Locating Wireless Devices Where GPS May Not Be Available Ofcom

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Locating Wireless Devices Where GPS May Not Be Available – Ofcom Study

Progress to date...

Steve Methley, Chris Davis

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www.QuotientAssociates.com

Agenda

1. Introduction to wireless devices which need location

2. What we need from location

3. Our location technology survey in brief

4. What didn’t surprise usAbsence of a ‘one for all’ solution

‘Headline’ accuracy results

Negative effects of environment

5. What has surprised usAccuracy often defined without confidence or at low confidence

Partially characterised performance of position solutions

Dearth of user integrity monitoring

6. What’s next for our study



Wireless devices which need location

Cognitive devices will use spectrum opportunistically

Lots of potential – ‘Wi-Fi on steroids’?

Potential spectrum availability depends on where you are

But opportunistic use of spectrum will be on a secondary basisFigure: Ofcom




Protecting primary users

Operational area

Exclusion zone

Separation

distance

Separation distance ~ 1km

CEP-98 ~ 74m

==> CEP-67 ~ 40m




The impact of height

1. At 3m height, separation distance ~ 1 km

2. At 30m height (+10dB), separation distance ~ 2.1 km

==> 4x exclusion area



What we need from location

AccuracyHigh; 100m or better, everywhere, all environments

Height to < 10m would be advantageous

ConfidenceVery high, e.g. 99% confidence limits (assuming Gaussian)

Reliability & IntegrityCritically important in ensuring low probability of interference

Figures: GPS SPS Signal Spec.



Our location technology survey in briefPreliminary results – technology accuracies example (CEP-95)

Altimeters need regular calibration for weather pressure changes. UWB, Wi-Fi, IMES need infrastructure

Barometric altimeter, Wi-Fi, IMES: floor of buildingUWB: 3cm

Height methods

Low cost inertial navigation has performance too poor for navigation and positioning

Inertial Navigation (INS) drift is 1.5km/hr, even for military grade

Non-wireless

Similar accuracy to cellular, but here more of a problem since indoor distances are shorter. Multipath is the main issue. Solved by UWB but at a cost. All methods scale poorly due to infrastructure needed

RSS, TOA: From cell radius for proximity down to 5m for fingerprintingUWB: 30cm

Local area and short range

Needs corrections for operation over land mass10m for differential eLoranDedicated navigation systems

Results suggest that multipath effects may limit accuracy to no better than 35 to 50m

60 to 90mBroadcast networks

Many possible variations exist, some need extra equipment to be installed and some require phone firmware update

From cell radius for proximity down to 5m for fingerprinting

Cellular networks

Good reliability and global availability.Poor indoors and in urban canyons, where accuracy may degrade to >100mConcerns of interference with pseudolites and re-radiatorsIMES = Indoor messaging system, a non-ranging GPS beacon

10m: stand-alone2m: differential<1m: carrier phase, pseudolites and re-radiators10m: IMES

GPS



What didn’t surprise us

No ‘one for all’ solution exists

‘Headline’ accuracy results as expected

Negative effects of environmentHow hard is a 100m target accuracy in reality?



How hard is a 100m accuracy target?

Native performance of the technologiesas surveyed

Externally induced limitations

1. Multipath

For all time of flight

methods.

e.g. GPS accuracy

can degrade to

50-200m

2. Near-far problem for Spread Spectrum (e.g. GPS)

A code cross correlation problem; GPS has only 23dB margin

May result in no position report (zero availability)

Figure: Grewal et al.



How hard is 100m? - examples

Poorer Accuracy100m

GPS

Cellular

Wi-Fi

eLORAN

clear sky multipath

fingerprinting

small cell-ID

fingerprinting

larger cell-ID

SSID

over sea over land or buildings

?

time of flight

Better Accuracy

(failure)

(range limited)



What has surprised us

Accuracy is commonly defined without confidence

or at low confidence

We need very high confidence limits

Only a partially characterised performance of the

position solution in many cases

Our need is for trustworthy solutions

A dearth of integrity monitoring solutions

How to know when a solution (GPS, cellular..) becomes

inaccurate due e.g. to local multipath?



Confidence levelsConfidence – the ‘spread’ of the location estimates

Any location system needs to state confidence along with accuracy, ideally to high confidence levels

We need distributions for other technologies (e.g. Wi-Fi) and other methods (e.g. Fingerprinting). These do not seem to exist...?

Figure: Nokia



Reliability and Integrity

Reliability – how many (false?) ‘outliers’ we have

There is very little published data on the reliability of communications based positioning systems such as Cellular or Wi-Fi

Integrity monitoring – how we catch false reports

System level integrity vs. user’s position integrity

GPS has Receiver Autonomous Integrity Monitoring, intended for aircraft

This is not available on consumer GPSNot enough satellites can be seen from the ground (today)

Integrity monitoring is an under-researched areaNeeds to cope with local disturbance, e.g. multipath

Can it be added ad hoc?

What about when the solution is not over-determined?



What’s next

Accuracy is but one of our parameters

Find the best fit between application needs and technology capabilities, via gap analysis

Note that we can and will consider technology combinations (GPS + cell-ID + whatever..)



Thank you

Feedback invited ...

[email protected]

Date post:	04-Feb-2022
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Locating Wireless Devices Where GPS May Not Be Available Ofcom

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