To track a mobile phone involves several main ways of determining 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 needs software programs installed on the cell phone 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 techniques to make best use of available data and to make position phone tracking faster.
Mobile phone GPS is what people commonly think of when looking at tracking cell phones. GPS (Global Positioning System) using satellites is the most common and more accurate way of tracking. But GPS requires satellites to be in direct line of site of the handset. It doesn’t work as well indoors or in dense cities. If the phone is in a structure, for example your office, restaurant, or often sitting in an automobile the signals might not reach the smartphone. Sometimes thick cloud cover and dense foliage impedes with signals. Some mobile phones will retain the last known GPS location, others might not.
Another thing with cell phone GPS tracking is the possibility of battery drain. It is important to be able to remotely adjust the frequency of taking GPS position. Choosing real-time or periodic sampling affects both the resolution of determining position along with how long the battery will last.
GPS receivers, whether in a mobile phone, or a dedicated GPS tracking device, compute position by precisely timing the signals transmitted by GPS satellites. This data includes the time the message was transmitted, precise orbital information (the ephemeris), and the general system health 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 is sometimes caused when the GPS smartphone has been unused for days or weeks, or has been moved a far 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 acquire signals and determine initial position faster.
GPS Hot Start is when the GPS enabled handset remembers its last known location, the satellites that were in range at the time, the almanac information in memory, and attempts to connect to the same satellites and compute a new position based upon the previous data. This is usually the quickest GPS lock but Hot Start only works if the phone is in the same general area 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 performs a reset and tries to connect to satellite signals and computes a new position.
The GPS receiver narrows the choice of which satellites tolook for because it stored its last known position and the almanac data helps identify which satellites are in range. 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 data, and attempts to locate satellites and accomplish a GPS lock. This takes the longest because there is no known reference information. The GPS enabled smartphone receiver has to attempt to lock onto a satellite signal from any available satellites.
In order to have better GPS lock times mobile phone manufacturers and telco operators developed Assisted GPS technology. It downloads the ephemeris and helps triangulate the cell phone 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, enhances the performance of standard GPS in smartphones connected to the cell network. In the United States Sprint, Nextel, Verizon Wireless, and Alltel all use A-GPS. Which is a means of utilizing the cellular network to accelerate finding of GPS satellites. A-GPS improves location tracking functions of mobile phones (and other connected devices) in a couple of ways:
The first way is by assisting to obtain a more rapid “time to first fix” (TTFF). A-GPS acquires and archivesdata about the location of satellitesusing the cellular network so the coordinates information does require to be downloaded from the the satellite.
Another method is by helping position cell phones when GPS signals are weak or impeded. As discussed above GPS satellite signals may be impeded by tall buildings, and do not penetrate building interiors well. Assisted GPS utilizes 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 useful alternative to GPS cell phone tracking. The position of the handset can be calculated by the cellular network cell id, that identifies the cell tower the phone is connected to. By knowing the location of this tower, then you can know approximately where the cell phone is. But, 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 location using CellID still presents a very useful substitute.
Another way 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 estimate location.
To comply with Federal Communications Commission guidelines, cell phone companies must be able to provide authorities with handset latitude and longitude to an accuracy of 50 to 300 meters. Cell Tower Triangulation doesn’t always meet this requirement. By way of comparison, commercially available GPS systems are able to obtain accuracy down to less than 10 meters. This depends upon many factors, as GPS signals are often very weak and are impacted by many variables. With Mobile Location Services (MLS), the GSM cellular network provider utilizes triangulation techniques to compute the position of the handset, its accuracy is proven to be less than than that of GPS. MLS is also impacted by factors similar to GPS in the sense of the barriers affecting signal quality and the density of GSM towers to assist in the triangulation calculation. In remote areas location accuracy may be off as much as a mile.
Generally speaking 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 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 using the Internet. How often GPS samples are taken and how often and by what method the data is sent to the server impact usefulness and costs.
Keep in mind that there is a fundamental difference between smartphone GPS Tracking and Navigation. GPS cell phone tracking is typically associated with a third-party maintaining records of either real-time or historical handset position, while Navigation deals with the mobile phone user determining how to get from point A to point B.
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Methods for Phone GPS Tracking and Mobile Location raise the question: Do you really know where they are?
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