Smartphone GPS Tracking Introduction

Much of the discussion dealing with GPS tracking, cell phone GPS and mobile phone track software could be helped by a GPS Satellite primer.

GPS satellites broadcast signals from space that GPS receivers use to determine three-dimensional location (latitude, longitude, and altitude) plus precise time. GPS stands for Global Positioning System and is a system that is made up of 3 primary segments: Space Segment, Control Segment and User Segment.

The GPS Space Segment is comprised of twenty-four to thirty-two satellites that orbit the earth at a height of about 12,000 miles. These satellites are referred to as the GPS Constellation, and they make an orbit twice a day. They are not geostationary, but rather move at over 7,000 mph. They are solar powered but have battery backup for when they are on the dark side of the earth. They are placed so that there are at least 4 satellites ?visible? from any point on earth. Small rocket boosters on each satellite keep them properly positioned. The satellites last about ten years until all their fuel runs out.

GPS Satellites are not communications satellites. Geostationary or communications satellites are at a much higher orbit of about 22,300 miles above the equator. These satellites are used for weather forecasting, satellite TV, satellite radio and most other types of global communications. At exactly 22,000 miles above the equator, the earth’s gravitational force and centrifugal forces are canceled and are in equilibrium. This is the best location to park a communications satellite. The earth rotates at about 1,000 miles an hour, and because of their high earth orbit the geo-synchronous satellites need to move at about 7,000 mph to keep position. This is approximately the same speed as GPS satellites, but since earth-synchronous satellites are 10,000 miles further away they don?t move relative to the earth.

The GPS Control Segment incorporates Master Control Station, an Alternate Master Control Station, and numerous dedicated and shared Ground Antennas and Monitor Stations that work together to ensure the satellites are working correctly and the data they beam down to earth is accurate.

The GPS User Segment includes of GPS receivers taking the shape of handsets and , laptops, in-car navigation devices and hand-held tracking units along with the people that use them, and the software programs that make them work.

GPS receivers sometimes take longer 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 slow start is sometimes caused if the GPS device has been turned off for days or weeks, or has been transported a far 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 signals and determine initial position more quickly.

In the event that satellite signals are not accessible, or precision is less important than life of the battery, making use of Cell-ID is a viable alternative to GPS mobile phone location. The position of the device may be determined by the cell network cell id, that determines the cell tower the mobile phone is connected to. By knowing the position of this tower, you may know roughly where the device might be. However, a tower can cover an enormous area, from a couple of hundred meters, in high populationdensity zones, to several miles in lower density zones. For this reason location CellID precision is less than than GPS accuracy. Nonetheless location using CellID still can provide a very useful substitute.

Smartphone GPS Tracking Introduction