To track a mobile phone involves several main ways of formulating cell 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 data from the cellular provider. Hybrid systems combine techniques to make best use of available data and to make location cell phone tracking faster.
Mobile phone GPS is what people commonly think of when looking at locating smartphones. GPS (Global Positioning System) using satellites is the most common and more accurate means of tracking. But GPS requires satellites to be in direct line of site of the handset. It doesn’t work particularly well indoors or in dense cities. If the phone is in a building, for example your office, mall, or often riding in a car the signals might not reach the mobile phone. Sometimes heavy cloud cover and thick trees impedes with signals. Some smartphones will retain the last known GPS location, others might not.
Another thing with mobile phone GPS tracking is the potential of draining the battery. It is important to be able to remotely adjust how often of taking GPS position. Choosing real-time or periodic sampling affects both the accuracy of determining location along with how long the battery will last.
GPS receivers, whether in a smartphone, or a dedicated GPS tracking device, compute 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 condition and estimated orbits of all GPS satellites (the almanac). GPS receivers sometimes take longer to become ready to use after being turned on because it must acquire some basic information in addition to capturing GPS satellite signals. This slow start can be caused when the GPS smartphone has been turned off for days or weeks, or has been moved a significant distance while turned off 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 capture signals and calculate initial position more quickly.
GPS Hot Start is when the GPS enabled mobile phone recalls its last known location, the satellites that were in range before, the almanac information in memory, and tries to connect to the same satellites and calculate a new position based upon the previous data. 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 cell phone keeps its last known position, and almanac used, but not which satellites were in view. It resets and tries to lock onto satellite signals and computes a new position.
The GPS receiver has a general idea of which satellites toseek because it stored its last known position and the almanac data helps identify which satellites are visible in the sky. The Warm Start will take more time than the Hot Start but not as long as a Cold Start.
With GPS Cold Start, the device deletes all the previous data, and attempts to locate satellites and achieve a GPS lock. This takes longer than other methods because there is no known reference information. The GPS enabled cell phone receiver has to try 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 mobile phone general position. GPS Receivers can get a faster lock in exchange for a few kilobytes of data transmission.
Assisted GPS, also known as A-GPS or AGPS, improves the performance of standard GPS in smartphones connected to the cell network. In the United States Sprint, Nextel, Verizon Wireless, and Alltel all use AGPS. This is a method of using the cell network to accelerate acquisition of GPS satellites. A-GPS assists location tracking functions of smartphones (and other connected devices) in two ways:
One way is by helping to obtain a faster “time to first fix” (TTFF). A-GPS acquires and archivesdata about the location of satellitesusing the cell network so the position information does need to be downloaded via the satellite.
The second method is by assisting locate cell phones when GPS signals are weak or blocked. 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 calculate location 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 good alternative to GPS smartphone tracking. The position of the cell phone can be determined by the cellular network cell id, which identifies the cell tower the phone is connected to. By knowing the location of this tower, then you can know approximately where the handset is. However, a tower can cover a huge area, from a few hundred meters, in high populationdensity areas, to several miles in lower density areas. This is why location CellID precision is lower than GPS accuracy. Nevertheless tracking using CellID still presents a very good substitute.
Another way of calculating device 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 estimate position.
To comply with Federal Communications Commission guidelines, cell phone companies must be able to provide authorities with smartphone 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 are able to 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 cell network provider uses triangulation techniques to calculate the position of the handset, its accuracy is proven to be much worse than that of GPS. MLS is further impacted by the same issues as GPS in the sense of the interference affecting signal strength and the density of GSM towers to assist in the triangulation effort. In rural 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 might be important to consider how GPS location software programs handle the data and controls handset settings. Having real time tracking on demand, or preferring to minimize battery use and data transmission should be expected. Generally 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 over the Internet. How often GPS samples are taken and how often and by what method the information is sent to the server impact effectiveness and costs.
Consider that there is a basic difference between cell phone GPS Tracking and Navigation. GPS mobile phone tracking is normally related to someone keeping records of either real-time or historical smartphone location, while Navigation deals with the handset user figuring out how to get from point A to point B.
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Methods for Cell Phone Tracking and Cell Location raise the question: Do you really know where they are?
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