Different Approaches to Being a Cell Phone Tracker Raise the Question: Do you really know where they are?
Mobile communications means more than just making a phone call while on the move. The latest cell phones include GPS position functionality to track phone location. These features, along with others such as text messaging, internet access and the ability to utilize other applications make smartphones great gadgets. However GPS satellites aren’t always available, such as when the handset is in a building such as an house, mall, or even in a car. That doesn’t mean smartphone tracking isn’t available, but it does mean there are other ways of being a locator.
To track a cell phone involves several main ways of determining mobile phone position. GPS Global Positioning System-Satellites, Triangulation, and CellID. All these technologies convert cell phones into mobile tracking devices. 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 mobile phone along 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 information and to make location mobile phone tracking faster.
GPS on cell phones is what people usually think of when looking at tracking cell phones. GPS (Global Positioning System) using satellites is the most common and more accurate technology of tracking. But GPS needs satellites to be in direct line of site of the smartphone.
It doesn’t work particularly well indoors or in dense cities.
If driving the signals might not reach the smartphone. Some smartphones will keep the last known GPS location, others might not.
Another thing with cell phone GPS location is the potential of draining the battery. 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 cell phone, or a dedicated GPS tracking device, compute location by precisely timing the signals transmitted by GPS satellites. This information 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 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 acquire signals and compute initial position more quickly.
GPS Hot Start is when the GPS enabled handset keeps its last calculated position, the satellites that were in range at the time, the almanac data in memory, and tries to obtain the same satellites and calculate a new position based upon the previous data. This is almost always the quickest GPS lock but Hot Start only works if the phone is generally in the same location as when the GPS was last turned off.
GPS Warm Start is when the GPS enabled device recalls its last calculated position, and almanac used, but not which satellites were in view. It resets and tries to obtain satellite signals and computes a new position.
The GPS receiver narrows the choice of which satellites toseek because it kept its last known position and the almanac data helps identify which satellites are within view. 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 information, and attempts to locate satellites and accomplish a GPS lock. This takes longer than other methods because there is no known reference information. The GPS enabled cell phone 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 telco operators introduced Assisted GPS technology. It downloads the ephemeris and helps triangulate the handset general position. GPS Receivers can get a faster lock at the expense of a few kilobytes of data transmission.
A-GPS assists location tracking performance of cell phones (and other connected devices) in two ways:
The first method is by assisting to obtain a more rapid “time to first fix” (TTFF). Assisted GPS acquires and storesinformation about satellite positionusing the cell network so the position information doesn’t require to be downloaded via the satellite.
Another way is by assisting locate mobile phones when GPS signals are weak or blocked. As discussed above GPS satellite signals may be impeded by tall buildings, and do not penetrate building interiors well. AGPS utilizes proximity to cellular towers to estimate 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 useful alternative to GPS mobile phone location. The location of the cell phone can be computed by the cell network cell id, that identifies the cell tower the phone is connected to. By knowing the position of this tower, then you can know approximately where the device is. However, a tower can cover a huge area, from a few hundred meters, in high population areas, to several kilometers in lower density areas. This is why location CellID accuracy is less than than GPS accuracy. Nevertheless location from CellID still presents a very viable substitute.
Another way of calculating handset 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 cell 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 are able to achieve accuracy down to 3-10m. 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 estimate the position of the cell phone, its accuracy is proven to be much worse than that of GPS. MLS is also affected by factors similar to GPS in the sense of the barriers affecting signal strength and the density of GSM towers to help in the triangulation calculation. In rural areas position accuracy may be off as much as a mile.
In general it comes down to what location tracking system is available, and the need for accuracy. Hybrid methods are emerging that use various techniques in tandem to provide best available location given available resources. Generally the application determines the location with a GPS receiver and transmits the tracking data to a server through a 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 data 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 typically associated with someone maintaining records of either real-time or historical smartphone position, while Navigation deals with the handset user determining how to get from point A to point B.
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