GPS reception in tunnels

[weeds]

why doen't my GPS work when i am driving through a tunnel??

haha, well i know why but if these tunnel cost hundreds of millions of $$$ you would think somebody would have come up with technology to keep your GPS in the right spot and maintain speed display while in a tunnel

[Lotz-A-Landies]

The problem is that GPS works by a very complicated algorithm which calculates using the constants of the speed of light and the time difference between satellites with known positions when the time signal is received by the receiver on the ground.

The only way to reproduce this would be to install multiple artificial satellites transmitting time signals throughout all the tunnels and have this data installed into every GPS receiver in the country. Then the accuracy of all these devices would have to be increased to better than that in surveying equipment because the time difference between artificial satellites in the roof of the tunnels will be so close as to render most devices useless.

The only way to get them to actually work in tunnels would be to have a second function in the GPS receiver that calculates speed, using signals emitted by transponders at fixed intervals along all tunnel ceilings. This function could activate when the GPS signal is lost as the vehicle enters a known tunnel.

You could always use the speedo!

[Eevo]

when i visted syd (from adel) last year i used gps to get around syd. missed the turn off in the tunnel, stupid gps didnt know where i was.

[OffTrack]

GPS doesn't work underground for reason given above. You can't blame the device for a user who doesn't know the limitations of the equipment they are using. a saying about workmen and tools springs to mind.

[weeds]

to increase reception in my defender years ago i purchased an antenna that took signal from the roof and transferred to inside the car for better reception

drilling holes in our tunnels might cause some leaks

just figured with more and more tunnels coming online there would be a smart cookie out there inventing a simple solution

i cannot read my speedo, not enough back lighting when it gets dark......

[weeds]

GPS doesn't work underground for reason given above. You can't blame the device for a user who doesn't know the limitations of the equipment they are using. a saying about workmen and tools springs to mind.

i couldn't remember which was the best exit to take on sat, when the GPS re-connected i discovered i should have taken the one prior....oh well

btw, i understand the limitation of the device in its current form but in this modern world i am sure there will be a solution some time in the future. just imagine if nobody thought outside the square

[Lotz-A-Landies]

If Governments and tunnel owners worldwide could get together with manufacturers of GPS receivers I'm sure it could be solved. The real issue is that the GPS system was launched by the US military and there is no benefit to them to solve the civilian tunnel problem.

If transponders in tunnels could transmit their location rather than a time signal and GPS receivers had a function to calculate from it. There is no reason that speed and turn-by-turn navigation functions couldn't operate in tunnels.

It's just getting an agreement on an international standard and a committment from tunnel owners to install and maintain the equipment.

[p38arover]

The in-built GPS in our 2010 Subaru Forester works in the Sydney M5 tunnel. I assumed it had some sort of inertial system to maintain track. It's accurate, too.

[weeds]

The in-built GPS in our 2010 Subaru Forester works in the Sydney M5 tunnel. I assumed it had some sort of inertial system to maintain track. It's accurate, too.

Well there you go, progress is being made

[goingbush]

The two latest Gaermin Nuvis I have all are smart enough to know your going into a tunnel and keep directing you at the speed you were going when you entered the tunnel.

[OffTrack]

There is work being done on indoors gps which I believe is reasonably advanced. From what I understand it relies on the gps signal being received by an antenna on the roof off the building being retransmitted on individual floors. I wouldn't be surprised if the technology was applied to tunnels at some point.

Googling reveals that at least one company has commercialised this technique for various uses including tunnels.

http://www.gps-repeating.com

[101RRS]

The in-built GPS in our 2010 Subaru Forester works in the Sydney M5 tunnel. I assumed it had some sort of inertial system to maintain track. It's accurate, too.

At first glance mine does too however it is just the software in the GPS knowing what road you are on, that you are in a tunnel and continues to calculate and display your position based on the speed it has programmed for the tunnel - all is OK normally unless there is a traffic jam and you have to stop. If there is a turn off in the tunnel and you have it programmed in your route unless you have had to stop the exit command from the GPS will be close enough for Government work.

Garry

[Lotz-A-Landies]

There is work being done on indoors gps which I believe is reasonably advanced. From what I understand it relies on the gps signal being received by an antenna on the roof off the building being retransmitted on individual floors. I wouldn't be surprised if the technology was applied to tunnels at some point.

Googling reveals that at least one company has commercialised this technique for various uses including tunnels.

GPS Repeater (http://www.gps-repeating.com)But if you read further, what it is actually doing is re-transmitting the GPS data for the location of the initial receiver on the roof which will remain static even though your car is moving within the tunnel. So the reality is that speed measurement will likely fall to zero while you are in the tunnel and then jump as your receiver starts having direct line-of-sight to the actual satellites.

What it will do is reduce the time to acquisition when exiting the tunnel and why it is important for Police, ambulance and fire authorities.

[Lotz-A-Landies]

There is work being done on indoors gps which I believe is reasonably advanced. From what I understand it relies on the gps signal being received by an antenna on the roof off the building being retransmitted on individual floors. I wouldn't be surprised if the technology was applied to tunnels at some point.

Googling reveals that at least one company has commercialised this technique for various uses including tunnels.

GPS Repeater (http://www.gps-repeating.com)But if you read further, what it is actually doing is re-transmitting the GPS data for the location of the initial receiver on the roof which will remain static even though your car is moving within the tunnel. So the reality is that speed measurement will likely fall to zero while you are in the tunnel and then jump as your receiver starts having direct line-of-sight to the actual satellites.

What it will do is reduce the time to acquisition when exiting the tunnel and why it is important for Police, ambulance and fire authorities.

Remember that a GPS requires a minimum of three satellites to calculate position in three dimensional space.

[manic]

I thought there were a number of GPS systems that read speedo input. A fallback for temporary GPS drop outs which works well for tunnels. Perhaps some use magnetic compass as well?

[richard4u2]

brilliant, another bit of electronic junk in a tunnel that will on a hickup close down every tunnel in oz:nazilock:

[Lotz-A-Landies]

I thought there were a number of GPS systems that read speedo input. A fallback for temporary GPS drop outs which works well for tunnels. Perhaps some use magnetic compass as well?OEM In Car nav systems maybe but not after-market ones.

The other problem is that my D4 speedo over-reads by ~ 6KPH so while in the tunnel I won't know whether I was reading GPS +/- 0.5KPH or speedo -6 KPH.

[tangus89]

There was an article in azimuth or position magazine i cant remember which about a land based positioning system. Basically the same as gps but the 'satelites' are sitting on top of hills/buildings/in tunnels etc. and because they aren't moving there are no complex calculations to determine their position, as well as a hell of a lot less atmosphere to interfere with. The result was that you could, just from your phone be able to locate yourself to the chair you are sitting in, in your house. A few large mines already use similar systems, and i think a few euro countries have or are setting up systems. i will try and find the article and scan it. but basically this solves the gps tunnel issue as the 'satelites' can be mounted anywhere.

cheers
Tangus

[Lotz-A-Landies]

I do know that GPS used to have an amount of fuzz added to the system (by randomly changing the time signal on particular satellites) to create positioning errors and prevent the enemy using the system for accurately positioning it's troops against the US military. The US were able overcome the error by knowing when to get an accurate fix from the satellites and use inertial navigation between fixes. The US could also turn off the satellites at will and intermittantly did so over the middle east during Gulf War Mk1.

The whole fuzz system came undone when the CSIRO testing automated pilot systems for Port Phillip Bay fitted a GPS receiver in the Point Lonsdale Lighthouse. From the known location of the lighthouse they could calculate the error in the GPS signal and then transmitted a correction signal to the Port Phillip Bay area. Once this research was published and the world knew of the workaround the fuzz became redundant and the US Military removed the error generation.

[tangus89]

GPS satelites emit 2 signals on seperate frequencies, the C/A and P waves. the c/a is the wave our handhelds recieve, it repeats its coded signal fairly regularly (I cant remember exactly the time, 12 min comes to mind but may be wrong) and the Yanks put a bit of error into it which is that fuzz.
The P-wave's code is repeated over a long period of time, i think its a number of days from memory, i havent got my notes nearby so cant get actual numbers.
so basically the american military use the c/a code to find out where in the p code they are, then they can use the difference between the two waves to eliminate atmospheric errors quite well as well as use the p code which is error free to get their position. The c/a code is still "fuzzed", there was a brief period of time that they cleared it but its back to its fuzzy ways.
the russians have a satelite system up called Glonass, about as old as GPS, it also has errors put in by the russians. Recently some handheld GNSS units and most surveying GNSS recievers pick up both, giving access to 50 something satelites. making it more likely to get a good fix wherever you are. us surveyors do basically the same thing as the CSIRO test to get accurate positions, fix one receiver over a known location, and use another portable one to do the survey. they are connected by radio link so the position difference can be calculated on the fly by the machine (RTK - real time kinematic) or post processed without a radio link, but it takes time back in the office.

I did a job last week which we did a bit of testing for ****s and giggles with the accuracy difference between our sub centimeter GNSS sytem ($50000) and a handheld ($500) some points were as much as 11 meters different, even though the hand held was saying its accuracy was 5m. We also occupied the same point a number of times and got up to 13m difference just with the hand held. if the fuzz was switched off again handhelds theoretically could have sub meter accuracy.

will have to dig my notes out and freshen up on it, something i am supposed to know.

[manic]

OEM In Car nav systems maybe but not after-market ones.

The other problem is that my D4 speedo over-reads by ~ 6KPH so while in the tunnel I won't know whether I was reading GPS +/- 0.5KPH or speedo -6 KPH.

Actually yes some aftermarket ones do have this feature. My old man has a pioneer flip out screen media/gps system that has a VSS input (Vehicle Speed Sensor). Its over 3 years old! I also would not be suprised if the unit uses GPS to calibrate the VSS input so that it is accurate.


BAE developed a GPS fallback navigation system for military incase GPS satellites get shot out of space or more likely jammed.. it uses known radio frequecy amplitudes or something like that. Mobile phone towers and such. Apparently works very well in built up areas.

Edit- found an article on it: http://atwonline.com/aircraft-engines-components/news/bae-systems-unveils-potential-alternative-gps-0711

[PhilipA]

LORAN - Wikipedia, the free encyclopedia

Look up LORAN navigation.
We were using this in Saudi Arabia in 1985.
Still wouldn't work in tunnels though.
Regards Philip A

[Bushie]

Fuzz - or Selective Availability was turned off in May 2000 at the direction of Clinton.
Differential GPS was already available to the public by then, and GPS was already well entrenched in civilian systems (particularly aviation).
The US can still deny their satellite constellation to any region of the globe that they wish.

Drilling holes in tunnels so they "leak" GPS signal :) an interesting concept especially for the Sydney Harbour tunnel - oh hang on GPS doesn't work under water anyway :eek::eek::eek:;).


Martyn

[tangus89]

LORAN is similar but uses different radio waves and I'm not sure but I don't think it is coded the same. LORAN was fairly poor in accuracy compared to GNSS which is why it has pretty much died out. This is basically gps without the atmospheric and positions errors. I'll search for the article.

[Blknight.aus]

actually..

if your gps is good enough you dont need the satelites.

you can put up any number of transmitters (on their dedicated frequency) that transmit as part of their time code their location. This gets done for AGPRS stuff already

The real problem its the distances involved. GPS works better when you have your transmitters randomly located nice and far apart from each other and as far away from you as possible. In a tunnel because of the short distances, the speeds likely to be involved and the relatively symetrical pattern youd wind up having to get the coverage required youd loose the accuracy of the triangulation.

GNSS augmentation - Wikipedia, the free encyclopedia

ELTA : Elt, ground station, military radio transmission, physico-chemical analysis... (http://www.elta.fr/uk/transmission-and-communication/4/rf-hf-transmission/16/gps-repeater/89)

Heres some primers for the relative info.

[Quarks]

GPS satelites emit 2 signals on seperate frequencies, the C/A and P waves. the c/a is the wave our handhelds recieve, it repeats its coded signal fairly regularly (I cant remember exactly the time, 12 min comes to mind but may be wrong) and the Yanks put a bit of error into it which is that fuzz.
The P-wave's code is repeated over a long period of time, i think its a number of days from memory, i havent got my notes nearby so cant get actual numbers.
so basically the american military use the c/a code to find out where in the p code they are, then they can use the difference between the two waves to eliminate atmospheric errors quite well as well as use the p code which is error free to get their position. The c/a code is still "fuzzed", there was a brief period of time that they cleared it but its back to its fuzzy ways.
the russians have a satelite system up called Glonass, about as old as GPS, it also has errors put in by the russians. Recently some handheld GNSS units and most surveying GNSS recievers pick up both, giving access to 50 something satelites. making it more likely to get a good fix wherever you are. us surveyors do basically the same thing as the CSIRO test to get accurate positions, fix one receiver over a known location, and use another portable one to do the survey. they are connected by radio link so the position difference can be calculated on the fly by the machine (RTK - real time kinematic) or post processed without a radio link, but it takes time back in the office.

I did a job last week which we did a bit of testing for ****s and giggles with the accuracy difference between our sub centimeter GNSS sytem ($50000) and a handheld ($500) some points were as much as 11 meters different, even though the hand held was saying its accuracy was 5m. We also occupied the same point a number of times and got up to 13m difference just with the hand held. if the fuzz was switched off again handhelds theoretically could have sub meter accuracy.

will have to dig my notes out and freshen up on it, something i am supposed to know.

The ground based system you saw in Position would be Locata.

12.5 minutes is the length of time it takes to download the entire navigation message (almanac, etc). The C/A and P/Y codes repeat much faster.

The C/A code is not "fuzzed", the signal is at a tenth of the frequency than the P/Y code, so is inherently less precise.
Selective Availability isn't even an option on satellites launched after '09 (Block IIF). Civilian users can get mm precision by using the phase of the L1 and L2 carrier frequencies - which is what quality (surveying) GNSS receivers do.

What is more useful for vehicle applications is the L2C signal (Block IIR-M on), which is intended to improve signal acquisition and reliability, so helpful in cities where multipathing and poor sky view are issues.

Still doesn't help with inside tunnels - there isn't a standard augmentation system, and any augmentation costs extra to implement, so won't ever be a standard feature of receivers.

:)

[OffTrack]

But if you read further, what it is actually doing is re-transmitting the GPS data for the location of the initial receiver on the roof which will remain static even though your car is moving within the tunnel. So the reality is that speed measurement will likely fall to zero while you are in the tunnel and then jump as your receiver starts having direct line-of-sight to the actual satellites.

What it will do is reduce the time to acquisition when exiting the tunnel and why it is important for Police, ambulance and fire authorities.

Remember that a GPS requires a minimum of three satellites to calculate position in three dimensional space.

That was the first example of the technology I was talking about. Google upon the idea and you'll find other companies and other products.

for example....

GPS Source - Commercial - Railways GPS Retransmission, Re-radiator, GPS Repeating, GPS Retran, L1 Antennas, L1/L2 Antennas, GPS Antenas, GPS Amplifiers, GPS Indoors, GPS Power Dividers, GPS Antenna Dividers, DAGR Antenna, Power Splitters, Signal Cond (http://www.gpssource.com/commercial/railways)

It's pretty obvious that you can't get GPS signal underground as it requires direct line of sight to the minimum three satellites.

With the first product I linked to it would be pretty daft to repeat a single point to the length of a tunnel. The obvious solution would be to have multiple receivers along the length of the tunnel, or strategically positioned before and at off ramps etc. It wouldn't be real continuous gps coverage but would give warning for turns and a granular indication of position.

cheers
Paul

[Bigbjorn]

Simple solution. Don't use tunnels.

I decided years ago to not use toll roads, bridges, or tunnels as an insignificant personal protest against over-taxation of motorists. The only exception I make is the Sydney Harbour Bridge when i am down there. it being a bit of a drag to go over via Gladesville.

[Lotz-A-Landies]

Simple solution. Don't use tunnels.

I decided years ago to not use toll roads, bridges, or tunnels as an insignificant personal protest against over-taxation of motorists. The only exception I make is the Sydney Harbour Bridge when i am down there. it being a bit of a drag to go over via Gladesville.So why not use the M5 East Tunnel in Sydney?

Its the only place in Sydney where you can get free all-day undercover parking! :twisted:

[Bigbjorn]

So why not use the M5 East Tunnel in Sydney?

Its the only place in Sydney where you can get free all-day undercover parking! :twisted:

Oh, Diana, do I detect just a little sarcasm there. Strike a little traffic getting between POW & home?:D

How is life in Mohammed Alley? Are you still the only lady in the neighbourhood who doesn't wear a bag over her head?:angel:

[mikehzz]

If you have assisted gps like in smart phones then the gps still works in a tunnel if you have mobile reception. It uses both satellite reception and mobile phone tower triangulation as inputs. If one drops out it still gets info from the other.

[weeds]

If you have assisted gps like in smart phones then the gps still works in a tunnel if you have mobile reception. It uses both satellite reception and mobile phone tower triangulation as inputs. If one drops out it still gets info from the other.

My iPhone with Tom Tom doesn't work....umm not that I have checked reception

[THE BOOGER]

Its an option you have to turn on as it can use data download and cost a bit:)

[Lotz-A-Landies]

Oh, Diana, do I detect just a little sarcasm there. Strike a little traffic getting between POW & home?:D

How is life in Mohammed Alley? Are you still the only lady in the neighbourhood who doesn't wear a bag over her head?:angel:I've stopped using the Middle-Eastern Distributor and the tinting of the D4 allows me to exit Mecca without having the Religous Police stopping me from driving. They have somehow modified my D4's radio so it does uncommanded channel changes from ABC Classic to SBS so I still get the Imam's teaching.

In shal lah Land Rover can fix the radio.

[mikehzz]

Its an option you have to turn on as it can use data download and cost a bit:)

No not correct. The data download is just for on the go maps from places like google if you haven't stored them on the phone. The triangulation doesn't use data but is part of normal background communication with the cellular network. I triple checked it for an overseas trip.

[Eevo]

If you have assisted gps like in smart phones then the gps still works in a tunnel if you have mobile reception. It uses both satellite reception and mobile phone tower triangulation as inputs. If one drops out it still gets info from the other.

this is incorrect
a-gps helps you get a fix quicker

Assisted GPS - Wikipedia, the free encyclopedia
Assisted GPS, generally abbreviated as A-GPS or aGPS, is a system which can under certain conditions improve the startup performance, or time-to-first-fix (TTFF), of a GPS satellite-based positioning system.

[slug_burner]

Inertial navigation systems are also coming down in price. For tunnel use they will just measure the acceleration you subject the system to and determine changes in velocity and turns to determine your speed and location relative to your last known speed and location.

[mikehzz]

this is incorrect
a-gps helps you get a fix quicker

Assisted GPS - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Assisted_GPS)
Assisted GPS, generally abbreviated as A-GPS or aGPS, is a system which can under certain conditions improve the startup performance, or time-to-first-fix (TTFF), of a GPS satellite-based positioning system.

I've tested mine against normal gps all over the place from the city to the deserts and overseas. My smart phone gives me a fix indoors where the normal gps doesn't. The smart phone works better in the city between tall buildings where the normal can lose satellites. The normal gps is better by far out in the country. Cloudy weather can make the phone drop gps signal when there is no phone coverage. I think the phone has a poor gps antenna. Without cell coverage, the phone can take forever to find satellites and then lose them quite easily. A 3g ipad is the best gps I've used, it must have a better antenna because it seems to work well everywhere, gets a quick fix due to the agps in cell tower coverage and holds it. I've found it gets a pretty quick fix out in the desert too and the screen is great.

Oh and my data has been turned off. I checked with the provider to make sure that this wouldn't affect the gps. Perhaps it may in places where they may charge for everything like the US. I think you pay for incoming calls over there...I may be wrong but that's what I heard.

[FFR]

If Governments and tunnel owners worldwide could get together with manufacturers of GPS receivers I'm sure it could be solved.


no thanks, I do not want to pay for that thing too...

[Lotz-A-Landies]

If Governments and tunnel owners worldwide could get together with manufacturers of GPS receivers I'm sure it could be solved.
no thanks, I do not want to pay for that thing too...Without a worldwide standard there will be no innovation drivers for the modification. If there is a standard the changes to the receiver hardware will likely be miniscule in terms of cost (economies of scale across the Worldwide sale of GPS receivers/in-car technology).

Who do you think currently pays for the radio and telephone re-transmission in tunnels. Mostly the phone companies and the GPS tunnel infrastructure will also be minimal in-terms of the tunnel maintenance and management.