Creating Location Services for the Wireless Web by Johan Hjelm

By Johan Hjelm

Every thing is okay with its content material. I simply don't love its variety. RFCs are extra relaxing to learn than this ebook. the author says that this bankruptcy offers you whatever yet you should locate it, no bullets, no balds, no italics, only a simple textual content. To sum up, i do not locate it readable. back i do not say something approximately its content material. This ebook supplies thought (nothing extra) approximately situation providers for instant net, yet try to be able to learn four hundred web page simple textual content. a few could like this type of books. to be able to get pleasure from whereas analyzing please think carefully earlier than deciding to buy.

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Before you develop a location-dependent service, however, you need to understand how the data should be encoded and how you can get the position information. This is what Chapters 3, 4, and 5 are about. ” And with that, let us look at some of the prerequisites for positioning: coordinates and positioning services. CHAPTER 2 15 Positioning Technologies hen you can measure time precisely, you can measure your position if you have a point of reference. In the mobile telephone network, the position of the base station antennas is fixed and can be used as reference points.

You also need to know where the satellite is in the sky to be able to calculate where you are. Receivers maintain an almanac or long-term model of the satellite trajectories as well as the ephemeris data (which is short-term) for all satellites, and they update these almanacs and ephemeris tables as new data comes in (through the satellites, as mentioned earlier). Mobile phones with GPS receivers can get the almanac from the mobile network, which means they can look for the satellites when they are known to be overhead, saving the battery—which is critical for mobile phones.

So, if the information about where the satellites are can be provided to the handset before it starts searching for them, it will save a lot of time and thus battery life—something that is crucial in mobile telephone systems, where maximizing the time between the chargings is a major selling point. Knowing where to find the satellites also enables higher sensitivity in the positioning (because more satellites can be used). If we know in which cell of the mobile telephone system the handset is (in other words, an accuracy of up to 9 km given the maximum size of a cell) and a precise time signal, it enables the calculation of the satellite orbits so that the antenna can point at approximately the right places, get a fix, and calculate the position faster.

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