Channel Sounding: Initiator with Ranging Requester

Overview

Application demonstrates the BLE requester role in an RAP (Ranging Profile) system and the initiator role for Channel Sounding. It can connect with a BLE responder application (Refer to ras_rrsp_reflector). And then gets channel sounding ranging procedure indication and data using GATT Ranging service control point write commands to the BLE Ranging Responser role.

Requirements

  1. Atmosic EVK <board | serial>

Note

  • Currently, the ATM34/e and ATM53/e series of Atmosic devices are supported.

  • ATM52 does not support channel sounding.

  1. Button

    • Press Button2 to unpair the device.

    Note

    • The default pin for Button2 is P6.

    • Install the JP27 and JP25 jumpers to enable Button2.

  2. Antenna_switch: connect IO to switch antenna as channel sounding enable

  • Need to connect external antenna switch board for EVK

  • For the related pin setting, please refer to the overlay file.

  • If there is no overlay file, the function is disabled.

  • Refer to atmosic,antenna.yaml for below properties.

    • e.g. P5 as antenna switch (JP29 in EVK board).

      In the case, Button1 can not be used, since it is also used with P5.

    / {
 aliases {
  sw0 = &button1;
 };
};
&atm_antenna {
 ant-out5-pin = <5>;
 mdm-ant-rx-3to0 = <0x00002000>;
 mdm-ant-tx-3to0 = <0x00002000>;
 mdm-ant-idle =<0>;
 status = "okay";
};

    • e.g. P16 as antenna switch, and antenna0 with P16 high

    &atm_antenna {
 ant-out0-pin = <16>;
 mdm-ant-rx-3to0 = <0x00000001>;
 mdm-ant-tx-3to0 = <0x00000001>;
 mdm-ant-idle =<0x01>;
 status = "okay";
};

Configuration Options

Bluetooth Transmit Power Control

To enable Bluetooth transmit power control reporting functionality, add the following configuration option to your project configuration file (prj.conf):

CONFIG_BT_TRANSMIT_POWER_CONTROL=y

This option enables:

  • Transmit power control information reporting to the host

  • Support for transmit power reporting procedures in BLE connections

  • Power control status monitoring and feedback mechanisms

  • Enhanced visibility into power control operations for channel sounding

Note

This feature enables the reporting of power control information rather than direct power adjustment. It is useful for monitoring and debugging power control behavior in ranging applications.

RSSI Reading Support

To enable RSSI (Received Signal Strength Indicator) reading functionality, add the following configuration option to your project configuration file (prj.conf):

CONFIG_READ_RSSI=y

This option enables:

  • RSSI measurement and reporting capabilities

  • Signal strength monitoring for BLE connections

Note

RSSI readings provide valuable signal strength information that can be used to improve connection quality assessment.

BLE PHY Mode Selection

To enable BLE PHY mode selection and automatic PHY updates, add the following configuration options to your project configuration file (prj.conf):

CONFIG_ATM_BT_PHY_UPDATE=y
CONFIG_ATM_BT_PHY=0

These options enable:

  • Flexible PHY mode selection (0=1M, 1=2M, 2=Coded)

  • Automatic PHY update to the configured mode if a different PHY is detected during connection

  • Retry mechanism for PHY update failures

Configuration Details

CONFIG_ATM_BT_PHY_UPDATE: Enable/disable automatic PHY updates

  • When enabled, the system will automatically attempt to update the PHY to the configured mode if a different PHY is detected

  • Up to 3 retry attempts are made if PHY update fails

CONFIG_ATM_BT_PHY: Select the preferred PHY mode

  • 0: 1M PHY (default) - Enhanced range and signal penetration for long-distance testing

  • 1: 2M PHY - Higher data rate for improved throughput

  • 2: Coded PHY - Extended range with lower data rate

Example configurations:

# For long-distance Channel Sounding with 1M PHY
CONFIG_ATM_BT_PHY_UPDATE=y
CONFIG_ATM_BT_PHY=0

# For high-throughput scenarios with 2M PHY
CONFIG_ATM_BT_PHY_UPDATE=y
CONFIG_ATM_BT_PHY=1

# For extended range with Coded PHY
CONFIG_ATM_BT_PHY_UPDATE=y
CONFIG_ATM_BT_PHY=2

Note

This feature is specifically designed for Channel Sounding applications where PHY mode selection is critical for optimal performance. The automatic PHY management ensures consistent PHY usage throughout the connection lifecycle.

Important

Reflector Configuration Requirement: When testing with a reflector device (e.g., ras_rrsp_reflector), the reflector must disable auto phy CONFIG_BT_AUTO_PHY_UPDATE=n. If not, PHY mismatches may occur during the connection, potentially affecting Channel Sounding performance and range measurements.

Antenna Configuration

For Channel Sounding, a few antenna combinations are supported as mentioned below.

Note

On ATM34, ATM53/e devices, a 2×2 or 2x1 or 1x1 antenna configuration is supported with CS as an initiator:

# For 2x2 Antenna configuration
CONFIG_ATM_BLE_CS_NUM_ANTENNAS=2
CONFIG_CS_PROC_ANT_CFG_SEL=7 (2x2 2 Antenna on Initiator; 2 on Reflector)

or

# For 2x1 Antenna configuration
CONFIG_ATM_BLE_CS_NUM_ANTENNAS=2
CONFIG_CS_PROC_ANT_CFG_SEL=1 (2x1 2 Antenna on Initiator; 1 on Reflector)

or

# For 1x1 Antenna configuration
CONFIG_ATM_BLE_CS_NUM_ANTENNAS=1
CONFIG_CS_PROC_ANT_CFG_SEL=0 (1x1 1 Antenna on Initiator; 1 on Reflector)

CS Inline PCT Transfer (CS IPT)

CS IPT is only supported on ATM53/e platform.

To enable CS (Channel Sounding) Inline PCT (Phase Correction Term) Transfer support, add the following configuration option to your project configuration file (prj.conf):

CONFIG_ENABLE_CS_REF_IPT=y

This option enables:

  • Detection of CS Enhancement 1 (CS IPT) capability on the remote reflector by reading its extended feature pages

  • Automatic activation of the Inline PCT Transfer flag (cs_enhancements_1) in the CS configuration when the reflector supports it

  • Logging of CS IPT enablement status during CS configuration

The following dependencies are automatically selected when this option is enabled:

  • BT_LE_EXTENDED_FEAT_SET — enables reading of extended LL feature pages from the remote peer

  • ATM_ENA_LL_FEAT_CS_ENH1 — enables local CS Enhancement 1 (CS IPT) support at the link layer

Note

On ATM53/e devices, a 2×2 antenna configuration is supported with CS reflector IPT. CONFIG_CS_PROC_ANT_CFG_SEL=7 selects the 2×2 antenna configuration when using this feature on ATM53/e:

CONFIG_ENABLE_CS_REF_IPT=y

CONFIG_ATM_BLE_CS_NUM_ANTENNAS=2
CONFIG_CS_PROC_ANT_CFG_SEL=7 (2x2 2 Antenna on Initiator; 2 on Reflector)

Important

Reflector Requirement: The paired reflector device must also have CS Enhancement 1 support enabled (e.g., CONFIG_ATM_ENA_LL_FEAT_CS_ENH1=y on the reflector side). The initiator reads the reflector’s extended features after connection and only enables CS IPT in the CS config if the reflector advertises support.

Reduce RAS Data from Reflector

Two configuration options are provided to reduce the amount of ranging data reported by the reflector.

Note

These options are particularly recommended when CS reflector Inline PCT Transfer (CS IPT) is enabled (CONFIG_ENABLE_CS_REF_IPT=y), because the Q (imaginary) part of the reflector’s ranging data is always zero in that case and carrying it wastes bandwidth.

Disable Ranging Data Subscriptions

To skip all ranging data subscriptions and receive only the RAS Control Point notifications, add the following option to your project configuration file (prj.conf):

CONFIG_RREQ_DISABLE_RD_SUB=y

When enabled, the initiator skips all ranging data subscriptions in the RREQ_SMF_RAS_SUBSCRIBE state. This covers:

  • The real-time ranging data subscription (when RAS_CLIENT_REAL_TIME_RD is enabled)

  • The on-demand ranging data subscriptions (ranging data overwritten, ranging data ready, and on-demand ranging data)

Only the RAS Control Point subscription is kept.

Set RAS Mode 2 Ranging Data Filter

To filter out selected Mode 2 fields from ranging data reported by the reflector, add the following options to your project configuration file (prj.conf):

CONFIG_RREQ_SET_RAS_FILTER=y
CONFIG_RREQ_RAS_FILTER_MODE_2_MASK=0x3FF8

When CONFIG_RREQ_SET_RAS_FILTER is enabled, the initiator sends a Set Filter CP command with Mode 2 and the mask value configured by CONFIG_RREQ_RAS_FILTER_MODE_2_MASK after subscribing to the RAS Control Point and before subscribing to ranging data.

CONFIG_RREQ_RAS_FILTER_MODE_2_MASK: 14-bit mask (0x0000–0x3FFF) that controls which Mode 2 fields are kept in the ranging data. A set bit retains the corresponding field; a cleared bit filters it out.

Mode 2 Mask Bit Assignments

Bit(s)

Field

0

Antenna Permutation Index

1

Phase Correction Term

2

Quality Indicator and Extension Indicator

3–6

Antenna Path 1~3 unsupported indication

The default value 0x3FF8 clears all step data for Mode 2.

Note

CONFIG_RREQ_RAS_FILTER_MODE_2_MASK depends on CONFIG_RREQ_SET_RAS_FILTER and has no effect unless the filter is enabled.

Testing

The EVK running this application is the Channel Sounding initiator. Connect it to a compatible reflector EVK running the ras_rrsp_reflector application. Connect UART0 from the initiator EVK to the Atmosic CS Plot Tool using a baud rate of 2000000. The distance result is displayed in the CS Plot Tool.

Default configuration (without Inline PCT Transfer)

  1. Build and flash this application using the default target below.

  2. Build and flash a compatible reflector using its default target, then scan for Atmosic_RRSP and complete pairing.

  3. Connect the initiator EVK UART0 to the Atmosic CS Plot Tool at 2000000 baud.

  4. Start a Channel Sounding session from the initiator application and verify the distance result in the CS Plot Tool.

Inline PCT Transfer (CS IPT) configuration for ATM53/e

CS IPT is only supported on ATM53/e platform.

Build both peers with their Inline PCT Transfer targets: use applications.ras_rreq_initiator.atm.ipt for this application and applications.ras_rrsp_reflector.atm.ipt for the reflector.

Building and Running

This application is built from openair/applications/ras_rreq_initiator.

Build with UART0 as console and shell command:

west build -p always -b <BOARD> openair/applications/ras_rreq_initiator --sysbuild -T applications.ras_rreq_initiator.atm

Build with Inline PCT Transfer (CS IPT) support for ATM53/e:

west build -p always -b <BOARD> openair/applications/ras_rreq_initiator --sysbuild -T applications.ras_rreq_initiator.atm.ipt

Flash command:

west flash --no-rebuild --device <DEVICE_ID> --jlink [--erase_all]