SiRFDRive® series Dead Reckoning software solutions enable Factory-fit and Tier 1 automotive manufacturers to create automotive GNSS solutions that maintain accurate positioning information in the most challenging environments.
Dead reckoning (DR) is the process of estimating current position based on a previously determined position, or fix, and advancing that position using heading and known or estimated speeds over time. DR navigation tracks changes in heading and velocity using sensors. The results can be very accurate if the sensors used to observe velocity and heading are accurate and the precise position is entered into the system as an update. This is required because any slight error in DR will accumulate and compound itself over time.
Even under ideal conditions, where there is a full view of the sky, the accuracy of GNSS navigation is decreased by factors such as clock errors, ionospheric effects, and inherent system noise, but it can still give a position with an expected horizontal accuracy of <5 meters. In most automobile navigation cases, this level of accuracy is acceptable. However, in real-life situations, a vehicle often experiences less-than-ideal conditions and so needs assistance to maintain accuracy, especially at times when the GNSS signals are blocked. This assistance, in the form of heading and velocity aiding information, enables the system to give its position accurately.
Devices supporting SiRFDRive: SiRFstarV 5ea.
- A gyroscope providing heading data
- An odometer speed pulse
- A vehicle forward/reverse direction signal
The DR data is sampled directly by the SiRFstarV hardware. The gyroscope is sampled through I2C port. There is an internal odometer counter for counting speed pulses. The system uses a GPIO input for the Forward/Reverse input.
SiRFDRive2 uses automobile data bus (e.g. CAN bus, or ODBII) information without using a dedicated gyroscope and connecting the speed pulse. It requires an external application to monitor the bus, capture relevant messages, translate and format them for SiRFDRive2 use. There is a dedicated CSR message to feed car bus data into the SiRFDRive2 system.
The differential wheel ticks (DWT) uses wheel speed/pulse messages from the ABS system to compute the heading and speed data. The forward/reverse direction message is also required.
A second variant of SiRFDRive2 uses the Gyroscope data (typically from the Stability Control System), Speed, and the Forward/Reverse messages. SiRFDRive2 using Gyroscope data will typically outperform SiRFDRive2 using individual wheel tick/speed messages as it directly measures heading changes while DWT DR derives the heading from the wheel pulses and the geometry of the car.
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- SiRFDRive 1 and SiRFDRive 2
- SiRFInstantFix™ extended ephemeris technology
GSC3e/LPa Chipset Package
- Type: 121-ball grid array (BGA) with a pitch of 0.80 mm / Pb free
- Dimensions: 10 mm x 10 mm / Height: 1.4 mm
SiRFDRive 1 Dead Reckoning Sensor Requirements
- Gyro for directional measurement
- Wheel speed signal
- High-resolution 13-bit A/D converter
Data Update Rate
- 1 Hz
Position Fix Availability
- GPS and DR 99%
Horizontal Position Error, GPS and DR
- Static open sky <10 m
- Dynamic open sky <15 m
- Dynamic foliage <20 m
- Dynamic urban canyon <20 m
Speed Error in 98% of Positions
- Static open sky <0.5 mph
- Dynamic open sky <0.5 mph @ >25 mph
- Dynamic foliage <1.0 mph @ >25 mph
- Dynamic urban canyon <1.0 mph @ >25 mph
Heading Error in Open Sky
- @ speed >10 m/s, 22 mph <3 deg
- @ speed >30 m/s, 66 mph <1 deg
- SiRFDRive navigation engine allows OEM and tier 1 automotive manufacturers to build robust location-enabled devices for automotive markets such as in-vehicle navigation, asset tracking, and telematics
- Unlike most Dead Reckoning systems, SiRFDRive leverages our expertise to create a highly coupled system that incorporates information from both the GPS and the Dead Reckoning sensors to provide unparalleled accuracy
- When SiRFDRive is used in combination with the GSC3e/LPa chipset, users can maintain accurate positioning information in urban canyons, tunnels, and parking lots. SiRFDRive also supports SiRFInstantFix technology, which delivers fast time to first fix performance
- SiRFDRive 1 provides customers a turn-key solution with well-defined interfaces for gyro and odometer input. This enables customers to minimise the complexity of their system and achieve faster time-to-market
- SiRFDRive 2 does not require a dedicated gyro and can access sensor information directly from the vehicle bus
- SiRFDRive 2 allows high-volume customers the ability to achieve substantial cost savings while maintaining accurate Dead Reckoning accuracy and performance
- Navigation available within three seconds of start-up without reliance on map matching
- GPS measurements continually calibrate Dead Reckoning data to ensure optimum speed and heading accuracy
- Dead Reckoning measurements validate and correct GPS fixes during signal blockage and multipath conditions
- Enables devices to achieve improved urban canyon accuracy
- Navigation availability in tunnels and parking garages
- Seamless integration with the GSC3e/LPa GPS chipset
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