Ask Dr. Ramsey Faragher About Navigation/Positioning Technology

Dr. Ramsey Faragher graduated from the University of Cambridge in 2004 with a first-class degree in Experimental and Theoretical Physics. He then completed a PhD in 2007 at Cambridge in Opportunistic Radio Positioning under the direction of Dr. Peter Duffett-Smith, a world expert in this field. He is now a Principal Scientist at the BAE Systems Advanced Technology Centre specializing in positioning, navigation, sensor fusion and remote sensing technologies in the land, air, sea and space domains. We recently covered his NAVSOP project, an advanced positioning system that exploits existing transmissions such as Wi-Fi, TV, radio and mobile phone signals, to calculate the user’s location to within a few meters. Dr. Faragher has graciously agreed to answer any questions you may have about NAVSOP, the future of GPS, or what a theoretical physicist puts on his business card. Ask as many questions as you like, but please confine your questions to one per post.

Comments

Faragher's Slashdot Post on How NAVSOP Works

[eldavojohn]

He seems to have written a post on how this works and then later made an account. Sorta verified here. His post is very informative and might answer a lot of questions and generate more meaningful ones.

Most Surprising Correction?

[eldavojohn]

I'd imagine a lot of positioning calculations involve accounting for or adjusting for known effects or noise. For example, accounting for general relativity in GPS. What is the most surprising correction you've ever come across (even on an exam or done in theory)? Have you ever found yourself saying "I didn't think that could affect the calculations so much."

Indoor Positioning System

[gshegosh]

What kind of accuracy is possible to achieve using NAVSOP - or other systems you know of - if I can place stuff like APs, mobile phones, etc. myself in a factory area? Do you have methodology for designing placement of such devices so positioning accuracy is reached at every point? How low can one get with costs of such solutions?

In-Building and Underground GPS

[GeneralTurgidson]

Will there ever be a way to accurately use GPS without open sky access in a building or underground?

Re:In-Building and Underground GPS

[witherstaff]

Yes, I know Western Michigan University Library technology staff have an in-house built app for an in-out board that uses wifi signal strengths to locate staff. It's been active for over a year. It does have to be initially trained for any different location. Not hard with the push of a button. Also android only, iphone doesn't let you sniff information on other wifi nodes, just the one you're connected to. I don't have the published article reference offhand but there are a variety of papers on similar ideas.

Privacy

[girlintraining]

It would seem that to use this technology, the client would need to have a much larger datastore than with GPS: Whereas only the positions of the GPS satellites need to be known to make a calculation, the dataset here is in the many thousands to millions. In addition to the data required for map storage, it would seem any implimentation of this would require an internet connection to download the data in a geographically-restricted fashion. This opens the door to privacy issues that standalone GPS clients do not have.

How do you plan on addressing the privacy issue with your product?

Re:Privacy

[kav2k]

I think you're misunderstanding the point. OP talks about finding bare coordinates, not position on a map. Not all applications of GPS are tied to the map data, and map data is "external" to finding your position anyway (but can be used to correct it with assumption like "you're on the ground and on a road").
Sure, maps are big, but all the data needed to get raw coordinates is quite small. But with this system, you need a database of all your new "reference points" - cell towers, wifi, etc.
What's worse, this data becomes obsolete fast, while GPS constellation is not radically changing often, and all (most?) changes are communicated automatically via almanac data.

Precise Positioning in Deep Space?

[eldavojohn]

Something that surprises me is that we're so obsessed with the exact positioning of things on Earth but at great exo-solar distances, we seem to be okay with measurements to the nearest million light years. A couple days ago I read about a new method devised to measure location to within a few hundred meters of something 200 million kilometers away from Earth and it struck me as odd that more effort isn't put into this. While the practicality of Earthbound work is far greater, the implications for physics and verifying theories seems to be an obvious benefit for better positional measurements in space. I know satellites and objects near Earth are heavily measured but why isn't there more attention paid to precision of deep space objects? What problems prevent sensor fusion from being applied to space? Too much noise? No way to actually verify your results?

Automation?

[eldavojohn]

How much of this can be done automatically and how much of this must be hand guided? For example you talked about fingerprints changing over time and being used only as a guide. Is there a measurement or confidence variable that you can employ to automate when the fingerprint is still valid or has morphed too much? Or is that something that a human overlord must monitor and do research to notice that a new apartment building has just been opened and there are now hundreds of new signals? It feels like you are using an open domain that could have outliers and irregularities that require a human to clean the data before it can be trusted to give you low false positives and true negatives. What statistical methods do you use to overcome these sort of real world problems so that your system can be put anywhere and work?

your best guess on the GPS successor?

[Sem_D_D]

Hi, Dr Ramsey!
What is your best estimate as to what is the US DOD's current GPS backup system?
IIRC Obama cut the budget for LORAN around 2010 and till then the system was financed with the explicit explanation and purpose - GPS backup. But no more...
I am currently teaching ECDIS systems to mariners and I always emphasize the weaknesses of GPS under jamming. Ever since Selective Availability has been switched off, the jamming topic pops up more and more as a soft spot of the whole process, so I think we are not fooling ourselves that the US would let down such a gaping hole in its systems uncovered...

Post Processing

[Matt_Bennett]

Does your system record data so that the position data can be enhanced with Post Processing?

Regulatory approval?

[k(wi)r(kipedia)]

Wouldn't this thing require a whole slew of regulatory approvals since you'd be fishing for different types of signals? Or would this involve mere processing of data already available to, say, the smartphone armed with this technology?

Dr. Faragher

[geekoid]

Can you please tell me the whereabouts of Carmen San Diego and/or Waldo?

Cambridgeshire pub preferences

[hotdiggity]

Might I ask your favourite pub in Cambridge and the local area? It doesn't need to still exist.

Sensor fusion (accelerometer etc.)

[LifeIs0x2A]

What potential do you see in the combination of these "opportunity" signals (Wifi etc.) that are to be used in NAVSOP and data from sensors like an air-pressure sensor, accelerometers etc.?

Sensor fusion

[Arthur B.]

In order to combine all the sources of information, are you relying on a messy approach, something based on many signature machine learning algorithms (think boosting, SVNs, random forests etc) or are you writing an explicit generative model for the noise and then applying filtering to it, with a particle filter for instance?

Computers using Traditional Navigation?

[bill_mcgonigle]

I found it striking that in the case of the drone that was forced down in Iran (e.g.) the 'return to base' failsafe seemed to be completely dependent on electronic signals.

It would seem much harder to spoof the position of the sun, the Earth's magnetic field, the position of the stars, etc. I presume, perhaps naively, that the sensors and algorithms to do this wouldn't be all that expensive or complex. What's the challenge in getting computers to use traditional navigation techniques?