commit 95df8e8e0a17bd4c4196056d2911e076f64ef3fd
parent 4997af87aadb620f6a652e56bc731931641d1a9d
Author: Egor Achkasov <eaachkasov@edu.hse.ru>
Date: Mon, 24 Mar 2025 22:09:40 +0100
Impl doppler freq shift
Diffstat:
2 files changed, 56 insertions(+), 12 deletions(-)
diff --git a/compute_paths.c b/compute_paths.c
@@ -518,8 +518,8 @@ void compute_paths(
IN size_t num_tx, /* number of transmitters */
IN size_t num_paths, /* number of paths */
IN size_t num_bounces, /* number of bounces */
- OUT PathsInfo *los, /* output LoS information */
- OUT PathsInfo *scatter /* output scatter information */
+ OUT PathsInfo *los, /* output LoS information. los->num_paths = 1 */
+ OUT PathsInfo *scatter /* output scatter information. scatter->num_paths = num_bounces*num_paths */
)
{
/* Load the scene */
@@ -604,6 +604,29 @@ void compute_paths(
float free_space_loss_multiplier = 4.f * PI * carrier_frequency * 1e9 / SPEED_OF_LIGHT;
float free_space_loss;
+ /* Doppler frequency shift carrier frequency multiplier */
+ float doppler_shift_multiplier = carrier_frequency * 1e9 / SPEED_OF_LIGHT;
+
+ /* Initialize the doppler frequency shift using the tx velocities */
+ /* The scatter->freq_shift has the shape of (num_rx, num_tx, num_bounces*num_paths) */
+ /* The first num_tx*num_paths elements are the same for each rx and bounce */
+ /* so we can initialize them only once and memcpy them to the rest */
+ for (size_t tx = 0; tx != num_tx; ++tx)
+ for (size_t path = 0; path != num_paths; ++path) {
+ size_t off_rays = tx * num_paths + path;
+ size_t off_scat = tx * num_paths * num_bounces + path;
+ scatter->freq_shift[off_scat] = vec3_dot(&tx_vel_v[tx], &rays[off_rays].d);
+ scatter->freq_shift[off_scat] *= doppler_shift_multiplier;
+ }
+ for (size_t bounce = 1; bounce < num_bounces; ++bounce)
+ if (!memcpy(scatter->freq_shift + num_tx * num_paths * bounce,
+ scatter->freq_shift, num_tx * num_paths * sizeof(float)))
+ exit(70);
+ for (size_t rx = 1; rx < num_rx; ++rx)
+ if (!memcpy(scatter->freq_shift + num_tx * num_paths * num_bounces * rx,
+ scatter->freq_shift, num_tx * num_paths * num_bounces * sizeof(float)))
+ exit(70);
+
/***************************************************************************/
/* LoS paths */
/***************************************************************************/
@@ -633,6 +656,8 @@ void compute_paths(
los->a_te_re[off] = los->a_tm_re[off] = 1.f;
/* Set delay to 0 */
los->tau[off] = 0.f;
+ /* Set doppler shift to 0. */
+ los->freq_shift[off] = 0.f;
continue;
}
@@ -648,12 +673,13 @@ void compute_paths(
/* Calculate the distance */
t = sqrtf(vec3_dot(&r.d, &r.d));
/* Calculate the direction */
- los->directions_tx[off * 3] = r.d.x / t;
- los->directions_tx[off * 3 + 1] = r.d.y / t;
- los->directions_tx[off * 3 + 2] = r.d.z / t;
- los->directions_rx[off * 3] = -los->directions_tx[off * 3];
- los->directions_rx[off * 3 + 1] = -los->directions_tx[off * 3 + 1];
- los->directions_rx[off * 3 + 2] = -los->directions_tx[off * 3 + 2];
+ Vec3 d = {r.d.x / t, r.d.y / t, r.d.z / t};
+ los->directions_tx[off * 3] = d.x;
+ los->directions_tx[off * 3 + 1] = d.y;
+ los->directions_tx[off * 3 + 2] = d.z;
+ los->directions_rx[off * 3] = -d.x;
+ los->directions_rx[off * 3 + 1] = -d.y;
+ los->directions_rx[off * 3 + 2] = -d.z;
/* Calculate the free space loss */
free_space_loss = free_space_loss_multiplier * t;
if (free_space_loss > 1.f) {
@@ -663,6 +689,9 @@ void compute_paths(
los->a_te_re[off] =los-> a_tm_re[off] = 1.f;
/* Calculate the delay */
los->tau[off] = t / SPEED_OF_LIGHT;
+ /* Calculate the doppler shift */
+ los->freq_shift[off] = vec3_dot(tx_vel_v, &d) - vec3_dot(rx_vel_v, &d);
+ los->freq_shift[off] *= carrier_frequency * 1e9 / SPEED_OF_LIGHT;
}
/***************************************************************************/
@@ -758,6 +787,12 @@ void compute_paths(
/* Advance the ray origin a bit to avoid intersection with the same triangle */
*h = vec3_scale(&r.d, 1e-4f);
r.o = vec3_add(&r.o, h);
+
+ /* Calculate the doppler shift caused by the reflection */
+ Vec3* mesh_vel = (Vec3*)&scene.meshes[mesh_ind].velocity;
+ Vec3 d_rd = vec3_sub(&r.d, &rays[off_tx_path].d);
+ scatter->freq_shift[off_tx_path] += vec3_dot(&d_rd, mesh_vel) * doppler_shift_multiplier;
+
/* Save the reflected ray */
rays[off_tx_path] = r;
@@ -768,10 +803,13 @@ void compute_paths(
/* Scatter a path from the hit point towards the rx */
Ray r_scat = { .o = r.o };
for (size_t rx = 0; rx < num_rx; ++rx) {
+ /* [rx, tx, bounce, path] */
size_t off_scat = ((rx * num_tx + tx) * num_bounces + bounce) * num_paths + path;
+ /* Create a ray from the hit point to the rx */
r_scat.d = vec3_sub(&rx_pos_v[rx], &r_scat.o);
- float dist2rx = sqrtf(vec3_dot(&r_scat.d, &r_scat.d));
+ float d2rx = sqrtf(vec3_dot(&r_scat.d, &r_scat.d));
r_scat.d = vec3_normalize(&r_scat.d);
+ /* Check if the ray has a LoS of the rx */
t = -1.f;
mesh_ind = face_ind = -1;
moeller_trumbore(&r_scat, &scene, &t, &mesh_ind, &face_ind, &theta);
@@ -804,9 +842,9 @@ void compute_paths(
scatter->directions_rx[off_scat * 3 + 1] = -r_scat.d.y;
scatter->directions_rx[off_scat * 3 + 2] = -r_scat.d.z;
/* Calculate the delay */
- scatter->tau[off_scat] = tau_t[off_tx_path] + dist2rx / SPEED_OF_LIGHT;
+ scatter->tau[off_scat] = tau_t[off_tx_path] + d2rx / SPEED_OF_LIGHT;
/* Calculate the free space loss */
- free_space_loss = free_space_loss_multiplier * dist2rx;
+ free_space_loss = free_space_loss_multiplier * d2rx;
free_space_loss *= free_space_loss;
if (free_space_loss > 1.f) {
scatter->a_te_re[off_scat] /= free_space_loss;
@@ -814,6 +852,10 @@ void compute_paths(
scatter->a_tm_re[off_scat] /= free_space_loss;
scatter->a_tm_im[off_scat] /= free_space_loss;
}
+ /* Calculate the doppler shift */
+ Vec3 d_rd = vec3_sub(&r_scat.d, &rays[off_tx_path].d);
+ float freq_shift = vec3_dot(&d_rd, mesh_vel) * doppler_shift_multiplier;
+ scatter->freq_shift[off_scat] -= freq_shift;
}
/***********************************************************************/
diff --git a/inc/compute_paths.h b/inc/compute_paths.h
@@ -17,7 +17,7 @@ typedef struct {
float *a_tm_re; /* shape (num_rx, num_tx, num_paths) */
float *a_tm_im; /* shape (num_rx, num_tx, num_paths) */
float *tau; /* shape (num_rx, num_tx, num_paths) */
- float *freq_shift; /* shape (num_rx, num_tx, num_paths) */
+ float *freq_shift; /* Hz, shape (num_rx, num_tx, num_paths) */
} PathsInfo;
/** Compute gains and delays between tx and rx in a 3D scene.
@@ -29,6 +29,8 @@ typedef struct {
*
* The output PathInfo structure is defined in compute_paths.h
*
+ * The output parameters are allocated by the caller (including the fields).
+ *
* \param scene_filepath path to a scene .hrt file
* \param rx_pos receiver positions, shape (num_rx, 3)
* \param tx_pos transmitter positions, shape (num_tx, 3)
