# Does gps receiver need synchronization with atomic clock

1. Aug 3, 2011

### rajeshmarndi

with synchronization what the gps receiver does is compute time difference between his current time (synchronized with atomic clock onborad each satellite) and the time tag of a satellite when the signal was sent. This difference gives the travel time of an signal from the satellite and hence the distance and position of the satellite in its orbit.

so, Why do we need the receiver to compute the positions of the satellite, if satellite itself sends their position with the signal everytime where they were?

2. Aug 3, 2011

### xts

This difference gives the travel time of an signal from the satellite and hence the distance and position of the satellite in its orbit.
No!
This difference gives the distance to satellite. - true.
But it is needed to compute receiver's position, having known satellite position.

3. Aug 3, 2011

### willem2

The satellite only sends its orbital parameters, wich will keep valid for up to 4 hours. The receiver has to calculate the position of the satellite at the time the message was sent from this.

4. Aug 5, 2011

### rajeshmarndi

each satellites in their signal send their time at which they were transmitted. And this time information of the satellite when received by different receiver will be different, which should give the receiver location.

Also is it not possible for the satellite to send its positions in its orbits, each time it transmit. Then similarly different receiver at different location at a given time, will receive different position of the satellite bcoz of their distances from the satellite which will be unique and should give the location of the receiver.
In this way, it seems the distances from the satellite is not required, only the information of their positions in their orbit, could give the receiver location.

5. Aug 5, 2011

### sophiecentaur

The receiver can get away without having an atomic clock because its internal quartz clock is, effectively, being regularly compared with the time standard of the GPS system. It only needs to be stable enough not to drift too much between updates. It can measure, relatively easily the differences in arrival times of the different signals - which gives it the relative distances from the satellites (after some clever jiggery pokery) and, hence, the receiver position.

When you bear in mind the naff little receiving antenna and the very low power of the GPS transmitters, it really is a clever bit of engineering. You have to forgive the fact that you can't just expect to switch on the receiver and use it. It can take many seconds when you are starting from a brand new position. Even longer than waiting for the old valve telly to warm up!

6. Aug 5, 2011

### Staff: Mentor

The receiver gets a clock correction by comparing its computed position with three satellites to the error indicated when adding a fourth. The wiki on gps has a section on this.

7. Aug 5, 2011

### rajeshmarndi

my question was, it is still possible for the gps to locate its postion without any need to sychronize with the atomic clock.

just the information of the time of transmission and also along with it the position of the satellite at the instant of transmitting is only required at the receiver end. As i have mentioned above.

any help where am i wrong.