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Autonomous vehicles demand rigorous testing that can be difficult to conduct on real roads. Here’s how we helped Italdesign create a flexible, integrated simulation platform.

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By On November 7, 2018
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BeiDou, BDS-3, GNSS, APAC

Since the completion of the first and second phase of the system – BDS I and BDS II - BeiDou has been widely used in China and the Asia-Pacific region. The development work on BeiDou phase 3 started 2013, and will extend BeiDou passive PNT service coverage from Asia to the whole world by approximately 2020. Here we take a look at the system development, and what Spirent is doing to support testing.

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By Will Thornton On December 15, 2016
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Galileo, GNSS, GPS

With the Declaration of Galileo Initial Services being available (15th December 2016), Galileo officially moves from a testing phase to the provision of live services. For the first time ever, users around the world can be guided using the positioning, navigation and timing information provided by Galileo’s global satellite constellation.

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I’ve had the privilege of working closely alongside Aston Martin Racing during this year’s FIA World Endurance Championship. My time in the paddock at Silverstone and Le Mans – and in the Prodrive lab – has yielded some important findings, both for the team, and for GPS engineers in general.

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Location tracking with GPS is becoming a staple feature in many consumer devices. However, consumers expect a high level of accuracy, and reviews are noting discrepancies between GPS readings from wearable devices and smartphones. In this blog we look at how wearables manufacturers can improve position accuracy.

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If you’re testing RTK GNSS assistance systems under a live-sky, you won’t know how your systems perform across all use-cases, potentially compromising user satisfaction and your brand reputation. However, if you already have a GNSS simulator or R&P system, you can start thoroughly testing RTK systems straight away. We explain how.

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Whether it's a Spanish university revealing a smarter in-vehicle SatNav or bold predictions about the self-driving car, 2013 has seen increasing evidence that the next gear shift in automotive positioning technology could be just around the corner. But for the engineers developing and testing new systems, there are more immediate challenges ahead.

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Whether you are developing a smartphone for immediate global sale, or designing the Global Navigation Satellite System (GNSS) technology of the future, BeiDou-2 is big news. For those outside the world of GNSS, keeping track of China’s developing satellite constellation—and its developing nomenclature—can be far from easy.

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By Paul Argent On September 21, 2012
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Wi-Fi is becoming quite ubiquitous. In smartphone and tablet devices, it’s increasingly used as an avenue for offloading 3G and 4G data use when the availability of mobile signals is low. It’s also fast finding new applications in the automotive industry—in everything from in-car entertainment to sophisticated navigation systems—so much so, that Ford expects to have Wi-Fi in 80% of its cars by 2015. All of this amounts to a great deal of pressure on manufacturers, to e...

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By Rahul Gupta On September 19, 2012
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The automotive industry has long since represented one of the most influential and exciting areas of global positioning R&D. Mid-way through 2012, this is truer than ever. In today’s vehicles GNSS positioning takes its place amongst a host of technologies: From on-vehicle infotainment systems and inertial sensors, to the emerging vehicle-to-vehicle and vehicle-to-infrastructure positioning solutions that promise to transform the safety and efficiency of traveling by car. As on-vehicl...

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By Stuart Smith On September 17, 2012
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Today, the satellite positioning and navigation market is moving with phenomenal speed. Most vendors and manufacturers of GNSS-enabled devices are conscious that—to give their new products the best chance of thriving—they must deliver them to market as rapidly as possible. And one of the greatest obstacles for many is the process of product certification. Minimising the impact of certification on time to market In terms of minimising certification’s impact on time to market...

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By Rahul Gupta On September 13, 2012
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Accelerometers, barometers, magnetometers and gyroscopes are all common components in the latest generation of smartphones—and the information such inertial sensors provide can be used to augment a device’s positioning capabilities, improving accuracy where GNSS is weak or denied. Marrying the output of a device’s GNSS receiver with that of its MEMS inertial sensors, however, is far from simple. It requires the development of unique sensor fusion algorithms—a process tha...

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By Spirent On September 5, 2012
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For manufacturers of location-aware devices, the decision on where to place the GPS/GNSS receiver within the overall product design is a critical one. “You’re holding it wrong” Many people will remember the problematic Apple iPhone 4 design that resulted in dropped calls if the handset was held “the wrong way”. Earlier this year it was Samsung’s turn, as issues with the location of the GPS antenna in its Galaxy S III smartphone prompted the company to issue ...

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By Paul Argent On August 30, 2012
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In the space of a few years, Near Field Communication (NFC) looks set to transform our daily lives. Recent forecasts from Juniper Research predict that, by 2017, a quarter of US and Western European mobile phone owners will use their NFC-enabled device to pay for goods in-store. And the potential of NFC extends far beyond revolutionising retail transactions. The market for non-payment applications—from smart posters to simplifying the setup of more complex Wi-Fi connections—is&...

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By Rahul Gupta On August 27, 2012
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The ability to find out exactly where we are, wherever we are, is something many of us are already starting to take for granted. As governments, businesses and individuals increasingly rely on technologies founded on GNSS positioning, the race is on to provide accurate, reliable positioning in environments where GNSS has traditionally been weak or denied. Ubiquitous positioning promises multiple applications—from extending and completing the fabric of augmented reality, to facilitating t...

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By Rahul Gupta On August 23, 2012
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The Record and Playback approach to performance testing GNSS-enabled devices has been with us for some time now. Spirent’s own, industry-leading Record and Playback system is over a year old, and has just been upgraded with some brand new features. Given this, it’s surprising how often we still encounter R&D teams attempting to test the performance of their location-aware devices against a live, constantly-changing sky. Just in case you’re among those still in need ...

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By Andy Walker On August 20, 2012
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Should manufacturers use live satellite signals to test location-aware devices? One challenge for manufacturers of location-aware devices is to ensure that every single unit leaving the factory will perform exactly as it should. A malfunctioning product will be found out as soon as it gives users an inaccurate position or delivers navigation instructions that are patently wrong. And thanks to the power of social media, news of a poorly-functioning product can go viral, causing reputational and...

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By Rahul Gupta On August 6, 2012
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Spirent Helps Developers Solve the Indoor Positioning Challenge Perfecting indoor positioning is the next great challenge for developers of location-aware devices. To meet the challenge, developers are increasingly drawing on a combination of technologies. As well as cellular and Wi-Fi networks, many device developers are now taking advantage of the microelectromechanical systems (MEMS) inertial sensors included as a matter of course in most smartphones and automotive navigation systems. Comm...

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By Stuart Smith On July 18, 2012
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The Uses of Automated Testing Software: Choosing a GNSS Chipset Selecting a GNSS chipset for a new location-aware device is a critical R&D decision. Many factors need to be taken into consideration, and many factors—both intrinsic and extrinsic—can influence the accuracy and performance of the chipset within the final device design. One thing’s for certain—getting it wrong can be an expensive, even dangerous mistake. To give a basic example, an inexpensive GPS chips...

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By Rahul Gupta On July 12, 2012
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Manufacturers of the latest consumer devices are under pressure to produce more units, faster, to satisfy global demand. According to Gartner, for example, worldwide smartphone sales were up 45% in the first quarter of 2012 compared to Q1 2011. At the same time, devices are incorporating more and more functionality that needs to be tested on the production line. Connectivity options now include cellular (GSM, GPRS, EDGE, 3G, 4G …), wireless (Wi-Fi, WiMAX), Bluetooth and increasingly...

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By John Pottle On June 22, 2012
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Today, GPS applications and services are everywhere, and accessible to almost everyone. In the UK you can now purchase a portable “SatNav” system, admittedly from a manufacturer you might not have heard of, for less than it costs to fill your car with fuel! This is great news indeed, right? Well, maybe … but then maybe not. When was the last time you opened your morning paper and did NOT find an article about a lorry blocking a country road or a car getting stranded somewher...

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By Spirent On June 18, 2012
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One of the most economically successful applications of GNSS has been in precision agriculture: a concept that was developed in the USA during the 1980s. Since that time techniques have improved and have seen more widespread adoption, improving both yields and productivity. Although GNSS receivers are not the only technology involved, they do play a key role providing positional feedback to enable agricultural machinery to operate in exactly the right spot and to cover large areas with the grea...

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By Spirent On June 11, 2012
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One of the most important benefits of testing a GNSS receiver using an RF simulator rather than using either live or recorded signals from real-world satellites is the ability to simplify the test in order to observe a specific response from the receiver. The formula for calculating the estimated position error of a GNSS receiver is a complex one that takes into account many outside factors. When using a simulator, the majority of these outside variables can be eliminated from the equation...

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By Spirent On June 8, 2012
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One of the critical performance parameters for almost any GNSS receiver is reacquisition time–or how long it takes the receiver to make sense of the available satellite signals after an obstruction has been cleared. Applications in which reacquisition time is particularly important include automotive sat-nav devices and the railway industry. In both these cases, the vehicle housing the receiver is likely to experience periodic interruptions from overhead obstructions, such as tunnels...

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By Spirent On June 6, 2012
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Narrow correlator spacing is a key technique for multipath mitigation in GNSS receivers. Whereas earlier GPS receivers used a 1.0 chip spacing in their delay lock loops (DLLs), the reduction of this spacing offers a number of benefits, reducing tracking errors in the presence of both general noise and multipath phenomena. The reduction in noise is achieved with narrower spacing because the noise components of the early and late signals characterised by multipath interference are correlated and ...

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By Spirent On June 4, 2012
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The SCDM is the System for Differential Correction and Monitoring, which is a key part of a Russian-operated satellite based augmentation system (SBAS) for both GLONASS and GPS. The SCDM uses a ground network of monitoring stations on Russian territory as well as some overseas stations. The stated object for the SCDM is to provide metre-level accuracy for GLONASS users, with target levels of 1-1.5m for horizontal accuracy and 2-3m for vertical accuracy. The correction and integrity data will b...

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By Spirent On June 1, 2012
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In any testing regime at any stage in the lifecycle of a GNSS receiver repeatability of tests is essential. Regardless of whether you are designing a receiver from scratch, comparing different receiver designs, developing new applications, integrating receivers into end equipment or production testing finished kit, if you are not able to run exactly the same test (or test sequence) time and time again then the results of the tests will not be conclusive. In development work, for example, the ab...

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By Spirent On May 30, 2012
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Among the inevitable problems with any global navigation satellite system, relativistic effects such as time dilation, gravitational frequency shift and eccentricity effects all have to be accounted in order for the system to function correctly. As explained by the theory of relativity, the clocks on each satellite will run fractionally faster than those on Earth because of their constant movement and height relative to the Earth-centred nonrotating reference frame. Gravitational frequency shi...

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By Spirent On May 25, 2012
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Another of the major improvements that is scheduled in the modernisation of the Global Positioning System (GPS) is the L1C signal. This is a freely available civilian-use signal that will be broadcast on the same 1575.42MHz frequency as the L1 signal broadcast be the existing GPS constellation. As it is broadcast on the same frequency as the existing L1 signal, older receivers will still be able to receive the C/A signal from the new L1C signal. The L1C will be available with first Block III GP...

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By Spirent On May 21, 2012
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One of the most important aspects of testing the reliability and performance of any GNSS receiver is testing the dynamic performance of the system in its intended application. And while this may seem like a prime case for taking the receiver on the road (or rail, sea, air etc.) for “live-sky” testing, all the usual limitations of this methodology will apply: the tests are inherently random and non-repeatable, and the costs associated with taking staff and equipment out of the la...

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By Spirent On May 18, 2012
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One of the fastest-growing sectors for the use of GNSS receivers is the sporting goods industry, where data from such devices are used for a wide range of activities, from analysing the workrate of footballers as they move around the pitch to keeping track of competitors in all manner of races. One of the first sports to embrace the technology was golf, where GNSS receivers are used to plot the position of a player's ball in relation to a map of the hole that is being played. The map display wi...

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By Spirent On May 16, 2012
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An RTK receiver is a high-accuracy dual-frequency device that uses the real-time kinematic (RTK) technique for centimetre-level accuracy in surveying applications. The RTK technique uses carrier phase measurements of the GNSS signals, rather than reading the navigation message. Any GNSS can be used, but GPS RTK is also known as carrier-phase enhancement (or CPGPS). The RTK technique uses at least two GNSS receivers, which are usually connected by UHF radio. One GPS receiver is set up as a fixed...

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By Spirent On May 14, 2012
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MEO, or medium Earth orbit, is the region of space surrounding the Earth that is commonly used by navigation satellites. Also referred to as intermediate circular orbit (or ICO), MEO is found between the low Earth orbital altitude of 2000km and the geostationary orbital altitude of 35,786km. The MEO region is becoming increasingly congested, with the GPS constellation orbiting at an altitude of 20,200km, the GLONASS constellation at an altitude of 19,100km, the Galileo constellation at an altit...

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By Spirent On May 11, 2012
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Although the concept of the Faraday cage is generally well understood, it is all too easy to fail to appreciate that many of today's structures can easily incorporate Faraday cages—or at least partial electromagnetic screens. The net result can be that a perfectly designed and constructed GNSS receiver can fail to operate, or (potentially worse) will show greatly degraded performance. The classical Faraday cage is a structure that comprises a contiguous enclosure made from any conducting ...

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By Spirent On May 9, 2012
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DGPS, or differential GPS, is a ground-based enhancement system for the Global Positioning System. The system comprises a network of ground stations, each broadcasting the difference between its known position and its position as indicated by the GPS satellite constellation. In operation, each DGPS reference station calculates differential corrections for its own location and time. The signals from each station are valid up to 370km from the station. However, because some of the compensated err...

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By Spirent On May 7, 2012
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The old saying “time is money” has never been more true than today, with almost every aspect of modern living governed to some extent by precision timing. The world's financial markets require split-second timing to seal every transaction. Wireless communications networks need to be precisely synchronised to enable optimum use of the radio spectrum. Similarly, power companies need precision time synchronisation throughout their distribution networks for optimal power efficiency and f...

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By Spirent On May 4, 2012
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Carrier phase tracking is a highly accurate means of positioning used in GNSS surveying applications. The product of the period of the carrier frequency times the speed of light gives the wavelength, which is about 1900mm for the GPS L1 carrier. With a 1% of wavelength accuracy in detecting the leading edge, this component of pseudorange error can be as low as 2mm, compared with 3000mm for the C/A code and 300mm for GPS P code. However, in order to employ carrier phase tracking and make use of...

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By Spirent On May 2, 2012
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Although there is no specific product standard for EMC in GNSS receivers, testing for immunity to electromagnetic interference has to be an essential part of the product development process. Any receiver designed for low-level signals will inevitably be susceptible to electromagnetic interference. And GNSS receivers inevitably are required to operate reliably in areas where they will be subject to any number of sources of interference. These range from natural phenomena such as solar radio...

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By Spirent On April 30, 2012
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Developed specifically to meet the demands of the mobile phone industry, the Land Mobile Multipath (LMM) model provides a pragmatic approach to assessing the multipath performance of location aware mobile handsets. Rather than taking the analytical approach to multipath performance testing typically used for other GNSS receivers, the LMM model provides a database of ready-written test scenarios and allows the test engineer to define the signal conditions from this database. This enables th...

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The International Earth Rotation and Reference Systems Service (IERS), the organisation which monitors and manages the difference between the atomic Universal Coordinated Time (UTC) and Earth-rotation-based time, UT1, has decided that a further leap-second will be inserted on 30th June 2012 at 23 hours, 59 minutes and 59 seconds. This insertion - the first since 2008 - is intended to compensate for the accumulated difference between UTC and UT1, and the fact that the Earth’s rotation is cu...

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“We are in Testing Times” A phrase being used more and more these days in relation to many things. However ‘Testing Times’ is also a concern to anyone responsible for planning, resourcing and carrying out GNSS testing. We all want our products to be designed, developed and out to the market in ever-shorter timescales. The time taken to perform important testing is often significant. How great it would be to be able to reduce this time, make things more efficient? Well, ...

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Today, GPS applications and services are everywhere, and accessible to almost everyone. In the UK you can now purchase a portable “SatNav” system, admittedly from a manufacturer you might not have heard of, for less than it costs to fill your car with fuel! This is great news indeed, right? Well, maybe … but then maybe not. When was the last time you opened your morning paper and did NOT find an article about a lorry blocking a country road or a car getting stranded somewhere...

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One of the major considerations in designing a GNSS receiver for automotive applications is to ensure that the performance is not unduly affected by roadside buildings. Such structures can both obscure satellite signals from the receiver and reflect them, leading to potentially complex multipath effects. Clearly, it is impractical for a receiver designer to take his or her latest project “on the road” to test out its performance in the presence of every possible size, shape and combina...

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With the latest report from market research guru ABI Research predicting that the high-precision GNSS sector is set to double in size between 2011 and 2016, there will be strong temptation for new companies to enter this potentially lucrative part of the market. Already consumer chipset manufacturers are looking to exploit the potential of the forthcoming open L2C and L5 signals, and with China accounting for around half of the market in 2010, new manufacturers from that locality are s...

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Pseudorandom noise (PRN) codes are an important element of code division multiple access (CDMA) based satellite navigation systems. Each satellite within a GNSS constellation has a unique PRN code that it transmits as part of the C/A navigation message. This code allows any receiver to identify exactly which satellite(s) it is receiving. The PRN codes act as spreading codes in the spread-spectrum communications system, and must be carefully chosen to minimise interference between each satellite...

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While the Russian GLONASS constellation is slowly approaching full operational status, developers of future multi-GNSS systems also need to focus on the likely timeline for availability of the Chinese Beidou-2 or Compass system. The successful launch of the latest satellite for the Beidou-2 constellation means that nine such satellites have been placed into orbit since 2007. Further launches are planned for this year and next. And the Chinese authorities reckon to be on course to provi...

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Although there is no specific product standard for EMC in GNSS receivers, testing for immunity to electromagnetic interference has to be an essential part of the product development process. Any receiver designed for low-level signals will inevitably be susceptible to electromagnetic interference. And GNSS receivers inevitably are required to operate reliably in areas where they will be subject to any number of sources of interference. These range from natural phenomena such as solar ra...

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CNAV is the name for the civilian navigation message that will be carried by the modernized GPS system. And while the CNAV message will carry similar data to the existing NAV message, its structure will be completely different, with a packetised format that will increase message bandwidth to allow for greater information density and pave the way for future system expansion. To this end, the system is designed to support 63 satellites, compared with 32 for the L1 NAV message. Each packe...

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With a recent report predicting that consumer and precision GNSS receiver IC shipments will reach two billion units by 2016, it is important to remember that quantity must be underscored by quality. The report, by ABI Research, highlights the importance of new vertical markets, such as tablets, cameras and fitness equipment, as well as the growth of LBS (location-based services) and LBA (location-based advertising) applications, all of which will contribute to a quadrupling of the market within ...

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The integration of GPS and GLONASS systems within the same receiver offers many advantages to both the manufacturer and the end user. And now that this integration is happening at the chipset level, several further advantages can be added to the list. On the basic technology level, the combination of GPS with GLONASS will provide greatly improved performance for the end user. The ability for the receiver to access signals from both constellations will provide greater availability, impr...

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The traditional logic that all RF testing should be carried out in a screened enclosure has much to recommend it. But do you always need to go to this level of protection when testing a GNSS receiver with a simulator? The short answer is no, because the preferred method of testing is to remove the antenna from the equation and connect the simulator directly to the receiver. However, there will be occasions where the antenna cannot be removed. And there will also be certain acceptance tests that...

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All Global Navigation Satellite Systems (GNSS) work by measuring the transmission-time delay from a satellite to the receiver. With a clear view of the sky and an unobstructed path to multiple satellites a modern GNSS receiver is able to calculate its position rapidly and accurately. However atmospheric propagation effects can alter the speed of the signals to an indeterminate degree, signals can be obscured by buildings or reflected off surfaces such as the sea, all of which will compromise the...

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By Spirent On June 6, 2011
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We very rarely talk about specific products in this Blog, we prefer to discuss applications and trends within the GNSS community but for this particular entry we thought we’d make an exception. The Navigator is a space-qualified GPS receiver, being developed by a team led by Dr. Carl Adams at the NASA Goddard Space Flight Center (GSFC), designed to highly elliptical and geosynchronous orbits. It has flown as part of a Remote Navigation Sensor experiment on the Hubble Space Telescope Servi...

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Binary offset carrier modulation (or BOCM) is a split-spectrum modulation scheme used by the Galileo navigation satellite system. BOCM is a square subcarrier modulation. A signal is multiplied by a rectangular subcarrier of a frequency that is equal to or higher than the CDMA rate. Following this subcarrier multiplication, the spectrum of the signal is divided into two parts. The purpose for using BOC modulation in Galileo is to reduce interference with BPSK-modulated signals such as C/A GPS co...

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Although satellite-based navigation systems are the preferred means for establishing location in “open” terrain, they do suffer shortcomings in areas where the satellites are obscured from the receiver, particularly by man-made structures such as buildings. In short, the performance of GNSS receivers cannot be guaranteed indoors or in densely populated “urban canyon” environments. Wi-Fi positioning is a technique that has been developed to overcome these limitations and a...

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The GPS Aided Geo Augmented Navigation or GPS and Geo Augmented Navigation system (GAGAN) is a space-based augmentation system (SBAS) funded by the Indian government. Interestingly, Gagan is not just an acronym: it is also a Sanskrit word for the sky. The GAGAN space transponder is due to be launched on 19th May 2011 on an Ariane-5 launcher from the European Space Agency (ESA) spaceport in Kourou, French Guiana. This will be the second attempt to get GAGAN into orbit. The first satelli...

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Record and playback systems (RPSs) such as the new Spirent GSS6400 can be used at many stages of the GNSS receiver design cycle and for many different tasks. However, one application that may not seem immediately obvious is in testing the ability of multi-GNSS receivers to work with both existing and future satellite systems. Clearly, the RPS cannot be used to playback signals from non-existent satellites. But used in conjunction with a simulator, the RPS can play a key role in inves...

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Introduction The FCC, LightSquared and GPS industry have all agreed that the many questions around the potential for LightSquared’s proposed L-Band terrestrial/satellite network to cause interference with GPS can only be answered with accurate and thorough testing. As mandated by the FCC, LightSquared and the United States Global Positioning System Industry Council (USGIC) have established a GPS Technical Working Group (TWG) to investigate the issues surrounding potential interference. ...

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CNSS is the Compass Navigation Satellite System, which will eventually comprise up to 30 medium-earth-orbit satellites and five geosynchronous satellites to provide true global coverage. This Chinese system is distinct from that country's existing Beidou I satellite system, which has been operating since 2003 but provides only domestic coverage using three geosynchronous satellites. Like other systems, the CNSS will provide two levels of service. The free service for civilian users will offer p...

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Record and playback systems (RPSs) such as the new Spirent GSS6400 can be used at many stages of the GNSS receiver design cycle and for many different tasks. However, one application that may not seem immediately obvious is in testing the ability of multi-GNSS receivers to work with both existing and future satellite systems. Clearly, the RPS cannot be used to playback signals from non-existent satellites. But used in conjunction with a simulator, the RPS can play a key role in investigations i...

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In the wider world, an almanac is an annual publication dedicated to information such as weather forecasts, tide tables, lunar cycles etc. A typical almanac will contain tabular information covering a particular field or fields, and will be arranged according to the calendar. However, in the world of satellite navigation systems, the almanac is a regularly updated digital schedule of satellite orbital parameters for use by GNSS receivers. The almanac for any g...

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An important part of the current GPS modernization program, M-code is the name given to a new signal that is designed to improve both the security and anti-jamming properties of military navigation using GPS. Importantly, the M-code is designed to be autonomous, and so users will be able to calculate their positions using only the M-code signal (unlike the existing military P(Y) code, which also requires use of the C/A code). Radically, in addition to the normal wide-angle broadcast, t...

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Although a GNSS receiver requires only four satellite signals to provide a complete positional fix in three dimensions, the accuracy of this fix depends to some degree on the exact positions of the four satellites relative to the receiver. If the four signals acquired come from satellites spread throughout the sky relative to the receiver, then the fix should be highly accurate. But if all four are observed in close proximity to each other within a single quadrant, then the fix will be less ...

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GPS and inertial sensors complement each other extremely well. GPS works best with a good view of the sky. When the sky view gets obstructed, for example in an aircraft roll or when a smartphone gets taken indoors, GPS will not continue to track and the navigation capability is lost. Inertial sensors continue working in all conditions – move them and you get an output from the sensor. The biggest weakness of inertial sensors is that errors are cumulative. By combining GPS and inertial, t...

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By Spirent On April 25, 2011
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RAIM, SimGEN

RAIM stands for receiver autonomous integrity monitoring, a technology used in GNSS receivers to assess the integrity of the GNSS signals that are being received at any given time. It is particularly applicable to receivers intended for safety-critical applications, and in particular in aviation applications. The RAIM concept makes use of redundant satellite signals – i.e., any that are available above and beyond those needed to produce a position fix. If the pseudorange data in any ...

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By Spirent On April 22, 2011
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WGS-84

The World Geodetic System provides a standard co-ordinate frame for the Earth, a standard spheroidal reference surface (or ellipsoid) for raw altitude data, and a gravitational equipotential surface (or geoid) that defines the nominal sea level. WGS-84 is the most recent version of the system, which was originated in 1984 and revised in 2004. Earlier schemes included WGS-72, WGS-66 and WGS-60. WGS-84 is the reference coordinate system used by GPS. The origin of the WGS-84 co-ordinate s...

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Particularly relevant for ground-vehicle-based GNSS receivers, terrain obscuration is the phenomenon of temporary and intermittent masking of GNSS signals when manoeuvring at low altitude in mountainous terrain. This can be a critical limiting factor on the performance of GNSS receivers in certain applications, and so the ability to simulate such effects is an important tool in improving the reliability and performance of GNSS receiver designs. Spirent SimGEN™ software contains a compr...

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One of the major issues in testing GNSS receivers designed for use with multiple satellite systems is that the different systems do not necessarily share the exact same time-bases. And while the differences may be tiny, time is such a critical quantity in satellite navigation that even microsecond differences can create large accuracy errors. The problem is a legacy of the GPS system, which has used its own time-base (GPS time) since it began in the early 1980s, rather than the globally accepte...

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L2C is the name given to one of the new signals to be broadcast from the satellites in the modernised GPS constellation. This new signal is intended for civilian use (hence the “C”), and will be broadcast on the L2 frequency at 1227.6MHz by all satellites from block IIR-M onwards. The L2C signal is one of the key means by which the modernized GPS will offer improved accuracy and availability for civilian applications based on dual-frequency receivers. Not only is the signal int...

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One of the more surprising consequences from the March 2011 earthquake in Japan was that the forces unleashed shifted the earth's mass sufficiently to accelerate its rotation, shortening each day by no less than 1.8 microseconds, according to calculations by NASA. And while such effects are clearly imperceptible to humans, their cumulative effect on GNSS timekeeping would cause significant inaccuracies that would be unacceptable to any GNSS application. Each GNSS will deal with the time variati...

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In addition to the new signals to be broadcast under the GPS modernization project, there are to be two significant changes to the existing civilian signals, both designed to improve the performance of GPS receivers. The first is an additional data-free pilot signal and the second is the addition of forward error correction (FEC) encoding to the navigation message. The new data-free signal will be broadcast alongside the normal data signal, acting as an easy-to-acquire pilot signal. Once a...

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The official opening on 20th December 2010 of the Fucino Galileo Control Centre, 130km east of Rome, has brought the Galileo global navigation satellite system one step closer to fruition. However, a continuing shortage of funding for the project suggests that while Galileo will be available by 2014, the service will initially be limited. Earlier in 2010, the European Commission confirmed that funding was available to launch four in-orbit validation (IOV) satellites by 2014, with the first two ...

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For most GNSS receivers, static navigation accuracy is only part of the story. The ubiquitous automotive satnav system is the most common case where dynamic accuracy is essential. And users will only be satisfied with the performance of their receivers if turn-by-turn navigation instructions are both accurate and timely. So while you may be familiar with the concept of testing the performance of a GNSS receiver in the lab with a GNSS simulator, how can this be extended to take into account the ...

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The recent certification of the European Geostationary Navigation Overlay Service (EGNOS) for safety of life applications now means that its performance is of a high enough standard that it can be used for aviation. Pilots can reliably use it as a navigation tool, enhancing the performance of stand-alone GPS. This means navigations systems for aircraft can now be produced knowing that the systems they will use are certified, robust and reliable. Designers and manufacturers of these systems will...

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There’s a simple, compelling, theory around using GPS in trains: by using GPS for position information, coupled with train communication systems, the need for track-side signalling goes away. The massive infrastructure cost associated with signalling goes away as everything needed is on-board each train. The reality surrounding this vision, however, is that rail infrastructure has to be heavily regulated and standards-driven due to the safety critical nature of the industry. The vision i...

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The Russian Federation has come up with further “encouragement” for manufacturers to support the GLONASS satellite navigation system with the threat of import duties to be levied on any mobile handsets without GLONASS functionality. Deputy Prime Minister Sergei Ivanov has revealed that the duty will be “about 25%”, will be introduced by 2012 and will be levied on handsets imported to the Russian Federation with GPS-only positioning technology. Three more GLONASS -M satell...

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The integrated in-vehicle navigation system (IVNS) is becoming an increasingly popular feature in many automotive applications, ranging from relatively straightforward driver information systems right through to sophisticated tracking and fleet management systems. Such systems, which combine a GNSS receiver with one or more dead reckoning (DR) sensors, provide superior positional accuracy over GNSS alone, and are particularly useful in areas prone to signal obscuration or complex multipath effec...

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Over the past few years the ability of consumer grade devices, typically smart phones but also PNDs, to navigate indoors has improved significantly. This is because GPS has been supplemented by other navigation technologies, such as cell tower identification and, more recently, navigation using Wi-Fi to localise position. To get reliable sub-10metre accuracy indoors, however, will require more than GPS, cellular and Wi-Fi positioning. Use of other sensors, particularly MEMS inertial sensors, as...

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In a recent post I explained the concept behind QZSS (What is QZSS) – Since the publication of that post and to further help in the development of the Quazi-Zenith Satellite System (QZSS) programme, the Japanese Aerospace Exploration Agency (JAXA) has selected Spirent’s GSS8000 Multi-GNSS Constellation Simulator to verify QZSS receivers. The highly elliptical orbits of QZSS allow satellites to dwell at high elevations, improving coverage in urban canyons and providing additional...

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The use of GNSS in navigation, timing and related systems for transportation is ever increasing. The railways are no exception. There are various programmes underway looking at the application of GNSS to the railway for safety-critical functions. Significant among these is train location and control. Traditional line-side signalling is expensive through installation, operation and maintenance. It is inflexible; signalling headways and hence capacity are determined by physical location of signals...

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The Quasi-Zenith Satellite System (QZSS) is a GPS augmentation system that aims to greatly improve GNSS accuracy over Japan and the rest of East Asia. The first satellite in the system, dubbed Michibiki, was successfully launched from the Tanegashima space centre on 11th September and reached its quasi-zenith orbit on 27th September 2010. QZSS aims to enhance GPS services both by improving the availability of GPS signals and by performance enhancement to increase the accuracy and relia...

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By Spirent On January 31, 2011
ポジショニング
pseudolite

A pseudolite (or pseudo-satellite) is any device that performs a specific task that would otherwise require a satellite. So, for example, a dedicated transmitter might be deployed to extend the reach of a GNSS to areas where the satellite signals are either blocked or jammed, and there has been considerable success with deployment of pseudolites to extend GPS coverage indoors. These are relatively simple devices that only transmit the coarse acquisition code. Pseudolites are also used ...

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There is no doubt that testing GNSS receivers is a complex business. Today's GNSS simulators are sophisticated instruments with increasing levels of features and complexity. Yet time-to-market pressure on GNSS receiver designers and manufacturers dictate that these simulators must be easy to understand and intuitive to operate. The key to this ease of use is in the graphical user interface (or GUI). And properly designed, the GUI will help simulator users access important information q...

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The pseudorange is an approximation of the distance between a satellite and a GNSS receiver. A GNSS receiver will attempt to measure the ranges of (at least) four satellites as well as their positions when their positional data were transmitted. With the satellites' orbital parameters supplied in the almanac within the message, each position can be calculated for any point in time. The pseudoranges of each satellite are obtained by multiplying the time taken for each signal to reach the receiv...

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All Global Navigation Satellite Systems (GNSS) work by measuring the transmission-time delay from a satellite to the receiver. With a clear view of the sky and an unobstructed path to multiple satellites a modern GNSS receiver is able to calculate its position rapidly and accurately. However atmospheric propagation effects can alter the speed of the signals to an indeterminate degree, signals can be obscured by buildings or reflected off surfaces such as the sea, all of which will compromise the...

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Of all the performance metrics for a GNSS receiver, navigation accuracy is probably the most important. More to the point, pinpoint static navigation accuracy is essential to the end user. And if he or she doesn't get the exact location fix expected when the receiver is powered up for the first time, there will be little confidence in the overall performance of the receiver. Whether the initial “user test” takes place in the shop before purchase or at home when taking a new unit out...

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The Local Area Augmentation System (LAAS) is a ground-based augmentation system (GBAS) specified by the US Federal Aviation Authority for use at airports to augment the accuracy of GNSS-based navigation. The LAAS focuses its service on the airport area (around 30-50km radius) for precision approach, departure procedures and terminal area operations. It broadcasts its correction message over a VHF radio datalink from a ground-based transmitter. The FAA plans to replace legacy navi...

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In many production environments, a single channel GPS simulator is the preferred way to ensure that each device meets defined parameters. The Spirent GSS6300 Multi-GNSS Signal Generator has been designed specifically for high volume production test applications for devices that use commercial GPS/SBAS, GLONASS and/or Galileo receivers. Controlled testing is vital in ensuring correct assembly and verification of expected performance parameters in GPS only and Multi-GNSS manufacturing enviro...

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The core requirement of any GNSS receiver test, whether for development, integration or production purposes, is for a controlled, repeatable signal. For many tests, the signal control includes flexibility over test case, or scenario, conditions that enable performance testing at nominal and extreme or error-state conditions. Real-world, live-sky testing has significant drawbacks which, in practice, preclude controlled testing. These drawbacks of live-sky testing include: ...

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Ionospheric scintillation is the term given to irregularities in the ionosphere caused by so-called “space weather”. Key sources of ionospheric scintillation include solar winds and magnetic storms. Historically, the level of scintillation has been seen to follow the 11-year solar cycle and peak at the time of maximum sunspot activity. Therefore the next peak is due in 2012. Scintillation occurs most frequently at tropical latitudes at night. It occurs less frequently at high latitu...

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Although the word “scenario” has been much overused (and misused) in common language, it has particular relevance in terms of testing GNSS receivers. The word can be correctly defined as “an outline or model of an expected or supposed sequence of events”, and this provides an insight to the importance of a test scenario in assessing and/or comparing the performance of one or more GNSS receivers. A GNSS simulator under software control can be used to generate test scenarios of varying d...

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One of the simplest and most popular ways of improving the accuracy of navigation systems is to combine GNSS-based navigation with inertial navigation using MEMS sensors. But what are they? MEMS stands for micro-electromechanical systems, and MEMS sensors comprise a class of devices that are micromachined from bulk silicon. As they are made from silicon, it’s possible to produce devices such as accelerometers that combine both a sensing element and the associated signal conditioning circu...

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The ionosphere is the single largest error source in point positioning after the application of precise GNSS orbit and clock products, and there are a number of mathematical models that have been proposed to mitigate its effects. Of these, the model developed by John A Klobuchar is used by the GPS system and broadcast by every satellite. The Klobuchar model is something of a compromise between computational complexity and accuracy. However, it is reckoned to be capable of correcting up to 70% o...

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On the face of it, the marine environment might appear relatively benign for GNSS receivers. After all, there is virtually no chance of signal obscuration from buildings or trees (although the odd cliff might come into play), so logically, the design of a marine GNSS receiver should be a piece of cake. However, such devices are particularly prey to multipath interference – both from the surface of the sea and from the superstructure of the vessel itself. And left untreated multipath effec...

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In the past, designers of satellite-based navigation systems have been mostly restricted to using a single system and service, the GPS C/A code. The current revolution in the industry is giving rise to not only new GNSS systems, some GNSS systems, notably GPS and Galileo, have multiple services available to the commercial GNSS designer. The question of which system or blend of systems a GNSS designer should consider, along with the potential for multiple services is thus an entirely new conside...

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Today most commercial receivers are GPS L1 C/A code only. However, for many applications, the single frequency GPS performance is inadequate and many technology developers are turning to other sensors to compliment GPS. Today we have many forms and functions, depending on the application and hence needs. Integrated in-vehicle navigation systems often compliment the GPS position with dead reckoning navigation information from wheel rotation sensors. Often these are the same sensors used...

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We are generally being encouraged through government sponsored advertising to spend less time in our cars or not to rev our car engines too much. By doing so we can help to save fuel, the world’s resources and, by implication, do our bit towards reducing climate change. The European Union has a long-standing target for car manufacturers to reduce average CO2 emissions for their vehicles to 120g/km by 2012. A longer term target is 80g/km by 2020. The view of the industry has been that this ...

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No matter how well any GNSS receiver might be designed, there are a number of outside influences that can have major effects on the performance of the receiver in the real world. In particular, atmospheric conditions can significantly degrade performance in some designs, and unless suitable compensatory measures are taken companies can find themselves selling equipment that can only operate accurately under “ideal” conditions. Ionospheric Scintillation is one such phenomeno...

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By Spirent On September 7, 2010
ポジショニング
GLONASS, multi-GNSS

With global coverage of the GLONASS constellation now scheduled before the end of 2010, Russian Prime Minister Vladimir Putin has announced plans for a major expansion in its use on the nation's roads. In announcing the deadline for total coverage, Mr Putin revealed that all new vehicles sold in the Russian market from 2012 will be required to include GLONASS receivers. GLONASS tracking devices are already routinely installed in commercial and emergency services vehicles throug...

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That was one of the questions put to John Pottle Marketing Director, Spirent Communications, Positioning Group by Coordinates magazine. You can find his answer and the Spirent view on many other interesting questions regarding future GNSS trends and applications at the following link. http://mycoordinates.org/eventually-all-receivers-will-be-multi-gnss/

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As new GNSS systems appear, it becomes more apparent that you need a Multi-GNSS test solution. Here at Spirent we’ve been advocating Multi-GNSS for quite some time but now someone else has taken up the mantle. If you haven’t already done so, check out this comprehensive article in Inside GNSS magazine. Three receiver designers and researchers explain how they view Multi-GNSS simulators as an essential tool throughout the entire receiver development cycle: from research, development, de...

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On the face of it, the marine environment might appear relatively benign for GNSS receivers. After all, there is virtually no chance of signal obscuration from buildings or trees (although the odd cliff might come into play), so logically, the design of a marine GNSS receiver should be a piece of cake. However, such devices are particularly prey to multipath interference–both from the surface of the sea and from the superstructure of the vessel itself. And left untreated multipath effect...

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Hosted by the European Space Agency, the European Commission and Eurocontrol, EGNOS is the European Geostationary Navigation Overlay Service, and is the first pan-European satellite navigation system. EGNOS comprises just three satellites, and acts as an enhancement to the US-based GPS system for safety critical applications in aviation and marine environments. The EGNOS Open Service has been up and running since 1st October 2009. This provides freely available positioning data through...

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An ephemeris is quite simply a table giving the coordinates of a celestial body at specific times during a given period. The word comes from the same Greek root as “ephemeral”, which strictly means short-lived, but has come to mean inconsequential. However, in terms of GNSS systems, the ephemeris is certainly not inconsequential. Each GNSS satellite includes ephemeris data in the signal it transmits. This comprises a set of parameters that can be used to accurately calculate the loc...

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GPS/GLONASS - You may not be working on it, but many of your competitors are Work continues apace on the GLONASS constellation, with the commencement of a headquarters building that will also house an office of the United Nations IT and satellite navigation agency. And the head of the Russian Space Agency, Anatoli Perminov, took the opportunity of laying the foundation stone of the new building to confirm that the GLONASS constellation would achieve full global coverage before January 2011. He a...

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Today, navigation and positioning technology is no longer just about GPS L1 C/A code. GPS is being modernized, the GLONASS constellation is nearly complete, new systems including QZSS, IRNSS, Galileo and Compass are on the way. Multi-GNSS offers significant opportunities and challenges to GNSS technology, system and application developers. Spirent multi-GNSS simulation systems are now being purchased by customers developing commercial systems and most chipset manufacturer...

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A new US national space policy document unveiled recently by President Obama marks a major change of direction on the relationship between the country's GPS system and other GNSS systems around the world. And the change can only accelerate the development and interoperability of systems such as GLONASS, Compass and Galileo. Whereas US policy as affirmed in a December 2004 national security directive was focused on maintaining the country's lead in GNSS on a unilateral basis, the new initiative ...

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The latest contender in the global navigation sweepstakes has moved a little closer with the launch of the fourth satellite in China's second-generation Beidou constellation during the first week of June 2010. Beidou (which means Big Dipper) will cover all of China and neighbouring lands by 2012, and will then be expanded to provide global coverage through a constellation of 35 Compass satellites by 2020. Compass will differ from other GNSS systems in that five of the intended 35 satellites wil...

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Many world governments have a long-standing target for car manufacturers to reduce average CO2 emissions for their vehicles. The European Union target is 120g/km by 2012 and longer term to 80g/km by 2020. The view of the industry has been that this is very challenging and unlikely to be met via conventional approaches alone. Indeed, the 2012 target already represents a slip from an original 2005 target date. As most manufacturers will not be able to meet the 2012 target, further slippages (possi...

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GPS specifically, and GNSS more generally, works fantastically well in its native mode of operation with an open view of the sky. High vehicle speeds, even in an aircraft manoeuvring at several times the speed of sound, are well within the capabilities of the GPS system. To use more specific language, the accuracy and continuity of positioning information is very high in open sky conditions. Back down to earth, a person walking with their GPS on the edge of the street in a typical town or c...

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Time is an important component of any satellite navigation system, and it is essential that any receiver attached to the system has a clock that is fully up to date. The current GPS system uses its own timescale, which is closely linked to (but not completely in sync with) Co-ordinated Universal Time (or UTC). And to allow GPS receivers to give users the precise time according to UTC, the precise value of the current offset between the two clocks is broadcast by the satellite system. While UTC i...

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Despite continuing delays in its introduction, when the new European Union funded Galileo constellation goes live in 2014 it will provide a number of novel services. Designers of next-generation Multi-GNSS systems need to factor in these new capabilities in order to keep their equipment ahead of the competition. Importantly, Galileo is designed provide more precise location data from that provided by GPS or GLONASS, and will be accurate down to the one-meter range. The data will ...

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To those engineers more familiar with automotive or marine navigation systems, the concept of using GNSS receivers for navigation on railways might seem a case of “overkill”. After all, there are only so many places a train can go, and these are firmly bounded by two steel rails. However, the exact knowledge of the position of any train on any rail system allows the rail operator to both improve service and increase traffic density by reducing the headways associated with fixed line-...

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When the worst happens, seconds count. E-call, the European Commission's telematics project, is expected to save 2,500 lives annually in the EU by saving time in getting the emergency services to the right place as promptly as possible. An e-call can be initiated manually by vehicle occupants or automatically by the vehicle itself. Once communications is established with the emergency services (Public Safety Answering Point or PSAP), a data stream known as the Minimum Set of Data or MSD can be s...

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Have you been tasked with the integration of GPS (or GLONASS) chips into a product or system? If so you will be facing a number of challenges. Selecting which chipset or module to use Ensuring that the tiny RF signals are getting through Evaluating the performance Designing for test and manufacturability whilst providing rapid time to market. Your first step should be to consider what characteristics you need in your receiver… they are NOT al...

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Manufacturers of consumer products routinely perform functional testing on all production output, and it would appear that adding some form of location testing to these production test routines would be sufficient to verify the reliability of the GNSS receiver within the end product. However, it is all too easy to adopt the attitude that the simplest of tests will suffice – particularly when the duration of each test can have a significant impact on productivity. Although it may be the...

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Traditionally, civilian use of GPS was seen as free and to a large extent “at your own risk”. The typical performance one might expect was stated in the relevant Interface Control Documents (ICD’s) but no guarantee of service was given. The reason for this was the historical remit of GPS as a system to satisfy US military requirements, the civilian use of the coarse acquisition (C/A) ranging code being essentially a by-product of its primary use, which was to provide class...

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One of the most significant additions among the raft of changes that are being made to the GPS system is the addition of a second safety-of-life signal for civilian use. This new L5 signal is centred at 1176.45MHz in the worldwide Aeronautical Radio-navigation Services band, and will be broadcast at roughly twice the power of the existing L1 and L2C signals. It also features wider bandwidth and longer spreading codes, and will be particularly useful for enabling aircraft to make precision landin...

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One question that regularly crops up in discussions about GNSS receiver testing concerns exactly how the signals get from the GNSS simulator to the device under test. Is it better to radiate the simulator signal to the receiver's antenna, or should you couple them directly? The short answer to this is that a direct connection from the simulator to the receiver's antenna port will always provide the most controlled test environment with no risk of outside influence. The connection is us...

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By Spirent On April 28, 2010
ポジショニング
NMEA data

The navigation industry often refers to NMEA data. But what is it? And why is it so important for the GNSS receiver industry? The NMEA is the US National Marine Electronics Association, which acts, among other things, as a standards body for the industry. And one of its most important standards is NMEA 0183, which defines electrical and data specifications for serial communications between all manner of marine electronic devices. These include everything from echo sounders, sonars and anemomete...

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It goes without saying that any RF device as sensitive as a GPS receiver will be inherently vulnerable to interference. Clearly, care needs to be taken at both the design and integration stages to minimise interference effects. But what interference sources need to be considered? And how do you know if your receiver can deal with them? Most potential sources of interference are obvious and predictable: The effects of fixed-frequency transmitters for TV, radio and the like can easily be modelled...

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The ability to integrate a GNSS receiver into an end product offers new possibilities for manufacturers in a wide range of both consumer and industrial markets. However, designers of such products need to be aware that even the most highly integrated GNSS receiver module is not a “fit and forget” component. As with any radio frequency system, there are design rules that must be followed, and even then the interaction of the receiver with the other functions of the product can create some sur...

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The Russian Deputy Prime Minister Sergei Ivanov has confirmed that the country's GLONASS system will have 100% global availability before the end of 2010. The news follows the launch of three new satellites during March 2010, bringing the GLONASS constellation up to 19 operational satellites of the 24 required for full service. GLONASS, or Global'naya Navigatsionnaya Sputnikovaya Sistema (literally Global Navigation Satellite System) had fallen into severe disrepair after the fall of the USSR,...

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Location-Based Services put Pressure on GNSS Receiver Performance The addition of GPS receivers to today's smartphones, netbooks and other internet enabled devices is allowing mobile operators and other service providers to exploit a growing market for location-based services. These can range from social networks offering “find a friend” applications, to location based marketing and advertising. And you can be sure that developers will come up with many more new applications for loc...

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Time to first fix is a crucial performance parameter for any satellite navigation system because it is the first and most easily appreciated evidence that the end user will have of the quality of the receiver. When you consider that this applies equally to potential users trying out receivers in the shop and to users maintaining satisfaction with the systems they have bought, then a few seconds here and there can make the difference between a happy customer and one that buys your competitor'...

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If you're a GNSS technology, system or application developer involved in the design and implementation of a GNSS project today, you need to take into account the full range of satellite systems and signals that will be available in the near future and understand the challenges and opportunities you face. Using satellites from more than one system brings special challenges and design choices for receiver design and evaluation. But what exactly is the timescale before these new systems are operati...

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Like any form of radio receiver, a global navigation satellite system receiver will be subject to interference from multipath effects arising from the reflection and refraction of its intended satellite signals by both natural and man-made artifacts. However, unlike some radio systems in which a small degree of interference may be tolerable to the end user, multipath interference will have an unacceptable effect on a GNSS receiver, making the output both unstable and inaccurate. There are ...

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A few years ago the Sat Nav system in your car was considered a luxury now almost every PDA, mobile phone and PC has built-in GPS technology. However, navigation and positioning technology is no longer just about GPS L1 C/A code. The GPS constellation is being modernized, the GLONASS constellation is nearly complete with 19 satellites transmitting as you read, new systems including the Japanese QZSS, the European Galileo and the Chinese Compass constellations are on the way. GPS, the back...

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Why would I use a GPS / GNSS simulator, if I want to do any testing I just stick my antenna out of the window, attach it to my receiver and away I go. Well that’s all good and well but for those requiring a rigorous GPS test environment, live sky testing has some serious limitations including a lack of repeatability, control and scalability. Not to mention the fact that you can’t test future signals in space e.g. GPS L2C and L5, partially deployed constellations or constellations tha...

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We sometimes get carried away into thinking everyone must know what a GNSS simulator is but in reality the proliferation of GPS / GNSS applications into many aspects of technology in such a short time span means that some people have had very little experience with GPS / GNSS technologies. So for those non-experts out there, I’d like to help. A GNSS simulator is a signal generator that provides an effective and efficient means of testing GNSS receivers and the systems that rely on the...

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