Methods for Cell Phone Tracking and Mobile Location raise the question: Do you really know where they are?
Cell tracking, cell phone GPS and cell phone GPS track software are getting a lot of attention from consumers, mobile phone companies and program developers. Mobile communications means more than just placing a phone call while on the move. The hottest mobile phones have GPS locator features to track phone location. These features, and others such as SMS texting, internet access and the capability to use other software make mobiles great gadgets. However GPS satellites aren’t always available, such as when the phone is in a building such as an house, mall, or even in an automobile. That doesn’t mean smartphone locating isn’t available, but it does mean there are other ways of being a tracker.
To track a cell phone involves several primary methods of determining mobile phone location. GPS Global Positioning System-Satellites, Triangulation, and CellID. All these technologies convert smartphones into mobile tracking systems. These systems can be viewed as Network Based, Handset Based or a Hybrid approach. GPS location is Handset based as it requires software applications installed on the smartphone in conjunction with GPS hardware. Triangulation and CellID are Network Based as they use the equipment and information from the cellular provider. Hybrid systems combine methods to make best use of available data and to make position phone tracking faster.
GPS on cell phones is what people usually think of when looking at tracking smartphones. GPS (Global Positioning System) using satellites is the most popular and more accurate method of tracking. However GPS needs satellites to be in direct line of site of the cell phone. It doesn’t work particularly well indoors or in dense cities. If the phone is in a structure, for example your house, mall, or often riding in a car the signals might not reach the cell phone. Sometimes heavy cloud cover and thick trees interferes with signals. Some mobile phones will keep the last known GPS location, others might not.
Another thing with mobile phone GPS location is the possibility of battery drain. It is important to be able to remotely adjust how often of taking GPS position. Selecting real-time or periodic sampling affects both the accuracy of finding position along with battery life.
GPS receivers, whether in a mobile phone, or a dedicated GPS tracking device, determine position by precisely timing the signals sent by GPS satellites. This data includes the time the message was transmitted, precise orbital information (the ephemeris), and the general system health and rough orbits of all GPS satellites (the almanac). GPS receivers sometimes take a long time to become ready to use after it’s turned on because it must acquire some basic information in addition to finding GPS satellite signals. This delay is sometimes caused if the GPS device has been unused for days or weeks, or has been moved a significant distance while unused for. The GPS must update its almanac and ephemeris data and store it in memory. The GPS almanac is a set of data that every GPS satellite transmits. When a GPS receiver has current almanac data in memory, it can acquire satellite signals and find initial position faster.
GPS Hot Start is when the GPS enabled handset keeps its last calculated location, the satellites that were in view at the time, the almanac data in memory, and makes an attempt to connect to the same satellites and calculate a new position based upon the previous information. This is usually the quickest GPS lock but Hot Start only works if the phone is generally in the same location as when the GPS was last switched off.
GPS Warm Start is when the GPS enabled smartphone recalls its last known location, and almanac used, but not which satellites were in view. It performs a reset and tries to connect to satellite signals and calculates a new position.
The GPS receiver has a general idea of which satellites tolook for because it kept its last known position and the almanac data helps identify which satellites are within view. The Warm Start will take longer than the Hot Start but not as long as a Cold Start.
With GPS Cold Start, the device dumps all the previous information, and attempts to locate satellites and accomplish a GPS lock. This takes more time because there is no known reference information. The GPS enabled device receiver has to attempt to lock onto a satellite signal from any available satellites.
In order to have better GPS lock times cellular manufacturers and network operators introduced Assisted GPS technology. It downloads the ephemeris and helps triangulate the smartphone general position. GPS Receivers can get a faster lock at the expense of a few kilobytes of data transmission.
Assisted GPS, also known as A-GPS or AGPS, improves the performance of standard GPS in mobile phones connected to the cell network. In America Sprint, Nextel, Verizon Wireless, and Alltel all use A-GPS. Which is a means of utilizing the cellular network to speed up acquisition of GPS satellites. A-GPS improves location tracking functions of cell phones (and other connected devices) in two ways:
The first method is by helping to obtain a faster “time to first fix” (TTFF). A-GPS acquires and archivesinformation about satellite locationusing the cell network so the position information doesn’t need to be downloaded from the the satellite.
The next way is by helping position handsets when GPS signals are weak or impeded. As mentioned before GPS satellite signals may be interfered with by tall buildings, and do not penetrate building interiors well. Assisted GPS uses proximity to cellular towers to estimate position when GPS signals are not available.
If satellite signals are not available, or accuracy is less important than battery life, using Cell-ID is a viable substitute to GPS mobile phone tracking. The position of the smartphone can be determined by the cell network cell id, that identifies the cell tower the phone is using. By knowing the location of this tower, then you can know approximately where the cell phone is. However, a tower can cover a huge area, from a few hundred meters, in high population areas, to several miles in lower density areas. This is why location CellID precision is lower than GPS accuracy. Nonetheless location from CellID still presents a very good alternative.
Another method of calculating smartphone location is Triangulation or Mobile Location Services (MLS). Cell Tower Triangulation uses signal analysis data to calculate the time it takes signals to travel from your phone to at least three cell towers to determine position.
To comply with Federal Communications Commission guidelines, cellular phone companies must be able to provide authorities with mobile phone latitude and longitude to an accuracy of 50 to 300 meters. Cell Tower Triangulation doesn’t always meet this requirement. For comparison commercially available GPS modules can achieve accuracy down to 3-10m. This depends upon many factors, as GPS signals are often very weak and are affected by many variables. With Mobile Location Services (MLS), the GSM cellular network provider uses triangulation algorithms to estimate the position of the handset, its accuracy is proven to be much worse than that of GPS. MLS is also affected by the same issues as GPS in the sense of the interference impeding signal strength and the density of GSM towers to assist in the triangulation effort. In remote areas location accuracy may be off as much as a mile.
In general it is a matter of what location tracking system is available, and the requirements for accuracy. Hybrid methods are emerging that use various techniques in tandem to provide best available location given available resources. It may be critical to consider how GPS location software programs handle the data and controls device settings. Having real time tracking on demand, or preferring to minimize battery use and data transmission should be expected. Typically the application determines the location with a GPS receiver and transmits the tracking data to a server through a cellular packet data connection. The data connection to the server is usually made via the Internet. How often GPS samples are taken and how often and by what method the information is sent to the server impact usefulness and costs.
Consider that there is a basic difference between smartphone GPS Tracking and Navigation. GPS cell phone tracking is normally related to someone maintaining records of either real-time or historical handset location, while Navigation deals with the handset user determining how to get from point A to point B.
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