All About Symbian - Symbian, Nokia and S60 unwrapped.
How to: Get faster GPS locks - and how to stay patient when you can't
Published by Steve Litchfield at 9:23 UTC, January 4th 2010
Summary:
GPS, like many modern technologies, is often taken for granted. Yet it's quite a bit more fragile, in terms of operation, than you might think. Here are some facts and tips that may help your own smartphone GPS experience.
Having been with us now for over twenty years, from hardcore tech enthusiast territory to mass market gadget, GPS has certainly come of age. On a marketing board outside a phone shop, GPS is mentioned and the user immediately assumes that the phone will, more or less instantly, know where it is on the planet. Just like that. Just like magic. It says 'GPS' so it must do what it says on the tin. A bit like "3G" or "5MP camera". Simply facts and things that will just 'work'.
Unfortunately, this is misunderstanding the technology in the case of GPS. You've got a network of a couple of dozen satellites orbiting the Earth at a huge altitude of 16,000 miles (approx, see this article for all the tech detail on GPS), while your humble battery-powered electronic device attempts to receive their transmissions, do a staggering amount of complex mathematics and somehow derive where you are. As quickly as possible and using as little power as possible.
Standing in the way (usually literally) of such a feat are:
- Buildings and terrain - under an open sky, your phone's GPS receiver might 'see' a dozen satellites at best. In a typical suburban environment, with trees, houses, wires, plus (typically) metalwork in your car, the number of satellites consistently visible might be as low as 4 or 5. In an urban environment, the number can be as low as 1 or 2. Oh, and at least four good satellite signals are needed for a 'lock'.
- Signal reflections - following on from the first point, direct obstruction, we have confusion from receiving GPS signals 'bounced' off objects. In the worst case, in a city, the poor receiver sees far more reflected signals than originals, and, somehow, has got to work out which is which.
- Weather - the thicker the cloud cover and the worse the weather, the weaker the GPS signals. These radio signals are weak enough as it is (remember that altitude), it doesn't take much to block them. A brick wall is more than enough. And think how much matter there is in 10,000 feet of dense cloud/rain etc.
- Angle - along similar lines, the lower in the sky a GPS satellite is, the weaker its signal, since it has to travel through far more weather/cloud to get to your phone. Satellites high in the sky will deliver the best signal and the most reliable fixes.
- Time - your smartphone's GPS should certainly remember a last calculated position (and also the positions and velocities of the GPS satellites) if it was only a few hours ago. But what if you've moved since that time? What if it's several days later? What if you've moved a few hundred miles and it's a week later? The GPS chip has to start, literally, from scratch, in terms of tracking down where the satellites are and how they're moving.
- Movement - when starting out on a journey, a navigation app is often kicked off when you're already moving, potentially making the triangulation calculations much, much harder.
- Relativity - yes, that theory of relativity. The satellites are high enough and moving fast enough that there are genuine relativistic effects to all the time calculations. Don't ask about the maths needed to correct for these effects - your head would explode!
Armed with the above information, you can quickly see why GPS receivers can struggle indoors, even near a large window. And you can see why they might take longer to 'lock on' when you haven't used the functionality for a while. And why they don't work very well in cities. In each case, it's not your smartphone's GPS that's faulty - you're simply running up against the laws of physics.
Luckily, there are factors that work in your favour too. Because you have a smartphone, with its own Internet connection, it's able to look up orbital data about the GPS satellites to give the sky-scanning process a massive head start. This is what's called 'Assisted GPS' and is why one of the first things you should do when troubleshooting a GPS problem is to dive into the 'Positioning' settings and make sure that there's a valid Internet access point specified. (And, for pay as you go data users, that you have credit on this account!) Don't worry about data usage, the orbital data is highly compressed and only amounts to a few kilobytes, but note that many pay-as-you-go operators now (annoyingly) charge the full (e.g.) 30p/50p/day even if you only use a few kilobytes.
Armed with this data, the receiver knows exactly where the satellites should be in the sky and can look for the right ones on the right frequencies, saving a lot of scanning time. And, having grabbed the orbital data from an Internet server, this is usually valid for a few days, meaning that if you try and get a GPS lock again within that time period, the receiver already knows the satellite orbits and can jump quickly to looking in the right places.
Other factors that play a part in the time taken to get a GPS lock are the complexity of the receiver chip (the number of 'channels') and the quality of the GPS antenna. You'll remember the latter playing a part in the development of the Nokia N97, where the first few months of models off the production line came with an antenna design that was prone to electronic interference - the end result was bad GPS radio reception and, ultimately, poor GPS locks.
In short, even with help from Assisted GPS/data, it's a veritable miracle that GPS works at all, considering the obstacles in the technology's way. But it does work, given appropriate help from you the user:
- Make 100% sure there's a valid Internet access point set up in Settings|Positioning.
- Be patient when getting a lock is slow and try to understand the reason why it's slow in this particular instance. For example, "Oh, I get it. It's taking 2 minutes to lock on because I haven't used it since last month, when I was in France." Or "It's slow because I'm in a metal-framed bus and the weather's lousy". That sort of thing....!
- Try not to cover the GPS antenna in your phone with your hand - flesh and blood is also moderately good at blocking GPS radio signals. If you don't know where the antenna is on your device, Google it and find out.
- Try to remain stationary while getting a fix - there's no point in making the GPS chip's job much harder!
- Do everything you can to maximise the phone's GPS antenna's view of the open sky.
As time goes on, the technology is improving, mind you. With better satellites (they're being launched and replaced regularly), transmitting on better frequencies using better encodings and with better receiver designs, we may even get to the point where tutorial features like this one become redundant because GPS will work so quickly for so many people that troubleshooting becomes almost unheard of. But we're not quite there yet.
Steve Litchfield. All About Symbian, 5th Jan 2010
PS. If you're often in an urban area and cursing the blockages/reflections mentioned above, I can recommend Maps Booster, a small and cheap utility that adds Wi-Fi-based positioning into the mix. Install it and fixes from Wi-Fi networks get used by Symbian's Positioning sub-system - it means that you then have strong position fixes in both the country and the town....
Discussion
Anyway, my answer to all of the above is to dump the phone GPS and just use a proper dedicated satnav unit. I'll never go back except in emergencies.
Now of course that's not going to break the bank (and the rest of the tariff really suits her needs) but the extra £5-6 on the first few bills was a bit of shock to us both - especially as she was only using it to get an aGPS link.
Gav
PS - just to second Steve's recommendation of Maps Booster. I've got it on my N97 and it works flawlessly. Best £3 I've spent at the Ovi Store
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Originally Posted by daos
Here we go. Since i've Omnia HD, even cold start is no more then 10 sec, a warm one is always instant, regardless of area (mountains, town etc.).
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re: i8910 HD, no, it simply has a great GPS antenna. But then you'd hope so - the thing is large enough 8-)
I think it happens more often than our Guru thinks.
8-(((
This info changes quite a lot, IMHO - maybe the networks are trying to force us towards contracts. And yes, this info does rather make using Assisted GPS for occasional fixes relatively expensive. Hmmm...
Summary of changes
From 26th September we're making the cost of browsing the whole Internet on your phone with web'n'walk simpler. Rather than pay for the amount you download until you spend £1, there will be a simple daily fee of £1 which gives you 24 hours unlimited browsing.
I'm appalled at the way Vodafone changed the way they billed data to my payg account *without telling me*. Must have been in the very small print etc. And I was wondering why my credit had been going down so fast..... Gah.
when you compare the samsung i8910 to any of the latest nokia in terms of gps capabillities the samsung walks all over them
its a shame as gps can be really good in phones yet we are allways making excuses saying its probably the clouds or iam holding it at the wrong angle , well iam sorry with a sensitive gps chip them things shouldnt come into play
i just loaded garmin on my i8910 and instantly indoors all the bars went green
even on the 1st start with agps on it took around 10-25 seconds to get lock
it outperforms any dedicated sat nav ive used as it has agps and the chip is just as sensitive as any tomtom etc
iam sitting here now on the ground floor in my sitting room surrounded by daouble glazing and double brick walls with another floor above me and then a roof and loft with insualtion and iam getting a 12m-17m accuarcy range which is pretty dam good
i hope nokia follow samsungs suit and start using better gps chipsets , i think the last nokia for me to have amazing gps quality was the n96 it seems to have gone backwards from there
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Originally Posted by slitchfield
Re: i8910 HD, no, it simply has a great GPS antenna. But then you'd hope so - the thing is large enough 8-)
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You know, if only Samsung could sort the DRM so that I could download BBC iPlayer programmes, I'd be back on the i8910 HD and probably loving it about now....
i do use agps and i have a data plan and i am a firm believer that people that use these kinds of phones without data plans should not complain when things dont go right for them as these devices are built to be used with a data plan.
on gps front gps+ downloading once a week on prepaid or everytime like nokia makes a lot of difference if provider chooses to charge daytime max. + plus faster locks for the whole week in comparison to having to connect, then download, then triangulate.
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Originally Posted by gdigenis
i do use agps and i have a data plan and i am a firm believer that people that use these kinds of phones without data plans should not complain when things dont go right for them as these devices are built to be used with a data plan. |
No, but it's a prerequisite. i.e. any phone that DOESN'T have iPlayer programme downloading (about half the current Symbian world?) is ruled out, IMHO, for a UK resident, anyway.
Effectively, it adds another huge convergence factor into the smartphone mix - TV on the go.
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Originally Posted by slitchfield
Eh? GPS+ is just Assisted GPS by another name. Grabs data once a week rather than every time, but essentially the same thing 8-)
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What boggles the mind of someone like me (with RF and engineering background, mind you) is a comment that Nokia need more sensitive GPS chipsets!
I can only conclude that such a comment was made by someone who has not used an LD-3W, or an E71, or a 5800XM. I have a 'proper' Garmin handheld GPS unit, complete with WAAS support. Comparison? There is none. Lock times are similar if AGPS is not used, as is to be expected (as any chipset without a network connection will have to receive the almanac and ephemeris data from the sats themselves, which takes time). Once AGPS enters the mix, the Garmin is left in the Nokia devices' dust in terms of lock time.
In terms of sensitivity, the Garmin is outclassed almost indescribably by all three Nokia devices. The Nokias will all easily obtain a solid position lock in a remote part of a given basement, where the Garmin is absolutely incapable of receiving even a single satellite. In some real-world, side-by-side geocaching usage, I found that the Garmin (even with the advantage of WAAS) would lose lock totally with just a little bit of tree cover, while it was almost impossible to lose a lock with the E71. In practice, the vastly higher sensitivity of the chipset in the E71 led me to multiple caches before a much more experienced cacher with a more recent and expensive Garmin unit as well.
Yes, the newer dedicated GPS units are tending toward more sensitivity, but they still lack the network connectivity, and thus will take longer to get a lock under almost all circumstances. They also lack nearly all of the other converged features of a good smartphone, requiring multiple devices to be carried rather than one, and offering few real advantages over said smartphone.
OK, from personal experience, I have seen that the E75 is not quite as sensitive in GPS terms as the devices mentioned above, but it still easily blows away the aforementioned Garmin unit.
Which Nokia devices are being regarded as not having sensitive GPS chipsets?
