Archive for July, 2011

How GPS Bends Time

Saturday, July 16th, 2011

Equation section, WIRED magazine:

GPS-time.png

Einstein knew what he was talking about with that relativity stuff. For proof, just look at your GPS. The global positioning system relies on 24 satellites that transmit time-stamped information on where they are. Your GPS unit registers the exact time at which it receives that information from each satellite and then calculates how long it took for the individual signals to arrive. By multiplying the elapsed time by the speed of light, it can figure out how far it is from each satellite, compare those distances, and calculate its own position.

For accuracy to within a few meters, the satellites’ atomic clocks have to be extremely precise—plus or minus 10 nanoseconds. Here’s where things get weird: Those amazingly accurate clocks never seem to run quite right. One second as measured on the satellite never matches a second as measured on Earth—just as Einstein predicted.

According to Einstein’s special theory of relativity, a clock that’s traveling fast will appear to run slowly from the perspective of someone standing still. Satellites move at about 9,000 mph—enough to make their onboard clocks slow down by 8 microseconds per day from the perspective of a GPS gadget and totally screw up the location data. To counter this effect, the GPS system adjusts the time it gets from the satellites by using the equation here. (Don’t even get us started on the impact of general relativity.)

 

courtesy: wired.com

A GPS without GPS

Monday, July 11th, 2011

gsmlocalizerWow, that sounds weird. It’s actually a mini GSM-based localizer without any GPS devices attached. It’s an old device with the cheaper SimCom module SIM900.  Here is a complete working GSM localizator which is pretty cheap and small too.

As introduction, this system allows localization without directly using GPS technology; we are able to locate the desired object fairly precisely by using database availability together with the geographic position of the cells themselves. In some country the cell coordinates are not publicly known (i.e. in Italy). If so, where do we find such data? Through Google Maps… Google has been able to store billions of data regarding the location of its clients’ cell phones. But how does GSM localization work? The radio mobile network is made up of a number of adjacent radio cells, each of which is characterized by an identifier consisting of four data: a progressive number (Cell ID), a code related to the area in which that given cell is (LAC, or Local Area Code), the code of national network to which the cell belongs (MCC, an acronym for  Mobile Country Code), and finally the company code (MNC, or Mobile Network Code), which obviously identifies the phone company itself. For this reason, once a cell name and coordinates are known, and considering the maximum distance allowed between this cell and a phone  before the phone connects to a new cell, it is possible to find out, approximately, the most distant position of the phone itself. For example, if the maximum distance has been determined to be one mile, the cell phone can be within a one-mile radius. It can be deduced that the more cells are found in a given area, the more precisely one can determine where the phone is located (up to 200-350 feet). The idea of employing only a GSM device to build a remote localization system occurred to us when we realized that Google Maps Mobile, which had been conceived to allow smartphones equipped with a GPS receiver to use Google for satellite navigation, was extended to all cell phones, as long as they were able to support GPRS or UMTS data.  Naturally, this method allows but for a rough estimate: determining the precise position of the cell phone hinges on data regarding the coverage of a given cell which can only be provided by the Google server.

DataCell

The circuit

Compared to traditional localizers based on GPS, this device presents many advantages, primarily because it is lighter and less bulky, has a cost lesser and greater autonomy to exercise. This means that about one battery lithium ion, such as 1 Ah, our tracker can be in operation for several days (it all depends on the number of SMS that have to do). A locator based on cellular network may answare more immediately: the GPS receiver may take several minutes to determine its position. Our tracker works battery and thus can be brought on by people who may have the need to ask help or be tracked, but also placed on board motor vehicles (without installation) or simply introduced in goods in transit. To avoid unnecessarily draining the battery, the localizator provides its position via SMS, on requesto with a simple phone call. Among the functions implemented there is the SOS: By pressing the button the localizator sends a text message asking for help, containing the coordinates of position, the sending can be done to a maximum of eight thelephone numbers. When queried or with the autoreport function, sends an SMS with the localization.To know the location of remote device must send an SMS request cell is connected and sends a request (via GPRS) to Google’s site, the latter responds with the coordinates and the figure for the precision. Everything happens in seconds.

0908_Schema

Well, you can get hell of these stuff from link provided afterward. Design files and the firmware are included. A fun stuff to experiment with at your disposal. Mini GSM localizer without GPS at open-electronics.org.

All images are courtesy of open-electronics.org

Japan setting out to get its own GPS off the ground

Sunday, July 3rd, 2011

japan-gps.jpgHow’s your Sunday? ah-ha, here some GPS-related article for your weekend technological feed, have a nice weekend.

The Japanese government – with the the assistance of private firms – is ramping up research on a Japanese version of the Global Positioning System in a bid to turn satellite-based technologies into a key export, the Nikkei reports. As far as we know,  it’s already runs. But turning it into an export – is really a good idea to me.

Plans are afoot to conduct joint research and development on this – nine firms and two organisations are slated to participate in a study group to be formed by the Ministry of Economy, Trade and Industry at the end of the month, with an aim to come up with new services in five years, the report says.

The venture will include companies such as NEC and Mitsubishi Electric Corp, which develop satellites or ground facilities, as well as those with a broad range of businesses, including transport systems, logistics and machinery.Having launched a quasi-zenith positioning satellite last September, the addition of two or three more satellites will enable an around-the-clock service, though specific plans for the second satellite haven’t been drawn up yet.

The Japanese satellite system is designed to supplement the GPS currently operated by the US, and is meant to cover the region, including that of Southeast Asia and Australia.A domestic GPS would yield many benefits beyond just making and launching satellites – with a projection that the overall market will grow from around four trillion yen in 2008 to roughly 10 trillion yen in 2013, a wide range of infrastructure-related fields will stand to grow as well.

Courtesy: paultan

Related:  Quasi-Zenith Satellite System, QZSS