© 2018 POSITIONEERING

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Positioning Philosophy

Positioning is All About Availability

A Position is available when :

  • It is physically present and on time

  • It is within its specified accuracy

  • It possess the required levels of reliability

  • It is resilient - the ability to continue within specified accuracy when one or more failures occur

  • It posseses integrity including the ability to conduct quality control (QC)

  • It Is able provide a full assessment of its performance (QA)

Accuracy

 

  • Position accuracy can be quoted in many ways

  • Normally position accuracy is statistically qualified – typically 2Sigma or 95%

  • To meet required practial specifications statistical significance should be much higher

  • We adopt a 6Sigma value or 99.9997%

  • If the real user specificaiton is 0.5m then this should be 0.5m (99.9997%)

  • To achieve this then the usually quotated 95% accuracy level must be better than 0.23m

Maximum Possible Accuracy is desirable but…

More accuracy =

  • more complexity and dependencies

  • More dependencies = more chance of failure

  • More chance of failure = less availability

 

Less accuracy =

  • Less complexity and fewer dependencies

  • fewer dependencies = less chance of failure

  • Less chance of failure = more availability

So What are the elements Impacting Position Availability

Position accuracy outside specification

  • Periods spent initialising upon switch-on and restarting after an interruption

    • Impact higher-accuracy more than ​standard solutions

  • Periods of lost or perturbed GNSS signals

    • Higher-accuracy solutions rely on some weaker signals

    • More affected during periods of raised atmospheric activity or radio interference

  • Loss of augmentation signals

    • Line-of-sight to satellite interrupted or local interference

    • Periods spent outside augmentation coverage

  • Degraded Position Integrity

    • Absence of quality assessment

    • Absence of quality control or integrity – i.e. we don’t know if the position is acceptable or not

So what is Our Philosophy?

  • A single augmentation service should provide an entire solution with 100% overall availability 

  • The service will achieve this via multiple independent solutions

  • Transition between solutions should be operationally transparent to the user and seamless 

  • Position availability includes all anciliary aspects including Accuracy, QA, QC, physical presence and timeliness

Isn't This Already the Normal Solution?

  • Current high-accuracy solutions can meet this but what happens when they fail?

  • A system may switch to a back-up of similar accuracy but...

    • If the element that has failed is common to both solutions then this does not work

  • Usually a back-up solution is used but is normally an order of accuracy less - typically 1-3m

  • This measn that the customer operation is now out of specification

  • An example of a traditional service combination and the Positioneering-A1 (P1 & S1 combination) in an operaitonal sccenario is shown below...