Active Heading Stabilization (AHS)

Active Heading Stabilization (AHS) is an algorithm that estimates the gyro bias in the horizontal plane, enabling a better heading tracking performance. In different products, AHS is activated in different situations. For the MTi-7 and MTi-G-700/710, AHS is still in beta.

One powerful feature when it comes to heading estimation is Active Heading Stabilization (AHS). AHS can be a solution when the MTi is used in a disturbed magnetic field. When AHS is applied to a filter profile that uses the magnetic field as a reference, the magnetic field will no longer be used as a reference. Heading output will be heading tracking with respect to startup, instead of referenced heading. Upon initialization of the sensor, the heading estimate will therefore be 0 degrees. With AHS enabled, drift in heading can be as low as 1 degree after 60 minutes for the MTi 100-series and 3 degrees after 60 minutes for the MTi 10-series.

When activating AHS, there are several considerations to keep in mind. First, during initialization of the sensor, AHS requires the MTi to be motionless for a short period of time. Depending on your configuration, this initialization process may take between 10 and 30 seconds. In addition, there is one known situation where AHS may have a detrimental effect on the heading estimation performance. When either the MTi or the magnetic field rotates very slowly, it will be difficult to distinguish between the two from a sensor point of view. This may result in additional heading tracking errors. The best performance is most likely to be reached when the MTi is not moving, and when engines of your application are turned off. If the MTi is warmed up sufficiently (>10 minutes), the estimated gyro bias accuracy based on AHS will degrade only slowly so that a gyro bias estimation is required only several times per hour.

AHS is off by default from firmware version 1.4.12, also when using the VRU_general filter profile. Activate it by checking its box under MT Settings > Device Settings in MT Manager and clicking 'Write to MT', or by setting the flag in SetOptionFlags. The message for enabling AHS is FA FF 48 08 00 00 00 10 00 00 00 00 A1  (see the MT Low Level Communication Document).


MTi 1-series, 10-series and MTi 100-series

When AHS is enabled, this feature will override magnetic reference tracking. This means that the accelerometer parameters in e.g. the dynamic filter profile are preserved, but that AHS is used for heading tracking. 

Heading (tracking) information in MTi 1-, 10-, 100-series


Filter profiles with magnetic reference
Gyroscope integration (heading tracking) Yes Yes
Magnetic reference (heading reference)


AHS off: Yes

AHS on: No



MTi-G-700/710 (note: AHS in beta)

When AHS is enabled, this feature will override magnetic reference tracking (for the MTi-G-700/710, this is the GeneralMag filter profile). However, heading reference with GNSS/accelerometer comparison still functions when there is GNSS visibility. When there is movement, heading from GNSS/accelerometer comparison is the most accurate heading source of the MTi-G-700/710. In the MTi-G-700/710, gyro bias is also estimated using the GNSS/accelerometer comparison next to AHS. This makes that the gyro bias can actually always be estimated and that heading drift in the MTi-G-700/710 is minimal.


Heading (tracking) information in MTi-G-700/710 Filter profiles with magnetic reference Filter profiles without magnetic reference Automotive filter profiles
Gyroscope integration (heading tracking) Yes Yes Yes
Magnetic reference (heading reference)

AHS off: Yes

AHS on: No


GNSS/accelerometer comparison (heading reference) Yes, when accelerating or making turns when there is a GNSS fix Yes, when accelerating or making turns when there is a GNSS fix Yes, when accelerating or making turns when there is a GNSS fix
Holonomic constraints (heading tracking, GNSS course = heading) No  No Yes 






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