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Why is Reacquisition Time Important?
One of the critical performance parameters for almost any GNSS receiver is reacquisition time–or how long it takes the receiver to make sense of the available satellite signals after an obstruction has been cleared.

Applications in which reacquisition time is particularly important include automotive sat-nav devices and the railway industry. In both these cases, the vehicle housing the receiver is likely to experience periodic interruptions from overhead obstructions, such as tunnels, of from deep embankments, cuttings or urban canyons. And in some instances these interruptions can last for durations of several minutes – or longer still in some extended rail or road tunnels.

In each case, the GNSS receiver needs to reacquire the satellite signals as soon as is possible after it has left the tunnel or cutting so that it can continue to perform its given role. This may be a safety critical tracking application in the case of a train, or giving turn-by-turn navigation instructions in an automotive application.

In automotive navigation applications, the consequences of poor reacquisition time performance can be unfortunate for the user, and can damage the reputation of a manufacturer's products. For example, a route might involve an important turn shortly after emerging from a tunnel or canyon. If the receiver is still "flying blind" for several seconds after emerging from the obstruction the instruction may not be given until it is too late. And the faster the vehicle is travelling, the greater the likelihood of this happening.

This is why reacquisition time is one of the essential tests that should be performed in developing and manufacturing any GNSS receiver.
By: Andy Walker - 6/27/2012 12:30:45 PM

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