Positioning is All About Availability

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A Position is available when :

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• 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)

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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​

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Maximum Possible Accuracy is desirable but…

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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

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So What are the elements Impacting Position Availability

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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

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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

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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...

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