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Hybrid Positioning
The ChallengeAs the adoption of location based services becomes more main-stream, developers are looking for increased acc...
Ideally such a marriage of technologies allows the strengths of one tocounter the weaknesses of the other in a truly compl...
By intelligently combining data from multiple sources the designeraims to retain the best of each and to mitigate their we...
Existing TechnologyGNSS alone“Global Navigation Satellite Systems (GNSS) enable youto locate your position anywhere on the...
On the face of it, GNSS would appear to be the panacea for allnavigation and timing requirements. Relatively low cost, low...
So what are we left with? Accuracy of a metre? A few metres?Hundreds of metres? The answer is yes to all of these, because...
There are many factors that alter how a GNSS receiver performsagainst these measures, so let’s restrict ourselves to the k...
Go indoors, and things will probably getmuch worse. The extremely weak(c.-130dBm) signals arriving atthe Earth’s surface w...
Accuracy is another measure which is significantly affected. Thesatellite signals, even if they are not obscured, may be r...
So, in practice, the continuously-available millimetric accuracyheralded at the start is rarely achieved, indeed, accuracy...
The need for test.With so many potential issues, testing of GNSS navigation systems isessential. Spirent has been the lead...
Options: SensorsA modern smartphone contains an array of sensors incorporated for anumber of purposes but all potentially ...
Options: WiFiAs we have seen, the properties of radio wave propagation mean thatthey lend themselves to being used for nav...
So, with that in mind, what is to stop other radio-based techniquesbeing used for the same purpose? Well, actually, in som...
Spirent is the only test equipment provider to offer a Wi-Fi testsolution. The GSS5700 Wi-Fi Access Point Positioning Simu...
Options: CellularWhat is Cellular Positioning?Cellular positioning utilizes the cellular networkinfrastructure to compute ...
Cell Identification (Cell-ID), the simplest location technology, locatesa user based on the cell they are using, though th...
Cellular positioning methods currently in use comprise: Cell identity(Cell-ID) positioning; Enhanced cell identity (Ecell-...
Why Cellular Network Positioning?Pros:• Cellular Networks cover majority of populated areas•  ellular technology is built ...
Even though all these techniques have some limitations, it is possibleto use some as stand-alone or in conjunction with GN...
Other SensorsThe complications faced by engineers aiming to meet the everincreasing requirements of emerging location base...
Comprehensive, End-to-End Location Technology TestingSpirent’s 8100 Location Technology is the evolution of the solutionkn...
Blending– a conclusion of sortsAn unfortunate but inescapable conclusion is thatwhilst each technology has its strengths n...
We hope you found this Hybrid Positioning E-Book of interest.We are continually adding new content to our websiteon a regu...
Spirent                       Spirent Federal Systems   Got a smartphone?+44 1803 546325               +1 714 692 6565    ...
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Hybrid Positioning

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To meet the increasing demands that current and emerging location based services (LBS) are placing on location-aware technology, engineers are turning to hybrid positioning – but what is it?

Discover:
- Why hybrid positioning is an increasingly common feature in smartphone and tablet designs
- How Wi-Fi, MEMS inertial sensors and cellular networks can all augment GNSS positioning

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Transcript of "Hybrid Positioning"

  1. 1. Hybrid Positioning
  2. 2. The ChallengeAs the adoption of location based services becomes more main-stream, developers are looking for increased accuracy and availabilityfrom positioning solutions. For example services that targetmarketing messages need to know which display the user lingered at,not merely which store they are in, and ideally they would know inwhich direction the user is facing!To provide ubiquitous positioning that reaches indoors and positivelyidentifies location and orientation in a multi-story building requiresblending the best of multiple sources of information, in other words,a hybrid solution.SPIRENT eBook Page 2
  3. 3. Ideally such a marriage of technologies allows the strengths of one tocounter the weaknesses of the other in a truly complementary way.For example the high availability of local low cost inertial sensorscan offset GNSS which may not be available within buildings; whilstthe drift over time inherent in inertial systems can be managed usingregular high accuracy fixes from GNSS, when available.And the sensors may not be those traditionally associatedwith positioning. For example a tourist guideapplication describing the scene presented to theuser answering the question “What am I lookingat now ?” may use the users smartphone cameraand cloud computing to overlay captions on thedisplay with links to appropriate informativewebpages in an augmented reality format.SPIRENT eBook
  4. 4. By intelligently combining data from multiple sources the designeraims to retain the best of each and to mitigate their weaknesses.Truly a case of the whole exceeding the sum of the parts…if it works!The peculiar test challenge presented is that development of such asystem cannot be done one sensor at a time. The effective blendingof position information from disparate sources is predicated on anunderstanding of their strengths and weaknesses, this will requirecareful development and importantly, a test environment whichprovides total control over multiple, coherent sources to facilitateiterative improvement.This e-book aims to introduce the technical challenges andsome of the ideas that Spirent has to provide thedevelopment tools required.SPIRENT eBook Page 4
  5. 5. Existing TechnologyGNSS alone“Global Navigation Satellite Systems (GNSS) enable youto locate your position anywhere on the earth – or aroundit – to within millimetres”. Now, you have to admit that isan amazing statement, and in some cases it is perfectlytrue, but there are limits to this incredible technologiescapability. Navigating, autonomously, using signals fromsatellites orbiting some 12500km away is an almostunbelievable technological achievement and has been thesolution to a myriad of application needs, where knowing‘where’ and ‘when’ you are is important. And, the list ofapplications for GNSS navigation is growing all the time.SPIRENT eBook Page 5
  6. 6. On the face of it, GNSS would appear to be the panacea for allnavigation and timing requirements. Relatively low cost, low power,compact devices enable you to locate yourself and know the currenttime with pinpoint precision. GNSS is brilliant but is it sufficient tomeet all positioning needs on its own.While there is absolutely no doubt that GNSS is a must-havetechnology for the “where” and “when” needs of today’s applications,it is not without its limitations and trade-offs. Going back to the“within millimetres” statement, closer inspection reveals that toachieve this level of accuracy takes some very sophisticated andrelatively expensive GNSS receiver technology. This is out ofthe question for many of the applications thatneed accurate timing and navigation.SPIRENT eBook Page 6
  7. 7. So what are we left with? Accuracy of a metre? A few metres?Hundreds of metres? The answer is yes to all of these, because theperformance of GNSS is so variable and depends on so many factorsthat it is impossible to state exactly how it will perform in a genericway. We can however consolidate performance into 4 measures:-• Availability - The percentage of time a Position, Navigation and Time (PNT) solution is available• Continuity – Performance without non-scheduled interruptions• Integrity – The level of trust in the information provided• Accuracy – The degree to which PNT data conforms to the actual positionSPIRENT eBook Page 7
  8. 8. There are many factors that alter how a GNSS receiver performsagainst these measures, so let’s restrict ourselves to the key issuesfor consumer applications.Availability is perhaps the most significant measure to consider giventhe kinds of environments consumer devices have to operate in. Theurban scene is undoubtedly a hostile one for a GNSS receiver. Tallbuildings obscure the line of sight navigation signals, and in somecases - if the obscuration is combined with poor satellitegeometry (not enough satellites in view) – therewon’t be enough signals available to compute aPNT solution. A minimum of 4 satellites in viewis required.SPIRENT eBook
  9. 9. Go indoors, and things will probably getmuch worse. The extremely weak(c.-130dBm) signals arriving atthe Earth’s surface which are notblocked by a building are furtherattenuated by its fabric. Highlysensitive receivers are required,but these have to spendlonger and take more powerto extract the weaker signalsfrom the noise.SPIRENT eBook
  10. 10. Accuracy is another measure which is significantly affected. Thesatellite signals, even if they are not obscured, may be reflected, andtake multiple paths to the receiver antenna, much longer than thedirect path, causing false ‘copies’ of the signals to arrive, late, at thereceiver corrupting the PNT calculations. Even worse is the case wherethere is no line of sight signal, and the multi-path version is the onlyone the receiver sees. Because the receiver uses the satellite’s signalsas ‘radio tape-measures’ any distortion in the signals (e.g. time delay,phase error) will degrade the PNT solution accuracy. In the case ofweak signals, a high sensitivity receiver may help, but they are moresusceptible to multipath signals.SPIRENT eBook Page 10
  11. 11. So, in practice, the continuously-available millimetric accuracyheralded at the start is rarely achieved, indeed, accuracy of severalmetres can be a challenge. Therefore it is clear that GNSS alone is notenough. We need to consider how to optimise its benefits and howto bring the four measures of performance up to acceptable levelsfor our application. This can only be achieved by augmenting GNSS.Adding another system or multiple systems alongside GNSS to help it,correct it or substitute for it is the practical way forward. Collectively,this approach is known as Hybrid Positioning, the big opportunityfor performance improvement arising from the complementary natureof the strengths and weaknesses of the various technologies. Incombination the technologies can perform better (more accurate,higher availability etc) than any of the technologies independently.Team work rather than competition is the way forward it seems!SPIRENT eBook Page 11
  12. 12. The need for test.With so many potential issues, testing of GNSS navigation systems isessential. Spirent has been the leader in this field for over 25 years,and has solutions for testing receivers on all existing and plannedGNSS systems, as well as new solutions for Hybrid Positioning.SPIRENT eBook Page 12
  13. 13. Options: SensorsA modern smartphone contains an array of sensors incorporated for anumber of purposes but all potentially available for positioning. MEMsgyros and accelerometers, barometric sensors and magnetometers allhave a direct application in estimating position.The inertial sensors can be used in the estimation of position bysensing the movement of the body from a known initial position.In this way GNSS technology, which provides accurate positions butnot all the time, and inertial technology which allows a positionestimate to be advanced in the absence of any external signals, forma perfect partnership. The addition of magnetometers to provideheading and barometric sensors to provide height completes a veryuseful set of sensors.SPIRENT eBook Page 13
  14. 14. Options: WiFiAs we have seen, the properties of radio wave propagation mean thatthey lend themselves to being used for navigation – after all, that’sthe foundational principle of GNSS.SPIRENT eBook Page 14
  15. 15. So, with that in mind, what is to stop other radio-based techniquesbeing used for the same purpose? Well, actually, in some casesnothing much. One such technique is Wi-Fi positioning. You have – inmost urban areas – many Wireless Access Points transmitting radiosignals with identifying properties. You can therefore determine yourposition by looking for a ‘fingerprint’ of Access Point visibility in alarge database of such devices. Combining this with a measure ofthe power level received versus the database’s record of the accesspoint’s transmit power to determine range, will enableyou to trilaterate from multiple Access Points.This technique is gaining traction in the marketplace,with both database technology suppliers and phonehandset/chipset manufacturers offering or looking Spirent GSS5700 Wi-Fi Access Pointto offer solutions. Positioning SimulatorSPIRENT eBook Page 15
  16. 16. Spirent is the only test equipment provider to offer a Wi-Fi testsolution. The GSS5700 Wi-Fi Access Point Positioning Simulatorconsists of a ‘smart’ signal generator using a core applicationrunning on an internal CPU with touch-screen, remote MMI controlvia Ethernet. Access Point Control includes the ability to specify/change, MAC address, SSID, TX channel power level/dynamic pathloss and simulated ‘visibility’. Supporting up to 24 Access Points inone chassis, and being able to operate with Spirent’s GSS6700 GNSSsimulators to give coherent GNSS/Wi-Fi test signals, makesthe GSS5700 Wi-Fi Access Point Positioning Simulator anessential test solution for this positioning technology.SPIRENT eBook Page 16
  17. 17. Options: CellularWhat is Cellular Positioning?Cellular positioning utilizes the cellular networkinfrastructure to compute position and obtain a fastand coarse location estimate. Compared to A-GPS/A-GLONASS, cellular network positioning is generallyfaster (~5 seconds), but it is less accurate (50 metersto several kilometres). It is quite often used as“fallback” technology when GPS, GLONASS and Wi-Fisignals are unavailable.SPIRENT eBook Page 17
  18. 18. Cell Identification (Cell-ID), the simplest location technology, locatesa user based on the cell they are using, though the accuracy ofthis technique varies widely. Cell-ID positioning establishes the cellto which a user equipment (UE) is currently connected and usesthat cell location as a rough estimate of the UE’ s current position.Ecell-ID positioning extends the Cell-ID positioning technique withsupplementary information that narrows down the location within thecell where the UE is located. This supplementary information includesTiming advance and Neighbour cell measurements.Cellular network triangulation, either signal strength-based or time-based, can be used to improve accuracy and time-based methodssuch as Time Difference of Arrival are common.SPIRENT eBook Page 18
  19. 19. Cellular positioning methods currently in use comprise: Cell identity(Cell-ID) positioning; Enhanced cell identity (Ecell-ID) positioning;Assisted Global Positioning System (A-GPS) positioning; AdvancedForward Link Trilateration (AFLT) in CDMA networks, EnhancedObserved Time Difference (E-OTD) in WCDMA networks and Uplinktime difference of arrival (UTDOA) positioning. Observed downlinktime difference of arrival (OTDOA) positioning technique is currentlyunder discussion for LTE networks.SPIRENT eBook Page 19
  20. 20. Why Cellular Network Positioning?Pros:• Cellular Networks cover majority of populated areas• ellular technology is built into all mobile phones and increasing C number of other mobile devices (like connected PNDs)• Works indoors and in urban environments• Very fast response time• omplementary to GNSS and C other Location TechnologiesCons:• ➢ Relatively poor accuracySPIRENT eBook Page 20
  21. 21. Even though all these techniques have some limitations, it is possibleto use some as stand-alone or in conjunction with GNSS and othertechnologies to overcome the individual limitations. Considering theglobal scale and spread of cellular networks, cellular positioningwould form an integral part of any hybrid strategy.SPIRENT eBook Page 21
  22. 22. Other SensorsThe complications faced by engineers aiming to meet the everincreasing requirements of emerging location based services (LBS)on accuracy and availability of positioning solutions mean lookingfor different and sometimes novel sources of positioning information.Use of cell-id techniques, Wi-Fi and other sensors such as low costMEMs inertial are becoming more common and present uniquetest challenges. The GSS6400 rises to the challenge by enablingthe user to record two channels of serial digital data alongside thedigitized GNSS spectra. Signals direct from sensors or via a bus suchas CANbus are captured and buried within the GNSS data ensuringcoherent playback. An alternative use of this facility is to record atiming signal such as a GPS-derived 1pps which allows subsequentsynchronization of external systems such as rate tables etc.SPIRENT eBook Page 22
  23. 23. Comprehensive, End-to-End Location Technology TestingSpirent’s 8100 Location Technology is the evolution of the solutionknown for years as the “Spirent ULTS”. It offers the most advanced,comprehensive environment available for testing A-GPS/GLONASS-enabled GSM, UMTS and LTE devices.Location testing can be performed for standalone or hybrid locationtechnology using A-GPS and A-GLONASS with Wi-Fi, Cell ID and ECID.This fully automated, flexible and configurable solution offers Controland User Plane implementations, including complete SUPL support.Spirent plays a major role in the development of test requirementsand specifications for location technologies within leading standardsorganizations.SPIRENT eBook Page 23
  24. 24. Blending– a conclusion of sortsAn unfortunate but inescapable conclusion is thatwhilst each technology has its strengths none are ontheir own sufficient to satisfy the accuracy, availability,integrity and cost requirements of the burgeoninglocation based services market. A combination ofcomplementary technologies would appear to hold theanswer but blending the approaches to get the bestof each is a challenging technical task. Spirent aimsto support this endeavour by drawing on its extensiveexperience and wide range of tools to provide bespoketest solutions for hybrid positioning developers.SPIRENT eBook Page 24
  25. 25. We hope you found this Hybrid Positioning E-Book of interest.We are continually adding new content to our websiteon a regular basis. Bookmark this link:www.spirent.com/positioningVisit the Spirent GNSS Blog, there are currentlymore than 90 posts with 2 to 3 new posts addedper week. Catch up on what’s new:www.spirent.com/Blog/PositioningNeed more information?gnss-solutions@spirent.comShare?Facebook LinkedIn Twitter Technorati Google Buzz Digg Delicious Reddit Stumbleupon MCD00185
  26. 26. Spirent Spirent Federal Systems Got a smartphone?+44 1803 546325 +1 714 692 6565 Scan the QRglobalsales@spirent.com info@spirentfederal.com Code for morewww.spirent.com/positioning www.spirentfederal.com information
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