ST Shoots to Improve Automotive Navigation Using an Inertial Measurement Unit

October 27, 2021 by Jake Hertz

Positioning in tunnels and garages can be difficult. Taking on this challenge comes STMicroelectronics' newest GNSS chipset using an inertial measurement unit (IMU) for better positional accuracy.

Global navigation satellite systems (GNSS) have found themselves increasingly important within the past couple of years. If you were to look inside many electronic devices today, such as a phone, smartwatches, and cars, chances are you would find GNSS hardware. 


GNSS loses accuracy in critical environments like tunnels.

GNSS loses accuracy in critical environments like tunnels. Image used courtesy of Furuno


GNSS traditionally requires the receiver to have a line of sight with three or four satellites simultaneously; anything less will degrade accuracy and performance. This degradation makes GNSS challenging to operate in critical environments such as tunnels, under bridges, or beneath tall buildings in a city. 

This week STMicroelectronics (ST) released a new GNSS chipset that aims to address these challenges and allow for high positional accuracy regardless of environment. 


Dead-Reckoning with an IMU 

To solve this problem, ST has turned to a solution called "dead-reckoning," which is a historical term for calculating one's position by estimating the direction and distance traveled. 

In the context of GNSS and electronic systems, dead-reckoning is often achieved through an IMU. An IMU is an electronic sensor that consists of a fusion of accelerometers, magnetometers, and gyroscopes. 

IMUs detect linear and rotational acceleration in 3-axes to measure precise relative movement in 3D space. With this information from an IMU and some clever computation, one can compute a relative position over time. 


An IMU can provide information in six degrees of freedom.

An IMU can provide information in six degrees of freedom. Image used courtesy of Ceva


Hence, in a situation where a GNSS loses line of sight with satellites, the system can instead turn to dead-reckoning with an IMU to maintain positional accuracy. 


ST’s New Chipset 

This week, ST released its newest GNSS chipset for automotive, the Teseo-VIC3DA

As mentioned, the most notable aspect of this new chip is its use of dead-reckoning to supplement the loss of position in critical environments. 

To achieve this, the Teseo-VIC3DA essentially takes ST's Teseo III GNSS1 IC and integrates an automotive-qualified 6-axis MEMS IMU. While using these techniques, the chip achieves a tracking sensitivity of 163 dBm and accuracy positioning as low as 1.5 m CEP. Fully loaded with dead-reckoning software, the chip hopes to be an easy-to-use, standalone GNSS module.


Block diagram for the Teseo VIC3DA chipset.

Block diagram for the Teseo VIC3DA chipset. Image used courtesy of STMicroelectronics


The IC itself comes in a 16.0 mm x 12.2 mm x 2.42 mm LCC package, also featuring an onboard Temperature Compensated Crystal Oscillator (TCXO) and embedded flash. It consumes a standby power of 17 µA at 3.3 V and supports a temperature operating range from -40 °C to +85 °C. 


Final Remarks 

As GNSS finds its way into more and more electronic devices, finding ways to overcome dead zones will become increasingly important. By using an IMU and dead-reckoning, ST has achieved this for automotive, which is a very positive step in the right direction.



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