© 2018 POSITIONEERING

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Today, the determination of one’s position is relatively straightforward and what used to be the domain of highly specialised operations and great expense, is now readily available in any smartphone. This ability has enabled many new applications and significantly enhanced others.

 

Despite the apparent ease with which position is derived, there are still many applications that require more than the basic positioning available from a smartphone or other consumer device. 

 

For operations that require very high accuracy and often more importantly guarantee of position, additional information is required that can be added to achieve this this is GNSS Augmentation.

 

Normal GNSS positioning is derived from measuring the distance between a receivers antenna and a number of orbiting satellites. These contain a range of errors above those inherent in measurement process and include delays caused by the signals passing through the earth’s atmosphere or inaccuracies in the satellite orbits. The result of this is a subsequent error in the calculated user position.

 

Stand-alone GNSS error varies over time and location and may be accurate 1 or 2 metres in one scenario but could be inaccurate by as much as tens or even hundreds of metres in another. Furthermore and without some form of external verification, there is no means of knowing when accuracy is actually good or bad.

 

So What is Different with the Position We Produce?  

 

Our customers operate in the most remote and harshest environments around the globe and not only require extreme levels of position accuracy but also integrity and complete availability.

 

These elements can be readily provided individually but to satisfy all requirements whilst achieving the desirable 100% availability is more challenging. We have conducted a comprehensive review of the Position solution and have development something quite different and with new levels of performance and availability.

Traditional approaches have tended towards the "numbers game" - throwing quantity rather than an objectively defined and designed solutions.

We have created a solution that delivers the best possiby accuracy with maximum attainable availabilty

The Position - A Closer Look!

 

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

Positioning Requirements

The figure below shows were current position solutions fit within the context of availability.

The ultimate target is maximum accuracy and physical availability indicated by the green target icon. Each acceptable solution resides in the green shaded area whilst any solution outside this is not acceptable, either in terms of accuracy or availability or both.

The ultimate solution is to have at least two separate solutions in the green area that are not dependent upon the same elements such as the same radio frequencies.

The table following describes each solution and whether it meets user requirements or not and why.

 
 

Our Solution

So what is Our Philosophy?

  • The overall solution will be achieved with multiple positions

  • Rather than separate systems these solutions will be different elements of the same service

  • This will then provide an entire solution with 100% overall availability 

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

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

Isn't This Already the Normal Solution?

  • Current services provide single positioning solutions with different performance levels

  • An overall solution normally consists of two discrete services

  • Current high-accuracy solutions can meet this individually 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 means that the customer operation is now out of specification

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

Example:

  • The positioning solution shown below demonstrates when a high-accuracy positioning solution fails.

  • A 2nd high-accuracy solution also failed as the cause of failure (interference of L2) was common to both

  • The system then fell back to final back-up solution - a single-frequency DGNSS solution (1-3m)

  • The accuracy of this fall-back solution was outside user specification impacting vessel operation

  • The figure below shows our P1+S1 solution on the same vessel

  • Although our P1 solution, which also relies upon L2, continued to perform, to simulate the effect the position was forced to S1 at the same time that the other system switched to its back-up solution

  • Our position reverted to 0.20m positioning with no discernible impact on vessel operation