To users with slow GPS locks

[gtcard]

I am using RC33, unlocked G1 on AT&T network. I have been experiencing extremely slow GPS lock times, which seem to get worse over time. I downloaded GPS Status, from the android app market, hopefully to see what the heck is my gps radio doing. Interestingly, I find 2 reasons to be the cause of the slow GPS lock.

I try my best to get consistent results; I fire up my GPS during my daily walk from my house to the local train station (20min walk). Also I fire it up after getting off the train during my commute to work from the train station (30m commute). These are the only times I test the GPS, and this is what I find after doing this for the past 4 days.

1. Either GPS Status sees multiple satellites overhead, but the GPS radio doesn't lock onto them, or

2. At the same locations, GPS Status only sees 1 or 2 satellites, where it saw multiple (10+) the day before, in the same area.

*For the record, my GPS did not achieve lock at all in 3 out of the 4 days. That's three 20 minute and three 30 minute segments where the phone just has no idea where the heck it is.

It almost feels like either the phone or the satellites are actively refusing to communicate with one another. Out of frustration, I decided to just yank the battery out of the phone and boot it up cold. And viola, GPS locks in 2 seconds. This is from standing in the same spot where before pulling out the battery, GPS status did not see more than 2 satellites. After the reboot, GPS status saw 8 satellites immediately.

Can anyone with GPS lock problems give this a shot? Just powering the phone off by holding the power button down doesn't seem to do the trick; you have to pull the battery out and pop it back in.

I have no idea how cell phones work but my guess is that something, perhaps the OS itself, is causing delay between GPS and satellite communication. This problem gradually worsens as the phone stays on, and seems to be corrected when the battery is pulled out (ie: completely cut the power off).

I can't draw any conclusions here, but I'm hoping with some feedback and verification, someone else that is tech savvy can make sense of this.

[XDViPeR]

Before RC33, my gps would lock in right away, after the 33 update. It takes about 2 to 5 mins to find an gps and lock in. I'm thinking its more of an software issue than an hardware issue.

[PumaB]

I have had this happen also but very rarely. I usually leave my gps on for about 30 minutes a day to gather almanac data.

[notxel21]

I've been having this issue with my gps taking several minutes to get a lock.
Just tried removing the battery and replacing and it locked in seconds.

[foxdie]

I too am having lock issues with JF v1.43 RC9 (UK equiv of JF v1.43 RC33). Google Maps can never get a fix even outdoors, if I fire up Velox and look at the available satellites it varies inconsistently, whereas both my Qstarz BT810 Bluetooth GPS module and the GPS receiver in my HTC Artemis will religiously pick up 6+ satellites and get a fix within 30 seconds if not sooner.

[gtcard]

I tried this again just now and got lock in under 5 seconds. GPS status saw 5 satellites as soon as i launched the app, for the first time. i guess this is a temp fix until someone can figure out what it is exactly thats causing the slow lock.

[patientzero]

wow -- been getting this same problem. Will try this fix at lunch -- that slow lock has been ticking me off.

[extorian]

Getting a fast lock on a GPS depends on a number of factors:

* Satellite coverage - the satellites are in a low orbit and hence are moving relatively fast over your position, so just because you could see 20 satellites one day doesn't mean you will an hour later. You need at least 4 satellites that are spread out across the sky to get a decent fix.

* Satellite signal strength - you really need line of site to the satellites above. Trees, being indoors, electrical noise, heated windscreens, etc, will vastly reduce the signal.

* Almanac data - The expected position of a given satellite changes frequently, and this information is constantly being transmitted by the satellites. As a rule of thumb, you will need to use your GPS for at least 15 minutes every week to keep your Almanac data up to date. Your GPS can't use the data from a satellite until it has up to date Almanac data for that satellite and hence knows precisely where it is located. This is why you sometimes see strong signal strength for some satellites but your phone doesn't use them.

* Distance from the location you last had a GPS fix - the GPS will assume you're at the same location as the last time you had a GPS fix and look for the satellites it expects to be able to see from that location. If you've moved more than 100 miles or so from that location then your lock will take longer. The futher you've moved, the longer a lock will take.So, in short, the longer it's been since your last lock, and the further you've moved, and the less you use your GPS, the longer it will take to get a lock.

Try keeping a GPS lock for half an hour, then turning your GPS off and on - you'll find it gets a lock very quickly as it'll have up to date almanac information for every satellite it can see, and you won't have moved.

It should never take longer than 20 minutes to get a lock if you can get a good signal from at least 4 satellites.

[JPH3]

@extorian Totally accurate information; however, does not apply to this issue. I've been aware of this problem ever since RC33. Without a reboot, GPS locks take either a long time, or does not happen at all.

As soon as I power cycle the phone, GPS locks in immediately. I average 8-10 satellites overhead at any given time, so the problem is definitely the phone. I'm under concrete right now, but I never tried toggling to/from Airplane mode. That might also be a workaround without having to power down the phone.

[extorian]

It could be the satellite search algorithm messing up too. If the GPS can't get a lock quickly they start to search the sky for satellites. They do this by taking a satellite it can receive, and assuming that satellite is straight upwards. Based on its current known almanac data it will then search for the satellites that it should theoretically be able to see in the sky based on the above assumption. When it finds another it assumes the position directly between those two satellites is straight up. When it finds 3 satellites it attempts to calculate a 2D fix, at which point it should know which other satellites to look for.

This algorithm can screw up. Especially as the satellites are moving so fast. It can end up looking for satellites that it may never see for a long time (hours?).

A power on/off would snap it out of that (well, it would retry it).

It's just a theory of course...

I'd be hesitent of blaming the RC33 update yet though. If it's only a firmware issue then everyone on RC33 would have this problem. It could be a combination of factors of course - one of them being RC33.

Old almanac data would definately account for what you're experiencing however - it can send the auto-search way off.

It's easy to test - keep the GPS on after getting a proper lock for about half an hour. I'm not sure if the GPS turns off when the phone screen turns off. For the next few days (3, say), you should be able to get a lock in under 2 minutes if you have a clear view of most of the sky. This test would eliminate it just being the almanac being out of date.