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your position is our focus
1 Dead Reckoning Fundamentals
1.1 Dead Reckoning enabled GPS (DR)
Dead Reckoning is a feature to make GPS more accurate and reliable in urban canyon environments and during
GPS outages. It uses additional sensors to measure speed, heading and direction (forward / backward). Therefore
a DR enabled GPS receiver consists of a GPS receiver, a turn rate sensor (gyroscope) and a speed indicator
(odometer
1
). By combining the information of all sensors a position can be determined even if GPS positioning is
degraded or impossible due to restricted sky view. This means that a DR enabled receiver continues to report
positions when GPS signals are blocked, such as in tunnels or in heavy urban canyon environments.
GPS Kalman Filter
GPS
receiver
Dead Reckoning
Parameter
Enhanced Kalman Filter (EKF)
Position,
Speed,
Direction,
Time
Calibration
Turn Rate
Speed
Forward/Backward
GPS
Signals
GPS Position,
GPS Data
Figure 1: Dead Reckoning Block diagram
1.2 Dead Reckoning Principle
In contrast to GPS, which delivers absolute positions, Dead Reckoning is a relative method. The sensors give
information for a defined measurement period, and the location is calculated relative to the previously known
position. Therefore an absolute GPS position is required as a starting point, which is the last known GPS position.
δ
s
y
n
x
n
y
n+1
= y
n
+ dy
x
n+1
= x
n
+ dx
Known parameters:
s
= Traveled distance (odometer, direction)
δ
= New angle (gyroscope)
dy = s cos (
δ
)
dx = s sin (
δ
)
= last GPS position
= DR position
x
y
Figure 2: Dead Reckoning Principle
Parameters used for the relative position calculation are:
1
An odometer is by definition a device, which measures linear distance traveled. GPS receivers can also include software (also known as an
odometer) used to calculate this distance.
LEA-4R / TIM-4R - System Integration Manual / Reference Design Dead Reckoning Fundamentals
GPS.G4-MS4-05043 Page 7