Does GPS take longer to calculate speed more accurately?

I am using a battery powered GPS tracker which has the GPS sleeping most of the time.
The unit wakes up the GPS, gets a position, speed & heading, transmits that information via satellite then goes back to sleep.
Speed resolution is only 4 knots and heading resolution is only 45 degrees which isn't really sufficient for our needs.
The manufacturer says that the reason for the lack of resolution is that they only wake up the GPS for a short time in order to gain a GPS fix, which is primarily to determine location and then the unit goes back to sleep.

This is the first I have heard of this. Would a GPS have to wake up for a longer period in order to get a more accurate speed & heading?

My suspicion is that the reason for the lack of resolution is more to do with the extra transmission cost - a few more bits need to be sent and also a bit more battery power to transmit those extra bits.

Interested to know whether I have missed this and a first fix would not be able to have an accurate speed/heading. Seems to me if they can have 4 knots of resolution they must know the speed to better than 4 knots of accuracy. If it isn't accurate then how are they to know that it isn't actually moving at 50 knots?

 

Ok, thanks for the information. I will have to research more. I did have a pretty good look for info on speed vs time after turn-on for a fixed GPS, or even position vs time after turn-on but couldn't find any graphs or other info to prove it one way or the other.

For the transmissions, these devices typically transmit position, speed & heading in about 8 bytes - 64 bits. So if they had to transmit 2 more bits I guess we would be looking at 3% increase in time to send and 3% extra battery cost for transmissions. These devices are advertising battery lives up to 9 years so transmitting the extra bits could waste up to 3 months of battery life over 9 years.

However, having to wait for a 2nd or even a 3rd fix to get better speed/heading accuracy would drain the battery a lot more than that. Pity these units don't have the ability to adjust TTFF so we could adjust to balance battery vs accuracy!

 

Possibly the 'first fix' is actually the 2nd internal fix as the unit already puts out speed & heading on the 'first fix' and both parameters are always within 2 knots & 22.5 degrees of the actual vessel values. Makes me wonder how close it would be if we had better resolution.
I think most GPS these days have doppler calculations to get instantaneous velocity but I have no idea how they would calculate heading (cmg) without at least 2 updates.

There would definitely be other overheads in transmission time & battery life that I didn't take into account. But it seems these trackers are favouring battery life over accuracy.