diff --git a/sw/airborne/booz_nav.c b/sw/airborne/booz_nav.c
index d91578f18a..ee5ea6bc6c 100644
--- a/sw/airborne/booz_nav.c
+++ b/sw/airborne/booz_nav.c
@@ -61,8 +61,13 @@ void booz_nav_init(void) {
 
 void booz_nav_run(void) {
 #ifndef DISABLE_NAV
-  booz_nav_vertical_loop_run();
-  booz_nav_hovering_loop_run();
+  static uint8_t prescaler = 0;
+  prescaler++;
+  if (prescaler > 50) {
+    prescaler = 0;
+    booz_nav_vertical_loop_run();
+    booz_nav_hovering_loop_run();
+  }
   BoozControlAttitudeSetSetPoints(booz_nav_phi_command, booz_nav_theta_command, 
 				  booz_nav_horizontal_psi_sp, booz_nav_power_command);
   booz_control_attitude_run();
diff --git a/sw/simulator/booz_sensors_model.c b/sw/simulator/booz_sensors_model.c
index 301e1a9ee1..2bac8bcf49 100644
--- a/sw/simulator/booz_sensors_model.c
+++ b/sw/simulator/booz_sensors_model.c
@@ -80,6 +80,7 @@ static void booz_sensors_model_accel_init(void) {
 
 
 static void booz_sensors_model_gyro_init(void) {
+
   bsm.gyro = v_get(AXIS_NB);
   bsm.gyro->ve[AXIS_P] = 0.;
   bsm.gyro->ve[AXIS_Q] = 0.;
@@ -115,11 +116,19 @@ static void booz_sensors_model_gyro_init(void) {
   bsm.gyro_bias_random_walk_value->ve[AXIS_P] = bsm.gyro_bias_initial->ve[AXIS_P];
   bsm.gyro_bias_random_walk_value->ve[AXIS_Q] = bsm.gyro_bias_initial->ve[AXIS_Q];
   bsm.gyro_bias_random_walk_value->ve[AXIS_R] = bsm.gyro_bias_initial->ve[AXIS_R];
+
 }
 
 static void booz_sensors_model_gps_init(void) {
+
   bsm.speed_sensor = v_get(AXIS_NB);
   v_zero(bsm.speed_sensor);
+
+  bsm.speed_noise_std_dev = v_get(AXIS_NB);
+  bsm.speed_noise_std_dev->ve[AXIS_X] = 1e-1;
+  bsm.speed_noise_std_dev->ve[AXIS_Y] = 1e-1;
+  bsm.speed_noise_std_dev->ve[AXIS_Z] = 1e-1;
+
   bsm.pos_sensor = v_get(AXIS_NB);
   v_zero(bsm.pos_sensor);
 
@@ -241,6 +250,8 @@ static void booz_sensors_model_gyro_run( double dt) {
 }
 
 static void booz_sensors_model_gps_run( double dt, MAT* dcm_t ) {
+
+  /* simulate speed sensor */
   /* extract body speed from state */
   static VEC *speed_body = VNULL;
   speed_body = v_resize(speed_body, AXIS_NB);
@@ -249,6 +260,9 @@ static void booz_sensors_model_gps_run( double dt, MAT* dcm_t ) {
   speed_body->ve[AXIS_W] = bfm.state->ve[BFMS_W];
   /* convert to earth frame */
   bsm.speed_sensor = mv_mlt(dcm_t, speed_body, bsm.speed_sensor);
+  /* add a gaussian noise */
+  bsm.speed_sensor = v_add_gaussian_noise(bsm.speed_sensor, bsm.speed_noise_std_dev, bsm.speed_sensor);
+  
 
   /* simulate position sensor */
   bsm.pos_sensor->ve[AXIS_X] = bfm.state->ve[BFMS_X];
diff --git a/sw/simulator/booz_sensors_model.h b/sw/simulator/booz_sensors_model.h
index a4a6c292bd..6cbb885e65 100644
--- a/sw/simulator/booz_sensors_model.h
+++ b/sw/simulator/booz_sensors_model.h
@@ -25,6 +25,7 @@ struct BoozSensorsModel {
 
   /* imaginary sensors - gps maybe */
   VEC* speed_sensor;
+  VEC* speed_noise_std_dev;
   VEC* pos_sensor;
   VEC* pos_noise_std_dev;
   VEC* pos_bias_initial;