54L15 and a RF switch (QPC6044 switching in less than 240ns).
I want to use the two antennas connected to my RF switch, but I dont manage to make a working configuration: if i set BT_LE_CS_TONE_ANTENNA_CONFIGURATION_A1_B2 in the initiator, i get this error:
bt_hci_core: opcode 0x2093 status 0x12 BT_HCI_ERR_INVALID_PARAM
app_main: Failed to set procedure parameters (err -22)

Here's my setup:
Initiator -> nRF54L15DK

struct bt_le_cs_create_config_params config_params = {

.id = CS_CONFIG_ID,

.mode = BT_CONN_LE_CS_MAIN_MODE_2_SUB_MODE_1,

.min_main_mode_steps = 2,

.max_main_mode_steps = 5,

.main_mode_repetition = 0,

.mode_0_steps = NUM_MODE_0_STEPS,

.role = BT_CONN_LE_CS_ROLE_INITIATOR,

.rtt_type = BT_CONN_LE_CS_RTT_TYPE_AA_ONLY,

.cs_sync_phy = BT_CONN_LE_CS_SYNC_1M_PHY,

.channel_map_repetition = 1,

.channel_selection_type = BT_CONN_LE_CS_CHSEL_TYPE_3B,

.ch3c_shape = BT_CONN_LE_CS_CH3C_SHAPE_HAT,

.ch3c_jump = 2,

};

const struct bt_le_cs_set_procedure_parameters_param procedure_params = {

.config_id = CS_CONFIG_ID,

.max_procedure_len = 1000,

.min_procedure_interval = realtime_rd ? 5 : 10,

.max_procedure_interval = realtime_rd ? 5 : 10,

.max_procedure_count = 0,

.min_subevent_len = 16000,

.max_subevent_len = 16000,

.tone_antenna_config_selection = BT_LE_CS_TONE_ANTENNA_CONFIGURATION_A1_B2,

.phy = BT_LE_CS_PROCEDURE_PHY_2M,

.tx_power_delta = 0x80,

.preferred_peer_antenna = BT_LE_CS_PROCEDURE_PREFERRED_PEER_ANTENNA_1,

.snr_control_initiator = BT_LE_CS_SNR_CONTROL_NOT_USED,

.snr_control_reflector = BT_LE_CS_SNR_CONTROL_NOT_USED,

};

CONFIG_BT_CHANNEL_SOUNDING=y

CONFIG_BT_RAS=y

CONFIG_BT_RAS_RREQ=y

CONFIG_BT_RAS_MODE_3_SUPPORTED=n

CONFIG_BT_RAS_MAX_ANTENNA_PATHS=2

CONFIG_BT_CTLR_SDC_CS_MAX_ANTENNA_PATHS=2

CONFIG_BT_CTLR_SDC_CS_NUM_ANTENNAS=1

CONFIG_BT_CTLR_SDC_CS_STEP_MODE3=n

CONFIG_BT_CTLR_SDC_CS_ROLE_INITIATOR_ONLY=y

Reflector -> custom board base on nRF54L15 with two antennas

const struct bt_le_cs_set_default_settings_param default_settings = {

.enable_initiator_role = false,

.enable_reflector_role = true,

.cs_sync_antenna_selection = BT_LE_CS_ANTENNA_SELECTION_OPT_REPETITIVE,

.max_tx_power = BT_HCI_OP_LE_CS_MAX_MAX_TX_POWER,

};

const struct bt_le_cs_set_procedure_parameters_param procedure_params = {

.config_id = 0,

.max_procedure_len = 1000,

.min_procedure_interval = 1,

.max_procedure_interval = 100,

.max_procedure_count = 0,

.min_subevent_len = 1000,

.max_subevent_len = 75000,

.tone_antenna_config_selection = BT_LE_CS_TONE_ANTENNA_CONFIGURATION_A1_B2,

.phy = BT_LE_CS_PROCEDURE_PHY_2M,

.tx_power_delta = 0x80,

.preferred_peer_antenna = BT_LE_CS_PROCEDURE_PREFERRED_PEER_ANTENNA_1,

.snr_control_initiator = BT_LE_CS_SNR_CONTROL_NOT_USED,

.snr_control_reflector = BT_LE_CS_SNR_CONTROL_NOT_USED,

};

CONFIG_BT_CHANNEL_SOUNDING=y

CONFIG_BT_RAS=y

CONFIG_BT_RAS_RRSP=y

CONFIG_BT_RAS_MODE_3_SUPPORTED=n

CONFIG_BT_RAS_MAX_ANTENNA_PATHS=2

CONFIG_BT_CTLR_SDC_CS_MAX_ANTENNA_PATHS=2

CONFIG_BT_CTLR_SDC_CS_NUM_ANTENNAS=2

CONFIG_BT_CTLR_SDC_CS_STEP_MODE3=n

CONFIG_BT_CTLR_SDC_CS_ROLE_REFLECTOR_ONLY=y

cs_antenna_switch: cs-antenna-config {

status = "okay";

compatible = "nordic,bt-cs-antenna-switch";

ant-gpios = <&gpio0 0 GPIO_ACTIVE_HIGH>, <&gpio0 1 GPIO_ACTIVE_HIGH>;

multiplexing-mode = <0>;

};

Those are the default configuration, I just changed CONFIG_BT_RAS_MAX_ANTENNA_PATHS to 2 on both side, CONFIG_BT_CTLR_SDC_CS_NUM_ANTENNAS to 2 on the reflector, added the cs_antenna_switch on the reflector and changed tone_antenna_config_selection to BT_LE_CS_TONE_ANTENNA_CONFIGURATION_A1_B2 on both sides.

My switch works as I can advertise on the different antennas by setting P0.0 or P0.1 to high. I can also use channel sounding just fine with just one antenna path by keeping this configuration and only setting BT_LE_CS_TONE_ANTENNA_CONFIGURATION_A1_B1. I tweaked the settings to allow more time per subevent or a larger procedure interval but i never get past the error coming from bt_le_cs_create_config. I also tried using NCS 3.1.1.

I saw on the channel sounding page that up to 4 antennas paths are supported. If you have any example code working, it would be greatly appreciated.

R. Saboret