bluetooth: services: Add Channel Sounding Distance Estimation library

First draft of a mini-toolkit for processing CS results.

Signed-off-by: Olivier Lesage <olivier.lesage@nordicsemi.no>

Author: olivier-le-sage

include/bluetooth/cs_de.h

@@ -0,0 +1,96 @@
+/*
+ * Copyright (c) 2025 Nordic Semiconductor ASA
+ *
+ * SPDX-License-Identifier: LicenseRef-Nordic-5-Clause
+ */
+
+#ifndef DE_H__
+#define DE_H__
+
+#include <zephyr/bluetooth/conn.h>
+#include <zephyr/net_buf.h>
+
+/**
+ * @brief Container of IQ values for local and remote measured tones
+ */
+typedef struct {
+	/** In-phase measurements of tones on this device */
+	float i_local[80];
+	/** Quadrature-phase measurement of tones on this device */
+	float q_local[80];
+	/** In-phase measurements of tones from remote device */
+	float i_remote[80];
+	/** Quadrature-phase measurements of tones from remote device */
+	float q_remote[80];
+} cs_de_iq_tones_t;
+
+typedef enum {
+	CS_DE_TONE_QUALITY_OK,
+	CS_DE_TONE_QUALITY_BAD,
+} cs_de_tone_quality_t;
+
+typedef struct {
+	/** Quality indicator for tones on this device */
+	cs_de_tone_quality_t qi_local[80];
+	/** Quality indicator for tones on peer device */
+	cs_de_tone_quality_t qi_remote[80];
+} cs_de_quality_indicators_t;
+
+/**
+ * @brief Container of distance estimate results for a number of different
+ * methods, in meters.
+ */
+typedef struct {
+	/** Distance estimate based on IFFT of spectrum */
+	float ifft;
+	/** Distance estimate based on average phase slope estimation */
+	float phase_slope;
+	/** Best effort distance estimate.
+	 *
+	 *  This is a convenience value which is automatically set to the most
+	 *  accurate of the estimation methods.
+	 */
+	float best;
+} cs_de_dist_estimates_t;
+
+/**
+ * @brief Quality of the procedure
+ */
+typedef enum {
+	CS_DE_QUALITY_OK,
+	CS_DE_QUALITY_DO_NOT_USE,
+} cs_de_quality_t;
+
+/**
+ * @brief Output data for distance estimation
+ */
+typedef struct {
+	/** IQ values for local and remote measured tones.
+	 */
+	cs_de_iq_tones_t iq_tones[CONFIG_BT_RAS_MAX_ANTENNA_PATHS];
+
+	/** Quality indicators for the tones in iq_tones[0] */
+	cs_de_quality_indicators_t tone_quality_indicators[CONFIG_BT_RAS_MAX_ANTENNA_PATHS];
+
+	/** Distance estimate results */
+	cs_de_dist_estimates_t distance_estimates;
+
+	/** Quality indicator */
+	cs_de_quality_t quality;
+} cs_de_report_t;
+
+/**
+ * @brief Partially populate the report.
+ * This populates the report but does not set the distance estimates and the quality.
+ * @param[in] local_steps Buffer to the local step data to parse.
+ * @param[in] peer_steps   Buffer to the peer ranging data to parse.
+ * @param[in] role Role of the local controller.
+ * @param[out] p_report Report populated with the raw data from the last ranging.
+ */
+void cs_de_populate_report(struct net_buf_simple *local_steps, struct net_buf_simple *peer_steps,
+			   enum bt_conn_le_cs_role role, cs_de_report_t *p_report);
+
+/* Takes partially poulated report and calculates distance estimates and quality. */
+cs_de_quality_t cs_de_calc(cs_de_report_t *p_report);
+
+#endif /* DE_H__ */

samples/bluetooth/channel_sounding_ras_initiator/prj.conf

@@ -53,3 +53,6 @@ CONFIG_FPU=y
 CONFIG_FPU_SHARING=y
 
 CONFIG_CBPRINTF_FP_SUPPORT=y
+
+CONFIG_BT_CS_DE=y
+CONFIG_BT_CS_DE_1024_NFFT=y