Global Positioning: Technologies and Performance (Anglais) Relié – 29 avril 2008
|Neuf à partir de||Occasion à partir de|
- Choisissez parmi 17 000 points de collecte en France
- Les membres du programme Amazon Premium bénéficient de livraison gratuites illimitées
- Trouvez votre point de collecte et ajoutez-le à votre carnet d’adresses
- Sélectionnez cette adresse lors de votre commande
Descriptions du produit
Revue de presse
"Global Positioning will appeal to engineers for its detail, to scientists for its breadth and scope, and to the curious public who will choose to read it without concentration on its detail. Highly recommended." (CHOICE, October 2008)
Présentation de l'éditeur
From outdoors to indoors
From ancient to future applications
From techniques to technologies . . .
The field of radionavigation signals and systems has seen significant growth in recent years. Satellite systems are very efficient, but owing to their limited exposure and/or availability in some environments, they do not cover the whole spectrum of applications. Thus, many other positioning techniques are being developed.
Now, Global Positioning presents an overview of the strengths and weaknesses of various systems with a specific emphasis on those that are satellite–based. Beginning with a description of the evolution of positioning systems, the book provides detailed coverage of the three main Global Navigation Satellite System (GNSS) constellations, discusses how to cope with indoor positioning, defines development activities and commercial positioning, and proposes a vision for the future of the field.
Special features of the book include:
Exercises to test and challenge the reader′s understanding
Direct comparison between constellations and other positioning systems
Mathematical content kept to a minimum in order to maximize accessibility and readability
Descriptions of European and U.S. discussions for Galileo
Historical aspects and links between the distant past and current systems
Footnotes that provide hints and comments to the reader
At a time when the positioning domain is experiencing such immense transformation, it is vital to have a solid understanding of the fundamental principles, current tech–nologies, and future improvements that will help estimate the performance and limita–tions of existing systems. Global Positioning fills an important need for professionals and students in a variety of fields who want a complete and authoritative overview of global positioning techniques.
Aucun appareil Kindle n'est requis. Téléchargez l'une des applis Kindle gratuites et commencez à lire les livres Kindle sur votre smartphone, tablette ou ordinateur.
Pour obtenir l'appli gratuite, saisissez votre numéro de téléphone mobile.
Détails sur le produit
Commentaires en ligne
Meilleurs commentaires des clients
Le livre semble complet, c'est clair, mathématique et de très haut niveau.
Commentaires client les plus utiles sur Amazon.com (beta)
This segues into a vital concept that prevades the rest of the book. Current methods of global positioning are dominated by the use of a constellation of satellites. It turns out that an essential need is for very stable time synchronisation; just as in earlier centuries. Current American GPS satellites each have 4 atomic clocks on board that vote on the time. Analogous to how the now defunct space shuttle was reputed to have 3 computers to make key decisions, and where a majority vote was used to pick the right one.
Most of the book discusses 3 constellations. The oldest and most widely used is GPS, which is deployed and maintained by the US Department of Defense. It arose during the Cold War, as a means for US military units and perhaps ICBMs to navigate across the globe. Glonass is the Russian [nee Soviet] counterpart, while Galileo will presumably be fully deployed in a few years by the Europeans. The book tries to be evenhanded in its descriptions of all 3. But there is probably unavoidably an emphasis on GPS. Indeed, the very term GPS is generally conflated by people as a shorthand for any satellite navigation method. Not unreasonable from a pragmatic standpoint, if you are an end user with a device that needs to know its location, or a company that makes such items. However Samama uses the term GNSS [Global Navigation Satellite System] to refer to all 3 constallations.
The need for very accurate clocks on the satellites can be seen from a simple observation made in the book. To know a person's location on the Earth relative to a satellite means that we need to know the satellite's location, where the satellite is broadcasting a pulse that will be picked up by the person's device. If the time on the satellite is known to 1 nanosecond, then multiplying by the speed of light [3 x 10^8 m/s] gives 30 cm. This is the uncertainty in the satellite's position. Roughly, this then becomes the minimum uncertainty in the person's location. The actual uncertainty is significantly larger; at least 1 meter. And the use of 3 or more satellites to pin down that location doesn't really resolve this error. So crudely, clocks stable to 1 nanosecond can give at best 1 meter resolution on the ground. The book goes into a far more rigorous analysis. But you can appreciate the amazing progress in electronics that has led to such good time determination. Where you should remember that once launched, the satellites are never repaired. They have to operate continuously for years. Hence the need, at least on the GPS satellites, for several clocks.
By the way, the book points out that one common layman's assessment of the 3 constellations is flawed. Some have suggested that combining the signals from 2 or 3 constellations might provide more accurate location data. This is not so. Because the limiting factor is knowing the accuracy of a given satellite's position. Having more satellites does not help. Where using multiple constellations is plausible is in the context of accessibility to 4 or more satellites within the line of sight of the person on the ground. There are some situations, like in an urban canyon with skyscrapers all around, that you might not be able to see 4 satellites from a given constellation. So being able to possibly access a satellite from another constellation and integrate its signal with what you can get from the first constellation can help.
One neat observation is that GNSS uses Einstein's theory of General Relativity. It turns out that a satellite's reference frame as it orbits the Earth needs to be properly described via GR, and not Newtonian gravity. The latter was first done in the early years of GPS, but a systematic error was found. It was removed once a deeper analysis invoked GR. Every time someone uses a GNSS device, she is validating GR!
The book also quickly talks about non-satellite methods. These could involve sensors embedded in a mobile device that needs to know its location. The sensors can be an odometer for distance travelled, a barometer for altitude, a gyroscope or magnetometer for orientation and an accelerometer for acceleration and velocity. The other main method is to use the cellphone network. At the simplest level, the cell that a person's cellphone is in is immediately a location region, by definition. There are efforts to improve on this, in part by integrating any data from GNSS.
The limiting cases in the text are in urban environments and especially inside buildings. The latter is hard. No satellites in line of sight unless you are at a window. And even then, you are unlikely to see 4 satellites. While attenuation of signals from a cellphone network by the building's walls and floors can reduce the efficacy of any positioning method that uses the network. Samama describes some attempts at deploying specialised transmitters [beacons] inside buildings. The overarching problem is that this has to be done building by building. Slow and expensive. And different buildings might opt for different methods, which could then necessitate different sensor hardware on the user's mobile device. No global solution, and likely even no citywide solution. Given that the book is about global positioning, this limiting case is useful because it shows the conceptual perimeter of the book's topic.
I do have to make one slight addendum to the book's remark on page 385 - 'Positioning could be used to help reduce the energy consumption of the western world'. The remark was in the context of using a person's location to help her better plan her travels and hence minimise fuel consumption. I would just add that this can be vital in China and other large developing countries, where mobile phones are also affordable. Those nations also need more efficient per capita energy consumption.