# RF Wireless World

Dead Reckoning Navigation System determines position of a vehicle based on its heading and distance traveled even in the absence of satellite signal.

The DR navigation uses gyroscope (Gyro) to estimate heading. Later it uses heading along with distance traveled to determine position of a vehicle. The major challenge in this navigation type is when satellite signal will be lost for longer time due to long tunnel or other blockage of this type. In this condition error due to accumulated angle will become very large resulting into inaccurate position estimation.

• Let us understand how DR navigation works. The idea is to determine location after some amount of time. We will assume known position at start. The start position is taken at certain time. Course is being noted as per true heading or compass heading.
• A gyroscope measures rotation rate of vehicle in degrees/second.
• Instantaneous heading of vehicle is calculated using integration of rotation rate over time.
• Distance is determined based on speed and time of travel (some duration after which we would like to determine the position).
• Based on initial known location (i.e. position at beginning of time of test) and distance traveled as mentioned above, exact position of the vehicle can be estimated. The figure-1 depicts the distance calculation. Let us assume coarse given is about 125 degree and position is known at start of time i.e. 8AM. Let us determine position after 45 minutes of time. 45/60 gives us 0.75 decimal time. We know speed of vehicle that is 10 knots/sec. Now draw line parallel to coarse line (as shown in the circle) which represents 125 degree. On this drawn line, we will get vehicle position using following formula.
Distance = speed x time duration
We get 7.5 knots as distance traveled on the coarse.