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Free eBook: What You Need to Know About Leap Seconds

eBook Cover What you need to know about GNSS leap seconds

Every GNSS receiver needs to be able to cope accurately with leap second insertions—micro-adjustment to navigation satellite time signals to bring them into line with global UTC time.

But when leap second insertions only occur sporadically, how can you accurately test a new receiver to ensure it handles the adjustment satisfactorily?

Download a free eBook to learn everything you need to know about GNSS leap seconds, including:

  • The difference between GNSS time and internationally-recognised UTC time
  • How leap second insertions work and how receivers should respond to them
  • How to simulate leap second insertions for lab testing of receiver performance

Simply enter a few details opposite to receive your free eBook—and happy reading!

About Spirent

Spirent has been the global leader in GNSS testing for near 30 years. Spirent delivers navigation and positioning test equipment and services to governmental agencies, major manufacturers, integrators, test facilities and space agencies worldwide.

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    What you need to know about GNSS leap seconds Testing to ensure GPS receivers keep track of leap seconds 1 The importance of time For many people, time is the ultimate paradigm. Financial markets, military campaigns, transport networks and industrial processes are just a few of the activities that depend on timekeeping that must be both 100% accurate and simultaneously available to all participants. Global navigation satellite systems are no exception. nulleir proper function depends on all ground control stations, satellites and receivers keeping exactly the same time. Page 2SPIRENT eBook 2 UTC nulle global standard for time is nullnull or nullnullrdinated nullniversal nullime, maintained by the nullnternational nullureau of nulleights and nulleasures nullnullnull in France, which collects data from more than null0 atomic clocks and a few primary nullabsolutenullfrenullency standards from more than null institutions around the world. nullch month the nullnull publishes standard international references for frenullency and time, nullnternational nulltomic nullime nullnullnullnulland nullnull which is enullal in rate to nullnull, but adjusted every so often by an integer number of seconds to account for variations in the rotation of the nullrth. nullese adjustments are known as leap seconds. SPIRENT eBook nullGPS time Gnull time is a composite timescale denulled on the basis of measurements from a number of atomic frenullency standards in use at monitoring stations and onboard the satellites of the Gnull constellation. Gnull time is continuous, and so has no leapnull second insertions, but is nullsteerednullto be within 1 microsecond of nullnull null a result, Gnull time is always a number of whole seconds plus a fraction of a microsecond different to nullnull nullis offset is declared in the Gnull navigation message, allowing all receivers to provide time to their users according to nullnull Page nullSPIRENT eBook nullnullap second insertion nullap second events can happen at any time during the year, although to date they have generally occurred at midnight on nullst nullecember or nullth nullune. nulle event is communicated to all receivers in advance within the normal navigation message by changing four parametersnull The week number in which the change will occur The day number on which the change will occur The current leap seconds offset The new leap seconds offset How is a GPS signal made up? Consider just the L1 signal from the satellite... The satellite transmits a PRN (Pseudo Random Noise) ranging code The PRN is unique to each satellite and is the ‘radio tape-measure’ SPIRENT eBook nullnullow receinullers should respond nullen a leap second event occurs there are three phases through which every receiver must pass. First, up to six hours before the event, receivers should continue to use the existing nullnulltonullnull offset. nullen, during the six hours before and six hours after the event, receivers will begin a transition from the existing nullnulltonullnull offset and the revised one. Finally, six hours after the event, all receivers will use the new nullnulltonullnull offset. Page nullSPIRENT eBook null The importance of testing nullearly, as time is such an important factor in satellite navigation, it is essential that any Gnullnullreceiver will cope with a leap second insertion event in the correct manner. nulld the only way a manufacturer of Gnullnull receivers can be connullent that a receiver design will behave correctly is to test the unit and observe the results. nullowever, as leap second insertions are such rare events, there is no practical way that this testing can be performed in the nullld using a live satellite navigation message. Page nullSPIRENT eBook null Simulating leap second insertions nulle solution to the test problem is to use an null simulator in the controlled environment of the test laboratory. nulle ease of setting up a leap second insertion test will depend on the software used by the simulator, and there may be several alternative methods, either by creating data nulles or by inputting the renullired data via a graphical user interface. nullch method will allow the user to modify the contents of the simulated navigation message, and create the leap second event by changing the week number, the day number, the current nullnulltonullnull offset and the future nullnulltonull Gnull offset. Page nullSPIRENT eBook null nullalysing the results nullen the test is run, a correctly functioning receiver that is navigating from the simulatornulls output signal should detect and apply the leap second insertion. nulle results can be observed either by directly monitoring the receivernulls nullnulltime data output or by logging the receivernulls nullnulltime data to a nulle for subsenullent analysis. For a single leap second insertion the time count will appear to stop for 1 second before continuing. For example, nullnullnullnullnullnullnull where nullwas the time at which the leap second event occurred. Page nullSPIRENT eBook 9 The complete solution null null constellation simulator reproduces the environment of a Gnullnullreceiver on a dynamic platform by modelling satellite motion, signal characteristics, atmospheric and other effects, so that the receiver will actually navigate, in the lab, according to the parameters of the test scenario. null with other Gnullnullreceiver nullality assurance tasks, a suitably specinulld null simulator will allow leap second insertion tests to be performed with total accuracy and full repeatability. nullerefore, should a receiver fail any test, the design can be modinulld and the revised unit can be subjected to exactly the same test conditions. Page 1nullSPIRENT eBook nulle hope you found this What you need to know about GNSS leap seconds nullnullok of interest. nulle are continually adding new content to our website on a regular basis. nullokmark this linknull www.spirent.comnullositioning nullisit the Spirent GNSS nulllognull there are currently more than null posts with nullto nullnew posts added per week. nulltch up on whatnulls newnull www.spirent.comnulllognullositioning nulleed more informationnull gnssnullolutionsnullpirent.com nullharenull Facebook nullnkednulln nullwitter nullechnorati Google nullunull nulligg nullelicious nulleddit nulltumbleupon null Spirent nullnull1nullnullnullnullnull globalsalesnullpirent.com www.spirent.comnullositioning Spirent nullederal Systems null nullnullnullnullnullnull infonullpirentfederal.com www.spirentfederal.com Got a smartphonenull Scan the QR Code for more information